Mineral Resources Management and the Environment

MINERAL RESOURCES MANAGEMENT AND THE ENVIRONMENT

Dedicated to Prof. M.S. Swaminathan, the eminent scientist and humanist, in appreciation of his untiring efforts to promote the use of science and technology to sustain a hunger-free and violence-free Developing world, through job-led economic growth.

Mineral Resources Management and the Environment U. ASWATHANARAYANA Adviser on Environment & Technology, c/o Ministry of Environment, Maputo, Mozambique Former Commonwealth Visiting Professor, Universidade Eduardo Mondlane, Maputo, Mozambique

A.A. BALKEMA / LISSE / ABINGDON / EXTON (PA) / TOKYO

This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.” Copyright © 2003 U. Aswathanarayana All rights reserved. No part of this publication or the information contained herein may be reproduced, stored in a retrieval system, or transmitted in any form of by any means, electronic, mechanical, by photocopying, recording or otherwise, without written prior permission from the publishers. Although all care is taken to ensure the integrity and quality of this publication and the information herein, no responsibility is assumed by the publishers nor the author for any damage to property or persons as a result of operation or use of this publication and/or the information contained herein. Published by: A.A. Balkema Publishers, a member of Swets & Zeitlinger Publishers www.balkema.nl and www.szp.swets.nl

ISBN 0-203-97122-1 Master e-book ISBN

ISBN 90 5809 545 2 (hardback)

Contents

FOREWORD

ix

PREFACE

xiii

COPYRIGHT ACKNOWLEDGEMENT

xvii

1.

INTRODUCTION 1.1 Status of the World Mining Industry 1.2 Mining and the Environmental Agenda 1.3 Technology Trends in the Mining Industry 1.4 Extraction Costs vs. Environmental Acceptability 1.5 e-Business in the Mining Industry

1 1 7 12 16 17

2.

MINING METHODS AND THE ENVIRONMENT 2.1 Introduction 2.2 Mine Design Process 2.3 Opencast Mining 2.4 Underground Mining 2.5 Mass Mining 2.6 Offshore Mining 2.7 Artisanal Mining 2.8 LKAB Iron ore Mine, in Kiruna, Sweden – A Case Study

25 25 26 40 45 53 58 62 66

3.

MODE OF OCCURRENCE OF MINERAL DEPOSITS 3.1 Metallic Minerals 3.2 Industrial Minerals 3.3 Coal 3.4 Oil and Natural Gas

69 69 70 79 81

4.

ENVIRONMENTAL IMPACT OF MINERAL INDUSTRIES – INDUSTRY-WISE 4.1 Steel Industry

83 83

vi Contents

4.2 4.3 4.4 4.5

Aluminium Industry Base Metals Industry Coal Industry Industrial Minerals

92 95 99 101

5.

IMPACT OF MINING ON THE ENVIRONMENT – WASTE-WISE 5.1 Introduction 5.2 Impact of Mining on the Geoenvironment 5.3 Hydrogeological and Geotechnical Forecasting 5.4 Solid Wastes from Mining 5.5 Liquid Wastes from Mining 5.6 Emissions Due to Mineral Industries 5.7 Loss of Biodiversity

105 105 106 112 113 115 118 121

6.

MINING AND HEALTH HAZARDS 6.1 Introduction 6.2 Dust Hazards 6.3 Other physical Hazards 6.4 Chemical Hazards 6.5 Biological Hazards 6.6 Mental Hazards 6.7 Coal Cycle and the Environmental Health

123 123 124 131 137 140 140 140

7.

PROCESS TECHNOLOGIES AND THE ENVIRONMENT 7.1 Preparation of Coal 7.2 Preparation of Metallic Ores 7.3 Flotation 7.4 Hydrometallurgy 7.5 Bioleaching 7.6 Gold Processing Technology – A Case Study

145 145 146 147 153 155 157

8.

CONTROL TECHNOLOGIES FOR MINIMIZING THE MINING ENVIRONMENTAL IMPACT 8.1 Acid Mine Drainage 8.2 Tailings Disposal 8.3 Dust Control 8.4 Low-waste Technologies 8.5 Treatment of Wastewater 8.6 Subsidence 8.7 Noise and Vibration 8.8 Planning for Mine Closure

167 167 181 197 200 204 208 210 213

MITIGATION OF MINING IMPACTS 9.1 Monitoring of Mining Impacts

215 215

9.

Contents vii

9.2 9.3 9.4 9.5

Ways of Reducing the Mining Impacts Rehabilitation of Mined Land Beneficial Use of Mining Wastes Reuse of Mine Water

218 222 235 239

10. SOCIO-ECONOMIC DIMENSIONS OF THE MINING IMPACT 10.1 Environmental Impact Assessment 10.2 Environmental Regulations 10.3 Environmental Audits 10.4 Environmental Code – The Swedish Model 10.5 International Initiatives 10.6 Total Project Development – A Visionary Approach

245 245 252 254 255 256 257

REFERENCES

259

APPENDIX A – CONVERSION CONSTANTS

265

APPENDIX B – PARTICULARS OF IMPORTANT OF METAL MINES IN THE WORLD

269

APPENDIX C – WORLD PRODUCTION OF MINERALS/METALS

283

APPENDIX D – LIST OF MAJOR ACCIDENTS RELATED TO MINING SINCE 1975

285

APPENDIX E – INDUSTRY STANDARDS (ISO 14001)

287

AUTHOR INDEX

289

SUBJECT INDEX

291

Foreword

I have known my good friend, Professor Uppugunduri Aswathanarayana, since 1967, when we shared a room during a very pleasant field trip in the Arctic region of Yellowknife, Canada, in the context of the First International Geochronology Conference, held in Edmonton. At that time, he was a very competent isotope geochemist, spending some time as an Associate Professor at the University of Western Ontario, Canada. He had a very solid background in that subject, obtained essentially in India, where he was attached to the Andhra University, and complemented with post-doctoral positions held at the very respected research centers of Caltech, USA, and Oxford, UK. During his academic career, as a Professor at three very relevant institutions in developing countries, namely; the University Saugar, India, the University of Dar-es-Salaam, Tanzania, and the University Eduardo Mondlane, Mozambique, Aswathanarayana has developed special competence in dealing with socioeconomic issues important to the developing world, such as natural resources and environmental management. For instance, I have heard of his highly successful effort in building a modern Institute of Earth Sciences in Dar-es-Salaam, and later about his activities in Mozambique, where he served as a consultant and investigator in many projects related to natural resources and environmental management. Because of his international expertise, he has been a consultant, always in Africa, to the UNIDO, the World Bank, the SIDA organization of Sweden, the M/S Louis Berger Int. Inc., USA, and to some governmental institutions of Tanzania and Mozambique, related to environmental matters. Human activities are transforming the global environment profoundly. That the quantity of mine tailings produced globally (about 18 billion cubic meters per year) should be of the same order of magnitude as the quantity of sediments discharged in the oceans, is an indication of the enormity of the anthropogenic impact. Mineral resources will always be needed by man, despite significant increase in industrial recycling and the development of new synthetic materials. Environmental issues are expected to gain great importance all over the world, including the less industrialized countries, and the challenge will be to find the best possible geologic locations and the best mining technologies, while minimizing the environmental impact of mining operations.

x

Foreword

During many years of my association with the International Union of Geological Sciences, I have got acquainted with the environmental issues pertaining to the mining industry, in the context of the vision of sustainable development, first mooted with great fanfare in Rio-92. That there has been very little progress in Agenda-21 became evident in the summit in Johannesburg in 2002. As mining costs in the industrialized countries of North America and Europe have increased steeply, investments in the mining sector have been diverted to the developing countries, because of their lower costs, and less stringent environmental regulations. This centrifugal movement of capital of the mining sector could be taken advantage of by the developing countries with mineral potential, if mining and mineral extraction are carried out diligently without degrading the environment. “Mineral Resources Management and the Environment” deals with ways of managing the environmental impact of mining and related operations, through an understanding of the processes that cause environmental degradation. It is written in a clear, objective and direct way and its contents are quite lucid. The first seven chapters of the book cover a complete description of mining worldwide. They include the main modes of occurrence of mineral deposits, and the main mining methodologies employed internationally. They deal with the environmental impact of mining and of mineral industries, and also of process technologies, with emphasis on emissions, wastes, contamination and associated environmental problems, and their bearing on health. The rest of the book is devoted to technologies developed to control, mitigate and minimize mining impacts. The final chapter reports social-economic aspects, including the laws and regulations adopted by many countries. Aswathanarayana makes a very good use of the available experience in the description of the mining methods and industrial processes, by means of examples taken from real developments, in industrialized countries with strict regulations, such as Sweden. For instance, the book describes the mining technologies used at the LKAB iron ore mine at Kiruna, and the advanced decyanidation technology for the gold extraction process used at Boliden. He also deals with the environmental impact of the mining activities through the report of many case histories. Examples are taken from all parts of the world, such as Elliot Lake and Sudbury, Canada, Nizhi Tagil, Russia, Goa, India, and many other places in the US, Europe, Australia, Brazil, South Africa, China, etc. Quite illustrative is the report on the land degradation that occurred in Rajasthan, India, as a result of haphazard mining of industrial minerals such as gypsum, limestone, phosphate, and sandstone. The final chapter of the book is especially relevant to the future of the mining industry, because it is focused on the social-economic dimensions of the mining impact, and describes the environmental regulations that are being adopted by many communities. These are related to rehabilitation of mined lands, as well as actions to mitigate contamination by liquid and solid wastes and by gas emissions from mineral industries. Regulatory requirements are becoming increasingly stringent, because the general public is becoming more and more concerned

