Conservation And Recycling of Resources: New Research

CONSERVATION AND RECYCLING OF RESOURCES: NEW RESEARCH

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CONSERVATION AND RECYLING OF RESOURCES: NEW RESEARCH

CHRISTIAN V. LOEFFE EDITOR

Nova Science Publishers, Inc. New York

Copyright © 2006 by Nova Science Publishers, Inc.

All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Conservation and recycling of resources : new research / Christian V. Loeffe (editor). p. cm. Includes index. ISBN 978-1-60876-513-3 (E-Book) 1. Recycling (Waste, etc.) 2. Conservation of natural resources. I. Loeffe, Christian V. TD794.5.C664 2006 628.4'458--dc22 2006008429

Published by Nova Science Publishers, Inc. New York

CONTENTS Preface

vii

Chapter 1

An Overview of Recent Advances and Trends in Plastic Recyling Sati Manrich and Amélia S. F. Santos

Chapter 2

The Consequences of the Use of Platinum in New Technologies on its Availability and on Other Metals Cycles Ayman Elshkaki and Ester van der Voet

Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

Chapter 8

Index

Vegetation Recovery after Environmental Damage by Metallurgic Industry in the Arctic Region: Transformation of Soil Chemistry in Restored Land Ryunosuke Kikuchi and Tamara T. Gorbacheva

1

61

93

Solid Waste Management, Recent Trends and Current Practices for Secondary Processing of Zinc and Lead Industries in India Archana Agrawal and K. K. Sahu

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Recycling of Wastes (Agricultural Residues and Used Tires) for Activated Carbon Production A. A. Zabaniotou

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Energy Recovery from Waste Incineration: Linking the Systems of Energy and Waste Management Kristina Holmgren

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Artificial Aggregate Made by Cementitious Granulation of Waste Incinerator Fly Ash R. Cioffi, F. Colangelo, F. Montagnaro and L. Santoro

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The Chemical Properties of Municipal Solid Waste Incinerator Ashes and the Effects of Their Utilization as Landfill Cover on Landfill Biostabilization Huang-Mu Lo, Min-Hsin Liu, Chao-Yang Lin, Wen-Fung Liu, Tzu-Yi Pai, Chun-Hsiung Hung, Pin-Hung Cheng, Yuan-Lung Liao, Tsu-Ying Fu and Chao-Chan Yang

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PREFACE The preservation and careful management of the environment and of natural resources and recycling or the processing of used or abandoned materials for use in creating new products must become key parts of the equation for the Earth’s continued sustainable development. At the present time, most developed countries are massively wasteful throughout almost all sectors of the economy ranging from energy use to consumer lifestyles. One of the main obstacles to conservation and recycling of resources is the lack in most countries of national mindsets encouraging such practices as well as the infrastructures to support their carrying out. This new book presents important research in this frontal field. Since the discovery of plastics several decades ago, the widespread consumption of plastic products and their subsequent inappropriate disposal and accumulation have recently generated new societal concerns of waste management due to their inherent slow degradability, high volume increase and low recycling rates, which are negative on the basis of self-sustainability. Regulations imposing waste reduction, reuse and recycling indices and responsibilities, as well as effective collecting system and the development of new, environmentally clean recycling technologies are some of the efforts to achieve the selfsustainability goals. The efficiency of the collection and sorting systems impacts directly on the amount of recycled plastics and on their cleanness and quality, therefore, enlarging their market potential. The development of new recycling technologies is diversified and can be classified into mechanical, chemical and energetic recycling. In mechanical recycling, successful technologies are achieved through the improvement of existing processes using additives, blends with other plastics and alternative processing routes in order to maintain the original properties of the virgin resin and even allowing them to return to the same application as originally intended. Chemical recycling processes to obtain intermediary products for new polymers become feasible due to the cost reduction of the raw materials involved. Lastly, despite the under use of the gross energy potential of the raw materials employed, energetic recycling plants are gaining a proportion of residues whose technological solutions for separation and/or reprocessing are deficient, but which, on the other hand, are voluminous, consequently solving the problem of both residue accumulation in densely populated regions and their respective insufficient energy supplies. In chapter one, the authors proposed to present an overview of the current state of this whole plastic recycling sector including their recent advances, and highlighting new markets and recent trends on recycling technologies around the world. However, mechanical recycling has been emphasized owing to the experimental and published work of Manrich’s workgroup at the 3R Residues

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Recycling Center, which has concentrated on studying all the steps in the process of mechanical recycling. Recently, fuel cell vehicles (FCV) are being developed to reduce the environmental impacts related to the conventional internal combustion engine vehicles. Although on the short term the newly proposed technology might serve the intended purpose. On the long term, there may be bottlenecks in the supply of specific metals required for the technology and new emissions may replace the old ones. Fuel cell technology requires the use of platinum, which is cited as a possible bottleneck for a more widespread use of the new technologies. Moreover, an increase in platinum demand ultimately implies an increased production of the co-produced metals Cu and Ni. Consequently an increased supply may well have environmental consequences on Ni and Cu recycling system. Chapter two is aimed at investigating the potential long-term impact of the increase use of platinum in fuel cell technology and other applications in terms of resource depletion and evaluating the long-term consequences of the increased demand of platinum on the cycles of other co-produced metals especially Ni and Cu. The analysis is carried out using a dynamic substance flow-stock model for platinum, nickel and copper. The model consists of a set of differential equation describing the change of the magnitude of the substance stock in the system compartments (production, use and waste management of platinum applications, primary production of platinum in South Africa, Russia, USA, Canada and others and secondary production of platinum) over time and several model relations. The model is implemented in Matlab/SIMULINK environment. The main driving force in the model is the global demand for platinum. The global demand for platinum is estimated based on the demand for its applications (fuel cell, catalytic converters, and the other applications) and platinum required for each application. In turn, the demand for platinum applications are modeled based on socio-economic variables such GDP, per capita GDP, population size, material price and the cost of these applications. Platinum required for each application is modeled as a function of cumulated production using the learning curve. In addition, several other factors are important in determining the main outcome such as the applications life span, the applications collection rates and the efficiency of the production processes (primary and secondary). The main model outcomes are the amount of primary platinum required for FCVs and other applications and the consequences on platinum current reserve, platinum identified resources and the co-produced metals recycling and primary production from other ores. The model shows that the demand for primary platinum will increase dramatically with the introduction of FCVs despite the possibility of the decrease of platinum loading of FC. This is mainly due to the increased demand for vehicles. Without changes in management, the current platinum reserve would be exhausted in three decades and the identified resources in roughly 60 years. The model also shows that the demand for the co-produced materials is increasing over time. The supply of these metals from Pt ores is, combined with only a part of their current secondary production, sufficient to meet the rising demand. Consequently the primary production of these metals from other ores than those of Pt ores will not be needed. Recycling of these metals is expected to decrease. Forest ecosystems are valuable both as species’ habitat and as one of the important lifesupport systems for the biosphere. The most severe effects of metals on forest ecosystems are from local pollution in the Subarctic regions, and the Kola Peninsula (66-70°N and 28°30'-

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41°30'E) in Russia is one of the most seriously polluted regions: since it is close to nickelcopper smelters, the deposition of metal pollutants has severely damaged the soil and ground vegetation, resulting in an industrial desert. The methods used for restoring an industrial wasteland should have regional character; i.e. features of the ecosystem and specificity of the nutritional regime. Global production of sewage sludge is estimated at ∼30 million tons/yr, and 70% of this amount is disposed of; however, it is recognized that compost produced from sewage sludge is effective in soil conditioning. Podzol is the most common soil type on the Kola Peninsula, and this type of soil is generally nutrient-poor. Plant growth is severely limited by nutrient availability in the Arctic (or Subarctic) ecosystem. Nutrients in pools of soil organic matter show slow turnover rates, so nutrients become available to plants at a low rate. Land remediation using compost seems to be effective in such podzol forest land damaged by the metallurgical industry. Using a soil-like substratum consisting of compost produced from sewage sludge, a rehabilitation test was conducted in the above-mentioned metal-polluted land (67º51’N and 34º48’E) over an area of 4 ha for the purpose of contemplating the feasibility of combining the application of unused sewage sludge with the recovery of damaged forest land. In chapter three, the following items were studied: (i) chemistry of the original sewage sludge; (ii) its transformation during composting; (iii) the effect of liming on compost properties; and (iv) abiogenic and biogenic transformation of soil-like substrata in the test field for assessing whether the effect of current pollutants on local vegetation is constrained. Based on field observation during 2003-2005, the obtained data showed the redistribution of organic matter and heavy metals. This suggests that the content of heavy metals in old artificial substrata may be less than that in fresh artificial substrata. In conclusion, the test field of 4 ha is recovering from degradation of the podzol forest land. Almost all the metallurgical processes are associated with the generation of wastes/residues which may be hazardous or non-hazardous in nature depending upon the criteria specified by institutions like US EPA etc. The wastes containing heavy and toxic metals such as arsenic, cadmium, chromium, nickel, lead, copper, mercury, zinc etc. are present beyond permissible limits deemed to be disposed of. Due to the implementation of stricter environmental laws and economic reasons all the metallurgical industries are now forced to go for eco-friendly technologies to produce metal and other related products world over. However, generation of wastes is the integral part of metallurgical industries which can not be ruled out, therefore if the wastes/residues are hazardous in nature they generally have to be treated or disposed off in safe and designated dumping sites. If these wastes/residues are non-hazardous in nature then they may be suitably used as secondary raw material for the recovery of metals which are in growing demand all over the world. Zinc is in growing demand all over the world. In India a major amount of zinc is imported and therefore processing of zinc secondaries will supplement in satisfying the gap between demand and supply to some extent. Similarly processing of lead secondaries is important because of their relative high metal content, besides low energy and cost involved in recovering the metal. Chapter four highlights the production capacity, type and quantity of solid wastes generated, their chemical composition and treatment/disposal options for the Indian lead and zinc industries. Zinc tailing, slag, leach residue, jarosite residue, β-cake, etc. from zinc industries and BF slag, flue dust, ISF slag etc. from lead industries are the major solid waste generated from various process and needs attention. Although all the metal producing industries in organised sector are now taking care of the environment and waste management related

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problems, but pollution from unorganized lead units are the major cause of concern. Permissible limits of toxic constituents in zinc based secondaries and threshold zinc concentration for both indigenous and imported raw materials were worked out at National Metallurgical Laboratory (NML). An overview of the current practices and recent trends in the secondary processing of zinc and lead and the attempts made to recycle/recover metal values and production of value added products, are discussed in the text. Various processes, particularly hydrometallurgical ones, already developed or in the developmental stages, are discussed. Attempts made by various laboratories and industries towards the development of eco-friendly processes for the recovery of zinc and lead from secondary raw material are also described. A review of the production of activated carbons from wastes, such as agricultural and used tires, by using atmospheric pyrolysis, is presented in chapter five. Pyrolysis of waste is a CO2-neutral process and can transform biomass to energy and materials. It is a possible way for chemical recycling of the organic matter. This study evaluates pyrolysis of olive kernels, olive wood, and cotton ginning waste and used tires, by studying the effect of temperature on the pyrolysis product yields and investigates production of activated carbon from pyrolytic char. A comparison in characteristics and uses of activated carbons from agricultural residues and tires with commercial carbons have been made. Energy recovery from waste incineration has a double function as a waste treatment method and a supplier of electricity and/or heat. Waste incineration thereby links the systems of waste management and energy. Chapter six addresses the importance of taking this into consideration when e.g. making investment decisions or designing policy instruments. The design of two policy instruments will be described as examples of the conflicting goals in the two systems. A conflict is also that increased waste incineration can decrease production of combined heat and power in the district heating systems. Since policy instruments in Sweden are dependent on the common legislation of the European Union this will be addressed, together with trading in waste and electricity and how this impacts waste incineration in Sweden. Conflicts between the internal market in the European Union and waste management goals are shown. When making investment decisions, various models are often used as decision support tools. Some models for assessing waste incineration/management are therefore described together with strengths and weaknesses when dealing with the dual function of waste incineration. The waste employed in this work presented in chapter seven comes from an incineration plant in which municipal, hospital and industrial wastes are treated. The plant is equipped with rotary and stoker furnaces and both fly ash samples coming from these two equipments have been individually employed. Ash from waste incineration plant is classified as hazardous and cannot be utilized or even landfilled without prior treatment. This chapter reports the results of an extensive investigation on stabilization/solidification of the above ash samples by addition of hydraulic binders in a granulation equipment. A rotary plate granulator was used with binders based on cement, lime and coal fly ash. Granulation was carried out with several mixes in which the ash content was up to 70%. In some cases, the granules obtained in this way are suited for matter recovery by reusing the waste for the manufacture of building materials. To achieve this in most cases, two-step granulation is required with pure binder being used in the second one. In this way the granules from the first step can be encapsulated within an outer shell able to improve the technological and leaching properties. The possibility to get matter recovery from incinerator ash is a crucial issue for making the

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granulation process environmentally and economically sound. In fact, the most direct application of granules is in the field of artificial aggregates for road construction and concrete manufacture. The granules obtained from the treatment of fly ash samples have been tested to assess their physico-mechanical and leaching properties. Specifically, measurements have been carried out regarding the following properties: density, water adsorption capacity, compressive (crushing) strength and leaching behavior. Moreover, concrete mixes have been prepared with some of the artificial aggregates made by granulation. Once hardened, these mixes have been successfully tested from the technological point of view, proving to be suitable for the manufacture of classified concrete blocks. Chapter eight investigated the properties of municipal solid waste incinerator (MSWI) ashes and the effects of their addition on the municipal solid waste (MSW) anaerobic digestion as co-disposed or co-digested with MSW in landfill or digester. Five anaerobic bioreactors with the size of 1.2 m height and 0.2 m diameter were employed to conduct the experiment. Four layers were arranged each with 6.5 liter of MSW and anaerobic seeded sludge mixture covered by 2.5 liter of MSW and anaerobic seeded sludge mixture blended with the designed ashes added ratios as well as the control bioreactors without ashes addition. The synthetic MSW used in this experiment was typical of organic fraction of MSW and was comprised of newspaper, food waste, office paper and hay etc. MSWI ashes were obtained from a mass burning incinerator in central Taiwan. Also, the seeded anaerobic sludge was taken from a municipal wastewater treatment in central Taiwan. As the experiment was proceeded with, the leachate of 100 mL was recirculated per day and another more 100 mL one was collected and filtered for parameters analysis such as pH, conductivity, alkalinity and chemical oxygen demand (COD) etc. In addition, the gas production rate was recorded every day to measure the bacterial activity in the MSW biodegradation. From the results, it showed that 10 and 20 g l-1 fly ash added (g ashes addition per liter MSW ratios) bioreactors and 100 g l-1 bottom ash added bioreactors were found to enhance the gas production rate and the soluble concentration of alkali metals such as Ca, Mg, K, and Na as compared to the control one. The six soluble heavy metals of Cd, Cr, Cu, Pb, Ni and Zn in leachate were also found to be under inhibitory concentration for anaerobic digestion. Other trace metals such as Co and Mo etc were assumed to serve as the stimulatory micronutrients rather than to exert inhibitory effects on the microorganisms in the MSW anaerobic digestion.

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 1-60 © 2006 Nova Science Publishers, Inc.

Chapter 1

AN OVERVIEW OF RECENT ADVANCES AND TRENDS IN PLASTIC RECYLING Sati Manrich∗ Universidade Federal de São Carlos, São Carlos, São Paulo, Brazil

Amélia S. F. Santos Instituto de Pesquisas Tecnológicas do Estado de São Paulo, São Paulo, Brazil

ABSTRACT Since the discovery of plastics several decades ago, the widespread consumption of plastic products and their subsequent inappropriate disposal and accumulation have recently generated new societal concerns of waste management due to their inherent slow degradability, high volume increase and low recycling rates, which are negative on the basis of self-sustainability. Regulations imposing waste reduction, reuse and recycling indices and responsibilities, as well as effective collecting system and the development of new, environmentally clean recycling technologies are some of the efforts to achieve the self-sustainability goals. The efficiency of the collection and sorting systems impacts directly on the amount of recycled plastics and on their cleanness and quality, therefore, enlarging their market potential. The development of new recycling technologies is diversified and can be classified into mechanical, chemical and energetic recycling. In mechanical recycling, successful technologies are achieved through the improvement of existing processes using additives, blends with other plastics and alternative processing routes in order to maintain the original properties of the virgin resin and even allowing them to return to the same application as originally intended. Chemical recycling processes to obtain intermediary products for new polymers become feasible due to the cost reduction of the raw materials involved. Lastly, despite the under use of the gross energy potential of the raw materials employed, energetic recycling plants are gaining a proportion of residues whose technological solutions for separation and/or reprocessing ∗

Corresponding author: [email protected], phone: 55-16-3351-8503.

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Sati Manrich and Amélia S. F. Santos are deficient, but which, on the other hand, are voluminous, consequently solving the problem of both residue accumulation in densely populated regions and their respective insufficient energy supplies. In this chapter, the authors proposed to present an overview of the current state of this whole plastic recycling sector including their recent advances, and highlighting new markets and recent trends on recycling technologies around the world. However, mechanical recycling has been emphasized owing to the experimental and published work of Manrich’s workgroup at the 3R Residues Recycling Center, which has concentrated on studying all the steps in the process of mechanical recycling.

INTRODUCTION For sustainable development and the limitation of environmental impacts to become a realistic goal, reduction of the currently growing consumption of non-renewable natural resources, reuse of products following consumption and appropriate recycling of discarded residues are of paramount importance. The effective practical application of the “3R” concept is especially important for the burning of carbon-releasing energy sources to be minimized. Some studies have indicated that, even if all emissions of CO2 and other greenhouse gases were stopped immediately, the climate changes that have already occurred on the planet would remain for some decades. Since from the stand-point of thermodynamics and engineering practice, it is impossible to end such emissions altogether, efforts have to be made to reduce the risks to the environment, whenever the opportunity arises [1-3]. The reuse and various types of recycling of waste residues can lead to reductions in the use of non-renewable material and energy resources, with the energy savings generally ranked as follows: reuse > material recovery > energy recovery (energy from waste). Conversely, burying the residues in landfills, entailing as it does the total loss of material and energy, makes no such contribution [2, 4]. In the case of plastics, whose main current source of raw material is the petroleum, all recycling methods are technically viable and are briefly described next [5,6]. Mechanical recycling consists of the reprocessing of plastic residues into new products, different from or similar to the original products. The waste plastic used may come from the manufacturing process or from post-consumer products. This is the simplest way of recycling plastic waste, demanding the lowest initial investments. Chemical or feedstock recycling consists of using heat or chemical treatment to break down plastic residues into their basic chemical components, the monomers or other products, which can then be recombined into polymers or used for other applications. Typical examples of tertiary recycling processes are hydrolysis and pyrolysis. Unfortunately, this kind of recycling demands huge investments and is therefore viable only for large-scale operations where the volumes processed are comparable to those in the petrochemical industry (thousands of tons annually). Quaternary or energy recycling is the recovery of the energy bound in the plastic, by combustion, thus economizing on fossil fuels. However, the operation of such processes must guarantee that the emission of volatiles is controlled, to prevent the environment being contaminated by other paths [7, 8]. Recently, this type of process has been excluded from the normal concept of recycling and mentioned only as a form of energy recovery. In fact, this

An Overview of Recent Advances and Trends in Plastic Recyling

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line of recycling is often regarded as a wasteful underutilization of the gross energy stored in the plastic. Even though all the methods of material and energy recovery from plastic waste are technically feasible, in practice they encounter economic, legislative, market and other barriers. Published contributions in regulations, management and recycling of plastic waste using all forms of media are numerous around the world. Frequently, in books of edited contributions dedicated to plastic waste, each chapter deals separately with one of the topics covered. In this chapter, we present an overview of the current state of the whole plastics recycling sector, if somewhat sketchily in some areas, including a brief review of the recent research and development in the fields of mechanical, chemical / thermochemical and energy recycling of plastic waste. However, there is an emphasis on mechanical recycling, owing to the experimental and published work of Manrich’s workgroup at the 3R Residues Recycling Center, which has concentrated on studying all the steps in the process of mechanical recycling.

WASTE MANAGEMENT OF PLASTICS RESIDUES Since the emergence of plastics in the 1940s, which was impelled by their notable costbenefit advantages over the traditional materials they replaced, the concepts of security, comfort and hygiene have been improved. In addition, their intrinsic characteristics of lightness, low processing temperatures, durability, low thermal and electric conductivity, transparency and flexibility, among others, had an immediate and growing impact on the correlated manufacturing sectors, reducing consumption of both energy and natural resources. Furthermore, the plastics industry was enormously successful in developing novel materials such as plastic wood, synthetic leather and paper. On the other hand, the mounting volume of plastic residues, coupled with their extremely low biodegradability, generated a serious problem regarding the amount of space they took up. In the developed countries, the large urban centers have real difficulties in finding space for all the refuse, needing in some cases to transport solid waste over long distances to its final destination [9]. This problem, along with those arising from poor disposal methods and the associated environmental impact, the high added value of waste, the need to promote sustainable development of the production chain and to educate people to be more aware of the environment, has stimulated much research and practical activity in the fields of the recycling, degradability, reuse and reduced generation of plastic waste. In view of the fact that plastic is said to compose between 5% and 10 % by weight of municipal solid waste (MSW) [10-12] and yet is the material of which the smallest fraction is recycled [13, 14], there is an ongoing discussion among government, society and the manufacturing sector on the apportionment of responsibility for the management of plastic residues in MSW [15]. The difficulty in recycling plastics arises largely from the big fraction of plastic products considered unsuitable for recycling from the outset and from the high operational cost of plastic´s collection systems. Several mechanisms have been employed to increase the viability of the reversed logistics of returning the end-product packing material to the recycler: taxation of the

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manufacturing sector about government regulations [16] the establishment of taxes on nonrecyclable packaging [17] the mandatory use of recycled materials in some sectors [9] incentives on the use of articles made entirely of such materials, with the removal of all licensing requirements on those who wish to produce them [18] the opening of new markets for recycled plastic, implementation of policies of exchanging post-used packages etc. for toys, spendable vouchers, or sports material in needy communities [19, 20] and lastly programs to inform, raise public awareness and provide opportunities for consumers to play their part [21]. In parallel, initiatives used to improve the recyclability of packaging by manufacturing plastics parts with fewer different resins and with easier separation of components that contain distinct resins, and reduce the use of multilayered material [13] adhesives, additives and labels on packs also play an important role [9]. Thus, in various parts of the world regulations have been adopted in order to achieve short and medium-term recycling targets [13]. In the European Community (EC), which became the European Union (EU) in 1992, the goals for rates of recovery and recycling in the packaging sector were set by the Directive 94/62/EC [22] to member countries, establishing June 2001 as the deadline by which these goals had to be reached: recycling of at least 25% and at most 40% by weight of all waste packaging and recovery of at least 50% and at most 65%. In addition, for each specific type of material, the fraction recycled should be at least 15%. The available data confirm that these projected rates have been achieved in paper recycling in the EU [23]. Considering the plastic packaging sector, in Germany, the country that recycles the highest fraction of its waste in Europe, these targets have also been accomplished, or at least approximated, except in the case of composites. New EU targets for individual types of plastic waste have already been outlined for 2006, in which at least 20% of each type should be recycled [23]. These targets are currently being revised by the EU, but national governments, such as the UK, are also reconsidering their own packaging recycling and recovery targets for 2008 [21]. The particular concern over post-consumer plastic from the packaging sector can be explained by its short useful life, which reflects in its fraction 75% of all plastic waste [24]. In the EU, the recovery of plastic packaging residues was boosted mainly by improvements in mechanical recycling that resulted from better solid residue management practice [25]. The system of selective waste collection used in Germany, organized by Dual System Deutschland (DSD), is a worldwide reference [26]. In the EU countries in the decade from 1993 to 2003, generally speaking, the mechanically recycled fraction of all discarded plastic rose from 5.6% to 14.9%. Over the same period, largely because of the contribution made by energy recycling indexes, the fraction of plastic in landfill fell from 75.7% to 61% [14, 25, 27]. In Japan, the equivalent fraction for solid residues in sanitary tips is around 40% and much of this waste goes for energy recovery. The use of energy recycling in those countries is justified by the reduced combustion of fuels to produce energy, by the release of oil for the manufacture of virgin plastics and by the provision of an alternative source of energy that reduces the problem of energy shortage. Similarly, in 2000, about 11% of all plastic produced in the USA was recycled. This represents a great advance, since a mere 1% of plastic residues were recycled in 1987 [9]. Nevertheless, this advance in recycling indexes has been achieved by formal recycling

An Overview of Recent Advances and Trends in Plastic Recyling

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regulations [28]. Relating to Poly(ethylene terephthalate) (PET) recycling indexes, the USA is currently going through a period of stagnation in the recycling of this resin, according to the annual reports published by the American Plastics Council (APC), in spite of the very high recycling levels of PET achieved in 1995. At most, the amount of recycled PET is increasing in proportion to the growth in production of the resin [17, 29]. In 2001, the fraction recycled did not actually fall, but only because the slack in the home demand was absorbed by the export market [17, 30]. In 2004, the fraction of recycled PET was of the order of 21.6%, according to the National Association for PET Container Resources (NAPCOR) [31]. Turning to Brazil, in a national survey carried out by Plastivida, the plastics division of the Association of the Brazilian Chemical Industry (ABIQUIM), the proportion of plastic residues transformed by mechanical recycling is around 16.5%, higher than that in Europe [32]. Furthermore, Brazil is the third biggest market in the world for bottle-grade PET [18, 32] and the amount of this resin sent for recycling is of the order of 35% [20, 34, 35]. Given the precarious state of waste collection system in Brazil, such high rates of recycling are achieved only with the spontaneous involvement of low-income families whose earnings come largely from collecting plastic residues [20, 35]. This segment of the population currently represents about 500,000 informal workers [32]. Finally, another type of residue demands our attention: the great volume of rubber tires discarded annually in Brazil and accumulated annually around the world [36, 37]. Since the beginning of the nineties, many Federal and State Government ministries have been developing their own legal responsibility for this residue. In Brazil, resolution 258, passed by CONAMA (National Council for the Environment), obliges tire manufacturers and rebuilders (of retreads, remolds) to provide an environmentally correct destination for an amount of used tires proportional to their volume of production since 2002 and 2004, respectively [38].

FIRST STEPS OF PLASTIC MATERIAL RECOVERY PROCESS: SORTING AND CLEANING Sorting One of the stages of plastic recycling that most threaten its feasibility as a productive operation is the sorting of plastic material from mixed waste and, especially, separation of the different types of plastic, which is hindered by the fact that quite different plastics may be used for the same end. In other words, a given product can be fabricated with very similar characteristics from distinct plastics and these act, in mixed residues, as impurities of each other after separation. This reduces the viability of the process and, in serious cases, can cause a whole production line to be shut down [39, 40]. Related problems that must also be taken into account are those of multicomponent items, good examples being car parts and plastic electric and electronic devices with embedded metal inserts, and multilayered products such as laminated, co-extruded or metalized flexible packaging [39-41]. The ideal practical solution to this problem would be to make suitable alterations in the plastic residues at source; that is, to redesign the original plastic product. At the design stage, then, priority should be given to reducing the number and variety of components in one

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product and the variety of materials employed as consumer goods with identical functions. Such ideas are exactly the opposite of current design trends, particularly in the packaging and disposable goods sectors. In most cases, the existence of multicomponent and multilayer residues is justified primarily on technical grounds, while the reasons for fabricating essentially the same product from diverse materials are based on economics and marketing [41]. It is thus hard to imagine the above-mentioned reversal in product design trends becoming a manufacturing priority on the grounds of purely environmental gains. Nevertheless, on the positive side, all over the world we see a lot of effort being put into the research and development of appropriate technology that will minimize the problems caused by mixed plastic waste and varying materials. These studies concentrate on two fronts: the efficient separation of different plastics and other components, and optimization of the composition of compatible blends, or plastic composites of different materials, that combine, profitably, the distinct properties of the component polymers [39-46]. The first of these research areas will be discussed here and blends and composites in later sections. The techniques used to separate mixed plastic residues can be classified in several ways, but here they will be grouped as manual or automatic and each will be approached in a specific way.

Manual Separation The efficiency and productivity of this method depend entirely on the experience of the workers responsible for identifying and sorting the plastic residues. This is the method used in the vast majority of micro and mini-enterprises in developing countries, where manual labor is cheap, and in Materials Recovery Facilities (MRFs) worldwide, although it is still used even in some large organizations that recycle electro-electronic residues in developed countries [39, 42]. When training technical personnel in the manual separation of plastics, basic notions of how to distinguish between these materials have to be introduced. A systematic procedure for the identification of components of municipal plastic waste, especially the most prevalent plastics, which was proposed in an earlier publication of the Manrich’s workgroup, has until now helped the Brazilian public to achieve this aim [39]. This method consists of three steps: in the first, the identification is made directly by codes; in the second, the identified product is correlated with the most likely material, and in the third, certain properties specific to each material are determined. The three steps are briefly described next. −

−

Step 1: Locate the identification code and note the number or abbreviation found in the recyclable plastic symbol: 1 = PET, 2 = HDPE, 3 = PVC, 4 = LDPE/LLDPE, 5 = PP, 6 = PS and 7 = others, where HDPE, LDPE and LLDPE are high density, lowdensity and linear low density polyethylene, respectively, PVC is poly(vinyl chloride), PP is polypropylene, and PS is polystyrene. However, the residue from a product, part or component does not always display a code, which may be molded in relief or printed on the surface. If the code is missing or identified as 7, the procedure has to move on to the following steps. Step 2: Consult a table of data, such as Table 1, which helps the user to identify the most likely material in a given product. It is found that, contrary to what would be

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7

environmentally correct, the number of most probable materials rises through the years, albeit rather slowly. Hence, from time to time, these tables need revising. Table 1. Polymers used most frequently in fabrication of packaging material. Type of packaging

Bottles

Pots, containers and trays

Lids

Plastic bags

Typical use Carbonated soft drinks Cleaning materials and toiletries Cooking oil Mineral water Vinegar Yoghurt drinks Margarine Yoghurt Sweets and chocolates Disposable plastic cups Prepacked fruit & vegetables Soft drinks Cleaning materials and toiletries Cooking oil Vinegar Yoghurt Margarine Mineral water Sweets and chocolates Supermarket bags Fruit and vegetable bags

Films† Biscuits and snacks bags

Most probable material* PET HDPE, PP, PVC PET, PVC PET, PP, PVC PP, PVC HDPE, HIPS, PP HIPS, PP HDPE, HIPS, PP PET, PP, PS, PVC HIPS, PP PS, PVC PP HDPE, PP HDPE, PP LDPE HIPS, PP HIPS, PP LDPE, HDPE, PP HDPE, HIPS, PP, PS HDPE, PP LDPE, LDPE/LLDPE, HDPE, PP LDPE, LDPE/LLDPE, PP

*

While these materials are the most likely ones, the packaging can be made from others. † Film is a term used for plastic sheets 254 µm or less thick, normally used in shopping bags.

−

Step 3: Given the list of most likely plastics, determine some specific distinguishing properties that are simple to compare; these are indicated below, for the case of postconsumer plastic packaging. Here we will omit the techniques of differential scanning calorimetry and infrared spectroscopy. Depending on the plastics in question, identification may be achieved by testing only one of these properties, or a sequence of tests may be required. This sequence varies from case to case and an example will be given later, for the case of plastic bottles. − Transparency: transparent ⇒ PET, PP, PVC, PS; translucent or opaque ⇒ HDPE, PP, high-impact polystyrene (HIPS), LDPE/LLDPE, PET. − Whitening: exhibit whitening when folded ⇒ PP, HIPS, PS, PVC. − Hinge: PP is the only plastic that withstands the repeated force used to open and close the pack with a one-part device, the hinge.

8

Sati Manrich and Amélia S. F. Santos − − − −

−

Density: the polyolefins, (HDPE, LDPE, LLDPE, PP) and expanded polystyrene (EPS) float on water, being less dense (ρ < 1.0 g.cm-3). Combustion: the flames and smoke given off by burning plastic are characteristic of each type. Table 2 describes these features of several plastics. Solubility: ability to dissolve in various liquids or solvents is specific to each plastic. Table 3 shows some examples. Halogen or Beilstein test: if a copper wire is heated to redness, rested on the plastic and then returned to the flame, and the flame turns green, the residue is a halogenated plastic, such as PVC, which contains chlorine. Hardness and malleability: it is very hard to distinguish polyolefins from each other by means of simple tests alone. Experienced technicians differentiate the polyethylenes, LDPE and HDPE, from other plastics, including PP, as they are readily scratched with the fingernail, whereas the rest are too hard. Since LDPE is more malleable than HDPE and PP, it can be distinguished by bending or pressing the article.

Table 2. Behavior on combustion of the main polymers found in MSW. Material

pH of smoke Odor of smoke

HDPE, LDPE, LLDPE PS, EPS, HIPS, ABS PP

Neutral

PVC

Acid

PMMA

Neutral

NYLON

Basic

PET PC

Neutral Neutral

PU

Neutral

Cellophane (regenerated cellulose)

Basic

Neutral Neutral

Burnt candle

Color of flame

Yellow with blue base Styrene smell / Yellow with blue with much soot base Burnt candle Yellow with blue base Acrid Yellow with green base Methyl Yellow with blue methacrylate base (acrylic) Burnt hair Blue with yellow tips Sweetish Yellow Phenolic Yellow (carbolic) Acrid, pungent, Yellow with blue sour base Burnt paper or Greenish-yellow plant material

Ignition/ selfextinguishing

Ignites Ignites Ignites Self-extinguishes Ignites

Ignites Ignites Ignites Ignites Ignites

An Overview of Recent Advances and Trends in Plastic Recyling Table 3. Solubility of polymers in various solvents. Polymer Soluble in HDPE Decalin*, tetralin*, xylene† LDPE Heptane*, xylene*, decalin*, tetralin LLDPE Xylene†, decalin*, tetralin* PP Xylene†, decalin*, tetralin* PET o-chlorophenol*, nitrobenzene*

EPS, PS ABS, HIPS PVC NYLON

PC PMMA PTFE * †

Chloroform, xylene, tetrahydrofuran (THF), ethyl ether Chloroform, xylene, THF, methylene chloride Cyclohexanone, MEK, DMF, THF Formic acid, phenol, trifluoroethanol, concentrated sulfuric acid Chloroform, cyclohexanone, DMF, cresol, methylene chloride Acetone, toluene, chloroform, MEK, THF Insoluble (soluble only in fluorinated kerosene at 300°C)

Insoluble in Ethyl alcohol, chloroform, benzene, acetone Ethyl alcohol, chloroform, benzene or petroleum ether, acetone Ethyl alcohol, chloroform, benzene, acetone Ethyl alcohol, chloroform, benzene, acetone Xylene, ethyl alcohol, chloroform, benzene, acetone, cyclohexanone, methyl ethyl ketone (MEK), dimethyl formamide (DMF), THF Alcohols

Alcohols, benzene Chloroform, alcohols, xylene Alcohols, chloroform, xylene, acetone

Alcohols, benzene, acetone

Soluble at temperatures above 50oC. Soluble at temperatures above 100 oC.

Table 4. Practical test sequence suggested for plastic identification from a mixture of waste plastic bottles. Property

Transparent

Translucent

Probable material

PET, PP, PVC

HDPE, HIPS, PP

Property

Opaque HDPE, HIPS, LDPE/LLDPE, PP, PET Density < 1 Density > 1

Whiten Do not Whiten Do not when folded whiten when folded whiten Probable material PP, PVC PET, PVC HIPS, PP HDPE HDPE,LDPE HIPS, PET / LLDPE, PP Density Hardness Comb. Halogen test Halogen test Density Further tests Comb. Comb. Malleability Solubility Density Comb. needed to Solubility Solubility Comb. complete or Solubility confirm identification

9

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Sati Manrich and Amélia S. F. Santos

The test sequence suggested for the specific case of bottles is shown in Table 4. It must be said that manual separation of a mixture of PET and PVC bottles etc is quite easy, since carbonated soft drink bottles are all of PET and the rest can be differentiated by inspecting the base. If the bottle was injection molded as a preformed, then blow-molded with an injectionpoint at the middle of the base, it is made of PET; if it was extrusion parison blow-molded, with a weld-line across the base, it is PVC.

Automatic Separation Automatic separation, like manual, is based on differentiating a given plastic in the waste from the rest by means of its physical or chemical characteristics. The main properties exploited are density, chemical structure, solubility, surface character and electrostatic and thermomechanical properties. Density In plastics recycling, apart from the traditional and modern hydrocyclones that separate materials by density differences as little as 0.01 g.cm-3, there are simpler processes, with separating tanks containing aqueous solutions of various densities. The sketch in Figure 1 shows how this might be done in the case of typical mixed municipal plastic waste.

LLD/ LDPE PP

Floating waste

Sinking waste

HDPE LLD/ LDPE PP

HDPE Water + 40-45 wt% ethanol

PP LLD/ LDPE Water + 50-55 wt% ethanol

PS PET PVC PS

100% Water

PVC PET Water + 20-27 wt% NaCl

PP LLD/LDPE HDPE PS pPVC uPVC PET

ρ (g/cm3) 0.89-0.91 0.91-0.94 0.94-0.96 1.04-1.10 1.16-1.35 1.35-1.45 1.33-1.39

Figure 1. Separating tanks with water solutions for sorting municipal plastic waste.

Tsunekawa et al [42] have developed a process using density differences, based on experiments in the laboratory and in a pilot plant designed to separate plastics, recovered from scrapped copying machines, by a jigging method, which has culminated in a commercial plant, built recently to recycle office equipment, domestic appliances and automobile shredder residue. Jiggers have been used in the technology of separation for a long time and are widespread mining sector. In this technique, water covering the material is pulsed at given amplitudes and

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frequencies, and the jolting of the solid particles results in their forming stratified layers arranged in order of density. In this plant, the TACUB Jig [42] was used and adapted to separate a ternary mixture of milled PS, acrylonitrile butadiene styrene (ABS) and PET, whose respective densities are 1.06, 1.18 and 1.71 g.cm-3. Water density was raised by adding zinc chloride. The pilot studies showed that, apart from the amplitude and frequency of the pulses in the water, other factors affected separation efficiency, including: height of the liquid (bed thickness), float level, water flow-rate and waveform. When performance was optimized by varying these conditions and analyzing the results, the plant separated 99.8% of the PS, 99.3% ABS and 98.6% PET for the ternary mixture.

Chemical Structure Plastics can be differentiated and separated on the basis of atoms or bonds specific to their chemical structure, with the aid of devices based on infrared (IR) spectroscopy. Plastic residues, whole or ground into flakes, can be placed on a conveyor belt and scanned continuously by such a device, whose IR radiation source is adjusted to the absorption wavelengths of the plastic in question. Any change in the absorption spectrum discloses the presence of an impurity at a specific point on the belt at that moment, thus defining the exact position and time, moments later, where a jet of compressed air should be activated. The foreign object is blown off the belt, to land on another, below the first, moving at right-angles to it and so effecting the separation [44]. By exchanging the IR source for one radiating in the ultraviolet-visible range (UV-VIS), the traditional technique used to separate glass by color can be employed. The advantage of equipment of this type is that plastic residues previously ground into flakes can be automatically separated, using different sources of radiation. Solubility The solubility profile of each plastic, already mentioned in connection with manual separation, is also the basis of automatic separation by selective dissolution. This can be used in two ways: either the plastic to be separated is extracted in a solvent that does not dissolve the others, or the residue is extracted batchwise with a common solvent that dissolves each plastic at a different temperature [45, 46]. Van Ness and Noster [46] presented the outline of a selective extraction process and the results of trials of the proposed method, performed by Linch Naumam with a mixture of known composition, containing virgin resins (LDPE, HDPE, PP, PS, PVC and PET), and a real mixture of post-consumer plastic residues. The efficiency of separation was found to be better than 99% in the case of the virgin resins, when tetrahydrofuran (THF) and xylene were used for selective dissolution at more than one temperature. However, it was not possible to separate PS from PVC at room temperature, or HDPE from PP at 160 °C, with THF. In general, for the plastic mixtures discussed here, separation by density (see above) is more practical, as it is cheaper and environmentally friendly; however, it will not separate PVC from PET. When these are present, selective dissolution could be alternatively employed as a complementary final step, using xylene at 138 °C. In addition, solvent extraction is suitable for multicomponent or multilayer residues [41, 47].

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Sati Manrich and Amélia S. F. Santos

Surface Properties Most plastics exhibit low surface energy, making them hydrophobic. Despite this, the surface of plastics can be wetted by treating them with surfactant solutions, making them hydrophilic. The surfactants normally used for surface treatments consist of molecules with an affinity for organic polymers, but which also have hydrophilic groups. These surface modifiers are not equally efficient with all plastics, so that a given surfactant may be most effective for a specific plastic. These differences are exploited in the separation of residues by the method of froth flotation [48, 49]. The method is basically to put the treated plastic residues in a tank of water containing a frother and then introduce air-bubbles, which tend to stick to the hydrophobic particles, for which the surfactant was less effective. The clusters of bubbles and particles usually rise to the surface of the bath, in contrast to the hydrophilic particles, allowing the different materials to be separated. Research on selective froth flotation focuses mainly on binary mixtures of PET and PVC [48, 49]. Drelich et al [48] applied the surface treatment in strongly alkaline solutions of caustic soda and used C9-11 ethoxylated alcohols as frothers in the flotation tank. The preliminary treatment made the PET hydrophilic, while hardly affecting the hydrophobicity of the PVC, and this was confirmed by measuring the advancing and receding water contact angles on each surface. The efficiency of separation attained was 95-100% in a variety of PET/PVC mixtures and flotation conditions. In the work of Marques and Tenório [49], the surfactant used was calcium lignin sulfonate and the frother methyl isobutyl carbinol. Some of the experimental conditions were again varied, as were the sizes of PVC and PET particles. In the best conditions, 98.9% of the PVC and 99.3% of the PET were separated, at purities of 99.3% and 98.9% respectively. Electrostatic Properties The separation of several types of plastic packaging on the basis of differential triboelectrification was investigated by Hearn and Ballard [50]. The triboelectric effect is induced by rubbing two materials together so that, on separation, one retains a negative electrostatic charge and the other, a positive one. If two different plastics are rubbed against a third material chosen as a suitable reference, the charge generated on the latter should be positive with one plastic and negative with the other. In the cited work, polyvinylidene fluoride (PVDF) and poly(butylene terephathalate) (PBT) were tested as triboelectric probes for the separation of mixed packaging residues of HDPE, PET, PP, PS and PVC. From the results, a separation line was proposed for domestic waste in which the PVDF and PBT probes were mounted in sequence along a conveyor belt. At the first probe, PP would be separated from the rest as the only component to be charged negatively by PVDF. At the second point, PET and PS would receive a negative charge from PBT and thus be separated from the remaining mixture of HDPE and PVC, which would be positively charged. No method was suggested to separate PET from PS, but it was proposed that a visible light-based device could recognize and separate transparent objects like PVC from opaque ones such as HDPE. Once again it is worth remembering that, to separate this kind of mixture, it would be preferable to try other techniques that are simpler, cheaper, more practical and efficient.

An Overview of Recent Advances and Trends in Plastic Recyling

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Thermo-mechanical Properties The mechanism by which a material suffers mechanical fracture, brittle or ductile, depends mainly on the temperature and rate of strain. If a mixture of two plastics is ground under specific conditions that cause each material to break in a distinctive way, the resulting particles will have different shapes and sizes that might be separable later by sieving or by means of air cyclones or hydrocyclones. This way of separating binary mixtures of plastics can be applied when there is a temperature range where the two brittle-ductile transition temperatures are different from each other, in which the two plastics would break in different failure mode. In their study, Green et al concluded that the processing window of temperatures for selective impact grinding of a mixture of PET and PVC could be predicted from tensile stress tests and measurements of β-relaxation properties of each plastic [51]. Green et al [51] refer to two cases of processes, one in a patent and one used by a company, which produced particles of PVC smaller than PET after mixtures were crushed or subjected to impact grinding. In the case of cryogenic grinding, it was possible to recover PVC, 99% pure. A more recent approach to separating mixtures of plastics by their thermal transitions, which took into account the effect of dirt present in the residues, was proposed by Saito and Satoh [52]. In this study, the differing thermal adhesion behavior of different plastics was analyzed by employing two unsteady heat conduction apparatus. One consisting of a plate to heat, press and then to pull the adhered plastic pellets, so as to determine the adhesion temperature and the effects of varying some parameters, and the other counter-rotating twin rollers were used to improve the efficiency of adhesion. Tests were carried out on a mixture of pellets of PET, LDPE, PS, HDPE and PP. Generally, the thermal adhesion temperature of a polymeric substance is specific to each material and related to its glass transition or melting point. Saito and Satoh [52] showed that the size and shape distributions of the pellets affect adhesion, but within a characteristic temperature range for each material. Their proposed method succeeded well in separating a mixture of three plastics, PET, PS and PP. While these authors and collaborators showed that dirt caused only a slight rise in the adhesion temperatures, it remains true that a real mix of residues is very different from pellets, especially in terms of the shape and size of the particles. The separation of wasted plastic flakes needs to happen before extrusion into pellets, which would remains as a great challenge to be solved by this methodology.

Cleaning As previously mentioned, the collection of the residues from which used plastic is salvaged play an important role in raising the recycling indexes [31, 35]. On the other hand, that activity is also directly responsible for the extent of contamination of plastic residues, which in turn has a strong influence on the cleaning process and hence on the effluent discharged. It is clear that plastics, during their use and disposal, come into contact with other compounds, and their composition may be changed by contaminants permeating through and

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Sati Manrich and Amélia S. F. Santos

impregnating the material [53]. Thus, before recycling it is necessary to determine the extent of contamination, the contaminating chemicals and the intended use of the end-product, in order to adapt the cleaning technique as appropriate. Processes employing aqueous solutions are normally used to remove surface contaminants [54, 55]. However, these are not so effective in removing hydrophobic compounds or those that have migrated into the polymer matrix. These solutions generally contain caustic soda and surfactants, the proportions and flow-rates varying according to the type of material being recycled. Usually this is a continuous process in which the plastic, previously grinded into flakes, is vigorously shaken in the cleaning solution. The concentration of the alkali depends basically on the amount of glue and labels attached to the flakes [54]. The removal of adhesives is important, especially for polymers susceptible to degradation in acid conditions, because at reprocessing temperatures, adhesives decompose to acids compounds. Apart from sodium hydroxide, alkaline reagents commonly used include calcium hydroxide (lime), potassium hydroxide, sodium silicate, etc. The preferred alkaline fluid for this purpose is normally a mixed solution of 33% sodium hydroxide and 15% potassium hydroxide (caustic potash), although the susceptibility of a given polymer to degradation in alkaline conditions has to be taken into account when choosing these reagents [56]. The concentration of caustic soda used is usually adjusted to provide the desired alkalinity [54]. The concentrations of surfactants used are normally between 75 and 200 ppm. These agents are important in many real situations where the surfaces are contaminated with soil or microorganism. To choose a particular cleaning agent, it is necessary to consider the soil type, oil residues and unusual paints likely to be encountered. Other factors, such as the cleaning equipment, pH, liquid or solid state, work safety, environmental laws and costs of disposal should also affect the choice of the correct cleaning agents [55]. The cleaning step, in most cases, takes between 5 and 20 minutes at temperatures up to 88 °C. Short times do not suffice to remove adhesives, while periods exceeding 20 minutes give a low return, while the use of baths at high temperatures facilitates the removal of glue [55]. In view of the nature of the cleaning process and its relevance to the quality of the recycled product, it is vital that recycling activities that involve washing procedures go hand in hand with an evaluation of the effluents generated and discharged during this stage, so as to avoid merely swapping pollutants. Furthermore, the need to comply with both the international code ISO 14000 and local obligations to preserve the quality of water (in Brazil written into the Federal Constitution) make it essential to analyze the effluent from mechanical recycling. Therefore, on the basis of previous studies about which thermoplastics are present in greatest amounts in MSW [12, 25], the Residues Recycling Center, 3R-nrr, at Federal University of São Carlos (UFSCar) have conducted laboratory-scale tests to characterize the liquid effluent produced by the cleaning of the three plastics found in largest proportions in rigid plastic packaging residues, viz. PET and two polyolefins, high density polyethylene (HDPE) and polypropylene (PP). The polluting load of these effluents demonstrated that they were comparable to that of domestic sewage with a medium concentration of pollutants. No significant differences in the effluent characteristics were found between the two types of plastic studied, except for those differences intrinsic to the cleaning processes (temperature, surfactant, caustic soda

An Overview of Recent Advances and Trends in Plastic Recyling

15

concentration, pH) or arising from contamination of the plastics (oils and fats, solids). Generally speaking, these effluents would need to be treated before being discharged into bodies of water or even into sewage systems. Therefore, any plans for implementation of plastic recycling units should include an appropriate destination for such effluents in accordance with their final composition [57]. On the other hand, selective collection of these wastes proved to generate a much lower polluting load, as reported by Heyde and Kremer [58], indicating the importance of this type of collection since, among other advantages, it reduces the pollution deriving from the recycling process. Yet another advantage of selective separation of waste is that it reduces the need for and concentration of the cleaning agents used during recycling, thereby reducing its environmental impact and cost. Another aspect of the work performed in 3R-nrr is the use of the effluent characteristics to evaluate the process parameters in terms of cleanness efficiency. Good correlations were shown, since there is no addition of chemicals and all the performance was evaluated through only one batch [57, 59-61].

MECHANICAL RECYCLING As defined earlier, mechanical recycling is the process of converting discarded plastic into new products, principally by melting and molding. In this form of recycling, the macromolecular nature of the polymer is not destroyed, so that the degradation reactions that directly affect the physical and chemical properties of the polymer and, at times, its appearance, are minimized and controlled, irrespective of the processing method chosen. Nevertheless, chemical changes that occurred during the original processing and in-service use may have a negative effect on the quality of products reprocessed by mechanical recycling, in comparison with those manufactured from virgin resin. Mechanical recycling involves several steps, which generally include the following: collection, separation, grinding for large or thick objects or agglutination for films and thin objects, cleaning of the plastic to eliminate organic matter, drying (particularly important for polymers that are hydrolyzed) and reprocessing (Figure 2). Some of these steps are also important in chemical or energy recycling and may be taken out or added according to the needs of the material/object being recycled, the desired end-product and available conditions. The importance of the collection, separation and cleaning steps has already been mentioned. The stage of breaking into flakes or binding together, which normally occurs between separation and cleaning of the plastics, is mainly done to reduce the overall volume taken up by the plastic residues and to promote the interaction of those residues with the cleaning solution [62]. However, the size of the flakes produced at this stage may interfere with the cleaning efficiency, as the mass-transfer rate between the liquid and solid phases depends on the velocity gradient of the liquid near the surface of the flake [63]. Also, during extrusion of the plastic, depending on the system used, the size of flakes in the feed can be a hindrance to the feeding process [64].

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Sati Manrich and Amélia S. F. Santos

Figure 2. Complete recycling scheme (identification, separation and classification of different types of plastics (1); grinding (2); washing with or without addition of cleaning agents (3); drying (4); silos (5); agglutination (films and products with fine thickness) (6); extrusion (7); and granulation (8)).

After cleaning comes the drying step. This is mainly important in the subsequent reprocessing of molten polymers susceptible to hydrolysis and in the production of composites with inorganic fillers. The conditions chosen for drying depend, among other factors, on the type of humidity and the way it is bound to the material [65]. According to published work on this topic, there are three distinct kinds of moisture on recycled material: surface moisture, in the form of an external film, maintained by surface tension; freemoisture, which is inside nonhygroscopic materials, and bound moisture, either hygroscopic or dissolved, which exerts a lower vapor pressure than the pure liquid at the same temperature. Materials classified as hygroscopic are those that contain water in a homogeneous solution in the solid phase, whose vapor pressure is below that of pure water. In these materials, water is normally extracted by diffusion. However, if the water content exceeds the maximum hygroscopic content, so that part of the water is free, then until the latter water is removed the material will behave as a nonhygroscopic material. The drying conditions for hygroscopic solids are generally more aggressive than for others, since the lower the vapor pressure of the water, the higher its temperature of vaporization. By definition, the latter is the temperature at which the vapor pressure of the water is equal to the ambient pressure [66]. Consequently, drying processes for hygroscopic materials normally use high temperatures, with a supply of a suitable gas or a vacuum. The duration of this stage will depend on the temperature, the concentration gradient of water in the atmosphere, the relative velocity of the air, the residual humidity required and the pressure in the system. In vacuum drying, the concentration gradient and reduced vaporization point of the water, due to low pressure, are attractive features in view of the shorter time taken and the high quality of the end-product [66] if compared with other drying systems. Its chief benefit arises from the fast

An Overview of Recent Advances and Trends in Plastic Recyling

17

internal migration of the liquid resulting from the increased internal pressure gradient, which forces the water out to the edge of the material [67]. Finally, other factors affecting the drying time in hygroscopic materials are the size and shape of the particle and the degree of crystallinity. The bigger the particle, the larger is the path for water to migrate from the middle to the surface of particle. Conversely, the smaller the particle, the greater is the equilibrium water content, since the surface area available for absorption is larger [68]. Regarding crystallinity, the higher the proportion of crystalline phase in the polymer, the lower will be its final equilibrium water content. On the other hand, higher crystallinity also implies a lower diffusion coefficient of the water in the polymer matrix [68]. Owing to the first of these known correlations, commercial granules are normally sold in the crystalline state. Moreover, in polymers that crystallize relatively slowly, cold crystallization may occur alongside drying. In this case, especially if the recycled material contains flakes in the amorphous state, the drying is normally carried out with agitation or in a fluidized system, to prevent the particles sticking together because of the heat liberated during crystallization. After the water content has been reduced, the material proceeds to the remelting / restabilizing step, which directly affects the eventual quality of the end-product. At this point, the polymer mixture is formulated in accordance with the target application. Besides stabilizers, various other agents may be added to the polymer: reinforcements, other kinds of polymer, coupling agents, flame retardants [69], foaming agents [70, 71] and so on. Variations that have been employed to add more value to the recycled product and/or to widen its market niche include, for example, solid-state polymerization to recover the original properties of virgin PET, dissolution and reprecipitation to obtain high quality, very pure material [72, 73], electrospinning to make nanofibre from recycled expanded polystyrene (EPS) [74], civil engineering [75] and road construction [76] applications and synthetic paper. While all these initiatives are highly relevant to the goal of raising the fraction of waste plastic that is recycled, only a few will be described in more detail in this section.

Remelting-restabilization During reprocessing, it is necessary to limit the polymer degradation processes and thus guarantee its performance, to protect its added value. Degradation leads to molecular-weight variation, the inclusion of new groups in the polymer structure and undesirable changes in the appearance and properties of the material. Hence, this mechanical recycling step depends crucially on studying the degradation and restabilization behavior of recycled plastics. Some researchers have reported that, during reprocessing, thermoplastics exhibit the same processes of degradation as the equivalent virgin plastics, but accelerated. This occurs because of structural elements introduced by previous thermomechanical degradation, thermooxidation and photooxidation, and sensitized oxygenated chromophore groups that are products of oxidation. These elements affect both the susceptibility of the polymer towards further degradation and its miscibility with others. For this reason, polymer residues destined for mechanical recycling must not have been degraded to the extent that they have lost their original properties, nor can they contain high concentrations of sensitized oxygenated chromophore groups.

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During reprocessing, the polymer cannot be stabilized to block the oxidizing action of these groups, nor can a degraded polymer be transformed into a high quality recycled product, since its original rheological and/or optical properties cannot be recovered all at once [77]. Restabilization only ensures that the reprocessing is performed without a significant advance in the state of degradation and that the degradation mechanism proceeds at a much slower rate than would otherwise be the case. Another factor that contributes to the loss of stability of polymers while undergoing their first cycle of use is the consumption of protective additives in the materials during their production, service life and disposal. Thus, information on the resistance of recycled polymers to degradation, obtained by determining their susceptibility to oxidation and their residual stabilizer contents, would allow the stabilizing agents to be used more effectively and efficiently to block the advance of further degradation [78, 79].

Degradation Mechanisms Degradation occurs by various types of reaction classified as follows: thermal degradation, mechanical degradation, chemical degradation, photodegradation, biodegradation, thermomechanical degradation, mechanochemical degradation and photobiodegradation [78]. During reprocessing, the commonest types of degradation for most polymers are thermooxidation combined with mechanical degradation. In the special case of hydrolyzable polymers, hydrolysis is the predominant reaction and an extremely low residual water content is required, such as 20ppm (0.002%) for PET blow molding or injection molding. Oxygen acts as a catalyst of several types of degradation reaction, according to published evidence from various studies [80, 81]. In fact, the chromophore groups responsible for yellowing in PET are formed by thermooxidation reactions in the polymer [82-85]. Research carried out by the authors and co-workers indicates that the discoloration of PET can be accelerated by the relative humidity of air [86]. Hence, the temperature, the shear rate, the atmosphere and water content have significant effects on recycled plastic processing, in accordance with the type of polymer and its main mechanism of degradation. However, irrespective of the predominant mechanism, the initiation reactions that lead to free radicals being formed take place typically via cleavage of either the main backbone or branches of the polymer. During the propagation of polymer degradation, the following may occur [87]: −

polymer free radicals recombine to form crosslinks or branches. On the whole, this propagation reaction does not predominate, since such free radicals have low mobility in the polymer matrix (slow physicochemical process of diffusion) and only rarely will they recombine. On the other hand, polymers with occasional unsaturated groups (such as vinyl, vinylidene) in their structure may favor this type of reaction under certain conditions of temperature and oxygen content in the atmosphere and in the presence of specific additives such as peroxides [88]. The predominance of this reaction is reflected in a drop in the fluidity or melt flow index (MFI) and intrinsic viscosity of a solution of the polymer (reduction in the free volume of the polymer chains in dilute solution) and increases in the polydispersity (PD) and viscosity of the melt.

An Overview of Recent Advances and Trends in Plastic Recyling −

disproportionation of radicals to form linear products.

CH3 C CH2

Iniciator Iniciador

CH3

CH2

C CH2

C

CH3 +

CH3

H − −

19

CH (1)

liberation of monomers by depolymerization. chain reactions via free radicals in the presence of oxygen. These reactions are widespread and give rise to peroxy radicals (RO2•) (Eq.2), which readily remove hydrogen from the polymer matrix by forming hydroperoxides (ROOH) and other radicals (Eq. 3) [78]. In turn, the hydroperoxides, initial products of oxidative degradation of polymers, are easily decomposed by heat or light (at near-UV wavelengths) to alkoxy (C-O•) and hydroxyl (OH•) radicals, since the O–O bond is weak.

C O2

C + O2

(2)

H C O2

+

C

kr

C OOH +

C (3)

As a result of the action of the disproportionation and chain reactions promoted by free radicals in the presence of oxygen, the proportion of high-molecular-weight polymer chains is observed to fall, resulting in reduced viscosities of both the melt and the polymer solution and a narrowing in the molecular-weight distribution (MWD) [88]. Polymers are thought to have a critical molecular weight (Mc), below which they become brittle. Among polyolefins, this is generally assumed to correspond to the point during degradation when the number average molecular weight ( M n ) has fallen to around half of the original value [87]. Some authors claim it can be taken to be in the region of 10 kDa. For example, polycarbonate has an estimated Mc of 14 kDa and for polyamide 11, Mc = 15 kDa [89]. This critical value relates to the fact that scission of the polymer chain is confined to the amorphous regions and tie segments that connects the amorphous and crystalline regions. As consequences of chain scission in amorphous phase, the stress transmitted between adjacent crystalline zones decreases dramatically reducing the elongation at break. Additionally, the chain segments released from previously entangled regions are allowed to crystallize, causing a rise in the density (crystallinity) during oxidation. This last phenomenon, known as chemicrystallization, may lead to the formation of surface fissures, which act as stress concentrators during elongation under tension or flexure [87].

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Finally, processes that terminate degradation can occur either by the recombination (branching and/or crosslinking) or dissociation (chain scission) of free radicals, thus transformed into inert or stable products. If the dominant reaction is recombination, there will be a rise in the thermal distortion temperature and the creep and softening points, simultaneously with reductions in flexibility and in the elongation at break of the polymer [87]. Conversely, if dissociation predominates, there will be a fall in M n and in the breaking tension. It follows that the type of reaction prevailing during degradation is what determines the eventual properties of the compound or polymer. Concerning the kinetics of polymer oxidation, the rate of these reactions depends on a series of factors, apart from the structural properties of the polymer previously commented, including the duration of oxygen absorption, the oxygen content in the polymer, pressure, action of light, temperature and traces of transition metals. These reactions also characteristically exhibit induction periods, are self-catalyzing and can be inhibited or retarded with additives [87]. The reaction rate of oxidation (Eq.2) is controlled mainly by the direct attack of oxygen at the most vulnerable sites in the various chemical structures of the polymer, such as the immediate neighborhoods of unsaturated bonds or tertiary carbon atoms [78, 87]. The probability of these initial reactions to occur is higher when the polymer has more reactive hydrogen. A classic example of this is the lower oxidation stability of polypropylene (PP), compared to high-density polyethylene (HDPE), due to the presence in PP of a larger number of tertiary carbons. Thus, PP is rarely used without antioxidants. The decomposition of hydroperoxides can be accelerated by traces of metals (Zn, Ti, Fe, Cr, Cd, V, Al and Cu from cable insulators, etc.), originating from impurities, pigments and residues of catalysts (polyolefins), acid residues (chlorine from TiCl3, AlR2Cl or MgCl2), fillers and antistatic agents. The catalytic power of the transition metals can be put in the following order: Ba < Mg < Al < Ti < Ni < V < Fe < Cr < Co [90]. These impurities can allow oxidative degradation of the polyolefins by chain scission to occur at lower temperatures (< 150°C), if the number of unsaturated groups is minimal (<<0.1% by weight) [88]. An example is PP formulations with stearates that contain transition metals, which suffer thermal oxidation at 125°C. At low temperatures, the proportions of unsaturated bonds and tertiary carbons seem to be secondary factors compared to transition metals and acid residues. Nevertheless, if an olefin polymer has low crystallinity and a high content of unsaturated groups (>> 0.2 ωt%), such as diene terpolymers, e.g. ethylenepropylene-diene elastomers (EPDM), crosslinked networks can be formed at low temperatures (<< 150°C) [88]. Hydroperoxide decomposition reactions (Eq.4) induced by metals can be outlined as follows [78, 87]: +++ → RO• + M + OH ++ + + ROOH + M → ROO• + H + M or traces of metals 2ROOH RO• + ROO• + H2O ROOH + M

++

(4)

The alkoxy radicals produced in these decompositions reactions, or by the recombination of tert-peroxy (PP), generally combine with H from the polymer matrix, forming alcohols,

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water and new free radicals (Eq.5), or suffer β-cleavage (Eq.6). Alkoxy radicals are less selective in their reaction targets than peroxy radicals, as they may oxidize tertiary, secondary or primary carbon atoms and unsaturated groups [87]. In practice, it has been found that βcleavage of alkoxy radicals is one of the principal mechanisms of polymer degradation.

CH X C O

X C OH +

C (5)

X C O

X +

C O (6)

Another possible degradation mechanism is ionic scission, which happens in most polymers possessing heteroatoms in their chain. An example of this type of chain scission occurs in ester groups, which suffer a substantial amount of hydrolysis above the Tg, resulting in a rise in the number of carboxylic groups and small molecule fragments [91]. These fragments are usually formed by cleavage of the chain ends. In some cases, they are undesirable in the product that will be kept in the polyester package being reprocessed. One familiar contaminant produced in PET is acetaldehyde; its presence in aromatized and carbonated drinks is imperceptible, but it has a drastic effect on the organoleptic properties of mineral water [81]. Hydrolytic reactions are catalyzed by acid or alkali and their rate increases in proportion to the concentration of solvated H+ and OH¯ ions in dilute acid or alkaline solutions [92]. Acid-catalyzed hydrolysis involves the protonation of the oxygen atom of an ester group in the claim, following by reaction with water to form equivalent quantities of carboxylic and hydroxyl end-groups. It should be pointed out that this hydrolysis is self-propagating, since one of its products is an acid (Eq.7) [91]. In the case of alkaline hydrolysis (Eq. 8), the hydroxyl ion attacks the carbonyl carbon, again forming equivalent quantities of –COOH and –OH end groups.

H+ X

R

X+ R

H2O

RH + HO

Y

+ + H

H

O X C

(7)

O+ O2 B-

X C B

O H2O

C

X H +

+ B

HO (8)

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Sati Manrich and Amélia S. F. Santos

Hence, contaminants of polyesters such as PVC and gummed labels, which release acids (hydrochloric and acetic, respectively) at reprocessing temperatures, serve as catalysts in the hydrolysis of ester groups. Similarly, if PET residues are not rinsed well after exposure to alkaline solutions during cleaning, the ester bonds are likely to be broken by base catalysis. In any case, irrespective of the prevailing type of catalysis, thermal degradation (Eq. 9) always takes place alongside hydrolytic degradation, during reprocessing. Consequently, the content of carboxylic end-groups rises in parallel with the falling molecular weight of the polyester [93]. -RCOOCH2CH2OOCR- ⇒ -RCOOH + CH2=CHOOCRCH2=CHOOCR- + HOCH2CH2OOCR- ⇒ -RCOOCH2CH2OOCR- + CH3CHO (9) Since degradation reactions occur after diffusion of a reactive agent (O2, H2O, etc.), the rate of reaction in the solid state also depends on the shape of the residue, its morphology, crystallinity index, ambient relative humidity and temperature [91]. It follows that changes in the crystallinity of a polymer during its degradation are especially important with respect to its susceptibility to hydrolysis and chain scission [94, 95]. Indeed, it is possible to estimate a critical amount of crystallinity, above which the diffusion of oxygen and water drops, occasioning a fall in the rate of degradation. This behavior has been observed in many polymers [94, 96, 97], which exhibit the chemi-crystallization mechanism parallel to chain scissions. To sum up, all the polymer degradation processes involve some oxidation reaction as a component, which varies little from one case to another and is limited by the rate of an initiation step. The degradation may occur through the cleavage, crosslinking or branching of chains. Usually, one of these predominates, depending on the composition of the material and oxidizing conditions (mainly temperature and oxygen) [88]. It should be stressed that, whatever the case, oxidation in solid polymers is restricted to small domains because of the relative immobility of the macro-radicals involved. Furthermore, the hydroperoxides, being unstable, tend to reinitiate new chains of oxidation within the domain that has already been oxidized [87]. Lastly, differences that exist in the behavior of different polymers are mainly due to the chemical bonds, functional groups and types of chain found in their structures, as well as the presence of impurities.

Restabilization Methods The commonest means of restabilizing polymer residues is by adding stabilizing agents to the polymer during processing. This method is known as restabilization with additives, or external stabilization [78, 98]. In choosing an additive, a compromise has to be found between its effectiveness as a stabilizer and the restrictions of the application; for example, in food packaging, it must be non-toxic. Further requirements of an additive include: resistance to attack by oxygen, humidity and microorganisms; good mixing capacity, compatibility with other components, solubility; adequate knowledge of its effects on the physical properties of the polymer, including rheological, mechanical and electrical characteristics, etc., and on the appearance of the reprocessed plastic, before and after its exposure to heat and light; and, finally, a costbenefit analysis [78].

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The concentration of the stabilizer added to the polymer will depend on the polymer matrix, the type of stabilizer; the color, intended service life, shape and size of the product; the presence of other additives and quantity of residual additives from the original product(s); the extent of irreversible change already suffered by the polymer; the cost and other factors. To balance all these requirements and conditions, it is common to use more than one in the formulation, in a search for synergistic action [78]. Generally, the target is to achieve the highest ratio of performance to concentration. This approach is reflected in a yearly decline in the consumption of antioxidants for plastics processing during the period from 1977 to 1992 [99]. Notwithstanding this, the production of plastics continued to rise over this period, while the requirements concerning the performance and stability of the polymers became stricter. Stabilizers are grouped into classes, according to their mechanisms of action: primary antioxidants; secondary antioxidants (hydroperoxide decomposers) and deactivators of metals; UV absorbers; sterically-hindered amine light stabilizers (HALS), among others [78]. Primary antioxidants intercept the free radicals (ROO•, RO•, etc.) formed at the start of the degradation process and thus delay their propagation. They may react with free radicals by an addition reaction (combination), electron transfer or, more often, hydrogen transfer. Thus they are classed as free-radical trappers, electron donors or hydrogen donors. Primary hydrogen-donating antioxidants, also known as thermal stabilizers, are the class most often found in practice. They neutralize peroxy free radicals, generating a by-product that is stabilized by resonance across four different forms that coexist in equilibrium. These resonant forms may react with other peroxy radicals, neutralizing them by forming inert products. The mechanism of these reactions can be seen in Figure 3 [78, 98]. OH

O

POO

+

+

R

POOH

R

O

O

R

R

O

R

R

R POO

POO

POO O

O

O

OOP

R

POO

OOP

O

R

Figure 3. Outline of reaction mechanism of polymer stabilization by the sterically-hindered phenol class of hydrogen-donating antioxidants.

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Sati Manrich and Amélia S. F. Santos

Chemical structures of primary antioxidants of the sterically-hindered phenol type are exhibited in Table 5 [78, 98]. This type of additive is preferably used to stabilize the melt or, in some instances, as photo-antioxidants. However, they do not function so well in the latter role as their reaction kinetics are far superior in thermal processes [98]. It is important to note that the activity of these phenols falls dramatically above 220°C, the limit being around 230270°C, above which they do not function. This is connected with changes in the mechanisms both of the oxidation of the polymer matrix and of the action of the phenols [99]. Other examples of primary antioxidants are some sulfur compounds, such as thiophenols, and secondary aromatic amines. Table 5. Chemical structures of some primary antioxidants in the sterically-hindred phenol class. Chemical structure

HO

Systematic and trade names 2,6-di-tert-butyl-p-cresol BHT (Uniroyal) and Ironol (Shell)

C H3

O HO

CH 2 C H 2 C O (C 10 H 37 )

O HO

C H2 C H2 C C

O C H2

Octadecyl-3-(3.5-di-tert-butyl-4hydroxyphenyl) propionate Irganox 1076 (Ciba Geigy)

Pentaerythritol-tetrakis 3– (3.5-di-tert-butyl-4-hydroxyphenyl) propionate Irganox 1010 (Ciba Geigy)

4

Secondary antioxidants act on the initiation stage of thermooxidative processes, decomposing hydroperoxides into stable products. The simplified mechanism of their action is drawn in Figure 4 [78].

1: organic phosphite * , (ArO)3P: (ArO)3P + ROOH → (ArO)3PO + ROH organic phosphite organic phosphate 2: thioether †, (R1)2S: (R1)2S + ROOH → (R1)2SO + ROH thioether sulfoxide (more efficient decomposer of hydroperoxide than original sulfide) Figure 4. Simplified mechanism of action of hydroperoxide-decomposing stabilizers (secondary antioxidants). * used with phenolic antioxidants, these are recommended for stabilization during processing. † used with phenolic antioxidants, these are recommended for long-term thermal stabilization.

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However, Neri et al [100] concluded that above 250°C the reactions shown here are very unlikely, given the low thermal stability of hydroperoxides, which normally decompose into the radicals RO• and •OH at such temperatures. Therefore, from their studies on PP, they proposed that the phosphites, during processing, countered the oxidation of the polymer by reacting preferentially with the oxygen, being converted into phosphates. Furthermore, they found that completely aliphatic phosphites are more effective stabilizers than aromatic phosphites, since the former consumed more oxygen. The proposed mechanism of the phosphite reaction with oxygen is thus: (RO )3 P

E

(RO )3 P*

(RO )3 PO O (RO )3 P* + O 2

+ (RO )3 P O O

(RO )3

P

2 (RO )3 P

O

O (RO )3 P O

(10)

The organic phosphorus compounds (phosphates and phosphonites) and thioethers (also called thioesters) are the antioxidants used most frequently. However, when using organophosphorus compounds, it should be borne in mind that they are readily hydrolyzed, generating phosphoric acid which may corrode the equipment. Normally, combinations of primary and secondary antioxidants are used to obtain the benefit of the synergism between them in the thermooxidative stabilization of polymers [77, 78, 101]. This effect may be explained by a model in which the phenols convert peroxy radicals into hydroperoxides, slowing down the propagation reaction, while the secondary antioxidants decompose the hydroperoxides into stable alcohols. Even so, these antioxidants do not totally inhibit the oxidative degradation, but merely cause a substantial reduction in its rate of propagation [101]. A feature of stabilizing systems in the solid state is that the agents are normally segregated in the amorphous phase of the polymer matrix, as they have low solubility in the crystalline phase. This does not affect their effectiveness, however, owing to the similarly low solubility of oxygen in this phase. In the vast amount of published research on polyolefin stabilization, there is a consensus that the best protection is provided by combinations of high-molecular-weight phenolic antioxidants with phosphites or phosphonites; in the case of PP, the phosphite : phenol ratio is usually 1:1 or 2:1, whereas for HDPE it can vary between 2:1 and 4:1 [77, 102]. Phosphitephenol combinations not only maintain the molecular weight of the polymer, but also improve the shelf-life of the product, delaying natural and thermal aging by protecting and preserving other stabilizers [77, 79]. For the restabilization of recycled polyolefins, Popisil [79] recommends using about 0.05% more phosphite than would normally be used to stabilize the virgin polymer, in particular for PE. Similarly, Henninger et al. [77] suggest using a blend of stabilizers containing high phosphite: phenol ratios, to provide a safety margin for the protection of the

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Sati Manrich and Amélia S. F. Santos

residual additive systems found in most recycled material [73, 77, 79, 103, 104]. In this sense, when the present authors and co-workers conducted tests on post-consumer HDPE packaging, to establish the properties of the recycled plastic before and after reprocessing without adding any stabilizers, they found that the concentration of residual stabilizers in the plastic was sufficient to maintain its useful properties during the first reprocessing cycle [105]. Other synergistic combinations commonly found are: thioesters with phenols, which offer increased heat resistance of the polymer over prolonged periods; organophosphites with phenols, to increase stability during processing [106] and also to prevent discoloration, as organophosphites inhibit the formation of colored quinoid compounds from the phenols, when the latter donate their hydrogens to peroxy radicals; and aryl phosphite with a chain slipping agent, as a low-cost alternative system that proved to be as efficient as standard formulations in the reprocessing stage of PP recycling [107]. Metal deactivators are also important, as they neutralize the effects of metals that decompose hydroperoxides into active free radicals, promoting polymer degradation. Some compounds derived from hydrazine and hydrazone act as metal deactivators; for example, a bis-hydrazone that, by chelating metals, renders them unavailable to catalyze degradation processes. According to Drake, cited by Malik et al [108], a mixed system of additives needs to be balanced, not only in terms of the chemistry of its components, but also in their molecular properties, such as the size, polarity, linearity and so on, of the constituent molecules. For Malik et al [108], in a “cocktail” of stabilizers, the amount and kind of mutual interactions among the constituents depend on the individual concentrations of the additives, the characteristics of the polymer matrix (including the mean molecular weight and its distribution), processing temperature, shearing rates, etc. Specifically for PET, alongside published reports on the use of conventional antioxidants (phenol derivatives, aromatic amines) as stabilizers [81, 109], research has also focused on the use of chain extenders and solid-state polymerization to recover the original molecular weight of recycled PET. The adoption of restabilization procedures is of fundamental importance, since normally the degradation of recycled PET proceeds faster than that of virgin PET, even in trials in which the initial molecular weight of the virgin PET is lower than that of the recycled plastic [93]. Among the factors responsible for this difference are impurities in PET residues that catalyze hydrolysis and the shape and crystallinity index of flakes as opposed to pellets, which affect the amount of water absorbed initially: flakes absorb much more due to their larger surface area and lower crystallinity. In reactive extrusion, the multifunctional chain extenders are designed to react with terminal carboxylic and/or alcohol groups in PET, counteracting the molecular weight losses caused by the reprocessing and concomitantly reducing the content of carboxylic acid groups (-COOH), when these are the site of attack of the additive [93, 109, 110]. Solid-state polymerization is performed at a high temperature under a flow of inert gas or reduced pressure, so that the polymer chain ends gain sufficient mobility to react with each other, the by-products being removed so as to displace the reaction equilibrium toward the product side. In general, whatever procedure is used to overcome the degradation reactions, restabilization is an essential prerequisite to ensure the desired final performance of the recycled product, especially in the case of closed-loop recycling.

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Blends Research into and development of mixtures of different polymers has opened up a wellmapped path to the production of ´novel´ polymers and to the mechanical recycling of polymer residues, especially over the last two decades. This has occurred in spite of the unfavorable thermodynamics for miscibility: for most polymer pairs, the enthalpy of mixing is unfavorable and the entropy is negligible [111-115]. This being so, the blending of polymers inevitably leads to a heterogeneous system of multiphase morphology. When a blend consists of two components, A and B, and component B, say, is present in small amounts, the morphology is mainly of the droplet-matrix type, or discrete (dispersed) phase structure (DPS). Steadily increasing the proportion of B will lead to the percolation limit, characterized by a co-continuous or bi-continuous phase structure (BPS), in which each phase is connected continuously throughout the volume of the blend. Beyond this point, phase-inversion eventually occurs, with phase A in discrete drops in a continuous matrix of B [112, 114]. The physical and mechanical properties of a given polymer pair are strongly influenced by the multiphase morphology, which depends on the composition of the blend. Thus, it is possible to obtain a blend with desired properties by controlling its composition and hence its microscopic structure. For example, the BPS structure is particularly interesting when it is desired to maximize barrier properties, conductivity or impact strength [114]. Lyngaae-Jorgensen and Utracki [114] describe well-established correlations between microscopic structures of polymer mixtures and their bulk properties, such as Young´s modulus, electric conductivity, permeability, etc. According to Willense et al. [115], the elastic modulus, measured under tension, is mainly determined by the matrix phase when the blend has the droplet-matrix structure (DPS). Conversely, this modulus is determined by the dispersed phase when the DPS is of the fibrous type, especially in oriented specimens. The co-continuous BPS structures exhibit an intermediate behavior, with neither phase predominating, and the modulus is high and isotropic, owing to the interpenetrating phase structure. However, the properties of a mixture of immiscible polymers, even though the composition may be fixed, can vary over time, since its structure may change as a result of not being stabilized soon after the blending stage, when the end-product was fabricated. Furthermore, the two or more phases formed by the mixture may show high values of interface tension and low adhesion between phases, impeding the transfer of stresses across the interface. This could result in a preferred path for fracture, along the interface, when the material is subjected to stress [116]. A third component may be added to reduce interface tension and make the phases more compatible: this would promote a structure with finer phases (smaller domains) and enable the development of technically interesting blends. The compatibilizing additive normally has three main functions: to reduce interphase surface tension by exerting an emulsifying effect; to improve interphase adhesion through its chemical affinity, enabling the transfer of stresses, and to stabilize the phase separation, preventing the dispersed phase from coalescing into larger domains [116, 117]. Several kinds of compatibilizing processes and reactions have been developed and applied to products made from virgin resin blends for decades, and more recently in the case of products from recycled plastics [116-127]. In this chapter we shall focus on blends of

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Sati Manrich and Amélia S. F. Santos

recycled material; published work in this field is found to concentrate on post-consumer packaging residues and scrapped electric-electronic and automobile parts [120-127]. Block and grafted copolymers are widely employed as compatibilizing agents; thus, the commonest of these used in blends of polyolefins with styrene-derived polymers is a styreneelastomer copolymer [116-120]. Cherian and Lehman [120] report that the commercial use of such blends is growing in structural engineering, a prominent example being the recycled PS/HDPE blends incorporated into railroad ties and bridge beams. Manrich’s workgroup works with several blends, among them rHIPS/rHDPE, PP/PS, rPP/rHIPS, rPET/AES, PP/EVA and rPP/EVA, where r denotes recycled materials, aiming at recycling plastic residues into products of high added value. The accomplishment of such high quality recycled blends should be enabled by additive or synergistic combination of the properties of the blend components, as they are optimized for a specific application, in this case ecological synthetic paper for printing and writing. Some of these results are outlined in this chapter. In polyolefin/styrene-derivative pairs, the compatibilizers used were block and grafted copolymers of styrene-butadiene, styrene-ethylene and styrene-propylene [118, 128-130]; in rPET/rPoliolefinas, ethylene-g-maleic anhydride copolymer [131]; in rPET/acrylonitrile ethylene-propylene-diene styrene copolymer (AES), MMA-glycidyl methacrylate (GMA) copolymer [132], while for PP/EVA, rPP/EVA and PP/rubber from scrap tires, no compatibilizer was added [133, 134]. In the case of rPET/AES and PP/rubber blends alone, the aim of blending was to toughen the thermoplastic. We analyzed the effects of the composition and presence of MMA-GMA on the brittleductile transition temperature, impact strength and phase morphology of blends of PET recovered from beverage bottles with AES. The interphase modifier MMA-GMA is miscible with the SAN-rich AES phase and reacts with the polyester. It was shown to be indispensable as a reactive compatibilizer, causing a favorable modification of the morphology of recycled PET/AES blends and lowering the brittle-ductile transition point by up to 70°C, in the blend with 40% AES. At room temperature, the impact strength of this blend was increased 10-fold by this additive [132]. The remainder of this section is devoted to the investigation of blend intended for use mainly in ecological synthetic paper. In the PP/PS blends, we used three interface tension reducers, PE-PS, PP-g-MAH and PP-g-PS, the last one synthesized for the purpose in this laboratory [118]. Two types of PP and two of PS were evaluated by micro-rheological tests in order to choose the best PP/PS pair for blending. Recycled plastics were not used at this stage, to limit the variability of the material. The viscosity ratio of each of the four polymer pairs was determined. According to Navrátilová and Fortelný [135], the best polymer pair should be one whose viscosity ratio is lower than unity, as in this case the coalescence of the minor phase, which is less fluid, should be hindered more than if the viscosities were equal. In our study, however, all the ratios were fractional and an interesting observation was made when phase morphology was examined: the PP/PS blend whose ratio was nearest to 1.0 exhibited much finer dispersion of the PS phase than the others. Therefore, this blend was used for all further experiments [118]. Also, by determining the sizes of PS domains, it was concluded that PP-g-PS gave the best performance of the three compatibilizing additives.

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In studies of PP/HIPS blends, made from recycled and virgin polymers, only one additive was tested: SEBS Kraton G was added at 5, 6 and 7 wt% to the compositions PP:HIPS of 2:1, 3:1 and 6:1 (w:w). The results of mechanical and morphological evaluations showed that the blends of recycled material had better properties than those made from virgin material and that the composition favored for the fabrication of synthetic paper was PP:HIPS = 2:1, plus 5% SEBS [128]. In the latest work on ecological synthetic paper, blends were prepared from rHIPS/rHDPE, rHIPS/rPP and PP/EVA [129, 130, 133]. In the blends based on rHIPS, comparative tests were performed on specimens containing the additives SEBS Kraton G and multibloc SBS from BASF [129, 130]. In mixtures containing each of the additives, the glass transition (Tg) of the PS phase in HIPS and the melting peak temperature Tm of the PP phase were measured by differential scanning calorimetry (DSC). Whereas the Tm of PP did not change with the addition of either HIPS or the compatibilizer, Tg of PS was lowered. In the case of mixtures of PP and EVA, preliminary tests on tubular films showed that these were compatible at low levels of EVA. For this reason, no interfacial agent was added. Indeed, a growing tendency in recent research is to try and use compatible polymer pairs, in concentrations at which a third component is unnecessary [40, 134, 136, 137]. One such study was developed in our laboratory with the aim of toughening virgin PP by adding powdered rubber (rubber shaving particles) from post-consumer scrap tires [134]. Neither additives nor compatibilizing treatments were necessary in the blends, and the results indicated a positive effect and close interactions between the rubber-plastic interphases when 5 to 10% of rubber particles were added to PP. Figure 5 shows the morphology micrograph for 15 wt% rubber addition.

Figure 5. SEM micrograph of PP composite with 15% rubber shavings particles from scrap tires (250x).

Similar results were obtained recently by Scaffaro and co-workers [137]. They investigated the possibility of blending recycled PE (rPE) and post-consumer ground tire rubber (GTR) in order to obtain good mechanical performance blends without any additives. High temperature devulcanized GTR was also used in a comparison of two weight ratios rPE/GTR: 75/25 and 50/50. They found that good processability and mechanical performance

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Sati Manrich and Amélia S. F. Santos

was achieved at the lower amount of GTR in the blend. Moreover, the results suggested that high-temperature devulcanizing promoted reduced incompatibility by destroying the rubber cross-inking, though too high a devulcanizing temperature resulted in the viscosity, elastic modulus and tensile stress being increased by the carbonized rubber acting as a filler.

Recycling Composite Plastics The proportion of composite materials that is recycled is one of the lowest, owing mainly to the lack of available technology that would allow these residues to be processed into viable products for new markets. Nevertheless, their economic impact is far from negligible, even if they represent a small fraction of all recycled plastics. In theory, just as in the case of virgin resin, the addition of reinforcement to the recycled polymer matrix allows the composite to have a combination of properties that could not be attained by the individual components. Thus, while contributing to produce a composite with desired properties and therefore a product of higher aggregate value, the reinforcement is responsible for carrying most of the applied load, if the transference of mechanical load by the interface is efficient, resulting in the effective strengthening and stiffening of composite. On the other hand, the polymer matrix allows load to be transferred from fiber to fiber, prevents the catastrophic propagation of cracks between the fibers and protects the fibers against aggressive surrounding conditions such as humidity [138-140]. The effect of the reinforcement addition into recycled matrices on the mechanical properties of the resulting composite (Young’s modulus, ultimate tensile strength, elongation at break etc.) is usually the same for conventional polymer composites. The presence of fillers and/or reinforcements in the polymer matrix affects mechanical and rheological properties of the composite. The extent of this influence depends on many factors such as type and size of fiber/reinforcement, volume fraction, degree of dispersion and its interaction with polymer. The incorporation of fillers usually decreases tensile strength, while an opposite effect is observed by the addition of reinforcements. Elongation at break is decreased and viscosity increased by the addition of fillers and reinforcements due to the restriction of chains mobility [141-145]. These restrictions, on the other hand, may be beneficial to increase the Young’s modulus (E), since for a same value of load applied to the composite, elongation is decreased, thus giving rise to higher modulus, i.e., composite stiffening and hardening. Another important factor which is crucial for the composite to have a good performance is the polymer-filler/reinforcement interface. As previously mentioned, the load transference depends on this interaction. Therefore, when it is relatively weak, some approaches have been used to outcome this problem. The most common methods are the use of interfacial compatibilizers or coupling agents, which are substances used to promote interfacial adhesion and thus, improve the load transfer at the polymer-fiber/filler interface due to their compatibility with matrix. The mechanisms of compatibilization are based on modification of surface surface energy of reinforcements through chemical, mechanical or electrostatic adhesion with the matrix [146]. Reinforcing fibers in common use include both natural and synthetic fibers. The main advantage of using synthetic fiber is the possibility of producing fibers of unlimited length, while a natural fiber has a fixed range of finite lengths. Nonetheless, in applications calling

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for (that use) short fibers, many natural fibers compete successfully with synthetic varieties [146]. In the last few decades, natural fibers have been used increasingly, for reasons like low cost, the growing interest in exploiting materials from renewable instead of mineral sources, biodegradation of residues and non-toxicity. The natural fibers being widely incorporated into plastics recycled from MSW are that based on lignocellulose matrixes, in the form of wood fiber or wood flour. There have been various reports of the reactive extrusion of composites of plastic residues with this type of fiber, in which compatibilizers, flame retardants, foaming agents (when recycling the heavy fraction of MSW) and chemical treatment of the surface of the fibers are all employed [147-152]. Other natural fibers, albeit less exploited for plastics recycling, are those of jute, cotton, sisal and banana. While there are innumerable reasons for using natural fibers, they also have disadvantages. For example, their hydrophilicity makes them less compatible with hydrophobic polymer matrices, and they show poor environmental and dimensional stability. Organic textile fibers may also be used in polymer composites, despite their rather low stiffness, in order to reinforce matrices with even worse mechanical properties, such as rubber and thermoplastics. A good example is the fact that synthetic fibers made from recycled PET are capable of improving substantially the mechanical properties of PP [153]. When composites reinforced with glass fiber are recycled, they are first ground in a mill. Depending on the type of mill and extent of grinding, the recovered material may fall into two categories: (a) a fibrous fraction containing most of the reinforcement or (b) a fine powder containing most of the polymer matrix. It is important to separate these fractions, owing to the high added value of the used reinforcing fibers when they are mixed with a relatively small proportion of virgin glass fiber in new recycled composites [154]. In an alternative approach, chemical recycling is used to convert the polymer matrix into low-molecular-weight organic compounds and thus isolate and recover the valuable fiber fraction [155]. In spite of various other methods have been developed for the recycling of composite materials, the most widely used being to grind the composite scrap and incorporate it into a new composite structure, mainly thermoset molding structures. However, the inclusion of scrap during the actual fabrication of a recycled composite would lead to a very low-quality product unless the scrap content was kept low [156]. This limitation restricts the market of recycled composite that could be included in structural composites designed for the aerospace, naval and automobile industries. One scheme that adds value to the recycling of thermoset materials, given that such residues cannot be melted during reprocessing and homogenized into the polymer matrix, consists of cryogenic grinding of the uncured flashes discarded during the respective molding process of the thermoset composite [157]. Finally, it should be noted that the extent of dispersion and homogeneous distribution of additives, reinforcement and fillers in the polymer matrix is greatly influenced by the type of process and the way it is carried out. Processes can be classified as continuous or batch, and also by the intensity of the shear stresses generated [64, 158]. In most batch processes, the degree of dispersion and distribution of system components is low, compared to continuous processes. This is due to the differences in stress and/or shearing rates that develop within the mixing chambers, generating large non-homogeneities in the dispersion and distribution of the particles. Hence, the end-product may have many distinct regions, in terms of the filler particle distribution.

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Among continuous processes, extrusion is, without doubt, one of the commonest [158, 159], although a variety of alternatives does exist, such as injection, pultrusion, reactive injection of structural composites (SRIM), sheet molding compound (SMC), and others.

New Markets and Technology Recycled Plastics for Food Packs The return of food packaging for reuse in the same cycle (closed-loop recycling) represents a victory for the plastics recycling industry, as it is responsible for a large fraction of all plastics consumed and also of the rigid plastics component in MSW, owing to the brief service life of food containers. On the other hand, this type of recycling is a great challenge to the recyclers, as they are under obligation to ensure minimum potential risk to public health and not change the organoleptic properties of the packed food. Both before and after the plastic packs are discarded, there are possibilities that toxic chemicals, arising from the reuse of containers for other ends by consumers (storage of pesticides, herbicides, insecticides, household chemical products, car-maintenance products, solvents, disinfectants, products of microbial decay of food scraps, etc.), from adsorption and absorption of substances from the original contents and from contamination by contact with other residues, could migrate from the plastic to the food [27, 160, 161]. These possibilities are of real concern because of the non-inert nature of polymer matrix that allows sorption and diffusion of organic chemicals into plastics and due to the relative low temperatures of the recycling processes. Nevertheless, concerns related to the presence of microorganisms in the recycled plastic are neglected, as they adhere only superficially to the plastic and can easily be deactivated during recycling, by the pH of the cleaning solution and the polymer reprocessing temperature [162, 163]. In light of these considerations, the key criterion for the return of recycled plastic into direct contact with food regards to the assurance the decontamination of recycled plastic to a level that offers a negligible risk to public health and does not compromise the organoleptics properties of the packed food [164]. As ultra-conservative assessments, levels were set with reference to levels of carcinogenic substances at which short-term exposure offers a risk of contracting cancer below one in a million. Starting with these levels, a safety margin was added, so that the proposed maximum permitted level of contaminating chemicals migrating to the food was set at 2000 times lower than the cancer reference [161, 165]. Even after chronic exposure, this level includes a safety factor of 200 times. Based on the above discussion, the principle of “threshold of regulation” (T/R) was proposed, which established 0.5 ppb as the permitted limit for daily ingestion with negligible risk of a substance of unknown toxicity [165-167]. Hence, any contaminant in recycled plastic food packs which leads to daily ingestion of less than the T/R limit can be assumed inoffensive to human health. Consequently, a food-packaging recycling process has to demonstrate its capacity to extract contaminants from the polymer matrix, treated here as food additives arising from indirect contact, reducing them to a residual concentration that does not expose the consumer to levels above the T/R limit. The evaluation of the process requires standard methods, to eliminate the great diversity of variables representative of the real contamination routes of these plastic containers.

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These standard methods and its variations used to assess the suitability of a plastic recycling process for the production of food packs [27, 161-163, 168-176], consist, briefly, in contaminating flakes of packaging from post-industrial waste, free of any absorbed compound not inherent in its production, with model contaminants in a standardized and reproducible way and then submitting these contaminated flake through the recycling process in order to determine the level of residual contamination present in the plastic container produced by recycling. The recycled container or its food contents have to exhibit mean residual concentrations of the model contaminants equal to or below the T/R limit, for the suitability of the recycling process for production of recycled plastic packs for direct contact with food. Since evaluation of the residual contents of the model contaminants in the container takes no account of the barrier properties of the packaging, the process conditions determined by tests of migration of model contaminants to the food are generally more competitive. However, the complexity of the analysis and its costs are appreciably greater. In the current view, conventional mechanical recycling is not considered suitable for the production of packaging to be used in direct contact with food, since the cleaning, drying and extrusion steps of these processes are inefficient at removing hydrophobic, polar and nonvolatile contaminants, owing to the inbuilt limitations of each step [160, 161, 171, 173, 174, 177, 178]. In these circumstances, there now exist a variety of available techniques on the market, mainly concentrated in the fields of chemical and physical (monolayer and multilayer) recycling. Monolayer physical recycling methods, known as super-clean processes, are generally based on the steps of conventional mechanical recycling, to which further steps are added that employ heat, vacuum, inert atmosphere, solid-state polymerization [179-189], solvent extraction [190, 191], chemical surface treatments [192], vacuum degassing, supercritical fluid extraction (SFE) [193, 194] and steam distillation [195].These techniques have been tested experimentally and/or put into commercial practice, to enable recycled plastic to gain entry into the food packaging market. Historically, the first super-clean process approved for use in direct contact with any class of food, under any conditions of use, appeared in 1994 for PET. The company that filed the application was Johnson Controls Inc. (Milwaukee – Manchester), the relevant division of which was later taken over by Schmalbach-Lubeca AG (Ratingen, Germany) [196-199], which nowadays belongs to AMCOR PET Global Packaging. Since that date, several other super-clean processes have been emerged; these are economically viable, but still run up against the limited quality and availability of the residues. Recently, at the Residue Recycling Center at UFSCar, comparative tests of the rates of extraction of benzophenone from PET in dry air, vacuum or inert gas demonstrated that the diffusion of this contaminant from the plastic surface was fastest in dry air. On the basis of this result, a new super-clean process was proposed, which differed from others by using the conventional drying and crystallization recycling steps, at the upper temperature limit, to decontaminate the recycled plastic until reaching the residual contaminant level allowed for direct contact with food [200]. Besides the work reported in the patent, the authors and co-workers investigated the joint effect of using a liquid-phase extraction step followed by solid-state polymerization on the efficiency of contaminant removal. The liquid-phase extraction was carried out on d-limonene at atmospheric pressure and on water and acetone in subcritical conditions [201]. These results are shortly to be published.

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In multilayer processes, two or three-layer packages are produced by co-extrusion of recycled and virgin polymer, the virgin layer of PET or PS, acts as a barrier to contaminants, since it is placed in direct contact with the food. In this arrangement, the recycled plastic can be made by conventional mechanical recycling, as it does not touch the food, but the disadvantage of this kind of process is that the fraction of recycled plastic in the pack is restricted. Overall, PET is the polymer with the highest number of recycling techniques approved by the FDA, because the costs of the various super-clean processes developed are competitive with production of PET from virgin resin and the performance of the recycled PET, in some cases, approaches that of the virgin resin. Furthermore, the quantity of post-consumer PET collected is expected to increase, in tandem with the expansion of its market in the packaging sector [18], which will improve the viability of PET recycling processes, since the cost of installations rises more slowly than the production capacity [202]. On the other hand, food packaging applications that involve only limited contact at cool or refrigerated temperatures, a high ratio of the mass of wrapped food to the contact area, individually-packed food items or types of food that have to be washed before consumption, normally do not incur restrictions on the use of plastics obtained by conventional mechanical recycling processes. Examples of such applications are: recycled PS egg boxes, supermarket bags, recycled PE and PP crates and PET baskets for the transport of fresh fruit and vegetables [203].

Ecological Synthetic Paper When articles of substantial added value are produced from discarded plastic, there is ample opportunity to market them as useful goods offering a viable return. This is particularly so when the sources of plastic are consumables (commodities); the recycling of these residues is much more efficient, as they are used and discarded in far greater volumes than durable goods. In this light, we have put considerable effort into developing special films, designed to receive writing and print, from post-consumer recycled plastics. The films, known as ecological synthetic paper, would substitute synthetic paper made from virgin resins and even cellulose paper in some potential applications [204-206]. The motivation for this project is the possibility of finding one innovative and practical solution to several economicenvironmental problems, three of which are especially urgent: a) The need to create novel manufacturing techniques and new markets for goods produced from plastic residues, so as to minimize the damage to the environment caused by their disposal, given the clearly expected growth of plastics waste, considering the current growth trends in plastics consumption not only in developed countries but also, and particularly, in highly populated developing countries. b) The need to meet the growing demand for cellulose paper; apart from the problem of insufficient supply for future demand, the current process of paper-making causes serious pollution, even though the raw material comes from a renewable resource. With regard to recycled post-consumer cellulose fiber, it is thought this could not be supplied in sufficient quantity at a viable cost-benefit ratio. As a measure of the scale of this problem in Brazil alone, the mounting investments in the paper and cellulose sector announced by the government for the years 2005 to 2014, intended to boost

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supply to the level of demand, are predicted to reach the vast sum of US$ 14.4 billion [207]. c) The crying need to reduce, perhaps even to stop, the cutting down of native forest, which occurs in part because of reforesting with monocultures of the exotic species preferred by cellulose manufacturers. This problem is particularly pressing in developing countries like Brazil, where, although the rate of increase in forest clearance in 2005 was lower than in 2004, we must not forget that 2004 witnessed the highest level of devastation of the Amazon rainforest in all history. Add to this the fact that for 2004, the projected timber requirements of the Brazilian cellulose industry were 135 million m3 of planted forest, while the market forecast estimated availability at 125 million m3, well short of the required volume [208]. Synthetic paper consists basically of laminated or co-extruded multilayer cavitied films with writing and printing properties similar to those of cellulose paper. It is practical, especially in industrial printing, when the supply of cellulose paper cannot fulfill demand, and when cellulose fiber hygroscopic properties are inconvenient. It may be used on several products: packaging including those for food, in personal documents manufacturing, maps, books, menus, billboards, envelopes, labels, instruction manuals, safe cards, pasteboards, paper currency, “busdoors” and “backbus” advertising panels etc [205, 206]. Practically all of the published information on synthetic paper is found in patents [209217]. A basic feature of such documents is that the description of materials and methods is general and superficial. What can be gleaned is that multilayer films with the properties of cellulose paper can be made from thermoplastic composites with mineral fillers (CaCO3, TiO2 and SiO2) and/or immiscible polymer blends, the polymer matrix consisting mainly of the polyolefins polypropylene (PP) or polyethylene (PE). In a survey of recent patents, that of Squier et al. [217] refer to a thermoplastic film label that can be made by co-extrusion or lamination of uniaxially or biaxially oriented films, in five layers, comprising a central core (support), two adhesive and two external surface layers. In a general way, the patent include all of the principal materials, compositions and processes in frequent use. The printing processes covered include, among others, offset, silk screen, electrostatic and photographic methods, lithography, flexography, letterpress, thermal transfer and hot stamping. Inks mentioned are those employed in rotogravure, flexography and lithography, as well as in inkjet and hot melt printers, water and solvent based. It can be seen that this patent embraces practically every aspect of synthetic paper that has been protected in various patents around the world [217]. One very common feature in publications in general on synthetic paper is their reference to an important step in its fabrication, in which microcavities and microvoids are formed. Microvoid is a more general term, although it is often used as a synonym for microcavity. According to inventors, microcavities are small cavities that form along the interface between phases, owing to the delamination of layers by shearing during an extended orientation of multiphase film below the polymer melting-point. The dispersed phase of inorganic filler particles, immiscible polymer or even crystallites, may provide nuclei for the formation of new microcavities [210, 211, 218-220]. The mineral fillers, usually CaCO3, are considered responsible for both the high mechanical rigidity of the films and the nucleation of microcavities. The latter, in turn, provide lower density, greater opacity and better printing qualities. The opacity is increased

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by microvoids as they provide a large number of points at which visible light are refracted in random directions. The dispersed filler particles distributed evenly over the surface, besides providing a key that anchors the ink, increase the roughness of the surface and so enlarge the surface area, leading to improved printability. In the research done so far by Manrich’s workgroup using mono-oriented and partially bioriented films, it has not been possible to prove these correlations between film composition/structure and printability. Several compositions have been studied, consisting mainly of post-consumer residues of PP and/or HDPE, to which another polymer component was added to improve printability, as well as inorganic fillers and white pigment [131, 205, 220-222]. As mentioned earlier in sub-section Blends, the plastics added to polyolefins to form blends were PS, HIPS, PET and ethylene vinyl acetate copolymer (EVA), along with compatibilizing agent in most cases. Because of the limited availability worldwide of laboratory scale bioriented film-casting co-extrusion machines to introduce microcavities, our studies have been based so far on monolayer films fabricated by extruding flat mono-oriented films and blown tubular partially bioriented films. These films have not yet been submitted to tests that show whether colaminating them into multilayer paper is a viable proposition [131,204-206, 220-222]. On the other hand, trials have been run very recently in a pilot plant on the co-extrusion of bioriented polypropylene (BOPP) in three layers, and the films obtained are currently being characterized in order to further being evaluated comparatively to commercial synthetic paper and cellulose paper. Recently, a brief review of the work we had completed by then was published in the Proceedings of the international symposium REWAS’2004 [205]. We present next a summary of the work reviewed and more recent results from the ongoing research on ecological synthetic paper. All recycled material was post-consumer; virgin PP, PS and EVA were resins supplied by Polibrasil Resinas S.A., BASF and Polietilenos União resin companies, respectively. The plastics residues were all from discarded rigid packaging. The inorganic additives were as follows: CaCO3 from Imerys and TiO2 from Polibrasil Resinas S.A. Organic additives were: PP-g-PS (proprietary), PE-g-MAH from Uniroyal, SEBS and multibloc SBS from Kraton Polymers; thermal stabilizers / antioxidants B 215FF and PS 802FL (purchased from Ciba). Conventional plastic waste recovery processes published elsewhere [128, 223, 224], including pre-grinding in knife mill, washing in caustic water solution, rinsing, drying, grinding into flakes or agglutinating into coarse powder, were used for the waste recycling. Treated and untreated CaCO3 filler particles of different average sizes and size distributions were added, at 10-40 wt%, to PP, PP/EVA, PP/PS, rPP, rPP/rHDPE, rPET/rHDPE/rPPr, rPP/rHIPS and rHIPS/rHDPE (where r denotes recycled samples). The Drais high speed mixer and Baker & Perkins (b&p) or Werner Pfleiderer twin-screw extruders were used in this step, depending on each case. In the case of the blends, the polymers were premixed in single screw extruders with the addition of 0.2 wt% of thermal/oxidation stabilizers, prior to incorporation of the filler. Flat dye casting extrusion (Gerst) and tubular film blowing extrusion (Ciola IF40) were the processes used to obtain the mono-oriented and partially bioriented polymer composite films, respectively. UV radiation treatment and a “solvent etching” were applied only to rPP/rHIPS [206] and rPET/rHDPE/rPP [131] film surfaces, respectively, in order to increase the concentration of polar chemical groups. Qualitative evaluations of visual appearance,

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writing quality and microscopic morphology, and several quantitative characterizations of physico-mechanical, optical, surface and printing properties were performed, in accordance with the following technical standards: − − − − − − − −

Grammage, according to ASTM D646; Apparent density, according to ASTM D 792, when feasible; Tear propagation resistance and Tensile modulus and stress, following technical standard procedures ASTM D689 and ASTM D882, respectively; Optical properties - Opacity (ASTM D1003), Gloss (ASTM D2457), Whiteness Index (L*a*b*) Friction coefficient, according to ASTM D4917; Water absorption, according to Cobb’s Method – ASTM D779 Printability characterization – Ink absorption and Ink adherence, through modified procedures according to ASTM D780 and ASTM D3359, respectively. Surface properties: Surface energy according to ASTM D724; Surface phase dispersion and morphology, characterized mainly through Scanning Electron Microscope.

As the surface free energy γs of a polymer is a property that will be referred to many times in this chapter, it will be convenient to explain it here. Its value is found indirectly from measurements of the contact angle (θ) or wettability angle of a drop of liquid on the surface of the polymer. This angle is measured between the solid surface and the tangent to the liquid-gas interface, at the point where the three phases meet. To calculate γS, equation 11 can be used [220, 225, 226], where γSV, γSL and γLV are solid-gas (polymer-air), solid-liquid (polymer-drop) and liquid-gas (drop-air) surface tensions, respectively. According to the theory described in the references [220, 225, 226], the total surface free energy γS (γSV, eq. 11) is the sum of polar and dispersive components, i.e. γS = γSp + γSd, which can be estimated by measuring θ with two or more liquids, as long as the surface tensions and respective polar and dispersive components of the liquids are known. Two equations exist to calculate the surface free energy, referred as the harmonic mean and geometric mean formulae, but the former (eq. 12) is more often used for polymers.

γ SL + γ LV cosθ = γ SV  γ dγ d γ pγ p  γ SL = γ LV + γ SV − 4 d s L d + p S L p  γ S +γ L γ S +γ L  where: γSd is the dispersive component of the solid surface free energy; γsp is the polar component of the solid surface free energy; γLd is the dispersive component of the liquid surface free energy; γLp is the polar component of the liquid surface free energy.

(11)

(12)

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One of the main aims in much of the research carried out by Manrich’s workgroup has been to reveal and comprehend possible correlations between the characteristics of the inorganic filler CaCO3, or of polymers with high surface energy γS, and the mechanical and optical properties and printability of ecological synthetic paper films. We have analyzed the possible relation between γS and the printability of the specimens, as well as the possible effects of the type of process used and the process conditions on the formation of microvoids and the effects they have on the above-mentioned characteristics. The results of these analyses, presented elsewhere [205], do not allow any well-grounded conclusions to be drawn concerning these correlations. Nevertheless, our investigation results did show that some of the variables studied had a more significant effect than others on properties of interest. Thus, to reduce light transmittance, opaque polymer has more effect than inorganic powder filler or white pigment; to enhance the specific offset ink printing properties, electric corona discharge (ECD) is more effective than thermochemical surface treatment and rHIPS-containing blends are preferable to PS-containing blends. Also, the simple presence of highly polar chemical groups on the film surface does not ensure ink absorption; rather, to achieve this, the surface polar groups and type of printing ink have to be compatible. The possible correlation between the properties of surface energy γS, including its polar (γSp) and dispersive (γSd) components, and the absorption properties of printing inks on the ecological film paper have also been investigated. For synthetic paper composed of polymer blends and inorganic fillers, this is both a challenging and an interesting question to be elucidated. Thus, when ECD treatment is applied, provided the processing conditions and surrounding atmosphere are kept constant, the type and quantity of the polar groups formed by the electric discharge are critically dependent on the chemical structure of the polymer and probably that of the whole composite being treated [205, 225]. From the data cited [205] in Table 6, it is seen that the replacement of PS by rHIPS in corona-treated films of PP composites increased the polar component γSp and the offset ink absorption. This was attributed to a probable higher “susceptibility” to ECD shown by HIPS than by PS. Some data not published in the cited review, referring to tests on composite films of rPP/rHIPS blends, are also given in the Table 6 [227]. The data in Table 6 clearly indicate that rPET/rHDPE/rPP/CaCO3 solvent-etched films exhibited lower offset ink absorption, even though their γSp was higher than those of coronatreated films of rPP/CaCO3 and PP/PS/CaCO3 and similar to that of films of rPP/rHIPS/CaCO3. This behavior was taken as evidence for our conclusion that high polarity is not the only and sufficient condition for the printability of the composite films. Qualitative writing tests, showing good absorption of different inks, e.g., pencil, organic solvent and ballpoint pen, corroborated these results for all samples. Apart from the investigations referred to above [205], the influence of the concentration of CaCO3 filler and ECD treatment intensity on the surface energy and its components was studied when the type of printing ink was changed from offset to serigraphy ink, for films of rPP/rHIPS/CaCO3 composites. Possible correlations between the surface energy properties and the absorption and adherence of that kind of ink were analyzed [227]. A significant increase of γS and γSp values with the surface ECD treatment and with its intensity was observed, as expected, and also a tendency for superficial energy γS to increase with the concentration of CaCO3 filler. The dispersive component was only slightly affected by the intensity of the treatment, with a tendency to fall as the ECD level increased, in highly

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filled films. No correlation was observed between the absorption of serigraphy ink on the films and the values of γS and therefore between ink absorption and the concentration of filler. When filler concentration was maintained constant, the corona treatment affected significantly the absorption of ink on films of all compositions studied; however, the absorption increased as the intensity of the treatment increased only in composite films of relatively low CaCO3 concentration, as can be verified in Table 6. Table 6. Surface energy (γS, γSd, γSp) and ink absorption (IA) of ecological synthetic paper. Films PP/CaCO3 and rPP/CaCO3 PP/PS/CaCO3 rPP/rHIPS/CaCO3 rPET/rHDPE/ rPP//CaCO3 Cellulose Paper rPP/rHIPS/CaCO3 ECD level (%V) Filler concentration %CaCO3 - 15 %CaCO3 - 20 %CaCO3 - 30

γS (dyn/cm)

γSd (dyn/cm)

γSp (dyn/cm) 1.7 – 2.7

IA (g/m2) 1.06 – 1.96

2.3 – 3.7 5.2 – 15.7 8.88 – 14.78

0.76 – 1.28 0.9 – 6.6 0.03 – 0.30

21.7

14.6

0

20

40

20

40

20

40

20

40

30.5 28.8 39.1

41.4 41.8 44.5

46.6 45.8 47.3

37.5 39.2 41.6

38.9 38.1 37.4

3.91 2.64 2.96

7.71 7.67 9.92

5.24 4.59 5.93

6.40 6.23 5.77

Similarly, by maintaining the filler concentration at a constant low level, it was found that both qualitative adherence and absorption test results were better for substrates with a higher polar component (γSp) of surface energy and thus a more polar character, presumably due to stronger ink-substrate interactions [227]. On the other hand, for high concentrations of filler particles, it is possible that an effect of surface roughness prevails, so that equations 11 and 12 above are not applicable to these composites [228]. With regard to the study of microcavity formation and its effect on the properties of ecological synthetic paper, some recent results will be presented here. Composite films based on rPP/CaCO3 and rHIPS/rHDPE/CaCO3 were characterized in terms of surface morphology, apparent density (ρ) according to pycnometry and theoretical density (ρt), whose mean value was calculated from the weight fraction and density of each component [221, 222]. The mean value of ρ was obtained from only two determinations, as there were no significant deviations. When calculating ρt, it was assumed that the degree of crystallinity of rPP and rHDPE did not vary significantly with composition or processing conditions, which had been shown to be true in earlier tests on composites based on PP and rPP/rHIPS. Surface micrographs were taken by scanning electron microscopy (SEM) with a field-emission gun, as a palliative means of observing whether microcavities were formed, given that in these 40 to 100 µm thick film samples it was not possible to measure them by quantitative techniques based on water or gas absorption or porosimetry. In this work, two types of CaCO3 were used, each one treated with the same interfacial agents, stearic acid and stearate, giving a total fatty-acid content of 1% according to the

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supplier information. The difference between them was granulometric, the particles of Carbital C110S ranging up to 10.0 µm, with a mean value of 2.0 µm, while those of Supermicro KRVA ranged up to 13.0 µm, with a mean value of 3.0-4.5 µm. The results of these tests are displayed in Table 7, where the following codes are used: Pcel and Psin represent an A4 sheet of cellulose paper and a commercial synthetic paper; P and T signify flat casting mono-oriented and tubular partially bioriented films; rP and rH are for rPP and rHIPS/rHDPE–based composites; C and S for Carbital and Supermicro CaCO3, filler, and the numbers 0, 10, 20, 30 and 40 show the filler loading in wt%. In all experiments, the blend rHIPS/rHDPE was mixed first, in the fixed ratio 80:20 (w:w), together with the compatibilizing agent multibloc SBS at 5 pphr (parts per 100 of resin). Table 7. Apparent density ρ and theoretical density ρt of films of various composition.

PrPS0 PrPS10 PrPS20 PrPS30 PrPS40 TrPS301* TrPS302†

ρ (g/cm3) 0.90 0.95 1.05 1.11 1.22 1.11 1.07

ρt (g/cm3) 0.90 1.05 1.22 1.36 1.49 1.38 1.38

ρ – ρt (%) 0 –9.3 –13.8 –17.8 –18.3 –19.6 –22.7

PrHS10 PrHS20 PrHS30 Pcel

1.13 1.21 1.29 0.72

1.26 1.42 1.56 ––

–11.7 –13.5 –16.6 ––

Sample

Sample TrPS0 TrPS10 TrPS20 TrPS30 TrPS40 TrPC301 TrPC302 TrPC303‡ PrHC10 PrHC20 PrHC30 Psin

ρ (g/cm3) 0.90 0.95 1.10 1.11 1.22 1.11 1.18 1.14 1,15 1.19 1.32 0.91

ρt (g/cm3) 0.90 1.06 1.23 1.38 1.51 1.36 1.36 1.36 1.28 1.42 1.57 ––

ρ – ρt (%) 0 –10.3 –10.9 –19.6 –18.9 –18.3 –13.3 –16.0 –11.5 –19.4 –19.2 ––

* Condition 1: film pulling rate 9.5 m/min † Condition 2: film pulling rate 14.6 m/min ‡ Condition 3: film pulling rate 22.0 m/min

The monoglyceride Dimodan, an antistatic agent used with polyolefins, was added at 0.2 wt% to rPP/CaCO3 mixtures, while 0.2 wt% Dimodan and 1.0% titanium dioxide (TiO2) were added to rHIPS/rHDPE/SBS/CaCO3 mixtures. These additives were ignored in the calculation of ρt, owing to their relatively negligible proportions in the final composite. The apparent density of the films rose continuously with the CaCO3 loading, which was entirely as expected given that the inorganic filler (ρ = 2.6 g.cm-3) is much denser than the plastic. However, it can be seen that, as the loading rises, the apparent density deviate further and further from the theoretical value, going from 10% below ρt at 0% CaCO3 to around 1819% below ρt in films with 30-40% loading. This implies that the CaCO3 incorporated provoked an effect leading to a drop in density of the films, irrespective of which CaCO3 (C or S) or which plastic matrix (rP or rH) was used. This effect was observed even when the composite films were not submitted to biorientation, which, as pointed out earlier, should induce the formation of microcavities and thus would have furnished a ready explanation for the values lower than the theoretical densities. The films made from rPP with 30 wt% CaCO3 were also drawn at various speeds,

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to test whether this parameter affected the quantity of microcavities and hence the density. It was predicted that the greater shear stresses produced at the polymer-filler particle interfaces by higher drawing speeds would lead to microvoids being formed in larger numbers and therefore to lower densities. Nevertheless, according to the data in Table 7, no such effect occurred, as the film-drawing speed had no detectable influence on the apparent density. Furthermore, reducing the size of the CaCO3 particles had no direct effect on ρ, irrespective of the polymer matrix. Samples of the flat films PrPS30 and 40, PrHS20 and 30 and PrHC20 and 30 were subjected to extended biorientation in bench-scale tests. Only the microstructure formed during the orientation was analyzed, since the restricted size of the samples impeded the use of pycnometry or normalized grammage (grammage/thickness - g/m2/m) techniques. This test procedure involved using a device, inserted in a muffle, capable of stretching the film uniaxially at a controlled temperature, as shown in Figure 6. The stretching was applied transversely across the films up to four times, at 135 0C for films based on rPP and 110 0C for rHIPS/rHDPE films [221, 222].

Figure 6. Extended film biorientation device: sample holder (left) and the heating muffle (right)

Irrespective of the polymer matrix, composition, filler type, kind of extrusion (flat or tubular film) or the speed at which film was drawn, no microcavities were seen in any specimen, at least near the surface. On the other hand, microvoids due to shear-stresses at the polymer-filler particle interface were observed at the surface of every film submitted to extended biorientation. Figures 7a, b and c show this behaviour clearly. The composite films of rPP/CaCO3 were evaluated for possible use as a supporting core layer in multilayer films, so that there was no need to determine their optical and printing properties. Conversely, the PP/EVA/CaCO3 and rHIPS/rHDPE/CaCO3 films were studied as potential surface layers, whose printability and appearance would clearly be of supreme importance.

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a)

b)

c) Figure 7. Surface SEM micrographs of PP/CaCO 60/40 films: (a) flat casting (1000x); (b) tubular partially bioriented (5000x); and (c) extended bioriented (1000x).

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The flat mono-oriented films of rHIPS/rHDPE/CaCO3 produced in the laboratory were tested in several ways. For example, it was found that both the type and concentration of CaCO3 affected the adherence of offset printing ink. The ink was applied at Gráfica Suprema, São Carlos, Brazil, by inserting samples of ecological synthetic paper into a routine offset print run. The adherence of the ink was tested by fixing a length of adhesive tape (1.5 cm wide, Adere, Brazil) across the printed film, allowing a 560 g roller to run three times over the tape and then pulling the tape off the film rapidly. The adherence of the ink to the synthetic paper was classified qualitatively as bad, good or excellent, according to the amount of ink removed by the tape. The results are shown in Table 8. After this test, the specimens were photographed as a visual record of the quality of adherence. The worst and best cases are shown in Figure 8. Table 8. Adherence of offset ink to rHIPS/rHDPE/CaCO3 films. Film

SM10 SM20 SM30 Pcel

Without surface treatment

With surface treatment

Film

Without surface treatment

With surface treatment

Excellent Excellent Excellent Excellent

Excellent Excellent Excellent -

C10 C20 C30 Psin

Bad Bad Bad Excellent

Bad Good Excellent -

Figure 8. Visual illustrations of the worst and best cases of Offset ink adherence on rHIPS/rHDPE/CaCO3 films: (a) C20 without ECD, and (b) SM30 with ECD treatment.

In the case of PP/EVA/CaCO3 composites, the computer program MINITAB was employed to plan a factorial experiment, to analyze, with the help of a response surface, the influence of the inorganic filler and antistatic agent on the whiteness, coefficient of friction and quality of offset printing. These experiments were used to optimize the proportions of these components in the film for its intended use as a surface layer in ecological synthetic paper, and we hope to publish these results in the near future. Furthermore, optimized compositions have already been tested in a pilot plant, biorienting the PP (BOPP) by coextrusion in three layers. Only virgin raw materials were used in this test. Results from the various tests used to characterize these three-layer films are still under analysis. While the measurements of gloss showed values within the accepted reference values, the surface appeared rather shiny, typical of plastic films. I t is planned in the near future, another pilot plant trial will be made, with the same compositions as before, except

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that post-consumer plastics will be used in all three layers, in the hope of reproducing in the pilot plant the normal appearance of synthetic paper, without a plastic shine, obtained in lab tests by extrusion of tubular film composed of recycled residues.

CHEMICAL RECYCLING Chemical recycling consists in using depolymerization and decomposition reactions to convert polymers into low molecular-weight products. According to the type of reaction, a variety of chemical products are generated that can be used as raw materials in several sectors. Chemical recycling is generally divided into two types: thermolysis and solvolysis [229, 230]. Thermolysis, also termed thermochemical recycling, works with high temperatures, from 350 °C to 1000 °C. It is based on three main processes: pyrolysis, gasification and hydrogenation. Solvolysis, which is often referred to simply as chemical recycling, involves the use of solvents and much more moderate temperatures than those used in thermolysis. Several kinds of solvolytic reaction are found in practice: hydrolysis, glycolysis, methanolysis, aminolysis, alcoholysis and acidolysis. Solvolysis is chiefly used to recycle poly (ethylene terephthalate) (PET) [229-231], poly (butylene terephthalate) (PBT) [232], nylon [233] and polyurethane (PU) [234, 235]. Up to now, the industrial processes most frequently used to recover PET have been glycolysis and methanolysis. Nonetheless, hydrolysis has been attracting a lot of attention in recent years, as it can be classified as a green technology due to its simplicity, low energy consumption and low environmental impact. Furthermore, the fact that terephthalic acid (TPA) is currently taking over from the traditional monomer dimethyl terephthalate (DMT) in the synthesis of PET means that hydrolysis yields a readily usable raw material, even if the rather high cost of purifying TPA and ethylene glycol (EG) is a disadvantage of this process [230, 236]. Hydrolytic depolymerization of PET can be done in alkaline, acid or neutral conditions. Acid hydrolysis causes considerable problems, both on the economic and environmental fronts, due to the concentrated acids used. On the other hand, neutral hydrolysis, which is performed with hot water or steam at high pressure, is the most environment-friendly method, but it produces the TPA of lowest purity. Alkaline hydrolysis is generally carried out in aqueous solutions of sodium or potassium hidroxides, but other solvents may be used, especially when PET is salvaged from highly contaminated residues such as metalized and Xray films and magnetic recording tape. Karayannidis and co-workers [231] have developed a method of recycling spent PET by alkaline hydrolysis, which can be applied on the industrial scale to multilayer or contaminated residues, using 0.1 M KOH in methyl cellosolve. Assuming that the co-monomer isophthalic acid does not constitute an impurity, the TPA is found to be 99.6% pure. The TPA produced was tested by forming a co-polyester with EG, the result being a pure white polymer of intrinsic viscosity η = 0.54 dL/g. When discussing recycling by solvolysis, an important aspect is the research effort being spent on novel media such as supercritical fluids. In this field, Goto and co-workers [237] developed a method of recycling PET waste by depolymerizing it in supercritical methanol at a pressure of 20 MPa and temperature of 300 °C, in an atmosphere of N2. A continuous

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kinetics model was developed, tested on the experimental data and proved to simulate changes in the molecular-weight distribution (MWD) and monomer concentrations over time. This model included decomposition reactions such as random and specific scissions and secondary reactions for monomer components. The largest yields of DMT and EG were obtained at 7,200 s, 80 mol %, and at 3,600 s, 60 mol%, respectively. The first of the thermochemical recycling methods, pyrolysis is carried out in an inert atmosphere, at 350-600 °C, and generates chemical feedstock with a composition similar to crude oil or even to naphtha, depending on the polymer residue used. Generally the liquid fractions predominate, the type of reactor, dwell time and process temperature being crucial to the product selectivity [229, 230, 238, 239]. Gasification is done at higher temperatures than pyrolysis and in an oxidizing atmosphere, the main aim being to produce syngas, a mixture of hydrogen and carbon monoxide used to synthesize basic organic chemicals. The material is commonly raised to 1000 °C and gasifying reagents such as oxygen, carbon dioxide, air or steam are introduced in separate or mixed flows. This technique is normally, but not exclusively, used on the residue of plastics already decomposed by pyrolysis [229, 230, 240]. Hydrogenation is effectively the cracking of polymers with hydrogen gas, at high temperatures, to convert them to liquid fuels. In this process, previously depolymerized plastic residues are submitted to cracking at around 480 °C and a pressure of 200 bar, generating various products, including gasoline and diesel oil, whose economic value is considerably higher those obtained by pyrolysis and gasification [229, 241, 242]. Judging by the published reports consulted, there was a period of intense research and development in the field of thermochemical recycling of plastic by the techniques outlined above between 1995 and 2000, focusing on plastic waste in general [238-243]. After that period, however, such publications suddenly thinned out as researchers began to concentrate on one kind of plastic, a current industrial problem or some specific question not resolved in earlier studies [244-246]. For example, the thermolysis of polyesters like PET and PBT had always given problems due to sublimation of the acids produced by the decomposition, which corroded the reactor and could also neutralize the lime (CaO) used as a chlorine filter, even blocking the pores in the filter bed. In addition, the sublimated TPA itself, by condensing in cooler regions, caused blockages in the equipment and generated an undesirable fraction of solids [230, 246]. Yoshioka and co-workers [246] considered an interesting solution, in which the pyrolysis was performed in a fixed-bed reactor in the presence of calcium hydroxide (Ca[OH]2), and carried out experiments on PBT and poly (ethylene naphthalate) (PEN), similar to previous tests with PET, but now using helium gas as the inert atmosphere. A benzene yield as high as 85% had been achieved by decomposing PET at 700 ºC in a steam atmosphere. In the case of PBT and PEN, respectively, a benzene yield of 67% at 700 ºC and a Ca(OH)2/PBT ratio of 10, and a naphthalene yield of 80% at 600 ºC and a Ca(OH2)/PEN ratio of 5, were obtained along with reduced carbonaceous residues. These authors attributed the difference in benzene yield between PET and PBT to hydrolytic degradation of PET by the steam flow. Similarly positive results had been reported by Masuda et al. [247], who proposed a new system with the catalysts FeO(OH) (hydrated ferric oxide) and Ni supported on a rare-earth metal exchanged-Y zeolite (Ni-REY), consisting of three reactors connected in series. Among eight plastics (polyurethane, two polyolefins, two polyamides and three polyesters), it was found that only in the case of the

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polyesters (PC, PET and PBT) did the introduction of steam affect the reaction mechanism; besides this, the amount of carbonaceous residue was negligible in this system. Another interesting approach was developed by Kaminsky et al. [245], who had to deal with the real problem of applying pyrolysis to poly (methyl methacrylate) (PMMA) carrying a big load of alumina trihydrate (ATH), a filler used at concentrations of up to 67% as a fire retardant. The aim was to study the influence of this additive on the pyrolysis of PMMA. In fluidized-bed reactors operating at 450 °C, the decomposition of PMMA attained a monomer yield of up to 97.2 wt%. In the presence of ATH at 450º C, filled PMMA yielded only 58% MMA monomer and not only did the ATH present no catalytic effect but also water formed by its dehydration was found to lower the monomer yield.

ENERGY RECYCLING Energy recycling differs from the recovery of fuels by thermolysis in the fact that residues are incinerated at temperatures above 1000°C, so that their energy content is used directly for heating or to generate steam and electric power. The calorific value varies with the composition of the residue. Typical values for waste materials are shown in Table 9. It can be seen that the amount of energy recovered from plastics is, in general, among the highest, the polyolefins attaining the level of fuel oil [248-251]. Table 9. Heating values of some combustible materials and residues in MSW [248]. Materials, Residues Polyethylene Polypropylene Polystyrene Tire chips* Polyvinyl chloride Polyurethane foam Nylon Phenol formaldehyde *

Heating values (kcal/kg) 18,720 18,434 16,082 13,000-14,000* 7,516 11,362 10,138 13,197

Materials, Residues Newspapers Pine wood* Vegetable oils Bituminous coal* Fuel oil* Food waste Textiles Corrugated boxes

Heating values (kcal/kg) 6,970 9,100* 14,770 11,000-14,000* 18,000-19000* 4,200 5,900 6,153

Data from [249], in BTU/lb.

During the 1990s, there was a lot of controversy about energy recycling, generated chiefly by an argument between the industry and environmentalists, concerning the emission of gases, release of dioxins and disposal of solid waste. While this argument was going on, at the end of the eighties and start of the nineties, several countries of the EU, North America and Japan sent most of their waste to “incineration facilities”, not all of which had installed energy-recovery equipment. In fact, in some facilities the refuse was simply burnt, to reduce its volume or to destroy pathogenic material, without any care being taken to avoid toxic and polluting emissions [248, 250]. In that period, if combustors both with and without energy recycling are considered, more than 40% of all MSW was incinerated in France (42%), Sweden (47%), Denmark (48%), Belgium (54%) and Switzerland (59%), and as much as 75% in Luxemburg. On the other

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hand, in the USA there was a marked fall in incinerated MSW, from 31% in 1960 to little more than 7% in 1988. However, according to projected trends published by Alexander [250], the number of ‘waste-to-energy’ plants in the USA would rise from 128, operating in 1990, to 188 in the late nineties. With this program, 37% of all residues would be incinerated, saving the equivalent of 57 million barrels of gasoline per annum. Already in the early nineties, almost every Japanese community operated a waste-toenergy facility, totaling 70% of garbage incinerated, even though their recycling rate was more than double that of the USA. On the other hand, in Canada in 1987, where domestic waste per capita was the highest in the world (1.7kg/day), a large part of this was buried and only a tiny amount burnt in the mere twelve incinerators possessed by the country. Maraghi argued in favor of using energy from waste in Canada, on the basis of his review of the subject [248]. Even in countries not described as developed, specific regional problems may motivate big investments in building combustion facilities. A typical example was mentioned by AbuHijleh and co-workers [251], who concluded that it would be economically feasible to build a waste incineration plant in Jordan at the end of the nineties. They used sensitivity analysis to investigate the profitability of a material recycling and electricity generation plant under different financial scenarios. The need for such a waste disposal alternative at that time was urgent, because of a substantial increase in household and commercial waste generation in Jordan, resulting from a rapid growth in the Gross National Product (GNP) of 6% simultaneously to a high population growth rate (3.6%) and increasing standard of living. Another typical example of specific local factors is provided by Sweden, a fullydeveloped country whose towns are having problems complying with the new waste management laws. According to Holmgren and Henning [252], these stipulated that, from 2005, combustible and organic residues were to be banned from landfills, and a new tax was imposed on landfill disposal of waste. This situation provoked plans for new combustion plants which, if carried out, would almost double the waste incineration capacity of these towns from 2.4 to 4.7 million tons a year, between 1998 and 2006. From the environmental viewpoint, the greenhouses gases, dioxins and other organic compounds, as well as heavy metals, generated by these incinerators are always seen as arguments against energy recycling. From the technical and economic point of view, the main obstacles are the need to separate food and organic garbage from non-combustible components, so as to obtain the highest possible energy harvest, and the massive investments demanded for new installations. On the other hand, the very important points in favor of this method of recovering waste are the drastic reduction in the volume of buried refuse and the savings in non-renewable resources that would otherwise be burned to generate heat and power [248-253]. According to certain authors and the power industry, the problem of pollution by emissions and effluent from incinerator plants was virtually solved a long time ago. Dangerous particulates such as fly ash and low-volatility metal vapors are retained in bagfilters and electrostatic precipitators. Acid gases like HCl and SO2 are neutralized with lime or caustic soda. On the question of the impact on global warming, the controlled incineration of a ton of residues in combustors liberates 6 to 10-fold less total greenhouse gas than does the same quantity decomposing in a landfill. In addition, the oxides of nitrogen (NOx) produced by combustion of residues are up to 250 times more efficient per molecule than CO2

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in trapping heat, and they can be reduced in combustors to NxO, by adjusting the amount of air in the combustion mixture or spraying with ammonia solution [248, 250, 253]. Regarding dioxins, without entering the unresolved argument about whether or not a real toxic risk to human health has been demonstrated in atmospheric concentrations of the order of parts per trillion or quadrillion, modern incinerators are designed to operate at a temperature between 925 and 1,315°C, to eliminate all dioxin emissions. This is done because the dioxins present in the residues are destroyed above 925°C, while those produced by the combustion do not form below 1,315°C [250]. Another controversy surrounds the heavy metals which are actually present in the ashes. The ashes are generated directly as the solid residue of combustion (bottom ash), with a quite limited potential for pollution, and also as particles removed from exhaust gases in the flue (fly ash) [248, 250, 253], which are heavily loaded with these metals. Heavy metals can be leached from these ashes, when they are inadequately buried in landfills, eventually contaminating the ground water. One of the cited authors [250] comments that the most important heavy metals, lead and cadmium, are leached from ash in laboratory tests in strongly acid solutions, whereas in practical industrial analyses, the ash residues are solely buried in the mildly alkaline conditions produced by the ash itself, resulting in a leachate that remains free of heavy metals even after 20 years of monitoring. Moreover, given that most of the lead and cadmium in MSW comes from discarded batteries, the mere separation of these items from the residues before incineration would substantially reduce the heavy-metal content at source and thus in the ashes. Nonetheless, Huang et al., [253] point out that, in order to comply with current local regulations such as those in, say, Taiwan, fly ash destined for sanitary landfills must first undergo intermediate treatments such as solidification, stabilization or others, specified in the criteria of the Taiwan Environmental Protection Administration (TEPA). Unfortunately, the explosive rise in the volume of refuse generated on that island-country, coupled with the lack of space, has led to the predominance of incineration of MSW over other disposal methods. Already in 2003, 70% by weight of all MSW in Taiwan was incinerated in 19 facilities, although the total capacity of the incinerators does not represent the whole potential capacity for energy recovery. Around 2007, all towns will be served by combustion plants, worsening the problem of what to do with the ash produced, which amounts to more than 18% of the incinerated MSW and already in 2003 totaled 1.05 million tons. Recently, there has been a focus on comparative evaluation of energy recovery and material recovery processes. Patel and Xanthos [4] have presented a summary of results obtained in earlier work, in which they used a method based on the principles of life-cycle analysis (LCA) to estimate the energy consumed in the various possible pathways followed by plastic residues. The values derived from the analysis of energy flow were converted to figures on a scale of merit, on which waste-to-energy incineration scores 100. For each kind of waste disposal, material and energy recovery were ranked in terms of energy-saving efficiency, values higher than 100 representing processes less efficient than waste-to-energy combustion of plastics. The authors concluded that landfill, where obviously all the energy content of the waste is lost, and thermolysis to fuels are less efficient than energy recovery, while, in the following order, thermolysis to monomers < mechanical recycling < reuse of articles are more efficient.

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Holmgren, Henning and co-workers have published several articles on this topic. In some of the most recent, they described important results obtained with the aid of the energy system optimization model MODEST (Model for Optimization of Dynamic Energy System with Time-dependent components and boundary conditions). Apart from being used to review the various studies made of the Linköping utility [254], MODEST was used for a comparative assessment of material and energy recovery from MSW in the energy utilities of two Swedish towns: Linköping, which at the end of 2003 already used several energy-sources, the basic heat supply coming from the incineration plant, and Skövde, which used a heat plant fired by wood chip and was planning to invest in the construction of a waste-incineration plant [252]. Holmgren and Henning concluded that investing in plants using waste as a fuel for electricity and heat production would be profitable for the two towns. However, noncombustible residues, such as metals and glass, give no heat contribution when incinerated; material recycling of metals saves a lot of energy, whereas glass material recycling saves less. Moreover, considering the energy efficiency calculation, waste-to-energy is preferable for cardboard and biodegradable waste, whereas material recovery should be applied to paper and hard plastics, even if a district heating system is able to use the energy generated by a waste of such high combustion energy [252, 254]. This conclusion for plastics is in agreement with the data presented by Patel and Xanthos that ranked energy savings of the different forms of plastics waste recovery [4]. In Brazil, not a single unit exists that produces energy from MSW. There was practically no discussion over alternative sources of power and heating, until this question began to acquire importance in 2001, with a power crisis provoked by a shortage in the supply of electricity. The government had to subject industry, commerce and the general public to a drastic rationing of power consumption. In November 2005, a technical cooperation agreement was signed between Federal Government companies (Eletrobrás and the Electric Power Thermal Generation Company – CGTEE) and the cleansing department of the municipal government of Porto Alegre in Rio Grande do Sul (DMLU), to promote the production of gas from the biodigestion of MSW. The biogas produced will be used to generate electric power at the Nutepa power Station of Porto Alegre [255]. We have no knowledge of any other plans for the construction of this type of plant or of a waste-to-energy incineration facility in the country.

REMAINING CHALLENGES While working on this chapter, the authors came to realize how much effort has been and is being invested by researchers and government bodies, enterprises and, not least, popular initiatives around the world, in attempts to make all stages of plastic waste recycling viable from the technical, economic and social points of view. It was also clear, though, that there is still a lot more to be done if the recovery of plastic residues is to make an effective contribution to reaching the goal of sustainable development in the strict sense. Thus, to end this chapter, the authors thought it worthy to mention some of the challenges in plastic recycling that still have to be overcome. The first is to increase the rate of material recovery, principally by mechanical recycling which, in terms of energy savings, is the most suitable form of plastics recycling in most

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cases [4, 256]. To achieve this there will need to be more national laws and international agreements/directives establishing targets and allocating responsibility for the final destination of residues mainly to the manufacturers, while not exempting the public at large from playing its important part. The compulsory taxation on non-compliance with these regulations may seem a rather imposed incentive, but it would be very effective, even though in high population countries of continental proportions, like the USA, Russia, China, Brazil and India, the difficulty of regular inspection would have to be considered. Nowadays, besides the short-life packaging, there has been an alarming rise in the generated volume of plastic residues from engineering, from scrapped vehicles and electroelectronic products such as computers, mobile phones and photocopiers, which accumulates year by year in a growing mountain of plastic. Often, these components are made out of polymer blends or multi-material systems that are hard to separate into non-contaminated homogeneous materials, or out of laminates produced by in-situ formation of the polymer matrix, as is the case in polyester or polyamide mats with a polyolefin-blend backing layer, which are not economically viable to be recycled separately using the current technologies [42, 122, 257-259]. On the other hand, Massura and co-workers [260] recently tested in a pilot plant a technique to separate the layers of multilayer flexible packages, typically constituted by the following components: PET/inks/adhesive/aluminum/ adhesive/PE. They achieved an efficient separation by using specific solvents to dissolve the adhesives and inks, frequently based on polyurethanes, and even put the separate components on the market. However, the enterprise could not advance, due to lack of interest on the part of national investors from this market sector in Brazil. Within the stream of plastic waste there are some residues considered harmful, such as containers used for toxic agrochemicals and pathogenic plastic residues from hospitals [261], and some that are not classed as dangerous, but are included in producer-responsibility recycling systems [262] or are banned from landfills by government regulations [256], such as combustible organic residues. There is an urgent need, therefore, to find solutions to this problem, creating suitable treatment facilities or destinations for these materials that cannot be buried. In the case of the agrochemical containers, apart from being left on the land without due care, they are commonly reused for the transport and storage of water and food by the landowners and rural workers, who frequently are ignorant of their polluting and toxic potential. Generally, after the toxic contents have been fully used, about 0.3% of the initial volume remains in the container and, following triple washing in clean water with a pressurized jet, 99.9% of that volume is removed, reducing considerably the problem of finding a suitable destination [263]. These residues that have already been the target of Brazil’s government, nowadays have their own market and recycling facilities established, due to their available collection system achieved through the enforced government regulations. From a total of approximately 14,000 tons of plastic agrochemical containers collected in these facilities, more than 50% were successfully recovered in 2004, mainly through mechanical recycling to manufacture products for the construction sector. One great challenge is the recycling of commodity plastics, including the various types of PET bottles, into high added-value products. These residues, in contrast to the engineering plastics, are of low value and generated in enormous quantities, and thus demand recovery facilities on a massive scale. We take the view that material recovery should be adopted in

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this case, employing both chemical processes for the production of monomers and mechanical recycling to produce valuable articles, such as the previously mentioned closed-loop bottle-tobottle product and ecological synthetic paper. As far as this synthetic paper is concerned, the forthcoming pilot-plant tests with recycled plastic residues should tell whether or not the present technique is viable for commercial application. On the commercial side, the Brazilian suppliers of synthetic paper are unanimous in the view that the substitution of recycled plastic for virgin resin in the same process to make multilayer films would afford substantial financial and environmental benefits. In the case of PET, PMMA, PS and PTFE, the industrial exploitation of depolymerization is well-established [264]. By contrast, selective depolymerization of polyolefins to generate high yields of monomers remains technically an unsolved challenge. High-yield recycling processes and mass production are needed for polyolefins, as they are the class of plastics found in greatest amounts in waste. In addition, although the method of pyrolysis of these residues is well-established, the various products derived from the reaction are determined mainly by secondary reactions, causing difficulties of control in production. Kaminsky and Hartman [264] have reported a process to degrade PE which they describe as particularly spectacular. According to these authors, the method was invented by Dufaud and Basset, who utilized a strongly electrophilic Ziegler-Natta catalyst, zirconium monohydride, at 150°C, resulting in the complete decomposition of the polymer into ethane and methane after 15h of reaction. Kaminsky and Hartman [264] also comment that this process is a random chain-cleavage reaction, which should not be considered a true depolymerization or retropolymerization. According to them, given that this is the first case of a catalyst actively involved in the primary reaction, Dufaud and Basset have made a remarkable discovery. However, it was still not possible to obtain the ethylene monomer and, while they consider that “catalytic monomer recovery is a large step closer”, this remains a challenge for the chemical recycling of polyolefins. The authors realize that sustainable development in plastics recycling will not be fully attained if only the ongoing scenario is to be continued, but also are optimistic in contributing to the needed development of economically viable and clean recycling technologies or even to the improvement of currently available recycling technologies. Furthermore, the authors realize that financial support from the private sector and the government enforcement regulations, together with public participation, are crucial to promote the recovery of the highest added value of recycled plastics before plastics become scarce and much of the valuable energy of their residues has been exhausted.

ACKNOWLEDGEMENTS The authors thank to São Paulo State Foundation for Research Support (FAPESP), PADCTIII/CNPq, CAPES, Polibrasil Resinas SA for the financial support and students scholarships. The authors are also grateful to Eliton Souto de Medeiros and Silvio Manrich for their valuable comments and special aid.

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REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33]

Ross, S.; Evans, D. J. Cleaner Production. 2003, 11, 561-571. Maeda, M.; Ikeda, T. Polym Adv Technol. 2000, 11, 388-391. (2005). Canada faces climate crisis. Carbon Brazil, http://www.carbonobrasil.com (in Portuguese). Patel, S.H.; Xanthos, M. Adv Polym Technol. 2001, 20(1), 22-41. Pagliarussi, M. S. M.S. thesis, Federal University of São Carlos, São Carlos, SP, 1995 (in Portuguese). Risso, W.M.; Wiebeck, H. Plastics recycling and their industrial applications, University of São Paulo, São Paulo, SP, 1994 (in Portuguese). Amaral, L.H. Folha de São Paulo. September 16, 1994 (in Portuguese). Fridman, I.J. Rev Limp Públ. 1997, 44, 11-12 (in Portuguese). Duchin, F.; Lange, G. M. Struct Change Econ Dynam. 1998, 9, 307-331. Agnelli, J. A. M., et al. Polím: Ciência e Tecnol. October/December, 1996, 9-18 (in Portuguese). Landsberger, S.; Chichestes, D. L. J. Radioanal Nucl Chemistry. 1995, 192, 289-297. Mancini, S.D., Zanin, M. In: Congress of Sanitary Engineering, Peru, 1998, 27th. Dent, I. Plast Packaging Recy. 1999. Warmer Bull. January 1997, 52. Broek, W. H. A. M., et al. Chemometr Intell Lab Systems. 1996, 35, 187-197. Tombs, G. Plast Packaging Recy., 1999. Toloken, S. Plást Rev November 2002, 38 (in Portuguese). Borges, A. Gazeta Mercantil. March 24, 1999, C-6 (in Portuguese). Plást Rev. June 2001, 28 (in Portuguese). Gimenez, K. Plást Rev. May 2002, 22 (in Portuguese). Davis, G.; Phillips, P. S.; Read, A. D.; Lida, Y. Resour Conserv Recy., 2006, 46, 115127. Daskalopoulos, E.; Badr, O.; Probert, S. D. Appl Energ. 1997, 58, 209-255. Onusseit, H. In: AFERA Technical Seminar, Düsseldorf, 2002, 1st. Mancini. S.; Santos, A. S. F.; Manrich, S.; Zanin, M. Pack. 2001, 46, 36-37 (in Portuguese). An Analysis of Plastics Consumption and Recovery in Europe. Plastics Europe Info Point: Bruxels, 2004. Dennison, M. T.; Mennicken, T. In: PACIA CONVENTION, Brisbane, 1996. Tawfik, M. S.; Devlieghere, F.; Steurbaut, W.; Huyghebaert, A. Acta Alimentaria. 1997, 26, 219-233. Tilman, C.; Sandhu, R. Resour Conserv Recy. 1998, 24, 183-190. Esposito, F. Plást. Rev, May 2001, 28 (in Portuguese). Toloken, S. Plást. Rev, September 2002, 33 (in Portuguese). Napcor Reports Increase in PET Recycling Rate and Record Volume of Recycled PET Containers. NAPCOR: Sonoma, CA, 2005. Performance and perspectives of plastic’s recycling in Brazil. PLASTIVIDA: São Paulo, SP, 2004 (in Portuguese). Mancini, S. D.; Zanin, M. Plást. Ind. September 2000, 118.

An Overview of Recent Advances and Trends in Plastic Recyling

53

[34] Plastic’s recycling in Brazil. CEMPRE: São Paulo, SP, 2004 (in Portuguese). [35] Embanews. January 2002, 46. [36] Lagarinhos, C. A F. M.S. thesis. Institute of Technological Research, São Paulo, SP, 2004 (in Portuguese). [37] Camponero, J. PhD. thesis. University of São Paulo, São Paulo, SP, 2002 (in Portuguese). [38] Resolution n. 258. Ministry of Environment, National Council of Environment, Brazil, August 26, 1999 (in Portuguese). [39] Manrich, S.; Frattini, G.; Rosalini, A. C. Plastics identification: a recycling tool. Editora da UFSCar (EdUFSCar): São Carlos, SP, Brazil, 1997; 23-42 (in Portuguese). [40] Kukaleva, N.; Simon, G.P.; Kosior, E. Polym Eng Sci. 2003, 43, 431-443. [41] Massura, A. C. M.S. thesis. University of São Carlos, São Carlos, SP, Brazil, 2005 (in Portuguese). [42] Tsunekawa, M.; Naoi, B; Ogawa, S.; Hori, K.; Hiroyoshi, N.; Ito, M.; Hirajima, T. Int J Miner Process. 2005, 76, 67-74. [43] Pascoe, R. D. Waste Manage. 2006 (in press). [44] SRH Simco/Ramic catalog. Simco/Ramic Corporation, Inc. 1992. [45] Collier, M. C.; Baird, D. G. Polym Comp. 1999, 20, 423-435. [46] Van Ness, K. E.; Nosker, T. J. In: Plastics recycling: products and processes; Ehrig, R. J.; Ed.; Hanser Publishers: Munich, 1992, 187-229. [47] Nauf, U.; Mäurer, A.; Holley, W.; Wiese, M.; Utschick, H. Kunststoffe. 2000, 90. [48] Drelich, J.; Payne, T; Kim, J. H.; Miller, J. D.; Kobler, R.; Christiansen, S. Polym Eng Sci. 1998, 38, 1378-1386. [49] Marques, G. A.; Tenório, J. A. S. Waste Manage. 1999, 20, 265-269. [50] Hearn, G. L.; Ballard, J. R. Resour Conserv Recy. 2005, 44, 91-98. [51] Green, J. L.; Petty, C. A.; Gillis, P. P.; Grulke, E. A. Polym Eng Sci. 1998, 38, 194-203. [52] Saito, T.; Satoh, I. Polym. Eng. Sci. 2005, 1419-1425. [53] Huber, M., Franz, R. J. High Resol Chromatogr. 1997, 20, 427-430. [54] Syrinek, A. R.; Tex, R. US Patent 5,330,581, 1994. [55] Sanko, G. Recycling product news, july/august 1999, 7. [56] Kao, C., Cheng, W., Wan, B. J Appl Polym Sci. 1998, 70, 1939-1945. [57] Santos, A. S. F.; Teixeira, B. A. N.; Agnelli, J. A. M.; Manrich, S. Resour Conserv Recy. 2005, 45, 159-171. [58] Heyde, M.; Kremer, M. Recycling and recovery of plastics from packaging in domestic waste. Ecomed Publishers: Freising, 1999, 5. [59] Santos, A. S. F.; Araújo, E. S.; Manrich, S. In: Brazilian Polymer Congress, Associação Brasileira de Polímeros: São Carlos, SP, 1999, 5th (in Portuguese). [60] Remédio, M. V. P. M.S. thesis, Federal University of São Carlos, São Carlos, SP, 1999 (in Portuguese). [61] Frattini, G. M.S. thesis, Federal University of São Carlos, São Carlos, SP, 1999 (in Portuguese). [62] Santos, A. S. F. M. S. thesis, Federal University of São Carlos, São Carlos, SP, 2000 (in Portuguese). [63] Oldshue, J. Y. Chem Eng. June 1983, 90, 82-108. [64] Rauwendaal, C. Polymer Extrusion. Hanser Publishers: Munich, 2001.

54

Sati Manrich and Amélia S. F. Santos

[65] Strumillo, C.; Kudra, T. Drying: principles, applications and design. Gordon and Breach Science Publishers: Montreux, 1986. [66] Porter, H. F. et al. In: Perry's Chemical Engineers Handbook. Perry, R. H. (ed.). 6. ed. Mc Graw-Hill: New York, 1984, 20-21. [67] Jomaa, W.; Baixeras, O. Drying Technol. 1997, 15, 2129-2144. [68] Piovan S.p.A. Piovan PET systems. Venice, 1997. [69] Laoutid, F.; Ferry, L; Lopez-Cuesta, J. M.; Crespy, A. Fire Mater. 2006 (in press). [70] Greco, A.; Maffezzoli, A.; Manni, O. Polym Degrad Stab. 2005, 90, 256-263. [71] Japon, S.; Leterrier, Y.; Manson, J-A. E. Polym Eng Sci. 2000, 40, 1942-1952. [72] Poulakis, J. G.; Papaspyrides, C. D. Advan Polym Technol. 2000, 19, 203-309. [73] Papaspyrides, C. D; Kartalis C. N. Polym Eng Sci. 2000, 40, 979-984. [74] Shin, C.; Chase, G. G.; Reneker, D. H. Colloid Surface. 2005, 262, 211-215. [75] Xanthos, M.; Dey, S. K.; Mitra, S.; Yilmazer, U. Feng, C. Polym Comp. 2002, 23, 153163. [76] González, O.; Muñoz, M. E.; Santamaría, A.; García-Morales, M.; Navarro, F. J.; Partal, P. Eur Polym J. 2004, 40, 2365-2372. [77] Henninger, F.; Drake, W. O.; Sitek, F. The role of processing stabilizers in recycling of polyolefins. Basel: Ciba-Geigy. [78] Agnelli, J. A. M. Degradation, stabilization and aging of polymers. Associação Brasileira de Polímeros (ABPol): São Carlos, SP, 1997, 196-204 (in Portuguese). [79] Popisil, J. Int Polym Sci Technol. 1994, 21, T/54-T/58. [80] Paci, M.; La Mantia, F. P. Polym Degrad Stab. 1998, 61, 417-420. [81] Villain, F., Coudane, J., Vert, M. Polym Degrad Stab. 1995, 49, 393-397. [82] Allen, N. S; Edge, M; Daniels, J; Royall, D. Polym Degrad Stab. 1998, 62, 373-383. [83] Ravindranath, K; Mashelkar, R.A. Chem Eng. Sci. 1986, 41, 2197-2214. [84] Edge, M; Allen, N.S; Wiles, R; McDonald, W; Mortlock S.V. Polym. 1995, 36, 227234. [85] Edge, M; Allen, N.S; Wiles, R; McDonald, W; Mortlock S.V. Polym Degrad Stab. 1996, 53, 141-151. [86] Santos, A. S. F.; Medeiros, E. S.; Agnelli, J. A. M.; Manrich, S. In: World Polymer Congress, IUPAC: Paris, 2004. [87] Paul, D. R., Keskkula, H. Encyclopedia of the polymer science and engineering. John Wiley: New York, 1986, 4, 630-691. [88] Foster G. N.; Wasserman S. H.; Yacka D. J. Die Angew Makromol Chem. 1997, 252, 11-32. [89] Launay, A.; Thominette, F.; Verdu, J. Polym Degrad Stabil. 1999, 63, 385-389. [90] Agnelli, J.A.M., Chinelatto, E. M. A. Polím: Ciência Tecnol. July/September 1992, 127-131. [91] Allen, N.S., et al. Polym Degrad Stab. 1994, 43, 229-237. [92] Zaikov, G. E. Int. Polym Sci Technol. 1991, 18, T/49-T/59. [93] Cardi, N., et al. J Appl Polym Sci. 1993, 50, 1501-1509. [94] Ballara, A.; Verdu, J Polym Degrad Stab. 1989, 26, 361-374. [95] Hendrickson, L.; Connole, K. B. Polym Eng Sci. 1995, 35, 211-217. [96] Zimmerman, H.; Kim, N. T. Polym Eng Sci. 1980, 20, 680-683. [97] Craig, I. H.; White, J. R.; Kin, P. C. Polym. 2005, 46, 505-512.

An Overview of Recent Advances and Trends in Plastic Recyling

55

[98] Agnelli, J. A. M., Sousa, J. A., Canevarolo Jr., S. V. Introduction to degradation and stabilization of polymers. Associação Brasileira de Polímeros (ABPol): São Carlos, SP, 1991, 24-30 (in Portuguese). [99] Pospísil, J. Polym Degrad Stab. 1993, 40, 217-232. [100] Neri, C. et al. Polym Degrad Stab. 1995, 49, 65-69. [101] Henninger, F.; Gugumus, F.; Pedrazzetti, E. Processing, heat and light stabilization of polyolefins. Buenos Aires: Ciba-Geigy, 1986. [102] Gugumus, F. Polym Degrad Stab. 1994, 44, 273-297. [103] Monteiro, M.; Nerín, C.; Reyes, G. R. Food Addit Contam. 1996, 13, 575-586. [104] Hesbst, H. et al. Restabilization produces high quality recycled polyolefins. Munique: Carl Hanser Verlag, 1992. [105] Santos, A. S. F.; Agnelli, J. A. M.; Trevisan, D. W.; Manrich, S. Polym Degrad Stab. 2002, 77, 441-447. [106] Herbst, H. et al. In: International Recycling Congress at the Re’93 Trade Fair. Palexpo: Genebra, 1993, 3, 332-34. [107] Angrawal, A. K.; Singh, S. K.; Utreja, A. J Appl Polym Sci. 2004, 92, 3247-3251. [108] Malík, J. et al. Polym Degrad Stab. 1995, 50, 329-336. [109] Awaja, F.; Pavel, D. Eur Polym J. 2005, 41, 1453-1477. [110] Pacheco, E. V; Dias, M. L. J Polym Eng. 2003, 23, 23-42. [111] Li, J.; Favis, B. D. Polym. 2001, 42, 5047-5053. [112] Zumbrunnen, D.A.; Chhibber, C. Polym. 2002, 43, 3267-3277. [113] Hage Jr., E.; Ferreira, L.A.S.; Manrich, S.; Pessan, L.A. J Appl Polym Sci. 1999, 71, 423-430. [114] Lyngaae-Jorgensen, J.; Utracki, L.A. Polym. 2003, 44, 1661-1669. [115] Willemse, R.C.; Speijer, A.; Langeraar, A.E.; Boer, P. Polym. 1999, 40, 6645-6650. [116] Halimatudahliana, H.I.; Nasir, M. Polym Test. 2002, 21, 163-170. [117] Wu, J.; Guo, B.; Chan, C-M.; Li, J.; Tang, H-S. Polym. 2001, 42, 8857-8865. [118] Danella Jr, O.J.; Manrich, S. Polym Sci. 2003, 45, 1086-1092. [119] Fortelny, I.; Michálková, D.; Mikesová, J. J Appl Polym Sci. 1996, 59, 155-164. [120] Cherian, Z.; Lehman, R. Int J Adhesion Adhes. 2005, 25, 502-506. [121] Bonelli, C.M.C.; Martins, A.F.; Mano, E.B.; Beatty, C.L. J Appl Polym Sci. 2001, 80, 1305-1311. [122] Balart, R.; López, J.; García, D.; Salvador, M.D. Eur Polym J. 2005, 41, 2150-2160. [123] Liu, X.; Boldizar, A.; Rigdhal, M.; Bertilsson, H. J Appl Polym Sci. 2002, 86, 25352543. [124] Elmaghor, F.; Zhang, L.; Li, H. J Appl Polym Sci. 2003, 88, 2756-2762. [125] Fraïsse, F.; Verner, V.; Commereuc, S.; Obadal, M. Polym Degrad Stab. 2005, 90, 250255. [126] Pawlak, A.; Morawiek, J.; Prazzagli, F.; Pracella, M.; Galeski, A. J Appl Polym Sci. 2002, 86, 1473-1485. [127] Yu, Z-Z.; Yang, M-S.; Dai, S-C., Mai Y-W. J Appl Polym Sci. 2004, 93, 1462-1472. [128] Santana, R. M. C.; Manrich, S. J Appl Polym Sci. 2003, 87, 747-751. [129] Manrich, S; Sanches, L. F.; Perez, I. S. B. Federal University of São Carlos, São Carlos, SP (unpublished). [130] Corrêa, A. C.; Manrich, S. In: International Macromolecular Colloquium, Gramado, RS, 2005, 10th.