Foreword xi

about the cleanliness of their environment as an integral part of the quality of life. Aswathanarayana avers that one of the main dilemmas facing the society today is how to balance the need for resource development with the need for conservation and protection of the environment. This volume of Professor U. Aswathanarayana is an excellent, state-of-art summary of the present status of knowledge in regard to the environmental aspects of mining. It will be useful to university students and professionals in the areas of geology, mining engineering, geography, and environmental science, as a whole. Sau Paulo, Brazil Dec. 2002

Umberto Cordani Former Director, Institute of Geosciences, Univ. of Sao Paulo Past President, International Union of Geological Sciences

Preface

The book seeks to elucidate ways and means of managing the environmental impact due to mining, beneficiation, transport, processing, etc. of ores, through an understanding of the processes that cause the environmental degradation. The issues are dealt with in terms of the linkages between the raw materials, methods of mining, process technologies, wastes generated, health hazards, etc., with emphasis on control technologies for the protection of environment. Mining, like the proverbial serpent in the Garden of Eden, has never been held in high esteem. Most people consider mining as an unmitigated evil, and some who are more realistic, concede that it is a necessary evil (but evil all the same). This is not a new development. In the olden days, mines were invariably worked by slaves – chained to pillars underground, the slaves used to die in a matter of weeks. In the medieval Europe, being condemned to work in the salt mines was a form of punishment worse than death. Presently, the horrendous consequences of mining are evident everywhere. The landscape in some countries (e.g. USA, Zambia, PNG) is pockmarked with gigantic pits. As pointed out by Förstner, the mass of the mine tailings produced worldwide (18 billion m3/year) is of the same order as the quantity of sediment discharge into the oceans. As progressively lower grades are worked, the mass of the mine tailings is expected to double in the next 20–30 years. Vast areas are either strewn with rock fragments, and in some areas, Acid Mine Drainage has rendered the soil and water so acidic that not a blade of grass grows there. Whole towns (e.g. eastern India) had to be abandoned due to subsidence caused by underground coal mining. Mine workers are exposed to a number of physical, chemical, biological and mental hazards, and mining is ranked as number one among the industries in the average annual rate of traumatic fatalities. Faced with these problems, the industrialized countries have gone in for high-tech solutions, with high degree of mechanization and fewer workers. For instance, the Endeavour 26 mine in Northparkes copper-gold porphyry deposit in New South Wales, Australia, which employs block caving, has achieved the phenomenal productivity of 42,600 t of ore per underground employee, including the contractors! The mining operations in the LKAB iron ore mine in Kiruna, Sweden, which employs sub-level caving methods to produce 30 million tonnes of ore per year, is almost wholly automated. By innovative use of technology, LKAB could

xiv Preface

enhance the mine productivity, while drastically bringing down the water, air and noise pollution (incidentally, below the statutory limits), and reducing energy consumption. This high-tech model is, however, not applicable to the Developing countries, for the following reasons: (1) the investments needed are high – for instance, a block cave mine may need an investment any where from USD 100 million to 1000 million, (2) what the developing countries need is job-led (and not job-less) economic growth. A sensible strategy for the developing countries is to use the mining industry to promote job-led economic growth through the adoption of employment-generating, economically viable and environmentally acceptable technologies. Neither the industrialized countries nor more so, the developing countries can afford to avoid mining altogether, as the whole spectrum of industrial activities (including energy generation) is based on minerals (mining accounts for 80–90% of the GDP of some African countries). What is possible and should be attempted, is to minimize the adverse environmental impact of the mining industry through steps such as recycling of metals, development of substitutes, low-waste technologies, bioleaching, beneficial use of mine wastes, rehabilitation of mined land, etc. The volume seeks to provide methodologies which both the industrialized and developing countries could use in developing plans for safe, efficient and ecologically sustainable mining and mineral development. The author is strongly convinced that if geology has to have socioeconomic relevance, and provide employment opportunities in the twenty-first century, it needs to be taught as earth system science, focused on the use of natural resources, namely, water, soil and minerals (rather than in the traditional form of subject disciplines, such as structural geology, stratigraphy, etc.). He tried to contribute to the movement in a small way by writing a quartet (including the present work) to provide the textual material to facilitate the switchover: “Geoenvironment: An Introduction” (A.A. Balkema, Rotterdam, 1995), “Soil Resources and the Environment” (Science Publishers, Enfield, NH, USA, 1999), and “Water Resources Management and the Environment” (A.A. Balkema, Lisse, Holland, 2001). The volume has been carefully structured to avoid overlapping, since some issues (e.g. dust) have to be examined from different perspectives, and therefore figure in more than one chapter. The book would be useful to the university students and professionals in the areas of geology, mining engineering, mineral economics, geography, resource management, environmental technologies, etc. I am greatly beholden to Prof. Umberto Cordani of Brazil for writing the Foreword for my book. Dr. Cordani is a role model for Third World geologists. As the President of the International Union of Geological Sciences, and the President of the International Geological Congress (Rio de Janeiro), he attained the highest scientific – administrative positions open to geologists in the world. That these honours sit lightly on him should be evident from the fact that during an official

Preface xv

visit to China, he found time to determine the SHRIMP ages of zircons from some Brazilian rocks. Asa Sjoblom (Sweden), A.N.L. Raja (India), Susan Gamon (France), and J.R. Ikingura (Tanzania) kindly provided reference material for the book. When I wrote my book on water resources, I indicated how the title of the book is related to the name my elder daughter, Indira, who was called Gangamai (Mother Ganga) in her childhood. Now my younger daughter came up with the demand for equal treatment. Though her official name is Vani (Hindu goddess of learning), the pet name given to her in her childhood (Sonal, which means gold), proved more prophetic – she is determined to become the first millionaire in the family. Hence the present book is “golden” and devoted to minerals! The togetherness in my family manifests itself in book writing – my wife (Vijayalakshmi) serves as cheerleader, and my children (Viswanath, Srinivas and Indira) help in the mechanics. Hyderabad, India July, 2002

U. Aswathanarayana

Copyright Acknowledgement

Grateful acknowledgement is made to the publishers, authors and editors of journals and books, from which some figures that appear in the volume have been redrawn or adapted. The particulars of the page nos. are shown against the book or journal concerned. Besides this consolidated statement, individual acknowledgement is made against each figure as it appears in the text. Beijer Inst., Stockholm, Mining Projects in the developing countries – A manual (ed. M.J. Chadwick et al.), 1987, Figures on p. 72, 78, 79, 83, 89, 111, 113, 115, 118, 121, 123, 150, 159, 160, 203 CRC Press, Constructed wetlands for wastewater treatment – municipal, industrial and agricultural, 1989, chap. 42f. (one fig.) J. Cent. – South Inst. Min. & Metall (China), v. 20(4), p. 339–345 (one fig.) Martinus Nijhoff, Water Resources and land-use planning – A systems approach, 1982, p. 4 MEND, 1997, (one fig.) MEND, 2001, (one fig.) Mining Mag., (one fig.) in Nov. 2000, (two figs.) in Aug. 2001, and (one fig.) in Sept. 2001 issues, Pergamon Press, The Heavy Elements – Chemistry, Environmental Impact and Health Effects. 1990, p. 208. Proc. Int. Conf. on Mining and the Environment, Skellefteå, Sweden, June 25 – July 1, 2001, p. 27, 53, 109, 129, 132, 134, 150, 220, 283, 356, 360, 373, 442, 488, 541, 694, 726, 802 Proc. Int. Symp. on Tailings and Mine Waste, 02, 2002, p. 47, 131, 132, 133, 150. Springer-Verlag, Environmental Impact of Mining (ed. J.M. Azcue), 1999, p. 13, 109, 113, 185, 189, 196, 263–294 (one fig.) UNEP – UNESCO, Mining and Geoenvironment (ed. G.S. Vartanyan), 1989, p. 43, 72, 170, 171. UNEP, 1986, Tech. Rev. on Environmental aspects of iron and steel production, p. 14, 42, 83, 99, 109. UNEP, 1991, The. Rep. No. 5, Environmental aspects of selected non-ferrous metals oremining. p. 10, 12, 13, 18, 20, 21, 33, 37, 53, 54, 83, 84.