56

Sati Manrich and Amélia S. F. Santos

[131] Ravazi, R. F. M.S. thesis, University of São Carlos, São Carlos, SP, Brazil, 2002 (in Portuguese). [132] Lima, C. R.; Hage, E.; Manrich, S. In: Conference of the Brazilian Society of Metals and Materials, Águas de Lindóia, SP, 2001 (in Portuguese). [133] Danella Jr, O. J.; Manrich, S. Federal University of São Carlos, São Carlos, SP (unpublished). [134] Manrich, S.; Radanitsch, J.; Manrich, S.; Almeida, M.C. In: Brazilian Polymer Congress, Associação Brasileira de Polímeros: São Carlos, SP, 2003, 7th (in Portuguese). [135] Navrátilová, E.; Fortelný, I. Polym Network Blend. 1996, 6, 127-133. [136] Scaffaro, R.; La Mantia, F. P. Polym Eng Sci. 2002, 42, 2412-2417. [137] Scaffaro, R.; Dintcheva, N.T.; Nocilla, N.A.; La Mantia, F.P. Polym Degrad Stab. 2005, 90, 281-287. [138] Mallick, P. K.; Newman, S. Composites materials technology: processes and properties. Hanser Publishers: Munich, 1990. [139] Chawla, K. K. Composite materials: science and engineering. 2nd Ed. Springer-Verlag: New York, 1998. [140] White, R. J.; De, S. K. Short-fiber polymer composites. Woodhead Publishing:Cambridge, 1996. [141] Manson, J.A.; Sperling, L.H. Polymer Blends and Composites. Plenum Press: New York, 1976. [142] Liang J. Z., Tang C. Y., Li, R. K. R., Wong T. T. Metal Mater. 1998, 4, 616-619. [143] Thio, Y.S.; Argon, A.S.; Cohen, R.E.; Weinberg, M. Polym. 2002, 43, 3661-3674. [144] Silva, A. L. N.; Rocha, M. C. G.; Moraes, M. A. R.; Valente, C. A. R.; Coutinho, F. M. B. Polym Test. 2002, 21, 57-60. [145] Nielsen, L. E. Mechanical Properties of Polymers and Composites, Marcel Dekker: New York, 2, 1974. [146] Medeiros, E. S.; Agnelli, J. A. M.; Joseph, K.; Carvalho, L. H.; Mattoso, L. H. C. Polym Comp. 2005, 26, 01-11. [147] Jiang, H.; Kamdem, D. P. J Vinyl Addit Technol. 2004, 10, 59-69. [148] Arbelaiz, A. et al. Comp Sci Technol. 2005, 65, 1582-1592. [149] Wu, Y.; Isarov, A. V.; O´Connell, C. Thermochim Acta. 1999, 340-341, 205-220. [150] Guffey, V. O.; Sabbagh, A B. J. Vinyl Addit Technol. 2002, 8, 259-263. [151] Ha, C. S.; Park, H. D.; Cho, W. J. J Appl Polym Sci. 1999, 74, 1531-1538. [152] Dintcheva, N. T.; La Mantia, F. P. Polym Advan Technol. 1999, 10, 607-614. [153] Santos, P.; Pezzin. S. H. J Mater Process Technol. 2003, 143-144, 517-520. [154] Kouparitsas, C. E.; Kartalis, C. N.; Varelidis, P. C.; Tsenoglou, C. J.; Papaspyrides, C. D. Polym Comp. 2002, 23, 682-689. [155] Liu, Y. ; Meng, L ; Huang, Y. ; Du, J. J Appl Polym Sci. 2004, 95, 1912-1916. [156] Licea-Claveríe, A.; Carrillo, F. J. U.; Alvarez-Castillo, A.; Castaño, V. M. Polym Comp. 1998, 20, 314-320. [157] Pannkoke, K.; Oethe, M.; Busse, J. Cryogen. 1998, 38, 155-159. [158] Rothon, R.N.; Hancock, M. Particulate-Filled Polymer Composites. Longman Scientific & Technical; England, 1995. [159] Tadmor, Z.; Gogos, C. G. Principles of Polymer Processing. John Willey & Sons, Inc.: New York, 1979.

An Overview of Recent Advances and Trends in Plastic Recyling

57

[160] Pierce, D. E., Pfeffer, R. L., Sadler, G. D. Nucl Instrum Meth Phys Res B. 1997, 124, 575-578. [161] Bayer, F. L. Food Addit Contam. 1997, 14, 661-670. [162] Food and Drug Administration. (2003). Points to consider for the use of recycled Plastics in Food Packaging: Chemistry Considerations. http://www.fda.gov [163] Devlieghere, F.; Huyghebaert, A. Lebensm-Wiss Technol. 1997, 30, 62-69. [164] Kuznesof, P. M.; Vanderveer, M. C. In: Plastics, Rubber, and Paper Recycling. American Chemical Society: New York, 1995, 389-403. [165] Begley, T. H. Food Addit Contam. 1997, 14, 545-553. [166] Code of Federal Regulations 58, Food and Drug Administration, United States of America, 1993, 52719. [167] Code of Federal Regulations 60, Food and Drug Administration, United States of America, 1995, 36582. [168] International Life Sciences Institute. Guidelines for recycling of plastics for food contact use. Brussels, 1997. [169] Bündesinstitut für Gesundheitlichen Verbraucherschutz und Veterinärmdizin. Use of mechanically recycled plastic made from polyethylene terephthalate (PET) for the manufacture of articles coming into contact with food. 2001. [170] Plastics Recycling Task Force; National Food Processors Association; The Society Of The Plastics Industry, Inc. Guidelines for the safe use of recycled plastics for food packaging applications. 1995. [171] Franz, R., Huber, M., Welle, F. Deut Lebensm-Rundsch. 1998, 94, 303-308. [172] Nielsen, T.; Damant, A. P.; Castle, L. Food Addit Contam. 1997, 14, 685-693. [173] Welle, F; Franz, R. Maack Business Serv. 1999, Session XII/3, 1-8. [174] Komolprasert, V.; Lawson, A. In: Annual Technical Conference. Society of Plastics Engineers, 1994. 2906-2908, 52nd. [175] Demertzis, P. G.; Johansson, F.; Lievens, C.; Franz, R. Packag Technol Sci. 1997, 4558. [176] Santos, A. S. F.; Manrich, S. In: Brazilian Polymer Congress. Associação Brasileira de Polímeros: São Carlos, SP, 2001, 6th. [177] Devlieghere, F., et al. Food Addit Contam. 1997, 14, 671-683. [178] Pierce, D. E.; King, D. B.; Sadler, G. D. In: Plastics, Rubber, and Paper Recycling; American Chemical Society: New York, 1995, 458-471. [179] Franz, R.; Welle, F. Deut Lebensm-Rundsch. 1999, 10, 424-427. [180] Nichols, C. S.; Moore, C. U.S. Patent 5,876,644, 1999. [181] Erema GmbH. Recycling News. Linz, 2000. [182] Christel, A.; Borer, C.; Hersperger, T. WO 01/34688, 2001. [183] Rule, M. U.S. Patent 6,103,774, 2000. [184] Rudiger, F. U.S. Patent 6,436,322, 2002. [185] Kosior, E. BR Patent P.I. 0,014,094-5, 2002 (in Portuguese). [186] Hayward, D. W. BR Patent P.I. 0,017,236-7, 2003 (in Portuguese). [187] Hayward, D. W.; Martin, A. S.; Scholoss, F. M. BR Patent P.I. 9,708,284-8, 2000 (in Portuguese). [188] Bayer, F. On the United Resource Recovery Process (URRC). São Paulo: Instituto Adolf Lutz, 2000.

58

Sati Manrich and Amélia S. F. Santos

[189] New technology allows recycled PET for food direct contact. Cempre Informa, 2000, 4 (in Portuguese). [190] Brownscombe, T. F.; Chuah, H. H.; Diaz, Z.; Fong, H. L.; June, R. L. F.; Kevin, L.; Semple, T. C.; Tompkin, M. R. BR Patent P.I. 9,602,163-2, 1998 (in Portuguese). [191] Recycling of soluble plastics by selective extraction. Fraunhofer Institute Verfahrenstechnik Und Verpackung: Freising, 1999. [192] Schwartz Jr, J. A. U.S. Patent 6,147,129, 2000. [193] Louise A. Defresne, L. A.; Agrawaí, R. D.; Moore. F. BR Patent P.I. 9,705,128-4, 1999 (in Portuguese). [194] Al-Ghatta, R. A. U.S. Patent 5,049,647, 1991. [195] Schloss, F. M. U.S. Patent 5,824,196, 1998. [196] Ford, T. Plastics News. September1994, 2. [197] Scrap Processing and Recycling. January/February 1995, 28. [198] Smith, S. S. Plastics News. March 1997, 5. [199] Center for Food Safety & Applied Nutrition Recycled plastics in food packaging. 2000, http://www.fda.gov. [200] Manrich, S.; Santos; A. S. F.; Agnelli, J. A. M. BR Patent P.I 002,993, 2004 (in Portuguese). [201] Santos, A. S. F. PhD. thesis. Federal University of São Carlos: São Carlos, SP, 2004 (in Portuguese). [202] Bühler AG. Popis B2B procesu švýcarské firmy Bühler. April 2002. http://www.petrecycling.cz/novinkysvet.htm. [203] Thorsheim, H. R; Armstrong, D. J. Chemtech. August 1993, 55. [204] Manrich, S. Polym Recy. 2000, 5, 213-222. [205] Manrich, S.; Ravazi, R.; Danella Jr, O. J.; Santana, R. M. C.; Manrich, S. In: Global Symposium on Recycling, Waste Treatment and Clean Technology; Madrid, 2004, II, 1671-1680. [206] Santana, R. M. C.; Manrich, S. In: International Conference on Polymer Modification, Degradation and Stabilization; Budapest, 2002, 2nd. [207] Celulose & Papel. 2004, 20, 3 (in Portuguese). [208] O papel. 2004, LXV, 98 (in Portuguese). [209] Desai, S. C. Pop Plast Packag. 1994, 39, 45-48. [210] Mannar, S. M. European Patent 605,938 A1 940,713, 1993. [211] Ohno, A.; Ishige, A.; Koyama, H.; Asami, K. European Patent 685,331 A1 951,206, 1995. [212] Lin, A. F. U.S. Patent 005,552,011 A, 1996. [213] Hibiya, T.; Miki, T. European Patent 0,795,399 A1, 1997. [214] Amon, M. U.S. Patent 66,183,856, 2001. [215] Williams, R.C. et al. U.S. Patent 6,150,005, 2000. [216] Goettman et al. U.S. Patent 6,171,443, 2001. [217] Squier, J. A. H.; Osgood Jr, R. W.; Perez, K. B.; Williams, D. R. US Patent 6,787,217, 2004. [218] Nagō, S.; Nakamura, S.; Mizutani, Y. J Appl Polym Sci, 1992, 45, 1527-1535. [219] Ito, K. et al. In: Polymer Processing Symposium, Guimarães, 2002, 18th. [220] Danella Jr.; O. J.; Santana, R. M. C.; Manrich, S. J Appl Polym Sci. 2003, 88, 23462355.

An Overview of Recent Advances and Trends in Plastic Recyling

59

[221] Corrêa, A. C. M.S. thesis. University of São Carlos, São Carlos, SP, 2005 (in Portuguese). [222] Santi, C. R. M.S. thesis. University of São Carlos, São Carlos, SP, 2005 (in Portuguese). [223] Manrich, S.; Herrera, J. C.; Rosalini, A. C.; Acconci, C. BR Patent M.U. 7901580, 2005 (in Portuguese). [224] Santana, R. M. C.; Manrich, S. Prog Rubber Plast Recy Technol. 2002, 18, 99-109. [225] Kaminska, A. Kaczmarec, H. Kowalonek, J. Eur Polym J. 2002, 38, 1915-1919. [226] Rangel, E. C.; Gadioli, G. Z.; Cruz, N. C. Plasm Polym. 2004, 9, 35-48. [227] Manrich, S.; Santana, R. M. C. In: Meetings on Macromolecules. Prague, 2005, C67, 23rd. [228] Nakae, H.; Inui, R.; Hirata, Y.; Saito, H. Acta Mater. 1998, 46, 2313-2318. [229] Sasse, F.; Emig, G. Chem Eng Technol. 1998, 21, 777-789. [230] Mancini, S. D. Ph.D. thesis, University of São Carlos, São Carlos, SP, 2002 (in Portuguese). [231] Karayannidis, C. P.; Chatziavgoustis, A. P.; Achilias, D. S. Advan Polym Technol. 2002, 21, 250-259. [232] Goje, A. S.; Chauan, Y. P.; Mishra, S. Chem Eng Technol. 2004, 27, 790-799. [233] Klum, U.; Kizan, A. Polym Advan Technol. 2002, 13, 817-822. [234] Modesti, M.; Simioni, F. Polym Eng Sci. 1996, 36, 2173-2178. [235] Hayashi, F; Omoto, M.; Ozeki, M. Imai, Y. In: Advances in Plastics recycling series; Frish, K. C.; Klempner, D.; Prentice, G.; Ed.; Technomic Publishing Company: Lancaster, PA., 1999, 1, 223-240. [236] Ramsden, M.J.; Phillips, J.A. J Chem Tech Biotechnol. 1996, 67, 131-136. [237] Goto, M.; Koyamoto, H.; Kodama, A.; Hirose, T.; Nagaoka, S.; Mc Coy, B.J. AIChE Journal. 2002, 48, 136-144. [238] Williams, E.A.; Williams, P.T. J Chem Tech Biotechnol.1997, 70, 9-20. [239] Pinto, F.; Costa, P; Gulyurtlu, I; Cabrita, I. J Anal Appl Pyrol. 1999, 51, 57-71. [240] Slapack, M. J. P.; Van Kasteren, J. M. N.; Drinkenburg, B. A. A. H. Polym Advan Technol. 1999, 10, 596-602. [241] Buekens, A. G.; Huang, H. Resour Conserv Recy. 1998, 23, 163-181. [242] Masuda, T.; Kuwahara, H.; Mukai. S.R.; Hashimoto, K. Chem Eng Sci. 1999, 54, 27732779. [243] Kaminsky, W.; Kim, J. S. J Anal Appl Pyrol. 1999, 51, 57-71. [244] Williams, P. T.; Bagri, R. Int J Energy Res. 2004, 28, 31-44. [245] Kaminsky, W.; Predel, M.; Sadiki, A. Polym Degrad Stab. 2004, 85, 1045-1050. [246] Yoshioka, T.; Grause, G.; Otani, S.; Okuwaki, A. Polym Degrad Stab. 2006, 91, 10021009. [247] Masuda, T.; Kushino, T.; Matsuda, T.; Mukai, S.R.; Hashimoto, K.; Yoshida, S. Chem Eng J. 2001, 82, 173-181. [248] Maraghi, R. In: Plastics waste management; Mustafa, N.; Ed.; Marcel Dekker, Inc.: New York, 1993, 369-405. [249] Snyder, R.H. Scrap tires: disposal and reuse; Society of Automotive Engineers, Inc.: Warrendale, PA, 1998, 47-56. [250] Alexander, J. H. In: Defense of garbage; Praeger publishers: Westport, CT, 1993, 147166.

60

Sati Manrich and Amélia S. F. Santos

[251] Abu-Hijlev, B. A-K.; Mousa, M.; Al-Dwairi, R.; Al-Kumoos, M.; Al-Tarazi, S. Energy Convers Mgmt. 1998, 39, 1155-1159. [252] Holmgren, K.; Henning, D. Resour Conserv Recy. 2004, 43, 51-73. [253] Huang, C-M.; Yang, W-F.; Ma, H-W.; Song, Y-R. Waste Manage. 2006. [254] Henning, D.; Amiri, S.; Holmgren, K. Eur J Oper Res. 2006 (in press). [255] (2005). www.cgtee.gov.br (in Portuguese). [256] Holmgren, K.; Henning, D. Resour Conserv Recy. 2004, 43, 51-73. [257] Ferrão, P.; Amaral, J. Technol Forecast Social Change. 2006, 73, 277-289. [258] Correnti, A.; Bocchino, M. Filippi, S.; Magagnini, P.L.; Polacco, G.; La Mantia, F.P. J Appl Polym Sci. 2005, 96, 1716-1728. [259] Saar, S.; Stutz, M.; Thomas, V. M. Resour Conserv Recy. 2004, 41, 15-22. [260] Massura, A. C.; Souza, E. A. M.; Crochemore, G. B. BR Patent PI 0,202,303-2, 2002 (in Portuguese). [261] (2005). www.andef.gov.br (in Portuguese). [262] Lee, C-H., Chang, C-T.; Tsai, S-L. Resour Conserv Recy. 1998, 24, 121-135. [263] Machado Neto, J.G. Pesticide packages disposal. University of São Carlos: São Carlos, SP, 2004 (in Portuguese). [264] Kaminsky, W.; Hartmann, F. Angew Chem Int Ed. 2000, 39, 331-333.

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 61-92 © 2006 Nova Science Publishers, Inc.

Chapter 2

THE CONSEQUENCES OF THE USE OF PLATINUM IN NEW TECHNOLOGIES ON ITS AVAILABILITY AND ON OTHER METALS CYCLES Ayman Elshkaki1∗ and Ester van der Voet1 1

Institute of Environmental Sciences, Leiden University, Leiden, The Netherlands

ABSTRACT Recently, fuel cell vehicles (FCV) are being developed to reduce the environmental impacts related to the conventional internal combustion engine vehicles. Although on the short term the newly proposed technology might serve the intended purpose. On the long term, there may be bottlenecks in the supply of specific metals required for the technology and new emissions may replace the old ones. Fuel cell technology requires the use of platinum, which is cited as a possible bottleneck for a more widespread use of the new technologies. Moreover, an increase in platinum demand ultimately implies an increased production of the co-produced metals Cu and Ni. Consequently an increased supply may well have environmental consequences on Ni and Cu recycling system. The chapter is aimed at − −

Investigating the potential long-term impact of the increase use of platinum in fuel cell technology and other applications in terms of resource depletion Evaluating the long-term consequences of the increased demand of platinum on the cycles of other co-produced metals especially Ni and Cu

The analysis is carried out using a dynamic substance flow-stock model for platinum, nickel and copper.

∗

Corresponding author. Tel.: +31-71-5277476; fax: +31-71-5277434; E-mail address: [email protected]

62

Ayman Elshkaki and Ester van der Voet The model consists of a set of differential equation describing the change of the magnitude of the substance stock in the system compartments (production, use and waste management of platinum applications, primary production of platinum in South Africa, Russia, USA, Canada and others and secondary production of platinum) over time and several model relations. The model is implemented in Matlab/SIMULINK environment. The main driving force in the model is the global demand for platinum. The global demand for platinum is estimated based on the demand for its applications (fuel cell, catalytic converters, and the other applications) and platinum required for each application. In turn, the demand for platinum applications are modeled based on socioeconomic variables such GDP, per capita GDP, population size, material price and the cost of these applications. Platinum required for each application is modeled as a function of cumulated production using the learning curve. In addition, several other factors are important in determining the main outcome such as the applications life span, the applications collection rates and the efficiency of the production processes (primary and secondary). The main model outcomes are the amount of primary platinum required for FCVs and other applications and the consequences on platinum current reserve, platinum identified resources and the co-produced metals recycling and primary production from other ores. The model shows that the demand for primary platinum will increase dramatically with the introduction of FCVs despite the possibility of the decrease of platinum loading of FC. This is mainly due to the increased demand for vehicles. Without changes in management, the current platinum reserve would be exhausted in three decades and the identified resources in roughly 60 years. The model also shows that the demand for the co-produced materials is increasing over time. The supply of these metals from Pt ores is, combined with only a part of their current secondary production, sufficient to meet the rising demand. Consequently the primary production of these metals from other ores than those of Pt ores will not be needed. Recycling of these metals is expected to decrease.

INTRODUCTION The increase in global population and the growth in consumption per head have led to an increase in materials and energy use. This has raised the concern about the exhaustion of limited resources and the environmental impact of resources during their life cycle. Several new technologies for sustainable development in the field of energy production, nanotechnologies and ICT aim at reducing the environmental pressure by decreasing the use of (fossil) energy and materials. Some of these technologies require the use of specific metals. Among these are platinum and palladium that are required for car catalysts and fuel cells technologies, indium and germanium that are required for solar cell technologies, and bismuth and germanium, in the case of lead free electronic solder. On the short term, each of the proposed technologies may serve the intended purpose of reducing environmental impact. Combined and on the long term, however, there may be bottlenecks in the supply of the required metals and new emissions may replace the old ones. The proposed technologies might reduce the environmental impacts related to the use of resources, however, on the long term, firms might start extracting low-grade ores to meet the demand for the required materials. This will lead to the use of more energy and will produce

The Consequences of the Use of Platinum in New Technologies …

63

more waste. Another concern stems from the fact that platinum and palladium are mostly coproduced with other, more abundant metals such as copper and nickel. The link between the required metals and their "host" metals in nature may have negative impacts on the host metals cycles. An increase in the demand for Pt or Pd ultimately implies an increased production of these host metals. This may well have environmental consequences, the more so as lower prices will make extraction of the metals from wastes for recycling less attractive. The assessment of the new technologies requires the inclusion of all above-mentioned environmental impacts in terms of long term availability of resources, emissions and waste generation, energy use, and co-produced metals. This chapter treats a case in point to illustrate the importance of the abovementioned problems. The long term potential use of platinum in fuel cells is evaluated in terms of platinum resource availability and the co-produced metals supply and demand. The other aspects are mentioned briefly. Platinum is a rare metal with a concentration of 5 part per billion (ppb) (British Geological Survey, 2005) in the earth crust. Platinum can be found in nature in three different types of ores; PGE dominants ores, Ni-Cu dominant ores and miscellaneous ores (Xiao and Laplante, 2004). Recently fuel cell vehicles are being developed to reduce the environmental impacts related to the conventional internal combustion engine vehicles. Fuel cell technology, one of the main items required for these vehicles, requires the use of platinum as an important element of the electrodes of the proton exchange membrane fuel cell (PEMFC). Pt is used to promote the rate of the electrochemical reactions required for H2 to release electrons and become H2 ions. In addition to the new proposed technologies, platinum is currently used in several applications due to its chemical and physical properties. It is used in catalytic converters to reduce the emissions of hydrocarbons, carbon monoxide, nitrogen oxide, and other atmospheric pollutants from vehicle exhausts. It is widely used in industrial applications (chemical, petrochemical, glass, and electrical and electronics) due to its relative inertness and its ability to catalyze specific chemical reactions. Moreover, platinum is used in dental alloys, spark plugs, sensors, turbine blade and biomedical applications. Moreover, it is proposed that Pt might be widely used to replace gold in electronic circuits (Gediga et al., 1998). This chapter is aimed at −

−

Investigating the potential long-term impact of the worldwide increase use of platinum in fuel cell technology and other applications in terms of resources depletion Evaluating the long-term consequences of the worldwide increased demand of platinum on the cycles of other co-produced metals especially Ni and Cu

The analysis is carried out using a dynamic substance flow-stock model for platinum, nickel and copper, which is implemented in Matlab/SIMULINK environment (Math-Works, 2005). The chapter is structured as follows. Section 2 outlines the general setup of the model. Section 3 contains the results of the model calculations and a discussion of the results. Section 4 is dedicated to the conclusions.

64

Ayman Elshkaki and Ester van der Voet

GENERAL SETUP OF THE MODEL The model described in this section is a dynamic substance flow-stock model. Figure 1 shows the modeled substances (platinum, nickel and copper), the main processes in their economic systems and their flows and stocks.

Mining of Ni

Production of Ni

Production of Ni applications

Consumption of Ni applications

Recycling of Ni applications

Stock

Mining of Cu

Production of Cu

Production of Cu applications

Consumption of Cu applications

Recycling of Ni applications

Stock

consumption of Pt applications

Production of other metals (Ni, Cu, Pd, Rh)

Catalytic converters

Mining of Pt

Production of Pt

Production of Pt applications

Other applications

Recycling of different Pt applications

Fuel cells

Stock

Stock

Environment

Figure 1: The main processes in the economic system of Pt, Ni and Cu and their flows and stocks

The model includes the extraction of platinum, the production of platinum from primary resources and its main co-products, the production, consumption and waste management of platinum applications (fuel cell, catalytic converter, chemical industry, electrical and electronic industry, glass industry, investment, jewelery, petroleum industry and other applications) and the production of secondary platinum. The model also includes the production of co-produced metals (Ni and Cu) from primary resources, the consumption and waste management of Ni applications and Cu applications and the production of Ni and Cu from secondary resources. Three types of platinum ores are identified, PGE dominants ores, Ni-Cu dominant ores and miscellaneous ores depending on the geographical distribution. Platinum resources in these ores can be classified as current reserve and identified resources. Current reserve includes all platinum resources that are economic to extract at current market price using existing technology. Identified resources include economic, marginally economic and subeconomic resources.

The Consequences of the Use of Platinum in New Technologies …

65

The demand in the model is the global demand for Pt, Ni and Cu and the supply of platinum is covered by four sources (Republic of South Africa, Russia, USA and Canada, and Other countries (Zimbabwe, Finland, China, Columbia and Australia)). The model consists of a set of differential equations (Eqs. 1-6) describing the change of the magnitude of the substance stock in the system's compartments over time. The change of the magnitude of the substance stock in the use phase over time is given by Eq. 1. The inflow into the stock-in-use is determined by external factors and the outflow is determined by the inflow, the product life span, and the emissions during use. The change of the magnitude of the substance stock in the production processes of platinum applications over time is given by Eq. 2 and equal to zero. The inflow into the stock is determined by the outflow from the stock, which is determined by the inflow into the stock-in-use. The change of the magnitude of the substance stock in the collection processes of platinum applications over time is given by Eq. 3 and equal to zero. The outflow from the stock is determined by the inflow into the stock, which is determined by the outflow from the stock-in-use. The change of the magnitude of the substance stock in the recycling processes of platinum applications over time is given by Eq. 4 and equal to zero. The outflow from the stock is determined by the inflow into the stock, which is determined by the outflow from the collection processes. The change of the magnitude of the substance stock in the mining processes of platinum over time is given by Eq. 5. The outflow from the stock is determined by the required primary platinum in the market. The change of the magnitude of the substance stock in the platinum market over time is given by Eq. 6 and equal to zero. The required platinum from primary resources (required to solve Eq. 5) is determined by the outflows from the recycling processes (estimated from Eq. 4) and the inflow of platinum into the production processes of its applications (estimated from Eq. 2) Moreover, the model consists of several model relations describing the inflow of substances into the stock-in-use as function of the socio-economic variables. Some of the variables in the model relations constitute exogenous variables (GDP and population) and others are endogenous variables (price). The historical data of the exogenous variables GDP and population size are given in Ayres et. al. (Ayres et al., 2003). In the future, GDP and population size are modeled as a function of time based on the historical data and the IPCC B1 Scenario for the future development in these variables. The model also includes the environmental flows and stocks of platinum and an analysis of the energy required for the production of platinum, however these issues will not be discussed in details here.

dS x ,C ,i dt

= F in x ,C ,i (t ) − F out x ,C ,i (t )

dS x, PP,i (t ) dt

= 0 = Fxin,PP,i (t ) − Fxout , PP,i (t )

(1)

(2)

66

Ayman Elshkaki and Ester van der Voet

dSx,SC,i (t ) dt

(3)

dSx,R,i (t ) dt

dSx,m(t) dt

= 0 = Fxin,R,i (t ) − Fxout , R,i (t ) (4)

dSx,Res (t ) dt

= 0 = Fxin,SC,i (t ) − Fxout ,SC,i (t )

in in = Fxin,Res (t ) − Fxout ,Res (t ) = Fx,Res (t ) − Fx,Pr (t )

(5) out in = 0 = Fxout ,R (t) + Fx,Pr(t) − Fx,PP(t)

(6)

where x’s are the different metals (Pt, Ni, Cu), i is the metal application, C is the consumption of metal applications, PP is the production processes of metal applications, SC is the collection of the scrap of metal applications, R is the recycling of metal applications, Res is the identified resources of metals, M is the metals market, S is the stock, Fin is the inflow and Fout is the outflow.

Consumption of Platinum Applications The change of the magnitude of the stock-in-use over time is the difference between the inflow and the outflow of platinum as given by the differential equation (Eq. 1).

Inflow of Platinum into Stock-in-use The inflow of platinum into the stock-in-use is the amount of platinum used in catalytic converters, other applications and fuel cell and is modeled as given by Eq. 7. The relations between different factors determining the total inflow of platinum into the stock-in-use in the economic system are shown in figure 2.

F in Pt,C (t ) = F in Pt,FC (t ) + F in Pt,CC (t ) + F in Pt,Others(t )

(7)

where FinPt,C is the inflow of platinum into the stock-in-use, FinPt,Fc is the inflow of platinum into the stock-in-use of fuel cells, FinPt,CC is the inflow of platinum into the stock-in-use of catalytic converters and FinPt,others is the inflow of platinum into the stock-in-use of other applications.

The Consequences of the Use of Platinum in New Technologies …

67

scenarios Socio-economic variables

price

CC market share

Vehicle production

FC market share

+ + +

+

+

CC inflow

FC inflow

Pt loading

+ Pt loading

cost

-

-

+

+

+

+

Pt CC inflow

Pt others inflow Pt FC inflow

FC accumulated production

+

+ +

+ Pt total inflow

Figure 2: Total inflow of platinum into the stock-in-use model relations

The inflow of platinum into the stock-in-use of fuel cell is modeled based on the demand for vehicles, the share of fuel cell in the vehicles market and the platinum content of fuel cell as given by Eq. 8 and 9.

T  F in FC ,V (t ) = F in v (t ) • λ FC (t ) •  v  T FC   F in Pt , FC (t ) = F in FC ,V (t ) • α Pt , FC (t )

(8)

(9)

where FinFc,V is the inflow of fuel cell in vehicles, Finv is the inflow of vehicles, TV is the life span of vehicles, TFC is the life span of fuel cell, FinPt,Fc is the inflow of platinum into the stock-in-use of fuel cells, λFC is fuel cell market share and αPt,FC is the platinum content of fuel cell The demand for vehicles is modeled based on socio-economic variables as given by Eq. 10.

FVin (t ) = a + b • GDP

(10)

68

Ayman Elshkaki and Ester van der Voet

Fuel cell market share (λFC) is modeled based on different scenario using the following formula.

λ FC (t ) =

100 • e 0.1( t −t1 ) 1 + e 0.1( t −t1 ) (%)

(11)

The platinum content of fuel cell is modeled based on the learning curve concept. The learning curve (Tsuchiya & Kobayashi, 2004) is adapted for the possible reduction in platinum loading as given by Eq. 12.

α Pt , FC (t ) = A • X − r (t )

(12)

α Pt , FC (t) is the platinum loading of fuel cell at time t, A constant, X (t) cumulated production at time t The progress ratio F = 2-r

[

r = − ln F

ln 2

]

(13)

Although, the progress ratio may increase overtime for some technologies (Junginger et al., 2003), in the model the progress ratio is assumed to be constant during the simulation time. For the recycling to be possible, the amount of platinum should not be lower than 20 g/FC. Therefore, the minimum Pt content in FC is set to 20 g in the model. The inflow of platinum into the stock-in-use of catalytic converters is modeled based on the demand for vehicles as given by Eq. 10, fuel cell market share, catalytic converters market share and the platinum content of catalytic converters as given by Eq. 14, 15, 16 and 17.

   T T  F in CC ,V (t ) =  F in v (t ) −  F in FC ,V (t ) •  FC    • λCC (t ) •  v  T T v   CC      F in Pt ,CC (t ) = F in CC ,V (t ) • α Pt ,CC (t ) 



 

 e

λ CC (t ) = 100 • 1 − 

1

(t − t 0 )

α Pt ,CC (t ) = stepfuncti on

TCC

  %   

(14)

(15)

(16)

(17)

where λCC is catalytic converters market share and αPt,CC is the platinum content of catalytic converters

The Consequences of the Use of Platinum in New Technologies …

69

As given by Eq. 16, the market share of catalytic converters is increasing over time, however, the number of vehicles occupied by catalytic converters is decreasing over time due to the impact of the introduction of fuel cell as given by Eq. 14. The model assumes that at the time the vehicles are completely occupied by fuel cell (100% market share of fuel cell), the number of vehicles occupied by catalytic converters will be zero. The inflows of platinum into the stock-in-use of other applications (chemical industry, petrochemical industry, glass industry, electrical and electronics industry, jewllery, investment and others (dental alloys, spark plugs, sensors, turbine blade and biomedical applications)) are modeled based on socio-economic variables such as per capita GDP (GDP and Pop), price and time. The socio-economic variables GDP, per capita GDP, and population size constitute exogenous variables and the price is an endogenous variable.

[

]

ln FPtin,i (t ) = β 0 + ∑i =1 ln[β i X i (t )] + ε (t )

(18)

ln [P (t )] = ln [a ] + b • ln [D (t )]

(19)

n

Outflow of Platinum from Stock-in-use The outflow of platinum from the stock-in-use of its applications is the outflow due to the discarded platinum products and the outflow due to the emissions during use.

FPtout,i (t ) = FPtout,E,i (t ) + FPtout,D,i (t )

(20)

The emissions of platinum during the use phase of platinum applications are estimated as a fraction of the stock as given by Eq. 21.

FPtout, E ,i (t ) = C Pt ,i • S Pt ,i (t )

(21)

where C is the emission factor and S is the stock-in-use The discarded outflow is estimated as a delayed inflow, corrected for the leaching that has taken place during use, as given by Eq. 22 and 23:

F

out

Pt,D,i

(t ) = F

(t − L ) − ∑C LU

in

Pt,C,i

U ,i

i =1

Pt,i

⋅ F in Pt,C,i (t − LU ,i ) ⋅ (1 − CPt,i )

i−1

(22)

where FoutPt,D,i(t) is the outflow of application i due to the delay mechanism at time t and LU,i being the average life span of the product in use.

70

Ayman Elshkaki and Ester van der Voet ∞

F out Pt,D,i (t ) = ∑Wj • F in Pt,C,i (t − j ) = j =0

t

∑W

j =−∞

t− j

• F in Pt,C,i ( j ) (23)

where the lag weights w’s are the probabilities of exiting the delay in any time period j and must sum to unity ∞

∑W j =0

j

=1 (24)

The total outflow at time t, Fout then is given by Eq. 25 n

F

out Pt,D

(t) = ∑FoutPt,D,i i=1

(25)

where FoutPt,D(t) is the total outflow due to the delay mechanism at time t

Production of Platinum Applications The change of the magnitude of the stock in the production of different platinum applications over time is the difference between the inflow and the outflow as given by the differential equation (Eq. 2).

Inflow of Platinum Into Production Processes The input of platinum into the production processes of different platinum applications is equal to the output of platinum from the production processes in the products and the emissions during the production processes as given by Eq. 26.

FinPt,PP,i (t ) = F outPt,PP,i (t ) = F outPt,PP,P,i (t ) + F outPt,PP,E,i (t )

(26)

Outflow of Platinum from Production Processes The output of platinum in the products is equal to the input of platinum into the stock-inuse as given by Eq. 27 and the emissions are estimated as a fraction of the input (Eq. 28).

FoutPt,PP,P,i (t) = FinPt,C,i (t)

(27)

F out Pt,PP,E,i (t ) = βi • F in Pt,PP,i (t )

(28)

The Consequences of the Use of Platinum in New Technologies …

71

From Eqs. 27 and 28, the inflow of platinum into the production processes

F in Pt,PP,i (t ) = F in Pt,C,i (t ) + βi • F in Pt,PP,i (t ) = F

in

Pt,C,i

(t )

1 − βi

(29)

Production of Platinum Secondary Production The discarded outflow of platinum is either collected for recycling or ended up in the landfill sites and incineration plants. The collected flow for recycling is estimated as given by Eq. 30 and the landfilled and incinerated flows are estimated as given by Eq. 31.

FPtin, SC ,i (t ) = δ i • F out Pt , D ,i (t )

(30)

FPtin,inc,land,i (t ) = F outPt,D,i (t ) − FPtin,Sc,i (t )

(31)

The change of the magnitude of the stock in the collectionof different platinum applications over time is the difference between the inflow and the outflow and equal to zero as given by the differential equation (Eq. 3). Therefore, the inflow into the collection processes is equal to the outflow as given by Eq. 32.

FPtin,SC ,i (t ) = FPtout,SC ,i (t )

(32)

The change of the magnitude of the stock in the recycling processes of different platinum applications over time is the difference between the inflow and the outflow as given by the differential equation (Eq. 4). Therefore, the inflow into the collection processes is equal to the outflow as given by Eq. 33.

FPtin, R ,i (t ) = FPtout, R ,i (t )

(33)

The inflow into the recycling processes is equal to the outflow from the collection processes

FPtin, R ,i (t ) = FPtout, SC ,i (t )

(34)

The outflow from the recycling processes is the refined platinum and the losses during the recycling processes (Eq. 35).

72

Ayman Elshkaki and Ester van der Voet

FPtout,R,i (t ) = FPtout,R,ref ,i (t ) + FPtout,R,losses,i (t )

(35)

The losses during the recycling processes are estimated as a fraction of the inflow into the recycling processes (Eq. 36).

FPtout, R ,losses ,i (t ) = δ • FPtin, R ,i (t )

(36)

The outflow (refined platinum) from the recycling processes (dismantling, smelting and refining) is estimated as given by Eq. 37.

FPtout,R,ref,i (t) = FPtin,R,i (t) • (1−δ )

(37)

Total refined secondary platinum

FPtout, R , ref (t ) = ∑ i =1 FPtout, R , ref ,i (t ) n

(38)

Primary Production The required platinum from primary resources is estimated as the difference between the total demand for platinum and the possible supply of platinum from secondary resources as given by Eq. 39. The total extracted platinum from ores is estimated based on the required platinum from primary resources and the efficiency of the production processes (mining, concentration, smelting, base metal separation, and refining) of primary platinum efficiency as given by Eq. 40.

FoutPt, pr (t) = Fptin,PP(t) − FPtout,R,ref (t)

(39)

FinPt, pr(t) = FoutPt, pr(t) •(1+κ)

(40)

κ is the processes efficiency of primary platinum production The losses during the production of primary platinum are estimated as give by Eq. 41.

F lossesPt, pr (t ) = κ • FPtin,Pr (t )

(41)

The Consequences of the Use of Platinum in New Technologies …

73

Resources Issues The change of the magnitude of the stock of platinum resources over time is estimated in each country based on the required primary platinum and the possible increase of platinum resources as given by the differential equation (Eq. 5). The resources of platinum included in the model are the identified resources, which include the economic, marginally economic and sub-economic resources. The increase in the resources of platinum is assumed to be zero, therefore the change of the magnitude of the stock of platinum resources is estimated as given by 42.

dSPt,Res, A (t ) dt

= −FPtout,Res, A (t ) = −FPtin,Pr,A (t )

(42)

The supply of Pt from the main producing countries (Republic of South Africa, Russia, USA and Canada and other countries such as Finland, Zimbabwe, China, Columbia and Australia) is estimated based on an average value of the supply from these countries in the last 29 years and the total primary Pt required as given by Eq. 43.

F in Pt , pr , A (t ) = α A • FPtin, Pr (t )

(43)

A in Eqs. 42 and 43 refers to the producing countries and αA is the supply from country A.

Co-production Issues Supply of co-produced metals as a result of Pt primary demand is estimated as given by Eq. 44.

S x , A (t ) = F in Pt , pr , A (t ) • β x , A

(44)

βx,A is the concentration of specific co-produced material in the ore in specific country, x is the co-produced metals and A represents different countries The total demand for different metal applications can either be estimated based on different scenarios or based on the socio-economic variables. The total demand for metals (Finx,C,total) are estimated based on socio-economic variables using Eqs. 18 and 19. The total inflow is divided into several applications based on the life span. Each one of these applications is estimated as given by Eq. 45.

Fxin,C ,i (t ) = χ i • Fxin,C ,total (t )

(45)

74

Ayman Elshkaki and Ester van der Voet

i represents the different products categories based on the life span The change of the magnitude of the stock of the metals in the metals market over time is estimated based on the demand for the metals and the supply of these metals from primary resources and secondary resources as given by the differential equation (Eq. 6). Based on Eq. 6, the demand for the metals is equal to the supply of these metals from primary resources (from Pt ores and other ores) and the supply from secondary resources as given by Eq. 46. out out Fxin,C (t ) = Fxout , R (t ) + Fx ,Pr,Pt (t ) + Fx , Pr,other (t )

(46)

4

out x,Pr,Pt

F

(t ) = ∑ S x, A (t ) i =1

(47)

The availability of the co-produced metals from secondary resources is estimated based on the discarded metals applications, the current collection rates and the efficiency of the recycling processes. The discarded outflows of the metal applications are estimated based on their inflow and their life span as in a similar equation used for Pt applications (Eqs. 22-25). The collected streams of co-produced metals applications are estimated based on the discarded outflow and the collection rate as given by Eq. 30. The possibility of oversupply is checked by the estimates of the total demand for coproduced metals and the estimates of the supply of primary co-produced metals due to the demand for Pt. The required metals from other sources are estimated based on the difference between the total demand and the possible supply from Pt ores. The required amount of these metals from other sources (secondary sources and primary from other ores) is estimated as given by Eq. 48 and compared with the possible availability of metals from secondary resources. out in out Fxout ,Pr,other(t) + Fx,R (t) = Fx,C (t) − Fx,Pr,Pt (t)

(48)

RESULTS AND DISCUSSION Platinum Stock and Demand Inflow of Platinum into Stock-In-use The total inflow of platinum into the stock-in-use is platinum inflow into the stock-in-use of its applications (fuel cell, catalytic converter and the other applications). The inflow of platinum into the stock-in-use of fuel cell vehicles is estimated based on the demand for vehicles, market penetration of fuel cell vehicles and platinum required for each fuel cell. The demand for vehicles is modeled as a function of GDP, several scenarios are used for fuel cells market penetration and platinum required for each fuel cell is modeled

The Consequences of the Use of Platinum in New Technologies …

75

based on the learning curve concept with initial loading of 60 g and a progress ratio of 0.97. Figure 3 shows the demand for platinum for fuel cell vehicles from 1975 through 2100 based on fuel cell vehicles market penetration scenarios. These scenarios are estimated as given by Eq. 11 to give values similar to those given by the UK department for transport (UK DFT, 2003) and listed in table 1. Table 1: Scenarios used for fuel cell market penetration Scenario

Sc1 Sc2 Sc3 Sc4 Sc5

2005

2020

2030

2040

2050

2070

2090

2100

1 3.5 0 0 0

4.7 50 5 2.4 0

12 90 26 5 0

27 99 70 10 0

50 100 94 20 0

88 100 100 53 0

98 100 100 84 0

100 100 100 100 0

Figure 3: worldwide platinum inflow into the stock-in-use of fuel cell vehicles under various scenarios regarding market penetration

The amount of platinum required for each fuel cell over time is estimated as a function of the cumulated production of fuel cells based on the learning curve concept. Figure 4 shows the demand for platinum from 1975 through 2100 based on different progress ratios. Although the amount of platinum required for one fuel cell is decreasing overtime reaching almost 20 g in 2100, the demand for Pt is increasing due to the increase demand for fuel cell vehicles. As shown in figure 2, the progress ratio is an important factor in determining the platinum content of fuel cells and consequently the total demand for Pt. The inflow of platinum into the stock-in-use of catalytic converters is determined by the demand for vehicles, the market share of fuel cells, the market share of catalytic converters and the amount of platinum required for each catalytic converter as given by Eq. 14 and Eq. 15. The demand for vehicles is modeled as a function of the GDP as given by Eq. 10, the

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market share of catalytic converters is estimated based on scenario using Eq. 16 and Pt required for each catalytic converter is modeled as a step function taking the value of 2 g from 1970 through 2005, 3 g from 2006 through 2012 and from 2013 onwards taking a maximum value of 4 g.

Figure 4: worldwide platinum inflow into the stock-in-use of fuel cell vehicles under various assumption regarding progress ratios

The inflow of platinum into the stock-in-use of the other applications of platinum is modeled as a function of the GDP, platinum price and the time is used as a proxy of other determinants variables. Regression analysis is used to determine the relation between the explanatory variables and the inflow of platinum in each application. The model parameters and the goodness of the relations are shown in table 2. The analysis is carried out for the inflow from 1975 till 1990 (Johnson Mathey, 2005) . The inflows of these applications from 1975 through 2100 are shown in figure 5 and the total inflow of platinum into the stock-inuse of all applications from 1975 through 2100 is shown in figure 6. Table 2: Parameters used in modeling other applications inflows and the goodness of the relations Application Chemical industry Petrochemical industry Glass industry Electrical and electronics industry Jewllery Investment Others

a 1475.4 13881.0 7071.8 2229.8 1573.2 2888.8 1312.4

b 1.861 28.61 16.17 4.917 5.359 8.494 1.098

c -0.081 -0.054 0.029 -0.205 -0.582 -0.502 -0.01

d -201.4 -1943.6 -989.5 -312.9 -227.2 -413.43 -177.1

R2 0.8 0.45 0.64 0.68 0.57 0.19 0.84

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Although the inflow of platinum into the stock-in-use of catalytic converters and some of the other applications is decreasing over time, the total demand for platinum is increasing due to the expected increase in demand for fuel cell vehicles and some of the other applications (jewellery and investment).

Figure 5: The inflow of platinum into the stock-in-use of other applications

Figure 6: Total inflow of platinum into the stock-in-use of other applications, catalytic converters and fuel cells

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The price of platinum is estimated as a function of platinum demand based on Eq. 19. The parameters a and b of this equation are estimated using regression analysis and their values are 12.1 and 0.942 consecutively. The outcome of the model shows that the increased demand for platinum caused an increase in the price of platinum and consequently a decrease in the demand in some of the other applications.

Platinum Stock-in-use The stock of platinum related to fuel cells, catalytic converters, and the other applications in the economic system is modeled from 1975 through 2100 based on Eq. 1 and shown in figure 7. The stock-in-use of platinum in fuel cells is increasing over time. For catalytic converters, the stock-in-use is decreasing overtime due to the substitution by fuel cells reaching zero in 2100. The stock of other applications is increasing overtime, although it contributes only little to the total stock of Pt in use. The increase in the stock is mainly due to the increased demand for fuel cell vehicles and the life span of the fuel cell. Platinum Losses The losses of platinum are due to the production of platinum from primary resources, the emissions of platinum during the production and consumption of catalytic converters and the waste management of platinum applications.

Figure 7: Worldwide platinum in the stock-in-use of its applications

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Table 3a: Parameters used in the estimates of the emission factors of catalytic converters* Parameters No of cars with CC Driving distance (Km/car) Emissions (µg/Km) Pt loading in CC (g/CC) *

D 19200000 15000 0.65 3

A 1607699 14374 0.5 3

NL 3307300 13580 0.5 3

Kümmerer et al., 1999

Table 3b: Emission factors in some EU countries Country D A NL Average

Emission factor 0.00325 0.0024 0.0023 0.00264

Table 3c: Emission factors of the consumption of platinum applications Application Catalytic converter Electrical and electronic industry Petrochemical industry Glass industry Others Production of catalytic converters

Emissions 0.0023 0 0.015 0.01 1.0 0.01

The emissions during use of platinum applications are estimated as a fraction of the stock in use as given by Eq. 21. The emission factor for catalytic converters (CC) is estimated using several parameters: the number of vehicles with CC, the average driving distance per vehicle, the emission per km, and the Pt loading. The emission factor is estimated for three countries, and the average is taken in the model. The parameters used in the estimates of the emission factor are listed in table 3a (Kummerer et al., 1999) and the emission factors for the three countries (Germany, Austria and The Netherlands) are listed in table 3b. The emission factors of the consumption of platinum applications and the production of catalytic converter are listed in table 3c. The losses of platinum in the production of platinum from secondary resources are estimated as given by Eq. 36 and the losses of platinum in the primary production are estimated as given by Eq. 41. The losses factors in platinum cycle are listed in table 4a (Hageluken, 2003) and table 4b (Rade et al., 2001). The losses of platinum from 1975 through 2100 are shown in figure 8.

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Ayman Elshkaki and Ester van der Voet Table 4a: Losses during the recycling of platinum applications* Application / processes Fuel cell Total recycling Catalytic converter Dismantler Collector Decanner Refiner Chemical industry Refiner Electrical and electronic industry Collection Mechanical processes Smelter Refiner Petroleum industry Refining Refining Glass industry Refining of spent GM equipments

*

Losses % 10 50 6 3.2 3.3 6 50 20 5 1.05 1.546 2.5 1.01

Hageluken C., 2003

Table 4b: Losses during primary platinum production* Processes Mining Concentrating Smelting Refining *

Losses % 10 10 2 1

Rade et al., 2001

The emissions to the air due to the production and consumption of catalytic converter are small compared to the other losses, however, these emissions are expected to keep increasing till 2043 and decreasing afterwards. This trend is mainly due to the increase platinum content of catalytic converters and the declining market share of catalytic converters. These emissions amount to almost 503 tons in the period till the depletion of platinum resources. The losses of platinum due to the production of platinum from primary resources constitute the largest source of the losses and are increasing overtime. These losses amount to almost 11337 tons in the period till the depletion of platinum resources. The losses of platinum due to the waste management of catalytic converters are the second largest source. These losses are expected to increasing till 2047 and decreasing afterwards. These losses amount to almost 7044 tons in the period till the depletion of platinum resources. The losses of platinum due to the waste management of fuel cell are the third largest source and also

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increasing overtime. These losses amount to almost 2358 tons in the period till the depletion of platinum resources. The losses of platinum due to the other applications are decreasing overtime. These losses amount to almost 315 tons in the period till the depletion of platinum resources. The total losses of platinum is 21559 tons which is almost 43% of the total platinum identified resources

Figure 8: Losses in platinum cycle

Platinum Resources and Primary and Secondary Supply Secondary Supply The possible supply of platinum from secondary resources is estimated based on the discarded platinum applications and the efficiency of the recycling processes. The discarded platinum applications are estimated based on the past inflow and the life span of these applications. The life span of platinum applications is listed in table 5 and the losses of platinum in the recycling processes are listed in table 4. The possible secondary supply of platinum from 1975 through 2100 is shown in figure 9. Table 5: Life span of platinum applications Application Fuel cell Catalytic converter Electrical and electronics

Life span (years) 10 10 5

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Figure 9: The possible worldwide supply of platinum from secondary resources

Figure 10: Platinum required from primary resources

The production of platinum from secondary sources is increasing overtime, however it covers only part of the total demand for platinum. The demand for platinum is increasing at higher speed. The percentage of the total demand for platinum, which is covered by

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secondary sources, is increasing overtime reaching about 70% at the end of the simulation time and about 55% at the time that platinum resources are depleted. The losses of platinum during the waste management of its application amount to 20% of platinum identified resources. These losses are mainly from catalytic converters and fuel cells. For both, the efficiency of the waste management could be increased.

Primary Supply Primary platinum required is estimated as the different between the total demand for platinum and the possible supply from secondary resources. The total demand for platinum is shown in figure 6, the possible supply from secondary resources is shown in figure 9 and the required primary platinum is shown in figure 10. The required platinum from primary sources is increasing overtime. This is mainly due to the increase in platinum demand at a higher speed than the increase supply of platinum from secondary sources. Resources of Platinum At present, the required primary platinum is supplied mainly from South Africa and Russia. Small quantities are supplied from USA, Canada, and other countries. Platinum reserve (Blair, 2001) and identified resources (Vermaak, 1995) and the average supply of platinum of the last 29 years in the producing countries (Johnson Mathey, 2005) are listed in table 6. The total world identified resources of platinum as given by another reference is estimated as 47500 tons (Cawthorn, 1999) Due to the limited reserve and identified resources in the current supplying countries, in the future, the required primary platinum will be supplied mainly from other countries than those of today. The assumption in the model is that once the reserve or the identified resources of platinum is finished (i.e. the stock is reached zero) in a specific country, the model shifts the supply of platinum from this country to the other countries. Platinum current reserve and the identified resources of platinum in the producing countries are shown in figure 11 and 12. Table 6: Platinum resources and the share in the world supply from different sites Site RSA RUS USA & Canada Other Total *

Resources (t0) tones 31408 3585 2027 12287 49307

Vermaak, 1995 www. Platinum.mathey.com ‡ Brad R. Blair, 2000 †

Reserve (t0) tones‡ 9437 1417 283 3939 14538

Supply (%)† 74.95 17.85 5.3 1.9 100

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Figure 11: Platinum current reserve in RSA, RUS, CAN, USA and Other Countries

Figure 12: Platinum identified resources in RSA, RUS, CAN, USA and Other Countries

As shown in figures 11 and 12, platinum current reserve will be depleted in three decades and the identified resources will be depleted in 2064. These estimates are based on the first scenario of fuel cell market penetration, progress ratio of 97%, fuel cell life span of 10 years and the losses in the waste management of fuel cell amount to 10 % of the total discarded outflow.

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Table 7: The impact of different parameters on the platinum world identified resources Fixed Paramters Progress ratio 97% Life span 10 Recycling losses 10%

Scenario 1 Life span 10 Recycling losses 10% Scenario 1 Progress ratio 97% Recycling losses 10%

Scenario 1 Progress ratio 97% Life span 10

Scenario 1 2064

Scenario 2 2058

Scenario 3 2058

Progress ratio 97% 2064

Progress ratio 99% 2055

Progress ratio 95% 2067

Scenario 4 2071

Scenario 5 2088

Life span 10 Life span 5 2064 2059

Recycling losses 10% 2064

Recycling losses 5% 2065

Recycling losses 15% 2063

Although the platinum identified resources will be depleted in the world in 2064, a large amount of platinum will be accumulated in the economy by that time. The model outcomes in terms of resources of platinum and co-produced Ni and Cu are sensitive to several parameters. These are the platinum content of fuel cell, platinum losses during the recycling processes of fuel cell and the fuel cell life span. Table 7 shows the consequences of changing certain parameter on the depletion time of platinum identified resources. The figures in the table show that the most important factor in determining the future availability of platinum resources are the progress ratio and the life span of fuel cells. The progress ratio influences the platinum content of fuel cell, which could minimize the total demand for platinum. An increase in the progress ratio of 2 % will lead to an increase of 9 years in platinum availability. The fuel cell life span is an important factor in determining the time required for Pt to be depleted. Longer life span will make platinum available for longer time. Although the decrease in the losses of platinum during the waste management of fuel cell will lead to an increase in the secondary supply of platinum, this will cover only small part of an increasing demand. Consequently it will increase platinum availability for short time. Although based on the assumption made platinum will be exhausted in about 60 years from now, there are several possibilities for increasing the time before platinum is depleted. If the fuel cell system is introduced gradually as it is in the forth scenario and the efficiencies of fuel cell production and waste management are increased (i.e. high progress ratio (increase by 2%) and low losses (decrease by 5%)) combined with an increase in the efficiency of the waste management of catalytic converters mainly in the Dismantling process (increase by 30%), this will increase the availability of platinum by 13 years.

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Moreover, there are other places for improvement such as the losses during the primary production of platinum and the possibility of collecting platinum from soil (Ely et al., 2001).

Co-Production of Metals with Platinum The consequences of the introduction of fuel cells are not limited to the resource availability and other environmental impacts related to platinum cycle itself. It also has consequences in terms of the metals that are co-produced with platinum such as Ni and Cu. Table 8: Metals concentration in different platinum ores Metal

Nickel (Ni) (%) Copper (Cu) (%) Platinum (Pt) (ppm) Palladium (Pd) (ppm) Rhenium (Rh) (ppm) *

Merensky RSA 0.28 0.17 4.82 2.04 0.24

UG2 RSA 0.16 0.03 3.22 3.24 0.54

Norilsk RUS 3.0 4.0 2.5 7.3 0.2

Stillwater USA < 0.1 < 0.1 6.0 20.0 0.21

Sudbury Canada 1.4-1.5 1.1-1.3 0.38 0.39 0.03

Athaus et al. 2003.

The amount of metals co-produced with platinum is estimated based on Eq. 44 and the concentration of each metal in the ore in different producing countries as listed in table 8 (Athaus et al., 2003). The co-produced metals produced from platinum ores in Soth Africa is given in other sources as mining of 1 kg of Pt, yield 0.5 kg of Pd, 0.1 kg of Rh, 300 kg of Ni, and 200 kg of Cu (Pehnt, 2001). Figure 13 shows the amounts of co-produced copper and nickel from 1975 through 2100 as a result of producing platinum from primary resources, considering the ore composition in the different producing countries. The next step is comparing this supply with the worldwide demand for copper and nickel. The demand is estimated using different models for those metals. These models estimate the inflow of these metals into the stock-in-use of their applications, the outflow out of the stock through discarded products, and the amount of Cu and Ni available for recycling. The inflow into the stock, or in other words the demand, is modeled based on the socio-economic variables as given by Eqs. 18 and 19. The parameters in these equations are estimated using regression analysis. The analysis is carried out for the inflow from 1975 through 1990 The values of the parameters and strength of these relations are listed in table 9. The outflow of Cu and Ni with discarded products is estimated based on the past inflow and the life span of the metal applications. The total demand for nickel and the total demand for cupper from 1975 through 2100 are shown in figure 14a and 14b. The demand for Ni and Cu is compared by the supply of these metals from Pt ores, and the difference is estimated as the required metals from other sources (primary and secondary) from 2000 through 2100 as shown in figures 15a and 15b.

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Table 9: Parameters used in modeling Nickel and Cupper inflows and the goodness of the relations Metal Nickel (Ni) Copper (Cu)

a 834.34 1182.433

b 2.6334 3.224

Figure 13: Worldwide supply of Ni and Cu from Pt ores

Figure 14a: Worldwide inflow of Ni into the stock-in-use

c -0.03194 -0.0578

d -118.707 -166.58

R2 0.87 0.93

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Figure 14b: Worldwide inflow of Cu into the stock-in-use

Figure 15a: Ni required from other sources than those of Pt ores

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Figure 15b: Cu required from other sources than those of Pt ores

From these figures, we can see that for nickel, the supply from Pt ores is already quite high compared to the demand, at least until the moment the Pt ores are depleted. For copper, the demand is much higher, therefore the supply from Pt ores only covers a fraction. This implies that for Ni, the production from other sources including secondary sources will hardly be needed. This can have important consequences for both the mining and the recycling sector. The possible supply from secondary resources from 2000 through 2100, shown in figure 16, will not be needed until the moment the supply from Pt ores starts to decline.

Figure 16: Worldwide secondary supply of Ni

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The required Ni from other sources (primary and secondary) is compared with the possible supply from secondary resources. The results show that there is no need for Ni from primary resources for sometime after the Pt ores are depleted (i.e. secondary supply is enough to cover the demand). This means that if the primary production of Ni will continue after the pt ores are depleted, the recycling of Ni will decline.

CONCLUSION This chapter investigates the potential long-term impact of the increase use of platinum in fuel cell technology and other applications on platinum resources and evaluates the long-term consequences of the increased demand of platinum on the cycles of other co-produced metals especially Ni and Cu. The model used in the analysis is a dynamic substance flow-stock model for platinum, nickel and copper and implemented in Matlab/SIMULINK environment. The model estimates the development in platinum resources based on the global demand for platinum, the possible supply of platinum from secondary resources and the availability of platinum as identified resources in different producing countries. The model estimates the development of the demand for the metals over time based on the development in the socio-economic factors. It estimates the possible supply of the metals from secondary resources based on the past inflow, the metal applications life span and the recycling efficiency. Moreover, it estimates the losses in the metals cycles. The model shows that platinum resources will be depleted before the end of the century, however, there are a few factors may make platinum resources available for longer time. The model shows that the most important parameters on the demand side are the efficiency of fuel cell production (indicated by the progress ratio) and the speed of fuel cell market penetration. An increase in the progress ratio of 2 % will lead to an increase of 9 years in platinum availability. This implies it is important to focus on technology development in this area. The model also shows that the main platinum losses are due to the waste management of fuel cell and catalytic converters and the production of platinum from primary sources and constitute about 43% of the identified platinum resources at the time platinum resources are depleted. On the supply side, the most important parameters are the efficiency of the waste management of fuel cell, the efficiency of the waste management of catalytic converters and efficiency of the production of platinum from primary sources. Another important factor is the life span of the fuel cell. The longer the life span, the longer platinum would be available. The model shows that if the fuel cell system is introduced gradually (scenario 4) and the efficiencies of fuel cell production and waste management are increased (progress ratio increased by 2% and the losses decreased by 5%) combined with an increase in the efficiency of the waste management of catalytic converters (dismantling process efficiency increased by 30%), this will lead to an increase in the availability of platinum by 13 years.

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Although the parameters in the model are affecting the availability of platinum, this effect is limited. This is mainly due to the growing demand for platinum, which is mainly driven, by the demand for vehicles and fuel cells that are increasing as long as the GDP is increasing. Moreover, there are other places for improvement such as the losses during the primary production of platinum and the possibility of collecting platinum from soil. The model also shows that the metals co-produced with platinum will be affected by the increased production of platinum. An increase in platinum production will lead to an increase in the production of co-produced metals. For the copper cycle, this will not have major consequences. Copper demand is very high compared to the supply from this specific source. For nickel, this is different: the supply of the metals from Pt ores exceeds its demand. This will have profound consequences for both mining and recycling of nickel.

REFERENCES Althaus, H.J., Blaser, S., Classen, M. & Jungbluth, N. (2003). Life cycle inventories of metals. Final report ecoinvent 2000 No. 10. EMPA Dubendorf, Swiss Center for Life Cycle Inventories, Dubendorf. Ayres, R., Ayres, L., Rade, I. (2003). The life cycle of copper, its co-products and byproducts. Kluwer Academic Publishers, Dodrecht, The Netherlands. Blair, B. R. (2000). The role of Near-Earth asteroids in long-term platinum supply. Second Space Resources Roundtable, 8-10 Nov, 2000. Colorado School of Mines, Colorado, USA. British Geological Survey. (2005). Commodity profile – The platinum group metals. www.mineral.uk.com/britmin/PGE-23Apr04.pdf Cawthorn R.G. (1999). The platinum and palladium resources of the Bushveld Complex. South African Journal of Science 95, 481-489. Ely, J. C., Neal, C. R., Kulpa, C. F., Schneegurt, M. A., Seidler, J. A. & Jain, J. C. (2001). Implication of platinum group element accumulation along US roads from catalytic converter attrition. Environmental Science & Technology, 35, 3816-3822. Gediga, J., Beddies, H., Florin, H., Schuckert, M., Saur, K., Hoffmann, R. (1998). Life cycle engineering of a three-way-catalyst system as an approach for government consultation. In: Total Life Cycle Conference Proceedings, Publ. P-339, Warrendale, PA: Society of Automotive Engineers, 477–81. Hageluken, C. (2003). Materials flow of platinum group metals – system analysis and measures for a sustainable optimization. The 27th International Precious Metals Conference, International Precious Metals Institute, Puerto Rico. Johnson Mathey. (2005). Platinum supply and demand. Available at www.Platinum.matthey. com/market_data/1132069464.html Junginger, M., Faaij, A., & Turkenburg, W. C. (2005). Global experience curves for wind farms. Energy Policy, 33 (2), 133-150. Kümmerer, K., Helmers, E., Hubner, P., Mascart, G., Milandri, M., Reinthaler, F., & Zwakenberg, M. (1999). European hospitals as a source for platinum in the environment in comparison with other sources. The Science of the Total Environment, 225, 155-165.

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Math-Works Inc. (2005). Matlab/Simulink, 3 Apple Hill Drive, Natick, MA 017602098, USA. Available at www.mathworks.com. Pehnt, M. (2001). Life-cycle assessment of fuel cell stacks. Int. J. Hydrogen Energy, 26, 91 – 101. Rade, I.& Andersson, B.A., (2001). Platinum Group Metal Resource Constraints for FuelCells Electric Vehicles. Dept. Report 2001:01. Department of Physical Resource Theory, Chalmers University, Goteborg, Sweden. Tsuchiya, H. & Kobayashi, O. (2004). Mass production cost of PEM fuel cell by learning curve. Int. J. Hydrogen Energy, 29 (10), 985-990. UK DFT. (2003). Platinum and hydrogen for fuel cell vehicles. (UK Department For Transport). http://www.dft.gov.uk/stellent/groups/dft_roads/documents/pdf/dft_roads_ pdf_02405 6.pdf Vermaak, C.F (1995). The Platinum Group Metals. In Cawthorn, R.G. Platinum group mineralization in the Bushveld Complex- a critical reassessment of geochemical modules, S. Afr. J. Geol., 102(3), 264-271. Xiao, z., & Laplante, a.r. (2004), Characterizing and recovering the platinum group minerals – a review. Mineral Engineering, 17, 961-979.

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 93-118 © 2006 Nova Science Publishers, Inc.

Chapter 3

VEGETATION RECOVERY AFTER ENVIRONMENTAL DAMAGE BY METALLURGIC INDUSTRY IN THE ARCTIC REGION: TRANSFORMATION OF SOIL CHEMISTRY IN RESTORED LAND Ryunosuke Kikuchi1 and Tamara T. Gorbacheva2 1

Department of Basic Science and Environment; Polytechnic Institute of Coimbra, Coimbra, Portugal 2 Institute of the North Industrial Ecological Problem - Kola Science Center; Apatity, Russia

ABSTRACT Forest ecosystems are valuable both as species’ habitat and as one of the important life-support systems for the biosphere. The most severe effects of metals on forest ecosystems are from local pollution in the Subarctic regions, and the Kola Peninsula (6670°N and 28°30'-41°30'E) in Russia is one of the most seriously polluted regions: since it is close to nickel-copper smelters, the deposition of metal pollutants has severely damaged the soil and ground vegetation, resulting in an industrial desert. The methods used for restoring an industrial wasteland should have regional character; i.e. features of the ecosystem and specificity of the nutritional regime. Global production of sewage sludge is estimated at ∼30 million tons/yr, and 70% of this amount is disposed of; however, it is recognized that compost produced from sewage sludge is effective in soil conditioning. Podzol is the most common soil type on the Kola Peninsula, and this type of soil is generally nutrient-poor. Plant growth is severely limited by nutrient availability in the Arctic (or Subarctic) ecosystem. Nutrients in pools of soil organic matter show slow turnover rates, so nutrients become available to plants at a low rate. Land remediation using compost seems to be effective in such podzol forest land damaged by the metallurgical industry. Using a soil-like substratum consisting of compost produced from sewage sludge, a rehabilitation test was conducted in the abovementioned metal-polluted land (67º51’N and 34º48’E) over an area of 4 ha for the

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Ryunosuke Kikuchi and Tamara T. Gorbacheva purpose of contemplating the feasibility of combining the application of unused sewage sludge with the recovery of damaged forest land. The following items were studied: (i) chemistry of the original sewage sludge; (ii) its transformation during composting; (iii) the effect of liming on compost properties; and (iv) abiogenic and biogenic transformation of soil-like substrata in the test field for assessing whether the effect of current pollutants on local vegetation is constrained. Based on field observation during 2003-2005, the obtained data showed the redistribution of organic matter and heavy metals. This suggests that the content of heavy metals in old artificial substrata may be less than that in fresh artificial substrata. In conclusion, the test field of 4 ha is recovering from degradation of the podzol forest land.

INTRODUCTION A common geographical definition of the Arctic is the region north of the Arctic Circle (66°32’N), and this region accounts for ∼13 million km2 land [Nilsson, 1997]. About one hundred thousand species live in the boreal or polar latitude [World Resources Institute, 1987], and forest ecosystems are valuable both as species’ habitat and as one of the important life-support systems for the biosphere [Yablokov & Ostrounov, 1991]. The most severe effects of metals on forest ecosystems are from local pollution in the Arctic/Subarctic regions, and the Kola Peninsula (66-70°N and 28°30'-41°30'E) in Russia is one of the most seriously polluted regions: since it is close to nickel-copper smelters, the deposition of metal pollutants has severely damaged the soil and ground vegetation, resulting in an industrial desert [Nilsson, 1997]. Dust emissions from Russian smelters have decreased from 334 thousand tons in 1995 to 267 thousand tons in 2000 [Ekimov et al., 2001]; however, an area of 10 – 15 km around the smelters (based on [Nilsson, 1997]) on the Kola Peninsula is today dry sandy and stony ground. The Sudburry project in Canada spent C$15 million (ca. 11 million Euro) to restore the polluted area of 3,700 ha during 1978-1993 [Winterhalder, 2000]. The severely damaged areas around smelter complexes (Severonikel and Pechenganikel) may exceed ca 20,000 ha on the Kola Peninsula. Considering the Canadian project, it seems impossible to restore these areas without a great amount of financial aid. In the past, chemical pollution in soil has been treated using a number of methods, and the costs are summarized in figure 1 (based on [Semple et al., 2001; Houghton, 1996]). The cost is a thorny subject in a remediation project and the balance between the promised effect and the financial cost is often highlighted; in other words, it may be important that the remediation project is competitive in terms of cost as well as in terms of efficiency. Figure 1 shows that physical and chemical processes are expensive. In addition, thermal treatment and removal to landfill are also expensive. However, biological methods are comparatively cheap. It is only a few years since the composting strategies of bioremediation were adopted; as a result, there is a lack of general information as well as a limited number of pollutants (or pollutant matrixes) treated [Semple et al., 2001]. Originally, composting is a method for solid waste treatment. This technique biologically decomposes organic components of waste, and the result is a product (so-called compost) that can be handled, stored and applied to the land [Gerba, 1996]. That is, composting helps to recycle wastes and reduce the burden of trash disposal. As seen in figure 1, it is ecumenically advantageous to

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use a biological method, but there is doubt as to whether biological methods are promising in the face of the harsh climate of the Arctic. To make matters worse, metal-related pollution is still being imposed upon the local ecosystem. The following test was conducted in order to clear up the doubts: a substratum was made from compost which originated from municipal sewage sludge. This artificial substratum was applied to restore the polluted land. That is, an attempt was made to combine forest recovery with reuse of sewage sludge. The presented chapter reports the obtained results of the pilot-scale field test (4 ha) using the abovementioned method in the Monchegorsk metallurgical district on the Kola Peninsula during 2003-2005; this research is ongoing for the collection of long-term data.

Figure 1. Treatment costs by method in soil remediation

GENERAL ASPECTS Plant growth is strongly limited by nutrient cycle and fertilization in the Arctic ecosystem [Chapin & Shaver, 1985]. Several characteristics of the Arctic soils influence availability of nutrients to plants as well as microbial activity and mineralization. Anthropogenic emissions of metals can have obvious impacts on the local environment, but signs of environmental changes on a broader scale across a large region are subtle and more difficult to interpret. Soil characteristics (based on [Nadelhoffer et al, 1992] and metal pollution (based on [Nilsson, 1997] in the Arctic region are outlined here.

Overview of Arctic Soil Soils of the Arctic ecosystem are overlain by a layer of poorly decomposed organic matter, which increases in thickness along gradients of soil moisture. This layer (or organic horizon) contains most of the organic carbon and nutrients in the Arctic ecosystem. It inhibits drainage by decreasing hydraulic conductivity and impedes the progression of soil warming during the growing season. Cold soil temperatures and short growing seasons restrict microbial activity, litter and humus decomposition, and nutrient mineralization. Thus, the

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availability of nutrients for plant uptake is generally low relative to the growth requirements of Arctic plants. Warmer growing seasons in the Arctic will likely increase soil microbial activity and the turnover rates of soil organic matter. As a result, in the Arctic ecosystem, soil carbon stocks and the thickness of the surface organic mat are likely to decrease. Growingseason soil temperatures and thaw depths will increase because of warmer air temperatures and the lower insulation values of thinner organic mats. Amounts of mineral nutrients made available annually should increase with microbial activity and the turnover of soil carbon. Seasonal patterns of nutrient availability could also change, with more soil nutrients becoming available in midsummer. Nitrate availability will increase in many ecosystems if nitrification rates increase with ammonium availability and temperature. Increases in phosphorus availability will depend on the depths to which mineral soils thaw, on clay mineralogy, and on increases in the turnover of organic matter. The degree to which element cycling rates and plant nutrient availability will increase will vary among the different areas of the Arctic ecosystem, with the greatest and least changes occurring in moist tundra and dry tundra ecosystems, respectively. Wet tundra ecosystems also have a high potential for change, but changes in drainage patterns and soil moisture will be critical determinants in these ecosystems. Wet ecosystems that continue to receive and retain large amounts of water from upland areas will respond only slightly to warming, whereas soil microbial activity and nutrient availability could increase greatly in those that become better drained.

Nutrient Cycle The Arctic ecosystem is generally short on nutrients because nutrients in pools of soil organic matter show a slow turnover rate, so nutrients become available to plants at a low rate. Slow decomposition leads to greater accumulation of organic matter in soil and it can lower nutrient mineralization rates, thereby decreasing primary productivity [Nadelhoffer et al., 1992].

Decomposition and Temperature Temperature is the most important predictor of decomposition rates in the Arctic ecosystem. Microbial respiration in litter and soil organic matter is measurable at –7ºC and increases with temperature between 5ºC and ∼25ºC [Nadelhoffer et al., 1992]. Below 10ºC, degradation of soluble organic compounds still varies with temperature, whereas cellulose decomposition is restricted both by the low number of active cellulolytic microbes and by greater thermodynamic constraints on cellulose activities [Nadelhoffer et al., 1992].

Decomposition and Moisture Moisture is also a critical determinant of decomposition in the Arctic ecosystem. Decomposition is very slow and relatively independent of temperature when moisture content is less than 20% of dry mass [Heal et al., 1981]. Above this level, temperature sensitivity

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generally increases until moisture content reaches 200% or more, with less moisture required for optimum decomposition as temperature increases [Heal et al., 1981]. Under highly saturated conditions, decrease of decomposition probably results from the effect of poor aeration on the rates and pathways of microbial metabolism.

Decomposition and Other Factors Of course the quality (i.e. decomposability) of input litter influences decomposition rates. Furthermore, there are other edaphic factors such as cation-exchange capacity, base saturation, porosity and bulk density; however, their effects are less clear because these factors are themselves strongly influenced by organic carbon content [Heal et al., 1981; Nadelhoffer et al., 1992].

Podzol Properties Podzol (known as bleached soil, see figure 2a) is the most common soil type on the Kola Peninsula. This soil is found under a layer of organic material in the process of decomposition, and its thickness usually does not exceed 30 to 50 cm [Koptsik, 2001]. The mean characteristics of Russian podzol are summarized in figure 2b on the basis of published data [Orlov, 1993]. Each value shown in figure 2b represents the total content of each chief element, so not all of this content would be readily available to plants (i.e. bioavailability). This type of soil is generally nutrient-poor [Bridges, 1997].

Figure 2. Podzol soil: (a) photograph of soil profile on the Kola Peninsula, and (b) mean characteristics (total contents) of Russian podzol

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Metal Pollution Metals occur naturally in the environment and are present in rocks, soil, plants, and animals. Metals occur in different forms: as ions dissolved in water, as vapors, or as salts or minerals in rock, sand, and soil. They can also be bound in organic or inorganic molecules, or attached to particles in the air. Both natural and anthropogenic processes and sources emit metals into air and water. Plants and animals depend on some metals as micronutrients. However; certain forms of some metals can also be toxic, even in relatively small amounts, and therefore pose a risk to the environment. While the effects of chronic exposure to trace amounts of some metals is not well understood, a legacy incident tells us about the seriousness of high levels of exposure to some metals, especially cadmium and methyl mercury. In the 1950s, chronic cadmium poisoning from rice, coupled with dietary deficiencies, caused an epidemic of kidney damage and a painful skeletal disease, known as the Itai-itai disease, among middle-aged women in Japan. In the Arctic, sources of heavy metals include weathering of rock. As elsewhere, there is also concern that human activities, such as mining, metal processing, and burning of fossil fuels, will increase the flux of metals that can be transported by wind and water and thus become available to plants and animals. Metals are elements and therefore cannot degrade, but can only change form. Unless precautions are taken, the legacy of exploiting natural resources that contain metals is thus likely to remain in the environment for a long time. Most of the deposition studies for metals have been made in the Subarctic region, especially around the nickel-copper smelters known to emit large amounts of metals. Measurements from the Kola Peninsula show that the yearly deposition of copper and nickel can reach a few hundred mg per m2 close to the smelter stacks. However, rise levels decrease to a few mg per m2 within a few tens of km. This lower value is also representative for northern Finland. In some parts of northern Scandinavia, deposition from smelters results in levels similar to those caused in southern Scandinavia by long-range transport from Europe. Lead is an exception, with higher deposition in the south; see map immediately above. Deposition of heavy metals on the Kola Peninsula has increased, and was at least one order of magnitude higher in the 1980s than in the 1960s. Trends over the past 30 years mirror emissions, and deposition has decreased in the 1990s (also see the introduction). However, metal concentrations in soil sometimes reach exceedingly high levels near the nickel-copper smelters on the Kola Peninsula and in Norilsk.

APPROACH AND COMPOST Considering the above-mentioned points, it is necessary to improve the fertilization rate (nutrient cycle) and physical soil properties in order to restore the damaged land as soon as possible. Moreover, the smelter is currently working, and the surrounding region is still suffering from smelter-related pollution; therefore, the applied measure should be effective as a preventive against the current pollution. The following method can be considered feasible: a bulk ground is created by introducing the substratum into the polluted land to improve the nutrition status and immobilize metal pollutants (e.g. reduce phytotoxicity), and tolerant

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vegetation is then planted. It is considered that a substratum similar to the soil can contribute to restoration of the metal-polluted land. It is recognized that application of compost made from sewage sludge is effective in improving soil properties physically, chemically and biologically in agriculture and forestry [Debosz et al., 1999; Etana et al., 1999; Balesdent et al., 2000]. It can be considered that components of municipal sewage are suitable for forming a soil-like substratum. Global annual production of sludge is estimated at around 30 million tons, and 70% of that is disposed of [Nriagu & Pacyna, 1988]. The use rate of sewage sludge is very low in Russia because sewage sludge sometimes contains fair amounts of organic contaminants such as polynuclear aromatic hydrocarbons, phthalate acid esters, polychlorinated biphenyls, dioxins and alkylphenols. In addition, it may contain heavy metals such as Cd, Ni, Pb and so on [Furr et al., 1976; Smith, 1996]. Although sewage sludge contains some plant nutrients such as N, P and K, generally it also contains some degree of heavy metals. For this reason, Monchegorsk municipality does not permit the application of municipal sewage sludge to agriculture. Recently some researches have reported that heavy metals contained in sewage sludge have no negative effect on soil biomass [Chander et al., 2001; Madejon et al., 2001]; based on these researches, it is assumed that the proper application of municipal sewage sludge can contribute to a solid waste strategy as well as a soil remediation strategy. The following factors are crucial in determining how successful the application of municipal sewage sludge will be: (i) chemical properties of the original sewage sludge; (ii) composting performance; (iii) liming effect on compost quality; and (iv) abiogenic and biogenic transformation of the substratum from which the compost originated in a field close to the smelter complexes.

TEST FIELDS The Arctic is a transition zone where continuous forest gives way first to tundra with sporadic trees and finally to treeless tundra, and a common definition of the Arctic is the area north of the Arctic Circle (66°32'N) [Nilsson, 1997]. Close by the nickel-copper smelters situated in the Arctic region, the deposition of metal pollutants has severely damaged the soil and ground vegetation. This polluted land near the "Severonikel" smelter in the Monchegorsk area (67°51'N, 32°48'E) on the Kola Peninsula was proposed as the location for a remediation test of a 4 ha area. With consideration given to the conservation of existing flora, this test was conducted during 2003 to 2005, and level sites (less than a 5% slope) were selected to prevent superficial drainage. In the test region, the annual mean temperature is about -1ºC, the maximum temperature (∼15ºC) is generally recorded in July, and snowmelt takes place during April to June. In the late autumn of 2003 (before snow cover), an artificial substratum was formed in the test field. The design of the rehabilitation plots was chosen at random: it was not always the straight stripe layout that is common practice. The chosen territory was divided into 12 single plots with random distances from one to the other. More than 6,000 deciduous tree seedlings were planted in the survey fields, and then observations were conducted on each plot to estimate the chemical variance of the soil-like substratum and the elemental characteristics of the vegetation state. Comparative observation was carried out in the background plots (conifers and birch), the tolerance zone (deciduous trees) and the

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industrial desert: (i) one background site of conifers is situated 260 km to the south-west of the Severonikel smelter. Plots have been under intensive monitoring there. Without special mention, this coniferous background field is simply expressed as the background field; (ii) the other site of birch is situated 100 km to the north of the smelter; (iii) the tolerance zone situated 15-30 km around the smelter shows greater soil contamination than the background field, but deciduous trees survive in such conditions; and (iv) industrial desert - dead trees and bare ground – is situated 5 km to the southwest of the smelter.

Figure 3. Views of observation fields: (a) the field proposed for the remediation test, (b) the industrial desert, (c) plant sampling in the tolerance zone, and (d) the background site.

The above-mentioned field test for rehabilitation of forest land was performed while manufacture was continuing nearby; that is, the survey fields are now suffering from pollution emitted by the metallurgical industry and moreover this suffering may continue in the future.

MATERIALS AND METHOD Preparation of the field test involved 5 main steps: (i) making compost from sewage sludge; (ii) setting up an artificial substratum in the survey fields; (iii) afforestation; (iv) evaluation by chemical analysis of the artificial substratum; and (v) plant diagnostics based on chemical analysis of the leaves. In addition, a snow core was sampled to study how pollutants contained in the snow core influence the terrestrial ecosystem. From a practical point of view, analytical attention was given to determine the content of elements that would be available (i.e. soluble, exchangeable, mobile, etc.) for plant uptake.

Preparation of Compost Sewage sludge composting was carried out to prepare the artificial substratum. Freestanding piles (< 3m height) of sewage sludge were built on level well-aerated spots, and they were occasionally turned for the purpose of material homogenization and re-oxygenation for a period of about 1 month (July to August 2003). The resulting compost was mixed with the additives excluding dolomite (see table 1). The reason why dolomite was not mixed in at

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this stage is that composting of sewage sludge with alkaline material may have an inhibitory effect on microorganism proliferation [Wong & Lai, 1996].

Artificial Substratum Each survey field was bulldozed and big stones were removed, then the compost (15-20 cm layer) was introduced to the prepared fields at an application rate of 2,000 tons ha-1. After this, dolomite was scattered on the fields. The mixed materials were stored for ∼1.5 months (August to mid-September 2003) prior to afforestation in September 2003. The specification for substratum preparation and promising effects are summarized in table 1. Table 1. Specification of artificial substratum and main effects Material Sewage sludge deposit for composting

Planned amount 1,200 tons ha-1

Sawdust

200 tons ha-1

Sand Dolomite

600 tons ha-1 2 tons ha-1

Main promising effect Nutritional effect, microbiologic effect on organic cycle and improvement of physical soil properties such as aggregation, thermo-keeping, and water-holding capacity with adequate drainage and fertilizer retenivity [Kikuchi, 2001]. Increase of moisture and improvement of air permeability. Drainage effect on surplus moisture. pH adjustment of soil and control of leaching of heavy metals.

Afforestation The smelter is currently operating, and the surrounding region is still suffering from smelter-related pollution. The existing plants (mainly deciduous trees) have withstood such pollution in the tolerance zone. Given these facts, willow and birch were used for afforestation in the autumn of 2003 after the above-mentioned artificial substratum had been prepared. Willows and birches have been left untrimmed since 1995 in an abandoned farm situated within the tolerance zone, so seedlings of these trees were collected from the farm. Each seedling (∼1m height) was put in a polyethylene sack where the local soil encircled its root zone in order to protect against root dry during transplantation. The seedlings prepared in this way were carefully transported to the test field. As soon as the seedlings arrived in the test field, they were taken out from the sacks and were planted 4 abreast at regular intervals of 2 m in a 10 m-wide strip; in addition, grasses were laid in the gaps between the seedlings (free space) to facilitate soil aggregation.

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Sampling of Test Materials The sampling procedure in the presented test is summarized as follows, and n in brackets shows the number of measurements: (i) Sewage sludge deposit was sampled in the Monchegorsk municipal treatment facility (n = 2 in 2003). After the composting of the sewage sludge with additives (see table 1) excluding dolomite (n = 12 in 2003), the obtained compost was mixed with dolomite to produce an artificial substratum (n = 39 in 2003), and this substratum was sampled 9 months (n = 28 in 2004) and 2 years (n = 34 in 2005) after its application to the land; (ii) soil samples were taken in a background survey field (n = 40 in the birch forest in 2003), tolerance survey fields (n = 45 in 2003) and the industrial desert (n = 11 to 12 in 2003) for the purpose of comparative research; and (iii) leaves (willow and birch) were taken in the rehabilitation test field (n = 12 in September 2003, n = 6 in August 2004 and n = 34 in August 2005) and in the background field (n = 12 in September 2003). This leaf sampling was carried out at the end of the growing season in order to avoid yellow coloring and leachate-related loss of elements. Plots for snow sampling were randomly chosen in the background field of pine and spruce forests (n = 6 in 2004 and 2005) located 260 km from the smelter, the rehabilitation test field (n = 3 in 2004 and n = 6 in 2005) and the industrial desert (n = 3 in 2004 and 2005). The precipitated snow cores were sampled in a pit wall using a plastic collector (plastic tube and restricting Plexiglas plate) and plastic bags. Increments varied from 15-20 cm to whole profile height depending on snow density. Each increment was transferred from the plastic tube to a plastic bag and transported to a chemical laboratory in a frozen state. The samples were melted in a plastic basin in the laboratory, and then the volume of each sample was recorded.

Sample Analysis All soil samples were dried at room temperature and put through a sieve with a 1 mm grid. After this pre-treatment, chemical analysis was carried out as follows: (i) each element was extracted from the pre-treated sample using 1M ammonium acetate under buffer pH = 4.65 (refer to [Halonen et al., 1983]), and the following elements were determined by atomic absorption spectrometry - K, Ca, Mg, Al, Zn, Fe, Cu, Ni, Mn, Pb, Cd and Co; (ii) total nitrogen was determined by Kjeldahl digestion using H2SO4-K2SO4-CuSO4 mix; (iii) total carbon was determined by Tjurin probe digestion in sulfuric acid-K2Cr2O7 mix; (iv) phosphorous composition was also extracted by ammonium acetate under the same pH buffer and an aliquote of the extract was analyzed by molybdate colorimetry to determine the P content; (iv) 10.0 g of the sieved sample was mixed with 25.0 ml of distillated water, and then the pH value of the sample was measured by the glass electrode method; and (v) humic substances (humic acid, fulvic acid and humin) in the sample were determined by the TyurinPanomareva volumetric method using acid-alkaline treatment (refer to [Ponomareva, 1957]). These substances were treated by different extractants, and then supernatants were analyzed. The applied procedure and each abbreviation are summarized in table 2. According to procedures and extractants shown in table 2, the properties in the extracted substances are basically categorized as follows: No.1 – free humic acid, and humic and fulvic acids (abbreviated as HA and FA, respectively) bound with mobile sesquioxides such as

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Al2O3 and Fe2O3; No.1a – free fulvic acid or fulvic acid bound with mobile sesquioxides; No.2 – humic and fulvic acid bound with alkaline earth metals such as Ca and Mg; and No.3 – humic and fulvic acids bound with immobile sesquioxides and/or clay materials. Total carbon in each extracted fraction was determined by Tjurin probe digestion (see method iii) in order to express the obtained results as a percent of total carbon because the main component (ca. 50% [Kononova, 1966]) of humic substances is carbon. Furthermore, Cu and Ni (as typical metal) in each extracted fraction were determined by atomic absorption spectrometry. Table 2. Procedures and extractants for analysis of humic substances No.

1 1a 2 3 Sum

Operation & extractant

0.1N NaOH 0.1N H2SO4 Decalcination + 0.1N NaOH Heating in a warm water bath + 0.02N NaOH

Extracted organic acid Humic acid (HA) Fulvic acid (FA) HA-1 FA-1 (not soluble) FA-1a HA-2 FA-2 HA-3 FA-3

ΣHA

ΣFA

Finally, leaf samples were dried at room temperature, and they were digested with concentrated nitric acid to destroy the matrix and dissolve metals. Metals in a sample solution were determined by atomic absorption spectrometry, and phosphorous composition was determined by molybdate colorimetry. Without the above-mentioned pre-treatment and extraction, snow samples were directly analyzed after filtration through filter paper using the following techniques - potentiometry for determining H+, atomic absorption spectrophotometry for determining Al, Fe, Ca, Mg, K, Mn, Zn, Ni, Cu, Na, Pb, Cd, Co and Sr, ion chromatography for Cl-, SO42- and NO3-, colorimetry for determining P, P-PO4, NH4+ and Si, and the oxidability method using permanganate and bichromate for C determination.

RESULTS AND CONSIDERATION The total element content is generally much different from the plant-available content because the major portion of the total content is less available or unavailable to plants; for example, less than 0.01% of the total content of nitrogen generally exists as plant-available form [Woodmansee et al., 1981]. As stated above, analytical attention was given to determine the element content that would be available for plant uptake. Without special mention, the amounts of elements extracted with ammonium acetate are simply expressed as the measured contents, and their amount can be mainly considered plant-available [Witting & Neite, 1989]. Many samples were measured in each test (see section on sampling), but there is not sufficient space in this chapter to show all the obtained values; without special mention, the average values are shown as representative data. The data of measured elements are classified into 5 types for convenience and are presented in this section: (i) essential elements – N, P, K, Ca and Mg; (ii) microelements – Fe,

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Mn, Zn and Cu; (iii) other rich metals – Al and Ni; (iv) trace metals – Cd, Pb and Co; and (v) other parameters – pH (or H+) and total carbon.

Snow Precipitation and Pollution Load The chemical qualities of the precipitated snow (i.e. wet precipitation of pollutants) were measured in the background field, the rehabilitation test field and the industrial desert in order to assess the pollution load. The data obtained during September 2003 to the first week of April 2004 (abbreviated as 2004) and September 2004 to the first week of April 2005 (abbreviated as 2005) are summarized in table 3. Table 3. Pollution load resulting from snow precipitation Element (g ha-1)

P K Ca Mg Fe Mn Zn Cu Al Ni Na Si Sr Cd Pb Co Cr SO42NO3PO43ClNH4+ H+ C

Background field 2004 2005

11.74 80.61 614.27 100.29 3.21 2.45 4.51 1.25 2.36 0.44 282.37 76.88 8.40 0.20 0.05 0.20 0.20 1,087.75 1,034.69 10.00 610.75 229.97 21.06 288.37

7.69 104.58 577.85 91.29 2.29 3.35 2.43 1.14 5.78 0.40 346.47 123.91 7.14 0.02 0.12 0.02 0.15 501.79 657.43 7.58 892.98 461.11 28.24 1,662.21

Rehabilitation field 2004 2005

5.52 74.46 1,154.31 192.52 26.76 4.76 18.42 752.63 16.26 448.14 340.88 105.96 12.27 0.67 1.47 10.84 0.51 5,667.71 554.97 5.52 789.34 226.79 4.18 373.13

12.00 518.28 4,375.34 515.59 19.08 34,89 58.09 2,695.62 28.54 2,407.11 11,834.74 188.65 24.65 2.28 0.73 45.73 0.22 21,118.52 429.13 6.73 25,606.63 294.27 8.76 794.40

Industrial desert 2004 2005

11.79 131.29 1,297.29 288.42 21.13 2.38 9.24 70.30 24.26 371.44 839.69 158.57 16.67 0.24 1.33 9.15 1.08 3,009.78 1,479.39 11.79 1,861.60 324.01 23.74 1,203.45

7.41 91.24 766.24 192.14 3.41 1.83 3.42 28.85 4.67 349.29 1,066.48 86.28 7.70 0.10 0.17 7.75 0.13 2,685.55 1,138.14 7.32 2,496.88 608.21 14.05 1,356.95

P values were calculated to statistically evaluate the significant difference in content between the background field and the rehabilitation test field in 2005. According to a Michelin guide scale of the P value, elements shown in table 4 are classified as follows: no significant group (P ≥ 0.05) = Fe, Si, NO3-, PO43- and NH4+; significant group (P < 0.05) = P, Cu, Cd, Cr and C; highly significant group (P < 0.01) = K, Ca, Ni, Na, Pb, Co and Cl-; and

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extremely significant group (P < 0.001) = Mg, Mn, Zn, Al, Sr, SO42- and H+. Among the 24 measured elements, only the 5 elements Fe, Si, NO3-, PO43- and NH4+ showed no statistical difference between the background field and the rehabilitation test field. As shown in table 3, the following remarkable differences in pollution load were observed between the background field and the rehabilitation test field in 2005: (i) the precipitation amount of SO42- in the rehabilitation test field was over 42 times greater than that in the background field; (ii) the Pb amount in the rehabilitation test field was 42 times greater than that in the background field; (iii) the Co amount in the rehabilitation test field was 2,285 times greater than that in the background field; (iv) the Cu amount in the rehabilitation test field was over 2,360 times greater than that in the background field; (v) the Ni amount in the rehabilitation test field was over 6,018 times greater than that in the background field; and (vi) the Cd amount in the rehabilitation test field was over 114 times greater than that in the background field. From these great amounts, it is evident that the main factor of environmental degradation (i.e. defoliation) around the nickel-copper smelter complexes is heavy-metal pollution, and the pollution load is still being imposed on the surrounding vegetation. In addition, it is possible to consider that the pollution source is not only the metallurgical industry but also urban activities. In 2004 and 2005, the H+ contents in the rehabilitation test field and the industrial desert were comparatively lower than those in the background field. It can be considered that local coal-combustion facilities such as house boilers, power stations and so on discharged dust (e.g. Ca) to the atmosphere in the winter and their alkalization effect buffered the H+ content. The contents of Na+ and Cl- in the rehabilitation test field were about 10 times greater than those in the industrial desert. As the rehabilitation test field is located near a road (see figure 3a), it is reasonable to consider the effects of traffic; anti-freezing agents were used in the snowy and/or icy road surface during winter, so there is a possibility that the saline contents of these agents may have increased Na+ and Cl- in the rehabilitation test field.

Soil Properties in Background Field, Tolerance Zone and Industrial Desert The long-term pollution load (over several decades) must have changed the soil properties of the land when pollutants were precipitated and stored in the soil. It can be considered that (i) the background field suffers less from phytotoxicity, (ii) the industrial desert is characterized by high contents of heavy metals and a deficiency of plant-available nutritional elements, and (iii) the tolerance zone allows deciduous tress to survive in spite of metal contamination. According to the data obtained in the field observation, there is no clear difference in pH value among the observed fields; 4.4 in the background field and the tolerance zone and a slightly higher value (5.5) in the industrial desert. There is also no clear difference in humic substances between the background field and the industrial desert; ∼25% C in the total fraction of humic acid (ΣHA, see table 2) and ∼25% C in the total fraction of fulvic acid (ΣFA, see also table 2). Therefore, the humification state in the background field must be similar to that in the industrial desert. Based on the measured soil properties, other parameters in the three fields are compared in figure 4. Figure 4 shows some remarkable points as follows: (i) the contents of nutritional elements such as P, K, Ca and Mg in the industrial desert are much less than those in the

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background field and the tolerance zone; (ii) the content of Al (449.1 mg kg-1) and Pb (8.3 mg kg-1) in the industrial desert is about 1.2 times greater than that in the background field and the tolerance zone; and (iii) the Cu content of 612.9 mg kg-1 in the industrial desert is over 190 times greater than that in the background field and about 24 times greater than that in the tolerance zone. Cu is generally accumulated in plant roots, so an excess amount of Cu damages the root system [Chino & Obata, 1988]. Although the toxicity level of each metal varies according to species and environmental conditions, it is possible to consider the defoliation must have been caused by multiple adverse effects of soil contamination by the above-mentioned metals on the plants. It can be concluded that the deforestation (see figure 3) resulted from unbalanced nutritional elements and an increase of metal pollution.

Figure 4. Comparison of soil properties in the background field (birch forest), the tolerance zone and the industrial desert

Characteristics of Sewage Sludge and Compost Composting is an aerobic process that relies on the actions of microorganisms to degrade organic materials, resulting in thermogenesis and production of organic and inorganic compounds. Some phenomena take place during this process; mass loss due to biodegradation of organic matter, humification (formation of humic acid and fulvic acid), formation of organo-metal complexes, dilution effect of co-composting materials (see table 1), etc. These phenomena affect the speciation of elements in compost. Table 4 summarizes the chemical properties of the sewage sludge (raw material for composting) and the obtained compost (non-liming, i.e. without dolomite). The acidity or alkalinity of soil affects nutrient availability, nitrogen fixation, decomposition of organic matter by soil organisms and function of the plant root [Bellows, 2001]. The pH value decreased from 6.7 to 5.7 during composting. It is considered that the carboxylic acidity increases a bit and slightly changes the pH value [Miikki et al., 1997]. The slight decrease in pH seems not to be problematic because most nutrients are generally most available for plant uptake at soil pH of 5.5 to 6.5 [Bellows, 2001].

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Living organisms are made of large numbers of C combined with small numbers of N, so the balance of these two elements (so-called C/N ratio) is important. Bacteria can work on organic material quickly at C/N ratios ranging from 10 to 30 [Fujita, 1995]. The ratio of 11.9 is calculated from the total contents of N and C in the sewage sludge, and this value is within the above-mentioned range. Table 4. Chemical properties of sewage sludge and compost Parameter

S. sludge (a) Compost Limit (b) Parameter S. sludge (a) Compost Limit b) Parameter (c) S. sludge (a)

pH

Total C

Total N

P

K

Ca

Mg

Fe

6.7 5.7 n.d. Mn mg kg-1 299 20 n.d.

% 30.8 2.8 n.d. Zn mg kg-1 234.9 9.1 7.5

mg kg-1 25,980 1,453 n.d. Cu mg kg-1 53.8 272.6 4.3

mg kg-1 631 41.2 n.d. Ni mg kg-1 146.6 35.5 0.4

mg kg-1 462 41 n.d. Al mg kg-1 78.1 504.8 n.d.

mg kg-1 14,451 496 n.d. Cd mg kg-1 1.20 0.07 0.09

mg kg-1 381 61 n.d. Pb mg kg-1 9.07 7.42 0.84

mg kg-1 677 114 n.d. Co mg kg-1 2.75 0.95 n.d.

FA-2 C% 0.0

FA-3 C% 3.6

HA-1 C% 5.3

HA-2 C% 3.2

HA-3 C% 10.1

FA-1a C% 1.7

FA-1 C% 9.6

Parameter(c)

Σ HA C%

Σ FA C%

Σ (HA + FA) C%

HA/FA

Residue

S. sludge (a)

25.5

23.6

49.1

1.1

66.4

C%

(a) sewage sludge for composting material; (b) limit value of element contained in sludge for land application [U.S. Environment Protection Agency, 1993]; (c) see table 2; and n.d. = no data

Table 4 shows a decrease in the contents of the measured elements except for Cu and Al. It can be considered that the main factor leading to the general decrease in elements is the above-mentioned dilution effect, and the increases in Cu and Al would originate in the transfer of these elements from the applied co-composting materials to the obtained compost. Other factors could also play a part: the formation of organo-metal complexes would decrease the plant-available contents of Ca and Zn, and phosphate formation would decrease the plantavailable content of P. These organo-metal complexes and phosphate have poor solubility in ammonium acetate, so the measured contents are low; ammonium is produced during composting [Bertoldi, et al., 1981], and then its volatilization would decrease the N content. As compared with EPA standards [U.S. Environment Protection Agency, 1993], the Cd content of the compost did not exceed the limit value, the Zn content was similar (∼9.0 mg kg-1) to the limit value, and the contents of Ni, Pb and Cu were greater than the limit values. As compared with the contents measured in the tolerance zone (see figure 4), the Ni content of the compost did not exceed that in the tolerance zone, the Pb content was similar (∼7.0 mg kg-1) to that in the tolerance zone, and the Cu content of the compost was over 10 times greater than that in the tolerance zone. It is necessary to study the distribution pattern of Cu in detail, so this subject is discussed later.

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Plant nutrients (e.g. N and phosphorus) are chemically bound to carbon in organic materials [Bellows, 2001]. For these nutrients to become available for plant uptake, soil organisms need to break down the chemical bonds (so-called mineralization). If the carbon amount is high, more bonds will need to be broken and nutrient release will be slow. During composting, the total C content decreased considerably from 30.8 mg kg-1 in the sewage sludge to 2.8 mg kg-1 in the compost. This decrease indicates that the contained nutrients became more plant-available. Nitrogen can be easily lost from the soil system through physical processes such as leaching, runoff and erosion; the chemical process of volatilization; and the biological process of denitrification. Therefore, nitrogen is often the limiting factor in plant growth and crop production [Bellows, 2001]. The obtained compost had a richer amount of N than that in Russian podzol (see figure 2a). It was expected that the compost application would enhance fixation and conservation of nitrogen. The K content in the compost was about one-twentieth of that in the tolerance zone (see figure 4). It is reported that it takes a long time to fully transform the K contained in organic waste to plant-available form because of the high capacity of the compost matrix for K fixation [Hernandez, et al., 1991; Villar et al., 1993]. However, it is not advisable to assume K deficiency because a great amount of K (∼520 g ha-1) precipitated and its amount statistically (P < 0.01) increased in the remediation test field (see table 3). It is advisable to observe the content variation of K over a long period. The P content in the compost was also low and about one-half of that in the tolerance zone, so it is important to assess whether P deficiency occurs in the plants. This subject is discussed later on the basis of leaf analysis. Humification is the process by which organic matter decomposes to form humus (complex organic polymers). During this process, all cellular makeup undergoes a pattern of transformations, modifications, and structural re-arrangements, resulting in polymeric humic substances [Jackson, 1993]. These substances include fulvic acids (soluble in water at any pH value), humic acids (soluble in water at high pH value), the salts of both fulvic and humic acids, and humin (insoluble in water at any pH value). They mainly perform the following functions in soil: (i) absorption of minerals and transformation of mineral materials into forms that can be taken up by plants as nutrients; (ii) adsorption of organic compounds and formation of organo-metal complexes by chelation - this function is effective in cleanup of toxic materials in the soil; (iii) buffer capacity helping to stabilize the soil’s pH; (iv) water holding capacity; and (v) darkening the soil color which increases the soil’s adsorption of solar energy. As stated above, humus plays an important role in soil remediation. The obtained results of humus analysis show that the applied sewage sludge is characterized by insoluble residue (∼70%), type HA-3 of humic acid and type FA-1 of fulvic acid (see table 2). In spite of the rich amount of Ca in the sewage sludge (14,451 mg kg-1, see table 4), this major property of humus (HA-3 and FA-1) indicates that organo-metal complexes mainly contain mobile and immobile sesquioxides (e.g. Al2O3). Fulvic acids become humic acids with more polymerization, and humic acids become humin with even more polymerization [Jackson, 1993]; therefore, the percentage of the humus which occurs in the various humic fractions generally varies from one soil type to another. The ratio of humic acid to fulvic acid (HA/FA) was measured in the background field as a reference. The ratio of HA/FA (1.3) in the sewage sludge was similar to that (1.0) in the background field. It is considered that the degree of humification in the sewage sludge was slightly greater than that in the background field.

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Transformation of Artificial Substratum during 2003-2005 As stated, sampling was carried out three times in the soil-like substratum made by cocomposting: September 2003 - the first sampling of the artificial substratum directly after liming and its application to the test field; May 2004 - the second sampling after the substratum had been left in the field for 9 months (September 2003 to May 2004); and September 2005 – the third sampling after the substratum had been left in the field for 24 months (September 2003 to September 2005). It is necessary to interpret the obtained data with consideration given to the connection between the sampling conditions and the climatic conditions in the field. According to the climatic record for 2002 in Monchegorsk, monthly mean soil temperatures show the following pattern: -13.5ºC in January, -13.8ºC in February, 11.5ºC in March, -4.5ºC in April, 7.5ºC in May, 15.4ºC in June, 18.8ºC in July, 13.4ºC in August, 6.8ºC in September, -2.9ºC in October, -14.9ºC in November and -17.2ºC in December. Temperature is the most important predictor of soil decomposition in the Arctic ecosystem [Heal et al., 1981]; as stated above (see section on decomposition and temperature), microbial respiration in soil organic matter increases with temperature between 5ºC and ca. 25ºC [Nadelhoffer et al., 1992]. It can therefore be contemplated that microbial activities were strictly restricted in the artificial substratum at freezing temperatures. It is reasonable to consider that the 2003 data on the artificial substratum represent its primary properties, the 2004 data mainly represent abiogenic transformation and the 2005 data represent abiogenic plus biogenic transformation. The pH value slightly changed: 6.0 in 2003 (after liming), 6.4 in 2004 and 5.4 in 2005. Although there is a statistical difference in pH value between 2004 and 2005 (p<0.001), these values are almost within the pH range where most nutrients are generally most available for plant uptake (soil pH of 5.5 to 6.5 based on [Bellows, 2001]). There was no clear difference in total C content, and the content slightly increased: 2.3% in 2003, 2.4% in 2004 and 2.9% in 2005. The analytical results in both 2003 and 2004 showed very small amounts of Co, Pb and Cd: 0.99 mg kg-1 Co, 6.05 mg kg-1 Pb and 0.06 mg kg-1 Cd in 2003; and 1.52 mg kg-1 Co, 6.44 mg kg-1 Pb and 0.14 mg kg-1 Cd in 2004. As all the measured values were obviously less than those in the background field of birch forest (2.27 mg kg-1 Co, 6.68 mg kg-1 Pb and 0.52 mg kg-1 Cd , refer to figure 4), these elements were not measured in 2005. Figure 5 summarizes the analytical results of the other components including humus substances. It should be emphasized that the test field was suffering from metal pollution during the observation (see table 3) and this suffering may continue in the future. It is necessary to consider this adverse effect on the artificial substratum. Comparing the plant-available contents in 2003 with those in 2004 (figure 5), the following remarkable points are noted and they mainly seem to be connected with the abiogenic transformation of the artificial substratum: (i) the Ca content more than doubled and consequently approximated ∼2100 mg kg-1 Ca contained in the tolerance zone (see figure 4). It is considered that Ca was transferred from co-composting materials (dolomite in particular) to the substratum and became bioavailable; (ii) the Mg content doubled in 2004, and the reason seems to be the same as that for Ca (e.g. originating in the co-composting materials). In spite of the remarkable increase, the Mg value (224 mg kg-1) was one-third of that in the tolerance zone (see figure 4). There may be a possibility of Mg deficiency; (iii) the distribution of humic substances in 2003 (HA/FA = 1.6) was different from that in 2004 (HA/FA = 2.1). The following hypothesis can be framed to explain the change in the HA/FA ratio: both HA and FA are polymeric, and the

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making of these polymers is partly the result of enzymes from soil microorganisms and partly that of soil chemistry [Jackson, 1993]. It can therefore be considered that soil chemistry dominantly contributed to changing the ratio. FA is soluble in water, so it is possible for it to be lost due to leaching. The losses of humin (a main component of residue) and HA due to soil respiration are also considered [Schlesinger, 1997]. As there are reversible reactions between humin and HA in belowground processes [Schlesinger, 1997], they may have changed the mass balance between HA and the residue.

Figure 5. Chemical properties of artificial substratum made by co-composting during 2003-2005

The third sampling in 2005 was carried out after the artificial substratum had passed the 2003 winter (limiting microbial activity), the 2004 summer (high microbial activity) and the 2004 winter (limiting microbial activity), so the characteristic change in the sample is connected with abiogenic plus biogenic transformation. Based on the P value (P < 0.02), the contents of P, K and Ma in 2005 were statistically different from those in 2004. The P content increased from 39.5 mg kg-1 in 2003 to 52.5 mg kg-1 in 2004. In contrast, it decreased to 17.7 mg kg-1 during 2004 to 2005. The plant-availability of P depends upon distribution of each P form between the hydrophilic fraction and hydrophobic fraction: the first mainly contains orthophosphate, organic monoester P and pyrophosphate; and the second mainly contains organic diester P [Gigliotti et al., 2002]. It is reported that seasonal variations in P availability are high in Arctic soils [Dowding, et al., 1981]. As with mineral N, pools of soluble and exchangeable phosphate are greatest at snowmelt, and these pools decline as soil temperature increases through the growing season. The second sampling was carried out in the spring of 2004, and the third was carried out in the autumn of 2005; for these reasons (distribution pattern and seasonal dependence), it is possible to interpret the difference in P content between 2004 and 2005. The K content has a tendency toward deficiency. The content of K (37.3 mg kg-1) in 2005 was about one-half of that (66.8 mg kg-1) in 2004. It is reported that K addition has been a common practice in production of compost from sewage sludge because of low K content [Gmez et al., 1992; Gadallah, 1994]. It is important to make up the deficiencies of P and K in future steps, so it is advisable to plan the amount and time of

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supplement fertilization on the basis of leaf analysis. The Mn content continued to decrease from 21.3 mg kg-1 to 14.3 mg kg-1 in the test field over 2003 to 2005, and its content was onetenth of that in the tolerance zone (see figures 4 and 5). Leaves suffer chlorosis over practically the whole tree in the case of Mn deficiency [Chino & Obata, 1988]. The diagnosis of specific deficiencies based on changes in the appearance of the leaves has played an important part in determining plant health: it is therefore advisable to assess whether Mn deficiency has occurred in the test field on the basis of leaf diagnosis. The contents of Al and Fe varied during 2003 to 2005 and their contents were comparatively great. It is known that mobile forms of aluminum negatively affect development of the root system and microbiological activity. However, the above-mentioned variations were statically insignificant. Thus, Al and Fe control should be recognized as a desirable factor rather than an obligatory factor.

Distributions of Ni and Cu in Humic Substances The Ni precipitation considerably increased over 2004 to 2005 in the test field (see table 3), and the Cu content in the artificial substratum was about 10 times greater than that in the tolerance zone (see figures 4 and 5). These metals may have an adverse effect on plants because free metal cations are incompatible with plant cells. It is well-known that humic substances form organo-metal complexes (i.e. chelates). Chelation of metallic elements reduces their toxicity as cations. When toxic heavy metals are chelated, these organo-metal complexes become less available for plant uptake. The contents of Ni and Cu fluctuated in the artificial substratum over 2003 to 2005 (see figure 5), so it suggests the relation between the varied contents and organo-metal complexes. The following parameters were measured to evaluate the state of organo-metal complexes in the field: the distributions of Ni and Cu in humic acid (HA), fulvic acid (FA) and plant-available form. According to the classification of organic acids shown in table 2, the obtained results are summarized in figure 6.

Figure 6. Distributions of Cu and Ni in humic acid, fulvic acid and bioavailable forms.

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In 1991, it was reported that Cu in FA fractions is predominant over that in HA fractions in compost made from municipal waste [Hofstede & Ho, 1991]; however, in 1995, it was reported that more Cu is recovered in HA fractions than in FA fractions in compost made from municipal waste [He et al., 1995]. It follows from figure 6 that both Cu and Ni are recovered in greater amounts in FA fractions (FA-1a and FA-2 in particular) than in HA fractions in the extracts of the artificial substratum made from municipal sludge waste. The results of metal distribution by fraction may be inconsistent because there are a number of influential factors – compost source, composting conditions, extracting regents, etc. They may be responsible for the difference in metal distribution. It is important that the contents of Ni and Cu in fractions of organic acids were about 2 times greater than those in bioavailable forms, and both Ni and Cu showed their selective preference for FA fractions rather than HA fractions in 2003 and 2004 (the period of abiogenic transformation). FA fractions are soluble in water under all pH conditions, so Ca and Ni distributed in FA fractions are more mobile than those in HA fractions. There were statistically no quantitative differences in bioavailable Ni and Cu between 2004 and 2005, but these metals’ distributions statistically (P < 0.001) increased in HA fractions over 2004 to 2005 (the period of biogenic plus abiogenic transformation). HA fractions are not soluble in water under acidic conditions but are soluble at relatively high pH values. To put it differently, this change in metal distribution reduced the mobile amounts of Ni and Cu. Reviewing the procedure of sequential extraction [Shrivastava & Banerjee, 2004], distribution patterns of selected metals are summarized in table 5 Table 5. Distribution patterns of selected metals Element

Cu Zn Pb Ni Cr Cd

Low degree

<

Distribution pattern <

<

High degree

Exchangeable Exchangeable Exchangeable Exchangeable Exchangeable Exchangeable

Reducible Oxidizable Acid-soluble Acid-soluble Reducible Oxidizable

Oxidizable Acid-soluble Oxidizable Reducible Acid-soluble Reducible

Acid-soluble Reducible Reducible Oxidizable Oxidizable Acid-soluble

Residual Residual Residual Residual Residual Residual

Based on distribution patterns shown in table 5 and figure 6, it can be considered that heavy metals should be less plant-available in the test field. However, it is of course necessary to continue monitoring the plant-available trends in heavy metals as long as they continue to disperse in the environment.

Diagnosis of Elements in Plants Diagnosis of element effects (deficiency and toxicity) in plants plays an important role in determining plant health. Based on the results of leaf analysis, it is advisable to assess whether supplement fertilization and/or more strict control of metals are necessary. Changes in elements in the sampled leaves of the test field are shown in table 6 compared with leaf properties in the background zone (sampling in 2003).

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As stated in the section on afforestation, the existing plants such as willow and birch have withstood metal pollution in the tolerance zone. The contents of P (17.7 mg kg-1 in 2005) and K (37.3 mg kg-1 in 2005) in the soil of the artificial substratum were considerably less than those (159.9 mg kg-1 P and 1,230 mg kg-1 K) in the background field (see figures 4 and 5). The 2005 data in table 6 show that the P contents in both willow leaves and birch leaves in the test field were about 30% less than those in the background field; on the other hand, the K contents of both leaves in the test field were greater than those in the background field. The Mn content (2005) of willow leaves in the test field was one-fifth of that (2003) in the background field and the Mn content (2005) of birch leaves in the test field was one-third of that (2005) in the background field. The Mn contents in both leaves increased during 2004 to 2005 and this increase was statistically significant (P < 0.05) in the case of birch. As the bioavailable Mn content decreases with an increase in the pH value [Sims & Kline, 1991], it is considered that the effect of compost liming caused a fluctuation in the Mn contents. From the above-mentioned points, the deficiencies of P, K and Mn cannot be obviously concluded on the basis of the data from 2003 to 2005; however, it is of course necessary to observe these elements over a long period. Attention should be paid to excess amounts of elements rather than deficiencies because microelements are required in very small amounts (e.g. a few mg kg-1) in plant tissue, being one or more orders of magnitude lower than for essential elements [Food & Fertilizer Technology Center, 2001]. Except for essential elements, willow and birch leaves in the test field generally contained much greater amounts of metals than those in the background field (see table 6). That is to say, these plants can survive even if the test field is suffering from metal pollution. During 2004 to 2005, metal contents (Mg, Fe, Zn, Ni, Cu, Pd and Co) statistically increased in willow leaves while their contents in birch leaves were comparatively stable. Table 6. Leaf elements (willow and birch) in the test field and the background field Element (mg kg-1)

BG

Willow leaf 2003 2004

P 2856.4 1680.2 2133.8 K 7635.2 10370.9 7458.6 Ca 10726.6 11965.7 14126.8 Mg 2034.3 4154.4 4713.3 Cu 2.3 18.9 590.7 Zn 161.3 238.3 121.4 Mn 845.3 1263.8 165.7 Fe 53.7 136.8 325.3 Ni 3.9 51.5 810.9 Al 44.2 69.1 219.0 Co 2.3 2.2 23.1 Pb 0.1 0.2 10.2 Cd 0.5 1.7 1.4 S 3249.0 BG = background field (sampling in 2003).

2005

BG

1909.2 9030.2 17235.6 3628.8 338.3 180.4 172.9 230.0 457.2 169.7 14.8 4.4 1.5 3247.0

2467.7 6215.2 8549.3 2465.2 5.0 180.5 2555.9 70.5 4.5 29.8 0.7 0.2 0.2 -

Birch leaf 2003 2004

2481.7 7348.0 7807.0 4507.0 18.5 126.0 1330.2 122.6 47.7 60.3 1.5 0.5 0.2 -

2301.0 7671.9 9595.0 3323.8 254.1 176.6 467.8 148.2 316.9 84.9 8.7 5.9 0.5 3535.7

2005

1858.3 7082.0 8569.7 3416.2 209.4 144.6 918.1 177.9 267.4 106.8 8.7 3.8 0.2 2610.0

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Leaf diagnosis based on elemental analysis shows a favorable trend in the rehabilitation test and indicates the possibility of phytoremediation using willow and birch in harsh Arctic (or Subarctic) regions. Phytoremediation is the use of plants to remove pollutants from the soil or render them harmless. In other words, this technique uses plants to vacuum heavy metals from the soil through their roots. While acting as vacuum cleaners, the plants must tolerate and survive high levels of heavy metals in the soil – such as Zn, Pd, Ni, etc. For essential elements, the safety margin beyond which plants are deemed to be consuming the elements in excess is fairly big, but for non-essential elements, the margin is generally very narrow: therefore, heavy metal availability sometimes induces ion stress. However, certain plants - known as metal hyperaccumulatos – have the ability to extract elements from the soil and concentrate them in plant stems, shoots and leaves that are later harvested. These plants' tissues can be collected, reduced in volume and stored for later use [Agriculture Research Service, 2000]. According to table 6, the Ni content (457.2 mg kg-1 in 2005) and the Cu content (338.3 mg kg-1 in 2005) of willow leaves in the test field were 117 times and 147 times greater, respectively, than those in the background field. These data suggest that Ni, Cu and the other metals can be removed from metal-contaminated land by harvesting the plants. However, more detailed research is necessary to assess whether metal superaccumulation has really taken place in the test field because there are basically two types of metal loading: (i) metals merely adhered to leaf surfaces (deposition of metal particles) and (ii) metals contained within plant tissues through air-foliar pathways and soil-root pathways (metal absorption). To put it differently, it is important to correctly determine a plant's concentration of each metal group – types (i) and (ii) – in order to evaluate the degree of metal accumulation in willow and birch. This is a subject for future study.

CONCLUSION The Arctic is characterized by a harsh climate and poor-nutrient soil; what makes it even harsher is that metal pollution is currently being imposed upon the test fields. Using an artificial substratum made from sewage sludge, a pilot-scale (4 ha) test was carried out to restore metal-contaminated forest land affected by such conditions. The artificial substratum was subjected to abiogenic and biogenic transformation during 2003 to 2005, and this transformation will continue in the future in the face of ongoing pollution. As seen in figure 7, the lost vegetation is being restored by the formation of an artificial substratum made from sewage sludge compost. Essentially, sewage sludge is a solid waste; however, the obtained data imply that sewage sludge is a helpful raw material for land remediation even where there is a harsh climate, poor-nutrient soil and metal-pollution load. The test results presented in this chapter seem to be a good example of how to combine natural conservation (remediation/maintenance of forest land) with recycling of resources (sewage sludge). Furthermore, leaf analysis suggests that heavy metal treatment by phytoremediation may be feasible in the Arctic. The General Assembly of United Nations accepted the World Charter of Nature on 28 October 1982. According to this charter, populations of all forms of life must be maintained at levels sufficient for their survival, and biological resources may be exploited only within the framework of their survival potential. It may be concluded that the presented field test applied the survival potential of local species

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(composting microorganisms and resistant vegetation such as willow and birch) wherever possible. This conclusion suggests that it is important to consider how to effectively apply the potential of a local ecosystem in an environmental project.

Figure 7. Remediation progress of metal-polluted forest land: test field (a) before remediation, (b) in the middle of the project, (c) during abiogenic transformation (the winter of 2003) and (d) after remediation.

ACKNOWLEDGEMENTS This research project is supported by Monchegorsk Forestry Enterprise and Severonikel Company, and organized by the Institute of the North Industrial Ecology Problem – Russian Academy of Science. Funding is provided by RFFI grant No. 03-04-48628. The authors are grateful to Ms C. Lentfer for English review.

REFERENCES Agriculture Research Service (2000). Phytoremediation: using plants to clean up soils. Agriculture Research magazine, 48 (6), 4-9. Balesdent, J., Chenu, C. & Balabane, M., (2000). Relationship of soil organic matter dynamic to physical protection and tillage. Soil Tillage Research, 52, 215– 230. Beertoldi, M., Villini, G., & Pera, A. (1981). The biology of composting – a review. Waste Management and Research, 1, 157-230. Bellows, B. (2001). Nutrient cycling in pastures. Fayetteville, AR: National Center for Appropriate Technology. Bridges E. M. (1997). World Soils (3rd edition). Cambridge, UK: Cambridge University Press. Chander, K., Dyckmans, J., Joergensen, R. G., Meyer, B. & Raubuch, M. (2001). Different sources of heavy metals and their long-term effects on soil microbial properties. Biology and Fertility of Soils, 34, 241–247. Chapin, F. S. & Shaver, G. R. (1985). Individualistic growth response of tundra plant species to environmental manipulations in the field. Ecology, 66, 564-576.

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Chino, M. & Obata, H. (1988). Heavy metals and plants. In: M. Chino & H. Saito, (eds.), Heavy metals and life (pp. 81-143). Tokyo, Japan: Hakuyusha Co., Ltd. Debosz, K., Rasmussen, P. H. & Pedersen, A. R. (1999). Temporary variations in microbial biomass C and cellulolytic enzyme activity in arable soils: effects of organic matter input. Apply Soil Ecology, 13, 209– 218. Dowding, P., Chapin, F. S., Wielgolaski, F. E. & Kilfeather, P. (1981). Nutrients in tundra ecosystems. In: L. Bliss, O. Heal & J. Moore (eds.), Tundra Ecosystems – a comparative analysis (pp. 647-683). Cambridge, UK: Cambridge University Press. Ekimov, S. V., Samodova, I. V., Petrov, I. M., Troitsky, V. & Burstein M. A. (2001). Russian smelter emissions. Mining Journal, Nov. 23, 393. Etana, A., Hakansson, I., Swain, E. & Bucas, S. (1999). Effects of tillage depth on organic coal content and physical properties in five Swedish soils. Soil Tillage Research, 52, 129–139. Food & Fertilizer Technology Center (2001). Micronutrients and crop production (report No. bc 51009). Taipei, Taiwan: Food & Fertilizer Technology Center. Fujita, K. (1995). Composting Technology (2nd edition). Tokyo, Japan: Gihodo Shuppan Co., Ltd. Furr, A. K., Lawrence, A. W., Tong, S. C., Grandolfo, M. C., Hofstader, R. A., Bache, C. A., Gutenmann, W. H. & Lisk, D. J. (1976). Multi-element and chlorinated hydrocarbon analysis of municipal sewage sludges of American cities. Environmental Science & Technology, 10 (7), 683–687. Gadallah, M. A. (1994). Effects of industrial and sewage waste water on the concentration of soluble carbon, nitrogen and some mineral elements in sunflower plants. Journal of Plant nutrition, 17, 1364-1384. Gerba, C. P. (1996). Municipal waste and drinking water treatment. In: I. Pepper, C. P. Gerba & M. Brusseau (eds.), Pollution Science (pp. 301-319). San Diego, CA: Academic Press. Gigliotti, G., Businelli, D. & Giusquiani, P. L. (1999). Composition changes of soil humus after massive application of urban waste compost: a comparison between FTIR spectroscopy and humification parameters. Nutrient Cycling in Agroecosystems, 55, 23– 28. Gmez, T., Navarro-Pedreno, J. & Mataix, J. (1992). The influence of saline irrigation and organic waste fertilization on the mineral content (N, P, K, Na. Ca and Mg) of tomatoes. Journal of the Science of Food and Agriculture, 59, 483-487. He, X. T., Logan, T. J.& Traina, S.J. (1995). Physical and chemical characteristics of selected U.S. municipal solid waste compost. Journal of Environmental Quality, 24, 543-552. Heal, O. W., Flanagan, P. W., French, D. D. & MacLean, S. (1981). Decomposition and accumulation of organic matter in tundra. In: L.Bliss, O. Hewal & J. Moore (eds.), Tundra Ecosystems – a comparative analysis (pp. 587-633). Cambridge, UK: Cambridge University Press. Hernandez, T., Moreno J. I. & Costa, F. (1991). Influence of sewage sludge application on crop yields and heavy metal availability. Soil Science and Plant Nutrition, 37 (2), 201210. Hofstede, H. T. & Ho, G. E. (1991). The effect of the addition of bauxite refining residue (remud) on the behavior of heavy metals in compost. In: J-P Verner (ed.), Trace Metals In he Environment: Heavy Metals in the Environment (vol.1, pp. 67-94). Amsterdam, Netherlands: Elsevier.

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Houghton, J. (1996). Sustainable Use of Soil. London, UK: Royal Commission on Environmental Pollution. Jackson, W. R. (1993). Humic, Fulvic and Microbial Balance: Organic Soil Conditioning. Evergreen, CO: Jackson Research Center. Kikuchi, R. (2001). Application of sewage sludge to plant disease control. Floresta e Ambiente, 13 (52), 21 (in Portuguese). Kononova, M. M. (1996). Soil organic matter. Elmsford, NY: Pergamon Press. Koptsik, S. V. & Koptsik G. N. (2001). Soil pollution patterns in terrestrial ecosystems of the Kola Peninsula. In: D. Stott, R. Mohtar & G. Steinhardt (eds.), Sustaining the global farm (pp. 212-216). Ashland, OH: Purdue University Press. Madejon, E., Burgos, P., Lopez, R. & Cabrera, F. (2001). Soil enzymatic response to addition of heavy metals with organic residues. Biology and Fertility of Soils, 34, 144–150. Miikki, V., Senesi, N. & Hanninen, K. (1997). Characterization of humic material formed by composting of domestic and industrial biowastes. Chemosphere, 34, 1639-1651. Nadelhoffer, K. J., Giblin, A. E., Shaver, G. R. & Linkins A. E. (1992). Microbial processes and plant nutrient availability in arctic soils. In: F. Chapin, R. Jefferies, J. Reynolds, G. Shaver, J. Svoboda & E. Chu (eds.), Arctic ecosystem in a changing climate (pp. 281300). San Diego, CA: Academic Press. Nilsson, A. 1997. Arctic Pollution issues: a state of the Arctic environment report (No.827655-060-6). Oslo, Norway: Arctic Monitoring and Assessment Program. Nriag, J. O. & Pacyna, J. M. (1988). Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature, 333, 134–139. Orlov, D. S. (1993). Soil Chemistry (in Russian). Moscow, Russia: Moscow State University Press. Ponomareva, V. V. (1957). To the method for the study of soil humus after I.V. Tyurin’s scheme, Pochvovedenie, 8, 66-71 (in Russian). Schlesinger, W. H. (1997). Biogeochemistry, San Diego, CA: Academic Press. Semple, K. T., Reid, B. J. & Fermor, T. R. (2001). Impact of composting strategies on the treatment of soil contaminated with organic pollutants. Environmental Pollution, 112, 269-283. Shrivastava S. K. & Banerjee, D. K. (2004). Speciation of metals in sewage sludge and sludge-amended soils. Water, Air and Soil Pollution, 152, 219–232. Sims, J. T. & Kline, J. S. (1991). Chemical fractionation and plant uptake of heavy metals in soils amended with co-composted sewage sludge. Journal of Environmental Quality, 20, 387 –395. Smith, S. R. (1996). Agricultural Recycling of Sewage Sludge and the Environment. London, UK: CAB International. U.S. Environment Protection Agency (1993). Standards for the use or disposal of sewage sludge (part 503, Federal Register 58, 9387-9404). Washington D.C. Villar, M. C., Beloso, M. C., Acea M. J., Cabaneiro, A., Gonzles-Prieto, S. J., Carballas, M., Daz-Ranina, M. & Carballas, T. (1993). Physical and chemical characterization of four composted urban refuses. Bioresource Technology, 45 (2), 105-113. Winterhalder, K. (2000). Landscape degradation by smelter emissions near Sudbury, Canada and subsequent amelioration and restoration. In: J. L. Innes & J. Oleksyn (eds.), Forest Dynamics in Heavily Polluted Regions (pp. 87-119). London, UK: CAB International.

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Witting, R. & Neite, H. (1989). Distribution of lead in the soils of Fagus sylvatica forest in Europe. In: M. A. Oztur (ed.), Plant and Pollutants in Developed and Developing Countries (pp. 199-206). Izmir, Turkey: Ege University Press. Wong, J. W. C. & Lai, K. M. (1996). Effect of an artificial soil mix from coal fly ash and sewage sludge on soil microbial activity. Biology and Fertility of Soils, 23, 420-424. Woodmansee, R. Vallis, G., I. & Mott, J. J. (1981). Grassland Nitrogen. In: F. Clark & T. Rosswall (eds.), Terrestrial Nitrogen Cycles: Processes, Ecosystem Strategies and Management Impacts (Ecological Bulletins 33, pp. 443-462). Stockholm, Sweden: Swedish Natural Science Research Council. World Resources Institute (1987). World Resources 1987: an assessment of the resource base that supports the global economy. New York, NY: World Resources Institute.

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 119-153 © 2006 Nova Science Publishers, Inc.

Chapter 4

SOLID WASTE MANAGEMENT, RECENT TRENDS AND CURRENT PRACTICES FOR SECONDARY PROCESSING OF ZINC AND LEAD INDUSTRIES IN INDIA Archana Agrawal∗ and K. K. Sahu Metal Extraction and Forming Division, National Metallurgical Laboratory, Jamshedpur, India

ABSTRACT Almost all the metallurgical processes are associated with the generation of wastes/residues which may be hazardous or non-hazardous in nature depending upon the criteria specified by institutions like US EPA etc. The wastes containing heavy and toxic metals such as arsenic, cadmium, chromium, nickel, lead, copper, mercury, zinc etc. are present beyond permissible limits deemed to be disposed off. Due to the implementation of stricter environmental laws and economic reasons all the metallurgical industries are now forced to go for eco-friendly technologies to produce metal and other related products world over. However, generation of wastes is the integral part of metallurgical industries which can not be ruled out, therefore if the wastes/residues are hazardous in nature they generally have to be treated or disposed off in safe and designated dumping sites. If these wastes/residues are non-hazardous in nature then they may be suitably used as secondary raw material for the recovery of metals which are in growing demand all over the world. Zinc is in growing demand all over the world. In India a major amount of zinc is imported and therefore processing of zinc secondaries will supplement in satisfying the gap between demand and supply to some extent. Similarly processing of lead secondaries is important because of their relative high metal content, besides low energy and cost involved in recovering the metal. This chapter highlights the production capacity, type and quantity of solid wastes generated, their chemical composition and treatment/disposal options for the Indian lead and zinc industries. Zinc tailing, slag, leach residue, jarosite residue, β-cake, etc. from zinc industries and BF slag, flue dust, ISF slag ∗

Aothor for corrwspondance e mail address [email protected] or [email protected]

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Archana Agrawal and K. K. Sahu etc. from lead industries are the major solid waste generated from various process and needs attention. Although all the metal producing industries in organised sector are now taking care of the environment and waste management related problems, but pollution from unorganized lead units are the major cause of concern. Permissible limits of toxic constituents in zinc based secondaries and threshold zinc concentration for both indigenous and imported raw materials were worked out at National Metallurgical Laboratory (NML). An overview of the current practices and recent trends in the secondary processing of zinc and lead and the attempts made to recycle/recover metal values and production of value added products, are discussed in the text. Various processes, particularly hydrometallurgical ones, already developed or in the developmental stages, are discussed. Attempts made by various laboratories and industries towards the development of eco-friendly processes for the recovery of zinc and lead from secondary raw material are also described.

Key words: pollution measures, recycling, secondary zinc, lead, lead acid battery

INTRODUCTION Metallurgical industries generate vast quantities of solid wastes such as slag, ash, sludge, dross, grindings, turnings, clippings, residues and secondaries. During the last few decades rapid industrialization has led to many fold decline in the quality of environment. Some of the solid wastes produced during metal extraction are hazardous in nature due to the presence of certain toxic metals which contaminate the surface and ground water through the leachate generated at the dump-sites, posing a risk to the life of the living organism. Effects of pollution due to the toxic constituents of the above leachate, are usually noticed in the long run. It is for this reason that the industries are not much concerned about the solid metallic wastes that are invariably thrown and dumped unsystematically during metal production. The type of metallic waste generated, depends on the quality of raw materials used, the process and the treatment methods. Irrespective of the physical forms such as solid, liquid and gas, the wastes generated are eventually of two types: hazardous and nonhazardous. Amongst the heavy and toxic metals, arsenic, cadmium, chromium, nickel, lead, copper, mercury and zinc are considered deleterious to the environment, when their concentrations are more than the stipulated limits. The major environmental degradation is caused by copper, lead and zinc industries, often using imported zinc ash/residue, dross, skimming, lead scrap etc. It is therefore considered a major problem for allowing to process such material with out proper environment friendly technology and safety measures This chapter deals with an overview on the quantity and composition of the various solid wastes/ secondaries generated, processing options for such materials and their management and the current trends and recent practice in the utilization of various wastes containing zinc and lead. Zinc is the most used non-ferrous metals next to aluminum and copper. Apart from its major applications (about 70%) for galvanizing of steel, the other important areas of applications are as sheets, anodes, casting, chemicals, micronutrients, paints, dry cells etc. As the usage of zinc increases, the gap between demand and supply is widening [1,2], the possibilities of recycling of zinc exist from many of these applications. Out of about 10

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million tons of zinc production globally about 30% of zinc is produced from the secondary sources. Major raw materials available for secondary zinc units in India are zinc ash, dross and blowings from galvanising plants, brass waste such as brass dross/ash and scrap, electric arc furnace (EAF) dust, die-cast scrap, sheet cutting, old zinc roofing and anodes, skimmings and residues, pickle salt wastes etc. Since the indigenous availability of the above secondary raw materials is very limited these have to be imported from other countries. It was found that many of these imported secondaries were toxic in nature due to the presence of toxic radicals more than the permissible limits designated by US EPA [3]. Hence Basal Ban was implemented on the import (trans boundary movement) [4,5] of these secondary raw materials because of which secondary zinc industries had to face a major setback. Many of the industries in the organised and unorganised sectors were closed for the want of raw material. Both pyrometallurgical as well as hydrometallurgical processes are adopted worldwide, whereas mostly hydrometallurgical processes are being practised in India to treat secondaries, which comprises of leaching, iron removal, purification and electrowinning. The generation of zinc-based secondaries in our country is limited, whereas the zinc based processing industries have grown over the years in order to meet the demand of zinc metal and its compounds. Since processing of secondary zinc materials gives better returns, there has been a tendency to operate such industries in medium and small scale sectors using both the indigenous and imported materials. After the implementation of strict environmental rules all those secondary units which have opted for eco-friendly technology and have proper pollution control devices have applied for the registration and import licence to Ministry of Environment and forest and a few of them have got the clearance and come back to life. Thus an attempt has been made to focus upon the newer technologies for the secondary processing of zinc. Similarly with the increase in the usage of lead, the gap between demand and supply is widening [1]. In terms of worldwide annual tonnage consumption, lead is fifth important metal in use. The current demand for lead in India is about 1,61,000 TPA, of which about 50% is met through imports. Spent battery scraps are the source of 80% lead that is recycled in the country and the balance is imported [6]. Due to the depletion of the primary source for lead, primary production units of lead can never bridge this gap and therefore the concept of secondary metal production by using wastes/residues from primary metallurgical processing of metals, alloys etc., will help in supplementing the primary metal production. Raw materials for secondary lead production units are mainly spent lead-acid batteries, used scrap like wornout sheets, pipes, solder, dusts, drosses etc. The advantage of processing secondaries is the conservation of energy, which is far richer in metal content than the primary resource. An increasing number of eco-friendly technologies are available for the production of secondary metals. Major primary metal producing units and secondary producers in organised sectors already have the proper pollution control devices installed however, the main problems faced in production is simply the unavailability of the secondaries to them. Small scale secondary unit in unorganised sector, devoid of ecofriendly technology, uses lead acid battery as raw material causes maximum pollution. Newer technologies for the secondary processing of lead [7] are also given keeping all the above factors in mind. Some effort made by different laboratory in India in this area are also discussed.

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ZINC INDUSTRIES Earlier the installed smelting capacity for zinc in India was 199,000 tonnes of which HZL had 169,000 tonnes (Debari: 59,000 tonnes, Visakhapatnam: 40,000 tonnes, and Chanderia: 70,000 tonnes). After being taken over by Sterlite group, HZL has raised its production capacity to 220,000tonnes a year by removing bottlenecks and improving efficiency [8]. Recently HZL has further expanded the capacity to 400,000 tonnes [9]. The company estimated to produced about 300,000 tonnes (including 230,000tonns though domestic capacity and 70,000 tonnes through toll processing route) in the year 2004-05 against the actual output of 260,000 tonnes in 2003-03 (including 225,000 tonnes through domestic capacity and 35,000 tonne through toll processing route). Binani Industries Ltd (BZL) is estimated to produce 35,000 tonnes for 2004-05 against about 32,000 tonnes in 2003-04. Thus the total supply by these two industries is about 335,000 tonnes for 2004-05 against 290,000 tonnes in 2003-04 [10]. However the demand and supply gap would be around 65,000 tonnes for 2004-05 against 60,000 tonnes in 2003-04. The demand for refined zinc is 400,000 tonnes in the fiscal year of 2004-05 which is growing at a rate of 12-15% annually and likely to sustain for next few years [9]. HZL uses mainly indigenous zinc concentrate and ocassionaly imports from other countries while Binani Ltd. uses imported concentrates only. About 15-20% of zinc demand in India is met through secondary production against world average of 32-35%. There are about 40 secondary units and more that 200 zinc chemicals units (zinc oxide, zinc sulphide, zinc chloride etc). These play an important role in balancing the demand-supply gap in the country. The recyclers depend on the import to keep their units running economically since local wastes are insufficient to cater the demand. All zinc wastes containing zinc have been categorised as hazardous waste under the Basel convention. Some selected dross, zinc scrap and skimming are in green list of waste and zinc ash happens to be in amber list. The European union has placed all zinc containing wastes in the list of hazardous wastes. Because of the likely contaminants present in the zinc skimmings, a product of galvanising operation, they have been placed under the categories of wastes for which the level of contamination is essential to quantify. The residue generated from these materials by secondary units may have hazardous character depending on the concentration of the toxic constituents.

Waste Treatment/Disposal Practices in Zinc Industries The details of waste generated, their quantity, composition and treatment/disposal practices of some of the major zinc plants are incorporated in Table 1. At Binani Zinc smelter[11], the jarosite residue generated is pumped out and safely stored inside the company premises in a large pond of 1,40,000 M3 capacity. The residue contains toxic constituents in good amount like 3-5% Zn, 8-10% Pb, and 40-50% SO4. Ground water monitoring is periodically conducted from the tube wells installed around the ponds. Steps have been initiated for the construction of new jarosite ponds by conducting Rapid Environmental Impact Assessment (REIA). Based on the recommendation submitted by the public hearing panel, the government of Kerela notified the site for construction of jarosite pond. The design of the proposed pond is as per the guidelines of United States Environmental Protection Agency (USEPA) and Ministry of Environment and Forest (MoEF)

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for secure landfills. The pond design is based on geochemical investigations and compatibility studies with the waste. The pond is lined on all the sides and bottom with two layers of LDPE sheets of 250 micron thickness, heat sealed and protected by burnt clay bricks. The primary and secondary cake leach residues are also stored inside company premises in a covered shed provided with acid proof bricks at the bottom and disposed by way of sales. HZL has been in forefront of adopting appropriate pollution control and environmental protection measures in all its operations. Environment Impact Assessments are undertaken for new projects to formulate Environment Management Plans for mitigating any possible environmental impacts. The environmental measures at mining units of HZL include provision for dust suppression and collection system, disposal of beneficiation plant tailing into tailing ponds, recycling of tailing dam water to beneficiation plants as process water so as to maintain zero discharge, green belt development to improve landscape, to work as dust sinks and achieve noise attenuation. At its open pit Rampura Agucha Mine, a number of measures have been taken to ensure minimum ground vibrations due to blasting, and each and every blast is monitored for the vibration levels. At the smelting units, the environmental protection measures include sulphuric acid plants on Double Conversion Double Absorption (DCDA) technology to ensure minimum sulphur di-oxide emissions. Single Conversion Single Absorption (SCSA) Sulphuric Acid plants also have been provided with Tail Gas Treatment facilities for ensuring minimum sulphur dioxide emissions. In addition, other elaborate dust collection and gas cleaning facilities have been provided to ensure minimized gaseous emissions. Integrated effluent treatment plants have been provided to ensure that treated effluents meet all the criteria stipulated by the Central Pollution Control Boards. The waste generated as tailing in the concentrator plant at HZL though not included in this article is mostly dumped in the specific area, besides the back filling and in the tailing dams and also used in constructing embankment, mine road, play ground, filling low lying area etc. The major wastes generated from the smelters are the leach residues and the jarosite residues. The residue treatment plant at Debari, HZL is in operation to treat and recover zinc and other metal values. The final waste, jarosite cake is disposed off in storage pond after lime addition to render it inert. The intermediate residues like drum cake and cadmium containing cake are processed for the recovery of Ag and Cd in these units. β-cake is another material consisting of cobalt, and is mostly stored for Co recovery [16]. The process used for Co recovery involves fluidized bed roasting of β-cake followed by H2SO4 leaching, solution purification, solvent extraction and electrowinning. The pilot plant installed at Debari (HZL), Udaipur for Co recovery is not utilized for continuous production of this metal. Maximum recovery of cobalt from β-cake is reported to be about 60%. The imperial smelter furnace (ISF) slag generated at Chanderia unit is mostly stored in a separate dump yard with minor commercial disposal. Though the slag is vitreous in nature the toxic constituents are in sufficient amount and may prove to be hazardous due to mobility of the ions by weathering action.

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Table 1: Details of waste generated and treatment/disposal practices in zinc plant. Sl. No 1

Name of the Industry Binani Zinc Kerala10

2

HZL Chanderia Rajasthan11-13

3

4

Debari Smelter plant, HZL, Rajasthan10, 14-16

Zinc Lead Smelter plant, HZL, Visakhapat-nam10, 13,14

5

6

Sunrise Zinc Cuncolim, GOA15,17

Bharat Zinc10

Waste Generated: Quantity & Composition (%) -Jarosite residue: Zn: 3-5%, Fe: 20-28% Pb: 8-10%, SO4: 40-46% -Primary cake leach residue Zn: 2-4%, Cd: 0.5-2%, Cu: 40-50%, Co: 0.02-0.03% -Secondary leach residue Zn: 20-30%, Cd: 1.5%, Cu: 10-15%, Co: 0.2-.5% -ISF Slag - 42, 000 t/y Zn: 6-9, Pb: 0.6-0.7, Cu: 0.19, Sb: .01, Ag: 19 g/MT, Au: 0.04 g/t, FeO: 33 -Effluent plant sludge (Details of other wastes covered in lead section) -Drum Cake Zn: 17, Fe: 32, Pb: 5.4, S: 5.4, Cd: 0.25, Cu: 0.11, Co: 0.003, Ni: 0.005, MgO: 0.6, Mn: 2.1, Sb: 0.004, As: 0.05, CaO: 3.0, SiO2: 3.9, Ag: 0.038 -Cadmium cake Zn: 36, Cd: 14.0, Cu: 2.2, -Beta Cake Zn: 9.16, Cu: 0.05, Cd: 0.5, Mn: 2.6, Co: 1.45, Ni: 0.31, Fe: 3.33 -Jarosite residue: 41,000 t/y Zn: 3-4, Fe: 19-20, Pb: 3-4, Cu: 0.04, Cd: 0.07, CaO: 12.0, SiO2: 4.0, Al2O3: 4.4, -Zinc Tailing Zn: 16.3, Fe: 29.5, Pb: 7.0, Cu: 0.31, Cd: 0.26, Ag: 0.013, MgO: 0.8, CaO: 6.4, SiO2: 5.3, Al2O3: 5.9, S: 0.36 -Moore cake Pb: 5.6-5.8, Fe: 22-25, Zn: 20-22, Cd: 0.05-0.075, Ag: 0.0125, Ca: 3-4. -Raw Zinc Oxide: 6,950 t/y Zn: 55 - 60, .Pb: 7-10, Ag: 60ppm, Cu: 0.01-0.03, As: 0.03, Sb: 0.01-0.03, F: 0.05-0.09, C: 1-2, FeO: 1.0, Cd: 0.28, CaO: 0.2, MgO: 0.2, Al2O3: 0.8-1.0 -Sintered Zinc Oxide: 6950 t/y Zn: 65, Pb: 8-9, Cd: 0.02 -Clinker Product Zn: 58-62, Pb: 5-7, SiO2: 5.0, Fe: 3-5, Cd: 0.01-0.015, Ag: 0.0042 Sludge - 2,400 t/y Zn: 1.26, Cu: 1.65, Fe: 2.94, Al:0.6, Pb:1.42, Si: 3.8, Gypsum: 24.5 Filter Cake

Waste Reprocessing/ Dumping -Stored inside the premises in a large pond of 14,000 M3 lined with LPDE sheets - Both Primary and secondary Leach residue stored inside the premises in a covered shed provided with acid proof bricks at the bottom

-Dumped & commercial disposal -Goes for Cadmium recovery. -Goes for Ag recovery

-Goes for Cd recovery -For Co recovery (Mostly stored) -Dumping -Dumping -Transferred to Waelz Kiln for zinc recovery as zinc oxide -Goes to klinker klin for separation of zinc cadmium & lead and leaching of zinc in main unit.

-Waste is disposed off in a secured land fill -Secured land fill

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Manufacturers of the secondary zinc use indigenously available secondaries and imported materials (Zn ash/dross/skimming, EAF dust). Two types of dross namely top dross that floats on the top of the bath and the bottom dross that sinks to the bottom of the galvanising bath based on the specific gravity of the material, are obtained. They account for 10-20% loss of Zn during galvanising. Zinc content in drosses lies in the range 93-98% (Table 2). Table 2: Zinc waste from galvanising sectors Type of galvanising Sheet galvanising Pipe galvanising General galvanising Wire galvanising Total

Zinc consumption (T) 132500 79500 39750 13250 265000

25% zinc waste (T) 33000 19800 9900 3300 66000

Quite often the technology followed is hydrometallurgical based involving leaching, metal purification, separation, precipitation and electrolysis. In some of the units, ZnO is manufactured from the secondary zinc following pyrometallurgical processes, which involves carbon reduction and vaporisation of zinc followed by controlled oxidation to produce ZnO. Waste is mostly in the form of residues, which are often disposed off as unsystematic landfills, though some industries follow the safe handling and disposal procedure laid down officially by monitoring agencies. Over the years zinc sulphate industry dealing with micronutrients has developed technology for handling air, water and solid wastes[19]. The sludge obtained in the process from the filter press is washed to recover both water soluble and acid soluble zinc and washing is then recycled. This sludge is given a treatment of excess lime, which converts water-soluble zinc to insoluble form. Lead that is present originally in the zinc ash (0.3 – 0.8%) will also report in the sludge as insoluble form of lead metal/oxide or lead sulphate. To ensure that treated sludge does not carry any soluble salts of heavy metal ions, it is kept for 10-15 days for curing before final disposal. The treated sludge is disposed off which may cause some damage to the environment in the long run unless Environmental Impact Analysis (EIA) finds it otherwise.

Secondary Zinc Processing In India about 70% of the total zinc produced is used in galvanising sector of which 25% of zinc is lost as zinc waste (Table 2) [20] Apart from its major applications to the tune of about 75% as a protection material, the other important areas of applications for zinc and zinc alloys are as alloys and dye casting 15%, dry batteries 10%, chemicals, fertilizer and micronutrients, paints etc. 5%. Possibilities of recycling of zinc exist from most of these applications. India is a net importer of zinc and with rising demand there has been increasing interest in secondary zinc production. Recycling of zinc offers both environmental and economic benefits by: (i) reducing energy required for mining and processing (ii) reducing volume of material that end up on land filling (iii) relieving environmental impacts on the land and water and (iv) conserving zinc ores.

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The important sources of secondary zinc available for recycling are: pure zinc scrap in the form of sheet cuttings, zinc roofing, old zinc anodes etc., alloys containing zinc as a major constituent such as die casting alloys, brass dross/ash and scrap, other scrap alloys, zinc rich residues like zinc dross, zinc ash/skimmings and blowings from galvanising industries. The normal range of constituent in galvanising residues and other zinc sources are given in Table 3. Table 3: Range of constituents in secondary zinc sources Secondary Zn Source

Industry

Zn

Cu

Composition(%) Cd Fe

Cl

Others

Pb 0.0-0.5 Sn: 0-0.2 Al: 0.5-4.0 Pb 0.3-2.5 Sn: 0-0.2 Al: 0-1.5 Pb:0.2-1.25 Al: 0.0-0.3

Zinc dross ( Bottom)

Galvanising

93-98

0.0-0.1

0-0.2

2-5

0-0.1

Zinc dross (Top)

Galvanising

93-98

0.0-0.1

-

0.5-3.0

0-0.1

Zinc ash

Galvanising

-

-

0.5-1.0 2.0-4.0

Zinc Skimming

Galvanising

Zn(T) 80-90 Zn(metallic) 40-60 50-60

Brass dross Brass ash

Brass foundries Brass foundries

41-42 40-50

Copper cement Flue dust

Zinc plant Pb & Cu smelters Waelz process Steel furnace

Oxide dust Steel fumes

0-0.2

0-1

10 - 25

NH4Cl - 3.1

43-45 15-20

-

1-2 1.0-2.0

0.1-0.5

6.0-9.5 30-32

5.5-7.0 5-6

-

1-3 1.5-2

7-8

SiO2:1-2 SiO2:0.25-20, Al:0.0-0.5, Pb: 0.2-1.0 -

60-65 30-30.5

0.1-0.3 22-24

-

1-1.5 0.1-0.3

1.5-2 1.5-2

-

World over the contribution [2] from different sources of zinc for recycling include: Brass scrap : 32% Die casting scrap : 16% Galvanising residue : 23%

Zinc sheet Steel plant dust Others

: 10% : 8% : 11%

There are about 40 secondary zinc units in India having a capacity of about 60,000 tonnes but actually producing 30,000 - 35,000 tonnes play a balance role in bridging the demandsupply gap . Therefore the secondary raw material has to be imported but following Basel convention's 1989 decision where several developing countries put a complete ban on imports of hazardous and toxic wastes in to their territory. Among the items banned were lead and zinc ash and their skimming which has resulted in closure of most of the secondary units manufacturing zinc metal from scrap and wastes and consequently the country has to import an extra amount of about 35,000 tonnes per year (t/y) of zinc.

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Both pyro- as well as hydrometallurgical processes are practised world wide to treat zinc wastes. There are various pyro-metallurgical processes depending on the zinc concentration in the secondary feed, such as − −

Electrothermic process for high and low zinc contained residues Imperial Smelting Furnace (ISF) process for medium zinc contained [1]

Waelz kiln or QSL process, Larvic process, New Jersey's continuous vertical retort zinc distillation process, SKF plasma process [21], Mintek Enviroplas [22, 23] are used world wide. Waelz kiln process is most extensively applied in the pyrometallurgical treatment of residues. About 76% of total electric arc furnace (EAF) dust is treated by Waelz kiln in USA, Japan and Europe. Zinc dross is a metallic alloy of zinc and some iron which is generated during galvanizing operation is often processed by pyrometallurgical techniques. The commonly practiced methods for zinc dross processing [24] are:

Liquidation and Remelting In this process the material is kept on a sloping hearth at a suitable temperature so that the molten zinc trickles down without effecting iron. However liquation is not suitable for the production of high purity zinc for galvanizing since the zinc that trickles down carries fine dross crystals and is oxidized in the process. The working temperature is high as result zinc is contaminated with iron due to increased solubility. Recovery of zinc by this process is around 30% of the weight of dross treated. It has been reported that higher recovery of zinc from dross could be achieved by centrifuging and squeezing process. Aluminum Process Based on the aluminum addition Schmidt developed method for the recovery of zinc. Addition of aluminum leads to the displacement of zinc from crystals of zeta phases (FeZn13) as the affinity of Al for Fe is greater than that for Zn. The alloy of iron and Al(FeAl3) requires only 1.5 parts of Al to 1 part of iron compared to the 15.5 parts of Zn in zeta phase. Density of FeAl3 is much lighter than molten zinc, hence it floats on the surface and its skimming is easier and efficient than scooping from the bottom of the bath. The operation is carried out at about 720 oC and after the removal of skimming the metal is cooled and casted. Recovery of metal is around 85%. This process is feasible at small scale also. Electro Thermal Process This process of recovery of zinc has a number of advantages over the indirect distillation method such as: − − −

−

Electricity is used as a source of heating making the process energy efficient Recovery of zinc is 98% against 92% in distillation method Removal of solid residue left after distillation is easier because as the crust can be remelted and tapped out by raising the temperature making the temperature continuous one. No retort or pot is required for holding the dross for distillation.

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The process is feasible where the electricity is cheap. The capital investment is large and is feasible on large scale.

Distillation Process In this process zinc from dross is distilled off as zinc vapour from a retort and condensed in a suitable condenser. The process requires specialized equipments and operates at high temperature. The recovery and purity of zinc is high. Three types of furnaces namely stationary, horizontal and tilting type are commonly used. The stationary and horizontal furnaces are similar in construction and size. These are made of firebricks and fired with gas or oil. The tilting type furnace consists of a large cylindrical steel casing lined with firebricks and mounted on triunions, which facilitated tapping at an angle. In these furnaces retort is used for melting the dross. The metal vapour/fumes from the retort passes into the condenser where it is cooled either as metal or as dust depending on the design of the condenser, alternatively the fumes/vapours from retort is allowed to burn in the adjoining combustion chamber in presence of air to form zinc oxide. In India, the use of pyrometallurgical techniques for the recycling of zinc waste has been of less significant. Mostly hydrometallurgical processes are practiced in India. Hydrometallurgical methods are comparatively cleaner and can be adopted in small and medium scale industries. The three main hydrometallurgical methods for treating the secondaries such as zinc ash/skimming, brass ashes etc. are − − −

Electrowinning process, Solvent Extraction-Electrowinning process Crystallization process for manufacture of zinc sulphate,

Electrowinning process: The process generally uses zinc ash and other raw materials containing low level of impurities such as copper, cadmium etc. The processing steps mainly consist of material preparation, leaching and purification, electrowinning and melting. The material is crushed and pulverised to separate metallic zinc from fine ash. GOB (Good Ordinary Brand, 98.5% pure) zinc is obtained on melting and casting the separated metallic zinc. Fine ash is subjected to calcination to remove chlorides and pulverised again to get particle size of <100 mesh. The calcined fine ash is treated with sulphuric acid/spent electrolyte to get zinc sulphate solution as per equation 1. ZnO + H2SO4

ZnSO4 + H2O

(1)

During leaching. compressed air is passed and pyrolusite (MnO2) is added to oxidise ferrous iron to ferric state. Leaching is continued till the pH of the slurry reaches to 4.5-5. At this pH, ferric iron is hydrolysed to ferric hydroxide and precipitated along with other minor impurities such as Al and partially As, Sb, etc. A suitable flocculent is added to the slurry and discharged to a thickener for solid liquid separation. The solid filter cake generated is sent for disposal after suitable treatment and the filtrate containing concentrated zinc sulphate along with minor impurities like Cu, Cd, Co, Ni, As, Sb, Ge etc. goes for three stages of purification.

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ZINC ASH/ SKIMMINGS

PULVERISING

METALLICS

CALCINATION

MELTING

GOB Zinc

LEACHING

FILTER SLUDGE

WASHING

LIME TREATMENT

S

L

PURIFICATION-I Cu & Cd REMOVAL

EVAPORATION

CRYSTALLISATION

PURIFICATION-II Co & Ni REMOVAL CENTRIFUSING

RESIDUE FOR DISPOSAL

PURIFICATION-III ORGANIC & OTHER

ZINC SULPHATE CRYSTAL (For micronutrient)

ELECTROWINNING

MELTING

ZINC INGOT Figure 1: General flow sheet for producing electrolytic zinc metal and micronutrient from zinc ash and skimmings.

− −

First stage purification removes copper and cadmium as cement with the addition of zinc dust/powder at ambient temperature. Second stage of purification is done by cementation with zinc dust/powder at higher temperature of about 85 oC (hot purification) in presence of potassium antimony tartrate, which practically removes all the impurities. Alternatively, a few industries

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−

adopt sometimes-chemical precipitation method using di-methyl glyoxime (DMG) for Ni and β-naphthol for cobalt removal. In the third and final stage purification step, activated charcoal is added to the purified solution to absorb unwanted organics and other impurities. This step is also considered as the polishing stage.

The purified solution is cooled to a temperature of 35-40 oC and is electrolysed in an electrolytic cell using lead anodes and aluminium cathodes. The zinc metal is deposited at the cathode following the reaction, ZnSO4 + H2O

Zn + H2SO4 + 1/2O2

(2)

Acid generated during electrolysis is utilised for further leaching. Zinc metal in the form of sheets is stripped off manually from aluminium cathodes after 24 hours and melted in crucible furnace and cast as zinc ingots. The generalised flow-sheet for the process is given in Figure 1.

Solvent Extraction and Electrowinning (SX - EW) Process This is an integrated process with electrowinning approach. All processing steps other than purification step are similar to the process described above. In case of high copper containing material particularly brass ash, removal of copper by zinc dust cementation method is not attractive. Therefore copper is removed by solvent extraction to produce copper metal as shown in Figure 2. The solvent extraction process is carried out in a series of mixersettlers which consist of three sub sections, namely (i) extraction, (ii) scrubbing and (iii) stripping. After leaching and iron removal the clarified filtrate containing zinc and copper, comes in counter current contact with a suitable solvent in the extraction stage. Zinc is extracted selectively by the organic phase along with traces of copper. Copper is removed from the loaded organic phase in the scrubbing stage. The organic medium after scrubbing is brought into counter current contact with spent electrolyte in the stripping section. The resulting zinc electrolyte goes to cell house for zinc electro-winning and the barren organic is re-circulated to the extraction stage. Similarly for copper circuit, a parallel stream of clarified feed is taken for extraction with the help of another organic, which selectively picks up only copper and the depleted aqueous phase is sent back to leaching as raffinate. Stripping of copper from loaded organic phase and electrowinning are more or less same as that of zinc. Crystallisation Process Zinc ash fines are separated from metallic granules in pulverisers fitted with cyclone separator and bag filters and then processed for zinc sulphate manufacture. The fine ash containing mostly zinc oxide is treated with sulphuric acid to bring zinc values to sulphate form and filtered to get clear zinc sulphate solution as shown in Figure 1. The solution is evaporated in a crystalliser and crystallised by cooling through chilled water. Pure crystal of zinc sulphate are separated from mother liquor by centrifuging and are dried, packed and sold in the market for micronutrients and other applications.