CHAPTER 1

Introduction

1.1 1.1.1

STATUS OF THE WORLD MINING INDUSTRY Introduction

Förstner (1999, p. 1–3) gave an evocative vision of the directions in which the mining industry will have to make progress in order to cope with the increasingly serious environmental impacts of mining. The volume of non-fuel minerals consumed during the five decades since the Second World War has exceeded the total extracted from the earth during all the previous history of mankind. While the world population doubled during the period 1959–1990, the production of six major non-ferrous metals (aluminium, copper, lead, nickel, tin and zinc) increased eight-fold. The most serious problem facing the mining industry presently is the enormous mass of the mine tailings (about 18 billion m3/y), which incidentally is the same order as the quantity of sediment discharge into the oceans. As progressively lower grades are worked, the mass of the mine tailings is expected to double in the next 20–30 years. Great attention is being paid to the mitigation of the sulphidic mining wastes, which produce acidic leachate containing heavy metals that could contaminate soils and water. Multidisciplinary, multi-institutional research is going on countries like Canada (MEND project) and Sweden (MiMi project) to mitigate the adverse consequences of Acid Mine Drainage (AMD). The Industrialised countries are going in a big way for miniaturization, economies of scale, recycling and substitution. Consequently, the consumption of raw materials in the Industrialised countries is actually going down. The new trend in this regard has been described as “dematerialisation”, whereby less virgin material is used for extraction, the production of waste materials is minimized, and useful materials are recycled to the maximum extent possible. Future development will strongly depend upon the extent and the efficacy of recycling. Enhanced environmental awareness around the world has profound consequences. In future, an orebody will be mined only when it is found to be viable after the social and remediation costs are incorporated in the price of the product. Several industrialized countries have become strong adherents of the concept of “ecologically

2

Mineral resources management and the environment

sustainable development”, so much so that Ranger Uranium in Australia has placed A$ 2 billion in the bank to cover the final closure of the mining Zimmerman’s dictum, “Resources are not, they become”, has profound technosocioeconomic implications. According to him, what constitutes a resource is governed by two considerations: (1) knowledge and technical means must exist to allow its extraction and utilization, and (2) there must be a demand for materials and services produced. It is therefore perfectly possible that what was yesterday a non-resource, can now become a resource today because advances in science and technology made it possible for that substance to be put to economic use. This can be illustrated with the example of nickel. In 1887, when Sudbury (Canada) started producing nickel, they had trouble selling it – the total world demand for nickel at that time was less than 1000 t. During the twentieth century, the demand for nickel rose about 900 fold (to 900,000 t). This came about because numerous new uses were found for nickel (Ni-steels, Ni-Cd batteries, Ni plating, nichrome filaments, cupronickel compounds, etc.). A mineral resource is “a concentration of naturally occurring solid, liquid or gaseous material in or on the earth’s crust in such form and amount that economic extraction of a commodity from the concentration is currently or potentially feasible” (U.S. Bureau of Mines, 1989). Traditionally, mineral resources are divided into three categories: (1) metallic minerals (e.g. iron ore), (2) non-metallic minerals (also known as industrial minerals) (e.g. clays), and (3) fuels (e.g. coal). Until the early part of the twentieth century, metallic minerals dominated the mineral market. Presently, non-metallic minerals and fuels exceed the metallic minerals both in terms of quantity and the value of world production. More than two-thirds of the 92 natural elements are metals. Some of them, such as, Au, Ag, Cu, Pb, Sn, Hg, S, etc., have been known and used since ancient times. Improvements in analytical techniques led to the identification of a large number of metals. The specialized and exacting requirements of modern industries led to profound changes in the ways metals are detected, extracted, alloyed and used. New applications for metals are being found all the time, e.g., use of germanium in semiconductors, use of cerium in high temperature superconductors, development of zircalloys in nuclear industry, titanium alloys in aerospace industry, metal glasses, etc. On the other hand, some traditional metals (e.g., Fe and Cu) are being substituted by plastics, fiberglass, ceramics, etc., thus increasing the demand for industrial minerals. The non-metallic minerals are being increasingly used as insulating material, fillers, glasses, and construction material. The ever-increasing need for more fertilizers (due to the need to grow more food for the increasing population of the world) will greatly increase the consumption of fertilizer raw materials, like apatite, potash feldspar, etc. Thus, the demand for a given mineral depends upon technology and markets. Ore is defined as a “mineral or rock that can be recovered at profit”. Gangue is the useless material associated with the ore. Protore is mineralized rock that is too lean to be economically minable. The above definition of ore has the economic criterion

Introduction 3

built into it. Thus, a mineral does not remain an ore or non-ore for all time. A mineral can be regarded as ore so long as technology and market demand make it economical to mine it. Alternately, what was yesterday a non-ore may become ore today as technology and market demand make it economically worthwhile to mine it now. 1.1.2

Status of the metal mining industry

Appendix B carries a country-wise listing of about 400 large (
1 Mt/y production) metal mines in the world (source: Mining Magazine, Jan. 2000; M  million  106). Appendix C gives the world production of minerals/metals in 1998 (source: Minerals Yearbook, 1998, v.1, US Geological Survey, 2000). The information in the Appendix B is extracted and tabulated in Table 1.1. It may be noted that the production figures given for different kinds of mining are only estimates (based on the mean production level of a particular category of mines multiplied by the number of mines in that category). The following conclusions may be drawn from Appendices B & C: 1. The following ten countries have more than ten large metal mines: Australia (114), USA (81), Canada (67), South Africa (54), Chile (49), Brazil (30), Zimbabwe (23), Peru (21), Mexico (20), India (18). 2. Opencast mining is the most prevalent form of mining. It accounts for 60% of the number of mines (236 out of 395), and 69% (1095 Mt/y out of 1569 Mt/y) of the ore production. 3. Mining of iron ore: Virtually all the major iron ore mines (50 out of 52) are opencast. The only underground iron ore mine in the world is in Kiruna, Sweden. Opencast mining accounts for 95% of the production from large mines (267 Mt/y out of 281 Mt/y). Small-scale and artisanal mining of iron ore is invariably opencast. The gross production of iron ores (1020 Mt in 1998) from all types of mining is about 3–4 times that of the production from large mines. 4. Mining of ores of gold and silver (occasionally copper): Most commonly gold occurs in the form of intermetallic compound of Au-Ag, known as electrum. Opencast mining accounts for 59% of the number of mines (105 out of 178) and 68% of the production (422 Mt/y out of 619 Mt/y). It is significant that though the number of underground mines is 23% (41 out of total of 178 mines), they account for 14% of the production (88 Mt/y out of 619 Mt/y). The world production of gold from different types of mining in 1998 was 2480 t. Artisanal gold mining is almost invariably opencast, and has certain characteristics, which have a profound impact on mining. In the lateritic occurrences of gold, the metal tends to be enriched in the mottled zone, which occurs 3–5 m below the surface layer of red loam (“murram”). Artisanal miners use sluice boxes and panning to concentrate gold, and mercury amalgam method to extract gold. As against this, cyanidation is the most common method of extracting gold from ores produced in large mines. The environmental implications of different methods of mining and extraction of gold are discussed elsewhere (Section 7.6).

– – – – 1 7

8 18

C ( 2.25 Mt/y) Number of mines Estimated production (Mt/y)

D (1.25 Mt/y) Number of mines 4 Estimated production (Mt/y) 5 Total number of mines (395) 50 Total estimated production (1569 Mt/y) 267 – – 1 7

– –

– –

1 7

OP, UG

4 5 52 281

8 18

11 55

29 203

Total

22 28 105 422

25 56

34 170

24 168

OP

19 23 41 88

18 41

2 10

2 14

12 15 32 109

5 11

11 55

4 28

53 66 178 619

48 108

47 235

30 210

UG OP, UG Total

Au, Ag

9 11 65 325

11 25

13 65

32 224

OP

21 26 60 166

25 56

7 35

7 49

UG

5 6 24 107

5 11

4 20

10 70

35 43 149 598

41 92

24 120

49 343

OP, UG Total

Cu, Pb, Zn Ni, PGM

2 3 16 71

5 11

3 15

6 42

OP

Baux

A:
7.0 Mt/y; B: 3.0–7.0 Mt/y; C: 1.5–3.0 Mt/y; D: 1.0–1.5 Mt/y; OP  Opencast; UG  Underground; E: 0.5–1.0 Mt/y, and F: 02–0.5 Mt/y categories of mines number about 250, with estimated total production of 125 Mt/y.

– –

11 55

B ( 5.0 Mt/y) Number of mines Estimated production (Mt/y)

1 7

UG

27 189

OP

Fe

Important metal mines in the world (Source: Mining Magazine, Jan. 2000).

A ( 7.0 Mt/y) Number of mines Estimated production (Mt/y)

Table 1.1

4 Mineral resources management and the environment

Introduction 5

5. Mining of ores of base metals (Cu, Pb, Zn), Ni, Cr, PGM, As, etc.: Though the number of opencast mines (65) and underground mines (60) for these metals is comparable, the production from the opencast mines (325 Mt/y) is almost double that of the production from the underground mines (166 Mt/y). 6. Mining of bauxite: As bauxite deposits are usually surficial alteration blankets, they are invariably mined by opencast methods. Thus, all the 16 large mines producing 71 Mt/y of bauxite are opencast mines. Incidentally, the world production of bauxite in 1998 (122 Mt) is about six times the quantity of bauxite produced in 1980 (about 19 Mt) (Archer et al., 1987, p. 70). 7. The annual production of important metallic ores in the world (in millions of tonnes – Mt) are: bauxite (122), chromite (13), copper (12), iron (1020), lead (3), Mn-ore (19), nickel (1), titanium (5), zinc (8), totaling about 1203 Mt. The annual production of important industrial minerals in the world (in terms of Mt) are: asbestos (2), barite (6), boron minerals (4), cement, hydraulic (1520), clays (43), diatomite (2), feldspar (8), fluorspar (5), gypsum (107), lime (115), magnesite (11), nitrogen (106), peat (26), perlite (2), phosphate rock (145), potash (25), pumice (12), salt (192), sand and gravel (110), soda ash (32), sulphur (58), talc & pyrophyllite (8), totaling about 2539 Mt. Thus, the production of industrial minerals is more than double that of the metallic minerals. 1.1.3

Status of coal mining industry

An examination of the energy consumption (in the form of primary, commerciallytraded fuels) in different regions of the world in 2000 (Table 1.2; source: Mining Magazine, Sept. 2001, p. 103) leads to the following conclusions: (1) North America Table 1.2 Energy* production and consumption (2000) (Mt of oil equivalent) (source: Mining Magazine, Sept. 2001, p. 103).

Region

Oil Supply/ Demand

Natural gas Supply/ Demand

Coal Supply/ Demand

Nuclear Demand

Hydro Demand

Total Primary Demand

North America(1) C & S America Europe FSU Middle East Africa Asia Pacific

652/1065 348/219 329/753 394/173 1112/209 373/117 381/969

683/691 87/84 259/413 607/493 189/170 117/53 239/260

613/600 37/20 241/347 197/175 1/7 123/90 925/947

225 3 252 56 0 4 129

57 849 53 20 1 7 46

2638(2) 372 1818 918 387 269 2351(3)

World

3590/3504

2181/2164

2137/2186

669

230

8752

C & S America – Central and South America; FSU – Former Soviet Union. * Primary energy comprises only commercially-traded fuels, and excludes fuels such as wood, peat and animal wastes. (1) – Comprising US, Canada and Mexico. (2) – Of which US accounts for over 86%, representing 26% of the world’s primary energy consumption. (3) – Of which China accounts for 32%, Japan 22%, and India 13%.

6

Mineral resources management and the environment

Table 1.3 Particulars of important of coal producing countries in the world (source: Mining Magazine, Sept. 1999). Proven reserves of coal in Mt in 1998; Coal production in Mt in 1998. Reserves

Production Lignite/ brown Total

Country/region

Hard

Others

Total

Hard

USA Canada Mexico Total North America Brazil Colombia Venezuela Other Latin America Total Latin America Bulgaria Czech Republic France Germany Greece Hungary Poland Romania Spain Turkey UK Other Europe Total Europe Kazakhstan Russian Federation Ukraine Other FSU Total FSU South Africa Zimbabwe Other Africa Middle East Total Africa & Middle East Australia China India Indonesia Japan New Zealand North Korea Pakistan South Korea Other Asia Pacific Total Asia Pacific Total World

111,338 4,509 860 116,707 – 6,368 479 992 7,839 13 2,613 95 24,000 – 596 12,113 1 200 449 1,000 584 41,664 31,000 49,088 16,388 1,000 97,476 55,333 734 5,095 193 61,355 47,300 62,200 72,733 770 785 29 300 – 82 251 184,450 509,491

135,305 4,114 351 139,770 11,950 381 – 1,404 13,735 2,698 3,564 21 43,000 2,874 3,865 2,196 3,610 460 626 500 16,594 80,368 3,000 107,922 17,968 3,812 132,702 – – 250 – 250 43,100 52,300 2,000 4,450 – 542 300 2,928 – 2,275 107,895 474,720

246,643 8,623 1,211 256,477 11,950 6,749 479

934.20 63.59 10.00 1007.79 5.60 34.00 6.80

80.00 11.79 – 91.79 – – –

21,574 2,711 6,177 116 67,000 2,874 4,451 14,309 3,611 660 1,075 1,500 17,538 122,302 34,000 157,010 34,356 4,812 230,178 55,333 734 5,345 193 61,605 90,400 114,500 74,733 5,220 785 571 600 2,928 82 2,526 292,345 984,211

46.40 0.10 24.90 5.30 41.30 – 0.90 117.00 4.00 12.40 2.30 41.30 0.10 249.60 65.70 149.00 74.20

– 31.00 50.80 0.80 166.20 60.40 13.60 63.00 29.00 13.70 40.00 – 43.10 511.60 3.00 83.00 2.00

288.90 222.30 5.05

88.00 – –

1.81 229.16 289.70 1,185.50 300.00 61.20 3.60 3.50 60.00 3.10 4.30 4.70 1915.60 3737.45

– – 65.80 50.00 23.00 – – 0.20 15.00 – – 15.50 169.50 860.89

* Serbia/Montenegro; ** Iran; *** Thailand.

1014.20 75.38 10.00 1099.58 5.60 34.00 6.80 46.40 31.10 75.70 6.10 207.50 60.40 14.50 180.00 33.00 26.10 42.30 41.30 43.20 * 761.20 68.70 232.00 76.20 376.90 222.30 5.05 1.81 ** 229.16 355.50 1235.50 323.00 61.20 3.60 3.70 75.00 3.10 4.30 20.20 *** 2085.10 4598.34

Introduction 7

(USA, Canada and Mexico) account for about 30% of the total global energy consumption, with roughly equal contribution from oil, natural gas and coal, (2) The important consumers of energy in the Asia-Pacific region, are China, Japan and India, and because of the strong dependence of China and India on coal, the energy contribution from coal in their case far outweighs that from oil and natural gas. Table 1.3 carries the particulars of reserves and production of hard coal (anthracite and bituminous coal) and brown coal (sub-bituminous coal and lignite), arranged country-wise and region-wise (such as, North America, Latin America, Europe, Former Soviet Union countries, Africa and Middle East, Asia-Pacific). An analysis of the data given in Table 1.3 leads to the following conclusions: 1. The following eleven countries which have reserves of more than 10 Bt of coal each (all grades): USA (247), Russian Federation (157), China (115), Australia (90), India (75), Germany (67), South Africa (55), Kazakhstan (34), Ukraine (34), Poland (14) and Brazil (12), with aggregate reserves of 900 Bt, account for 91% of the total coal reserves of the world (984 Bt) (B  billion  109). 2. The following eight countries which produce more than 100 Mt/y of coal each (all ranks): China (1236), USA (1014), Australia (356), India (323), Russia (232), South Africa (222), Germany (208), Poland (180), with aggregate production of 3771 Mt, account for 82% of the global production of about 4600 Mt. Interestingly, two countries, China and USA, produce half of the coal in the world. As we will see later, the large quantities of coal produced and consumed in China has profound adverse consequences on the quality of environment in that country. 1.2 1.2.1

MINING AND THE ENVIRONMENTAL AGENDA Environmental challenges facing the mining industry