Solid Waste Management, Recent Trends and Current Practices …

ZINC ASH

131

BRASS ASH

PULVERISING

MELTING

FINE ASH RESIDUE FOR DISPOSAL LIME TREATMENT

WASHING

GOB Zinc

CALCINATION

LEACHING

IRON PRECIPITATION

FILTER SLUDGE

sludge Stream - I Zn EXTRACTION

ZINC ELECTROWINNING

ZINC METAL

Stream - II Cu EXTRACTION

COPPER ELECTROWINNING

COPPER METAL

Figure 2: Block diagram for solvent extraction and electrowinning process to treat copper rich zinc secondaries

Newer Technologies for Zinc Recycling Several new hydrometallurgical processes [7] have been developed which are considered to be energy efficient and eco-friendly. These are:

ZINCEX Process This hydrometallurgical process resembles conventional zinc electro winning and is readily integrated with such a plant. EAF dust is leached with sulphuric acid to solubilize zinc and cadmium oxide and halides. The impure zinc sulphate solution is treated by solvent extraction to remove zinc and cadmium and transfer them to purified, halide free,

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Archana Agrawal and K. K. Sahu

concentrated zinc sulphate solution. Cadmium is removed from the solution by cementation, which is sold. High purity zinc metal is electrowon from the purified solution and sulphuric acid generated is recycled to the process. The zinc ferrite containing leach residue is further treated to recover lead and is finally suitable for disposal [25-28].

AUSMELT Process Zinc is recovered from electric arc furnace (EAF) dust by bath smelting technology. Here oxygen, flux and coal are injected via a cooled lance into liquid slag in one furnace to melt the EAF dust and in the second furnace to reduce the zinc, lead and cadmium oxides. The fumed zinc, lead and cadmium are reoxidised above the bath and collected in a bag filter. Non-hazardous iron rich slag is prepared for sale or disposal [29] EZINEX Process This hydrometallurgical process is based on the leaching of the secondaries with ammonium chloride to solubilize zinc oxide, lead oxide and cadmium oxide. The leach solution is filtered, followed by purification of lead and cadmium by cementation on zinc dust and electrowon to produce high grade or hot dip grade zinc metal. The spent electrolyte is recycled to leaching. The iron rich zinc-ferrite containing leach residue is dried, palletized with coal, and recycled back to EAF, thus no byproducts are produced for disposal, Mixed KCl-NaCl salt is crystallized for sale as flux. [30-31]. WAELZ KILN Process In the two stage Waelz kiln process the raw dust is fed to the first kiln, to separate Zn, Pb, Cd and chloride from the non-hazardous partially metallized iron. The dust from the first kiln is retreated in the second kiln to produce impure ZnO for Zn smelter feed and lead-cadmium chloride for processing to separate lead and cadmium. The single stage Waelz kiln process is identical to the first stage of the two stage process. The ZnO is generally treated in the Imperial Smelting Process to produce zinc and lead metal or converted to zinc-based chemicals and fertilizer additives [7]. CENIM-LNETI Process This is based on ammonium chloride leaching of secondaries, followed by solvent extraction and electrowinning / precipitation of zinc. This technique uses integrated processes to prepare various other products and has flexibility to treat different raw materials of variable compositions. The process can be adopted in small and medium scale industries [32]. CARBOFER Process Recently a British service group to steel producers, gave an account of developments in the recycling of steel by-products by this new process known as Carbofer process. This process is used to recycle oily millscale at EAF operations. When post-consumer scrap is recycled, dust collected from furnaces contains significant amounts of zinc (5 – 20%), which can be recovered by the Carbofer process. A series of developments at a UK site has discovered that by including EAF dust in the blend, the zinc content of the dust is even higher, making it suitable for reprocessing by secondary zinc operations [33].

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LEAD INDUSTRIES India has two major primary lead producers namely Hindustan Zinc Ltd (HZL) with Visakapatnam plant producing 22,000 tons per year, Chanderia plant in Rajasthan with an annual capacity of 35,000 tons, and HZL Tundoo plant in Bihar producing 8,000 tons per year with a total of 65,000 tons per year [1] by all the three plants. India’s largest refinary being setup by Sterlite-managed by Hindustan zinc group with an annual capacity of 50,000 tonnes inside the premises of HZL’s Chanderia Lead Zinc smelter with the help of Australia based Ausmelt technology [34]. The Indian Lead Limited (ILL) with a capacity of 24,000 tons per year which is gradually shifting to the concentrate route due to the restricted availability of lead scrap. There are about seven medium size secondary lead plants (total capacity 55,000 tonnes/year), 40 small operations (combined capacity of 15,000 tonnes/year) and more than 250 tiny/backyard plants (estimated combined capacity 25,000 tonnes/year). The main source of lead in these plants is scrap batteries. The overall contribution of the secondary lead industry in the country is almost same as that of primary producers. Around 52,000 tons of secondary lead is produced from the organised sectors but only 30,000 tons are available in the open market as the remaining part goes to captive consumption. Lead production from unorganised sectors (backyard smelters) is about 15,000 tons per year. Thus by the end of ninth plan (1997-98 to 2001-02) the demand and supply gap was about 41,700 tons which would further increase to 114,500 tons and 192,200 tons by the end of tenth (2002-03 to 2006-07) and eleventh plan (2007-08 to 2011-12) [1] respectively, if the supply from the backyard smelters (bhatties) is not taken into account. Table 4 depicts the demand and supply details of lead in India[61]. The demand of lead, which cannot be met by primary production, can be compensated to some extent by secondary production. Table 4: Lead-Demand-supply Gaps

Year

10th Plan 2002-03 2003-04 2004-05 2005-06 2006-07 11th Plan 2007-08 2008-09 2009-10 2010-11 2011-12 12th Plan 2016-17

Demand (Tonnes) with 6% Growth

Supply

(Tommes)

HZL

ILL

137700 146000 154700 164000 173800

38700 70200 70200 70200 70200

184300 196100 208600 222000 236200 316000

Sec Lead

Total

Gap+ SurplusDeficit(Tonnes)

21600 21600 21600 21600 21600

45000 45000 50000 50000 50000

105300 136800 141800 141800 141800

-32400 -9200 -12900 -22200 -32000

70200 70200 70200 70200 70200

21600 21600 21600 21600 21600

6000 6000 6000 6000 6000

151800 151800 151800 151800 151800

-32500 -44300 -56800 -70200 -84400

70200

21600

7000

151800

-164200

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Archana Agrawal and K. K. Sahu

Lead is a wide spread constituent in the earth crust. It is virtually indestructible and has always been present in soils, water and air. It is extensively used by mankind and has been dispersed continuously over a long period of time into the environment. There are many ways by which lead can enter the environment. Lead acid batteries, their handling and reprocessing in an unorganised manner is one of the major source of environmental pollution. Today, the lead acid battery scrap both in developed and developing countries are the single largest source of lead metal in meeting the demand. The reason is lower capital investment and energy requirement per tonne of metal production. In India there are only few industries in the organised sector who are having pollution control facilities, however, in the unorganised the situation is totally different. Most of the waste lead acid batteries are reprocessed by the unorganised sectors causing problem to the workers and the nearby locality. This is mainly due to improper technology, cash crunch and lack of monitoring and implementation of pollution norms. For ecological awareness and environmental consciousness, it is necessary to control pollution particularly in the unorganised lead production units. Currently over 70% of the lead consumed by automobile industry world-wide is fed by the secondary lead smelting plants, mainly derived from the used acid batteries. Besides battery scrap there are a wide variety of damaged/old scrap, obsolete or worn-out products including bearing metals, sheets and pipes, cable sheathing and solder as well as dust and drosses containing lead. All these fall under the category of restricted materials and hence must be handled with utmost care owing to the toxic effects of lead and dangers of the sulphuric acid. Non-separation of the scrap batteries/compounds and smelting the whole battery with its plastic body produces poisonous dioxine, which is detrimental and hazardous to the public health causing damage to the environment and the people alike.

Waste Treatment/ Disposal Practices in Lead Industries The details of waste generated, their quantity, composition and disposal practices of some of the major lead plants are incorporated in Table 5. Dumping or stockpiling of lead blast furnace slag, ISF slag and flue dust is mostly followed in primary lead units. Though the slags are vitreous in nature this mode of disposal is now questionable on environmental and economical grounds. The by-products of these units like enriched silver crust/prest crust and copper dross in HZL plants are mostly processed for the recovery of silver and lead metals. Matte and speiss generated are stored or sold for copper recovery. Antimony dross of HZL Chanderia is stored or sold to battery makers. The ferrosilicate slag containing >2% lead generated in Indian Lead Limited is recycled to extract lead and discarded only after lead content is brought down to <2%. Presently the slag is stored inside the factory premises for want of suitable land site allocation by the respective State Pollution Control Board (SPCB). Since lead is a very toxic material, disposal of the solid wastes in the secured landfill is absolutely necessary. However, major problem is with the secondary lead smelting units and most of them do not follow the proper processing technologies and are handling the spent lead acid battery scraps without resorting to the pollution control norms with respect to the SPM level, SO2, CO and lead fumes. During the processing of spent lead acid battery in backyard units, operations like breaking, crushing, screening, dry mixing etc. generate airborne lead dust which directly or indirectly enter into the human system and the surroundings of the working area. Lead absorption into the human body in significant

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quantity causes lead poisoning. Several of these backyard smelters simply recover 60-70% of the metal using home made technologies because of the low melting point of the metal and simply throw the slag containing very high lead into the environment causing greater damage to nearby locality. The worst sufferers in the unorganised backyard smelters are the workers involved in these units and the environment affecting the local population. Table 5: Details of metallic waste in primary lead industry Sl.No

1

Name of the Industry Zinc lead smelter, HZL,Visakhap atnam62 (Presently shut down)

2

Tundoo lead smelter, HZL, Bihar63

3

HZL Chanderia, Rajasthan11,12

4

Indian Lead Ltd., Thane4

Waste: Reprocessing/ Dumping -Part of the slag is recycled -BF Slag: 15,000 t/y Pb: 1.5-2.0, SiO2: 20-22, FeO: 36-38, MnO2: 3.0, CaO: 14, MgO: & rest is dumped 2.0, Al2O3: 6-7, Zn: 5-7, S: 2.0 -Ordinary Cu dross Pb: 83.0, Ag: 0.09, Cu: 2.0, Zn: 1.0, Sb: 0.3, Bi: traces -Antimony dross Pb: 70.0, Ag: 0.05, Cu: 0.3, Zn: 1.0, Sb: 2.0, Bi: traces -Final refinery dross Pb: 72.0, Ag: 0.03, Cu: 0.2, Zn: 5.2, Sb: 0.5 -Enriched liquated silver crust Pb: 78.0, Ag: 5.8, Cu: 0.7, Zn: 14.0, Sb: 0.1 -BF Slag: 18, 000 t/y -Part of it is recycled in the Pb: 1.5-2, FeO: 32-35, ZnO: 9-12, sintered section. Rest is MgO: 4-4.5, Insoluble: 23-24, CaO:14-16, Al2O3: 9-10, Ag: dumped 0.001-0.002 -Copper & ordinary drosses: 300 t/y -For silver lead recovery Cu: 2-4.5, Pb: 80, As: 10-11 -Prest Crust: 375 t/y -Goes For Ag recovery Ag: 4-5, Zn 15-18, Rest: Pb -Dezincing & antimony drosses:1.5 t/y -Litharge: 480 t/y -ISP Slag: 42,000 t/y -Dumped and commercial Zn: 6-9, Pb: 0.6-0.7, Cu: 0.19, Sb: .01, Ag: 19 g/t, Au: 0.04 g/t, disposal FeO: 33 -Commercial disposal for Cu -Matte & Speiss: 1, 300 t/y recovery or stored Pb: 17.3,Cu: 44.6, Sb: 1.2, Ag: 19.50 g/MT, Au: 1.9 g/t -Stored or sold to battery -Antimony drosses: 1, 520 t/y makers Pb: 51.5, Cu: 0.9, Sb: 7.0 -Silver crust (enriched): 370 t/y, -Reprocessed for Ag Pb: 24, Cu: 2.4, Ag: 15 g/t, Au:0.012 recovery Ferrosilicate slag: 3,000 t/y -Slag containing lead >2% is FeO:40-50, CaO: 10-20, SiO2: 35-45, Pb: <2.0 recycled & discarded only when lead content is <2%. Waste Generated: Quantity & Composition (%)

Efforts need to be made to improve health protection of the workers and to reduce the quantity of lead entering to the environment, which can be met through − − −

Efficient collection of the acid battery scrap. Strict control over unorganised sectors. Modified working practice and adoption of eco-friendly process technologies.

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Secondary Lead Processing Lead is a versatile and strategic metal with many vital applications. Automobile sector is the largest consumer of lead because of its use in the production of lead-acid batteries. The total market for lead in the world is actually quite large, it's about seven million tonnes. A large component of that comes from recycling electrical battery units and about 40 per cent of the world's lead comes from primary sources [35]. Lead scrap in the main sources of secondary lead as more than two-third of the total lead produced is consumed battery sector. The battery manufacturers consume about two-third of the total lead produced. Lead is also used in the sheathing of a variety of cables e.g., fibre optics cables, as a shielding material for radioactive radiations because of it specific properties like low melting point, ductility and high density. Lead dampers have been developed for earthquake protection. Other uses of lead are protection coatings, paints, solders, and gasoline additives. However use of lead compounds as gasoline additives is decreasing in third world countries too because of the concept of unleaded automobile fuel. As already mentioned primary lead resources are depleting and environmental awareness is increasing, causing the concept of reuse/recycling to become mandatory which suits to lead recovery along with the recovery of other precious metals and non-ferrous metals. In fact primary resources are quite limited and major amount of lead production is through secondary processes. The various processing steps [36] of scrap battery are shown in Figure 3. The metallic lead of grids can be readily melted at relatively low temperatures and cast into ingots of secondary lead bullion. Whereas, the paste requires a more complex recovery operation. Almost all the secondary plants use the pyro-metallurgical smelting process. The newer secondary plants generally have larger smelting capacities, which are more efficient and environmentally safer. Globally over 60% of total lead is recycled. Secondary lead production in other countries is shown in Table 6 [61]. Battery scrap from automobile sector accounts for 80% of old scrap recycled as secondary lead raw material. A standard lead acid battery for starting, lighting, and ignition of vehicles has the following average composition by weight[37]: A B C D E

Lead metal Lead oxide paste Polypropylene Electrolyte (free sulphuric acid) Others (ebonite, PVC, paper etc

34% 39% 5 - 6% 11-12% 8 -10%

Table 6: Secondary lead production-world scenario Country USA Germany Japan UK Italy France Canada Spain Belgium Others

Secondary lead production-share(%) 35.7 7.1 6.0 5.9 5.3 4.5 4.1 3.9 3.5 24.1

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137

Scrap Batteries Free acid

Breaking & Treatment

PP

Ebonite etc.

Smelting

Slag

Lead Refining

New Battery

Figure 3: Flow sheet for recycling of lead acid battery adopted by Unorganized sector. (pp: polypropylene)

The pyrometallurgical smelting process employed at almost all secondary plants is essentially same as that used in the primary smelter, there are key difference in feed materials and the type of smelting furnaces in use. Choice of secondary smelting process is independent of the battery breaking procedure used, although there are difference in the type and form of feed preferred by various furnaces. The newer secondary plants generally have larger smelting units, which are more efficient and environmentally safer. The various processing steps [38] of scrap battery are: − − −

Separation of all the constituents namely acid, polypropylene, separator and ebonite, metallic and non-metallic lead fractions Smelting of metallic and non-metallic fraction Refining of lead along with production of lead and lead compounds of desired composition

Battery breaking and the feed preparation is the first operation in most plants. Through a sequence of crushing, screening, washing, heavy media separation and floatation process, segregated streams of battery grid metal, battery paste, polypropylene, rubber and waste acids are produced. The metallic lead of grids can be readily melted at relatively low temperatures and cast in to ingots of secondary lead bullion. Whereas the paste requires a more complex recovery operation as follows:

138

Archana Agrawal and K. K. Sahu −

− −

Desulphurisation, i.e. removal of sulphur from the lead sulphate by conversion to lead carbonate (the most common desulphurisation process used is sodium carbonate mixed with the oxide and sulphate paste). Reduction (lead carbonate and unreacted lead oxide into metallic secondary lead bullion, i.e. unrefined and impure lead) and Refining of secondary lead bullion into soft lead, lead calcium alloy and/or antimonial lead

It is most unlikely that backyard recyclers will have a furnace capable of recovering the lead from the paste and the sludge of scrap batteries. They use an open kiln or a pot called bhatties for smelting. The metallic lead in the battery grids is melted and cast into ingots (Figure 3). The recovery rates are thus hardly higher than 60% of the available lead in the scrap battery and consequently there are serious pollution problems. The pollution problems in lead industries are of great concern as they persist despite of modest provisions for the control of lead dust and fumes and for the protection of workers in the occupational environment. Keeping in mind the hazardous nature of lead, it is necessary to control pollution particularly in the unorganised secondary lead production units. Some of the drawbacks found in India are summarised as follows: −

−

−

−

−

−

During opening and breaking, the sulphuric acid is allowed to wash down to the street drain and percolate in to the ground and contaminate the ground water. Acids tipped in to the streams and river will lower the pH of the water and adversely affect the local ecosystem. The procedure to open the spent batteries and change the plates or remove certain cells causes the risk of acid splashes to the skin and eyes to the person undertaking the task without proper safety measures. The bags are opened manually and the contents are unloaded at the charge preparation area adjacent to the furnace. Cloudy dust generation during this activity contributes to the elevated lead levels in the atmosphere. Smelters in the unorganised sector are not equipped with proper facilities of recovering the lead from the paste. The residue after recovery of lead contains high lead and causes serious problem of pollution in case of disposal. During the smelting process sulphur in the charge comes out as sulphur dioxide and emit large amount of dust and solid particulate matter (SPM) containing high lead causes health hazards. During handling and processing of battery scrap such as breaking, charge preparation, smelting, refining and packing, very little precautions are taken by the workers.

Operations like preparation of alloys, oxide, powders, paste and dry mixing of oxides, filing, assembling etc. leads to air borne dust pollution. In the dry process lead concentrations in the air ranges from 0.13 – 3.1 mg/m3. Emission factor for typical uncontrolled emission is 8 kg of lead per 1000 number of batteries [39]. The 80% of which can be checked by simple measures in and around the pollution areas. Emitted lead is directly or indirectly enter in to the body of the workers and others surrounding the working area. Uptake of lead in to the

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139

body through inhalation is more. About 48-64% of the inhaled lead is deposited in the lungs. The gastrointestinal absorption is only 15%. Like anywhere else, India has sound technology for the recovery of lead via the recycling route in the organised sectors. Backyard recycling of lead from acid batteries is the most environmentally unacceptable practice and this has increased dramatically over the years in spite of the provisions of the Central Pollution Control Board. Also such materials are being imported from several countries even though India is a ratified signatory of Basel convention. In the recent past, a number of ecofriendly pyrometallurgical processes like, ISAMELT, AUSMELT, KIVCET, QSL, KALDO process etc. that have been developed and commercialised to process ores and concentrates are also suitable for treating secondary lead particularly the battery scrap. MRU process followed in Germany is quite eco-friendly in terms of energy consumption and lower Pb and SO2 emissions (Table 7). Table 8 shows a comparison between these primary lead smelting operations with regards to their ability to process secondary lead too [7]. QSL plants operating in Germany, Canada and Korea are using 30-35% lead secondaries in the feed [40] These technologies meet the norms of western countries and could also be applied in countries like India. Table 7: Energy requirement Pb and SO2 emission from different smelter technologies

Item

Energy [MJ/Mt] of lead SO2 emission [kg/Mt of lead) Lead emissionair[g/Mt of lead]

Primary lead production Sinter shaft QSL furnace with furnace energy recovery

Secondary lead production MRU technology

10,000

7,000

6,000

70

4

1

140

40

7

Table 8: New primary smelting processes and their ability to accept lead secondaries as feed Type of Smelting

Mode of Operation

Appetite for Secondaries

QSL

Bath

Continuous

Significant

Outokumpu Oy

Flash

Continuous

Little

Flash/Bath

Batch

Significant

Flash/Bath Flash

Batch Continuous

Significant Little

Process

Kaldo (Top blown rotary converter) Isasmelt Kivcet

Comment

Several plants are in operation Separate smelting/slag reduction furnaces Rotates and tilts, mechanically complex Lacks flexibility in feed Kivcet-CS can process 100% oxidised feed

Like the primary lead smelting operation, secondary plants also use pyrometallurgical processes with a difference in feed material and the type of smelters used. Table 9 shows the main feature of pyrometallurgical processes applied in the secondary lead production [7, 39-

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Archana Agrawal and K. K. Sahu

41]. Several new hydrometallurgical process for the recovery of high pure lead from spent lead acid battery have been developed in last two decades which has several advantages such as no dust and fumes generation, flexibility in scale of operation, location, environmental friendliness etc over thermal processing should be encouraged. Most of these processes are either on laboratory scale or tested on pilot scale of operation. The following text describes the processes in brief. Table 9: Main features of secondary Lead Smelting Processes Process Blast Furnace

Smelting /Mode Shaft/Continuous

Reverberatory Furnace

Bath/Continuous or Batch

Short Rotary Furnace

Bath/Batch

Kaldo Furnace

Flash or Bath/Batch

Electrothermic Furnace

Bath/Batch

Features/Current Status Can be used for a range of secondary feed like scrap lead, slags, drosses and flue dust. Widely used world wide Inherently non clean technology producing high silica mattes and slags. Used primarily for high oxidic and antimony containing feed Widely used worldwide Environmental problems. Used primarily for high metallic feed Widely used world wide Produces a reactive soda slag which can cause disposal problems. Used for smelting residues and scrap including unbroken batteries In operation in Sweden on secondary feed. Uses metallic and oxidic feed Russian companies offer the technology Costly equipments Status not known.

RSR Process In this process the PbSO4 portion of the sludge is treated with ammonium/alkali carbonate to produce lead carbonate and ammonium sulphate. PbSO4 + (NH4)2CO3

PbCO3 + (NH4)2SO4

(3)

Reduction of PbO2 is done in two ways: −

−

By addition of SO2 to an alkali/ammonium carbonate producing alkali sulphite/bisulphite which reacts with PbO2 to produce PbSO4. Sulphite/bisulphite are oxidised to sulphates and lead is precipitated as PbCO3 or PbCO3.Pb(OH)2. By heating the battery sludge to 290 oC in presence of some amount of organic.

Solid Waste Management, Recent Trends and Current Practices …

141

The desulphurised sludge is leached in H2SiF6 and HBF4 and lead is electro won. About 500 ppm of arsenic is added to the electrolyte in order to prevent PbO2 deposition on the anode. The leach solution may contain 70-200 g/L and at least 50 g/L of free acid. Insoluble PbO2, part of the sludge, can be reduced to soluble form either by addition of SO2 to alkali/ammonium carbonate producing alkali sulphite / bisulphite which reacts with PbO2 to produce PbSO4. Sulphite / bisulphite is oxidised to sulphates and lead is precipitated as PbCO3 or PbCO3. Pb(OH) 2, or by heating the battery sludge to 290 oC in presence of some amount of organics. This treated sludge is leached in H2SiF6 and HBF4, followed by electrolysis [42].

Bureau of Mines (USBM) Process Like RSR process the sludge (containing PbSO4 and PbO2) is pre-treated with ammonium carbonate to desulphurise PbSO4. Here the reduction of PbO2 to PbO is done by addition of metallic lead powder during leaching with H2SiF6. The drawback of this process is the requirement/recycling of large amount of powder lead, as the PbO2 content in the sludge is about 35-40%. This process utilises PbO2 coated titanium anodes and lead cathodes and about 1-2 g/L of phosphorous (using salts of phosphoric acid like, Na3PO4.12 H2O, (NH4)2HPO4, CaH4(PO4)2 to prevent PbO2 deposition on the cathode [43]. The lead content in the electrolyte may be as high as 150 g/L and depleted lead level is above 25-35 g/L. Engitech Process In this process the battery is broken to separate various fractions and desulfurize the sludge using Na2CO3 and NaOH to produce Na2SO4 which is crystallised to produce the crystals of Na2SO4 [44] The desulphurised sludge containing Pb, PbCO3, PbO, PbO2 and Pb(OH)2 is leached with HBF4 (Eq. 2). The process also uses H2O2 to dissolve PbO2 (Eq. 3). PbO2 + Pb + 4HBF4

2Pb(BF4)2 + 2H2O

(4)

PbO2 + H2O2 + 2HBF4

Pb(BF4)2 + 2H2O + O2

(5)

To avoid PbO2 diposition at anode, the Engitech process [45] utilises a specially designed composite anode, that operates at an extremely high anode current density e.g(320 A/m2 ). Lead is electrowon at this high current density.

Ginata Process In this process lead is extracted from all the ectrodes, and electrical connections of spent lead-acid electric storage batteries. The spent lead-acid battery is recharged to reduce the PbSO4 removing sulphuric acid from the recharged battery. The battery is immersed in an electrolyte (like Fluoborates, Fluosilicates, Dithionates, Perchlorates, Cyanides, Nitrates, Oxalates, and Pyrophosphates) in which lead from all the electrodes and electrical connections of a spent battery will form a complex with the electrolyte. Since each immersed battery is an electrochemical system composed of a series of electronically connected positive and negative couples of electrodes all immersed in the same electrolyte, in which the negative electrodes naturally dissolve anodically to release lead ions into the electrolyte thereby reducing Pb4+ to Pb2+, which dissolves in the electrolyte as lead complex [46]

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Archana Agrawal and K. K. Sahu

The resulting electrolyte containing lead is electrowon in presence of about 200 ppm cobalt as additives eliminating the need for PbO2 coated or special alloy anode. Cobalt enhances the evolution of oxygen and thus minimises the degradation of graphite anode. The electrowinning process is operated under periodic reverse current to oxidise antimony in the electrolyte to pentavalent state, which is precipitated from the electrolyte above the concentration of 3,000 ppm. High pure lead cathode is produced in the process.

AAS Process This process utilises ammoniacal ammonium sulphate (AAS) solution for the leaching of the battery scrap. The whole crushed batteries are fed to an upward moving leaching column, where the solution floats the case and separators out of the column, suspends and dissolves the lead compounds of the paste, separating the clean metallic lead fraction. The PbO and PbSO4 dissolve in AAS solution and undissolved PbO2 is separated and converted to PbSO4, using about 50% H2SO4 at high temperature. The resulting PbSO4 is fed back to the AAS leaching process. The lead is electrowon to get sponge lead. This process utilises ammonia and water as feed and recovers (NH4)2SO4 as byproduct through a bleed stream [48-49]. PbSO4 Slurry Process This process involves direct electrowinning of lead from the battery paste. PbSO4 and PbO from the battery paste are introduced in the cathode compartment by an ion selective membrane. The electrolyte of the cathode compartment consists of the slurry of PbSO4, PbO, H2SO4, Na2SO4, NaOH along with a complexing reagent like ethylene diamine tera-acetic acid (EDTA), acetic acid, oxalic acid etc. The cathode is a fluidized bed of particles connected to a current collector. During electrowining process, the slurry particles contact the cathode and are reduced to metallic lead. The sulphate ions diffuse through the membrane forming H2SO4. The PbO2 in the slurry is contacted with SO2 or Na2SO3 to produce PbSO4 which is recirculated in the cathode chamber. In this process the battery paste is converted to metallic lead and suphuric acid [50]. PLACID Process This process involves direct chloride leaching rather than disulphurisation and leaching with HBF4 or H2SiF6. The chemical equations of chloride leaching of battery paste are: PbO + 2HCl

PbCl2 + H2O

(6)

Pb + PbO2 + 4HCl

2PbCl2 + 2H2O

(7)

PbSO4 + 2NaCl

PbCl2 + Na2SO4

(8)

The soluble impurities are precipitated with lead powder as: Pb + MeCl2

PbCl2 + Me

(9)

The PbCl2 is dissolved in HCl and fed into the cathode compartment of a diaphragm cell for lead electrowining.

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Though the PLACID process [51] and other chloride processes are attractive from environmental point of view but have not found favour because lead is recovered as a sponge and large amount of lead powder is required to reduce PbO2. A comparative view of this process with other processes is given in Table 10. A conceptual block diagram for Placid process is shown in Figure 4. Table 10: Comparision of Placid Process with other electrowinning processes Process

Electrolyte

Additive

Pb [g/L]

Purification

Cell type

Current [A/m2]

RSR

None

Simple

100-200

25-150

None

Simple

150-250

Engitec

Fluoboric acid

>500ppm As + boric acid 3-6g/L H3PO4 + 0.05g/L Bone Glue + 4g/L Lignin sulphonate Glues

70-200

USBM

Fluosilicic or fluoboric acid Fluosilicic acid

50-100

None

AAS Placid

AAS HCl Brine solution

None none

25

Composite Anode None Cascaded cementation Ion Selective Membrane

320 1200

AAS: Ammoniacal Ammonium Sulphate

Paste

Leaching

Lime

Sulphate removal

Inert residue (Gypsum)

Electrowinning

Purification

Lead Powder

Melting and Casting

99.99 Lead Ingots

Lead Cement (Bi, Cu, As, Sb)

Figure 4: Placid Process (Conceptual block diagram)

PLINT Process This process is almost similar to that of PLACID process [52, 53]. The only difference between this and the PLACID process is in the substitution of a precipitation step for electrowinning. In the subsequent kettle the lead hydroxide product is first decomposed and then reacted with hot coal to obtain pure lead. All that takes place at a temperature not higher than that required for casting and alloying. The percentage recovery and the purity of the lead

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Archana Agrawal and K. K. Sahu

produced is same as in case of PLACID process, as the leaching and purification process remains unchanged. A conceptual block diagram is depicted in Figure 5. Lime H2SO4

Paste

Leaching

Lead Precipitation

Low Temperature Smelting

Melting and Casting

Lime

Sulphate Removal

Purification 99.99 Lead Ingots

Inert residue (Gypsum)

Lead Lead Cement (Bi, Cu, As, Sb)

Figure 5: PLINT process (Conceptual Block Diagram)

Lead Pollution and Permissible Limits Lead if absorbed into the human body in significant quantity, can pose a considerable threat to health. Individuals are at risk whether exposed to a single, large emission of lead, or facing prolonged low-level exposure. Lead poisoning occurs mainly in three organ systems[54]. − − −

Red blood cells and their precursors Central and perial nervous systems Renal system

Acute lead poisoning in human causes severe damage to the kidneys, liver, brain and the central nervous system. It has also been associated with carcinogenesis, reduced fertility, miscarriages and spermatotoxicity. It causes anaemia, colic and mental disorders viz. defective memory, mental dullness, fatigue, nervousness and anxiety. Lead exposure has also been found to cause hypertension, which causes thousands of deaths. The pollution control enforcement authorities are well aware of the ill effects of various means. The pollution control laws/rules in India have the same teeth as in the developed countries. However, its implementation is the main draw back of the system. For examples the norms of emissions from the stack as well as in the ambient air are as stringent as in any developed countries. A comparative statement of the norms are given in Table 11. Emission standard for SPM recommended by Maharastra Government in 1985 is 100 mg/m3. The organised smelters, being easily identifiable, come under the close scrutiny of the authorities and

Solid Waste Management, Recent Trends and Current Practices …

145

unless they meet the stipulated standard, they are not allowed to continue with their operation. Such units have started taking some corrective measures. Table 11: Emission control standards for lead plants Lead in emissions mg/NCM

Lead in effluents mg/L

Lead in atmosphere mg/NCM

70 * 30 † 100 *

10

0.05

1.5

10

0.05

-

70

29

15

-

0.10

50

#

0.1-0.5

2.0

EEC

0.15

70

-

-

2.0

Germany

0.10

5

0.2

2.0

India

0.15

70 * 30 † 80

10

0.1

1.5

UK

0.15

10

variable

2.0

USA

0.1

variable

variable

1.5

Lead in work area, mg/NCM

Lead in blood, mg/100mL

Australia

0.15

Austria Canada

0.10 * 0.02 † 0.15

Denmark

Country

70 * 40 † 50

*

men. † women. # limit set for individual plants.

Indigenous generation secondaries are required to be recycled, otherwise the disposal/dispersal of the same will cause greater harm to environment. A range of restrictions on the collection, handling, transport and processing of spent batteries are require monitoring of their movements both domestically and internationally. Generally it is the battery components that cause the difficulties not the lead as such. Extraction procedure for toxicity assessment is designed to identify wastes that are likely to attain hazardous concentrations of the particular toxic constituents into ground water as a result of improper management such as dumping. In this procedure the wastes are leached in a manner to simulate the leaching action that occurs in the landfills. The extract is analysed to determine if it possesses certain toxic contaminants. If the concentration exceeds the regulatory levels then the waste is classified as hazardous. Some of the regulatory levels [3] of the contaminants in the leached extract are given in Table 12 as per guidelines of Environment protection Agency (EPA), USA which is accepted in India as well. It is therefore essential to test all the solid wastes from nonferrous metal industries in general and copper, zinc and lead primary and secondary units in particular, that are dumped without following proper procedure or used for land filling.

146

Archana Agrawal and K. K. Sahu Table 12: Contaminants determined in TCLP test. Sl. No.

Contaminants

EPA Hazardous Waste No.

Maximum Concentration (mg/L)

1 2 3 4 5 6 7 8

Arsenic Barium Cadmium Chromium Lead Mercury Selenium Silver

D004 D005 D006 D007 D008 D009 D010 D011

5.0 100.0 1.0 5.0 5.0 0.2 1.0 5.0

The lack of informations in open literature on TCLP test results, clearly demonstrated the level of negligence prevailing in these industries on solid metallic waste management. The solid wastes produced from the liquid effluents are no longer the safer options unless these wastes are handled and managed/processed in eco-friendly manners adopting specified procedures laid down by the pollution enforcement agencies. NML, Jamshedpur is presently involved in the characterisation of solid wastes that are generated in Indian nonferrous metal industries to assess the environmental degradation.

Basel Ban and its Implication Approximately 5 million tonnes of wastes are generated annually without a single site identified for disposal, in addition India imports close to 2 million tonnes of lead and zinc waste. The hazardous waste management and handling (HWM & H) clearly prohibit in trade of wastes for dumping and impose that only recyclable waste could be permitted after clearance from the Ministry of Environment and Forest (MoEF) and State Pollution Control Board (SPCB). But in subsequent years, the HWM&H regulations were not reflected in the import procedure and hundreds of tonnes of waste were freely imported under open general licence category (OGL). Some wastes imported were not suitable for recycling because the residues generated are toxic. Ban on import of some hazardous wastes has been imposed in order to prohibit and restrict further toxic residual waste generation. In view of the problems arising due to ambiguity in the identification or characterisation of some of the wastes being imported as raw material in the industrial process, there is a need to classify the wastes in terms of their hazardous contamination. The presence of hazardous constituents in the secondary materials invites caution while processing and disposing off the residues or wastes generated after processing/treating such materials. Between 1992 and 1998, India has been a major destination of metal wastes which actually were meant for recycling but often found its way into dumping sites. Indiscriminate imports of wastes in violation of Basel Convention and irregularities in reprocessing the wastes have had serious impacts on environment in various parts of the country. Thus Basel convention was conceived as a means of preventing dumping of hazardous waste by the developed nations in countries, which do not have the facilities to handle them safely. India being a party to the Basel convention on the control and transboundry movement

Solid Waste Management, Recent Trends and Current Practices …

147

of hazardous wastes needs to regulate the import (transboundry movement of hazardous wastes) of such wastes under this framework. India signed the Convention on 15.3.1990, ratified it on 24.6.1992. Since April 1995, only usable wastes were permitted for the imports under license for Directorate general of Foreign Trade (DGFT). In May 1997 Supreme Court of India banned import of all wastes for recycling and subsequently constituted an expert panel to study the complex issue of recycling of waste. In the mean while the pressure from industry and industrial bodies forced the Government to lift the ban on zinc ash and skimming, citing economic reasons. In December 1997, the Planning Commission recommended lifting the ban for trade on zinc ash and skimming, citing that domestic zinc production was inadequate for local needs [55]. Accordingly, HW Rules, 1989, were amended on 6.1.2000 ostensibly to improve the applicability and implementation aspects with regard to imports of hazardous waste, and to bring the Rules in line with the requirements of the Basel Convention. The provisions relating to import and export of hazardous waste for recycling have been expanded and streamlined. A time limit has been imposed for processing of applications for import. A fee for processing of import licenses has been prescribed. As per the revised HW Rules, 1989/2000, the MoEF will grant permissions to importers/exporters and must satisfy itself that the importer has environmentally friendly/appropriate technology for reprocessing; that the importer has the capability to handle and reprocess hazardous wastes in an environmentally sound manner; and that the importer has adequate facilities for treatment and disposal of wastes generated. The CPCB is now responsible for ensuring implementation of the conditions of imports and for monitoring compliance with the conditions of import. The DGFT will now issue or refuse licenses for import of hazardous wastes with reference to whether the relevant permissions have been obtained by the importer from the MoEF.

Recent Development on Secondary Zinc and Lead Processing in India Recently some R & D work for the recovery of zinc from galvaniser's ash and similar byproduct compounds obtained as waste from various industries is carried out at various Council of Scientific and Industrial Research (CSIR) Laboratories in India. The optimum conditions were established on 500A scale, for producing 10 kg of zinc per day at Central Electrochemical Research Institute (CECRI), Karaikudi and a novel method (suspension electrolysis) has been developed for the recovery of zinc. The process has been commercialized. The zinc powder obtained is suitable for the production of hydrosulphite [1]. Regional Research Laboratory (RRL) Bhubaneshwar, developed an expertise for the processing of a variety of raw materials containing zinc like complex, dirty raw materials and secondary sources like waste/by-products from various primary zinc producers by hydrometallurgical routes which consists of pre-treatment, leaching, solid-liquid separation, solution purification solvent extraction and pure zinc metal recovery by electrolysis or recovery of a pure salt like zinc sulphate or zinc oxide. A method has been developed for the production of zinc and copper from spent catalyst from fertilizer industry at Kanpur by hydrometallurgical route [56]. Another process for the recovery of zinc from brass ash containing 30.6% zinc and 7.3% copper, and zinc ash containing 78.5% zinc, 2.9% chloride and other impurities like Cu, Fe, Ni, etc. to produce high pure cathodes of zinc is established

148

Archana Agrawal and K. K. Sahu

[56]. Chloride was removed by roasting the zinc and brass ash at about 950 oC, followed by water washing and acid leaching with a leaching efficiency of 90-95%. The leach slurry is filtered and leach liquor is subjected to purification steps. In case of brass ash, copper is removed and recovered as copper powder first under controlled and optimized electrowinning conditions. The purified leach liquor is then sent for electrowinning to produce pure zinc metal. On the basis of the process know-how, M/s Panthnagar Fertilizer is producing 350 kg/day zinc and 50 kg/day copper. With the operating condition for zinc electrowinning as Zn 55-65 g/L, H2SO4 110-125 g/L, organic additive 20-30 mg/L, current density 350-400 A/m2, cell voltage 3-3.2 V, current efficiency >90%, energy consumption 3,000 kWh/ton to produce a smooth, coherent, perfect sheet which was easily strippable. A flow sheet has also been developed for zinc oxide production from zinc ash with zinc content of 60-80% along with other impurities like Fe, Cu and Pb for a private party in Kolkata. The unit operations involved are dissolution of zinc ash, purification of leach liquor, preparation of zinc hydroxide/carbonate mixture and finally zinc oxide by controlled heating of this hydroxide/carbonate. The purity of ZnO is comparable to international standard [56]. Recently the drum filter cake(DFC) generated from zinc industry(Composition SiO2: 2055%, Fe: 5-20%, Al: 5-25%, Pb: 1-5%, MnO2: 1-10%) was used to prepare frit/glaze for ceramic industry[57] at RRL Bhopal. Silica present in DFC acts as glass former and lead as a flux for glass formation. Toxic leadgets complexed in the glass matrix to make the product non hazardous. The product was tested for its toxicity following TCLP test[57]. National Metallurgical Laboratory, Jamshedpur is actively involved in developing both pyrometallurgical as well as hydrometallurgical processes to recover zinc from zinc dross/ash and other residues. There are no efficient pyro/ hydrometallurgical processes available in India to treat the zinc dross and Effluent Treatment Plant (ETP) sludges without generating solid waste for disposal. Production of zinc oxide from ash by ammoniacal route developed earlier at NML has been found to be technically competitive to the sulphuric acid route [58]. A direct electrowinning process to recover zinc as zinc powder from an alkaline electrolytic bath is being developed on laboratory scale. The process requires less number of steps and is thus expected to be energy efficient. Zinc recovery from the dross by distillation process has been developed recently at NML with 90% overall recovery, from the dross produced in the galvanising plant of TATA STEEL.[24, 59-61]. From the environmental point of view, lead recovery from battery sludge via hydrometallurgical and electrowinning processes looks attractive. But none of the abovedescribed processes have become operational and only a number of pilot plant trials have been conducted. Some processes developed are at laboratory scale only. A full-scale lead hydrometallurgical and electrowinning plant need to be operational in the coming century to build the confidence among the lead producer and to reduce environmental impacts. Use of cupola for lead recovery from battery scrap is also being developed in NML. R&D work related to the lead recovery from spent acid batteries is also being carried out at CECRI, Karaikudi. A novel direct electrochemical reduction technique has been developed for the production of lead powders from spent lead acid batteries [1]. Binani industries is setting up an integrated battery-recycling unit in Wada, Thane District of Maharashtra, which would be implemented in two phases. The first phase was planned be for the manufacture of 25,000MT of secondary lead while the second phase was for the manufacture of 125,000MT of Primary Lead with imported Lead Concentrates. The plant would be one of India's first modern lead recycling plants. ENGITEC Technologies of

Solid Waste Management, Recent Trends and Current Practices …

149

Italy will provide the technical know- how for the manufacture of lead. This technology is not only environment friendly but also has some of the best safety measure in the industry. The recycling facility will also yield sulphuric acid and polypropylene as by-products. Manufacturers of lead-acid batteries, pigments, lead oxide and submarine cables would be the main users of the lead. In order to fix the limits of toxic elements in Zinc ash/skimming an effort was made at NML, based on the data available for head analysis and TCLP tests of several samples and recommended tentative threshold limits (Table 13) of metal components in zinc ash/skimming for import/export purposes. Based on the recommendation Ministry of Environment and Forest permitted import of zinc secondaries to a number of recycling units possessing necessary processing technology and waste handling and disposal expertise/facilities, in the overall interest of the nation. Table 13: The tentative limits fixed for toxic elements in zinc ash for imports Sl. No. Components 1 Zn Cu 2 As 3 4 Cd 5 Cr 6 Pb 7 Ba Hg 8 9 Se Work done at NML for MoEF.

Percentage 60 (min.) 1.7 (max) 0.1 (max) 0.1 (max) 0.01 (max) 1.25 (max) 0.005 (max) 0.002 (max) 0.004 (max)

CONCLUSION Most of the pollution control technologies adopted today convert the pollutant from one form to other like in effluent treatment plant aqueous pollutant may be converted into solid waste which is discharged either in open or secured landfill. Both are undesirable from the land point of view, which need to be preserved for future generation. As the leachate generating from the dumping of these hazardous wastes contaminates the environment, efforts must be directed towards not only effectively monitoring and managing the environment but also developing and applying viable and acceptable ecofriendly processes and waste handling/management technologies to cater to the pollution free environmental control of even the small and medium scale industries. −

Main source of raw material for secondary zinc plants in India is imported ash/dross as they are not available Indigenously. Thus all those units having proper pollution control devices, eco-friendly process technology and legal permission from Ministry of Environment and Forest (MOEF) can import zinc bearing raw material. From environmental point of view secondary zinc recovery process is technologically

150

Archana Agrawal and K. K. Sahu

−

−

− −

−

acceptable in India. Basel ban restricted the import of zinc ash, skimmings, drosses contaminated in plenty with several toxic elements. Various processes developed indigenously for secondary raw materials are running successfully at different parts of the country. There are some processes ready for commercialization and some are in developing stage. Collection and recycling of spent acid battery is the major cause of concern, which has not been achieved to a satisfactory level as compared to developed nations. A legislation as well as appropriate monitoring are to be evolved and enforced for a systematic collection and it’s recycling in the units having eco-friendly and waste management process technologies. The slags produced from the primary and secondary lead processing industries must be disposed off to the sites as per specification/instructions laid down by the Pollution Control Boards. Development of low cost and eco-friendly technology should be encouraged in order to sustain the recycling operation, which will not only meet the increasing demand of lead but also conserve the raw materials. For battery recyclers, pollution control boards must organise awareness programmes with respect to handling, transport and recycling of battery scrap. The existing wastes generated and accumulated from various nonferrous process industries over a long period should be characterized (TCLP and water extract) for its hazardous or non-hazardous nature and a procedure has to be evolved in consultation with industry and CPCB/SPCB/different laboratories for its safe disposal. In addition to increased utilisation of solid wastes, efforts are needed towards waste minimisation by attacking the problem at its source, which not only maximise production and product quality, but also minimise the overall environmental impact by: technology upgradation/use of eco-friendly technology, improvement in the quality of raw material, audit on waste minimisation, adopting innovative management strategies, conducting employee awareness programme.

ACKNOWLEDGEMENTS Authors wish to thank the Director, NML, Jamshedpur for giving permission to publish the paper and the Ministry of Environment and Forest (MoEF), New Delhi for financial support. Thanks are also due to the management of various industries for supplying the required information.

REFERENCE [1] [2]

[3]

Raghavan, M. (2001) Secondary recovery of lead and zinc, Minerals & Metals Review, 27(2), 28-34. Sahu K. K., Agrawal A., Pandey B. D. and Premchand (2001), Secondary zinc industries in India problems and prospects., Mineral and Metals Review, 27(2), 125132. Manhan, S. E., (1994) Environmental Chemistry, 6th Edition, Lewis Publishers, Tokyo, 546.

Solid Waste Management, Recent Trends and Current Practices … [4] [5]

[6] [7]

[8] [9]

[10] [11] [12] [13] [14] [15] [16]

[17] [18] [19] [20]

[21] [22]

[23]

151

Thadani, B. C., 1996. Challenges and opportunities for Indian Lead, Mineral and Metals Review, 58-68. Sahu K. K., Agrawal A., Pandey B. D. and Premchand (2001), Secondary zinc industries in India problems and prospects., Mineral and Metals Review, 27(2), 125132. http://www.cleantechindia.com/eicimage/2102_68/LRE.htm, July 25, 2003. Zunkel, A. D. (1997)Review of electric arc furnace dust treatment processes and environmental regulations, R’ 97, Int. Congress Proc., Feb. 4-7, Geneva Switzerland, V129-V137. Reuters news services, November 4, 2003, http://www.recyclingtoday.com/news/ news.asp?ID=4890&SubCatID=74&CatID=23. Phugzhenthy, L., Indian non ferrous metals industry-an era of consolidation begins, National Seminar on non ferrous metals- Stageties for competitiveness and Globalization, NF-2005 towards global Excellance, 22-23 sept, 2005, New Delhi, pp 22-23. Bhatt Dhimant, http://blonnet.com/2004/04/07/stories/2004040700331200.htm, April 2004. Thomas, George, Binani Zinc Ltd., Kerala, 1998. Personal Communication. Sharma, S. K., Proc. on Base Metal Tech., 8-10 Feb, 1989, Jasmshedpur, 161-176. Mackenzie, John and Smith, M. R., 18-20 Nov. 1981. The application of imperial smelting process in India, Pb-Zn-Cd International Symposium, C11-C34. Sharma, R. S., HZL, Udaipur, 1998. Personal Communication. Solanki, S. and Singh, Vakil, 1981. The electrolytic zinc plant of HZL at Debari and its development, Pb-Zn-Cd International Symposium, E92 - E112. Bhatnagar, Deepak and Jancy, A., Jan. 29 - 30, 1998. Cobalt recovery from metallurgical waste of zinc industry, Environmental Waste Management, NML, Jamshedpur, 230-241. Basu, K. and Swarnkar, S. R., 7 - 9 Feb., 1990, Proc. of Hydromet.-90, Udaipur, 6.14.1 - 6.14.7. Jaju, N., Sunrise Zinc, GOA, 1998. Personal Communication. Agrawal, K. C., 17-18 Dec. 1998. National Seminar on Lead and Zinc recyclingTechnology and Environmental, New Delhi. Phugazhenthy, L., Generation and Recycling of zinc wastes from the galvanising industry- Current status and future trends, National conference on lead and zinc recycling technology 2&3 Dec., 2004, New Delhi. Siroya G L, and Ramachandran T C (2000), Zinc recycling in India- An overview, MMR, 11, 40-44. Barcza N. A., Rpbertson. D. G. C., Schoukens A.F.S., Shaw F. Denton G M., Worcester T. W. and Bailey D. J.(1995), Enviroplas technology for the recovery of lead and zinc from lead blast furnace slag". Presented at Recycling lead and zinc into the 21st Century: 6th International Conference of the International Lead and Zinc Study Group, Madrid, Spain, 18-23 June, 73-89. Schoukens A S F., Denton, G.M. and Jones, R.T., Pilot-plant production of Prime Western grade zinc from lead A.F.S blast-furnace slags using the Enviroplas process. Proceedings of the third international symposium on recycling of metals and

152

[24]

[25] [26] [27]

[28]

[29]

[30] [31] [32] [33]

[34] [35] [36] [37] [38] [39] [40] [41]

[42]

Archana Agrawal and K. K. Sahu engineered materials, Point Clear, Alabama, 12 to 15 November 1995. Publication of the Minerals, Metals and Materials Society, 1995, pp. 857-868. Premchand, D Jha and K M Godiwala, Recovery of zinc from zinc dross, National conference on lead and zinc recycling technology and environment, 2&3 Dec., 2004, New Delhi. Nogueria E. D., Regife J. M. and Arcocha A. M., winning zinc through solvent extraction and electrowinning, Engineering Mining, 180(10), 1979, 92-94. Nogueria E. D., Regife J. M. and Blythe P. M., Zincex- The Development of a Secondary Zinc Process, Chemistry and Industry(2)(1980. 63-67. Nogueria E. D., Regife J. M. and Viegas M. P., Design Features and operating experience of the Quimigal Zincex plant, Chloride Electrometallurgy, ed. P D Parker, Warrendale, PA: The metallurgical society 1982, 59-62. Martin San Lorenzo; Daniel Regife Vega; Jose M. Nogueira; Eduardo D.(1983), Process for the production of electrolytic zinc or high purity zinc salts from secondary zinc raw-materials, U S Patent 4,401,531, August 30. Lightfoot, B.W., Short, W.E. and Guorgi, G.A., EAF dust processing with Ausmelt Technology, presented to: The extraction and application of zinc and lead. Sendai, Japan, May 1995. Olper, M(1993) The EZINEX process – A new and advanced way for electrowinning zinc from a chloride solution, International – World Zinc 93, Hobart, Oct. 10-13. Olper, M (1994), The EZINEX process – Proceeding EDP Congress TMS annual meeting, San Francisco, 513-524. Cole, P. M. and Sole, K. C (2003), Zinc solvent extraction in the process industries, Mineral Processing and Extractive Metallurgy Review, 24(2), 91 – 137. Hartwell T, “Sustainability – Steel and the Environment” Int conference organized by the Institute of Materials, Minerals and Mining on 1 – 2 November, 2004 in Birmingham, UK, http://www.iza.com/zwo_org/ZincNews/ZNmenu-F-g.htm#15) Pillai Venugopal . http://www.projectsmonitor.com/detailnews.asp?newsid=7760. New lead mine opens in WA, http://www.abc.net.au/rural/content/2005/s1472012.htm, Friday, 30/09/2005. Premchand and Rakesh Kumar, National Conference on Lead & Zinc Recycling – Technology & Environment, Dec. 98, New Delhi. Behrendt, H., Umwelttechnic, M. R., & Freiberg, R’97 Congress Proceedings Vol. I, p. 34, Pub. By EMPA, Lerchenfeldstrasse 5, 9014 Saint Gall, Switzerland, 1997. Viswanathan, S. and Thamhane, A. R., National Seminar on Lead and Environment, Indian Lead Zinc Information Centre, Feb. 91, p. 69. Queneau, P. E. and Siehmund, A., (1996) Industrial scale Lead making with the QSL continuous oxygen converter, JOM, 48(4), 38-44. Mackey T.S. and Perngaman, R. D., (1990), Lead-Zinc’90, TMS-AIME, 13-38 & 453548. Sahu, K. K., Agrawal, A, Pandey, B. D. & Premchand (2000) Lead industries and Environmental Pollution in India, Proceedings of the International Conference on Environmental Management in Metallurgical Industries, Ed. R. C. Gupta, 14-16 December, Institute of technology BHU, Varanasi, 125-132. Prengaman, R. D. and McDonald, H. D., (1980), US Patent, 4229271.

Solid Waste Management, Recent Trends and Current Practices … [43] [44] [45] [46] [47] [48] [49] [50]

[51]

[52] [53] [54]

[55] [56] [57]

[58]

[59] [60] [61]

[62] [63]

153

Cole E. R., Lee A. Y., and. Paulson D. L., Electrowinning of lead from H2SiF6 solution, US pat No. 4,272,340, June 9, 1981. Olper M., CX-EW Process - A comprehensive recovery system for lead acid battery, International Pb-Zn Study group, Rome (11-13 June 1991), 79-90. Reynolds R. M., Hudson E. K., Olper M, Lead-Zinc 90, ed. T. S. Mackeyand R D Perngaman (Warreldale, PA, TMS, 1990), 1001-1022. Ginatta M V, US Patent 4451340, May 29, 1984. Moure, W. B. and Etsell T. H., US Patent 5211818 (May 18, 1993). Bratt G. C. and Pickring R. W., (1970), Production of lead via ammoniacal ammonium sulphate leaching, Met Trans, 1, 2141-2149. Spijkerman J. B. and Groenen, R. J., (1991), U.K Patent application, 91029942. San Lorenzo D. M. and Nogeuira,G. D., (1991), Hydrometallurgical Treatment of lead secondaries: The Placid process, Interntionl Lead zinc study group, Rome (11-13 June), 315-336. Frías, C., García, M. A., Díaz, G., 2000. New clean technologies to improve lead-acid batteries recycling. In: Proceedings of the Lead–Zinc'2000 symposium. TMS, Pittsburgh, 791–80 Díaz, G., Martín, D., Frías, C. and Sánchez, F., (2001) Emerging applications of ZINCEX and PLACID technologies. Journal of Metals, 53 2, 30–31. Vincent Rich, The International Lead Trade, Woodhead Publishing Ltd., UK, p. 103, 1994. Rajagopal R, Tharian. J, and Harmati. Z, EMPA St. Gallen, Switzerland, Recycling in India - Environmental and Technological Imperatives, Paper presented at the R´99 Congress (Recovery, Recycling, Re-integration), February 1.999(http://www. environmental-expert.com/articles/article428/article428.htm). Edward Worden, AMM, Dec 27, 2000, http://www.findarticles.com/cf_dls/m3MKT/ 248_108/68769276/p1/article.jhtml Narayanan, P.A.I and Mathur G. P.(1984), Zinc oxide from zinc ash/zinc hydroxide, Internal report, National Metallurgical Laboratory. Chandra N, Bhasin S, Sarkar D and Sharma M, Solid waste minimization in secondary zinc industry, National conference on lead and zinc recycling –technology and environment, 2&3 Dec., 2004, New Delhi. Basak G, Lahari R N and Sahani M J(1981), Process parameter of zinc dust production and application technology, Pb-Zn-Cd International Symposium, 18-20 Nov, New Delhi, 307-340. Lahari R N (1980), Distillation of zinc: PartI Vacuum distillation of zinc, Trans. IIM, 33(4), 322-326. Basak G(1980), Distillation of zinc: PartII Study on lead constituent in distilled zinc, Trans. IIM, 33(4), 327-328. Thangaraj T, Tenth five year plan report, Lead recycling-Trends & Development, National conference on lead and zinc recycling –technology and environment, 2&3 Dec., 2004, New Delhi. Jagannathan, V., 18-20 Nov. 1981. Lead smelting operations at HZL Vizag, Proc. on Pb-Zn-Cd, Int. Symp., E50 - E72. Mukherjee, P., 18-20 Nov. 1981. Lead smelting operations at HZL Tundoo, Proceedings on Pb-Zn-Cd, Int. Symp., E1-12.

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 155-195 © 2006 Nova Science Publishers, Inc.

Chapter 5

RECYCLING OF WASTES (AGRICULTURAL RESIDUES AND USED TIRES) FOR ACTIVATED CARBON PRODUCTION A. A. Zabaniotou∗ Department of Chemical Engineering, Aristotle University of Thessaloniki Thessaloniki, Greece

ABSTRACT A review of the production of activated carbons from wastes, such as agricultural and used tires, by using atmospheric pyrolysis, is presented. Pyrolysis of waste is a CO2neutral process and can transform biomass to energy and materials. It is a possible way for chemical recycling of the organic matter. This study evaluates pyrolysis of olive kernels, olive wood, and cotton ginning waste and used tires, by studying the effect of temperature on the pyrolysis product yields and investigates production of activated carbon from pyrolytic char. A comparison in characteristics and uses of activated carbons from agricultural residues and tires with commercial carbons have been made.

Keywords: Pyrolysis; Activation; Agricultural residues; Used tires; Activated carbon

INTRODUCTION Agricultural waste is a form of biomass, which is readily available but not largely utilized in recovery schemes. Over the past decade, the biomass utilization field has been driven largely in response to oil supply disruptions and the challenge of meeting the Kyoto agreement on global warming. Biomass can play a dual role in greenhouse gas mitigation,

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both as an energy source to substitute fossil fuels and as a carbon sink. Biomass products are sustainable. The green plants from which biomass products are derived fix carbon dioxide as they grow, so their use does not add to the levels of atmospheric carbon. In addition, using residues/refuse as a source for energy and materials avoids polluting landfill disposal or combustion gases. Agricultural residues are among the major EU energy resources [1]. The potential of the available biomass in the form of agricultural wastes is sufficient for the supply of a big percentage of the energy demands regarding production, and have proved to be promising raw materials for the production of activated carbons [2, 3]. Literature survey indicates that there have been many attempts to obtain low-cost activated carbon or adsorbent from agricultural wastes such as wheat [4], corn straw [4], miscanthus [5, 20], sunflower shell [6], pinecone [6], rapeseed [6, 12], cotton residues [6, 10, 89], olive residues [5, 6, 20, 29, 30, 31, 32, 33, 34, 55,], almond shells [2, 22, 24], peach stones [9], grape seeds [2], straw [5, 11, 20], oat hulls [8, 13], corn stover [8, 13], apricot stones [2, 22], cherry stones [2], peanut hull [28], nut shells [2, 16, 17, 18, 23], rice hulls [21], corn cob [9 ,14, 15, 19] corn hulls [13], hazelnut shells [22], pecan shells [21], rice husks [26, 28] and rice straw [21, 25]. Agricultural residues are difficult and expensive to collect but they are available and at a low price [1]. Pyrolysis is one form of energy and material recovery process, which has the potential to generate char, oil and gas product [10]. Because of the thermal treatment, which removes the moisture and the volatile matter contents of the biomass, the remaining solid char shows different properties than the parent biomass materials. These changes in the properties usually lead to high reactivity, and hence, an alternative usage of char as an adsorbent material becomes possible [10]. Pyrolysis of the above residues, under a non-oxidizing atmosphere or gasification in-situ with energy or alternative fuels production could be a solution to the environmental problem that landfilling or combustion could create and furthermore, can establish a new approach for a more efficient utilization of biomass and wastes [3]. Fuels derived from biomass contain less sulfur. Pyrolysis, offers an environmentally attractive method of reducing the waste. Properly designed systems using local biomass can also reduce other atmospheric pollutants, and thus improve local air quality. Using residues will also improve the local environment; while in the same time can generate jobs, and improve rural economies and help maintain agriculture. Unlike incineration, the pyrolysis process does not lead to air emissions given that everything takes place within a closed system. One exception is the produced gas, which is mainly composed of methane and hydrogen and can be used in power production on site, or be burned in nearby boiler plants. Unwanted gasses, like SOx and NOx, are not developed in the pyrolysis process because the process is carried out without oxygen [31, 32, 33, 37]. The solid product of pyrolysis, named char, can be activated and produce active carbon, a high value added product. With the parallel use of char as feedstock for material production, the shorter term targets set out in the White Paper of EU could be reached; because optimization of use of the agricultural residues can be achieved and cost –effective integrated approaches can be developed. The char is an attractive by-product, with applications including soil amendments and production of activated carbons, which is useful as a sorbent for air pollution control as well ∗

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as for wastewater treatment [8] and concern many industries as diverse as food and beverage processing, chemical, petroleum, mining, nuclear, automobile and vacuum manufacturing [35]. In fact, activated carbon has some of the strongest physical adsorption properties of any material even known [36] because of the highly microporous form with both high internal surface area and porosity. They often serve as catalysts and catalyst supports [9]. They are widely used for the removal of toxic pollutants from fossil-fuel-fired power plants, storage of alternative fuels such as natural gas in vehicles, and the removal of volatile organic compounds from industrial gas streams were [35].

Olive Residues In Mediterranean basin countries olive cultivation is a typical activity. However, residues from olive plantations are hardly used as a renewable energy source. As pointed out in the literature [29, 30, 31, 32, 33, 34, 93] only few studies have dealt with olive residues, although olive residues could be a source for fuels, energy generation and activated carbon production. Proper management and exploitation of this potential could lead to economically profitable approximations and solutions for the agricultural industry Using residues will also improve the local environment; while in the same time can generate jobs, and improve rural economies and help maintain agriculture [1].

Cotton Ginning Wastes Waste management is a significant problem facing the cotton ginning industry. The ginning of one lint bale (227 kg) of spindle harvested seed cotton generates between 37kg and 147 kg of waste. The disposal of wastes associated with the processing of cotton is posing increasing problems. Traditional disposal methods, such as open-air incineration and landfilling are no longer adequate due to increasing environmental concerns. About 17.1 million bales of cotton were ginned in the United States [48] and the estimated cotton gin waste was 2.25Χ109 kg. Cotton gin waste (CGW) consists of sticks, leaves, burs, soil particles, mote, cotton lint, and other plant materials [49]. Slight differences in the proportions of the components are usually found between varying mechanical harvest methods .The traditional methods of CGW disposal include incineration, landfilling, and incorporation into the soil. The most recent directives further restrict particulate matter discharge into the atmosphere, thus eliminating incineration as an option for small cotton gins. Furthermore, because of the high ash content of the feedstock, there could be potential slagging problems associated with large-scale incineration. Landfilling is not a viable option because tipping fees are very high. The current method of choice is the incorporation of the waste into the soil, an option that is unsuitable for the climatic conditions of some countries. There is much concern over the presence of weed seeds, insect infestations, diseases, and excess chemicals in the waste that may degrade the receiving land. The conversion of CGW to value-added products has not been extensively studied. Brink [50] and Beck and Clements [51] studied the conversion of CGW to ethanol and concluded that 142.8lt ethanol per tonne could be produced from this feedstock.

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Cotton gin waste was collected from a cotton ginning plant in Virginia and characterized before and after steam explosion to evaluate its potential applications for higher value products such as ethanol by [92]. Griffin [52] and Schacht and LePori [49] analyzed cotton gin waste to assess its fuel value for combustion. These researchers proposed using the feedstock for the production of char, hydrogen, protein, and pyrolysis gases. Parnell et al. [53] investigated the gasification of cotton gin waste in a fluidized bed reactor. The gas produced had a low heating value and the projected net revenue from the process was very low. However, activated carbon produced from the gasification of the feedstock was found to be cheaper, but less effective than those produced from conventional carbon sources [54].

Used Tires Another abundant worldwide waste is used tires. Recently because of environmental lows and because used tires are in enormous supply, they have been the object of study by chemical and environmental engineers. It would seem that any step in the direction of economical utilization of an otherwise disagreeable waste material is a positive contribution to the protection of the environment. Potential commercial applications of tire-derived activated carbons for the removal of toxic pollutants from fossil-fuel-fired power plants, storage of alternative fuels such as natural gas in vehicles, and the removal of volatile organic compounds from industrial gas streams were studied by researchers [36]. Used tires represent a considerable quantity of solid wastes. Traditional disposal methods such as open-air incineration and landfilling are no longer adequate to increasing environmental concerns. Because used tires contain appreciable energy content, thermal treatment is considered an interesting disposal solution. Potential reuse of the polymeric contents of tires has received considerable attention. Processes have been evaluated for production of goods such as construction fillers; however, fillers and other reclamation applications have shown relatively small economic potential. Among the thermal treatment processes, pyrolysis has received increasing interest, as an alternative method to obtain raw materials and fuels [38]. Pyrolysis might be used for char production. The solid char may be used either as smokeless fuel, carbon black or for preparation of activated carbon. One of the alternative recovery methods applied of used tires is the Energy recovery in process/incineration plant: This treatment cannot really be characterized as recycling, but is the exploitation of the energy within the rubber mass. Energy recovery is recognized as equal to material recycling in the waste management hierarchy. Incineration solves a waste problem and reuses the waste as energy. However, advanced cleaning technology/filters is required to satisfy emissions to air requirements. The cement industry is today the largest recipient of used car tires, and it has become somewhat common to use automobile tires as a replacement for some of the coal in cement kilns [38]. Another alternative method is the Retreading which is a reuse and should be a proper method of taking care of resources. The life span for the tire cores would be doubled at minimum, and the total waste volume would be reduced. The retreading process, however, leads to rubber waste in the form of powder, and the retreaded tires will eventually return as waste. For this reason, retreading cannot be considered a final solution to the problem [38].

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Grinding to Powder/Granules is a method of transforming the tires into a saleable raw material. A possible market for this material can also be created, for example as an additive to road surfaces. From an environmental perspective, this use of rubber powder is not ideal, given that wear will eventually cause the rubber to spread uncontrollably into nature, although this problem is most likely small in comparison to the total spreading of asphalt dust. It is also possible to find other uses for rubber powder and granules as raw materials. The economics of these other uses is uncertain [38]. The process of interest is the pyrolysis of tires to produce liquid hydrocarbons and gases with high calorific values. Pyrolysis has studied by others researchers and data have been reported in the international literature [38, 39, 40, 41, 42, 43, 44]. Pyrolysis yields solid char residues which generally contain higher amounts of elemental carbon than the original tires. Most studies on conversion of tire char to activated carbon rely on further pyrolysis at 600850ºC under nitrogen atmosphere followed by activation with acid for reaction with superheated steam. All of the processes are energy intensive. Since tires are made mostly of rubber, the re-use of their carbon content in the form of activated carbon can be very rewarding. This form of carbon is a commercially important adsorbent of noxious materials in (for example) flue gases and/or waste steam. In adsorbing these toxics, carbon attaches them more or less firmly to its highly porous surfaces, which are very large. When the carbon is removed from the system it takes the impurity with it. Typical adsorbates are acetone, trichloroethane, and compounds of mercury. All are toxic in some degree and any or all may be found in flue gases from power plants. But tires are anything but biodegradable: they are designed and built to resist the ravages of the environment. As a result these piles of discarded tires remain year after year to spoil the appearance of the countryside. Any substantial new use for old tires can reduce and perhaps eliminate at least one source of pollution and marring of the landscape [45]. To reduce the negative environmental impacts by tires disposal in landiffils or by incineration, pyrolysis could be applied. Unlike incineration, the tires pyrolysis process does not lead to air emissions given that everything takes place within a closed system. One exception is the produced gas, which is mainly composed of methane and hydrogen and can be used in power production on site, or be burned in nearby boiler plants. Unwanted gasses, like SOx and NOx, are not developed in the pyrolysis process because the process is carried out without oxygen. Nevertheless, tires contain a significant amount of sulfur from vulcanization; however, after treatment, the majority of the sulfur remains as solid sulfides together with the carbon. The sulfides can be separated out through acid washing. Because the process allows for accurate control of temperatures in all phases, the resulting carbon will be of high and controllable quality. It can be further refined to a standard trading commodity with high market value [39, 40, 46, 47]. Because old tires are in enormous supply, they have been the object of study for some time by chemical and environmental engineers and associations [91]. Their most recent publications of research results, supported by both public and private funds, describes the direct production of activated carbon from waste tires by a relatively simple process, and shows that it is "within the ball park" as an effective adsorbent when compared with carbon from standard commercial sources [45]. The absorbency of the carbon was measured and found to be generally about half that of commercially available activated carbons [45]. In view of the extremely low cost of the discarded rubber, the economics of the process seem promising in competition with the

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standard commercial types. It would seem that any step in the direction of economical utilization of an otherwise disagreeable waste material is a positive contribution to the protection of the environment. Potential commercial applications of tire-derived activated carbons for the removal of toxic pollutants from fossil-fuel-fired power plants, storage of alternative fuels such as natural gas in vehicles, and the removal of volatile organic compounds from industrial gas streams were studied by the researchers. In these tests, the performance of the tire-activated carbon was comparable or superior to some commercial carbons. The present study reviews the current state of the production and characterization of activated carbons from agricultural wastes and used tires by using pyrolysis under atmospheric condition, as the recycling method. The aim of this study is to investigate the conversion of some of these abundant wastes, into high-quality activated carbons, under atmospheric conditions, that might be commercially viable. The experimental work, described in the present paper, includes: a) experimental and analytical work on pyrolysis, activation and characterisation of the carbons in laboratory scale and b) evaluation of findings and comparison of results with commercial active carbons.

USES OF ACTIVATED CHAR Activated carbons find application in processes both in the gas and liquid phase and their pore structure must be determined by combining gas and liquid-phase adsorption. Further the two methods give complementary information on porosity configuration. Therefore characterization of activated carbons has been mainly focused on determinations of surface area and pore size distribution by N2 adsorption at 77 K and adsorption of methylene blue from aqueous solutions. [55] Activated charcoal has been in use for centuries as an air/water purifier, health supplement and chemical 'scrubber', in fact activated carbon has some of the strongest physical adsorption properties of any material even known. Activated charcoal, also known as 'activated carbon' is made by burning hardwood, nutshells, coconut husks, animal cones and/or other carbonaceous materials. The charcoal becomes 'activated' by heating it with steam to high temperature levels in the absence of oxygen. This removes any non-carbon elements and produces a porous internal microstructure with an extremely high surface area. A single gram of a high quality activated charcoal can have 400 - 2000 m2 of surface area, 98% of which is internal. The actual active surface area, characteristics and performance of a particular activated carbon source depends largely on the nature of the material it was manufactured from and the process by which it was 'activated'. It is this huge surface area of activated charcoal where the unwanted molecules are adsorbed and trapped. Adsorption means the impurities in the air are attached to the surface of the activated carbon by a chemical attraction. When certain chemicals pass next to the carbon surface they attach to the surface and are trapped. Absorption is incorporation into the carbon's structure through pores, this occurs before the process of adsorption. Activated carbon can adsorb an extremely wide spectrum of adsorbates. This is because activated carbon has different types and/or sizes of pores within its internal structure.

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Activated carbon manufactured from coconut husk [87], has one of the largest activated surface areas combined with a high percentage of micro pores in the size range 5 - 10 Ao (Angstoms), making it ideal for removal of odorous compounds, gases from volatile organic compounds (VOCs), and gases of a low molecular weight. Removal of gases, originating from volatile organic compounds, is important in many different situations, as these come from organic chemicals that have a high vapor pressure and easily form vapors at normal temperatures. Many industrial and consumer products ranging from office supplies, building materials and in particular many plants, trees and micro-organisms such as bacteria, produce volatile organic compounds and activated carbon is the most effective way of removing these from the air. For this reason activated charcoal manufactured from coconut husk is used in a wide range of air purification systems from fume hoods, respirators, gas masks, cooker hoods and air purifiers for indoor gardening. Where indoor air quality is being compromised by odors and gases from volatile organic compounds, air filtration with coconut husk activated carbon is the safest and most effective way of dealing with the problem [87].

CHARACTERISTICS OF WASTES Agricultural residues are produced in huge amounts worldwide, their proximate and ultimate analysis are presented in Table 1 and 2. However, the composition of those materials differs significantly from woody biomass composition and the difference in gas composition would be due to the difference in the component composition of the feedstock. Therefore, fundamental search regarding the effects their composition on active carbon production is important in attempts to obtain a desirable product. It is imperative to have pre-normative research in order to investigate the influence of their composition on the products. Table 1. Agricultural residues availability, proximate and ultimate analysis Agricultural Wastes

Olive tree prunings Cotton stalks Durum wheat straw Corn stalks Soft wheat straw Vineyward prunings Corn cobs Sugar beet leaves Barley straw Rice straw Peach tree prunings Almond tree prunings Oats straw Sunflower straw Cherry tree prunings Apricot tree prunings

Moisture (%ww) 7,1 6 40 0 15 40 7,1 75 15 25 40 40 15 40 40 40

Ash (%ww) 4,75 13,3 n.a 6,4 13,7 3,8 5,34 4,8 4,9 13,4 1 n.a 4,9 3 1 0,2

Volatiles C H O N S HHV (%ww) (%ww,) (%ww) (%ww) (%ww) (%ww) (Kcal/Kg) n.a 49,9 6 43,4 0,7 4500 n.a 41,23 5,03 34 2,63 0 3772 n.a n.a n.a n.a n.a n.a 4278 n.a 45,53 6,15 41,11 0,78 0,13 4253 69,8 n.a n.a n.a n.a n.a 4278 n.a 47,6 5,6 41,1 1,8 0,08 4011 n.a 46,3 5,6 42,19 0,57 0 4300 n.a 44,5 5,9 42,8 1,84 0,13 4230 n.a 46,8 5,53 41,9 0,41 0,06 4489 69,3 41,8 4,63 36,6 0,7 0,08 2900 79,1 53 5,9 39,1 0,32 0,05 4500 n.a n.a n.a n.a n.a n.a 4398 n.a 46 5,91 43,5 1,13 0,015 4321 n.a 52,9 6,58 35,9 1,38 0,15 4971 84,2 n.a n.a n.a n.a n.a 5198 80,4 51,4 6,29 41,2 0,8 0,1 4971

The nature and characteristics of the feedstock plays an important role in the design of a thermochemical conversion system. The main characteristics concerning the applicability of

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various wastes in the thermochemical processes are the ash content, density, and particle size. For example, cotton gin waste has different characteristics than other types of biomass examined up to now and therefore research on the waste composition and product yields is necessary in order to avoid operational problems. Table 2. Literature review of agricultural residues pyrolysis for active carbons production Agricultural Residue Wheat Corn straw Corn cob Corn hulls Corn stover Olive residues and olive kernel Straw Birch Sugarcane bagasse Miscanthus Sunflower shell Pinecones Radiata Pine Rapeseed residue Cotton residues Eucalyprus Apricot stones Cherry stones Grapeseeds Nut shells Pistachio shells Macademia nut shells Hazelnut shells Peanut hulls Almond shells Oat hulls Oak Rice straw Rice husks Pecan shells Casava peel

Particle Size (µm ) 100 100 119 – 200 n.a n.a. 125 – 250 597 n.a. 100 – 200 n.a. 250 250 100 - 200 250 n.a. 100 - 200 20 - 125 20 – 100 20 - 100 20 – 100 200 - 280 212 - 300 100 - 125 20 - 200 100 10 – 20 ,12-40 mesh -//-

Reference 1 1 7,3,14 11 6,11 2,12,20 2,9,20 2,20 2,4,20,21 2,20 3 3 4 3 3,8 4 5, 22 5 5 15, 17 16 16 18 5,22,23,24 6 11 21 21,26,28 21 51

Cotton gin waste physical properties (density, particle size and shape, ash content) and heating value indicate that it is different from other biomass residues, especially wood therefore much more attention is needed in the design of the conversion process. Cotton gin waste is very loose compared to other biomass material. Its bulk density is about 25 kg/m3, which is even lighter than the straw waste (40-50 kg/m3), [57]. This could influence the steady steadiness of the operation of the reactor in the thermochemical conversion. If

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gasification is used as method for valorization, it is important to have steady state conditions. Due to the nature of the material, it may be difficult to have smooth fluidization operation and hence smooth continuous operation of the reactor. Cotton gin waste particle size and shape are not uniform. This might pose another operation problem of the gasifier. The ash content of the cotton gin is rather high (15wt. %), much higher than wood residues (Table 10). Therefore direct combustion of cotton gin wastes for a boiler operation will not be usually satisfactory, leading to severe ash fouling, intensified slogging and corrosion, necessitating frequent maintenance. Used tires are another type of solid wastes. Tires may be composed of various rubbers, such as natural rubber (NR), butyl rubber (BR) or styrene - butadiene rubber (SBR) [46]. The most commonly used tire rubber is styrene - butadiene copolymer (SBR), containing about 25 wt% styrene [47]. A typical composition for tire rubber is shown in Table 3. In Figure 1 all possible alternatives uses of used tires pyrolysis products is presented. Table 3. Typical tire composition Component

Wt% 62.1 31.0 1.9 1.9 1.2 1.1 0.7 99.9

SBR Carbon Black Extender Oil Zinc Oxide Stearic Acid Sulphur Accelerator Total

GAS

USED USED TYRES TYRES

PYROLYSIS PYROLYSIS

OIL

RECYCLE TO RUBBER MATERIALS PRODUCTION (Fenders, footgear, belts)

BOILER FUEL

ACTIVE CARBON (Water purification, Air purification, Special applications etc.)

CHAR

SOLID FUEL Co-combustion With other Solid fuel

GASIFICATION

BOILER FUEL Steam, CO2 SYN-CAS Raw materials for the Chemical Industry

Steam, CO2

Figure 1. Alternatives uses of used tires pyrolysis products.

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PROCESS LITERATURE OVERVIEW Pyrolysis Bibliographic survey has revealed many papers dealing with all kind of agricultural residues pyrolysis. Tables 4(a-q) present some pyrolysis and activating conditions for the production of carbons from agricultural residues. Pyrolysis temperature has the most significant effect - followed by pyrolysis heating rate, the nitrogen flow rate and then finally the pyrolysis residence time. Generally, increasing pyrolysis temperature reduces yields of both chars. According to Ayse E. Putun et.al., [10], increased temperature leads to a decreased yield of solid and an increased yield of liquid and gases. As the temperature is raised, there is a rise in ash and fixed carbon percentage and there is a decrease in volatile matter. Consequently, higher temperature yields charcoals of greater quality. The decrease in the char yield with increasing temperature could either be due to greater primary decomposition of biomass at higher temperatures or through secondary decomposition of char residue. The secondary decomposition of the char at higher temperatures may also give some non condensable gaseous products, which also contributes to the increase in gas yield, which is parallel to the increase in temperature of pyrolysis. Indeed, as the temperatures of primary degradation are increased or the residence times of primary vapours inside the cracked particle has to stay shorter, the char yields decrease [10]. Temperature also has studied of W. T. Tsai et.al. [9, 14]; it was noticed that char yield decreases with temperature, for preparation of activated carbons with chemical activation (ZnCl2), where. Corn stover with oat hulls for char production by Thermogravimetric analysis (TGA), was studied by M. Fan et.al., [8]. There was no pre-treatment prior to fast pyrolysis that was held in a nitrogen fluidized bed reactor. Table 4h presents details about pyrolysis conditions. More details about TGA conditions are presented in Table 4i. [8]. T.Zhang at al. [13], studied oak wood wastes, corn hulls and corn stover carbonization in a fluidized bed reactor at 500oC, Table 4j. In the study of H. Haykiri-Acma et.al [6]., TGA analysis was used to pyrolyse and then gasify chars obtained from sunflower shell, pinecone, rapeseed, cotton and olive residues pyrolysis, Table 4b. Obtained chars were heated in order to gasify under steam and nitrogen atmosphere and in equal volumetric ratio. For pinus radiate, eucalyptus maculate and sugar cane bagasse, atmospheric reactivity measurements were performed under isothermal conditions, using a thermogravimetric analyser [7], Table 4k. Sugarcane bagasse, rice hulls, rice straw, and pecan shells were also studied, [21], Table 4l. Table 4a. Olive, straw, birch, bagasse and miscanthus pyrolysis and activation conditions [5, 20] (one-step process). Activation conditions, T(oC/ h) 750/2 (10oC/min)

Activating agent steam/CO2

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Table 4b. Pyrolysis -TGA analysis conditions for sunflower shell, pinecoke, rapeseed, cotton and olive residues [6] (gasification up to 1000oC after pyrolysing). Feed rate (mg)

Gas flowrate (s)

Duration (hr)

n.a.