An Environmental impact may be defined as a change in the environmental parameters, over a specified period, and in a specified geographical area, resulting from a particular activity compared to the situation which would have existed had the activity not been performed. It is no longer possible for a mine to be started merely because its technoeconomic viability has been demonstrated. The mining project has to be socially acceptable as well. Sengupta (1993, p. 22–23) has drawn attention to the “shadow effect” of a mine site. Apart from the degradation of land directly connected to the mine site itself (due to the mine, supporting facilities, waste disposal arrangements, etc.), the shadow effect of the mine site may extend to large areas around the mine site as a consequence of the infrastructure (rail, road, housing, power plants, water storage, etc.) necessary for the performance of the mining operations. Thus, the responsibility of the mining company is not confined to the mine site, but to a large area around it. The mining company has thus to work harmoniously with a variety of land use authorities, concerned with (say) wildlife, forestry, recreation and tourism, fisheries,

8

Mineral resources management and the environment

environmentally-sensitive habitats (e.g., corals, mangroves), parks, reserves, historical sites, native reserves and rights of the indigenous people, urban growth, etc. Khanna (1999) gave a succinct account of the environmental challenges facing the mining industry. The adverse effects of mining on the geological environment include changes in the landscape, landslides, subsidence, pollution of water and soil, lowering of groundwater, damage caused by explosions, etc. The magnitude of the environmental impact is function of the volume of the material mined, methods of mining, mode of disposal of wastes, environmental protection measures undertaken, etc. The potential effects of the mining activities on the environment are summarized in Table 1.4 (source: UNEP, 1986). It has been estimated that there are more than 40,000 mines in the world, which process an aggregate volume of 33  109 m3/y of rock (Vartanyan, 1989). Mining has a negative image – some of the worst industrial disasters happen to be mining related (vide Appendix D). Mining industry has a characteristic, which is not shared by other industries. For instance, mining has to be undertaken where the ore occurs – direct relocation is not possible. There has been much controversy whether the concept of sustainable development is at all applicable to the mining sector, which is based on the production of non-renewable resources from finite deposits. Mining takes out the ore, but leaves nothing in its place – in other words, mining is inherently unsustainable. On the lines of the definition of the EcologicallySustainable Industrial Development (ESID), Sustainable Mining may be defined as those patterns of mining that enhance economic and social benefits for the present and future generations without impairing the basic ecological processes. This implies that any uses of mineral resources that lead to significant degradation of ecological processes, are deemed to be ipso facto unsustainable and hence unacceptable. Mining industry faces pressure to follow “good environmental practice” from the following kinds of institutions: (1) Environmental pressure groups, such as, Minewatch, Greenpeace, Friends of the Earth and the Mineral Policy Centre, (2) International organizations, such as, the World Bank, UNDP, and the International Council of Metals are using their financial leverage to make the mining companies follow certain guidelines, (3) Most national governments have prescribed regulations for the protection of the environment, amelioration of the mined land, and the responsibilities of the mining company in the event of the mine closure, (4) Mining associations which are developing “codes of practice”, and helping the mining companies to implement the “Best Practices” – this is a kind of corporate peer pressure which often has proved very effective, and (5) The coverage of “mining disasters” in the International media, particularly the Internet, can be so extremely intense that a mining company may be put in a tight corner, and may even have to fold up. In the context of the increasing public consciousness about environmental consequences of any commercial activity, it is no longer possible to take decisions about mining based on commercial rationale alone. A community may wonder whether the economic benefit from a mine is worth the ugly scar that would be left behind when

Surface water pollution

Degradation of aquatic fauna, Including the destruction of fish species, accumulation of toxic elements by fish

Degradation of aquatic flora

Deposition of sand in river channels and in the shallow zones of the sea

Fauna

Flora

Land use

Deposition of solids on agricultural lands, and in the shallow zones of the sea; Withdrawal of water for industrial purposes

Soluble contaminants in wells, springs, etc. (1)

Underground water pollution

Accumulation in plants of toxic elements carried by dust

Dust blown on inhabited or agricultural lands (2)

Air pollution

Potential effects of mining activity on the environment.

Human Soluble contaminants health and in domestic and/or activity agricultural use waters.

Table 1.4

Loss of habitat

Excavation

Remarks

Disturbance of habitat feature (3)

Spatial requirements of of mining operations are normally quite restricted; but within that area, the disturbance can be quite significant.

(3) Issues regarding unique habitat features (e.g. migration corridors, watering areas, etc.) for threatened or endangered species, should be specially addressed.

Effects of (1) Such impacts on noise on underground waters do human health not occur generally; it depends essentially Damage to on the hydrogeology buildings due of the area. to blasting (2) Plant, especially the vibration atmosphere of the underground mine.

Noise and vibration

Land disturbance; Land disturbance Withdrawal of Land subsidence agricultural land due to underground mining

Hazards related to lack of stability of waste deposits

Solid waste

Introduction 9

10

Mineral resources management and the environment

the mine is closed. Previously, mining companies used their public relations exercise to sell a project. Now they use community consultation techniques to develop the project in harmony with the stakeholders who will be affected by the mine. Poor communities may accept mining, as it may be the only way for social and economic development. But when once the mine is exhausted, the mine-dependent community is left with a big hole in the ground, plus the environmental problems associated with the contaminated soil and ground. In the past, companies simply closed the mine and walked out. Now a days, the communities and the government will not tolerate such a step. The mining companies do indeed have a responsibility for the well being of the community when once the mining ceases. A sensible approach would be for the mining company in cooperation with the government and the community concerned, to plan for a long-term development of the area to enable the sustainable development to continue after the mining ceases. In other words, the financial costs of the environmental and social protection have to be integrated into the business plan right at the start. Companies are finding that this kind of proactive approach of a long-term, mutually beneficial relationship with the community is better than a retroactive approach which tries to sort out the environmental and social conflicts after they become intractable. Mining companies are slowly getting reconciled to the fact that there is no way they can avoid issuing reports of their environmental performance, as such reports are demanded by the government regulations, by the public, and by the shareholders. It is good for the image of a company to show that it is environment-conscious. Companies, such Cambior Gold, are taking pride in fulfilling the requirements of Industry standard ISO 14001 (see Appendix E, for details of procedure for getting certified under ISO 14001). This is a good trend. 1.2.2

Mining, environmental protection and sustainable development – a case study of Indonesia

Miller (1999, p. 317–332) examines the dilemma facing the developing countries (such as Indonesia) as to how to reconcile environmental protection with sustainable development. The developing countries think that sustainable development as defined by the Brundtland Commission seems to imply a low rate of economic growth that impedes the development of their energy and mineral resources. They regard mining as the “engine of development” to promote technological and economic development of the country. Mining accounts for 80–90% of GNP in some countries in Africa. For instance, Botswana with a population of little over one million, earns almost USD 3 billion from the mining sector, principally diamonds. This works to about USD 3000 per capita per annum, which happens more than 20 times the GDP per capita of the neighbouring Mozambique. The mineral resources that mining exploits are non-renewable, but the resources that are affected by mining, namely, water, land, flora and fauna, are renewable. Sustainable mining has therefore to be understood to mean that the mining has to be carried in a manner that is ecologically sustainable.

Introduction 11

Mining activity in Indonesia faces formidable problems – heavy monsoon rainfall (2000–4000 mm/yr) can cause rapid erosion and sedimentation, making rehabilitation of mined land extremely difficult. In many places, the slopes are steep, and one has to contend with seismic activity. Corruption in the government is rampant. The Government of Indonesia has promulgated various laws to protect the environment, including regulations on “Polluter pays” principle. A reasonably comprehensive regulatory and enforcement scheme (AMDAL) is in place. But the real test is implementation on the ground. Unlike the US EPA regulations that demand quantification of various parameters for compliant effluents, the Indonesian regulations are not specific. Thus, when a mining company puts out an environmental impact document, the particulars provided by the mining companies are not precise enough to assess whether the regulations have been complied with (“If you cannot measure it, you cannot manage it” – Peter Drucker). Experience has shown that large mining companies do a better job of mine planning and achieve a higher level of environmental protection. This is so because they have operations in countries in which environmental controls are strict and effectively enforced. The technology for compliance is substantially transferable. The real culprits are state-run companies, and more so, the artisanal miners. Artisanal gold mining using the highly polluting mercury amalgam method is common. The Ministry of Mines and Energy has about 100 inspectors. It is an almost impossible task for them to monitor all the mining operations (the Indonesian archipelago is spread over 3700 km, with probably the world’s most difficult terrain to travel). 1.2.3

Economics of environmental protection in mining

Maxwell and Govindarajulu (1999, p. 7–17) gave a good analysis of the economics of environmental protection in mining, with particular reference to Australia. It has been estimated that mining companies in Australia spend upto 5% of capital and 5% of operating costs for new mining projects to maintain best practice environmental management. Of late, environment has been attracting considerable interest from the economics. It is generally held that markets do not allocate environmental resources efficiently. This is so because many environmental resources are public goods. There is obviously a need for environmental protection regulation. The point that Maxwell and Govindarajulu (1999) raise is how zealous that such a legislation should be. If it is too demanding, the mining operation would result in less than the optimal level of output. The diagram of Coase (1960, quoted by Maxwell & Govindarajulu, 1999) helps us to understand the economics of the environmental impacts of a mine in terms of curves for marginal damage to the environment (air, water, soil, noise, etc. pollution and aesthetic damage) versus marginal abatement cost (or marginal benefit). The most economically efficient level of environmental damage occurs where the marginal damage and the marginal benefit curves intersect (Fig. 1.1, source: Maxwell & Govindarajulu, 1999, p. 13).

12

Mineral resources management and the environment

Figure 1.1 Economics of environmental protection in mining (source: Maxwell & Govindarajulu, 1999, p. 13).

1.3

TECHNOLOGY TRENDS IN THE MINING INDUSTRY

Chadwick (2001) highlighted the implications of technological improvements on the performance of the mining industry. As is happening in other industries, Service and Automation are emerging as two over-riding trends in the mining industry as well. Technology is being increasingly applied to improve efficiency and safety, cut costs, and reduce the adverse impact of mining on the environment. Previously, manufacturers used to supply equipment and spares, and the mining companies were expected to take care of their own maintenance and repair work. Now a days, the manufacturers of equipment are undertaking all the related services, such as, managing of spare parts inventories, servicing, maintenance and repair work (even if the equipment concerned is not their own make), and optimizing the utilization of equipment. Mergers and acquisitions in all sectors of manufacture are allowing the manufacturers to achieve the critical mass and provide a truly global service (the role of ecommerce in this process is discussed in section 1.5). 1.3.1

Automation in the mining industry

Automation is helping the mining companies to optimize their mining and processing operations, depending upon the prevailing commodity prices. This may take the form of using the equipment in such a manner that render possible the selection and processing of specific ore grades, and extraction of specific metals in a polymetallic deposits, etc. This is similar to the customary practice in oil refining – different

Introduction 13

crudes are blended and process technologies adjusted, depending upon the product mix that the market needs at any particular point of time. Automation is revolutionizing exploratory drilling. Drilling can take place autonomously with high hole accuracy, and samples are recovered (and in some systems, analysed) automatically. Portable XRF devices are available for the geologist to check the ore grade in the drill core, or this could be done automatically. Niton’s new XL-500 Prospector can assay ore samples directly in situ (rock face or drill core). It is a single-piece, handheld analyzer weighing only one kg, including the battery. Typical in situ measurements can be made in 30–60 seconds, and 500–1000 measurements can be made per day. About 1000 measurements can be stored in the instrument internally, and can be downloaded as needed for the preparation of maps, grade control and other kinds of evaluations. Niton also markets a special device for precious metals (called Precious Metals Analyser), for the analysis of Au, Ag, Pt, Rh, Ru, Ir, Pd, Cu, Zn, Ni, Co and Fe in ores, and fire assay can be avoided. Details about Niton instruments can be had from www.niton.com. In surface mining, as the capacity of haulers is increasing, there has been concurrent increase in the capacity of loading and ancillary equipment. Blasthole drilling which can be isolated from other surface mining activities, has benefited most from automation. Emulsion explosives have emerged as safe, inexpensive and easy to use alternatives to the old nitroglycerine, water gels, ANFO, etc. These explosives are manufactured in the form of water-in-oil emulsions. As each micro cell of the oxidizer is coated with an oily exterior, the emulsion has excellent water resistance, and could therefore function efficiently under water. Glass microspheres dispersed throughout the basic emulsion serve as bulking agent and help in density control and sensitivity. The consistency of the emulsion can be varied depending upon the blasting applications. Bulk emulsion has a density of 1.25 g/cm3, VOD of 5500 m/sec, and energy of 1030 kcal/cm2. Studies have shown that the efficiency of the emulsions (93%) is much higher than those of the water cells (70%). Orica of USA has developed digital energy control software (ShotPlus) for the safe, accurate and efficient control of blasts. NPV Scheduler software enables the optimization of open pit mining through the identification of the unique path of extracting minerals in the pit, which will deliver the highest possible Net Present Value. With the increasing accuracy of GPS equipment, driverless trucks in open pits may indeed become a reality in the not too distant future. Automation has gone much farther in underground mining. Automated load and haul systems are being increasingly used in Australia, Sweden and Finland. In the Automine system operating in Kiruna, Sweden, LHDs with a tramming capacity of 25 t, load themselves from drawpoints under tele-remote control. The automatic tram and dump cycle starts. The LHD take its load to the overpass, dumps it, and returns to the drawpoint, all autonomously. Under the Sandvik Tamrock’s system, the LHD determines its position by dead reckoning. It gets its direction from the

14

Mineral resources management and the environment

onboard gyroscope, and the articulation angle and distance from the drive line (Mining Magazine, July, 2000, p. 12). Other navigation systems are based on reflectors suspended from the sides of the drifts, on the basis of which the LHD fixes its position. Tyre life has shown significant improvement, as the LHDs are driven more smoothly under automatic control. Unlike the operator-driven machines, which operate 10–12 hours per day, the automatic machines can work upto 19 hours a day. One operator can control three LHDs. The Kiruna mine expects that its production of 23 Mt/y of ore will be drawn, trammed and dumped by semi-autonomous LHDs (Mining Magazine, July, 2000, p. 12–16) (see section 2.8 for a case study of the Kiruna mine). The following considerations are likely to lead greater emphasis on underground mining: (1) decline in the availability of deposits which are amenable for surface mining, (2) the “greening” of the mining industry which wants to avoid the ugly scars on the surface, (3) reduced extraction of waste by the placement of the tailings back in the underground, particularly as backfill support, and (4) high degree of automation that is possible in underground mining. Automation in mineral processing allows large plants to be run with minimum staffing. Expert systems not only reduce the personnel costs, but also provide real time information on the processes as they operate, so that the recovery can be finetuned depending upon the market situation. Gravity separation is coming into vogue, particularly in situations where the use of cyanide is to be avoided. 1.3.2

Technology-driven developments in the mining industry

Technology is being increasingly used to address three major challenges of the mining industry: (1) increase in the global mineral consumption of minerals (for instance, the production of bauxite increased six-fold during the last two decades), (2) the reduction in the prices of minerals (for instance, the price of gold which has been oscillating around USD 350–400/oz, is currently around USD 300/oz), (3) Huge quantities of ever-lower grades are being processed by bulk mining methods (such as opencast mining). Such mining not only leaves big, unseemly pits in the ground and huge waste dumps above the ground, but also leads to increased pollution due to ore processing and increased tonnages of tailings that have to be disposed off. According to Khanna (1999), the following technological advances have an impact on the issue of Mining and Environment: (1) The total recovery of metals from ore is being improved, with the consequence that the waste material will have lower content of heavy metals, and hence lesser ability to contaminate the environment, (2) Process chemicals which are environmentally unacceptable are being replaced by those which are environmentally-friendly and recyclable. Bioleaching has the potential not only to revolutionize the extraction of metals, but also the detoxification of industrial waste products, sewage sludge, and soils contaminated by heavy metals. Several companies have resorted to in situ leaching