N2 / 40 ml/min

1,5

Temperature PROGRAMME Tambient – 1000 oC

Table 4c. Pyrolysis and activation conditions of apricot stones, [2, 22] (one-step process). References [2] [22]

Temperature / duration (oC/ h) Activating agent 800/ 1h steam 800/1h chemical (ZnCl2)

Table 4d. Pyrolysis and activation conditions of cherry stones, grape seeds and nutshells, [2] (one-step process).

Temperature / duration (oC/ h) 800/ 1h (15oC/min)

Activating agent steam

Table 4e. Pyrolysis and activation conditions of Pistachio-nutshells, Hazelnut shell and Macadamia nutshell, [16, 17, 18, 22]. References Raw material

[16] [18] [17]

[22]

Charring conditions Activation Activating (oC/ h) carbonization conditions (oC/ h) agent o Pistachio-nut 500/2 (10 C/min) 900/ 30min physical CO2 shells (10oC/min) Pistachio-nut 500/2 800/2.5 (10oC/min) physical CO2 shells Macadamia 1h 500 chemical nutshell (ZnCl2) 1h 800 chemical (KOH) Hazelnut shell 750/10 chemical (ZnCl2)

Table 4f. Pyrolysis and activation conditions of peanut hulls, [28]. Charring conditions (oC/ h) carbonization 500/2 -

Activation conditions (oC/ h) 700-900 600/2 300-750/6 500-700/3 500/3-6

Activating agent physical pure steam chemical (ZnCl2) chemical (KOH) chemical (H3PO4)

Additional information two-step process one-step process one-step process one-step process one-step process

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A. A. Zabaniotou Table 4g. Pyrolysis and activation conditions of almond shells, [2, 22, 23, 24].

References

Charring conditions (oC/ h) carbonization

[22] [23]

n.a.

[2]

800/ 1h (15oC/min)

[24]

400/1

Activation Activating conditions (oC/ h) agent 750/10 chemical (ZnCl2) n.a. chemical (H3PO4) 800/ 1h steam

Additional information

one-step pyrolysis/activation physical different samples (either with CO2 or N2)

850/1

Table 4h. Pyrolysis conditions for corn stover with oat hulls [8] Pyrolysis Temperature (oC) 500

Residence time (s) 1,5

Particle size (µm) <100

Table 4i. TGA analysis conditions for corn stover with oat hulls [8] Feed rate (mg)

25

Gas flowrate (s) N2 / 30 ml/min

Duration (hr) 0,5

Temperature programme Tambient – 750 oC (20 oC/min)

Table 4j. Pyrolysis TGA analysis conditions for oak, corn stover and hulls [13] Feed rate (Kg/hr)

Gas flowrate (ml/min) N2 / n.a.

7

Temperature (oC) 500

Table 4k. Pyrolysis-TGA conditions for pinus radiate, eycalyptus maculate and sugarcane bagasse [21] Temperature (oC)

n.a

Gas flowrate (s)

Duration (hr)

N2 / 15 ml/min

n.a

Temperature programme 40oC/min Isothermic

Table 4l. Pyrolysis conditions for Sugarcane bagasse, rice hulls and pecan shells, [6, 21] Temperature (oC) 750

Gas flowrate (ml/min)

Duration (hr)

N2 / n.a

1

Temperature programme n.a.

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Table 4m. Pyrolysis and activation conditions for corn cob, [9, 14, 15, 19] Ref.

[9]

Charring conditions Activation (oC/ h) carbonization conditions (oC/ h) 400-800 -

[14]

[15]

500/0.5h soak.time

-

500/2h soak.time

-

700/0.5h soak.time

-

700/2h soak.time

-

800/0.5h soak.time

-

800/2h soak.time

-

500-800/1h soak. time

-

500-800/1h soak. time

-

500/2

850/1 500/2

[19]

600-700/2

Activating Additional information agent chemical the impregnation ratio flactuates 20-175%wt (ZnCl2) chemical carbonization and activation are carried out simultaneously, (ZnCl2) optimal soaking time and temperature, impregnation ratio 175wt% chemical carbonization and activation are (ZnCl2) carried out simultaneously chemical carbonization and activation are (ZnCl2) carried out simultaneously chemical carbonization and activation are (ZnCl2) carried out simultaneously chemical carbonization and activation are (ZnCl2) carried out simultaneously chemical carbonization and activation are (ZnCl2) carried out simultaneously chemical chemical and physical (KOH) activation chemical chemical and physical (K2CO3) activation steam physical activation/ two-steps chemical chemical activation (H3PO4) pure steam steam- pyrolyzed/one-step scheme

Table 4n. Pyrolysis and activation conditions for olive kernel, [55] with KOH. Charring conditions (oC/ h) carbonization 800 / 1

Activation conditions (oC/ h) 800 / 1 800 / 2 900 / 1 900 / 2

Burn-off (%)

24 28 35 41

Table 4o. Pyrolysis and activation conditions for rice straw, [21, 25]. References

[25]

[21]

Charring conditions (oC/ Activation conditions h) carbonization (oC/ h) 700-1000/1 (10oC/min) 900 500-900/1(10oC/min)

750/1

900/4and20

Activating agent KOH chemical (KOH) CO2/N2

Additional information two-stage method one-stage method

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A. A. Zabaniotou Table 4p. Pyrolysis and activation conditions for rice husk, [26, 27].

References [26] [27]

Charring conditions Activation Activating (oC/ h) carbonization conditions (oC/ h) agent 400/1 600/1 steam activation n.a. 600/3 ZnCl2/CO2

Additional information

different salt solutions/CO2 partcipated to the activation method

Table 4q. Pyrolysis and activation conditions for pecan shells, [21, 23]. References

[21] [23]

Charring conditions (oC/ h) carbonization 700-800/1

Activation conditions (oC/ h) 800/2-8 450/1

n.a. n.a.

Activating agent

physical chemical chemical (H3PO4) steam

Activation Activated carbons can be produced either by physical or chemical routes. The former involves two steps: carbonization of the raw material followed by controlled gasification in a stream of oxidizing agent such as steam, CO2, or air. The chemical route consists in impregnating the carbonaceous precursor with a chemical reagent (mostly H3PO4 and ZnCl2) and heating. The current tendency is to abandon ZnCl2 due to environmental concerns and use H3PO4. During the 1970’s and 1980’s chemical activation of coals, coke and charcoal by KOH was reported [58, 59, 79]. In the 1990’s work on KOH and other potassium compounds activation was extended to other materials such as anthracites [60], resins [61], agricultural wastes included [62,63]. Table 5. Types of activation Activation Physical

Steps of process Reference two-steps 6, 13, 16, 18, 19, 21, 24, 25, 26, 28

Chemical

one-step

SteamPyrolysis

one-step

Material Pistachio-nutshells, sunflower shells, pinecone, rapeseed, cotton residues, olive residues, peanut hulls, almond shells, oak, corn hulls, corn stover, rice straw, rice husk, rice hulls, pecan shells, sugarcane bagasse 9, 14, 15, 17, 19, 22, Corn cob, olive kernels, rice husks, rice straw, 23, 25, 27, 28, 55, cassava peel, pecan shells, Macadamia nutshells, 64 hazelnut shells, peanut hulls, apricot stones, almond shells 2, 5, 8, 19, 20, 28 Olive, straw, birch, bagasse, miscanthus, peanut hulls, corn stover, apricot stones, cherry stones, grape seeds, nutshells, almond shells, oat hulls

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Basically, there are two main steps for the preparation and manufacture of activated carbon: the carbonization of the carbonaceous raw material below 800oC, in the absence of oxygen, and the activation of the carbonized product (char), which is either physical or chemical. The types of activation are represented in Table 5.

Physical Activation Physical activation is a two-step process. It involves carbonization of a carbonaceous material followed by the activation of the resulting char at elevated temperature in the presence of suitable oxidizing gases such as carbon dioxide, steam, air or their mixtures, as it can be seen in Table 6. The activation gas is usually CO2, since it is clean, easily to handle and it facilitates control of the activation process due to the slow reaction rate at temperatures around 800oC [13]. Rice husk, corn cob, oak, corn hulls, corn stover, rice straw, rice hulls, pecan shells, peanut hulls and almond shells, [6, 13, 16, 18, 19, 21, 24, 25, 26, 27], were the raw materials studied by this method. Carbonization temperature range between 400-850oC, and sometimes reaches 1000oC, and activation temperature range between 600-900oC. Table 6. Physical activation Activating agent Steam CO2

Reference

Material

6, 19, 26

rice husk, corn cob, sunflower shells, pinecone, rapeseed, cotton residues, olive residues 13, 16, 18, 21 oak, corn hulls, corn stover, rice straw, rice hulls, pecan shells, Pistachio nutshells, sugarcane bagasse, 24, 28 peanut hulls, almond shells,

Physical activation of oak, corn hulls and corn stover chars, [13], was performed at temperatures of 700 and 800oC and durations of 1 and 2h. For oak, the longer the activation duration, the greater the adsorption capacity of the resultant activated carbons, and vice-versa for the corn hulls and corn stover. Apparently, the activation durations of 1 and 2h did not appreciably affect the properties of activated carbons from oak at 700oC. In contrast, the surface areas, total pore volume, and pore volume of activated carbon obtained upon 1h of activation were much less than those upon 2h of activation at 800oC. Obviously, the pore structure of carbons from oak altered substantially for different durations of activation at 800oC. The surface areas and pore volumes of activated carbons from chars generated from corn hulls as well as from corn stover were appreciably greater after 1h of activation than after 2h of activation. This is in sharp contrast to the results from the activation of char from oak. Plausibly, in activating the chars from both corn hulls and corn stover, the rate of pore structure formation exceeded that of the destruction due to the pore enlargement and collapse at the earlier stage and vice versa at the later stage. A more thorough research for corn cobs was made by Abdel-Nasser et.al.[19]. The char was carbonized at 500oC, then soaked for 2h, and steam-activated at 850oC in a flow of steam/N2, for 1h. There is also an additional one-step treatment route, denoted as steam-pyrolysis, (see Table 7) as reported [2, 5, 8, 19, 20, 28], where the raw agricultural residue is either heated at moderate temperatures (500-700oC) under a flow of pure steam, or heated at 700-800oC under a flow of just steam. The residues studied with this method were olive, straw, birch, bagasse,

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miscanthus, apricot stones, cherry stones, grape seeds, nutshells, almond shells, oat hulls, corn stover, and peanut hulls. The samples in the study of Minkova V. et.al., [5], were heated with a heating rate of 10oC/min to a final temperature of 700oC, 750oC or 800oC and kept 1 or 2h at this temperature in the flow of steam, while the final carbonization temperature in the study of Savova D. et.al., 2001, [2] was 800oC for 1h. Table 7. Steam-Pyrolysis activation in one-step process

Steam Pure steam

Reference

Material

2,5,8,20

Olive, straw, birch, bagasse, miscanthus, apricot stones, cherry stones, grape seeds, nutshells, almond shells, oat hulls, corn stover, peanut hulls, corn cob

19, 28

Chemical Activation In the chemical activation process the two steps are carried out simultaneously, with the precursor being mixed with chemical activating agents, as dehydrating agents and oxidants. Chemical activation offers several advantages since it is carried out in a single step, combining carbonization and activation, performed at lower temperatures and therefore resulting in the development of a better porous structure, although the environmental concerns of using chemical agents for activation could be developed. Besides, part of the added chemicals (such as zinc salts and phosphoric acid), can be easily recovered [9, 13, 14]. However, a two-step process (an admixed method of physical and chemical processes) can be applied [25], Table 8. Chemical activation was used in most of the studies for corn cob, olive seeds, rice husks, rice straw, cassava peel, pecan shells, Macadamia nutshells, hazelnut shells, peanut hulls, apricot stones, almond shells [9, 14, 15, 17, 19, 22, 23, 25, 27, 28, 55, 64]. The most common chemical agents are ZnCl2, KOH, H3PO4 and less K2CO3. As it can be seen almond shells, hazelnut shells and apricot stones, [22], were activated with a solution of ZnCl2 (30wt. %) at 750-800-850oC respectively, for 2h. Zinc chloride was, also, used in the study of W. T. Tsai et.al, [9, 14], for the activation of carbons from corn cob in the range of 400-800oC, for 0.54.0 hours of soaking time, and as well in the study of Badie S. et.al., [28], where a 50% solution was mixed with sample of peanut hulls at 300-750oC for 6h. Additionally, ZnCl2 was used as an activating agent for Macadamia nutshells, [17], and rice husks, [27], at 500oC for 1h, and at 600oC for 3h in combination with CO2, respectively, and gave the best characteristics of the activated carbons than with any other agent (chemical or physical). Table 8. Chemical activation Activating Agent

ZnCl2 KOH H3PO4 K2CO3

Reference

Material

9, 14, 17, 22, 27, 28 Corn cob, Macadamia nutshells, peanut hulls, almond shells, hazelnut shells, apricot stones, rice husks 15, 17, 25, 28, 55, 64 Corn cob, Macadamia nutshells, peanut hulls, olive kernel, rice straw, Cassava peel 19, 23, 28 peanut hulls, almond shells, pecan shells, corn cob 15 Corn cob,

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Carbons from Macadamia nutshells, [17], and peanut hulls, [28], were activated with KOH at 800oC for 1h and 500-700oC for 3h, respectively. Activated carbons that were produced, did not have good quality as the ones produced with ZnCl2. Corn cob char, [15], that was activated with KOH at 500-800oC for 1h, did not generally give activated carbon with such good SBET. Activation of olive seed carbons, [55], took place at 800-900oC for 1-2h and gave activated carbons with high surface area and char yield. For rice straw char, [25], activation proceeded firstly in one-stage at 500-900oC for 1h and secondly in two-stages, at 700-1000oC for 1h (carbonization conditions) and then at 900oC for the activation. From the results, it became very obvious that the two-stage process was much more effective, as it gave activated carbons with higher porosity. In fact, this method (two-step chemical activation process), gave the higher surface area from all the studies being mentioned in the present review. Cassava peel char, [64], activated at 650oC and 750oC, the higher SBET appeared in the second case. Activation with H3PO4 was used for carbons from peanut hulls, [28], corn cob, [19], almond shells and pecan shells, [23]. The activating conditions for peanut hull chars were 500oC for 3h, while for corn cob chars 500oC for 2h. Corn cob gave better characteristics of the activated carbons in the respective research than peanut hull. Almond shell chars activated with H3PO4 gave carbons with a little lower surface area than those mixed with ZnCl2. Carbons from corn cob, [15], were activated with K2CO3 at 500-800oC for 1h, where the activated carbons produced, comparatively with the results with KOH, had a lower surface area and gave the maximum char yield.

Carbon Characterization N2 adsorption at 77 K was utilized to determine specific surface areas and porosities of these carbon samples. A simple gas adsorption manometer apparatus [72] was used in the N2 adsorption experiments. The specific surface area was determined through the BET equation. Micropore volumes were determined through the αs method and the Dubinin-Radushkevich equation. The amount of N2 adsorbed at relative pressures near unity corresponds to the total pore volume including both the micropores and the mesopores. Consequently the subtraction of the micropore volume, deduced from the αs method, from the total pore volume will provide the volume of the mesopores. B.E.T Surface The nitrogen adsorption-desorption isotherms of the resulting carbons, used for calculating their Brunauer-Emmett-Teller (B.E.T) surface areas and total pore volumes, were obtained by using an Micrometerics Co, USA apparatus. One form of the well-known B.E.T equation that describes the adsorption of a gas upon a solid surface is (P/Pa)/V{1-(P/Pa)] = 1/(VmC)+[(C-1)/(VmC)]P/Pa

(1)

where V is the volume (at standard temperature and pressure, STP) of gas adsorbed at pressure P, Pa the saturation pressure which is the vapor pressure of a liquified gas at the adsorbing temperature, Vm the volume of gas (STP) required to form an adsorbed monomolecular layer, and C a constant related to the energy adsorption.

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The surface area S of the sample giving the monolayer adsorbed gas volume Vm (STP) is then calculated from S=VmAN/M

(2)

Where A is Avogardo’s number which expresses the number of gas molecules in a mole of gas at standard conditions, M the molar volume of the gas, and N the area of each adsorbed gas molecule. The constant C of equation 1 is typically a relatively large number, i.e., C>>1, from which equation 1 reduces very nearly to (P/Pa)/V{1-(P/Pa)] = (1/Vm) (P/Pa)

(3)

which rearranges to Vm = V[1-(P/Pa)]

(4)

Another way of arriving at the same result is by recognising that the term 1/(VmC) of equation 1 is generally small. Taking it as insignificant changes the slope, and hence the value of Vm and the sample surface area as calculated by equation 2, only a small amount. Equation 1 can be rearranged with the contribution of the intercept term taken to vanishingly small to give also Vm = V[1-(P/Pa)]

(5)

Substituting equation 5 into equation 2 yields S= VAN [1-P/Pa]/M From which the sample surface area is readily determined once the volume V of gas adsorbed (or desorbed, which must be identical) is measured and appropriate values for the other terms are incorporated. For nitrogen gas adsorbed from a mixture of 30 mole % nitrogen and 70 mole % helium using a liquid nitrogen bath, the values are arrived as follows: −

− − −

The volume V of gas with which calibrates the FlowSorb 2300 is injected at room temperature and must thus multiplied by the ratios 273.2/ (Rm.Temp.,oK)x(Atm. Press., mmHg)/760 to convert it to standard conditions (oC and 760 mmHg). Avogardo’s number A is 6.023x1023 molecules/g mole. The molar volume M of a gas at standard conditions is 22.414 cm3/gmole. The presently accepted value for the area N of a solid surface occupied by an adsorbed nitrogen molecule (2) is 16.2x10-20 m2 (=16.2 Angstroms 2 ). P is 0.3x the atmospheric pressure in millimeters of mercury since the gas mixture is 30% nitrogen and adsorption takes place at atmospheric pressure. Pa, the saturation pressure of liquid nitrogen is typically a small amount greater than atmospheric due to thermally induced circulation, dissolved oxygen, and other factors. With fresh,

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relatively pure liquid nitrogen, the saturation pressure is typically about 15 mmHg greater than atmospheric pressure. It can be 40 to 50 mmHg greater if the liquid nitrogen is relatively impure. The saturation pressure should be determined by other means in the latter event. The result for a 30% N2 / 70 % He mixture adsorbed at liquid nitrogen temperature when room temperature is 22 oC and atmospheric pressure is 760 mmHg is the expression S = V [273.2/Rm.Temp.] [Atm. Press./760] [6.023x1023 x16.2x10-20 /22.414x103] [1((%N2/100)xAtm.Press.)] = V x 273.2/295.2 x 760/760 x [6.023x1023 x16.2x10-20]/22.414x103 x1-0.3x760/775 = 2.84 Where S: is the surface area in square meters. For Calibration purposes, this means that a syringe injection of V=1.00 cm3 of nitrogen at 22 oC and 760 mmHg should produce an indicated surface area of 2.84 m2. The value of S from equation 7 changes when ambient conditions differ significantly from 22 oC and 760 mmHg, pressure changes having relatively effect than temperature. For example, if the gas were 29.33 % N2, the ambient temperature was 25 oC, atmospheric pressure were 710 mm Hg, and the saturation pressure were measured to be 735 mm Hg, the value, instead of being 2.84, should be 2.67. The surface area of carbons and activated carbons was measured with FLOWSORB 2300 by determining the quantity of a gas that adsorbs as a single layer of molecules, a so called monomolecular layer, on a sample. This adsorption is done at or near the boiling point of the adsorbate gas. The area of the sample is directly calculable from the number of the adsorbed molecules, which is derived from the gas quantity at the prescribed conditions, and the area occupied by each. For a nitrogen and helium mixture of 30 vol. % nitrogen, conditions most favorable for the formation of a monolayer of absorbed nitrogen are established at atmospheric pressure and the temperature of liquid nitrogen. Surface area is computed from the data obtained when either the pore filling or emptying process is followed by exposing a porous material to progressively increasing or decreasing concentrations of nitrogen gas. Adsorption and desorption surfaces for each sample was measured and the specific surface was obtained by taking the average of both adsorption and desorption surfaces divided by the weight of the sample, weighed before the desorption and after. Estimation of a commercial active carbon NORIT B.E.T specific surface was also performed in order to compare surface values of tires issued activated carbons with the commercial ones.

Porosity In order to fully characterize the pore volume and size of carbons, a combination of methods can be used. The αs method is an empirical one, that compares sample isotherm with that of a reference non-porous carbon material possessing chemically similar surface. According to the αs plot characteristics; qualitative and quantitative information can be obtained about porous structure. At high pressures (αs >1) all αs plots present a linear part with some slop as a result of multiplayer adsorption in large dimension pores (mesopores).

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Total microporosity, Vtot,µ, is estimated from the intercept of this linear part as usual for the αs plots [55]. Surface coverage of the supermicropore walls is indicated by the appearance of a linear section at αs >0.5. Extrapolation of this section to αs =0 provides an approximate evaluation of the effective ultramicropore volume, Vuµ. Effective supermicropore volume can be regarded as the difference between Vtot,µ and Vuµ. Mesopores constitute a small percentage of the total porosity at low conversions (1-5 %) and increase slightly at high conversions to 10-15 %. In contrast samples posses in large part micropores as shown from the effective micropore volumes calculated from the αs plots. Micropore volume is distributed in larger dimension supermicropores at low conversions. At high conversions ultramicropores are created to some degree. The general trend is that as activation proceeds all kinds of porosity are increasing. At the final conditions of 900 oC and 4 h, an activated carbon is obtained possessing the entire spectrum of pore sizes, (super) micropores prevailing. Based on the trend of the experimental results, it can be anticipated that extension of the activation process will give a more mesoporous carbon with augmented percentage of ultra micro porosity [55] Dudinin-Radushkevich (DR) plots has been demonstrated to linearize type I isotherms over a wide range of relative pressures. Various types of deviations from linearity (and from type I isotherms) have been reported and were explained on the basis of porosity discrepancies from pure microporosity, [72]. Generally, long linear DR plots are given by carbons with narrow micropores, whereas the more restricted linearity is an indication of the presence of wider micro pores {super micropopres) and mesopores. From the DR plots the apparent micro pore volume can be estimated from the slop of the intercept of the linear part of the plot. Values of Vuµ and Vµ,DR should be in close agreement if the super micropores are absent.. Deviations are higher at higher degrees of burn-off and are attributed to the adsorption in wider pores with mechanisms such as filling of super micropores and multiplayer adsorption in the mesopores. It can be concluded that KOH activation produces at the early stages carbons with microporous structure. At late stages of activation carbons posses mixed micro- and mesoporous structure. During activation both pore ranges are evolving by generation of micropores and widening of the original narrow micropores.

KINETIC MODELLING Biomass pyrolysis is generally a complex process affected by biomass type, experimental system, temperature, pressure, residence time. The secondary reactions of the primary pyrolysis volatile products play an important role. At higher temperatures the secondary decomposition of liquids follows by high endothermic reactions. Shafizadeh [94] has studied the pyrolysis of wood by considering tree parallel reactions for the production of gas, liquids and char, as following: gas

k k

wood k

liquid char

k

H/C + CO + CO2

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−

where :

dW dt

= K ⋅ (W − W ∞

K = ko ⋅e

−E

)n

175

(1)

RT

W : Weight losses W∞ : Total weight losses (total decomposition) n : receiving ~1 K : Arrhenius kinetic constant ko : Pre-exponential factor of the reaction Ε : Activation Energy Anthony and Howard [56], Numm et al [95] have suggested another kinetic model for the estimation of the kinetic parameters koi, Ei, Vi f of biomass pyrolysis. This model is simple, useful in engineering calculations. In this model the rate of formation of a product is given by the expression:

(

dVi = K i ⋅ V ∞ − Vi dt

Where:

)

n

K i = k oi ⋅ e

− Ei

(2)

RT

Vi : Percentage of volatiles in time t V ∞ : Ultimate attainable yield Ki : Arrhenius kinetic constant koi : Pre-exponential factor Εi : Activation Energy The basic difference between the above models is that, the first assumes total decomposition of the raw material while the second considers an ultimate attainable yield of decomposition (ultimate yield of volatiles and gases). Many investigators in the past applied the single first order reaction model [83, 84], the two competing reaction model [85] or other more complicated model [86]. In the present work, the model of Anthony and Howard [56] was applied. It is based on the first order decomposition reaction model, but it assumed that the thermal decomposition of raw material consists of a large number of independent chemical reactions. Each of these reactions is described as irreversible first order in the amount of volatile yet to be released. In this model the rate of formation of a product is given by the expression:

(

dVi = K i ⋅ V ∞ − Vi dt

)

n

(1)

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A. A. Zabaniotou

K i = k oi ⋅ e

Where :

− Ei

RT

Vi : Percentage of volatile at time t V ∞ : Ultimate attainable yield Ki : Arrhenius kinetic constant koi : Pre-exponential factor Εi : Activation Energy Equation (1) can be integrated assuming a constant heating rate

dT = m , until final dt

temperature is reached:

  R ⋅ T2  − E   ⋅ exp Vi = V ∞ ⋅ 1 − exp −    R ⋅ T     E⋅m

(2)

Following the above model, kinetic parameters were obtained for cotton gin waste (E, Kio, V) using the Levenberg - Marquardt method of non-linear regression analysis.

EXPERIMENTAL Pyrolysis Pyrolysis of wastes was carried out in our laboratory reactor (Figure 2). The apparatus employed for the pyrolysis was a captive sample reactor, offering advantages such as: − − −

Independent control of parameters, such as final temperature, heating rate and residence time. Very effective heat transfer. Nearly zero residence time at the final temperature and rapid cooling of the gaseous products.

The experimental procedure is presented in Figure 3. The experiments were carried out in the temperature range 390 - 890 ºC, with heating rates of 70 - 90 ºC/sec at atmospheric pressure, under helium. The main procedure apparatus consisted of the following: − − − − − −

Reactor Electrical circuit Cooling of gaseous products Trap for moisture collection System for gas collection System of gas analyses (GC)

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Trap2 Pressure gauge

Trap1 Flange SS316 Connection Plexiglass

Flanges of bronze

electrode

Flange SS316 Support flange

Figure 2. Laboratory reactor.

The reactor is a cylindrical Plexiglass vessel, of an inner diameter of 7cm and is 12 cm high. The reactor vessel closes with two pairs of flanges (top and bottom). The upper pair of flanges is made of stainless steel SS316. Between the flanges, elastic o-ring is fitted, in order to achieve isolation. The stainless steel flange has a diameter of 12 cm and a thickness of 1cm. In the centre there a 0.3125 mm diameter hole serving for the gas exit, while on it are fitted a filter for tar collection and traps (T1, T2) for liquids collection. On the flange, a second similar hole serves for the fitting of a manometer, in order to measure the pressure in the reactor. About 200 mg of the waste material is spread in a layer on a screen of stainless steel, which is inserted between the electrodes. Helium is passed through the reactor at the rate of 30cm3/min. The sample temperature is raised at the peak temperature. The reaction effluent includes fine charcoal, gas and volatile compounds. Their quenching occurs by natural cooling. The charcoal remains on the screen and is determined gravimetrically. Tar is defined as the material condensed within the reactor vessel, on the wall, flanges and on a paper filter at the exit of the reactor, at room temperature. Tar condensed inside the reactor is removed by washing with CH2Cl2 soaked filter paper and is measured gravimetrically. Hydrocarbons (in the vapour phase at room temperature) are collected in two lipophilic traps placed at the exit of the reactor and containing 80/100 mesh Porapaq Q chromatographic packing and then measured gravimetrically.

178

A. A. Zabaniotou Cooling coil Volumetric cylinder Π2

Silica Gel

H/C trap Π1

Tar E2

B1 Ε5

Β2 Ε6

Ε4

E3

Pessure gauge

Tar filter

Ε4: Gas entrance Ε5: To gas collection Ε6: To trap

ΤΒ

Β2: 3-way valve

Ε1

H2O trap

Tar Thermocouple

Electrods Temperature recorder ΤΒ: 3-way electrovalve

E1: Gas Entrance Ε2: Exit to enviroment Ε3: To gas trap H2O

Sample

He

Micrometric valve

High amperage circuit

Gas collection trap

Figure 3. Experimental procedure

Gaseous products pass through two traps (T1 and T2), where the liquid HC are collected. Then, they pass through a water-cooling coil to be cooled to ambient temperature and then through a moisture collection trap, which is a cylindrical plexiglass tube containing silica gel. Finally they reach the gas collection trap through the electro valve TB. The volume of the removed water determines the gas volume. The gaseous products are selected in plastic sacs and they follow gas chromatography analysis. Gaseous products were passed through two traps (T1 and T2), where the liquid HC were collected. Then, they were passed through a water-cooled coil and cooled to ambient temperature and then through a moisture collection trap (a Plexiglass cylindrical tube containing silica gel). Finally, they reached the gas collection trap through the electrovalve TB. The volume of the water displaced determined the gas volume. The gaseous products were collected in plastic bags and analyzed by gas chromatography. Gaseous products were analysed in a Perkin-Elmer model Sigma 300 gas chromatograph, with thermal conductivity detector connected to a PC. A cart type HP 35900D A/D and a HP 3365 Series II ChemStations softword did the integration of the exit signal. The elemental analysis of biomass was carried out using a LECO COR Analyzer CHN800. C, H, N was measured directly, but oxygen was determined by difference. Determination of ash and moisture was performed according to ASTM Standards (D-1102-84 for ash in wood and D-2016-74 for moisture).

Olive Kernels Olive wood and kernels from Greece, ware used for pyrolysis experiments. Samples were prepared by cutting and crushing pieces of the raw material to fractions of the desired particle size (18-80 U.S standard mesh). The temperature range studied was 350-850oC and the

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heating rate was 80-100oC. The pyrolysis yielded char, liquid HC and tar and gaseous products. Composition of olive wood and kernel is presented in Tables 10, 11. Cotton gin waste from Central Greece was used as raw material for the experiments. The chemical composition of cotton gin waste and of other agricultural and forestry residues, as reported in the literature, are presented in Table 9, where a comparison of the chemical characteristics of the various wastes [57,65,66,67] is made. It can be deduced from Table 9 that the total organic matter (C, H, O) of the cotton gin waste is about 80% wt./wt. and the heating value is 15.780 kJ/kg. This convertible part is rather close to organic waste materials, such as rice straw and rice husks. The ash content of the cotton gin is rather high (15wt.%) which is much higher than that of wood residues (Table 10). Cotton gin waste is very loose compared to other biomass materials. Its bulk density is about 25 kg/m3, which is smaller than of straw waste (40-50 kg/m3) [57], and particle size and shape are not uniform. The heat content of cotton gin waste was estimated, by the following equation [68]:

Q = 146.58 ⋅ C + 568.78 ⋅ H − 51.53 ⋅ O Where Q is the gross heat content (Btu/lb) and C, H and O are respectively the amount of carbon, hydrogen and oxygen in weight percent. Table 9. Elemental Analysis and Characteristics of different types of biomass (wt.%, dry basis) Material

Cotton gin waste Cotton gin waste Cotton straw

C

H

N

S

41.23

5.03

2.63

43.8245.97 45.5

4.624.85 6.01

2.952.04 0.98

Ash

Moisture

Heating Value (kJ/kg)

13.3

6.0

15780

11.8812.46 17.2

0.0

15480

0.0

18330

O

Assumed 34.0 to be 0.0 0.43-0.45 32.6134.23 0.23 30.08

Table 10. Elemental analysis of waste Raw material characteristics (maf : moisture and ash free)

C *(wt. % maf) H (wt.% maf) N (wt. % maf) O (wt.% maf) Ash (wt. % mf) Moisture (wt. %) Heating value (kcal/kg)

Olive wood

Olive kernel

Cotton gin

Used tires

45.6 6.19 0.00 40.11 1.06 15.45 4658

44.30 5.85 0.00 49.85 3.90 21.50 4916

41.23 5.03 2.63 34.0 13.3 6.0 3775

79.89 6.74

0.51 8210.5

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A. A. Zabaniotou Table 11. Analysis of olive kernel waste and char

Raw material (% w/w), dry basis 1.95 49.74 6.06 0.18 39.07 3.0

N C H S O Ash

Char (% w/w) dry basis 1.35 75.68 0.79 0.00 12.18 10.0

Used Tires Pyrolysis of used tires has been performed in two scales: a) at the captive sample reactor (described previously) and b) in a pilot scale at the Compact Power Ltd at Bristol, U.K. Compact Power Ltd has developed a new advanced thermal conversion technology for a wide range of wastes using the process of pyrolysis, gasification and high temperature oxidation. The plant is designed as a closed system in which all waste materials are converted into simple gases and used to fuel conventional steam power circles. The used tires were pyrolyzed without elimination of their included metallic part. The pyrolysis was carried at 800 °C during 45 min in an inert atmosphere, in the Avonmonth’s industrial pyrolyser, with a capacity of 1 t/h. Tires were heated in the absence of oxygen to about 800 °C. Hydrocarbons were converted to simple gases, leaving a residue of carbon CBp, inert materials and heavy metals. In a next step, 11 kg of tires pyrolysis CBp issued from Compact Power were used for the preparation of 5 kg sample for batch activation. First, the maximum of steel content was eliminated. By manual magnetically removing, 23 wt. % of CBp has been separated. Those were large particles and Fe containing particles. 5 kg of that CBp have been used for activation. Caracteristics and composition of used tires are given in Table 12. Table 12. Elemental analysis, moisture and heat content of tires and char

Raw Material Char

Elemental Analysis %wt C %wt H 79,87 6,74 86,58 3,33

Moisture %wt 0,51 1,65

Heat Content MJ/Kg 36,65 34,32

RESULTS Olive Wood (Cuttings) Pyrolysis A set of experiments of olive wood pyrolysis was performed at a temperature range of 275- 610oC. The heating rate ranged between 100-300oC/sec. The residence time in the maximum temperature, varied between 0.5-1.0 sec. Data on the effect of temperature on the yields of char, gases and tar from pyrolysis of dry olive cuttings are presented in Figure 5. Weight losses increase with temperature (Figure 5), until 91% conversion to volatile material attained at 610oC. Most of devolatilization occurs between 300oC and 600oC [67].

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PI VENT PI BM

TI

PI

WTGM CO

PI 2

VENT

TI

SP

SAMPLE

FM

PI

BAGS

PI N

2

SP PI

: Sample Port : Pressure Indicator

TI

: Temperature Indicator

BM

: Bubble Meter

FM

: Flow Meter

WTGM : Wet Test Gas Meter Figure 4. Activation reactor 100 C harcoal

Yields of pyrolysis products (wt.-% of dry olive wood)

Tar G ases

75

Liquids

50

25

0 200

300

400

500

600

700

Peak Tem perature (°C ) Figure 5. Effect of temperature on the yields of char, gases and tar from pyrolysis of dry

The yield of charcoal decreases increasing the temperature. The charcoal yield reaches the value of 25 wt.%, at 550oC. Tar yield goes through a maximum of 35 wt. %, at about 550oC. Above this temperature, tar yields decrease due to secondary reactions producing more gaseous products. Tar and gaseous products are initially evolved at the same

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temperature (270oC). CO is observed at about 270oC and its yield increases with temperature to a value of 30 wt.% at 400 oC, remaining constant until 500oC and above 500oC increases rapidly reaching the double value (~ 60 wt.%) at 600oC. On a weight basis, CO dominates the gaseous products at the above temperatures. This is probably due to the fact that CO is also a product of secondary cracking of the tar [67].

Olive Kernel Pyrolysis A second set of experiments has been performed at a temperature range of 335-600oC, with samples of olive kernels. The heating rate ranged between 100-240oC/sec and the residence time varied between 0.1-0.5 sec in the maximum temperature. Data of the temperature effects on the yields of char, gases and tar from pyrolysis of dry olive kernels, are presented in Figure 6. 100

Charcoal

90

Tar 80

(wt.-% of dry olive kernal)

Yields of pyrolysis products

Gases 70

Liquids

60 50 40 30 20 10 0 300

400

500

600

Peak Temperature (°C) Figure 6. Effect of temperature on the yields of char, gases and tar from pyrolysis of dry olive kernel

The yield of charcoal decreases to a value of 33 wt.% of dry sample, at 500oC. Above 500 C, this yield tends to be stabilized to a value of 30 (wt.%). Char was analyzed and the results of the elemental analysis, as well as the moisture and the heat content of carbon residue are shown on Table 10. Weight losses increase with temperature and a conversion ~70% to volatile material is attained at 580-600oC (Figure 6). Most of devolatilization occurs between 400oC and 550oC. Tar yield goes through a maximum of ~30 wt.% at about 450500oC. Above this temperature, tar yield decreases, due to secondary reactions producing more gaseous products. The rate of this increase is lower than the analogous observed at olive o

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wood pyrolysis. Tar and gaseous products are initially evolved at the same temperature (350oC), [1, 67].

Cotton Ginning Waste Pyrolysis The effect of temperature on total weight loss from cotton gin waste pyrolysis is shown in Figure 7. A dramatic increase in weight loss is observed with increase in temperature, which approaches an asymptotic value of 60 wt.% at approx. 600oC. Figure 5 depicts the product yield (char, liquid and gas) in relation to temperature. Pyrolysis of cotton gin waste apparently starts before reaching the temperature of 350oC. The yield of char decreased with temperature approaching the asymptotic value of 35-40 wt.%, at nearly 700°C (Figure 7), [89].

Pyrolysis Product Yields (% wt of m.a.f. cotton gin waste)

100 Char Gases Tar Liquid H/C

90 80 70 60 50 40 30 20 10 0 300

400

500

600

700

800

900

Peak Temeperature (o C) Figure 7. Effect of temperature on the yields of char, gases and tar from pyrolysis of dry cotton gin

Pyrolysis of cotton gin wastes seems to give very low yields of tar and liquid H/C (almost negligible), probably due to the high cellulose content, as reported by other researcher [70]. This could be interpreted as reflecting competition between escape of freshly formed tar from elevated temperature environment and cracking of the tar in that environment. This may happen because at low heating rates, there is adequate time during the heat up period for most of the tar formed to escape the immediate neighborhood of the screen before the temperatures are sufficiently high for extensive cracking to occur [69]. This secondary cracking of tar is believed to be a significant pathway for production of H2, CO and several light HC such as CH4, C2H4 [69, 89]. The total amount of gases tends to sharply increase with temperature at low temperature levels. The rate of increase decreases at higher temperatures (600-800oC). Gas chromatographic analysis shows that the gaseous product consists of CO, H2, CH4 and small amounts of C2H4. The main gaseous product is CO [89]

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Used Tires Pyrolysis Figure 8 depicts the product yield (char, tar, liquid and gaseous products) in relation to the temperature of pyrolysis. Carbon black yield decreased with temperature reaching an asymptotic value of 20 wt. % of raw material, at about 830ºC. Gas yield increased with temperature reaching an asymptotic value of 73 wt. % of raw material, at about 830ºC. An increase in the amount of gases might have been expected and a consequent decrease in liquids, due to the stronger thermal cracking produced at higher temperatures. Tar and liquid hydrocarbon yields were small and increased slowly with temperature. With respect to gas pyrolysis products, gases have been analyzed by gas chromatography. As far as liquids are concerned, those were only measured and their contribution to the mass balance has only performed. No liquids characteristics were determined, since the purpose of the present study was the investigation of alternatives uses of char. 100 Yield of pyrolysis products (wt.%)

90 80 70 60 50 40 30 20 10 0 350

450

550

650

750

850

950

o

Temperature ( C)

Figure 8. Effect of temperature on the yields of char, gases and tar from pyrolysis of used tires

In contrary, char was analyzed and the results of the elemental analysis, as well as the moisture and the heat content of carbon residue are shown on Table 12. In the same table the analogous characteristics of tire as raw material, are presented. The C content of the carbon black is 86,58 wt. %, while that of coal is 71,6 [10] and the lower calorific value of the char was measured to be 34,32 Mj/kg, while that of coal is 29,0 Mj/kg [3, 36, 44].

Activation Physical and chemical activation has been used in this study. The more successful stories are presented following:

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Physical Activation of Char from Tires For tire char physical gasification has been applied in two scales: a) Tires char air gasification and activation tests have been conducted in the set-up shown in Figure 4. A tubular stainless steel reactor was used heated externally by an electric furnace. In our laboratory, various sizes of reactors were used, 1/2-2 ½’’ of nominal diameter alternatively, permitting experiments with varying sample weight. Quantities of 1 g to 1 kg of raw material can be fed to the reactor and heat treated up to 1000 oC. b) Tires steam/CO2 activation in a pilot unit at NESA Company.

Steam Activation of Char from Tires The activation of about 5 kg of char brut issued from tires, was activated in an activation kiln at NESA company, at Louvain la Neuve [90]. The steam activation of tires char has performed at 970 °C for 3 hours. Each half an hour during the activation process, a sample of activated carbon was taken cooled and inserted in a plastic bag for further characterisation [36]. The oxidizing agent tested in this study was H2O mixed with CO2 produced by the natural gas combustion in the combustion chamber of an industrial reactor used for the purpose, owned by NESA company in Belgium.; the hot combustion gases were ducted to the top of the reaction chamber in the NESA furnace where they came into contact with the tested material, simultaneously with the steam injection in the reaction chamber. The fact that the combustion gases were ducted came in contact with the char, resulted in steam/CO2 activation [36]. Chemical Activation of Olive Kernels Chemical activation with KOH has been performed for olive kernels char. Activation of the produced olive kernel char, [55], was conducted in the same apparatus of pyrolysis for chemical activation. The char was mixed with KOH, in a ratio C/KOH of 1:4 suggested in literature to be the optimum [71]. Activated carbons with various extents of burn-off were prepared by varying the activation temperature to 800 and 900 oC and time to 1, 2, 3 or 4 hrs. Carbonized products were cooled and washed by boiling with HCl for 1h for residual KOH removal. The acid washed samples were further washed with distilled water several times until neutral pH. The final carbon products were dried at 110oC for 24 hrs, for moisture removal [55].

Characteristics of Activated Carbons Activation carbons were analyzed afterwards in the Laboratory. N2 adsorption at –196oC and desorption at 250oC was utilized to determine specific surface areas of the activated carbons samples by an automated adsorption/ desorption apparatus (Micromeritics, ASAP). In this study the best produced activated carbons are those obtained from olive kernels with KOH activation and from tires obtained with steam activation and they are described as in following:

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Olive Kernels Best Activated Carbons The most important property of the activated carbon is its adsorptive capacity, which in general is proportional to the surface area. Although the BET equation is the most widely used for evaluating the surface area, there is a degree of uncertainty in determining the range of relative pressure over which can be applied. The problem is even more complicate when micro porosity is present. In such cases the range of applicability is narrower and as recommended in literature lies between P/Po=0.01-0.2, [72]. For activated carbons, the pore volume is another parameter that characterizes their pore structure. Total pore volumes are generally increased with time and temperature varying between 0.57and 1.52 cm3/g, Table 13, and follow a similar trend with surface areas i. e. they are increasing monotonically with burn-off. Table 13. Structural parameters of olive kernel carbons T, oC 800 800 800 800 900 900 900 900 F300

T, h 1 2 3 4 1 2 3 4 -

X 24 28 51 58 35 41 53 68 -

1-X 76 72 49 42 65 59 47 32 -

SBET 1339 1334 2578 2431 1550 1462 1798 3049 960

Vtot. 0.595 0.580 1.062 1.033 0.679 0.665 0.842 1.52 0.56

Vtot. µ 0.594 0.573 0.991 0.983 0.665 0.637 0.750 1.300 0.46

Vm 0.001 0.007 0.071 0.050 0.014 0.028 0.092 0.220 0.10

Vuµ 0.000 0.000 0.000 0.000 0.071 0.085 0.100 0.113 -

Vsµ 0.355 0.389 0.991 0.983 0.594 0.552 0.650 1.187 -

VµDR 0.482 0.459 0.768 0.705 0.458 0.400 0.627 0.790 -

In the production of commercial activated carbons, relatively high product yields are expected. Carbon yields are calculated by the difference between 100 and conversion. The yields of activated carbons produced from olive kernels range between 76 to 32 % by weight depending on activation time and temperature. Those values are satisfactory in virtue of a possible commercial use. Olive kernel active carbons produced by chemical activation, show the highest BET surface areas. These are increasing with activation time and temperature from a minimum value of 1339 at 1 h and 800o C to a maximum of 3049 m2/g at 4 h and 900o C. On the other hand, BET area shows an increase with an increase of the burn-off, regardless of the activation temperature. This indicates that the burn-off of the activated carbon has the most significant effect on the increase of the surface area. Indeed, the surface area depends on the mass, removed during the activation of the carbon, creating pores to the material. The range of linearity in the BET plots was found to be satisfactory within this range of values for the carbons prepared from olive seed residues [55]. For activated carbons, the pore volume is another parameter that characterizes their pore structure. Total pore volumes of olive kernel carbons are generally increased with time and temperature varying between 0.57and 1.52 cm3/g, and follow a similar trend with surface areas i. e. they are increasing monotonically with burn-off [55].

Used Tires Best Active Carbons Proximate analysis of produced active carbons is presented in Table 12. Active carbon is a carbonaceous material with a highly developed internal surface area and with strong

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adsorptive capacity. Theoretically, any carbonaceous material can be converted into active carbon by an appropriate physical activation process. A pore system is developed using oxidizing agents such as carbon dioxide, air or steam, heated to 700-100oC. The surface area was found to increase upon activation to reach a maximum at a burn-off level of 70 %. This was followed by decrease with further activation. The best activation time was 2.30 hr at 1000oC. After 2 hr of activation time, the best-activated material was produced yielding a medium level of microporocity. Higher times yielded high burn-off levels and a reduction in the surface area, microporocity and adsorption of N2. This is consistent with the previous work by C.I Saint –Diaz, A.J. Griffiths [73], where it seems that the initial stages of the activation process, the peripheral and more accessible single aromatic sheets can be burned off, producing mainly micropores. The availability of those sheets is decreasing and larger sheets start burning out converting more and more of the micropores into macropores decreasing therefore the surface area at higher activation time [73]. The best B.E.T surface area with a value of 431,2 m2/g were obtained at 2 ½ h of steam activation in pilot scale. The activated carbon produced after 3 hours of activation showed lower values of B.E.T surface area due to the destruction of pores. The surface area might be improved with other methods of activation. The acid treatment e.g prior to steam activation, such as with HNO3, performed by P. Ariyadejwanich et al [74], showed that highly mesoporous activated carbons could be obtained with a B.E.T surface area of 1119 m2/g. The surface area of activated tire carbons is not much lower than those reported in the literature. Helleur et al [75] produced activated carbon with surface not greater than 320m2/g. Their explanation to that was that reasons for the low surface area might be the activation conditions and the high ash content of the tire which is the case of this study also. Saint-Diaz et al [73] have reported medium surface area, 431m2/g from tire derived char at 1000oC. The above researchers in their study had mentioned that given that pyrolysis process generates large quantities of CO2 and heat (pilot-scale flaming pyrolyser), it is probable that either the CO2 method or steam activation would be used in an industrial scale. In the present study the activation has performed under CO2/steam and the results are better, reinforcing the conclusion of using the method at industrial scale. Both carbon dioxide and steam are mild oxidant and eliminate carbon atoms from the char particle [76]. F. Rodriguez-Reinoso et al [76] have studied the use of steam and CO2 as activated agents in the preparation of activated carbons and they invistigated that carbon dioxide produces an opening, followed later by widening, of narrow microporosity, whereas steam widens the microporosity, from the early stages of the activation process. The results of the present study are in agreement with this statement. A. Zabaniotou et al [36, 44] in a series of experiments investigating the operating conditions giving the maximum sample surface area, have measured B.E.T surface areas around 600m2/g for both CO2 and steam activation. However, the above mentioned study has performed in a laboratory scale reactor, using omogenous fine tire char particle of 200 µm. Ariyadejwanich et al [74] obtained activated carbons by activation of char with steam at 850oC with B.E.T surface areas up to 737m2/g, while San Miguel et al [77] obtained 1070 m2/g B.E.T surface areas. The B.E.T surface area of the pyrolysis tire chars found to be about 600m2/g, which is almost typical value for chars prepared from waste tires [74].

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Comparisons with the Commercial Active Carbons For the comparison of active carbons produced from olive kernel with chemical activation and commercial ones, the commercial grade carbons such as, Calgon Filtrasorb 300 (F300, Calgon Carbon Co., Pittsburgh, USA), have been used, their characteristics provided in Table 14. The BET surface areas and the pore volume of the produced activated carbons are much higher than that of the commercial carbon. Its pore size distribution is similar to carbons with high burn-off possessing large percentage of micropores. Olive seed super activated carbons present adsorption and porosity characteristics quite similar to those prepared from other raw materials by KOH activation. For example, Maxsorb, which is a commercial product prepared from petroleum coke, posses a BET surface area value of 3100 m2/g, very close to sample of 900o C-4 h. AMOCO carbon PX-21 and Anderson AX-21 present slightly higher areas and pore volumes, table 3, probably due to different activation conditions and starting materials [55]. Table 14. Surface areas and pore volumes of some super activated carbons Sample

AX21 PX21 Maxsorb

BET area (mg/m3) 3390 3700 3100

Total micropore volume 1.52 1.75 -

Ultra micropore volume 0.36 0.39 -

Super micropore volume 1.16 1.36 -

These enormous BET surface areas are created by a distinct KOH activation mechanism. Investigations [59, 78, 79, 80, 81] showed that KOH is dehydrated to K2O, which reacts with CO2 produced by the water-shift reaction, to give K2CO3. Intercalation of metallic potassium, which also formed above 700o C, appeared to be responsible for the drastic expansion of the carbon material and hence the creation of a large specific surface area and high pore volume. Olive seed super activated carbons present adsorption and porosity characteristics quite similar to those prepared from other raw materials by KOH activation. For example, Maxsorb, which is a commercial product prepared from petroleum coke, posses a BET surface area value of 3100 m2/g, very close to sample of 900o C-4 h. AMOCO carbon PX-21 and Anderson AX-21 present slightly higher areas and pore volumes, Table 14, probably due to different activation conditions and starting materials [55]. For the comparison of active carbons produced from tires with physical activation and commercial ones, the commercial activated carbon NORIT GL 50 is used. NORIT GL 50 is a powdered steam activated carbon with an extra fine particle size that can be used in a large range of applications. This carbon is especially suitable for the removal of dioxins, mercury and other contaminant traces from flue gases. Its fine particle contributes to its good adsorbion kinetics. Table 15 presents its specifications and general characteristics. All analyses based on NORIT Standard Test Methods (NSTM). General characteristics reflect average values of product quality. Specifications are guaranteed values based on lot to lot quality control, as covered by NORIT ’s ISO 9002 certification [36, 88].

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Table 15. NORIT GL 50 specifications and general characteristics. Molasses number (EUR) Apparent density (tamped) Particle size Iodine number Moisture (as packed) Critical Ignition Temperature

500 490 kg/m3 20 µm 700 2 mass-% 260 oC

Kinetic Modeling The kinetic modelling resulted to kinetics parameters for total weight loss of olive kernel, olive wood, cooton gin waste pyrolysis. These parameters are given in Table 16. Comparison is also made with kinetic parameters for cellulose pyrolysis. Table 16. Kinetic parameters of pyrolysis for total weight loss of various agro-residues Type of Biomass Total Weight Losses Olive wood Olive kernel Cotton gin waste Cellulose

Experimental system

Temperature logko E V Reference (oC) (sec-1) (kcal gmol-1) (wt.%)

Captive sample reactor Captive sample reactor Captive sample reactor Captive sample reactor

300-600 250-400 350-800 300-1100

0.92 4.6 3.25 8.3

2.624 11.142 11.424 31.79

91.00 67.60 65.26 94.08

[67] [67] [89] [71]

CONCLUSION The main conclusions of the study are: −

−

Activated carbon surfaces have a pore size that determine its adsorption capacity, a chemical structure that influences its interaction with polar and nonpolar adsorbates, and active sites which determine the type of chemical reactions with other molecules. Conversion of plentiful by-products into activated carbons that can be used in applications such as drinking water purification, waste treatments, treatment of dyes and metal-ions from aqueous solution would add value to agricultural commodities, help the agricultural economy with an additional market potential, offer solution to environmental problems and help reduce the cost of waste disposal. As the raw materials obtained from agricultural wastes are available freely and abundantly. Activated carbon from olive-kernel waste residues with chemical activation, using KOH as the activating agent, show higher adsorption capacities and higher surface areas than the commercial type. BET surface areas of carbons are increasing with activation time and temperature from a minimum value of 1339 at 1 h and 800o C to a maximum of 3049 m2/g at 4 h and 900o C. The absence of sulphur and the low ash content of the char are positive factors and make olive kernels a good precursor for the production of active carbons. Moreover, in comparison with the commercial

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−

carbon, which is mainly microporous, the produced carbons show a micropore distribution at low burn-offs, while at higher burn-offs an increase of the mesopore fraction was noticed. Used tire activated carbons posses surface areas around 600m2/g prepared by chemical activation with KOH, and 432m2/g prepared with CO2/ steam activation The use of catalyst can improve the surface areas making active carbons from tires acceptable substitutes of commercial products. From the experimental results, it can be concluded that a combination of a rotary kiln which presents good conditions for char preparation (low heating rate etc) with KOH activation could be a promising process in pyrolytic recycling of agricultural resisues for active carbon production

REFERENCES [1]

[2]

[3] [4] [5]

[6] [7] [8] [9] [10] [11] [12] [13]

Zabaniotou A.A. Value-added products (active carbon) from olive kernels pyrolytic char study in laboratory and bench/ilot scales. Submitted in Journal of Analytical Applied Pyrolysis. Savova D.; Apak E.; Ekinci E.; Yardim F.; Petrova N.; Budinova T.; Razvigorova M. and Minkova V. Biomass conversion to carbon adsorbents and gas. Biomass Bioenergy 21 (2001) 133-142. Zabaniotou A.A. and Karabelas A.J. Pyrolysis as a method for utilization of solid wastes in Greece (agricultural wastes and used tires). October 2002 Lanzetta M. and Blasi C.D. Pyrolysis kinetics of wheat and corn straw. J Anal Appl Pyrolysis 44 (1998) 181-192. Minkova V.; Razvigorova M.; Bjornbom E.; Zanzi R.; Budinova T. and Petrov N. Effect of water vapour and biomass nature on the yield and quality of the pyrolysis products from biomass. Fuel Proc Technology 70 (2001) 53-61. Haykiri-Acma H.; Yaman S. and Kucukbayrak S. Gasification of biomass chars in steam–nitrogen mixture. Energy Conversion Management (2005). Cetin E.; Moghtaderi B.; Gupta R. and Wall T.F. Influence of pyrolysis conditions on the structure and gasification reactivity of biomass chars. Fuel 83 (2004) 2139-2150. Fan M.; Marshall W.; Daugaard D. and Brown R.C. Steam activation of chars produced from oat hulls and corn stover. Bioresource Technology 93 (2004) 103-107. Tsai W. T.; Chang C.Y. and Lee S.L. Preparation and characterization of activated carbons from corn cob. (1997) 1198-1200. Putun A.E.; Ozbay N.; Onal E.P. and Putun E. Fixed-bed pyrolysis of cotton stalk for liquid and solid products. Fuel Processing Technology 86 (2005) 1207– 1219. Jensen P.A.; Sander B. and Johansen K.D. Pretreatment of straw for power production by pyrolysis and char wash. Biomass and Bioenergy 20 (2001) 431–446. Predel M. and Kaminsky W. Pyrolysis of rape-seed in a fluidized-bed reactor. Bioresource Technology 66 (1998) 113-117. Zhang T.; Walawender W.P.; Fan L.T.; Fan M.; Daugaard D. and Brown R.C. Preparation of activated carbon from forest and agricultural residues through CO2 activation. Chemical Engineering Journal 105 (2004) 53–59.

Recycling of Wastes (Agricultural Residues and Used Tires) … [14] [15]

[16]

[17] [18]

[19]

[20]

[21]

[22]

[23]

[24]

[25] [26]

[27] [28]

[29]

191

Tsai W. T.; Chang C. Y. and Lee S.L. A low cost adsorbent from agricultural waste corn cob by zinc chloride activation. Bioresource Technology 64 (1998) 211-217. Tsai W.T.; Chang C.Y.; Wang S.Y.; Chang C.F.; Chien S.F. and Sun H.F. Cleaner production of carbon adsorbents by utilizing agricultural waste corn cob. Resources, Conservation and Recycling 32 (2001) 43–53. Lua A.C.; Yang T. and Guo J. Effects of pyrolysis conditions on the properties of activated carbons prepared from pistachio-nut shells. J. Anal. Appl. Pyrolysis 72 (2004) 279–287. Ahmadroup A. and D.D.Do. The preparation of activated carbon from Macadamia nutshell by chemical activation. Carbon Vol. 35, No. 12, pp. 1723-1732,1997 Yang T. and Lua A.C. Characteristics of activated carbons prepared from pistachio-nut shells by physical activation. Journal of Colloid and Interface Science 267 (2003) 408–417. Abdel-Nasser A. El-Hendawy; Samra S.E. and Girgis B.S. Adsorption characteristics of activated carbons obtained from corncobs. Colloids and Surfaces A: Physicochemical and Engineering Aspects 180 (2001) 209–221. Minkova V.; Marinov S.P.; Zanzi R.; Bjornbom E.; Budinova T.; Stefanova M. and Lakov L. Thermochemical treatment of biomass in a flow of steam or in a mixture of steam and carbon dioxide. Fuel Processing Technology 62 (2000) 45–52. Ahmedna M.; Marshall W.E. and Rao R.M. Production of granular activated carbons from select agricultural by-products and evaluation of their physical, chemical and adsorption properties. Bioresource Technology 71 (2000) 113-123. Aygun A.; Yenisoy-Karakas S. and Duman I.. Production of granular activated carbon from fruit stones and nutshells and evaluation of their physical, chemical and adsorption properties. Microporous and Mesoporous Materials 66 (2003) 189–195. Ahmedna M.; Marshall W.E.; Husseiny A.A.; Rao R.M. and Goktepe I. The use of nutshell carbons in drinking water filters for removal of trace metals. Water Research 38 (2004) 1062–1068. Marcilla A.; Garcıa-Garcıa S.; Asensio M. and Conesa J.A.. Influence of thermal treatment regime on the density and reactivity of activated carbons from almond shells. Carbon 38 (2000) 429–440. Oh G.H. and Park C.R. Preparation and characteristics of rice-sraw-based porous carbons with high adsorption capacity. Fuel 81 (2002) 327-336. Malik P.K. Use of activated carbons prepared from sawdust and rice-husk for adsorption of acid dyes: a case study of Acid Yellow 36. Dyes and Pigments 56 (2003) 239–249. Yalc N. and Sevinc V. Studies of the surface area and porosity of activated carbons prepared from rice husks. Carbon 38 (2000) 1943–1945. Girgis B.S.; Yunis S.S. and Soliman A.M.. Characteristics of activated carbon from peanut hulls in relation to conditions of preparation. Materials Letters 57 (2002) 164– 172. Della Rocca P.A.; Horowitz G.I.; Bonelli P.; Cassanello M.C. and Cukierman A.L (1997). Olive stones pyrolysis: chemicaal, textural and kinetics characterization. In: Developments in thermochemical biomass conversion,(Ed. by A.V. Bridgwater and D.G.B Boocock), pp 176-189. Blackie Academic & Professional, London.

192 [30]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

[38] [39] [40]

[41] [42] [43] [44]

A. A. Zabaniotou Zanzi R.; Sjostrom K. and Bjornbom E. (1996). Rapid pyrolysis of olive waste at high temperature. In: Biomass for Energy and the Environment, 9th European Bioenergy Conference. (Ed. by P. Chartier, G.L. Ferrero, U.M. Henius, S. Hultberg, J. Sachau, M. Wiinblad), pp.1584-1588. Pergamon, Elsevier Science Limited, Oxford. Buttiglieri M. and Nicoletti G. (1995). Cheap fuel from olive husks, production and distribution for heating in residential buildings. In Biomass for Energy, environment agriculture and industry, 8th Biomass Conference.(Ed. by Ph. Chartier, A.A.C.M. Beenackers, G. Grass),pp. 740-747 Pergamon, Elsevier Science Ltd, Oxford, UK. Buttiglieri M. (1996). The energy use of the olive-husks in southern Italy - A feasibility study of low-cost production and distribution. In: Biomass for Energy and the Environment, 9th European Bioenergy Conference. (Ed. by P. Chartier, G.L. Ferrero, U.M. Henius, S. Hultberg, J. Sachau, M. Wiinblad), pp 1894-1899. Pergamon, Elsevier Science Limited, Oxford. Bosio A.; Cioli R.; Desideri U. and Marchi L. (1992). Alternative uses of olive husks: A technical-economic evaluation. In: Biomass for Energy, Industry and Environment, 6th E.C. Conference.(Ed. by G. Grassi, A. Collina, H. Zibetta), pp. 1116-1120.Elsevier Applied Science, London. Figueiredo J.L. (1990). Pyrolysis of Holm-oak and olive wood. In: Biomass for Energy and Industry, 5th European Community Conference. (Ed. by, G. Grassi, G. Gosse, G. dos Santos), pp 2.585-2.589. Elsevier Applied Science, London. Zabaniotou A.A. CO2 abatement by using pyrolysis as a valorization method for biomass and wastes. International symposium “Moving towards zero emissions plants” Leptokarya, Pieria, Greece, 20th-22 of June, TDT-3R multi-fuel project. Zabaniotou A.; Madau P.; Delplancke M-P; Oudenne P.D; Jung C.G and Fontana Activated carbon from used tires using industrial pyrolyser and pilot activation furnace. Journal of Analytical and Applied Pyolysis.72(2004), 289-297 Bridgwater A.V. (1977). Fast pyrolysis of Biomass in Europe. In: in Biomass Gasification and Pyrolysis – State of the Art and Future Prospects. (Ed. By M. Kaltschmitt and A.V. Bridgwater), pp53-67 , cpl Press, Newbury, UK. Sharma V.K.; Fortuna F.; Mincarini M.; Berillo M. and Cornacchia. Disposal of waste tyres for energy recovery and safe environment. Applied Energy (2000) 65: p. 381-394. Leung D.Y.C. and Wang C.L.. Kinetic study of scrap tyre pyrolysis and combustion. J.Analytical and Applied Pyrolysis, Vol.45, No 2, pp 153-169 (1998). Roy C.; Chaala A. and Darmstadt H. (1999). The vacuum pyrolysis of used tires Enduses for oil and carbon black products. J.Analytical and Applied Pyrolysis, Vol.51, pp 201-221. Cunliffe M. and Williams P.T. (1998). Composition of oils derived from the batch pyrolysis of tyres. J.Analytical and Applied Pyrolysis, Vol.44, No 2, pp 131-152. Senneca O.; Salatino P. and Chirone R. (1999). A fast heating –rate thermogravimetric study of the pyrolysis of scrap tyres. Fuel. Vol 78, No 13, pp 1575-1581 Coda B. and Tognotti L. (2000). The prediction of char combustion kinetics at high temperature (1999). Vol 21, pp 79-86. Zabaniotou A.A. and Stavropoulos G. (2003). Pyrolysis of used automobile tires and residual char utilization. J. Anal. Appl. Pyrolysis (2003). 00, pp 1-12.

Recycling of Wastes (Agricultural Residues and Used Tires) … [45]

[46] [47] [48]

[49]

[50] [51]

[52] [53]

[54]

[55]

[56] [57]

[58] [59]

[60]

[61] [62]

193

Al-Khalid T.T.; Haimour N.M.; Sayedand S.A. and Akash B.A. Activation of oliveseed waste residue using CO2 in a fluidized-bed reactor. Fuel Processing Technology (1998).Vol 57, pp 55-64. Conesa J.A.; Font R.; Fullana A. and. Caballero J.A (1998). Kinetic model for the combustion of tyre wastes. Fuel, Vol. 77, No 13, pp. 1469 - 1475. Williams P.T.; Besler S. and Taylor D.T. (1990) “The pyrolysis of scrap automotive tires” Fuel, Vol. 69, December, pp. 1474 - 1482. Adams G.; Lanclos K.; Boyd S. and Huffman M. The economic outlook for U.S. cotton. National Cotton Council of America; 2003 [http://www.cotton.org/pubs/ index.cfm]. Schacht O.B. and LePori W.A. Analysis of cotton gin waste for energy. In: Paper No. 78-3544, presented at the 1978 winter meeting of the American Society of Agricultural Engineer; 1978. Brink D.L. Making alcohol from cotton gin waste and cotton stalks. In: Proceedings of the symposium on cotton gin trash utilization alternatives; 1981. p.20-27. Beck R.S. and Clements L.D. Ethanol production from cotton gin trash. In: Proceedings of the symposium on cotton gin trash utilization alternatives; 1982. p.163181. Griffin Jr AC. Fuel value and ash content of ginning wastes. In: Paper No. 74-3038, 1974 annual meeting of American Society of Agricultural Engineers; 1974. Parnell C.B.; Lepori W.A. and Capareda S.C. Converting cotton gin trash into useable energy-technical and economic consideration. In: Proceedings beltwide cotton conference, vol.2; 1991. p.969-972. Capareda S.C.; Parnell C.B. and Lepori WA. Utilization of activated carbon produced from thermal gasification of cotton gin trash. In: proceedings beltwide cotton conference; 1989. p.159-163 [Book 1]. Stavropoulos G.G. and Zabaniotou A.A.. Production and characterization of activated carbons from olive-kernel waste residue. Microporous and Mesoporous Materials 82 (2005) 79–85. Antony D.B and Thesis Sc.D, Masaschusets Institute of Technology, Cambridge Mass. (1974) Sun I.; Gu Z.Z.; Guo D.Y. and XU M., Demonstration Systems of Cooking Gas Produced by Crop Straw Gasifier or Villages, Proc. of Development in Thermochemical Conversion, A.V. Bridgwater, D.G.B Boocock (eds), Blackie Academic & Professional, London, 1997. Wennerberg, A. N. and O’ Grady, T. M. US patent 4,082,694 Ehrburger P.; Addoun A.; Addoun F. and Donnet J.B. Carbonization of coals in the presence of alkaline hydroxides and carbonates: Formation of activated carbon. Fuel 65 (1986), 1447. Lillo-Rodenas M. A.; Lozano-Castello D.; Cazorla-Amopos D. and Linares-Solano A. Preparation of activated carbons from Spanish anthracite: II Activation by NaOH. Carbon, 39 (2001) 751-759. Teng H. and Wang S.C. Preparation of porous carbons from phenol-formaldehyde resins with chemical and physical activation. Carbon, 38 (2000) 817-824. Oh G. H. and Park C. R. Preparation and characteristics of rice-straw-based porous carbons with high adsorption capacity. Fuel, vol.81 (2002) 327-336.

194 [63]

[64]

[65] [66]

[67]

[68] [69]

[70]

[71]

[72] [73] [74]

[75]

[76]

[77]

[78]

[79] [80]

A. A. Zabaniotou Lozano-Castello D.; Lillo-Rodenas M. A.; Cazorla-Amopos D. and Linares-Solano A. Preparation of activated carbons from Spanish anthracite: I Activation by KOH Carbon, 39 (2000) 741-749. Sudaryanto Y.; Hartono S.B.; Irawaty W.; Hindarso H. and Ismadji S. High surface area activated carbon prepared from cassava peel by chemical activation. Bioresource Technology 97 (2006) 734–739. Lepori W.A. and Parnell C. Texas A&M University Syst (US), System and process for conversion of biomass into usable energy, US Patent 4 848 249, 1989. Zabaniotou A.A.; Gogotsis D. and Karabelas A.J. Product composition and kinetics of flash pyrolysis of Erica arborea (biomass). Journal of Analytical and Applied Pyrolysis, 29 (1994) 73-87. Zabaniotou A.A.; Kalogiannis G.; Kappas E. and A.J. Karabelas. Olive-residues (cuttings and kernels) rapid pyrolysis product yields and kinetics. Biomass and Bioenergy, vol.18 (5) (2000) p.411-420. Perry R.H.; Green D., McGraw-Hill 6th ed., New York 1984. Hajaligol M.R.; Peters W.A.; Howard J.B and Longwell J.P. Product composition and kinetics for rapid pyrolysis of cellulose. Ind. Eng. Chem. Prod. Res. Dev. 21 (1982) 457-465. Economou A.M.; Manglara E.; Koullas D.P. and Koukios E.G., in Biomass for Energy and Industry, 7th EC Conference, D.O.Hall, G Grassi and H. Scheer, Ponte Press, Bochum, Germany (1994) 498-503. Hayashi J.; Horikawa T.; Takeda I.; Muroyama K. and Ani F. N. Preparing activated carbon from various nutshells by chemical activation with K2CO3. Carbon, vol.40 (2002) 2381-2386. Rouquerol F.; Rouqoerol J. and Sing K. Adsorption by powders and porous solids, Academic Press, 1999. Saint-Diaz C.I and Griffiths A. J. Activated carbon from solid wastes using a pilotscale batch flaming pyrolyser Fuel. (2000) Vol 76, pp 1863-1871. Ariyadejwanich P.; Tanthapanichakoon W.; Nakagawa K.; Mukai S. R. and Tamon H. Preparation and characterization of mesoporous activated carbon from wastes tires. Carbon (2003) Vol 41, pp 157-164. Helleur R.; Popovic N.; Ikura M.; Stanciulescu M. and Liu D. Characterisation and potential applications of pyrolytic char from ablative pyrolysis of used tires. Journal of Analytical and Applied Pyrolysis. (2001) Vol 58-5, pp 813-824. Rodriguez-Reinoso F.; Molina-Sabio M. and Conzalez M.T. The use of steam and CO2 as activated agents in the preparation of activated carbons. Carbon (1995) Vol 33(1), pp 15-23. Miguel C.S.; Fowel G.D. and Sollars C.J. A study of the characteristics of activated carbons produced by steam and carbon dioxide activation of waste tyre rubber. Carbon (2003) Vol 41, pp 1009-1016 Yamashita Y. and Ouchi K. Influence of alkali on the carbonization process-I: carbonization of 3,5-dimethylphenol-formaldehyde resin with NaOH. Carbon, vol.20 (1982) 41-45. Marsh H.; Yan D.S.; O’Grady T.M. and Wennerberg A. Formation of active carbons from cokes using potassium hydroxide. Carbon, 22, (1984) 603-611. Hsu L.-Y. and Teng H. Fuel Processing Technology, 64 (2000) 155.

Recycling of Wastes (Agricultural Residues and Used Tires) … [81]

[82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92]

[93]

[94] [95]

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Lillo-Rodenas M. A.; Cazorla-Amoros D., and Linares-Solano A. Understanding chemical reactions between carbons and NaOH and KOH: An insight into the chemical activation mechanism. Carbon, vol. 41 (2003) 267-275. Zabaniotou A.A.; Lappas A.A; Kousisdis N. Flash pyrolysis of Greek lignite. Journal of Analytical and Applied Pyrolyis, vol.21 (3) (1991) 293-304. Badzioch S. and Hawksley, P.G. Kinetics of thermal decomposition of pulverized coal particles. Ind. Eng. Proc. Dev., 1970, 9, 521-530. Nsakal N.Y.; Essenhigh R.H. and Walker P.L., Combustion Science and Technology 1977, 16, 153. Kobayashi H.P; Howard J.B. and Sarofim A.F., 16th Symposium on Combustion, The Combustion Institute, Pittsburg 1977, 411 Sitnai O. National Conference, Institute of Energy, 1976, Volume 76 http://www.illinois.com http://www.norit.com Zabaniotou A.A.; Roussos A.I. and Koroneos C.J. A laboratory study of cotton gin waste pyrolysis. J.A.A.P. vol.56 (1) (2000) p.47-59. http://www.nesa.solution.be http://www.etra-eu.com Agblevor F.A.; Cundiff J.S.; Mingle C. and Li W. Storage and characterization of cotton gin waste for ethanol production. Resources, Conservation and recycling 46 (2006) 198-216. Bacaoui A.; Yaacoubi A.; Dahbi A.; Bennouna C.; Phan Tan Luu R.; MaldonadoHodar F.J.; Rivera-Utrilla J. and Moreno-Castilla C. Optimization of conditions for the preparation of activated carbons from olive-waste cakes. Carbon 39 (2001) 425–432. Shafizadeh F. Fast pyrolysis of biomass.Proc. Specialists workshop, Solar Energy Research Institute, Colorado, Usa (1980). Nunn, R.; Howard, J.B.; Longwell, J.P.; Peters, W.A. Studies of the rapid pyrolysis of sweet gum hardwood. Fundamentals of Thermochemical Conversion, R.P.Overent, T.A. Milne, L.K. Mudge, Elsevier Applied Science, London, 293-313 (1985).

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 197-220 © 2006 Nova Science Publishers, Inc.

Chapter 6

ENERGY RECOVERY FROM WASTE INCINERATION: LINKING THE SYSTEMS OF ENERGY AND WASTE MANAGEMENT Kristina Holmgren∗ Linköping Institute of Technology, Linköping, Sweden

ABSTRACT Energy recovery from waste incineration has a double function as a waste treatment method and a supplier of electricity and/or heat. Waste incineration thereby links the systems of waste management and energy. This chapter addresses the importance of taking this into consideration when e.g. making investment decisions or designing policy instruments. The design of two policy instruments will be described as examples of the conflicting goals in the two systems. A conflict is also that increased waste incineration can decrease production of combined heat and power in the district heating systems. Since policy instruments in Sweden are dependent on the common legislation of the European Union this will be addressed, together with trading in waste and electricity and how this impacts waste incineration in Sweden. Conflicts between the internal market in the European Union and waste management goals are shown. When making investment decisions, various models are often used as decision support tools. Some models for assessing waste incineration/management are therefore described together with strengths and weaknesses when dealing with the dual function of waste incineration.

∗

Corresponding author. Tel.: +46 13 286687; fax: +46 13 281788. E-mail address: [email protected]

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INTRODUCTION Energy recovery through waste incineration1 connects two vital systems in modern society: the waste management system and the energy system. In Sweden, with an extensive district heating (DH) system that supplies just over 40% of the total heating demand of buildings and premises, heat supply from waste incineration has a substantial share of the total DH supply of about 12% (Swedish Energy Agency, 2004). Furthermore, both these systems are the focus of attention due to environmental concerns, and for this reason, changes are being made in both systems. The European Union has common legislation which impacts both systems in the member countries. Apart from the legislation, the countries of the European Union are connected through trade; important in this case are the common electricity market and trading in waste. The aim of this chapter is to highlight two issues. The first is the dual purpose of waste incineration as a waste treatment method and as a supplier of electricity and/or heat. This chapter will emphasise the importance of taking this into consideration with regard to, e.g. decision making and when designing policy instruments. Two policy instruments that impact both technical systems will be described and the difficulties in handling the double function of waste incineration will be the central issue. These policy instruments are a recently proposed tax on incinerated waste in Sweden and green electricity certificates. Various models are often used as decision support tools in decision making processes, e.g. when municipalities make investment decisions. When designing and using these models, the dilemma of the two functions needs to be faced and the ways in which some models handle this will be described. Policy instruments in Sweden are highly dependant on legislation in the European Union, the policy instruments that will be described in this chapter are no exception. Therefore, the second issue in focus in this chapter is the connection via common legislation between countries in the EU. The consequences of this will be discussed, with a special emphasis on its impact on waste incineration in Sweden. Furthermore, the countries in the EU are connected via trade, and of special importance for waste incineration in Sweden is naturally the trade in waste, but also in electricity. The methodology applied to address these issues consists of a literature review and knowledge gained in earlier studies.

DEVELOPMENT OF WASTE INCINERATION IN SWEDEN This section will include a description of the historical development of waste incineration in Sweden. This information has been collected from a report from the Swedish Association of Waste Management (2005a) and from Hrelja (2006). The current situation with regard to waste incineration in Sweden will also be described, together with its impact on district heating, combined heat and power production and also the material recovery market. 1

Digestion also has this function, since it is a treatment method for easily biodegradable waste, where the residual products are a fertilizer and a gas which can be used for electricity and heat production or for transportation after cleaning, but this chapter will address only waste incineration.

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Historical Development Burning waste has been carried on for a long time; it has been done in the open at landfills or in simple furnaces in order to reduce waste volumes and decrease problems with vermin. This brought inconveniences, such as hazardous emissions to the atmosphere, and in 1903 Sweden’s first waste incineration plant began operations in Stockholm. However, it was not until the 1960s that waste incineration really began to show some development. The prerequisites for this were the district heating networks that began to appear after the Second World War, when municipalities’ interest in district heating was aroused. In 1948, Sweden’s first district heating network was operational in the city of Karlstad and other cities soon followed. This expansion created opportunities for waste incineration plants, since it provided an outlet for the heat produced, giving the waste a value. In the 1970s, waste began to be seen as a resource rather than a problem; in 1975 a proposition from the government stated that recovery had to increase in the future. The proposition did not state which technology was to be preferred, but incineration was regarded as preferable in bigger cities. As a result of the new view of waste as a resource, a number of plants with central sorting and composting were built. This venture failed since the plants did not work satisfactorily and there was no outlet for the residual product. This served to increase interest in waste incineration. Waste incineration expanded significantly, especially during the 1970s, over the years up until 1985. The number of plants increased from 2 in 1960 to 27 in 1985, and treatment capacity from 100,000 tons annually to 1,800,000 tons. The oil crises of the 1970s led to a growth in interest in waste incineration as an indigenous fuel, in order to decrease oil dependency.2 During the 1980s, researchers began to report widespread diffusion of heavy metals and dioxins in the environment and the effects on humans and animals. Waste incineration was found to be an important cause of this diffusion of hazardous substances in the environment.3 In 1985, a ban on investment in waste incineration was issued by the Swedish Environmental Agency, until the issues of emissions and technology had been solved. The Environmental Agency and the Energy Agency were commissioned to analyse the risks associated with waste incineration and concluded that it was possible to reduce the emissions to acceptable levels through a number of measures, including “cleaner” waste (i.e. more sorting of waste), more efficient combustion, advanced flue gas cleaning equipment, and the safe disposal of residual products. Limits were set for emissions. On the basis of these results, the ban on investment was lifted. Of the existing plants, 20 went through with modernisations while 7 were shut down. However, the debate on dioxins in the municipalities did not end there. Hrelja (2006) shows that in the 1980s the municipality of Skövde chose not to build a waste incineration plant due to lack of confidence in the treatment method. Later, however, Skövde went ahead and built the plant, which was inaugurated in 2005.