Introduction 15

of ores, but the environmental consequences of in situ leaching are not yet fully understood. Sulphur dioxide produced in the course of smelting of sulphidic ores, has been a major pollutant of air. Hydrometallurgical techniques avoid the use of smelting, and thereby eliminate the sulphur dioxide emissions. Copper industry is already using pressure leaching techniques in a big way. The patented Gold Haber process avoids the use of cyanide in the extraction of gold. The preliminary operation is the same as in conventional cyanide process, namely, crushing and grinding of ore, mixing it with water, and making a slurry. Before pumping the slurry to the leach tanks, Haber’s patented reagent suite is added. This involves the use of activated carbon to recover the gold in solution, which is then followed by electrowinning. The acidic tailings are neutralized before disposal. The most serious problem facing the mining industry is the disposal of wastes. The extent of the environmental impact of mine wastes can be illustrated with the example of gold. The world production of gold is about 2500 t. Since the gold content of the mined material is usually of the order of a few gms. per tonne, virtually all the mined material (⬃1.5 Bt/y ?) ends up as mine waste which needs to be disposed off. As mentioned earlier, 69% of the metallic ores are produced by opencast mining. As more and more low-grade ores are mined, the ratio of waste generated relative to the quantity of mineral produced rises steeply. Waste dumps make the landscape ugly to look at. Potential acid-producing material need to be encapsulated, so that the rainwater and surface runoff leaching the waste dumps do not contain too high concentrations of heavy metals. When tailings are discharged into impoundments, we not only have to manage the solid wastes but also the water/supernatant. The tailing impoundments need to be dewatered before the rehabilitation of the solid wastes. Failure of tailing impoundments is a kind of disaster that would attract the glare of adverse publicity. Khanna (1999) gives an example of this. A tailings spill at the Marcopper mine in the central Philippines has polluted a 26 km stretch of Makulapnit and Boac rivers. This raised a public furore. The Marcopper Mine was, however, too small a company to be able to afford the amelioration of the problem. Though Placer Dome had only a minority interest in the company, it came forward and cleaned up the rivers. Paste technologies and subaqueous disposal are some of the new technologies that are being developed to reduce the risk of failure of tailings impoundments. The management of waste rock and tailings has become such a major problem that some authorities are proposing that in future mining should be underground only, with the wastes being disposed off wholly underground. The advanced, low-polluting coal combustion system, called Low NOx Concentric Firing System (LNCFS) reduces the formation of NOx by nearly 40% in older coal burning plants. Power plants equipped with this burner now account for 56,000 MW of electricity in USA. Sales of this system reached over USD one billion (Mining Magazine, July, 2001).

16

1.4

Mineral resources management and the environment

EXTRACTION COSTS VS. ENVIRONMENTAL ACCEPTABILITY

Cyanidation process for the extraction of gold brings into focus most vividly the conflict between the economic and technical viability on one hand and the environmental acceptability on the other (see section 7.6 for details of gold process technologies). There has been increasing pressure from the environmental groups for substituting cyanide by more environment-friendly reagents. The following reagents have been tested and used by reputable firms: (1) Sodium hypochlorite stabilized by sodium chloride, (2) Bromine stabilized by sodium bromide, (3) Ammonium thiosulphate stabilized by ammonia, and catalyzed by cupric ion, and (4) acidic thiourea. Table 1.5 gives a comparative performance of the different lixiviants using the Cortez (Nevada, USA) ore (fully oxidized ore of low grade, with 0.87 g/t of Au, and 4.98 g/t of Ag). The great advantage of cyanide heap leaching is that there would be no discharging of process solutions, and minimum recycling of water. Treatment and discharge of process solutions would not be needed during the operation. In effect, there would be a single permanent large heap leach pad. Percolation of pregnant cyanide solutions downwards through hundreds of metres of leached ore can take place, without the solutions undergoing chemical change. On the other hand, other Table 1.5

Comparison of the effectiveness of different leaching systems.

Leaching system

Reagent

Consumption of reagent (kg/t)

Cyanide, pH: 10.5–11.0

NaCN CaO NaOCl HCl Br2 H2SO4 (NH4)2S2O3 NH3 CS(NH2)2 Fe(SO4)3 H2SO4

0.15 0.55 5.55 3.25 2.85 6.8 14.5 2.0 3.05 9.0 48.0

Hypochlorite, pH: 6.4–6.5, Eh: 1.138–1.183 mV Bromine, pH: 1.3–2.0, Eh: 1.089–1.099 mV Thiosulphate, pH: 9.4–9.5, Eh: 228–244 mV Thiourea, pH: 1.1–1.3, Eh: 437–450 mV

Table 1.6

Au dissolved (%) Ag dissolved (%) 73

23

68

22

57

13

37

16

57

22

Water treatment costs of different lixiviant systems (source: McNulty, 2001).

Lixiviant system

Total cost of water treatment (USD million)

Sodium cyanide/lime Bromine/bromide/sulphuric acid Hypochlorite/chlorine Ammonium thiosulphate/ammonia/copper Thiourea/ferric sulphate/sulphuric acid

22 208 605 242 194

Introduction 17

lixiviants require rigorous control of pH and Eh, and there is always the possibility of side reactions and precipitation of gold. The water treatment costs for different lixiviant systems are summarized in Table 1.6 (source: McNulty, 2001). It should be emphasized that the above considerations apply to the specific case of Cortez ore. Degussa-Hüls of Germany has developed a cyanide system, which automatically regulates the cyanide levels, such that neither overdosing nor underdosing of NaCN occurs and gold is not lost. Their Peroxide Assisted Leach (PAL) technology accelerates the leach kinetics, reduces the consumption of cyanide and increases the amount of gold recovered. The Degussa-Hüls technology is particularly attractive for transition and sulphide ores, which are generally difficult to leach. While it is true that sodium cyanide is toxic to human beings and other vertebrates, pragmatic consideration should be given to the following ground realities: (1) The mining industry accounts for only 13% of the total consumption of cyanide, (2) Despite the use of hundreds of millions of kilograms of cyanide during the twentieth century, there have been only three deaths in North America potentially attributable to cyanide poisoning in the mining industry in the last century. This is so because the manufacture, storage, use and disposal of cyanide are stringently regulated, and are handled by carefully trained personnel, (3) Out of the 14 incidents involving precious metal mining and processing, ten were caused by structural failings of the tailings dams, and two each were due to pipeline failures and transportation accidents. In sum, there is little doubt that assuming reasonable prices of gold and silver, cyanide is the only leaching system that is economically attractive.

1.5

e-BUSINESS IN THE MINING INDUSTRY

The following summary is largely drawn from the review articles on the topic that appeared in the Mining Magazine (Nov. 2000 & Aug. 2001). Now a days, it is fashionable to place the prefix e before a normal activity to make it appear modern and technologically exciting. This trend probably started with e-mail, and now we have a whole set of new terms: e-business, e-commerce, e-procurement, e-logistics, e-fulfillment, e-CRM (customer relationship management), etc. Besides, we have three-letter acronyms: B2B (business-to-business), B2C (business-to-consumer), etc. Business Schools are offering formal courses on these topics. How is e-business different from normal business? e-business is nothing more than business conducted through electronic media. In other words, every thing that is done in the course of normal business has to be done in e-business also – but only electronically. The recent crashing of many a dotcom is attributable to the failure to appreciate this basic principle. e-business should not be considered as an electronic

18

Mineral resources management and the environment

Figure 1.2

The linkages in e-business (source: Mining Magazine, Nov. 2000, p. 206).

add-on, to be handled separately by the technical department. If e-business is to succeed, it should be completely integrated with the company’s business methodology. The linkages in e-business are schematically shown in Figure 1.2 (source: Mining Magazine, Nov. 2000, p. 206). There are three primary channels of e-business: (1) Web storefronts, (2) electronic Procurement (e-procurement) and (3) electronic Marketplaces (e-markets). The Web storefront offers a low-cost channel to market and sell products and services to a global clientele. Sellers use the Internet to differentiate their product offerings, enhance customer service and reduce costs of marketing and order processing. e-procurement establishes virtual electronic markets, enabling a kind of self-servicing purchasing environment. The multi-buyer, multiseller e-markets allow dynamic e-commerce models, involving various combinations of sourcing, auctioning, exchanges, etc. The e-commerce models equally benefit all the participants as follows (source: Aberdeen Group): 1. Buyers can automate and streamline procurement processes and gain access to new market opportunities, 2. Suppliers can automate order and fulfillment processes, reduce order processing errors and costs, identify new sales opportunities, and capture increased value for excess inventories or assets,

Introduction 19 Table 1.7

Potential e-savings in cash costs.

Cost breakdown

%

Total cost ($ billion)

e-savings % of costs

e-savings ($ billion)

e-savings % of sales

Savings (AT) % cash flow

Labour Energy Stores Other Total

27 23 33 17 100

43 37 53 27 159

5 2 9 4 5

2.2 0.7 4.7 1.1 8.7

1 0 3 1 5

4 1 8 2 15

3. Market managers who are responsible for brokering content, value-added services, and transactional activities across the marketplace, can leverage e-markets by inserting themselves into the buyer-supplier trading relationships. Internet-based, business-to-business (B2B) or e-business, is growing at the rate of 200% per year. It is estimated to reach about USD 2 trillion by the year 2003. Global mining business is estimated to reach USD 200 billion in sales in the year 2000, whilst incurring cash costs of USD 159 billion. Table 1.7 summarize the mining cost structure and potential e-savings in cash costs (source: UBS Warburg, quoted in Mining Magazine, Nov. 2000, p. 208). Though there is little doubt that the events of Sept. 11, 2001 have adversely affected the e-business in the mining sector, the magnitude and direction of the impact is unclear. 1.5.1

How to start new e-business?