2 3

This was only one of a number of measures to decrease oil dependency. There are a number of sources, of which waste incineration is one. Industrial processes can also give raise to dioxins as can power plants using other fuels. Spontaneous fires at landfills are also a source of dioxins, where the contribution of emissions is hard to estimate.

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Waste Incineration in Sweden Today Today, there are 29 waste incineration facilities in Sweden, both hot water boilers (14) and combined heat and power plants (15) producing about 8.6 TWh heat and 0.74 TWh electricity (Swedish Association of Waste Management, 2005b). These facilities treat about 1.95 million tons of municipal waste and 1.2 million tons of other waste, mainly from the manufacturing industry. Cleaner fractions of waste can also be incinerated at other facilities and is not included in the figures presented here. Figure 1 shows the waste treatment methods for municipal waste in Sweden. As can be seen, energy recovery is the treatment method for almost half of the municipal waste today. This development is mainly a result of recent regulations in the waste management system aimed at decreasing landfill; the introduction of a tax on landfill in 2000, at present 46.3 €4/ton (Ministry of Finance, 2005a) and a ban on landfill of combustible waste from 2002 and from 2005 also of organic waste (Ministry of the Environment, 2001).

9%

1% 33%

47%

10%

Material recovery Biological treatment Energy recovery Landfill Hazardous waste

Figure 1. Treatment methods of municipal waste in 2004, total amount 4.2 million tons (Swedish Association of Waste Management, 2005b).

Capacity for waste incineration is currently increasing and is forecast to increase from 2.8 Mton in 2002 to 4.9 Mton in 2008, if all planned projects are carried out (Swedish Association of Waste Management, 2004), resulting in a total of 40 waste incineration plants. Despite these investments there will still be a lack of treatment capacity. The fact is that quantities of waste are also increasing, between 1985 and the present by some 2-3% per year. If this trend is not broken, additional waste treatment capacity will also be needed after 2008.

Waste Incineration and District Heating The role of waste as a fuel makes it part of the energy system. Therefore, the use of waste as a fuel is dependent on such factors as the prices of other fuels used, legislation, and policy instruments in the energy system. The value of using the waste is higher when the prices of e.g. fossil fuels or biofuel increase. Energy taxation in Sweden has had a significant effect on 4

An exchange rate is 1 € = 9.40 SEK is used throughout this chapter (January 2006).

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what fuels are used in the DH systems, since heat from fossil fuels has been heavily taxed.5 There has been a major shift from an almost total dependency on oil up until 1980 to a diversified supply where renewables represent a substantial proportion. This can be seen in Figure 2. A historical survey of the development of the DH sector can be found in Sjödin (2002).

60 Waste heat 50 40 30 20 10

Heat pumps Electric boilers Biofuel & peat Refuse Coal Natural gas Oil

19 70 19 73 19 76 19 79 19 82 19 85 19 88 19 91 19 94 19 97 20 00 20 03

0

Figure 2. Development of heat supply to the district heating networks between 1970 and 2003 (Swedish Energy Agency, 2004).

Palm (2004) shows that also institutional factors can connect the waste management system and the DH system. In the city of Linköping, one reason for the introduction of waste incineration was that the same municipal utility operated both the waste management system and the DH system and saw that with waste incineration they could solve two problems at the same time: both an acceptable waste treatment method and heat production for the DH system. A study by Sahlin et al (2004), which is an overview of the consequences of using waste as fuel in Swedish DH systems, also shows that waste incineration enables DH networks to expand due to the low cost of the heat.

Waste Incineration and Combined Heat and Power Production One disadvantage of waste incineration is the low electrical efficiency in the plants.6 This is due to the many impurities in the fuel; the temperature of the steam in the boiler can not exceed 400ºC without entailing high maintenance costs due to corrosion, as stated e.g. by Korobitsyn et al (1999). Combined heat and power (CHP) production is an efficient way to use resources and is recognized by the European Union as one of the measures needed to meet the demands in the Kyoto protocol (European Union, 2004a). Many utilities have 5

6

The carbon dioxide tax is at present 0.1 €/ton. More details of the energy taxation can be found e.g. in (Holmgren, 2006). The electrical efficiency of waste incineration plants is around 23% at capacity 30 MWe (Elforsk, 2003). By way of comparison, a natural gas fired CHP plant has an electrical efficiency of 46-49.5% at capacity 150 MWe and biomass fuelled power plants 34% at capacity 80 MWe (Elforsk, 2003).

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chosen not to invest in electricity production in their waste incineration plants due to difficulties in producing electricity in combination with historically low electricity prices in Sweden.7 However, electricity production at waste incineration plants is forecast to increase, from 0.7 to 1.7 TWh between 2002 and 2010. (Swedish District Heating Association, 2005). Existing waste-fired CHP plants will increase their electricity production and the total number of waste-fired CHP plants will double over the same period. The reason for the increase in electricity production at waste fired CHP plants is not clarified, but it is reasonable to believe that it is a result of the higher electricity prices anticipated when Swedish electricity prices are harmonized with those in continental Europe; this is further explained in the section on Impact on Waste Incineration of Trade in Electricity. The proposed tax on incinerated waste, which is designed to promote CHP production, is probably also a factor. In the municipalities that have a waste incineration plant, the plant is the base supplier of heat to the DH network, due to the negative operational cost of receiving the waste. This can remove the heat sink for more efficient plants and shorten their annual operational times. How to use the heat sink can in this perspective be seen as a conflict between waste management and the energy system. If waste incineration is chosen as the treatment method, it is vital to recover as much as possible of the energy content of the waste. This heat can occupy much of the heat sink leading to lower electricity production in the DH system, compared to if a plant with higher electrical efficiency were chosen instead of a waste incineration plant. Earlier studies have shown that this can be the case, e.g. for a municipal system (Holmgren and Bartlett, 2004) and an overall study of the DH systems in Sweden (Sahlin et al, 2004). This can of course vary between systems as shown by Holmgren (2006). This study deals with the ”competition” in the DH system in the city of Göteborg, where there is heat from waste incineration, waste heat from industries, and also investment in a natural gas fired CHP plant. There is room in the system for all types of waste heat; the new CHP plant mostly replaces heat boilers in the system.

Waste and Connection to the Material Market Waste management is connected to the material markets through the material recovery systems. However, the development of the material recovery system is highly dependent on political decision, such as the introduction of the concept of Producer Responsibility. The incentive to material recovery of municipal waste comes mainly from the Ordinance on Producer Responsibility, which includes packaging, cars, car tyres, newspapers, and electric and electronic devices (e.g. Ministry of the Environment, 1994; 1997). For the included fractions, levels of material recycling are stated. Packaging producers have set up companies to handle the collection of packaging. The companies have a deficit in financing this system, which the producers pay. This is different to newspapers, for example, which do not show this deficit in collection; a functioning market existed even before the legislation was introduced. Also, in industry, different metal fractions such as copper and steel have had a functioning market for recycling for a long time – half of the raw material used to produce steel comes

7

A more detailed explanation of this can be found e.g. in Trygg and Karlsson (2005).

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from collected scrap.8 The prices of materials naturally influence the attractiveness of material recovery.

CONNECTION BETWEEN COUNTRIES IN THE EUROPEAN UNION VIA LEGISLATION AND TRADE AND THE IMPACT ON THE SWEDISH WASTE INCINCERATION This section will describe the connections between EU countries in terms of common legislation and trade in waste and electricity. Differences and similarities in waste management and district heating will also be outlined.

European Legislation Affecting energy and Waste The common legislation in the European Union connects the countries to each other. This section will describe policies and directives that influence waste incineration. The European Union’s member states are obliged to implement the directives in their national legislation. The core of the European Union is the internal market which means free mobility of goods, services, people, and capital. This can be in conflict with waste management goals; examples are the principles of proximity and self-sufficiency, meaning that waste should be treated in the proximity of its origin and that member states should be self-reliant as regards treatment capacity. This is stated in the Framework Directive (European Union, 1975) which also defines waste as “any substance or object which the holder disposes of or is required to dispose of” and establishes the fundamental concept of the Polluter Pays Principle. One problem with the Framework Directive is that it does not clearly state when waste ceases to be waste and becomes a secondary material. In the Shipment of Waste Ordinance (European Council, 1993), waste is divided into two categories - for disposal and for recovery - where trading in the former is forbidden, in order to satisfy both the internal market and the proximity and self-sufficiency goals. Environmental concerns may be in conflict with free trade, both in terms of differing cost for waste treatment options due to varying standards and subsidies to the material recovery market. It is important to harmonise standards for waste treatment options in order not to “draw” waste to less controlled plants. The Directive on landfill (European Union, 1999) and the Directive on the incineration of waste (European Union, 2000) have this purpose. The Directive on the incineration of waste sets permitted maximum levels for emissions to the atmosphere and directions for monitoring the emissions. Emissions to water are also regulated, there are directions as to how the combustion process should be controlled, and how to take care of the residual products. It concerns both waste incineration plants and plants that burn both waste and other fuels, and has meant investment costs for the plants in Sweden in order to fulfil these demands. Whereas the directive is specific about emission levels, it is vague on how to classify efficient energy recovery of waste, which is a shortcoming. It says “the heat generated during the incineration and co8

Personal communication with Åsa Ekdahl, European Confederation of Iron and Steel Industries, 2003.

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incineration process is recovered as far as practicable e.g. through combined heat and power, the generating of process steam or district heating”. The performance of waste incineration plants differs widely, as can be seen from Figure 3, and is detailed further in the section on European differences in waste management and use of district heating. A definition of what an efficient energy recovery of waste is should be introduced. This weak point has been observed by the European Commission, which suggests that the energy efficiency of the plant should decide whether to classify it as a disposal plant or a recovery plant. The use of resources in other plants that the waste incineration plant could replace should also be taken into consideration (European Commission, 2005). The Landfill Directive specifies operational and technical requirements for landfills. It sets the demands that the pricing for receiving waste should include after-care for at least 30 years. It also dictates lower quantities of biodegradable waste in landfill and the collection of methane emissions. Apart from this, there is a directive on producer responsibility for packaging waste (European Union, 2004b), stipulating levels of material and/or energy recovery for different packaging materials. The EU’s waste policy is founded on the waste hierarchy, described in the Sixth Environmental Action Programme from the European Commission (2001) and states that first comes waste prevention, then recovery (reuse, material and energy recovery where material recovery, including biological treatment9 is preferred to energy recovery) and finally disposal, where landfill and waste incineration without energy recovery are included. Swedish waste policy is based upon this hierarchy. This does not go undisputed, however; in particular the question of whether energy recovery or material recovery, including biological treatment, is to be preferred, raises issues. Directives that impact the energy sector include the directive on the common electricity markets (European Union, 2003a), which states that Europe should have free trade in electricity in member states. This will mean higher electricity prices than historically in Sweden, since Sweden will be harmonized with continental Europe which currently has a higher electricity price (e.g. Trygg and Karlsson, 2005). This will further be described in the section on Impact on Waste Incineration of Trade in Electricity. There is a directive promoting CHP (European Union, 2004a), stating that CHP is an effective way to use resources and one measure to meet the demands in the Kyoto protocol. This has probably had an impact on the design of the proposed tax on incinerated waste, which will be explained in the section on Introduction of a tax on incinerated waste in Sweden. Recently, the European Union managed to agree on minimum energy tax levels (European Union, 2003b). There is a directive promoting electricity produced from renewable energy sources (European Union, 2001). Also this is seen as a measure to meet the demands in the Kyoto protocol and strengthening the domestic supply of energy. This has in Sweden led to the implementation of a system of green electricity certificates, which will be explained in the section on Green electricity certificates and waste incineration. Another directive regulates the emission allowance trading (European Union, 2003c). Waste incineration plants are not included in the trading sector, but are affected by the fact that the costs for fossil fuels increase as do

9

Biological treatment includes digestion and composting. When digested, biodegradable waste is degraded without access to oxygen, resulting in biogas which can be used as fuel for vehicles or for electricity and heat production, and a residual product which can be used as fertilizer. When composted, biodegradable waste is degraded with access to oxygen, and the residual product can be used as a soil amender.

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electricity prices due to marginal pricing, where the marginal power producer is coal condensing power in the European system, further explained by Trygg and Karlsson (2005).

European Differences in Waste Management and Use of District Heating This section presents some figures with regard to the amount of district heating in different European countries and waste management methods. Figures for electricity and heat output from waste incineration in different European countries are given. The aim is to investigate if any unambiguous trends can be seen in this material; is there a correlation between high DH production and/or high market share and high proportion of energy recovery as a waste treatment method? In Sweden this is the case, but what about other European countries?

100% 80% 60% 40% 20%

Au st Bu ria lg ar Cr ia oa ti Cz a e De ch nm a Es rk to n Fi i a nl an Fr d a G nce er m a Hu ny ng ar y Ita Ic ly el an d La Li tvi t a Ne hua th nia er la n No d s rw a Po y l Ro and m a Sl nia ov a Sw kia Sw ed itz en er la nd

0%

Coal

Oil

Natural gas

Renewables

Waste

Others

Figure 3. Fuels used for DH in the countries surveyed in a report by Euroheat and Power (2003).

Figure 3 shows the amount of fuel used for DH production by some European countries. It can be seen that the supply differs between countries. Coal is the major fuel used in the Central and Eastern European (CEE) countries and natural gas is also widely used; and the two fuels account for about 85% of the total supply. The CEE countries show a less diversified supply than the old EU member states and a large untapped potential exists for using more heat from waste incineration, renewables, and industrial surplus heat. As regards the proportion of DH produced in CHP plants, this is high in the old member States (64-94%) with the exception of Sweden.10 In the CEE countries, the proportion is lower (35-72%).

10

One reason for this is the historically low electricity prices in Sweden (Sjödin, 2002) and (Trygg and Karlsson, 2005).

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Kristina Holmgren Table 1. Treatment methods for municipal waste in European countries 2002 in 000s of tons (Eurostat, 2005)11

Belgium Czech Republic Denmark Germany Estonia Greece Spain France Ireland Italy Cyprus Latvia Lithuania Luxembourg Hungary Malta Netherlands Austria Poland Portugal Slovenia Slovakia Finland Sweden UK Bulgaria Romania Turkey Iceland Norway Switzerland

Recycling

Composting

Energy recovery

Incineration, destruction

1442 175 796 17250 13 375 3811 4715 463 3897 : 35 : : 67 : 2133 : 116 252 87 37 659 1295 3733 : 170 : 19 507 :

1088 122 555 7844 2 32 3914 4208 34 7335 : 24 : : 47 : 2365 : 215 135 11 39 : 354 1423 : : 383 3 225 :

1493 398 2008 153 0 : 1567 10235 : 2587 : 55 : : 288 : 3125 490 : 944 5 91 201 1675 2674 : : 9 7 492 :

134 3 : 11673 0 : : 875 : 111 : 0 : : : : : : 36 : 0 65 0 : 7 : : 0 3 :

Landfill

Total

594 2097 215 11266 419 4233 14723 12991 1967 18500 450 657 1000 : 3907 188 810 1500 10142 3388 699 1192 1512 825 27545 3188 6695 24573 245 482 80

4761 2845 3587 52532 553 4640 : 33024 2724 29929 500 866 1000 : 4646 187 9900 4634 10509 4618 956 1524 2372 4172 33535 3945 8365 33324 293 3061 4900

Figure 4 shows the total DH production in several European countries together with its share of the heat market. It can be seen that Poland and Germany are the largest producers. The highest market shares exist in some Nordic countries, along with some CEE countries.

11

The data in the Recycling, Composting, Energy recovery, Incineration destruction, and Landfill columns are taken from “Treatment of municipal waste”. The data in the Total column is taken from “Generation of municipal waste”. These were obtained from the Eurostat website. The data differs somewhat in some cases. This is done in order to compare data, to see whether anything has been omitted.

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Profu (2004) identifies a number of “key-factors” when assessing environmental impact of waste incineration, where one is energy recovery per ton waste. Figure 5 shows the extent to which the useful energy content of the incinerated waste is taken care of in a number of countries. Sweden has the highest energy recovery of the countries surveyed, mainly due to the country’s extensive DH network. The efficiency of using waste as a fuel varies between the countries surveyed. It should be noted, however, that if the data in the diagram were recalculated into oil equivalences, countries would show more similar figures. 120

100 90 80 70 60 50 40 30 20 10 0

100 80 60 40 20

DH production

UK

S witz erland

S weden

S lov ak ia

Rom ania

P oland

Norway

Lithuania

Netherlands

Latv ia

Italy

Ic eland

Hungary

G erm any

Franc e

Finland

E s tonia

Denm ark

Cz ec h

Croatia

B ulgaria

A us tria

0

DH market share

Figure 4. DH production (TWh) and DH market share (%) in the countries surveyed by the report in Euroheat and Power (2003).

3,5 3 2,5 2 1,5 1 0,5

Ita Ne ly th er la nd s Sp G re ai n at Br it a P o in rtu g Hu a l ng ar y

Sw ed en Au Sw stri it z a er la nd No rw De a y nm ar k Fr an ce G er m an y

0

Figure 5. Energy recovery by waste incineration (International Solid Waste Association, 2002; Swedish Association of Waste Management, 2000)

Table 1 shows different waste treatment methods in the European countries. The statistics are not exhaustive because not all data is available. Nonetheless, some comments can be made. Regarding the correlation between high amount of DH and energy recovery, this can mainly be seen in Sweden and Denmark. One thing that separates Denmark from Sweden is

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the high proportion of total electricity production that comes from CHP plants; about 40% in Denmark compared to around 8% in Sweden. The countries in CEE with a high amount of DH and/or large market share (the Baltic countries, Poland, the Czech Republic, Slovakia, and Romania) have not evolved their waste management sector and landfill is still the dominating treatment method. Some countries have a large proportion of heat from waste incineration in the DH systems, but the total amount of DH and/or market share is low, such as France, Norway, Italy and Switzerland. For Germany, the data is contradictory. In Table 1, it would appear that incineration is used mainly as a destruction method but as Figure 3 shows, some of the heat comes from waste. What can be said is that Germany has put a lot of effort into developing their material recycling. In general for Table 1, it can be said that waste treatment differs widely between countries and many still rely heavily on landfill.

Impact on Waste Incineration in Sweden of Waste Trade with Some European Countries Trading in waste in the European Union is regulated (European Council, 1993) and waste is divided into different categories: green, yellow and red. Green waste includes e.g. wood chips, logging residues, pellet, tall oil and sorted fractions of plastics, paper and rubber; imports of waste in this category do not have to be registered. Examples of yellow waste are chemically treated used woods, mixed fractions of used wood, paper, rubber and plastics, and municipal solid waste. Red waste is e.g. waste containing or contaminated with polychlorinated biphenyl (PCB) or polychlorinated dibenzo-dioxin. The information on what type of waste the categories include is taken from Ericsson and Nilsson (2004). The authors estimated imports of green waste in 2000 at 760,000 tons. The Swedish Environment Protection Agency must approve imports of yellow and red fractions. Imports of yellow waste increased from 200,000 tons in 1999 to 430,000 tons in 2002 (Olofsson et al 2005). Olofsson et al analyse which factors lie behind Swedish yellow waste imports, mainly intended for use in waste incineration plants with energy recovery. Both factors in the waste management system and the energy system are analysed. Five countries account for almost all imports to Sweden: Denmark, Finland, Germany, Norway, and Holland. The following factors may be significant; − − −

−

12

The infrastructure in Sweden, with DH systems that can utilise the heat, thus raising energy recovery significantly Energy taxation on fossil fuels is high12 in Sweden, and this increases the value of heat. Different types of bio fuel are the most common alternative for the base supply of heat. This means that clean fractions of waste are suitable to combust in existing plants, since the fuels are similar in composition. The quality of the imported waste has been higher than waste from Sweden, but this is starting to level out due to stricter sorting requirements in Sweden.

The carbon dioxide tax is at present 0.1 €/kg.

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Taxes on waste and a ban on landfill are also driving factors. Norway and Denmark both have taxes on waste incineration.

All the above factors lead to a difference in gate fees. The authors assume that in the future, the predominant factor to decrease the driving factors for import to Sweden would be the introduction of a waste incineration tax. A change in energy taxation in order to better fit in to the European Union legislation could also have a significant impact. In Sweden, business is divided into different sectors, with differentiated energy tax levels. This may be in conflict with the EU’s rules with regard to state aid, but Sweden has been granted temporary exemption. If the differentiation were changed and the same rules were valid for the whole of the business sector, the value of heat would be lowered, since the high taxes on fossil fuels would be lowered. Instead, it is suggested that there would be taxation on heat for consumers (Ministry of Finance, 2003). Table 2 shows the gate fees in Sweden for different treatment options for municipal waste. As can be seen, there is great variation between plants. Table 2. Gate fees for municipal waste, including VAT and taxes (Swedish Association of Waste Management, 2005b) Treatment method Cost (€/ton)

Landfill 74-128

Incineration 32-64

Biological treatment 43-106

Impact on Waste Incineration of Trade in Electricity The objective of the directive (European Union, 2003a) on a common internal electricity market is to open up the electricity market by subjecting it to competition. The reason for this is to increase efficiency in the energy sector. Industrial consumers can choose their supplier from July 1st 2004 and all consumers from July 1st 2007. The European Commission publishes a yearly report about the implementation of the internal market (European Commission, 2004) and that report states that the result of the implementation so far is unsatisfactory. One reason is barriers to cross-border trade, e.g. market structures and the need for additional investments in infrastructure. However, the report states that these problems must be solved. The impact of this directive in Sweden is that electricity prices will increase due to harmonisation with the electricity prices in continental Europe, which are higher than in Sweden. This is further described in Trygg and Karlsson (2005). Higher electricity prices increases interest in producing electricity in the DH systems, and naturally also interest in electricity production in waste incineration plants. It also effects the cost of heat in the DH networks. A higher electricity price reduces the cost of heat from CHP plants and their possibility to compete with other plants also improves. Waste incineration plants are base suppliers of heat due to their negative operational costs and the need to treat the waste. However, in the DH network of Göteborg (Holmgren, 2006), where the municipal

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energy utility buys heat from a waste incineration plant13 and also waste heat from industries, the municipal utility had a better negotiation position towards those companies when they invested in a natural gas fired CHP plant assuming electricity prices harmonized with those on the continent.

DISCUSSION OF TWO POLICY INSTRUMENTS Two policy instruments will be discussed in this section: the introduction of a tax on incinerated waste and the green electricity certificate system. The aim here is to show how policy instruments in one system affect the other, and the difficulties in handling the double function of waste incineration as a supplier of heat and/or electricity and as a waste treatment method.

Introduction of a Tax on Incinerated Waste in Sweden A government investigation on a tax on incinerated waste was presented recently (Ministry of Finance, 2005b), and a proposal of the tax was incorporated in the government budget proposition (Ministry of Finance, 2005c). The proposal is that waste should be incorporated in the existing energy taxation system by taxing the fossil content of the waste, meaning e.g. plastic packaging. However, at the time of writing, the tax has been postponed due to difficulties in measuring the fossil content in municipal waste. Table 3 shows the level of the tax on incinerated waste and how it applies to different energy conversion units. The design of the tax is in accordance with how existing energy taxation is applied to the DH sector; with a carbon dioxide tax and an energy tax, which is not applied to electricity production, since electricity is taxed for the consumer (industrial consumers are exempt), heat from hot water boilers is taxed in full, and heat from CHP plants is taxed at deducted levels as is heat to industrial consumers. For a more detailed description of energy taxation, see e.g. Holmgren (2006). It can also be noted that the DH networks are part of the emission allowance trading systems, and the plants included will therefore probable be granted additional deductions of carbon dioxide taxes. However, since waste incineration plants are not included in the trading system, this is not included here. The description of the assignment to carry out the governmental investigation of this tax includes several goals that should be taken into consideration. How the tax steers according to the waste hierarchy and to make material recovery including biological treatment more economically competitive is important, but also impacts on the DH networks and the incentive for CHP production from waste incineration. The problem is that the goals that are enumerated conflict.

13

In this case, another company, co-owned by several neighbouring municipalities owned the waste incineration plant and sold the heat to the utility operating the DH network.

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Table 3. Waste incineration tax as proposed (Ministry of Finance, 2005b). Energy tax (€/ton waste)

Carbon dioxide tax (€/ton waste)

Fossil content 100% Hot water boiler 16 355 Condensing power plant 0 0 14 51-62 CHP plant Fossil content: 14% of total weight (assumed value for municipal waste) Hot water boiler 2 45 Condensing power plant 0 0 CHP plant 0 6.5-8

Total (€/ton waste)

371 0 51-62 47 0 6.5-8

In the waste incineration tax proposal, resulting from the government investigation, the energy system perspective is the predominant; waste is seen primarily as a fuel, and therefore the main objective is that waste taxation be harmonized with energy taxes on other fuels. The investigation states that the fossil content of waste is subsidized in comparison to fossil fuels and that the value of the subsidization of biomass fuels is lessened if there is no tax on incinerated waste. This is corrected if the tax on incinerated waste is designed in this way, and it also provides the incentive for CHP production in waste incineration plants which has hitherto been lacking. The EU directive on promotion of CHP (European Union, 2004a) has influence over this. When summarizing the proposal, it can be said that the energy perspective has been given first priority and the waste management priority second. The only fraction which will have an increased incentive to material recover is various plastics. This fraction is appropriate for material recycling in an energy efficiency perspective; an earlier study has shown large energy savings when recycled plastic material is used instead of virgin material (Holmgren and Henning, 2004). Another study has analysed the consequences for a municipal energy utility of investing in waste incineration if a tax on incinerated waste were introduced. (Holmgren and Gebremedhin, 2004). Tax levels of 11 and 42.5 €/ton were analysed, since those were the levels proposed in an earlier government investigation (Ministry of Finance, 2002). The conclusion was that at the tax level of 11 €/ton, the investment was still profitable for the utility, but at the 42.5 €/ton level, the investment was not profitable. Note that in Table 3 these levels are in the proximity of the levels proposed for plants with CHP production and hot water boilers respectively. The prerequisite for the results is naturally that the utility can not raise the gate fee for receiving the waste. The results indicate, however, that at these tax levels, other treatment options begin to be of interest. Other questions which are raised concern the impact on gate fees of waste incineration plants. Plants with electricity production could maintain lower gate fees than other plants. Would that mean transportation of waste to those plants? This, however, is contradicted by the lack of waste treatment capacity (Swedish Association of Waste Management, 2004), due to waste management regulations. Another issue is to what extent the energy utilities will raise their gate fees to let consumers shoulder the increasing costs. Most existing plants 14

Electrical efficiency in the interval 15-28%.

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without electricity production can not easily convert to CHP production since they consist of hot water boilers,15 and conversion would virtually mean building a new plant. Of the planned waste incineration plans, all have electricity production16 (Swedish District Heating Association, 2005). One question in a waste management perspective is what will happen in terms of encouraging material recovery and biological treatment, in accordance with the waste hierarchy, since this opportunity to increase incentive was not taken.17

Green Electricity Certificates and Waste Incineration The green electricity certificate system is designed to increase electricity produced by renewables (Ministry of the Environment, 2003a, b). The certificate system is influenced by the directive on increased electricity from renewables (European Union, 2001). The producers of electricity receive a certificate when they produce electricity in approved conversion units. These are wind power, solar power, geothermal power, tidal power, hydropower in new or small plants (installed after the end of 2002, and also increased power in old plants renovated after April 2003 and hydropower in plants with a maximum capacity of 1.5 MW), biomass, peat, sorted wood waste from demolition waste, and electricity produced from biogas. It is also proposed that animal fat, meaning residual products from the food industry, should receive certificates (Ministry of Finance, 2005c). Consumers will need a quota of certificates in relation to their total electricity consumption, creating a demand for certificates and thus giving them an economic value. The aim is to increase annual electricity production from renewable energy sources by 10 TWh between 2003 and 2010. The system ends in 2010, but a proposal to extend it to 2030 is in place (Ministry of Sustainable Development, 2005). Electricity produced from municipal waste does not receive certificates in the Swedish certificate system, even if municipal waste is estimated to be of about 80% biological origin. If municipal waste were to be included, it would further increase the incentives for CHP in waste incineration plants since it pays off for every produced MWh of electricity. In the proposed tax on incinerated waste, the main issue is to be classified as a CHP plant, and in order to be so, the quota between electricity and heat needs to be at least 20% (Ministry of Finance, 2005b). The issue of whether municipal waste should receive electricity certificates has been debated since the electricity certificate system was originally designed and in the government investigation on a tax on incinerated waste (Ministry of Finance, 2005d) the question is analysed once again. The conclusion is that the new tax on incinerated waste is enough to steer towards increased CHP in waste incineration plants and if electricity certificates were given for municipal waste, it could steer waste of biological origin towards incineration and that would not comply with Swedish waste management goals.18 Again, the conflict between the goals in waste management and in the energy system can be seen. From an energy system viewpoint, it is logical to implement electricity certificates for municipal waste. It would increase electricity production in waste incineration which is in line with the 15 16 17 18

Personal contact with Anders Hedenstedt, Swedish Association of Waste Management. Personal contact with Anders Hedenstedt, Swedish Association of Waste Management. Again; except for fractions of plastic waste. The Swedish goals for biodegradable waste state that at least 35% should be biologically treated by 2010 (Swedish Environmental Protection Agency, 2005).

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European directive on promotion of cogeneration (European Union, 2004a). When the tax on incinerated waste is introduced, it is deemed important to remove the subsidies that the fossil part of municipal waste has enjoyed in comparison to fossil fuels. When the electricity certificate system is analysed, it is not important to insert the biological part in the system which benefits biomass fuels. When it comes to green electricity certificates, the government investigation states that the waste management goals are more important than the goals of the energy system. The directive on electricity from renewables (European Union, 2001) provides scope for interpretation by member states, e.g. as regards which sources should be included in a certificate system. A voluntary certificate system exists in Europe, The Renewable Energy Certificate System19 (RECS) which in contrast to the Swedish system does include municipal waste. This shows that opinions as to how to classify waste in terms of whether it is a renewable or not differ throughout Europe.

MODELS AS DECISION SUPPORT Various models are often used as decision support tools, e.g. when municipalities make infrastructural decisions, such as waste treatment capacity and energy utility plants. This section describes some models based on system analysis. The models have been used to assess waste management systems and waste incineration and the common theme is the dilemma of the two purposes waste treatment and production of heat and sometimes electricity, and how to handle this. System analysis can be a mean to assess complex systems in order to e.g. determine how available resources should be used to satisfy the aim of the system or to evaluate environmental impacts of various measures. A model can be built that should include the essential features of the system. By building a model, understanding and knowledge of the system and the correlation between components in the system is gained.

Models and How to Handle the Double Function of Waste Incineration The method used in earlier studies carried out by the author (Holmgren and Bartlett, 2004; Holmgren and Gebremedhin, 2004; Holmgren, 2006) is energy system modelling, using the MODEST model (Henning 1998; 1999). MODEST is a linear programming model which minimizes the cost of supplying heat and/or power demand during the analysed period. The main purpose of the model is to find suitable investments, but it can also be used to optimize the operation of existing plants. The results from these studies are mainly how waste functions as a fuel in the district heating system, e.g. the impact on other fuels used, the cost of supplying heat with different amounts of waste used as fuel, and the amount of electricity produced in the DH networks. The effects of various policy instruments are also an appropriate issue to assess. The influence of the waste management system in the model is mainly via economic signals as regards the cost of waste as a fuel. Limits on amount of

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available waste is also set. When analyzing the results, it is vital to be aware that also considerations, more related to the waste management sector, should be included. A study has also been made that has broadened the scope by comparing waste treatment options from an energy efficiency viewpoint (Holmgren and Henning, 2004). Assuming that there is a district heating system that can utilize the heat, which fractions of the waste are suitable to energy recover and which to material recover? Another example of a study with the energy system in focus is Sahlin et al (2004), which analyses the impact on Swedish district heating systems as a whole, using a questionnaire and a simulating energy model named HEATSPOT. Other methods have the waste management system in focus, as shown e.g. by Sundberg et al (1994). The paper describes the model MIMES/WASTE, which seeks the most costefficient way to treat waste. Another study has linked MIMES/WASTE with an energy system model, MARTES, by using both models in two case studies (Olofsson, 2001). Life cycle assessment (LCA) is a widely used method for evaluating the environmental impact of products and services (Rydh et al, 2002). How to perform an LCA is laid down in ISO standards. The methodology in short has four steps: 1. Goal and scope definition 2. Inventory analysis, where data is compiled 3. Life cycle assessment involving classification of data to different environmental impacts;20 characterization, where the data is analysed as to the extent to which they contribute to different impacts; and valuing or weighting. The step of valuing is however in question since it is considered to be subjective. 4. Interpretation of results. One model for assessing waste management options based on LCA methodology is ORWARE, see e.g. Eriksson et al (2002). This model handles the double functions of waste incineration by compensatory systems, in line with LCA methodology. A compensatory system, e.g. for waste incineration, apart from the function of waste treatment, also means district heating and/or electricity. To assess the robustness of the results, a sensitivity analysis of these compensatory systems is recommended, e.g. if district heating is produced by biomass fuel or oil. Finnveden and Ekvall (1998) compare LCA studies of recycling versus incineration of paper, and show the importance of assumptions made with regard to compensatory systems and also take up the question of biomass; what is made of the saved biomass when recycling paper? This question indicates a need to define how biomass should be regarded; should it be regarded as a scarce resource? A number of studies have attempted to estimate the potential biomass supply. Ericsson and Nilsson (2006) have assessed the potential in the 15 old EU countries (EU15), 8 newcomers21 and 2 candidate countries22 (ACC10) and also Belarus and Ukraine, and compared it with the EU’s targets for increasing the proportion of the total primary energy supply produced with biomass. Their assessment shows that, subject to certain restrictions on land availability, the potential is up to 11.7 EJ/year in the EU15 and 5.5 EJ/year in the 19 20 21 22

More information can be found at www.recs.org (November 2005). Such as greenhouse gases, eutrophication, acidification. Cyprus and Malta are not included. Bulgaria and Romania.

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ACC10. These figures can be compared with the fact that total energy supply in the EU15 in 2001 was 62.6 EJ. There are no resource limitations in meeting the EU target of 5.6 EJ/year in the EU15 by 2010, though it will probably not be met due to slow implementation of the renewable energy policy. Berndes et. al. (2003) are reviewing 17 studies on the contribution of biomass in future global energy supply. Both demand-driven studies23 and resource studies24 were reviewed. The resource studies showed large variations in the amount of biomass fuels. The studies with the highest assumptions assumed vast areas of Africa to be given over to energy crop production with exports to the rest of the world. The article criticizes the studies for not including other environmental effects of such expansion, such as biodiversity, and social factors are also overlooked. These studies give an indication that biomass utilization could increase substantially; this could, however, lead to environmental and social problems which are not taken into account when, for example, making a study where biomass fuel replaces fossil fuel as a compensatory system for district heating production, hence indicating lower environmental concerns. This is a significant issue, since it has been shown that these assumptions are often crucial for the results in LCA studies. One drawback of using MODEST when analyzing waste incineration is that few environmental effects have been taken into account. In earlier studies (Holmgren and Bartlett, 2004; Holmgren and Gebrenedhin, 2004; Holmgren, 2006), only carbon dioxide emissions from the analysed DH networks have been calculated. One solution could be to use external costs of environmental effects, and include these costs in the optimization calculations of the D networks. This has been done by Carlsson (2002). In that study, external cost data was obtained from the European Union’s ExternE-project.25 The basic idea behind the concept of external cost is that electricity and heat production give rise to several negative external effects,26 such as climate change, acidification and health impacts. The cost of these effects should be internalized in the price of the energy supply, otherwise a suboptimal consumption of energy occurs from a socio-economic perspective. This can be compared to the step of valuing or weighing in the LCA methodology, since that is essentially also to put a value on environmental effects. However, this step is not really accepted in LCA methodology since it is considered to be subjective and the recommendation is to use it with care.

CONCLUSION The double function of waste incineration, both as a waste treatment method and a supplier of electricity and/or heat is discussed in this chapter. A positive impact in one of the systems may be negative in the other, and strategies and goals in the two sectors can conflict. The main findings in this chapter are as follows.

23

24

25 26

The meaning of demand-driven studies is the potential of energy from biomass in competition with other energy carriers. The meaning of resource-driven studies is the possibility to produce biomass for energy purposes in competition with other land uses, such as food production. Information about the ExternE project can be found at http://www.externe.info/ Positive external effects, for example on local employment, can also occur.

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−

−

−

−

Sweden has extensive DH networks and therefore better possibilities to efficiently recover the energy content in the waste than countries with a less developed infrastructure. There is a correlation between extensive DH networks and substantial incineration as waste treatment method in Sweden, and the connection is both historical and organisational. This correlation can not be unambiguously shown to exist in any other EU country. In this context, Sweden differs from other Western European countries, since relatively little DH is produced in CHP plants. Waste incineration can decrease possibilities for producing CHP in DH networks and this can be seen as a conflict between the need to treat waste in an acceptable way and the goal of more CHP production in the energy system. There is a conflict in the European Union between the internal market and waste management policy, for example that waste should be treated close to its origin. This has been solved by prohibiting exports of waste for disposal but not for recovery. A shortcoming in the directives is that they do not clearly define what an energy efficient waste incineration plant is and hence not when a waste incineration plant should be defined as recovery versus destruction. The conflict between waste management goals and energy system goals when designing policy instruments has been shown. When designing the tax on incinerated waste, the energy system perspective was the predominant factor, the main objective being to harmonize taxes on incinerated waste with taxes on other fuels. The incentive for increasing material recovery and biological treatment was set aside, except in the case of plastic waste. In the design of the electricity certificate system, the waste management goals, for example more biological treatment, prohibits waste incineration plants from receiving certificates even if this would increase the incentive to produce CHP, consistent with the goals for the energy system. The double function is also addressed when different models for assessing waste incineration are reviewed; the importance of being aware of this and the impacts of different assumptions are discussed. Various models deal with the double function in different ways, and have their own strengths and weaknesses. It is also essential to be aware of the importance of assumptions. A model’s construction and the results from it should be seen as way of gaining knowledge of the system and as a support in decision-making. When actual decisions are to be made, there are other aspects that can be of importance that has not been included in the model.

ACKNOWLEDGMENTS The work was carried out under the auspices of The Energy Systems Programme, which is financed by the Swedish Foundation for Strategic Research, the Swedish Energy Agency and Swedish Industry. Tekniska Verken i Linköping AB is acknowledged for their financial support. The author is grateful to Maria Saxe, Mats Bladh and Björn Karlsson for valuable comments on the chapter.

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REFERENCES Berndes G, Hoogwijk M and van den Broek R. 2003. The contribution of biomass in the future global energy supply: a review of 17 studies. Biomass and Bioenergy 25:1-28. Carlsson A. 2002. Considering External Costs – Their Influence on Technical Measures in Energy Systems. Dissertation No 766, Linköping Institute of Technology, Linköping, Sweden. Elforsk. 2003. El från nya anläggningar – 2003. Jämförelse mellan olika tekniker för elgenerering med avseende på kostnader och utvecklingstendenser. (Electricity from new plants – 2003. Comparison between different technologies for electricity generation with regards to costs and development trends, in Swedish) Elforsk report no. 03:14, Stockholm, Sweden. Ericsson K and Nilsson L.J. 2004. International biofuel trade – A study of Swedish import. Biomass and Bioenergy 26:205-220. Ericsson K and Nilsson L.J. 2006. Assessment of potential biomass supply in Europe using a resource-focused approach. Biomass and Bioenergy 30:1-15. Eriksson O, Frostell B, Björklund A, Assefa G, Sundqvist J-O, Granath J, Carlsson M, Baky A and Thyselius L. 2002. ORWARE – a simulation tool for waste management. Resources, Conservation and Recycling 36:287-307. Euroheat and Power. 2003. District heating and cooling. Country by country 2005 survey. Belgium. European Commission. 2001. Environmental 2010: Our Future, Our Choices – The Sixth Environmental Action Programme. COM (2001) 31 final, Brussels, Belgium. European Commission. 2004. Report from the Commission – Annual Report on the Implementation of the Gas and Electricity Internal Market. COM/2004/0863 final, Brussels, Belgium. European Commission. 2005. Communication from the commission to the council, the European Parliament, the European Economic and Social Committee and the committee of the regions: Taking Sustainable use of resources forward: A Thematic Strategy on the prevention and recycling of waste, Brussels, Belgium. European Council. 1993. Council Regulation (EEC) No 259/93 of 1 February 1993 on the supervision and control of shipments of waste within, into and out of the European Community. Brussels, Belgium. European Union. 1975. Council Directive of 15 July 1975 on waste. Brussels, Belgium. European Union. 1999. Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste. Brussels, Belgium. European Union. 2000. Directive 2000/76/EC on the incineration of waste. Brussels, Belgium. European Union. 2001. Directive 2001/77/EC on the promotion of electricity produced from renewable energy sources in the internal electricity market. Brussels, Belgium. European Union. 2003a. Council Directive 2003/54/EC concerning common rules for the internal market in electricity and repealing Directive 96/92/EC. Brussels, Belgium. European Union. 2003b. Council Directive 2003/96/EC restructuring the Community framework for the taxation of energy products and electricity. Brussels, Belgium.

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European Union. 2003c. Council Directive 2003/87/EC establishing a scheme for greenhouse gas emission allowance trading within the Community and amending Council Directive 96/64/EC. Brussels, Belgium. European Union. 2004a. Directive 2004/8/EC on the promotion of cogeneration based on a useful heat demand in the internal energy market and amending Directive 92/42/EEC. Brussels, Belgium. European Union. 2004b. Directive 2004/12/EC amending Directive 94/62/EC on packaging and packaging waste. Brussels, Belgium. Eurostat. 2005. Statistical data obtained from: http://epp.eurostat.cec.eu.int/portal/ page?_pageid=1090,30070682,1090_33076576&_dad=portal&_schema=PORTAL. Site visited December 2005. Finnveden G and Ekvall T. 1998. Life-cycle assessment as a decision-support tool – the case of recycling versus incineration of paper. Resources, Conservation and Recycling 24:235256. Henning D. 1998. Cost optimisation for a local utility through CHP, heat storage and load management. International Journal of Energy Research 22:691-713. Henning D. 1999. Optimisation of local and national energy systems: development and use of the MODEST model. Dissertation No. 559, Linköping Institute of Technology, Linköping, Sweden. Holmgren K and Bartlett M. 2004. Waste incineration in Swedish municipal energy systems – modelling the effects of various waste quantities in the city of Linköping. In: Afghan NH, Bogdan Z, Duic N. Editors. Sustainable development of energy, water and environment systems. Proceedings of the Conference, 2-7 June 2002, Dubrovnik, Croatia. Holmgren K and Gebremedhin A. 2004. Modelling a district heating system: introduction of waste incineration, policy instruments and co-operation with an industry. Energy Policy, 32:1807-1817. Holmgren K and Henning D. 2004. Comparison between material and energy recovery of municipal waste from an energy perspective. A study of two Swedish municipalities. Resources, Conservation and Recycling, 43:51-73. Holmgren K. 2006. The role of a district heating network as a user of waste heat supply from various sources – the case of Göteborg. Applied Energy, in press. Hrelja R. 2006. I hettan från ångpannan – vetenskap, politik och miljö kring en kommunal energianläggning under två decennier. (In the heat from the steam boiler – science, politics and environment surrounding a municipal energy facility during two decades, in Swedish) Manuscript, coming dissertation from Linköping Universitet. International Solid Waste Association. 2002. Energy from Waste, State-of-the art Report, Statistics 4, Edition January 2002. Copenhagen, Denmark. Korobitsyn M.A, Jellema P and Hirs G.G. 1999. Possibilities for gas turbine and waste incinerator integration. Energy 24:783-793. Ministry of the Environment. 1994. Förordning (1994:1205) om producentansvar för returpapper (Ordinance 1994:1205 on producer responsibility for newspaper, in Swedish). Stockholm, Sweden. Ministry of the Environment. 1997. Förordning (1997:185) om producentansvar för förpackningar (Ordinance 1997:185 on producer responsibility for packaging, in Swedish). Stockholm, Sweden.

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Ministry of the Environment. 2001. Förordning (2001:512) om deponering av avfall (Ordinance (2001:512) on landfill of waste, in Swedish) Stockholm, Sweden. Ministry of the Environment. 2003a. Lag (2003:113) om elcertifikat (Law (2003:113) on electricity certificates, in Swedish). Stockholm, Sweden. Ministry of the Environment. 2003b. Förordning (2003:120) om elcertifikat (Ordinance (2003:120) on electricity certificates, in Swedish, Stockholm, Sweden. Ministry of Finance. 1994. Lag (1994:1776) om skatt på energi. (Law (1994:1776) on tax on energy. Stockholm, Sweden. Ministry of Finance. 2002. Skatt på avfall idag – och i framtiden (Tax on waste today – and in the future, in Swedish) SOU 2002:9, Fritze, Stockholm, Sweden. Ministry of Finance. 2003. Svåra skatter: betänkande från Skattenedsättningskommittén. (Difficult taxes, in Swedish). SOU 2003:38, Stockholm, Sweden. Ministry of Finance. 2005a. Lag (2005:962) om ändring i lagen (1999:673) om skatt på avfall (Law (2005:962) on changes in the law (199:673) governing waste tax, in Swedish), Stockholm, Sweden. Ministry of Finance. 2005b. BRASkatt? – beskattning av avfall som förbränns (GOODtax? – taxation of incinerated waste, in Swedish.) SoU 2005:23. Stockholm, Sweden. Ministry of Finance. 2005c. Budgetpropositionen för 2006 (Budget proposal 2006, in Swedish) Prop, 2005/06:1. Stockholm, Sweden. Ministry of Finance. 2005d. BRASkatt?- beskattning av avfall som deponeras (GOODtax? – taxation of landfilled waste, in Swedish) SOU 2005:64. Stockholm, Sweden. Ministry of Sustainable Development. 2005. Förslag om ett utvecklat elcertifikatsystem. Proposal for a developed electricity certificate system, in Swedish) Ds 2005:29, Stockholm, Sweden. Olofsson M. 2001. Linking the Analysis of Waste Management and Energy Systems. ISRN CTH-EST-R-01/5-SE, Department of Energy Conversion, Chalmers University of Technology, Göteborg, Sweden. Olofsson M, Sahlin J, Ekvall T and Sundberg J. 2005. Driving forces for import of waste for energy recovery in Sweden. Waste Management and Research 23:3-12. Palm J. 2004. Makten över energin – policyprocesser i två kommuner 1977-2001. (Influence over energy – the process of policy in two municipalities 1977-2001, in Swedish). Linköping Studies in Arts and Science 289. Linköpings Universitet, Linköping, Sweden. Profu. 2004. Evaluating waste incineration as treatment and energy recovery method from an environmental point of view. Collected from home page www.profu.se. Rydh CJ, Lindahl M and Tingström J. 2002. Livscykelanalys – en metod för miljöbedömning av varor och tjänster. (Life cycle assessment – a method for environmental assessment of goods and services, in Swedish), Studentlitteratur, Lund, Sweden. Sahlin J, Knutsson D and Ekvall T. 2004. Effects of planned expansion of waste incineration in the Swedish district heating systems. Resources, Conservation and Recycling 41:279292. Sjödin J. 2002. Swedish District Heating Systems and a Harmonised European Energy Market – Means to Reduce Global Carbon Emissions. Dissertation No. 795. Linköping Institute of Technology, Linköping, Sweden. Sundberg J, Gipperth P and Wene C-O. 1994. A systems approach to municipal solid waste management: a pilot study of Göteborg. Waste Management and Research 12:73-91.

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Swedish Association of Waste Management. 2000. Svensk Avfallshantering 2000 (Swedish Waste Management 2000, in Swedish), Malmö, Sweden. Swedish Association of Waste Management. 2004. Avfallsförbränning. Utbyggnadsplaner, behov och brist. (Waste incineration. Expansion plans, capacity need and lack thereof, in Swedish) RVF-report 04:02. Malmö, Sweden. Swedish Association of Waste Management. 2005a. Avfall blir värme och el. En rapport om avfallsförbränning. (Waste turn into heat and electricity. A report on waste incineration, in Swedish). RVF-report 2005:02. Malmö, Sweden. Swedish Association of Waste Management. 2005b. Svensk avfallshantering 2005 (Swedish Waste Management 2005, in Swedish), Malmö, Sweden. Swedish District Heating Association. 2005. Kraftvärme och dess kopplingar till elcertifikatsystemet. (Combined heat and power and the connection to the electricity certificate system, in Swedish), Sweden. Swedish Energy Agency. 2004. Energy in Sweden 2004. Eskilstuna, Sweden. Swedish Environmental Protection Agency. 2005. Strategi för hållbar avfallshantering. (Strategy for sustainable waste management, in Swedish), Stockholm, Sweden. Trygg L and Karlsson B.G. 2005. Industrial DSM in a deregulated European electricity market – a case study of 11 plants in Sweden. Energy Policy 33:1445-1459.

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 221-234 © 2006 Nova Science Publishers, Inc.

Chapter 7

ARTIFICIAL AGGREGATE MADE BY CEMENTITIOUS GRANULATION OF WASTE INCINERATOR FLY ASH R. Cioffi1, F. Colangelo1, F. Montagnaro2 and L. Santoro2* 1

Dipartimento per le Tecnologie, Università di Napoli Parthenope, Napoli, Italy 2 Dipartimento di Chimica, Università di Napoli Federico II, Napoli, Italy

ABSTRACT The waste employed in this work comes from an incineration plant in which municipal, hospital and industrial wastes are treated. The plant is equipped with rotary and stoker furnaces and both fly ash samples coming from these two equipments have been individually employed. Ash from waste incineration plant is classified as hazardous and cannot be utilized or even landfilled without prior treatment. This paper reports the results of an extensive investigation on stabilization/solidification of the above ash samples by addition of hydraulic binders in a granulation equipment. A rotary plate granulator was used with binders based on cement, lime and coal fly ash. Granulation was carried out with several mixes in which the ash content was up to 70%. In some cases, the granules obtained in this way are suited for matter recovery by reusing the waste for the manufacture of building materials. To achieve this in most cases, two-step granulation is required with pure binder being used in the second one. In this way the granules from the first step can be encapsulated within an outer shell able to improve the technological and leaching properties. The possibility to get matter recovery from incinerator ash is a crucial issue for making the granulation process environmentally and economically sound. In fact, the most direct application of granules is in the field of artificial aggregates for road construction and concrete manufacture. The granules obtained from the treatment of fly ash samples have been tested to assess their physicomechanical and leaching properties. Specifically, measurements have been carried out regarding the following properties: density, water adsorption capacity, compressive

*

Corresponding author. Tel.: +39-081674028; fax: ++39-081674090. E-mail address: [email protected]

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INTRODUCTION In the last few years the use of aggregates in the different fields of civil engineering has been steadily growing and the Italian yearly demand for this material was estimated to be about 1.3·108 m3 in 2002 [1]. As a consequence, the resulting environmental impact is an issue that must be faced to have sustainable development in all the fields of civil engineering. The replacement (at least partial) of natural aggregates with artificial ones can help solve the above problem and also can address waste management towards matter recovery. This possibility is of great importance in the light of the increasingly high availability of industrial solid wastes, marine and lake sediments as well as construction and demolition wastes. So, it is not surprising that many papers can be found in the literature on the replacement of natural aggregate with unprocessed wastes from several different sources [1-14]. However, artificial aggregate of improved technological and leaching properties can be manufactured from reprocessed wastes according to specific treatments that can be of different type depending on the nature of the waste and on the characteristics of the desired product. Specifically, the waste properties that can be of concern are the physical nature (homogenous, heterogeneous, monolithic, granular, sludge), the structure (amorphous, crystalline, compact, porous), the chemical composition and the compatibility with binding matrices. On the other hand, the characteristics of the desired product that are of concern are those linked to the specific use the aggregate is intended for. Among the above waste and aggregate characteristics, probably the most important one is the waste chemical composition. The reason for this is that, depending on this characteristic, the waste can or cannot be chemically involved in the treatment required for aggregate manufacture. Of course, this issue can affect not only the product quality, but also the release of the contaminants that may be contained in the raw waste. In the light of the above considerations, it can be said that a proposed process for aggregate manufacture from waste must be validated from the three-fold point of view: chemical, technological and environmental. From the chemical point of view it is important to understand how the waste components (pollutants included) are involved in the chemical processes that take place during waste treatment. That is, some waste components can be actively involved in the formation of the neo-formed phases and also the pollutants can be entrapped within these phases by means of chemical mechanisms such as diadochy, chemisorption, reprecipitation, etc. Alternatively, the waste components (pollutant included) can retain their chemical nature and in such a case the treatment would only rely on physical entrapment (micro- and macroencapsulation). From the technological point of view, it is important to assess the suitability of the treated waste to the application for which the treatment is intended. Of course, this requires the measurement of the pertinent physical and mechanical properties (density, porosity,

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compressive strength, etc.) and the assessment of their compliance to the technical specifications pertinent to the proposed application. Finally, from the environmental point of view it is important to assess the pollutants release that can take place during the artificial aggregate lifetime. Of course, under this point of view, the long-term release behavior can only be predicted, and, to this scope, proper basic characterization leaching tests can be helpful. Tests of this type can be static, dynamic, continuous, and can make use of leachants of different composition. Their scope is the understanding of the aggregate behavior, even at long-term, in any possible application scenario. Of course, these tests are to be carried out in addition to compliance tests which, different from country to country, are required for any proposed application. Artificial aggregates can be manufactured by means of two types of processes: cementbased granulation and high temperature sintering. Of these, the latter has been widely studied and the pertinent literature is rich of applications in which many waste materials proved to have potential for use as feedstock: bottom and fly ashes from combustors and municipal solid waste incinerators, metallurgical slags, dust from furnace, mine and quarry tailings, sediments, shredder waste, etc.[14-20]. On the other hand, although cement-based granulation processes have not yet been studied equally deeply, their suitability for the manufacture of artificial aggregates is undoubtedly worthy of consideration. First of all, it is well known that the treatment of wastes (often hazardous) largely relies on cement-based stabilization/ solidification processes which allow safer disposal and/or matter recovery for the manufacture of building materials [21-24]. Furthermore, the application of such processes has economical and environmental advantages due to the reduced energy requirement (process carried out at ordinary temperature) and the lack of secondary pollution (no gaseous emission is involved). As previously pointed out, cement-based processes can be equally well addressed towards safer disposal of the waste or matter recovery for the manufacture of building materials inasmuch as their twofold aim is to reduce the pollutants mobility and form monolithic products. The occurrence of physical and chemical stabilization/solidification mechanisms is necessary to warrant treatment effectiveness [21,22]. Under this point of view, it is useful to outline that cement-based processes have high potential and flexibility so that safer disposal may be favored in respect to matter recovery or vice versa depending on the optimization of the numerous variables that affect the same processes. In fact, the main operating conditions that can be optimized are: the binding matrix composition in respect to waste nature and composition, the waste/binder ratio, the time and temperature of curing, the use of specific additives and so on. More specifically, in addition to ordinary Portland cement and other established binders, alternative and innovative matrices have been successfully employed in many cases [25]. These alternative and innovative matrices can be obtained from industrial wastes such as coal fly ash, blast furnace slag, chemical gypsums. Furthermore, it has been recently proved that the use of additives based on organophilic bentonite allows the application of cement stabilization/solidification to wastes containing up to 55% organic matter [26,27]. In this article a cement-based granulation process has been studied for the manufacture of artificial aggregate starting from incinerator ash. This ash comes from an incineration plant in which municipal, hospital and industrial wastes are treated. The plant is equipped with rotary and stoker furnaces and both the fly ashes coming from these two equipments have been individually employed. These ashes are classified as hazardous and cannot be utilized or even

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landfilled without prior treatment. The treatment investigated in this article is based on cement stabilization/solidification and makes use of a rotary plate granulator with binding mixes composed of cement, lime and coal fly ash. In addition to one-step granulation, two-step granulation was carried out to have end product of improved properties in view of reuse for artificial aggregate production. In the one-step granulation the waste is incorporated within the binding matrix in a measure ranging from 50 to 70%. In the two-step granulation a second step is carried out with pure binder to get the granules from the one-step process encapsulated within an outer shell able to improve the technological and leaching properties. The granules obtained from these processes have been tested to assess their physicomechanical and leaching properties. Specifically, measurements have been carried out regarding the following properties: density, water adsorption capacity, compressive (crushing) strength and leaching behavior. Moreover, concrete mixes have been prepared with some of the artificial aggregates made by granulation. Once hardened, these mixes have been tested from the technological point of view.

MATERIALS AND METHODS The ash employed in this work comes from an incineration plant located in Melfi (Potenza, Italy) in which municipal, hospital and industrial wastes are treated. The plant is equipped with rotary and stoker furnaces and fly ash samples from both furnaces have been individually employed. According to the European Waste Catalog, this waste is given the code 19.01.13* and classified as hazardous. As such, it cannot be employed or even landfilled without prior treatment able to properly reduce its environmental impact. Table 1. Ash sample’s chemical composition, wt% Component Al2O3 Na2O K2O SO3 CaO Fe2O3 MgO MnO2 P2O5 TiO2 SiO2 ClCu, mg/kg Cd, mg/kg Pb, mg/kg Zn, mg/kg

Ash origin Rotary furnace 7.61 3.36 3.85 9.12 32.11 2.03 3.24 0.56 1.12 1.85 7.93 3.92 4927 62 3621 4643

Stoker furnace 3.89 2.62 2.32 7.12 41.23 1.02 1.69 0.11 0.53 0.42 11.06 1.41 2261 23 1720 2645

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Both the ash samples coming from the two different furnaces have been chemically characterized by means of the determination of the qualitative and quantitative compositions through X-ray fluorescence. The results are reported in Table 1 and show that the two ash samples have similar qualitative compositions. Differences can be mainly observed as far as the content of heavy metals of environmental concern is taken into account. Specifically, the ash sample from the rotary furnace incinerator has higher content of polluting metals, and this is a consequence of the different feed. Actually, the rotary furnace incinerator is fed with wastes from industrial processes, while the stoker furnace incinerator is fed with municipal and hospital wastes. Further characterization was carried out to determine the particle size distribution through laser light scattering. The results are reported in Table 2 and show that significant differences exist between the two ash samples. Specifically, the resulting volume weighted mean diameter is 36.6 µm for the rotary furnace incinerator ash sample and 64.4 µm for the stoker furnace incinerator ash sample. Table 2. Ash sample’s size distribution, vol% Size fraction, µm <1 1–10 10–20 20–45 45–80 80–120 >120

Ash origin Rotary furnace 0.21 8.46 19.98 44.04 20.28 5.31 1.72

Stoker furnace 1.81 14.02 12.22 21.49 19.76 14.13 16.57

The ash samples leaching behavior has been determined through test UNI 10802 [28]. This test is in force in Italy and derives from European Union directives. It makes use of distilled water and, in the case of granular materials, extents up to 24 hours without leachant renewals. The amounts released in this test are reported in Table 3 for the metals of environmental concern. Despite the differences in heavy metals content, the release is similar for the two ash samples. Table 3. Metal release by raw ash samples, mg/L Metal Cd Zn Pb Cu

Ash origin Rotary furnace 0.63 8.27 1.86 1.09

Stoker furnace 0.54 7.32 1.53 1.08

The granules leaching behavior has been determined according to the compliance test in force in Italy that allows matter recovery from wastes [29]. This test is dynamic and makes use of distilled water with several leachant renewals up to 16 days.

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The other materials employed for the manufacture of the granules are a CEM II/A-L 42.5R cement (European Standard EN-197/1), commercial hydrated lime and coal fly ash supplied by the ENEL (Italian Electricity Board) power plant located in Brindisi (Italy). The granules manufacture has been carried out by means of a granulator equipped with a rotating and tilting plate (Fig. 1). The rotating speed and the tilting angle can be adjusted between wide limits. In the experiment, the settings were 40 and 60 rpm for the rotating speed and 50° for the tilting angle.

Figure 1 Granulation equipment

The granules manufacture made use of the following technique. A weighted amount of solid mix was slowly and continuously poured into the granulator plate. Simultaneously, water was fed through a nozzle at a proper rate and, in the initial granulation phase, the rotating speed was adjusted at 40 rpm to favor the formation of the granules nuclei. This initial phase gives granules with a very wide size distribution. A further granulation phase followed in which neither solid mix nor water were added and the rotating speed was adjusted at 60 rpm. This makes smaller granules coalesce and favors granules compacting by the expulsion of part of the water employed in the initial phase. The whole manufacture process lasts about 20 minutes and the final product is composed of compacted granules with most of them in the range 4-18 mm. The amounts of solid mix and water employed, their feed rates to the granulator plate and the rotating speeds in the two granulation phases are the results of specific process optimization.

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The granules obtained as described were cured 12 hours in a climatic chamber where temperature and relative humidity were kept at 50°C and 95%, respectively. This curing phase favors granules hardening, necessary for successive handling. Finally, the granules were submitted to a 14-day curing at room temperature and humidity. It was checked that further curing in these conditions did not improve the technological properties of the granules. In all the granules preparations 800 g of solid mixes were used, whose compositions are reported in Table 4. All the systems listed in this table were submitted to a second granulation step in which a 50/50 cement/coal fly ash binder was used in amount equal to 40% of granules weight. In the following, these systems are distinguished by placing the + sign at the end of each label. The scope of the two-step granulation was to encapsulate the primary granulation products into an outer pure binder layer able to improve the technological properties and the leaching behavior of the final products. The granules obtained in the different experimental conditions were submitted to technological characterization through the determination of some selected physicomechanical properties. The granules size distribution was determined by sieving according to UNI EN 933-1 standard. The granules density was found to vary with size. Then, it was determined on two different size fractions: 4-12 mm and 12-18 mm. The technique was as follows. Each specimen was soaked into water at 20±2°C and then superficially wiped with a moist cloth. This was repeated every 24 hours until constant weight was reached. The water saturated granules were used for the determination of the specimen volume by means of water displacement. The mass of the same specimen was determined after drying at 105±5°C. Following this procedure, the granules apparent density was obtained. Table 4. Granules composition, wt%

System

R70C S70C R70L S70L R60LA S60LA R50LA S50LA

Ash origin Rotary Stoker furnace furnace

70 70 60 50 -

70 70 60 50

Binder type Cement

Lime

Coal fly ash

30 30 -

30 30 15 15 30 30

25 25 20 20

Water/solid ratio

0.25 0.41 0.25 0.36 0.32 0.39 0.35 0.40

The water absorption capacity (WAC) was determined as described in [30]. The water saturated granules (see the above paragraph) were dried at 40±2°C until constant weight was reached. Then, WAC was determined by means of the following relationship: WAC = 100(MW-MD)/MD where MW is the water saturated granules mass and MD is the 40±2°C dried granules mass.

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The Los Angeles coefficient is a measure of aggregate degradation resulting from a combination of actions including abrasion (attrition), impact and grinding in a rotating steel drum containing a specified number of steel spheres according to UNI EN 1097-2 standard (ASTM C131). The specimen is washed and oven dried at 110±5°C until constant weight is reached. Then, it is loaded into the rotating drum together with the specified number of spheres (depending on the charge weight). After 500 drum revolutions at 30-33 rpm, the specimen is discharged and sieved through a 1.7 mm sieve (No. 8 of UNI 2331/2332 sieve series or 12 mesh of ASTM E 11-70 series). The Los Angeles coefficient is exactly the difference between the original charge weight and the recovered one after sieving expressed in terms of percentage of the original weight. The result is rounded to 1%. The measurement of the granules compressive (crushing) strength was carried out according to UNI 7549/7 standard by means of a 3000 kN Controls MC60 press. Concrete was prepared by mixing 0.11 m3 of cement (density 3140 kg/m3), 0.17 m3 of water, 0.31 m3 of fine natural aggregate (density 2200 kg/m3) and 0.41 m3 of artificial aggregate in replacement of the coarse fraction. Concrete cubic specimens (15 cm in size) were employed for the measurement of compressive strength, according to UNI 6132 standard. The equipment was the same press referred to above. The concrete dynamic modulus of elasticity was determined using cylindrical specimens (15 cm in diameter and 30 cm in height) by means of ultrasonic pulse measurement. According to Rilem NDT 1 standard, this method links the elasticity modulus to the velocity with which an ultrasonic pulse passes through the material under investigation. A Matest apparatus was used for this measurement. In both cases of concrete compressive strength and elasticity modulus measurements, three specimens were used for each data point after 28 days of water curing.

RESULTS AND DISCUSSION Table 5 shows the results of density and WAC measurements separately carried out on the two different size fractions of all the granules tested. As far as the density is concerned, it is clearly seen that this property increases as the ash content increases. Furthermore, the density is greater for the smaller size fraction. This is due to the fact that, during the final compacting phase of granulation, water is more easily expelled in the case of smaller granules. The ash origin (from stoker or rotary furnace incinerator) has no significant effect on granules density, despite the greater water requirement in the granules manufacture starting from stoker furnace incinerator ash. Finally, analyzing the results for the systems containing 70% ash, it is possible to draw the conclusion that higher density is obtained when cement is used in the granules manufacture instead of lime. The values of density found for the granules manufactured in this study are such that they can be classified as lightweight aggregate. In fact, Lytag, a commercially available lightweight aggregate, was shown to have density in the range 1370-1490 kg/m3 [19], while typical natural aggregate density ranges from 2400 to 2800 kg/m3. The majority of our density data are lower than the Lytag lower limit of 1370 kg/m3, and only in a few cases

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values greater than 1490 kg/m3 have been found. Then, the proposed granulation technique proves to be suitable for the manufacture of lightweight artificial aggregate. Table 5. Density and water absorption capacity (WAC) of granules

System

R70C R70C+ S70C S70C+ R70L R70L+ S70L S70L+ R60LA R60LA+ S60LA S60LA+ R50LA R50LA+ S50LA S50LA+

Density, kg/m3 Size fraction, mm 4-12 12-18

1585 1596 1596 1612 1431 1445 1458 1452 1433 1428 1406 1442 1365 1368 1359 1375

1136 1196 1203 1226 1011 1037 1050 1081 1027 1051 1023 1101 976 995 989 1062

WAC, wt% Size fraction, mm 4-12 12-18

11.22 9.80 9.62 8.25 13.86 11.95 11.67 10.28 10.62 9.18 8.95 7.43 10.62 9.73 8.90 7.34

13.54 11.73 12.01 10.21 15.46 13.65 14.31 12.11 12.81 10.95 11.08 9.41 12.23 10.71 10.00 9.70

The values of WAC are clearly affected by the size of the fraction under consideration. In fact, higher values are found for the 12-18 mm fraction. This result is in agreement with those relative to density, inasmuch as less dense (more porous) granules are obviously able to absorb water to a greater extent. Another observation can be drawn once the results for the systems containing 70% ash are considered. It is seen that lime-based systems have greater WAC than those cement-based, again in agreement with density data. When compared to the commercial lightweight aggregate referred to above, the values of WAC found for the granules tested in this study lay within a range whose limits are lower. In fact, WAC ranges between 10 and 16% for Lytag aggregate [19], while, for the granules manufactured in this study, the range is 8.9-15.5% for one-step granulation and 7.3-13.7% in the case of two-step granulation. Table 6 shows the results of technological properties measurement, specifically compressive (crushing) strength and Los Angeles coefficient. It is seen that compressive strength is lower for the larger size fraction, in agreement with density data. Moreover, with a few exceptions, compressive strength is higher when the binder content is higher, as can be obviously expected. The effect of binder type can be observed once the data for the systems at constant ash content (70%) are taken into account. These data show that the use of cement offers advantages over lime. Finally, the data of Table 6 show that there is a clear and definite effect of ash type, as the one coming from the stoker furnace incinerator gives better compressive strength results.

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R. Cioffi, F. Colangelo, F. Montagnaro and L. Santoro Table 6. Compression (crushing) strength and Los Angeles coefficient of granules

System

R70C R70C+ S70C S70C+ R70L R70L+ S70L S70L+ R60LA R60LA+ S60LA S60LA+ R50LA R50LA+ S50LA S50LA+

Compressive strength, MPa Size fraction, mm 4-12 12-18

3.76 5.28 5.10 6.60 2.33 3.22 3.10 4.01 3.21 4.81 4.92 5.86 3.05 4.61 4.65 5.83

2.21 3.65 3.50 4.80 1.42 2.28 2.10 2.78 1.88 3.32 3.32 4.53 1.83 3.36 3.12 4.29

Los Angeles coefficient, wt% Size fraction, mm 12-18

48 44 46 42 59 56 57 53 48 43 44 41 48 43 44 40

In many cases the observed values of compressive strength are such that the granules tested in this study are suitable for use as lightweight aggregate in civil engineering applications. In fact, Lytag commercial lightweight aggregate has compressive strength in the range 4.8-9.2 MPa [19]. The results of Los Angeles coefficient measurement are presented in Table 6 only for the 12-18 mm size fraction and show no definite trend when the ash content is changed. The only clearly observable effects are those of binder and ash types. In fact, this coefficient is higher for lime-based granules than for cement-based ones, and is slightly lower when stoker furnace incinerator ash is used for the manufacture of the granules. Typical natural siliceous aggregate has Los Angeles coefficient of about 20% [14]. On the other hand, the values of this coefficient for artificial aggregates coming from crushed bricks and fired fly ash-clay mix are higher, reaching 30% [14]. The values of the Los Angeles coefficient found for the aggregates under investigation (Table 6) are still higher, but, according to the Italian regulation [31], no compliance minimum value is required for ordinary concrete manufacture. Table 7 shows the results of the leaching test carried out on the size fraction 12-18 mm of the granules manufactured starting from the rotary furnace incinerator ash. The size fraction 4-12 mm was excluded from this test because the granules were found of better physical properties (higher density, lower porosity) in this size fraction. Moreover, all the samples obtained from stoker furnace incinerator ash were not tested for leaching behavior. The reason for this is that granules based on this ash proved to have better physical and technological properties in relation to civil engineering applications. In addition, as can be seen in Table 1, stoker furnace incinerator ash is poorer of heavy metals of environmental concern than rotary furnace incinerator ash.

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Table 7. Leaching behavior of granules

System

R70C R70C+ R70L R70L+ R60LA R60LA+ R50LA R50LA+

Cd, µg/L Limit=5 Time, days 16 28 56

3 1 6 1 3 1 3 1

3 1 7 1 3 1 4 1

4 1 8 1 4 1 4 1

Zn, mg/L Limit=3 Time, days 16 28 56

2.13 0.67 3.62 0.92 2.31 0.58 2.21 0.61

2.49 0.79 4.31 1.02 2.38 0.73 2.48 0.70

2.71 0.91 4.87 1.09 2.93 0.78 2.83 0.86

Pb, µg/L Limit=50 Time, days 16 28 56

Cu, µg/L Limit=50 Time, days 16 28 56

12 3 47 3 12 3 13 3

27 10 41 13 24 9 23 10

15 4 54 3 17 4 14 3

21 4 68 4 19 4 20 4

32 12 59 16 26 9 28 13

38 15 68 19 29 11 31 15

The metal release values of Table 7 are cumulative and relative to three times: 16, 28 and 56 days. According to Italian regulation, only the cumulative release value after 16 days is to be taken into account for comparison with the limit fixed for each metal. The compliance leaching test employed for the granules was extended to 28 and 56 days to have a better understanding of the long term leaching behavior of the granules. As the leaching test is of compliance type, the first observation on the data of Table 7 must be related to the cases in which the limits are exceeded. This only happens for Cd and Zn in system R70L. In all the other cases the cumulative amounts of metals released after 16 days are below the relative limits. As expected, the release is much lower in the case of granules manufactured via the two-step granulation. Metal release is also affected by the type of binder. In fact, cement-based granules containing 70% ash behave better than the corresponding lime-based ones. This is quite an expected result, as the physico-mechanical properties of the granules based on lime alone as binder were found of the worst rank. The effect of ash content on leaching behavior does not seem significant, at least in the composition range investigated. A final consideration can be made with regard to release at times longer than 16 days (28 and 56 days). It is seen that in all the cases investigated the release at these longer times increases over that at 16 days but to a limited extent, and this is a very positive result in view of long-term behavior in civil applications. Table 8 shows some selected properties of concrete blocks incorporating different types of granules. Lime-based granules were not used for the manufacture of the concrete blocks due to their poor technological properties. According to Italian rules, concrete blocks that give at least 95% of compressive strength determinations greater than X MPa for cubic samples 15 cm in size or Y MPa for cylindrical samples 10 cm in diameter and 15 cm in height are classified as belonging to class CX/Y [32]. Nine classes exist starting from C12/15 to C50/60. The data of compressive strength reported in Table 8 show that all the granules tested are suitable for the manufacture of concrete blocks for civil engineering applications. Actually, blocks of the four classes C16/20, C20/25, C25/30 and C30/35 could well be manufactured. Table 8 also shows that blocks manufactured starting from granules obtained via two-step granulation have better compressive strength values, while no simple relationship exists

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between ash content in the granules and concrete blocks compressive strength. On the other hand, concrete blocks density is seen to decrease as the ash content in the granules decreases. Furthermore, any of the properties in Table 8 (density, compressive strength and elasticity modulus) increase when the concrete blocks incorporate the granules produced via two-step granulation. Table 8. Properties of concrete incorporating the granules Granules

R70C R70C+ S70C S70C+ R60LA R60LA+ S60LA S60LA+ R50LA R50LA+ S50LA S50LA+

Density, kg/m3

Compressive strength, MPa

Elasticity modulus, GPa

1908 1932 1949 1963 1742 1745 1734 1749 1665 1672 1659 1682

20.06 27.21 26.35 34.00 18.06 25.86 26.13 30.35 17.15 24.72 25.68 31.67

24.76 26.34 26.45 28.00 24.79 26.23 26.18 27.34 23.64 25.63 26.08 27.53

As far as the modulus of elasticity is concerned, it should be observed that typical values for concrete blocks containing natural aggregates range from 25 to 50 GPa [33]. Then, the measurements carried out on the blocks under investigation show values near to the lower limit of the range referred to above. This is a favorable property as low values of the modulus of elasticity are preferred for mitigating cracking due to shrinkage.

CONCLUSIONS First of all this work has proved that ash from municipal, hospital and industrial solid wastes incinerator can be successfully employed up to 70% content in the production of artificial aggregate in the form of granules. Different binders can be used for the production of the granules, but only cement and coal fly ash/lime give satisfactory technological properties. Lime alone proved to be unsuitable as granules binder. Of the two ash samples employed in this study, from stoker and rotary furnace incinerators, the former was able to give granules of better technological properties. In the majority of the cases tested, the release of heavy metals was below the limits fixed by Italian law for civil engineering applications. Exceptions to this have only been observed when lime alone is used as a binder for the production of the granules. All the relevant granules properties, mainly compressive strength and leaching behavior, improve when the granules are produced via a two-step granulation process. This was an

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expected result as the second granulation step produces an encapsulating pure binder outer layer. Finally, the granules tested in this study have proved to be suitable for the manufacture of concrete blocks. Depending on process variables (type of binder, granules composition, type of granulation) granules can be produced of physico-mechanical properties good enough to allow the manufacture of concrete blocks of middle range performance.

REFERENCES [1] [2]

[3]

[4]

[5]

[6] [7] [8]

[9] [10]

[11] [12]

[13]

Collivignarelli C. and Sorlini S., Reuse of municipal solid wastes incineration fly ashes in concrete mixtures, Waste Management 22 (2002) 909-912. Smith J.D., Fang H. and Peaslee K.D., Characterization and recycling of spent refractory wastes from metal manufacturers in Missouri, Resources, Conservation and Recycling 25 (1999) 151-169. Chang N.B., Wang H.P., Huang W.L. and Lin K.S., The assessment of reuse potential for municipal solid waste and refuse-derived fuel incineration ashes, Resources, Conservation and Recycling 25 (1999) 255-270. Montepara A. and Tebaldi G., Use of crushed waste aggregates for DBM road bases, Waste Management Series, Volume 1, Waste Materials in Construction – Wascon 2000, Pergamon Press, The Netherlands (2000). Van der Sloot H.A., Kosson D.S. and Hjelmar O., Characteristics, treatment and utilization of residues from municipal waste incineration, Waste Management 21 (2001) 753-765. Ahmadi B. and Al-Khaja W., Utilization of paper waste sludge in the building construction industry, Resources, Conservation and Recycling 32 (2001) 105-113. Hill A.R., Dawson A.R. and Mundy M., Utilisation of aggregate materials in road construction and bulk fill, Resources, Conservation and Recycling 32 (2001) 305-320. Huang W.L., Lin D.H., Chang N.B. and Lin K.S., Recycling of construction and demilition waste via a mechanical sorting process, Resources, Conservation and Recycling 37 (2002) 23-37. Forteza R., Far M., Seguí C. and Cerdá V., Characterization of bottom ash in municipal solid waste incinerators for its use in road base, Waste Management 24 (2004) 899-909. Cho Y.H. and Yeo S.H., Application of recycled waste aggregate to lean concrete subbase in highway pavement, Canadian Journal of Civil Engineering 31 (2004) 11011108. Topcu I.B. and Sengel S., Properties of concretes produced with waste aggregate, Cement and Concrete Research 34 (2004) 1307-1312. Sani D., Moriconi G., Fava G. and Corinaldesi V., Leaching and mechanical behaviour of concrete manufactured with recycled aggregates, Waste Management 25 (2005) 177182. Senthamarai R.M. and Manoharan P.D., Concrete with ceramic waste aggregate, Cement and Concrete Composites 27 (2005) 910-913.

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[14] Zakaria M. and Cabrera J.G., Performance and durability of concrete made with demolition waste and artificial fly ash-clay aggregates, Waste Management 16 (1996) 151-158. [15] Van der Sloot H.A., Hoede D., Cresswell D.J.F. and Barton J.R., Leaching behaviour of synthetic aggregates, Waste Management 21 (2001) 221-228. [16] Wainwright P.J. and Cresswell D.J.F., Synthetic aggregates from combustion ashes using an innovative rotary kiln, Waste Management 21 (2001) 241-246. [17] Wang K.S., Sun C.J. and Yeh C.C., The thermotreatment of MSW incinerator fly ash for use as an aggregate: a study of the characteristics of size-fractioning, Resources, Conservation and Recycling 35 (2002) 177-190. [18] Pioro L.S. and Pioro I.L., Reprocessing of metallurgical slag into materials for the building industry, Waste Management 24 (2004) 371-379. [19] Cheeseman C.R., Makinde A. and Bethanis S., Properties of lightweight aggregate produced by rapid sintering of incinerator bottom ash, Resources, Conservation and Recycling 43 (2005) 147-162. [20] Cheeseman C.R. and Virdi G.S., Properties and microstructure of lightweight aggregate produced from sintered sewage sludge ash, Resources, Conservation and Recycling 45 (2005) 18-30. [21] Conner J.R., Chemical fixation and solidification of hazardous wastes, Van Nostrand Reinhold, New York, NY, USA (1990). [22] Spence R.D., Chemistry and microstructure of solidified waste forms, Lewis Publishers, Boca Raton, FL, USA (1993). [23] Means J.L., Smith L.A., Nehring K.W., Brauning S.E., Gavaskar A.R., Sass B.M., Wiles C.C. and Mashni C.I., The application of solidification/stabilization to waste materials, Lewis Publishers, Boca Raton, FL, USA (1995). [24] Spence R.D. and Shi C., Stabilization and solidification of hazardous radioactive and mixed wastes, CRC Press, Boca Raton, FL, USA (2005). [25] Beretka J., Cioffi R., Santoro L., and Valenti G.L., Cementitious mixtures containing industrial process wastes suitable for the manufacture of preformed building materials, Journal of Chemical Technology and Biotechnology 59 (1994) 243-247. [26] Cioffi R., Maffucci L., Santoro L. and Glasser F.P., Stabilization of chloro-organics using organophilic bentonite in a cement-blast furnace slag matrix, Waste Management 21 (2001) 651-660. [27] Calvanese G., Cioffi R. and Santoro L., Cement stabilization of tannery sludge using quaternary ammonium salt exchanged bentonite as pre-solidification adsorbent, Environmental Technology 23 (2002) 1051-1062. [28] Italian Standard UNI 10802, Liquid, granular, semisolid wastes and sludges – Manual sampling, leaching and leachate analysis, Milano, Italy (1999). [29] Act of Italian Environment Ministry (DM), 5 February 1998. [30] Ramachandran V.S. and Beaudoin J.J., Handbook of Analytical Techniques in Concrete Science and Technology, Noyes Publications/Andrew Publishing, Norwich, New York, USA (2001). [31] Act of Italian Republic President (DPR), 21 April 1993. [32] Italian Standard UNI 9858, Concrete: performance, production, utilization and compliance criteria, Milano, Italy (1991). [33] Collepardi M., Il Nuovo Calcestruzzo, ENCO, Milano, Italy (2003).

In: Conservation and Recycling of Resources: New Research ISBN 1-60021-125-9 Editor: Christian V. Loeffe, pp. 235-245 © 2006 Nova Science Publishers, Inc.

Chapter 8

THE CHEMICAL PROPERTIES OF MUNICIPAL SOLID WASTE INCINERATOR ASHES AND THE EFFECTS OF THEIR UTILIZATION AS LANDFILL COVER ON LANDFILL BIOSTABILIZATION Huang-Mu Lo∗a, Min-Hsin Liua, Chao-Yang Linb, Wen-Fung Liuc, Tzu-Yi Paia, Chun-Hsiung Hungb, Pin-Hung Chengd, Yuan-Lung Liaoa, Tsu-Ying Fua and Chao-Chan Yanga a

Chaoyang University of Technology, Taiwan, R. O. C. b National Chung Hsing University, Taiwan, R. O. C. c Feng Chia University, Taiwan, R. O. C. d Taipei University of Science and Technology, Taiwan, R. O. C.

ABSTRACT This article investigated the properties of municipal solid waste incinerator (MSWI) ashes and the effects of their addition on the municipal solid waste (MSW) anaerobic digestion as co-disposed or co-digested with MSW in landfill or digester. Five anaerobic bioreactors with the size of 1.2 m height and 0.2 m diameter were employed to conduct the experiment. Four layers were arranged each with 6.5 liter of MSW and anaerobic seeded sludge mixture covered by 2.5 liter of MSW and anaerobic seeded sludge mixture blended with the designed ashes added ratios as well as the control bioreactors without ashes addition. The synthetic MSW used in this experiment was typical of organic fraction of MSW and was comprised of newspaper, food waste, office paper and hay etc. MSWI ashes were obtained from a mass burning incinerator in central Taiwan. Also, the seeded anaerobic sludge was taken from a municipal wastewater treatment in central ∗

Corresponding author. Tel.: +886-4-23323000 ext 4469; fax: +886-4-23742365. E-mail address: [email protected] (Huang-Mu Lo)

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Huang-Mu Lo, Min-Hsin Liu, Chao-Yang Lin et al. Taiwan. As the experiment was proceeded with, the leachate of 100 mL was recirculated per day and another more 100 mL one was collected and filtered for parameters analysis such as pH, conductivity, alkalinity and chemical oxygen demand (COD) etc. In addition, the gas production rate was recorded every day to measure the bacterial activity in the MSW biodegradation. From the results, it showed that 10 and 20 g l-1 fly ash added (g ashes addition per liter MSW ratios) bioreactors and 100 g l-1 bottom ash added bioreactors were found to enhance the gas production rate and the soluble concentration of alkali metals such as Ca, Mg, K, and Na as compared to the control one. The six soluble heavy metals of Cd, Cr, Cu, Pb, Ni and Zn in leachate were also found to be under inhibitory concentration for anaerobic digestion. Other trace metals such as Co and Mo etc were assumed to serve as the stimulatory micronutrients rather than to exert inhibitory effects on the microorganisms in the MSW anaerobic digestion.

Keywords: Anaerobic digestion, Landfill, MSW, MSWI ashes

INTRODUCTION Municipal solid waste (MSW) incinerator (MSWI) has been practiced in the MSW treatment as important as landfill, composting and resource recovery and recycling. This is because that the likely landfill site is getting more difficult to find for the MSW disposal particularly occurred in the dense population and lesser appropriate land for landfill in Taiwan. MSWI can take the advantage of MSW weight or volume reduction and the recovery of steam and electricity. However, the residues such as bottom ash and fly ash generated were still the primary environmental concern. Thus, they need to be carefully treated to prevent the potential secondary pollution. Particularly, the released metals, ions and other compounds if not properly treated might be toxic to the human health and ecological environment when utilized in different purposes. Therefore, MSWI residues treatment and disposal has become another environmental task in MSW treatment. MSWI residues have been utilized as aggregate, backfill, soil amendment and solidified for permanent landfill storage as well (Bertolini et al., 2004; Deschamps, 1998; Hjelmar, 1996). In addition, MSWI bottom ash has been practiced as landfill cover, however, the baseline information and landfill mechanisms were not fully clear. Only few research investigated the bottom ash co-digested with MSW in the semi-batch anaerobic bioreactor (Lo, 2005). This study showed that bottom ash addition could provide the alkalinity suitable for the anaerobic digestion thus enhancing the gas production rate. Another investigation also presented that NaHCO3 could provide alkalinity and facilitate the MSW anaerobic digestion process (Ağdağ and Sponza, 2005). As regard to MSWI fly ash, it is thought that using fly ash as landfill cover is an aggressive challenge for the landfill practice. It is further noted that fly ash has the potential to release the heavy metals which is considered to be hazardous to the soil and ground water if disposed improperly or leaked from the faulty geo-membrane liner in the bottom of landfill. The soil and ground water contamination by the release of MSWI ashes in landfill might have the potential to cause detrimental effects on human health and ecological environment. Therefore, using fly ash as landfill cover might be an aggressive challenge needing further theoretical and experimental investigation. In addition, it is noted that MSW landfill needs a long term period to obtain the MSW biostabilization. Thus, anaerobic landfill bioreactors

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were employed to conduct the experiment of MSW and MSWI ashes co-disposal to obtain the results in a short term. Particularly, the pH, alkalinity, COD, metals and gas production in the bioreactors were measured to assess the MSW biostabilization in landfill bioreactor simulating the real landfill site.

MATERIALS AND METHODS MSWI Ashes The MSWI bottom ash and fly ash required for the bioreactor experiment were derived from a mass burning MSWI in central Taiwan (Figure 1). Generally, bottom ash was obtained from the incinerator stoker which is the major part for the MSW incineration as well as the siftings leaked from the stoker. Fly ash was derived from the air pollution control device (APCD) such as semi-scrubber and bag filter. Fly ash has been measured to have smaller particle size as compared to that of the bottom ash by sieve analysis. Thus, it is expected that fly ash particle contains higher specific surface than that of bottom ash leading in the potential higher release of metals, ions and compounds. These released metals, ions and compounds might further influence the different utilization purposes. Particularly, the released heavy metals were reported to have the potential to cause the human health and ecological environment. The metal total content in MSWI ashes was characterized as Figure 2.

10 11

22 20

2

5 15

17

6 1

13

4

3

18

12 16

8

14 9

Refuse flow Air flow

7

19

Residue ash flow Steam flow

21 Fly ash flow Gas flow

1.Refuse unloading area 2.C rane operation room 3.Pit 4.Secondary air blower 5.Crane 6.Hopper 7.Air compressor room 8.Ash crane 9.Ash pit 10.Tap water 11.Boiler 12.Grate 13.Ventilation room 14.Ash conveyor 15.Economizer 16.Fly ash conveyer 17.Semi-dry scrubber 18.Central control room 19.Transformer room 20.Bagfilter 21.Induce fan 22.Stack

Figure 1. The treatment process of mass burning MSW incinerator

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Office paper (30%) Newspaper (30%)

Food waste (5%)

Shredder

Hay (35%)

Water (16 L)

Moisture adjustment with blender (TS 6%)

Amount of designed Ashes addition

Biogas production

Anaerobic bioreactor

Leachate or digestate filtration

Parameters analysis Performance assessment

Figure 2. Schematic diagram showing the preparation of feedstock, its component composition, and bioreactor outputs and analysis

MSW In order to reduce the interference of potential hazardous materials in MSW, synthetic MSW was prepared artificially in the laboratory. The MSW was comprised of newspaper (30%), office paper (35%), food waste (5%) as potato and hay (30%) etc. These constituents were typical of major organic fraction of MSW. With the measurement by elemental analyzer, the chemical composition consisting of C, H, O, N and others were about 46 %, 6 %, 41 %, 1.4 % and 5.6 % respectively. These constituents contained typical organic fraction of MSW and were easily to be biodegraded by microorganisms. For the convenience of microbial attack in the decomposition process, synthetic MSW was shredded by a shredder to pieces of less than 5 mm. Then, it was blended with distilled water to make a total solid (TS) of 6%. Although this percent of TS was lower than that of real landfill MSW, the carbon content is near the same. In addition, this investigation focused on the effects of MSWI ashes co-disposed with MSW to examine the metals and ions release on the MSW decomposition and their possibility of utilization as landfill cover. The MSW preparation procedure and metal total content in MSW were listed as Figure 2 and Figure 3.

Anaerobic Seeded Sludge To ensure the MSW biodegradation occurred without retardation, anaerobic seeded sludge was taken from a municipal waste water plant in central Taiwan. This plant collects the municipal waste water from Taichng city. The anaerobic sludge showed efficient bacterial

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activity that was beneficial for the startup and biodegradation of MSW in the anaerobic bioreactor. The metal content of anaerobic seeded sludge was indicated in Figure 3. 300

Sludge

MSW

Fly ash

Bottom ash

Total content, mgg

-1

250

1A

200 150 100 50 0 Ca

K

Mg

Na

Fe

P

S

Metal

4

Sludge

MSW

Fly ash

Total content, mgg -1

3.5

Bottom ash

1B

3 2.5 2 1.5 1 0.5 0 Ag Al B BaCd Co Cr Cu Hf In MnMo Ni Pb Sb Si Sn Ta Ti Tl V W Zn Zr Metal

Figure 3. The selected metal content in sludge, MSW, fly ash and bottom ash

Anaerobic Bioreactor In order to obtain the effects of MSWI ashes co-disposed with MSW in a short term, five anaerobic bioreactors (Figure 4) with the size of 1.2 m height and 0.2 m diameter were employed to conduct the experiment. Four layers of co-disposal simulating the landfill site operation were arranged. Two of them were set up for bottom ash co-disposal with MSW and the other two were for fly ash co-disposal with MSW. The fifth one was used to compare the results without any ashes addition. The designed added ratios of bottom ash were 100 and 200 g l-1 (100 and 200 g addition per liter MSW) and of fly ash were 10 and 20 g l-1 respectively. In these bioreactors, it consisted of 22 liter MSW and 12 liter of anaerobic sludge accompanying by the designed ashes addition. Each layer within the four ones of anaerobic bioreactor contained 6.5 liter of MSW and seeded sludge mixture and was covered with 2 liter

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of MSW and seeded sludge mixture blended with the designed MSWI ashes addition as previously stated. The 100 ml leachate at the bottom of the bioreactor was recirculated each day. In addition, another more 100 ml leachate was collected and filtered for parameters analysis such as pH, alkalinity, chemical oxygen demand (COD), total solid (TS), volatile solid (VS) and metals daily or weekly. Gas production was also measured with gas collector daily. The measured parameters and gas production rate can be used to assess the performance of the anaerobic bioreactors.

Gas meter

pH, COD, TS, VS, Alkalinity, metals analyses etc

Figure 4. The schematic diagram of anaerobic bioreactor in the experiment

Biogas 4 Methanogenesis -Methanosarcina -Methanothrix -Methanobacterium 3 Acetogenesis -Syntrophobacter -Syntrophomonas -Desulfovibro

Acetate

H2

CO2

Organic acids

Acetate

Alcohol

2 Acidogenesis -Acidifying bacteria -H2 producing acetogens 1 Hydrolysis -Clostridium -Eubacterium -Peptococcus

Breakdown products (amino acids, sugars, large carboxylic acids)

Substrates (carbohydrate, fat, protein, lipid)

Figure 5. Biochemical process in anaerobic digestion (Dichtl, 1997; House et al., 1997; Bhatti et al., 1996)

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pH was measured by a pH meter. Alkalinity and COD were measured with titration methods. TS and VS were analyzed with the oven at 105 and 600°C respectively. All these analysis methods followed the standard methods for the examination of water and wastewater (AWWA, 1995). Microorganisms play an important role on MSW anaerobic digestion process (Figure 5). Molecular biotechnology of FISH was used to characterize the selected methanogens such as Methanobacteriales, Methanococcales, Methanosarcinales and Methanomicrobiales and the target probes were MB310, MC1109, MSMX860 and MG1200 (Raskin et al., 1994) respectively. Methanogens detection could provide an indication of methanogenesis extent of MSW anaerobic digestion as the MSWI ashes were added.

RESULTS AND DISCUSSION Parameters Analysis From the experimental results, it showed that pH trends of bioreactors in leachate (Figure 6A) have shown lower values at the beginning in the five bioreactors. Thereafter, they reached to the steady values of about pH 6.2-7.5. The pHs in the bottom ash added bioreactors were found higher than that in fly ash added and control ones specifically found in the 200 g l-1 bottom ash added bioreactors with the pHs higher than 7.5 after about month six. Further, the lower pHs below 6 found in the five bioreactors at the beginning except first week was thought that large amount of VA was produced in the first stage of MSW hydrolysis leading to the higher volatile acids and lower pHs. However, the pHs returned to about pH 6.2-7.5 soon possibly due to the alkali metal hydroxides and carbonates release which could provide the buffer alkalinity and neutralize VA as a function of pH. This range of near neutral pHs were thought to be suitable for the anaerobic digestion (Lo, 2005; Parkin and Owen,1986). Conductivity was found higher in the ash added bioreactors than the control one (Figure 6B). Conductivity in the 20 and 10 g l-1 fly ash added bioreactor was found to be about three times and two times that of control one respectively. This is because that higher fly ash addition could release higher different kinds of ions such as metals and chlorides etc resulting to a higher conductivity. As regarding to alkalinity, the alkalinity concentrations in the five bioreactors had the same trends between 500 and 3500 mg l-1 and were found to be in the suitable range for the anaerobic digestion as described by Parkin and Owen (1986) and can be seen in Figure 6C. VA in the five bioreactors was found to decrease except that found to increase in the 20 g -1 l ash added bioreactor between week two and week five (Figure 6D). From the third month on, the VA started to increase slightly. VA found higher in the first month was thought that the MSW was hydrolyzed in the first digestion stage resulting to a large amount of VA production such as acetate, propionate, butyrate, valerate etc. VA concentrations were then maintained in a steady state within the five bioreactors from month two to about month three. In the mean time, VA was converted to the methane and carbon dioxide by methanogenic bacteria as the gas production rate was found higher in this period. In addition, the VA in the MSWI ashes added bioreactors was found slightly higher than that in the control bioreactors at the beginning. From the fourth month on, the VA in the five bioreactors was found to increase slightly. This phenomenon indicated that the methanogenic activity began to

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decrease possibly due to the MSW anaerobic digestion completion and the lesser MSW substrate left to be utilized. 25 Conductivity, ms/cm

6A 8.5 pH

7.5 6.5 5.5 4.5 0

50

100

150

200

5

0

3000 2000 1000 0 40

50

-1

Volatile acids, mgl

-1

Alkalinity, mgl

6C

4000

20 30 Week

10

50

100

150

200

250

Day

5000

10

15

0

250

Day

0

6B

20

2500

6D

2000 1500 1000 500 0 0

10

20 30 Week

40

50

Figure 6. The trend of pH, conductivity, alkalinity and volatile acids in leachate of MSW anaerobic digestion by five different addition ratios of MSWI fly ash added, bottom ash added and the control bioreactors (◇: control bioreactor without ash addition; □: 10 g l-1 fly ash added bioreactor; △: 20 g l1 fly ash added bioreactor; ＊: 100 g l-1 bottom ash added bioreactor; ●: 200 g l-1 bottom ash added bioreactor).

GAS PRODUCTION RATE AND METALS RELEASE Released metals have been found to influence the MSW anaerobic digestion. The gas production rate in the MSWI ashes added bioreactors was found higher as compared to that in the control one (Figure 7). Higher gas production rate in the ash added bioreactors was thought that the release of alkali metals such as Ca, Mg, K and Na and the associated OH-1 and CO3-2 have provided the pH buffer in neutral band which facilitated the anaerobic digestion. In addition, six heavy metals of Cd (0-0.001 mgl-1), Cr (0-0.014 mgl-1), Cu (0-0.05 mgl-1), Pb (0-1.75 mgl-1), Ni (0-0.025 mgl-1) and Zn (0-0.05 mgl-1) in leachate were measured to be under inhibitory soluble concentration. It is further noted that trace metals such as Co, W, Ni etc might serve as the micro nutrients (Takashima and Speece, 1990; Kayhanian and Rich,1995; Paulo et al., 2004; Fish, 1999; Zandvoort et al., 2004). Thus, the gas production rate was facilitated and the MSW digestion was accelerated. Moreover, microorganisms of selected methanogens were found higher in the period of higher gas production rate within the ashes added bioreactors. Microorganisms seemed to be stimulated by the suitable metals release which was beneficial to the anaerobic digestion. Therefore, MSW anaerobic digestion

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efficiency was enhanced and the gas production rate and MSW biostabilisation were increased. It was further noted that the highest gas production rate in all bioreactors seemed to take place about on day 30. The gas production rate of the ashes added bioreactors on the peak was found to be about 9000 ml per day nearly two times that of 4500 ml per day found in the control one. The gas production rate in the bottom ash added bioreactor decreased quickly from the peak to zero on day 42. Similarly, the gas production rate in the control bioreactor also decreased quickly from the peak to nearly zero on about day 90. The gas production rate in the 20 g l-1 ash added bioreactor appeared to have stayed at a constant rate of about 6500 ml lasting between day 38 and day 51. As a result, the gas production accumulation in the decomposition period of all the bioreactors ranked in the order of 20 g l-1 fly ash added bioreactor > control bioreactor > 10 g l-1 fly ash added bioreactor > 100 g l-1 bottom ash added bioreactor. The lowest gas accumulation happened to the 100 g l-1 bottom ash bioreactor was thought to be the higher amount and quicker release of metals hydroxides, carbonates and phosphates. These released OH-1, CO3-2 and PO4-3 etc were considered to give alkalinity buffer and was neutralized by the quick production and large amount of volatile acids generated in the first hydrolysis of MSW anaerobic digestion.

Gas production, mL

10000 8000 6000 4000 2000 0 0

50

100

150

200

Day Figure 7. The gas production rate of MSW anaerobic digestion by three different addition ratios of MSWI fly ash in the ash added and the control bioreactors (○: 100 g l-1 bottom ash added bioreactor; □: 10 g l-1 fly ash added bioreactor; △: 20 g l-1 fly ash added bioreactor; : control bioreactor without fly ash addition).

EVALUATION OF ANAEROBIC BIOREACTOR PERFORMANCE From this investigation, the designed ratios of MSWI ashes added bioreactors were found to be able to enhance the gas production rate as compared to the control one. This phenomenon was mainly attributed to the suitable pH, alkalinity and suitable released metals such as alkali metals, trace metals and heavy metals and associated hydroxides and carbonates. Alkali metal compounds and their dissolution of OH-1 and CO3-2 were thought to

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Huang-Mu Lo, Min-Hsin Liu, Chao-Yang Lin et al.

provide the suitable alkalinity and pH offer. In addition, alkali metals were found to be below inhibitory concentration (Parkin and Owen, 1986) and the trace compounds such as dioxin and PAH seemed not exert detrimental effects on bacterial activity and the MSW anaerobic digestion. Similarly, the released heavy metals were also measured to be under the threshold concentration that might be inhibitory on the effects of MSW anaerobic digestion. Further, trace metals were analyzed to be suitable for serving as micronutrients required for the anaerobic microorganisms. These results explained the higher bacterial activity and gas production rate and higher efficiency of MSW anaerobic digestion.

CONCLUSION The likely utilization of MSWI ashes as landfill cover was examined with anaerobic bioreactor. Four layers were arranged to simulate the co-disposal of MSW and MSWI ashes. From the analysis of leachate parameters and gas production, it was noted that MSWI ashes addition could provide the appropriate alkalinity, adequate released metals and near neutral pH offer. These results particularly with neutral pH 7 and adequate released metal concentration including alkali metals, trace metals and heavy metals associated with the hydroxides and carbonates ensure the suitable and beneficial anaerobic environment for the MSW digestion. The resulting environment suitable for the anaerobic digestion explained the higher gas production rate and stimulatory MSW anaerobic digestion found in the ashes added bioreactor as compared to the control one.

REFERENCES [1] [2] [3] [4] [5] [6]

[7]

[8]

Bertolini, L.; Carsana, M.; Cassago, D.; Curzio, A. Q.; Collepardi, M. (2004). MSWI ashes as mineral additions in concrete. Cement and Concrete Research 34, 1899-1906. Deschamps, R. J. (1998). Using FBC and stoker ashes as roadway fill: a case study. J. Geotech. and Geoenviron. Eng. 124, 1120-1127. Hjelmar, O. (1996). Disposal strategies for municipal solid waste incineration residues. J. Hazardous Materials 47, 345-368. Lo, H. M. (2005). Metals behaviors of MSWI bottom ash co-digested anaerobically with MSW. Resources, Conservation & Recycling 43, 263-280. Ağdağ, O.N., Sponza, D.T., (2005). Effect of alkalinity on the performance of a simulated landfill bioreactor digesting organic solid wastes. Chemosphere 59, 871-879. American Public Health Association, American Water Works Association, Water Environment Federation. (1995). Standard methods for the examination of water and wastewater. 19th edition, Hanover, Maryland, US. Raskin, L.; Stromley, J. M.; Rittmann, B. E.; Stahl, D. A. (1994). Group-specific 16S rRNA hybridization probes to describe natural communities of methanogens. Appl. Environ. Microb. 60, 1232-1240. Parkin, G. F.; Owen, W. F. (1986). Fundamentals of anaerobic digestion of wastewater sludges. J. Environ. Eng. 112, 867-920.

The Chemical Properties of Municipal Solid Waste Incinerator Ashes … [9] [10]

[11]

[12] [13]

[14] [15] [16]

245

Takashima, M.; Speece, R. E. (1990). Mineral requirements for methane fermentation. Crit. Rev. Environ. Control 19, 465-479. Kayhanian, M.; Rich, D. (1995). Pilot-scale high solids thermophilic anaerobic digestion of municipal solid waste with an emphasis on nutrient requirements. Biomass and Bioenergy 8, 433-444. Paulo, P. L.; Jiang, B.; Cysneiros, D.; Stams, A. J. M.; Lettinga, G. (2004). Effect of cobalt on the anaerobic thermophilic conversion of methanol. Biotechnology and Bioengineering 85, 434-441. Fish, C. Ph. D. thesis, Enhance of the anaerobic digestion of municipal solid waste through nutrient supplementation. University of Southampton, Southampton, UK, 1999. Zandvoort, M. H.; Gieteling, J.; Lettinga, G.; Lens, P. N. L. (2004). Stimulation of methanol degradation in UASB reactors: in situ versus pre-loading cobalt on anaerobic granular sludge. Biotechnology and Bioengineering 87, 897-904. Dichtl, I. N. (1997). Thermophilic and mesophilic (two- stage) anaerobic digestion. J. CIWEM 11, 98-104. House, S. J. & Evison, L. M. (1997). Hazards of industrial anaerobic digester effluent discharges to sewer. J. CIWEM 11, 282-288. Bhatti, Z. I.; Furukwa, K. and Fujita, M. (1996). Feasibility of methanolic waste treatment in UASB reactors. Wat. Res. 30(11), 2559-2568.

INDEX A access, 204 accumulation, vii, 1, 91, 96, 114, 116, 243 acetic acid, 142 acetone, 9, 33, 159 acid, 9, 14, 20, 21, 25, 26, 39, 44, 48, 99, 102, 103, 105, 106, 108, 111, 120, 121, 123, 124, 125, 128, 130, 131, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 148, 149, 150, 153, 159, 170, 185, 187, 191 acidity, 106 acrylonitrile, 11, 28 activated carbon, x, 155, 156, 157, 158, 159, 160, 161, 164, 169, 170, 171, 173, 174, 185, 186, 187, 188, 189, 190, 191, 193, 194, 195 activation, 159, 160, 164, 165, 166, 167, 168, 169, 170, 171, 174, 180, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195 active site, 189 actual output, 122 additives, vii, 1, 4, 18, 20, 22, 23, 26, 28, 29, 31, 32, 36, 40, 100, 102, 132, 136, 142, 223 adhesion, 13, 27, 30 adhesives, 4, 14, 50 adjustment, 101 adsorption, xi, 32, 108, 157, 160, 169, 171, 172, 173, 174, 185, 187, 188, 189, 191, 193, 221, 224 advertising, 35 aerospace, 31 affect, 13, 14, 15, 17, 25, 26, 46, 106, 111, 138, 169, 210, 222, 223 Africa, viii, 62, 65, 73, 83, 86, 215 agent, 14, 22, 26, 29, 36, 40, 43, 164, 165, 166, 167, 168, 169, 170, 185, 189 agglutination, 15, 16

aggregates, xi, 221, 222, 223, 224, 230, 232, 233, 234 aggregation, 101 aging, 25, 54 agriculture, 99, 156, 157, 192 air emissions, 156, 159 air quality, 156, 161 alcohol, 9, 26, 193 alcohols, 9, 12, 20, 25 alkaline earth metals, 103 alkaline hydrolysis, 21, 44 alloys, 63, 69, 121, 125, 126, 138 alternative, vii, 1, 4, 26, 31, 47, 49, 156, 157, 158, 160, 208, 223 alternatives, 32, 163, 184, 193 aluminium, 130 aluminum, 50, 111, 120, 127 ambient air, 144 ambiguity, 146 amendments, 156 amines, 24, 26 ammonia, 48, 142 ammonium, 96, 102, 103, 107, 132, 140, 141, 142, 153 amplitude, 11 anaerobic sludge, xi, 235, 238, 239 animals, 98, 199 anxiety, 144 APC, 5 appropriate technology, 6, 147 aqueous solutions, 10, 14, 44, 160 argument, 46, 48 Aristotle, 155 aromatic hydrocarbons, 99 ash, x, xi, 47, 48, 118, 120, 121, 122, 125, 126, 128, 129, 130, 134, 147, 148, 149, 153, 157, 161, 162, 163, 164, 178, 179, 187, 189, 193, 221, 223, 224,

248

Index

225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 236, 237, 239, 241, 242, 243, 244 assessment, 49, 63, 92, 117, 118, 145, 214, 218, 219, 223, 233 assignment, 210 assumptions, 214, 215, 216 atmospheric pressure, 33, 172, 173, 176 atoms, 11, 20, 21 attacks, 21 attention, ix, 5, 44, 100, 103, 120, 158, 162, 198 attractiveness, 203 Australia, 65, 73, 133, 145 Austria, 79, 145, 206 availability, ix, 33, 35, 36, 63, 74, 85, 86, 90, 91, 93, 95, 96, 106, 110, 114, 116, 117, 121, 133, 161, 187, 214, 222 awareness, 4, 134, 136, 150

B bacteria, 161, 241 barriers, 3, 209 base catalysis, 22 baths, 14 batteries, 48, 121, 125, 133, 134, 136, 138, 139, 140, 141, 142, 145, 148, 149, 153 beams, 28 behavior, xi, 13, 17, 22, 27, 38, 116, 222, 223, 224, 225, 227, 230, 231, 232 Belarus, 214 Belgium, 46 bending, 8 benzene, 9, 45 binding, 15, 222, 223, 224 bioavailability, 97 biodegradability, 3 biodegradation, xi, 18, 31, 106, 236, 238 biodiversity, 215 biofuel, 200, 217 biomass, x, 99, 116, 155, 156, 161, 162, 164, 174, 175, 178, 179, 190, 191, 192, 194, 195, 201, 211, 212, 213, 214, 215, 217 biomass materials, 156, 179 biomedical applications, 63, 69 bioremediation, 94 biosphere, 94 biotechnology, 241 bismuth, 62 blends, vii, 1, 6, 27, 28, 29, 35, 36, 38, 50 blocks, xi, 222, 231, 232, 233 blood, 144, 145 body, 134, 138, 144 bonds, 11, 20, 22, 108

boric acid, 143 brain, 144 branching, 20, 22 brass, 121, 126, 128, 130, 147 Brazil, 5, 14, 34, 50 buildings, 192, 198 Bulgaria, 206, 214 burning, xi, 2, 8, 98, 160, 187, 235, 237 butadiene, 11, 28, 163

C cables, 136, 149 cadmium, ix, 48, 98, 119, 120, 123, 124, 128, 129, 131, 132 calcium, 12, 14, 45, 138 calorimetry, 7, 29 Canada, viii, 47, 52, 62, 65, 73, 83, 86, 94, 117, 136, 139, 145 cancer, 32 carbon, x, 2, 20, 21, 45, 63, 95, 97, 102, 103, 104, 108, 116, 125, 155, 156, 157, 158, 159, 160, 161, 164, 169, 171, 173, 174, 179, 180, 182, 184, 185, 186, 187, 188, 189, 190, 191, 192, 194, 201, 208, 210, 215, 238, 241 carbon atoms, 20, 21, 187 carbon dioxide, 156, 187, 194, 201, 208, 210, 215, 241 carbon monoxide, 45 carbonization, 164, 165, 166, 167, 168, 169, 170, 171, 194 carboxylic groups, 21 carcinogenesis, 144 case study, 191, 220, 244 cast, 121, 130, 136, 137, 138 catalyst, 18, 51, 91, 147, 157, 190 catalytic effect, 46 cation, 97 CEE, 205, 206, 208 cell, viii, 61, 62, 63, 64, 66, 67, 68, 69, 74, 75, 76, 77, 78, 80, 81, 84, 85, 90, 92, 130, 142, 148 cellulose, 8, 34, 35, 36, 40, 96, 183, 189, 194 ceramic, 148, 233 certificate, 210, 212, 213, 216, 219, 220 chain scission, 19, 20, 21, 22 chelates, 111 chemical bonds, 22, 108 chemical degradation, 18 chemical industry, 64, 69 chemical properties, 15, 99, 106 chemical reactions, 63, 175, 189, 195 chemical structures, 20 China, 50, 65, 73

Index chlorine, 8, 20, 45 chloroform, 9 chromatography, 103, 178, 184 chromatography analysis, 178 chromium, ix, 119, 120 circulation, 172 classes, 23, 231 classification, 16, 111, 214 clean technology, 140 cleaning, 13, 14, 15, 16, 22, 32, 33, 123, 158, 198, 199 cleavage, 18, 21, 22, 51 climate change, 2, 215 closure, 126 CO2, 2, 47, 164, 165, 166, 167, 168, 169, 170, 185, 187, 188, 190, 192, 193, 194 coal, x, 46, 105, 116, 118, 132, 143, 158, 184, 195, 205, 221, 223, 224, 226, 227, 232 coatings, 136 cobalt, 123, 130, 142, 245 coke, 168, 188 colic, 144 combustion, viii, 2, 4, 8, 47, 48, 49, 61, 63, 105, 128, 156, 158, 163, 185, 192, 193, 199, 203, 234 commodity, 50, 159 common rule, 217 communication, 203 community, 47 compatibility, 22, 30, 123, 222 compatibilizing agents, 28 competition, 159, 183, 215 competitiveness, 151 complexity, 33 compliance, 50, 147, 223, 225, 230, 231, 234 components, 2, 4, 5, 6, 22, 26, 27, 28, 30, 31, 37, 38, 43, 45, 47, 49, 50, 94, 99, 109, 145, 149, 157, 213, 222 composites, 6, 16, 31, 32, 35, 38, 39 composition, ix, 6, 11, 13, 15, 22, 27, 28, 29, 36, 39, 40, 41, 45, 46, 86, 102, 103, 119, 120, 122, 134, 136, 137, 161, 163, 179, 180, 194, 208, 222, 223, 224, 227, 231, 233, 238 composting, ix, 94, 99, 100, 101, 102, 106, 107, 108, 109, 110, 112, 115, 117, 199, 204, 236 compounds, 13, 14, 24, 25, 26, 31, 47, 96, 106, 108, 121, 134, 136, 137, 142, 147, 157, 158, 159, 160, 168, 177, 236, 237, 243 concentrates, 122, 139 concentration, x, xi, 14, 15, 16, 21, 23, 26, 32, 36, 38, 39, 43, 63, 72, 73, 86, 114, 116, 120, 122, 127, 142, 145, 146, 236, 242, 244 concrete, xi, 221, 224, 228, 230, 231, 232, 233, 234, 244

249

conditioning, ix, 93 conduct, xi, 235, 237, 239 conduction, 13 conductivity, xi, 3, 27, 95, 178, 236, 241, 242 confidence, 148 configuration, 160 conflict, x, 197, 202, 203, 209, 210, 212, 215, 216 consensus, 25 conservation, vii, 99, 108, 114, 121 consolidation, 151 constant rate, 243 construction, xi, 17, 49, 50, 122, 128, 158, 216, 221, 222, 233 consumer goods, 6 consumers, 4, 32, 209, 210, 211 consumption, vii, 1, 2, 3, 18, 23, 34, 44, 49, 62, 64, 66, 78, 79, 80, 121, 125, 133, 139, 148, 212, 215 contaminant, 21, 32, 33, 188 contamination, 13, 14, 15, 32, 33, 100, 105, 106, 117, 122, 146, 236 context, 216 control, xi, 51, 101, 111, 112, 117, 121, 123, 134, 135, 138, 144, 145, 146, 149, 150, 156, 159, 169, 176, 188, 217, 235, 237, 241, 242, 243, 244 conversion, 138, 157, 159, 160, 161, 162, 180, 182, 186, 190, 191, 194, 210, 212, 245 cooling, 130, 176, 177, 178, 217 copolymers, 28 copper, viii, ix, 8, 61, 63, 64, 86, 89, 90, 91, 93, 94, 98, 99, 105, 119, 120, 128, 129, 130, 131, 134, 145, 147, 202 corn, 156, 164, 166, 167, 168, 169, 170, 171, 190, 191 corona discharge, 38 correlation, 38, 39, 205, 207, 213, 216 corrosion, 163, 201 cost-benefit analysis, 22 costs, 14, 33, 34, 94, 95, 201, 203, 204, 209, 211, 215, 217 cotton, x, 31, 155, 156, 157, 161, 163, 164, 165, 168, 169, 176, 179, 183, 190, 193, 195 couples, 141 coupling, 17, 30 coverage, 174 covering, 10 creep, 20 critical value, 19 Croatia, 218 crop production, 108, 116, 215 crude oil, 45 crying, 35 crystallinity, 17, 19, 20, 22, 26, 39 crystallites, 35

250

Index

crystallization, 17, 19, 22, 33 crystals, 127, 141 cultivation, 157 curing, 125, 223, 227, 228 currency, 35 cycles, viii, 61, 63, 90 cycling, 96, 115 cyclohexanone, 9 cyclones, 13 Cyprus, 206, 214 Czech Republic, 206, 208

D damage, 34, 98, 125, 134, 135, 144 decay, 32 decision making, 198 decisions, x, 197, 198, 213, 216 decomposition, 20, 44, 45, 46, 51, 96, 97, 106, 109, 164, 174, 175, 238, 243 decomposition reactions, 20, 44, 45 deficit, 202 definition, 94, 99, 204, 214 deforestation, 106 degradation, ix, 14, 15, 17, 18, 19, 20, 21, 22, 23, 25, 26, 45, 55, 94, 96, 105, 117, 120, 142, 146, 164, 228, 245 degradation mechanism, 18, 21 degradation process, 17, 22, 23, 26 degree of crystallinity, 17, 39 dehydration, 46 demand, viii, ix, xi, 5, 34, 35, 50, 61, 62, 63, 65, 67, 68, 72, 73, 74, 75, 77, 78, 82, 83, 85, 86, 89, 90, 91, 119, 120, 121, 122, 125, 126, 133, 134, 150, 198, 212, 213, 215, 218, 222, 236, 240 denitrification, 108 Denmark, 46, 145, 206, 207, 208, 209, 218 density, xi, 6, 10, 11, 14, 19, 20, 35, 37, 39, 40, 41, 97, 102, 136, 141, 148, 161, 162, 179, 189, 191, 221, 222, 224, 227, 228, 229, 230, 232 Department of Energy, 219 depolymerization, 19, 44, 51 deposition, ix, 93, 94, 98, 99, 114, 141 derivatives, 26 desorption, 171, 173, 185 destruction, 169, 187, 206, 208, 216 detection, 241 developed countries, vii, 3, 6, 34, 144 developed nations, 146, 150 DFT, 75, 92 diaphragm, 142 differential scanning, 7, 29 differential scanning calorimetry, 7, 29

differentiation, 209 diffusion, 16, 17, 18, 22, 32, 33, 199 digestion, xi, 102, 103, 204, 235, 236, 240, 241, 242, 243, 244, 245 dioxin, 48, 208, 244 directives, 50, 157, 203, 216, 225 discharges, 245 dispersion, 28, 30, 31, 37 displacement, 127, 227 dissociation, 20 dissolved oxygen, 172 distillation, 33, 127, 148, 153 distilled water, 185, 225, 238 distribution, 19, 26, 31, 45, 64, 107, 109, 110, 112, 160, 188, 190, 192, 225, 226, 227 district heating, x, 49, 197, 198, 199, 201, 203, 205, 213, 214, 215, 218, 219 diversity, 32 division, 5, 33 DMF, 9 domain, 22 donors, 23 drainage, 95, 99, 101 drinking water, 116, 189, 191 drying, 15, 16, 17, 33, 36, 227 DSC, 29 DSM, 220 ductility, 136 dumping, ix, 119, 145, 146, 149 durability, 3, 234 duration, 16, 20, 165, 169 dusts, 121

E earnings, 5 earth, 45, 63, 103, 134 Eastern Europe, 205 economic systems, 64 economics, 6, 159 ecosystems, viii, 93, 94, 96, 116, 117 effluent, 13, 14, 15, 47, 123, 149, 177, 245 egg, 34 elasticity, 228, 232 elasticity modulus, 228, 232 elastomers, 20 electric conductivity, 3, 27 electricity, x, 47, 49, 127, 128, 197, 198, 200, 202, 204, 205, 208, 209, 210, 211, 212, 213, 215, 216, 217, 219, 220 electrodes, 63, 141, 177 electrolysis, 125, 130, 141, 147 electrolyte, 128, 130, 132, 141, 142

Index electron microscopy, 39 electrons, 63 emergence, 3 emission, 2, 39, 46, 69, 79, 138, 139, 144, 203, 204, 210, 218, 223 employment, 215 energy consumption, 44, 139, 148 energy recovery, 2, 3, 4, 48, 49, 139, 192, 200, 203, 204, 205, 207, 208, 218, 219 energy supply, 214, 215, 217 England, 56 enlargement, 169 entropy, 27 environment, vii, viii, ix, 2, 3, 34, 44, 62, 63, 90, 91, 95, 98, 112, 117, 120, 125, 134, 135, 138, 145, 146, 149, 152, 153, 156, 157, 158, 159, 183, 192, 199, 218, 236, 237, 244 environmental awareness, 136 environmental change, 95 environmental control, 149 environmental degradation, 105, 120, 146 environmental effects, 215 environmental impact, viii, 2, 3, 15, 44, 61, 62, 63, 86, 123, 125, 148, 150, 159, 207, 213, 214, 222, 224 environmental protection, 123 Environmental Protection Agency, 122, 212, 220 environmental regulations, 151 enzymes, 110 epidemic, 98 equilibrium, 17, 23, 26 equipment, x, 10, 11, 14, 25, 45, 46, 199, 221, 226, 228 erosion, 108 EST, 219 ester, 21, 22 ester bonds, 22 Estonia, 206 etching, 36 ethanol, 157, 195 ethyl alcohol, 9 ethylene, 5, 20, 28, 36, 44, 45, 51, 142 ethylene glycol, 44 EU, 4, 46, 79, 156, 198, 203, 205, 211, 214, 216 Euro, 94 Europe, 4, 5, 52, 98, 118, 127, 192, 202, 204, 209, 213, 217 European Commission, 204, 209, 217 European Community, 4, 192, 217 European Parliament, 217 European Union, x, 4, 197, 198, 201, 203, 204, 208, 209, 216, 225 evidence, 18, 38

251

evolution, 142 exchange rate, 200 experimental condition, 12, 227 expertise, 147 exploitation, 51, 157, 158 exports, 215, 216 exposure, 22, 32, 98, 144 expulsion, 226 external costs, 215 extraction, 11, 33, 58, 63, 64, 103, 112, 120, 123, 130, 131, 132, 147, 152 extrusion, 10, 13, 15, 16, 26, 31, 32, 33, 34, 35, 36, 41, 44

F fabrication, 7, 29, 31, 35 failure, 13 farms, 91 fat, 212 fatigue, 144 FDA, 34 fermentation, 245 ferrite, 132 fertilization, 95, 98, 111, 112, 116 fibers, 30, 31 filler particles, 35, 36, 39 fillers, 16, 20, 30, 31, 35, 36, 38, 158 films, 15, 16, 29, 34, 35, 36, 38, 39, 40, 41, 42, 43, 44, 51 filtration, 103, 161 financial support, 51, 150, 216 financing, 202 Finland, 65, 73, 98, 206, 208 fires, 199 firms, 62 fixation, 106, 108, 234 flame, 8, 17, 31 flame retardants, 17, 31 flexibility, 3, 20, 132, 139, 140, 223 flora, 99 flotation, 12 flue gas, 159, 188, 199 fluid, 14, 28, 33 fluidized bed, 123, 142, 158, 164 fluorescence, 225 focusing, 45 food, xi, 22, 32, 33, 34, 35, 47, 50, 57, 58, 156, 212, 215, 235, 238 food additives, 32 food industry, 212 food production, 215 forest ecosystem, viii, 93, 94

252

Index

forests, 102 formaldehyde, 46, 193, 194 formamide, 9 fossil, 2, 62, 98, 156, 157, 158, 160, 200, 204, 208, 209, 210, 211, 213, 215 France, 46, 136, 206, 208 free energy, 37 free radicals, 18, 19, 20, 21, 23, 26 free trade, 203, 204 free volume, 18 freezing, 105, 109 friction, 43 FTIR, 116 FTIR spectroscopy, 116 fuel, viii, 46, 49, 61, 62, 63, 64, 66, 67, 68, 69, 74, 75, 76, 77, 78, 80, 83, 84, 85, 86, 90, 91, 92, 136, 157, 158, 160, 180, 192, 199, 200, 201, 204, 205, 207, 208, 211, 213, 214, 215, 233

G garbage, 47, 59 gasification, 44, 45, 156, 158, 162, 165, 168, 180, 185, 190, 193 gasoline, 45, 47, 136 GDP, viii, 62, 65, 69, 74, 75, 76, 91 generation, ix, 3, 47, 63, 119, 121, 138, 140, 145, 146, 149, 157, 174, 217 germanium, 62 Germany, 4, 33, 79, 136, 139, 145, 194, 206, 208 glass transition, 13, 29 global demand, viii, 62, 65, 90 global economy, 118 glycol, 44 glycolysis, 44 GNP, 47 goals, x, 4, 197, 210, 212, 215, 216 gold, 63 goods and services, 219 government, 4, 34, 49, 50, 51, 91, 122, 199, 210, 211, 212 government budget, 210 grafted copolymers, 28 granules, x, 17, 130, 159, 221, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233 graphite, 142 grasses, 101 gravity, 125 Greece, 155, 178, 179, 190, 192, 206 green belt, 123 greenhouse gases, 2, 214 grids, 136, 137, 138 groups, 12, 17, 18, 20, 21, 22, 26, 36, 38, 92

growth, ix, 5, 34, 47, 62, 93, 95, 96, 108, 115, 199 growth rate, 47 guidelines, 122, 145

H habitat, viii, 93, 94 HALS, 23 harm, 145 harvesting, 114 hazardous substances, 199 hazards, 138 HDPE, 6, 7, 8, 9, 11, 12, 13, 14, 20, 25, 26, 28, 36 health, 32, 48, 111, 112, 134, 135, 138, 144, 160, 215, 236, 237 heat, x, 2, 13, 17, 19, 22, 26, 33, 47, 48, 49, 55, 123, 176, 179, 180, 182, 183, 184, 185, 187, 197, 198, 199, 200, 201, 203, 204, 205, 206, 208, 209, 210, 212, 213, 215, 218, 220 heat transfer, 176 heating, x, 41, 46, 49, 127, 140, 141, 148, 158, 160, 162, 164, 168, 170, 176, 179, 180, 182, 183, 190, 192, 198, 199, 204, 214, 217 heating rate, 164, 170, 176, 179, 180, 182, 183, 190 heavy metals, ix, xi, 47, 48, 94, 98, 99, 101, 105, 111, 112, 114, 115, 116, 117, 180, 199, 225, 230, 232, 236, 237, 242, 243, 244 height, xi, 11, 100, 101, 102, 228, 231, 235, 239 helium, 45, 172, 173, 176 high density polyethylene, 14 hip, 49 host, 63 humus, 96, 108, 109, 116, 117 hybridization, 244 hydrazine, 26 hydrocarbons, 63, 99, 159 hydrogen, 19, 20, 23, 45, 92, 156, 158, 159, 179 hydrogen gas, 45 hydrogenation, 44 hydrolysis, 2, 16, 18, 21, 22, 26, 44, 241, 243 hydroperoxides, 19, 20, 22, 24, 25, 26 hydrophilicity, 31 hydrophobicity, 12 hydroxide, 14, 45, 128, 143, 148, 153, 194 hydroxyl, 19, 21 hypertension, 144 hypothesis, 109

I ideas, 6 identification, 6, 7, 9, 16, 53, 146

Index implementation, ix, 4, 15, 119, 121, 134, 144, 147, 204, 209, 215 imports, 121, 122, 126, 146, 147, 149, 208 impregnation, 167 impurities, 5, 20, 22, 26, 128, 129, 130, 142, 147, 148, 160, 201 incentives, 4, 212 inclusion, 17, 31, 63 income, 5 incompatibility, 30 India, v, ix, 50, 119, 121, 122, 125, 126, 128, 133, 134, 138, 139, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153 indication, 174, 215, 241 indices, vii, 1 indigenous, x, 120, 121, 122, 199 indium, 62 induction, 20 induction period, 20 industry, ix, 2, 3, 32, 35, 46, 47, 49, 64, 69, 76, 79, 80, 93, 100, 105, 125, 133, 134, 135, 147, 148, 149, 150, 151, 153, 157, 158, 192, 200, 202, 218, 233, 234 influence, 13, 30, 38, 41, 43, 46, 95, 100, 116, 161, 162, 203, 211, 213, 237, 242 infrared spectroscopy, 7 infrastructure, 208, 209, 216 ingestion, 32 initiation, 18, 22, 24 inorganic fillers, 16, 36, 38 input, 70, 97, 116 insight, 195 institutions, ix, 119 instruction, 35 instruments, x, 197, 198, 210 insulation, 96 insulators, 20 integration, 153, 178, 218 intensity, 31, 38 interaction, 15, 30, 189 interactions, 26, 29, 39 interest, 31, 38, 50, 125, 149, 158, 159, 199, 209, 211 interface, 27, 28, 30, 35, 37, 41 interfacial adhesion, 30 interphase, 27, 28 interpretation, 213 interval, 211 intrinsic viscosity, 18, 44 inversion, 27 investment, x, 69, 128, 134, 197, 198, 199, 202, 203, 211 investors, 50

253

ions, 21, 63, 98, 123, 125, 141, 142, 189, 236, 237, 238, 241 Ireland, 206 iron, 121, 127, 128, 130, 132 isolation, 177 isophthalic acid, 44 isotherms, 171, 174 Italy, 136, 149, 192, 206, 208, 221, 224, 225, 226, 234

J Japan, 4, 46, 98, 116, 127, 136, 152 jobs, 156, 157 Jordan, 47

K kidney, 98 kidneys, 144 kinetic model, 175, 189 kinetic parameters, 175, 176, 189 kinetics, 20, 24, 45, 188, 189, 190, 191, 192, 194 knowledge, 22, 49, 198, 213, 216 KOH, 44, 165, 167, 168, 170, 171, 174, 185, 188, 189, 190, 194, 195 Kola Peninsula, viii, ix, 93, 94, 95, 97, 98, 99, 117 Korea, 139 Kyoto agreement, 156 Kyoto protocol, 201, 204

L labor, 6 lack of confidence, 199 lamination, 35 land, ix, 11, 50, 93, 94, 98, 99, 100, 102, 105, 107, 114, 115, 124, 125, 134, 145, 149, 157, 214, 215, 236 land use, 215 landfills, 2, 47, 48, 50, 123, 125, 145, 199, 204 Latvia, 206 laws, ix, 14, 47, 50, 119, 144 lead, ix, 2, 18, 19, 27, 31, 41, 48, 62, 85, 90, 91, 118, 119, 120, 121, 124, 125, 126, 130, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 148, 150, 151, 152, 153, 156, 157, 159, 209, 215 lead-acid battery, 141 learning, viii, 62, 68, 75, 92 legislation, x, 150, 197, 198, 200, 202, 203, 209 liberation, 19

254

Index

licenses, 147 life cycle, 62, 91 life span, viii, 62, 65, 67, 69, 73, 74, 78, 81, 84, 85, 86, 90, 158 lifetime, 223 light scattering, 225 light transmittance, 38 lignin, 12 limitation, 2, 31 linear programming, 213 links, x, 197, 228 liquid phase, 160 liquids, 8, 37, 174, 177, 184 Lithuania, 206 location, 99, 140 logistics, 3 long distance, 3 long run, 120, 125 low density polyethylene, 6 low temperatures, 20, 32, 136, 137 lower prices, 63 Luxemburg, 46 lying, 123

M macropores, 187 management, vii, viii, ix, x, 1, 3, 4, 47, 59, 62, 64, 78, 80, 83, 84, 85, 90, 120, 145, 146, 149, 150, 157, 158, 197, 201, 202, 204, 212, 214, 216, 217, 218, 219, 220 manners, 146 manufacturing, 2, 3, 4, 6, 34, 35, 126, 157, 200 market, vii, x, 1, 3, 5, 17, 31, 33, 34, 35, 50, 64, 65, 66, 67, 68, 69, 74, 75, 80, 84, 90, 91, 130, 133, 136, 158, 159, 189, 197, 198, 202, 203, 205, 206, 207, 208, 209, 216, 217, 218, 220 market penetration, 74, 75, 84, 90 market share, 67, 68, 69, 75, 80, 205, 206, 207, 208 market structure, 209 marketing, 6 markets, vii, 2, 4, 30, 34, 202, 204 mass, xi, 15, 34, 51, 97, 106, 110, 158, 184, 186, 189, 227, 235, 237 mass loss, 106 matrix, 14, 17, 18, 19, 20, 23, 24, 25, 26, 27, 30, 31, 32, 35, 40, 41, 50, 103, 108, 148, 223, 224, 234 measurement, 222, 228, 229, 230, 238 measures, 91, 120, 123, 138, 145, 199, 201, 213 mechanical degradation, 18 mechanical properties, 27, 30, 31, 227, 231, 233 media, 3, 44, 137 Mediterranean, 157

MEK, 9 melt, 18, 19, 24, 35, 132 melt flow index, 18 melting, 13, 15, 29, 35, 72, 128, 135, 136, 139 memory, 144 men, 145 mercury, ix, 98, 119, 120, 159, 172, 188 metabolism, 97 metal extraction, 120 metal hydroxides, 241 metal recovery, 147 metals, viii, ix, xi, 20, 23, 26, 47, 48, 49, 61, 62, 63, 64, 66, 73, 74, 86, 90, 91, 93, 94, 95, 98, 99, 101, 103, 104, 105, 106, 111, 112, 113, 114, 115, 116, 117, 119, 120, 121, 134, 136, 151, 180, 191, 225, 231, 236, 237, 238, 240, 241, 242, 243, 244 methanol, 44, 245 methodology, 13, 198, 214, 215 methyl methacrylate, 46 methylene chloride, 9 MFI, 18 microcavity, 35, 39 micronutrients, xi, 98, 120, 125, 130, 236, 244 microorganism, 14, 101 microstructure, 41, 160, 234 migration, 17, 33 mineral water, 21 mining, 10, 65, 72, 86, 89, 91, 98, 123, 125, 156 missions, 48, 215 mixing, 22, 27, 31, 134, 138, 228 MMA, 28, 46 mobile phone, 50 mobility, 18, 26, 30, 123, 203, 223 mode, 13, 134 modeling, 76, 87 models, x, 86, 175, 197, 198, 213, 214, 216 modern society, 198 modules, 92 modulus, 27, 30, 37, 228, 232 moisture, 16, 95, 96, 101, 156, 176, 178, 179, 180, 182, 184, 185 moisture content, 96 molar volume, 172 mole, 172 molecular weight, 19, 22, 25, 26, 160 molecules, 12, 26, 98, 160, 172, 173, 189 monitoring, 48, 100, 112, 122, 125, 134, 145, 147, 149, 150, 203 monolayer, 33, 36, 172, 173 monomers, 2, 19, 48, 51 morphology, 22, 27, 28, 29, 37, 39 Moscow, 117 motivation, 34

Index movement, 121, 146 multilayer films, 35, 41, 51 MWD, 19, 45

N Na2SO4, 141, 142 NaCl, 132 naphthalene, 45 natural gas, 157, 158, 160, 185, 201, 202, 205, 210 natural resources, vii, 2, 3, 98 needs, ix, 13, 15, 26, 120, 147, 198, 212, 236 negotiation, 210 nervous system, 144 nervousness, 144 Netherlands, 61, 79, 91, 116, 206, 233 network, 199, 202, 207, 209, 210, 218 newspapers, 202 nickel, viii, ix, 61, 63, 64, 86, 89, 90, 91, 93, 94, 98, 99, 105, 119, 120 nitrification, 96 nitrobenzene, 9 nitrogen, 47, 63, 102, 103, 106, 108, 116, 159, 164, 171, 172, 173, 190 nitrogen fixation, 106 nitrogen gas, 172, 173 node, 142 nodes, 130, 141 noise, 123 non-renewable resources, 47 North America, 46 Norway, 117, 206, 208, 209 novel materials, 3 nucleation, 35 nuclei, 35, 226 nutrients, ix, 93, 95, 96, 99, 106, 108, 109, 242 nutrition, 98, 116

O obligation, 32 observations, 99 oil, 4, 7, 14, 45, 46, 128, 155, 156, 178, 192, 199, 201, 207, 208, 214 oils, 15, 46, 192 optical properties, 18, 38 optimization, 6, 49, 91, 156, 215, 223, 226 ores, viii, 62, 63, 64, 72, 74, 86, 87, 88, 89, 90, 91, 125, 139 organ, 144 organic chemicals, 32, 45, 161 organic compounds, 31, 47, 96, 108, 157, 158, 160

255

organic matter, ix, x, 15, 93, 95, 96, 106, 108, 109, 115, 116, 117, 155, 179, 223 organic polymers, 12, 108 organism, 120 organizations, 6 orientation, 35, 41 outline, 11, 223 output, 70, 122, 205 overtime, 68, 75, 78, 80, 82, 83 oxidability, 103 oxidation, 18, 20, 22, 24, 25, 36, 125 oxides, 47, 132, 138 oxygen, xi, 18, 19, 20, 21, 22, 25, 45, 132, 142, 152, 156, 159, 160, 169, 172, 178, 179, 180, 204, 236, 240 oxygen absorption, 20

P packaging, 4, 5, 6, 7, 12, 14, 22, 26, 28, 32, 33, 34, 35, 36, 50, 53, 57, 58, 202, 204, 210, 218 paints, 14, 120, 125, 136 palladium, 62, 63, 91 palliative, 39 parameter, 41, 85, 153, 186 particles, 11, 12, 13, 17, 29, 31, 35, 36, 39, 40, 41, 48, 98, 114, 142, 157, 180, 195 pastures, 115 patents, 35 pathways, 48, 97, 114 peat, 212 percolation, 27 permeability, 27, 101 permit, 99 perspective, 158, 202, 211, 212, 215, 216, 218 Peru, 52 PET, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 17, 18, 21, 22, 26, 28, 31, 33, 34, 36, 44, 45, 50, 51, 52, 54, 57, 58 PGE, 63, 64, 91 pH, xi, 8, 14, 15, 32, 101, 102, 104, 105, 106, 107, 108, 109, 112, 113, 128, 138, 185, 236, 237, 240, 241, 242, 243, 244 phenol, 9, 23, 24, 25, 26, 193 phosphates, 25, 243 phosphorus, 25, 96, 108 photodegradation, 18 photooxidation, 17 physical and mechanical properties, 27, 222 physical properties, 22, 63, 116, 162, 230 phytoremediation, 114 pilot study, 219 pine, 102

256

Index

planning, 49 plants, vii, ix, 1, 47, 48, 49, 71, 93, 95, 96, 97, 98, 101, 103, 106, 108, 111, 112, 113, 114, 115, 116, 121, 122, 123, 133, 134, 136, 137, 139, 145, 148, 149, 156, 157, 158, 159, 160, 161, 192, 199, 200, 201, 203, 204, 205, 208, 209, 210, 211, 212, 213, 216, 217, 220 plasma, 127 plastic products, vii, 1, 3 plastics, vii, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 13, 14, 15, 16, 17, 23, 27, 28, 30, 31, 32, 34, 36, 44, 45, 46, 48, 49, 50, 51, 53, 57, 58, 208, 211 plastics processing, 23 platinum, viii, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 90, 91, 92 PMMA, 8, 9, 46, 51 Poland, 206, 208 polar groups, 38 polarity, 26, 38 policy instruments, x, 197, 198, 200, 210, 213, 216, 218 politics, 218 pollutants, ix, 14, 63, 93, 94, 98, 99, 100, 104, 105, 114, 117, 156, 157, 158, 160, 222, 223 pollution, viii, x, 15, 34, 47, 48, 93, 94, 95, 98, 100, 101, 104, 105, 106, 109, 113, 114, 117, 120, 121, 123, 134, 138, 144, 146, 149, 150, 156, 159, 223, 236, 237 poly(vinyl chloride), 6 polyamides, 45 polycarbonate, 19 polydispersity, 18 polyesters, 22, 45 polyethylene sack, 101 polyethylenes, 8 polymer blends, 35, 38, 50 polymer chains, 18, 19 polymer composites, 30, 31, 56 polymer matrix, 14, 17, 18, 19, 20, 23, 24, 25, 26, 30, 31, 32, 35, 41, 50 polymer oxidation, 20 polymer structure, 17 polymerization, 17, 26, 33, 108 polymers, vii, 1, 2, 6, 8, 9, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 25, 27, 28, 29, 36, 37, 38, 44, 45, 54, 55, 108, 110 polyolefins, 8, 14, 19, 20, 25, 28, 35, 36, 40, 45, 46, 51, 54, 55 polypropylene, 6, 14, 20, 35, 36, 137, 149 polystyrene, 6, 7, 8, 17 polyurethane, 44, 45 polyurethanes, 50

pools, ix, 93, 96, 110 poor, ix, 3, 31, 93, 97, 107, 114, 231 population, viii, 5, 47, 50, 62, 65, 69, 135, 236 population growth, 47 population size, viii, 62, 65, 69 porosity, 97, 157, 160, 171, 174, 186, 188, 191, 222, 230 Portugal, 93, 206 potassium, 14, 44, 129, 168, 188, 194 power, x, 1, 20, 46, 47, 49, 105, 156, 157, 158, 159, 160, 180, 190, 197, 198, 199, 200, 201, 204, 205, 211, 212, 213, 220, 226 power plants, 157, 158, 159, 160, 199, 200, 201 practical activity, 3 precipitation, 104, 105, 111, 125, 130, 132, 143 prediction, 192 preference, 112 preparation, 101, 137, 138, 148, 158, 164, 169, 180, 187, 190, 191, 194, 195, 238 pressure, 16, 20, 26, 33, 44, 45, 62, 147, 161, 171, 172, 173, 174, 176, 177, 186 prevention, 204, 217 prices, 63, 200, 202, 203, 204, 205, 209 primary antioxidants, 23, 24 principle, 32 probability, 20 probe, 12, 102, 103 producers, 121, 132, 133, 147, 202, 206, 212 product design, 6 production, viii, ix, x, xi, 3, 5, 16, 18, 23, 27, 33, 34, 49, 51, 61, 62, 63, 64, 65, 66, 68, 70, 71, 72, 73, 75, 78, 79, 80, 82, 85, 86, 89, 90, 91, 92, 93, 99, 106, 108, 110, 116, 119, 120, 121, 122, 123, 125, 127, 133, 134, 136, 137, 138, 139, 147, 148, 150, 151, 152, 153, 155, 156, 157, 158, 159, 160, 161, 162, 164, 174, 183, 186, 189, 190, 191, 192, 193, 195, 197, 198, 201, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 215, 216, 224, 232, 234, 236, 237, 240, 241, 242, 243, 244 productivity, 6, 96 profitability, 47 program, 43, 47 proliferation, 101 propagation, 18, 23, 25, 30, 37 proposition, 36, 199, 210 propylene, 20, 28 protocol, 204 PTFE, 9, 51 public awareness, 4 public health, 32, 134 publishers, 59 Puerto Rico, 91 pulse, 228

Index pultrusion, 32 pure water, 16 purification, 121, 123, 125, 128, 129, 130, 132, 144, 147, 148, 161, 189 PVC, 6, 7, 8, 9, 10, 11, 12, 13, 22, 136 pyrolysis, x, 2, 44, 45, 46, 51, 155, 156, 158, 159, 160, 162, 163, 164, 166, 169, 174, 175, 176, 178, 180, 181, 182, 183, 184, 185, 187, 189, 190, 191, 192, 193, 194, 195 pyrolysis gases, 158 pyrophosphate, 110

Q quantitative technique, 39 quaternary ammonium, 234

R radiation, 11, 36 range, 11, 13, 30, 98, 107, 109, 125, 126, 140, 145, 160, 169, 170, 174, 176, 178, 180, 182, 186, 188, 226, 228, 229, 230, 231, 232, 233, 241 rape, 190 raw materials, vii, x, 1, 43, 44, 120, 121, 128, 132, 147, 150, 156, 158, 159, 169, 188, 189 reaction mechanism, 23, 46 reaction rate, 20, 169 reagents, 14, 45 recombination, 20 recovery, ix, x, 2, 3, 4, 36, 46, 48, 49, 50, 51, 53, 94, 95, 119, 123, 124, 127, 128, 134, 135, 136, 137, 138, 139, 140, 143, 147, 148, 149, 150, 151, 153, 155, 156, 158, 197, 198, 199, 202, 203, 204, 206, 207, 210, 212, 216, 221, 222, 223, 225, 236 recovery processes, 36, 48 recycling, vii, viii, x, 1, 2, 3, 4, 5, 10, 13, 14, 15, 16, 17, 26, 27, 28, 31, 32, 33, 34, 36, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 57, 59, 61, 62, 63, 65, 66, 68, 71, 72, 74, 80, 81, 85, 86, 89, 90, 91, 114, 120, 123, 125, 126, 128, 132, 136, 137, 139, 141, 146, 147, 148, 149, 150, 151, 152, 153, 155, 158, 160, 190, 195, 202, 208, 211, 214, 217, 218, 233, 236 redistribution, ix, 94 reduction, vii, 1, 2, 18, 25, 47, 68, 125, 139, 141, 148, 187, 236 refining, 72, 116, 138 regenerated cellulose, 8 regional problem, 47 regression, 78, 86, 176 regression analysis, 78, 86, 176

257

regulation, 32, 230, 231 regulations, 3, 4, 5, 48, 50, 51, 146, 151, 200, 211 rehabilitation, ix, 93, 99, 100, 102, 104, 105, 114 reinforcement, 30, 31 reinforcing fibers, 31 relationship, 227, 231 relaxation, 13 relaxation properties, 13 relevance, 14 remembering, 12 replacement, 38, 158, 222, 228 reprocessing, vii, 1, 2, 14, 15, 16, 17, 18, 22, 26, 31, 32, 132, 134, 146, 147 residues, vii, ix, x, 1, 2, 3, 4, 5, 6, 11, 12, 13, 14, 15, 17, 20, 22, 26, 27, 28, 30, 31, 32, 33, 34, 36, 44, 45, 46, 47, 48, 49, 50, 51, 117, 119, 120, 121, 123, 125, 126, 127, 140, 146, 148, 155, 156, 157, 159, 161, 162, 163, 164, 165, 168, 169, 179, 186, 189, 190, 194, 208, 233, 236, 244 resins, 4, 11, 34, 36, 168, 193 resistance, 18, 22, 26, 37 resolution, 5 resource availability, 63, 86 resources, vii, viii, 2, 3, 47, 62, 63, 64, 65, 66, 72, 73, 74, 78, 79, 80, 81, 82, 83, 84, 85, 86, 89, 90, 91, 98, 114, 136, 156, 158, 201, 204, 213, 217 respiration, 96, 109, 110 responsibility, 3, 5, 50, 204, 218 restructuring, 217 retardation, 238 returns, 121 revenue, 158 rice, 64, 98, 156, 164, 166, 167, 168, 169, 170, 171, 179, 191, 193 rice husk, 156, 168, 169, 170, 179, 191 risk, 32, 48, 98, 120, 138, 144 robustness, 214 Romania, 206, 208, 214 ROOH, 19, 20, 24 room temperature, 11, 28, 102, 103, 172, 173, 177, 227 roughness, 36, 39 rubber, 5, 28, 29, 31, 137, 158, 163, 208 rubbers, 163 runoff, 108 Russia, viii, ix, 50, 62, 65, 73, 83, 93, 94, 99, 117

S safety, 14, 25, 32, 114, 120, 138, 149 sales, 123 salts, 98, 108, 125, 141, 152, 170

258

Index

sample, 41, 102, 103, 110, 170, 172, 173, 176, 177, 180, 182, 185, 187, 188, 189, 225 sampling, 100, 102, 103, 109, 110, 112, 113, 234 saturation, 97, 171, 172, 173 savings, 2, 47, 49, 211 sawdust, 191 Scandinavia, 98 scanning calorimetry, 7, 29 scanning electron microscopy, 39 schema, 218 scores, 48 search, 23, 161 Second World, 199 security, 3 sediments, 222, 223 seed, 157, 171, 186, 188, 190, 193 selectivity, 45 self, vii, 1, 8, 20, 21, 203 SEM micrographs, 42 sensitivity, 47, 97, 214 sensors, 63, 69 separation, vii, 1, 4, 5, 6, 10, 11, 12, 13, 15, 16, 27, 48, 50, 72, 124, 125, 128, 134, 137, 147 series, 20, 45, 59, 130, 132, 141, 187, 228 services, 151, 203, 214 sewage, ix, 14, 93, 95, 99, 100, 102, 106, 107, 108, 110, 114, 116, 117, 118, 234 shape, 13, 17, 22, 23, 26, 162, 163, 179 shear, 18, 31, 41 shortage, 4, 49 sign, 227 signals, 213 silica, 140, 178 silver, 134, 135 simulation, 68, 83, 217 SiO2, 35, 124, 126, 135, 148, 224 sites, ix, 20, 71, 83, 99, 119, 120, 146, 150 skimming, 120, 122, 125, 126, 127, 128, 147, 149 skin, 138 slag, ix, 119, 120, 123, 132, 134, 135, 139, 140, 151, 223, 234 Slovakia, 206, 208 sludge, ix, xi, 93, 95, 99, 100, 101, 102, 106, 107, 108, 110, 112, 114, 116, 117, 118, 120, 124, 125, 138, 140, 141, 148, 222, 233, 234, 235, 238, 239, 245 smoke, 8 social problems, 215 sodium, 14, 44, 138 sodium hydroxide, 14 soil particles, 157 soils, 95, 96, 110, 115, 116, 117, 118, 134 solid phase, 15, 16

solid polymers, 22 solid state, 14, 22, 25 solid waste, ix, xi, 3, 46, 94, 99, 114, 116, 119, 120, 125, 134, 145, 146, 148, 149, 150, 158, 163, 190, 194, 208, 219, 222, 223, 232, 233, 235, 236, 244, 245 solidification processes, 223 solubility, 10, 11, 22, 25, 107, 127 solvents, 8, 9, 32, 44, 50 sorption, 32 South Africa, 83 Spain, 136, 151, 206 species, 35, 94, 106, 114, 115 specific gravity, 125 specific surface, 171, 173, 185, 188, 237 specificity, ix, 93 spectrophotometry, 103 spectroscopy, 7, 11, 116 spectrum, 11, 160, 174 speed, 36, 41, 82, 83, 90, 226 spindle, 157 sports, 4 stability, 18, 20, 23, 25, 26, 31 stabilization, x, 22, 23, 24, 25, 48, 54, 55, 221, 223, 224, 234 stabilizers, 17, 23, 24, 25, 26, 36, 54 stages, x, 5, 49, 120, 128, 171, 174, 187 standard of living, 47 standards, 37, 107, 145, 203, 214 statistics, 207 steel, 120, 128, 132, 177, 180, 185, 202, 228 stock, viii, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 79, 83, 86, 87, 88, 90 stockpiling, 134 storage, 32, 50, 123, 141, 157, 158, 160, 218, 236 strategies, 94, 117, 150, 215, 244 streams, 74, 137, 138, 157, 158, 160 strength, xi, 27, 28, 30, 86, 222, 223, 224, 228, 229, 230, 231, 232 stress, 13, 19, 27, 30, 31, 37, 114 stretching, 41 structure formation, 169 students, 51 styrene, 11, 28, 163 subsidization, 211 substitutes, 190 substitution, 51, 78, 143 substrates, 39 subtraction, 171 sugar, 164 sulfur, 24, 156, 159 sulfuric acid, 9, 102 sulphur, 123, 138, 189

Index summer, 110 Sun, 191, 193, 234 supervision, 217 suppliers, 51, 209 supply, viii, ix, 16, 34, 35, 49, 61, 62, 63, 65, 72, 73, 74, 81, 82, 83, 85, 86, 87, 89, 90, 91, 119, 120, 121, 122, 126, 133, 155, 156, 158, 159, 198, 201, 204, 205, 208, 214, 217, 218 supply disruption, 155 suppression, 123 Supreme Court, 147 surface area, 17, 26, 36, 157, 160, 169, 171, 172, 173, 185, 186, 187, 188, 189, 190, 191, 194 surface energy, 12, 30, 38, 39 surface layer, 35, 41, 43 surface tension, 16, 27, 37 surface treatment, 12, 33, 38, 43 surfactant, 12, 14 surplus, 101, 205 survival, 114 susceptibility, 14, 17, 18, 22, 38 sustainability, vii, 1 sustainable development, vii, 2, 3, 49, 51, 62, 222 Sweden, x, 46, 47, 92, 118, 140, 197, 198, 200, 202, 203, 204, 205, 206, 207, 208, 209, 210, 216, 217, 218, 219, 220 Switzerland, 46, 151, 152, 153, 206, 208 synthesis, 44 synthetic fiber, 30, 31 system analysis, 91, 213 systems, vii, viii, x, 1, 3, 15, 16, 25, 26, 50, 54, 64, 93, 94, 144, 156, 161, 197, 198, 201, 202, 208, 209, 210, 213, 214, 215, 218, 219, 227, 228, 229

T Taiwan, xi, 48, 116, 235, 236, 237, 238 targets, 4, 21, 50, 156, 214 taxation, 3, 50, 200, 201, 208, 209, 210, 211, 217, 219 technology, viii, 6, 10, 30, 44, 56, 58, 61, 63, 64, 90, 120, 121, 123, 125, 132, 133, 134, 139, 140, 147, 149, 150, 151, 152, 153, 158, 180, 199 teeth, 144 temperature, x, 11, 13, 14, 16, 18, 20, 22, 26, 28, 29, 32, 33, 41, 44, 45, 48, 96, 99, 102, 103, 109, 110, 127, 128, 129, 130, 142, 143, 155, 160, 164, 167, 169, 170, 171, 172, 173, 174, 176, 177, 178, 180, 181, 182, 183, 184, 185, 186, 189, 192, 201, 223, 227 tensile strength, 30 tension, 16, 19, 20, 27, 28 test procedure, 41

259

tetrahydrofuran, 9, 11 TGA, 164, 165, 166 theory, 37 thermal aging, 25 thermal decomposition, 175, 195 thermal degradation, 18, 22 thermal oxidation, 20 thermal stability, 25 thermal treatment, 94, 156, 158, 191 thermodynamics, 2, 27 thermolysis, 44, 45, 46, 48 thermooxidation, 17, 18 thermoplastics, 14, 17, 31 threat, 144 threshold, x, 32, 120, 149, 244 timber, 35 time, vii, viii, 7, 10, 11, 16, 17, 27, 45, 47, 62, 65, 66, 68, 69, 70, 71, 73, 74, 75, 76, 77, 78, 83, 85, 90, 98, 108, 110, 134, 147, 156, 157, 159, 164, 166, 167, 170, 174, 175, 176, 180, 182, 183, 185, 186, 187, 189, 199, 201, 202, 210, 223, 241 tissue, 113 titanium, 40, 141 toluene, 9 total energy, 215 toxicity, 31, 32, 106, 111, 112, 145, 148 toys, 4 TPA, 44, 45 trade, 24, 146, 147, 198, 203, 209, 217 trading, x, 159, 197, 198, 203, 204, 210, 218 training, 6 transference, 30 transformation, ix, 94, 99, 108, 109, 110, 112, 114, 115 transformations, 108 transition, 13, 20, 28, 29, 99 transition metal, 20 transition temperature, 13, 28 transitions, 13 transparency, 3 transplantation, 101 transport, 3, 34, 50, 75, 98, 145, 150 transportation, 198, 211 trees, 99, 101, 161 trend, 80, 114, 174, 186, 200, 230, 242 trial, 43 tundra, 96, 99, 115, 116 Turkey, 118, 206 turnover, ix, 93, 96

260

Index

U UK, 4, 75, 92, 115, 116, 117, 132, 136, 145, 152, 153, 192, 206, 245 Ukraine, 214 uncertainty, 186 uniform, 163, 179 United Nations, 114 United States, 57, 122, 157 urban centers, 3 UV, 11, 19, 23, 36 UV radiation, 36

V vacuum, 16, 33, 114, 156, 192 values, x, 27, 38, 40, 43, 46, 48, 75, 78, 86, 96, 103, 104, 107, 109, 112, 120, 123, 130, 159, 172, 173, 186, 187, 188, 228, 229, 230, 231, 232, 241 vapor, 16, 161, 171 variability, 28 variable, 69, 132, 145 variables, viii, 32, 38, 62, 65, 67, 69, 73, 76, 86, 223, 233 variance, 99 variation, 108, 209 VAT, 209 vegetables, 7, 34 vegetation, ix, 93, 94, 99, 105, 114 vehicles, viii, 50, 61, 62, 63, 67, 68, 69, 74, 75, 76, 77, 78, 79, 91, 92, 136, 157, 158, 160, 204 velocity, 15, 16, 228 vinyl chloride, 6 viscosity, 18, 28, 30, 44 volatility, 47 volatilization, 107, 108 vulcanization, 159

W washing procedures, 14 waste disposal, 47, 48, 189 waste incineration, x, 47, 197, 198, 199, 200, 201, 203, 204, 205, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 218, 219, 220, 221, 233 waste management, vii, viii, ix, x, 1, 47, 62, 64, 78, 80, 83, 84, 85, 90, 120, 146, 150, 158, 197, 198,

200, 201, 202, 203, 205, 208, 211, 212, 213, 214, 216, 222 waste treatment, x, 94, 189, 197, 198, 200, 201, 203, 205, 207, 210, 211, 213, 214, 215, 216, 222, 245 waste water, 116, 238 wastewater, xi, 156, 235, 241, 244 water, xi, 7, 8, 10, 11, 12, 14, 15, 16, 17, 18, 21, 22, 26, 33, 35, 36, 39, 44, 46, 48, 50, 96, 98, 101, 102, 103, 108, 110, 112, 116, 117, 120, 122, 123, 125, 130, 134, 138, 142, 145, 148, 150, 160, 178, 185, 188, 190, 200, 203, 210, 211, 212, 218, 221, 224, 226, 227, 228, 229, 236, 238, 241, 244 water absorption, 227, 229 wavelengths, 11, 19 wear, 158 weight loss, 26, 175, 183, 189 weight ratio, 29 Western Europe, 216 wettability, 37 wheat, 156, 161, 190 wind, 91, 98, 212 winter, 105, 110, 115, 193 women, 98, 145 wood, x, 3, 31, 46, 49, 155, 162, 163, 164, 174, 178, 179, 180, 183, 189, 192, 208, 212 words, 5, 86, 94, 114, 120 work, vii, x, 2, 3, 12, 14, 15, 16, 28, 29, 33, 36, 39, 48, 107, 123, 145, 147, 148, 160, 168, 175, 187, 199, 216, 221, 224, 232 workers, 5, 6, 18, 26, 29, 33, 44, 45, 47, 49, 50, 134, 135, 138 writing, 28, 34, 35, 37, 38, 210

Y yield, 45, 46, 51, 86, 149, 164, 171, 175, 176, 181, 182, 183, 184, 190

Z Zimbabwe, 65, 73 zinc, ix, 11, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 145, 146, 147, 148, 149, 150, 151, 152, 153, 170, 191 zinc oxide, 122, 124, 128, 130, 132, 147, 148 zirconium, 51 ZnO, 125, 128, 132, 135, 148