In effect, e-business deals with commercial transactions (principally B2B) carried on through Internet. A customary way of starting e-business is for a supplier company to set up a website, displaying its catalogue, and indicating how to order goods or services online. A good model of this kind of e-business is Amazon.com which is an online bookshop. Amazon.com can obtain for you any book published any where in the world in any language. If you know the title of the book, you can get a quote on it and order it. Alternately, one can browse through the particulars (titles, contents, reviews, etc.) of books on a particular topic, or by a particular author, and make up your mind. Amazon.com has been so successful that several other book publishers were forced to go online in order to remain competitive. Another approach is e-procurement. Under this, one or more buyers establish a website, and invite suppliers to submit tenders against specific requirements. Price setting may be based on quoted price procedure, or through a normal or reverse auction procedure. These procedures are automated, and performed through the use of appropriate software tools. The e-marketplace deals with more complex situations, in which buyers and sellers interact and negotiate prices and terms. This process would work well where the products involved are standardized, and price comparisons are possible.

20

Mineral resources management and the environment

There are five categories of business between mining companies and their suppliers: (1) new capital equipment, (2) used capital equipment, (3) consumables, (4) professional services, and (5) support services. Among these, consumables, and in some cases, capital equipment, are amenable to this kind of automated e-business solutions. e-business solutions do not seem to work well for other categories, where price is not the only consideration, and several issues have to be taken into account in making the final choice. Suppose a mining company needs a drilling service. It will not automatically go in for a company which quoted the lowest rate – it will make the choice on the basis of a number of factors, such as, the past technical performance of the drilling outfit, time-frame and terms offered, etc. Another myth about e-business has been that prices will be driven down. This is not inevitable, as suppliers can be expected to differentiate their offerings on the basis of the quality of service that they would be providing. It has been found in actual practice that the expected centralized purchasing arrangements did not happen, and the biggest buyers tend to pay higher prices. The value/volume relationship for different product categories, and the market positioning of different e-business sites, is shown in Figure 1.3 (source: Andrew Barriskell, as quoted by Mining Magazine, Aug. 2001). Since e-business is based on Internet, it is global in coverage. But where physical products have to be delivered (say, a drill rig), the suppliers have to take into account the costs of delivery, political barriers to the market entry, taxes and duties, and the margins to be allowed for local distributors, agents or dealers. The pattern that is emerging is that, instead of the middleman in the traditional business, we now have the IT (Information Technology) consultant who supplies the software, and manages the e-marketplace for a company.

Figure 1.3 The value/volume relationship for different product categories of e-business (source: Mining Magazine, Aug. 2001).

Introduction 21

A company, which wants to introduce e-business methods, must be willing to make large-scale changes in the organizational set-up (such as, establishment of call centers) and the management (such as, having IT-qualified staff in the highest levels of management) of the company. Instead of building in-house competence in e-business techniques, a company may go in for “outsourcing” through software enterprises. SAP has emerged as a leader in the management software. Globally it ranks third after Microsoft and Oracle as a software supplier. SAP provides the software for integrated ERP (Enterprise Resource Planning), which covers the whole range of e-business functions. The technical complexity of e-business led to the establishment of a new breed of software companies. Gartner Group predicts that 30% of the e-business ventures will fail by 2003 due to lack of attention to cultural issues. PLAUT is a software company, which specializes in the introduction of new software to the companies. They provide training, and advice on the management changes that are needed to obtain maximum benefit from SAP-type of complex software. Such IT management services, which are custom-made to suit the particular business environments, may improve the survivability of new e-businesses. The catch is that only companies with a turnover of at least USD 10–12 million can afford the SAP and PLAUT type of solutions. 1.5.2

Present status of e-business in the mining sector

A Cobalt Open Sales System, which was established in mid-1999, now sells 100% of the WMC cobalt. The success of this system led to the establishment of a nickel site in late 1999. WMC found to its great surprise a number of new customers for nickel of which WMC was not aware earlier. In May, 2000, Australia’s state-owned Macquarie Generation initiated the first on-line market in coal with all major producers bidding on 50,000 t of coal. This led to the reduction of time for negotiating spot contract from weeks to hours. US-based MetalSite launched by the end of 1998 hosts upto US $40 million of steel products per month (this site has failed recently, however). In Oct. 2000, fourteen leading mining companies in the world (Alcan, Alcoa, Anglo American, Barrick Gold, BHP, Codelco, CVRD, De Beers, Inco, Newmont Mining, Noranda, Phelps Dodge, Rio Tinto, WMC, etc.) joined together to form a consortium called Quadrem (www.quadrem.com) (as of Aug. 2001, Quadrem has 21 members). The founding shareholders have invested about USD 100 million to establish the systems. This is undoubtedly the most significant development in the e-business in the mining and the metals sector. The objective of Quadrem is to bring down the costs of the consumables and capital items needed by the mining companies, through lower transaction costs and a more efficient and liquid market. The purpose of Quadrem is thus to manage the marketplace efficiently. Quadrem is going out of the way to indicate that it is not a buyers’ cartel. For instance, they say that no individual shareholder can hold more than 15% of the Quadrem equity.

22

Mineral resources management and the environment

Despite the protestations, there is a general feeling that Quadrem may emerge as a powerful buyers’ cartel. Quadrem makes use of the expensive SAP software. They expect to recover the costs by charging membership and transaction fees both from buyers and sellers. The earlier catalogue-based, point-to-point B2B links are now being supplanted by exchange-based systems through collaborative hubs. Quadrem has already established e-market “hubs” in Australia, South Africa, Brazil and Canada, and a European hub is about to be launched. About 200 suppliers that have signed up with Quadrem are mid-sized companies. The major suppliers have not signed, probably because Quadrem is not sufficiently attractive to them, and small suppliers did not join probably because they are scared. Apart from Quadrem which is the most advanced, a number of other mining e-business have been set up during the last one or two years. One notable feature of the Australian e-business, which may become the norm elsewhere, is for the mining companies and suppliers to sign up with multiple B2B services. Examples of new mining e-business sites are: www.corprocure.com.au, www.freemarkets.com. Quadrem is developing common catalogues in multiple languages, which will allow buyers regardless of their location, to access and trade with a large pool of suppliers locally and around the world. The project will consist of a series of regional marketplaces linked to a single global site. It has been estimated that 60–70% of the global mining procurement spending is done on a regional basis, and about 30–40% on a global basis. The suppliers will be able to access a large number of potential buyers through a single system – it will no longer be necessary for a supplier to link their sales information into the individual purchasing system of each buyer. Any supplier can participate, as Quadrem is not a broker, and does not take any responsibility for credit risk. By promoting the use of industry-wide standards on goods and services supplied, Quadrem seeks to improve the health, safety, and environmental impact of the mining industry. Since Quadrem already represents more than 60% of the buyers (and more are expected to join), the suppliers are worried that the mining companies are attempting to squeeze their already shrinking margins, with the attendant adverse impact on R. & D. They point out that the cost of a product can vary tremendously on a geographical basis. This may be illustrated with an example of the explosives industry. Ammonium nitrate, which is used in the manufacture of explosives, is in plentiful supply in USA, but not (say) in Australia. So it is not possible for the Australia-based mining company to get a given explosive at the same price as the US-based subsidiary of the same mining company. Also, the freight rates for hazardous explosive products are different depending upon the product, and the regulations in the country concerned. A number of problems require to be sorted out. The big question is whether the volume leverage does lead to lower prices. There may be enormous difference between the overt (list) prices and the covert prices (after discounts and special

Introduction 23

considerations have been taken into account). The transactions have to keep in mind the risks involved in using multiple currencies, and local political pressures (favoring a particular supplier for political reasons). The mortality of mining e-business companies is high. Recently, metalsite.net and aluminium.com have failed. The presence of too many players may have contributed to the failure of dotcoms. Another cause of failure may be poor service. Many B2B portal sites have had poor customer service and continual delays. Lower unit value products where the price pressure is most intense, appear to be more amenable for e-business than high unit cost goods and services, which involve technical sophistication and where “off-the-shelf” solutions may not be applicable. 1.5.3

Future of internet technology in relation to e-business in mining

The future of e-business in the mining industry is shown schematically in Figure 1.4 (source: Andrew Barriskell, as quoted in Mining Magazine, Aug. 2001). Till now, Internet technology has been used only as a price setting marketplace or trading exchange. The development of Internet to serve as a knowledge base for the mining industry, has not been adequately explored by the mining companies. The buyers thought that they will use the Internet marketplace to drive down prices. This is a short-sighted view. In their own long-term interest, the buyers (mining companies) should allow sufficient margins for the suppliers to survive and to perform R&D to develop new products and services. The break-down of the supplier/buyer link would be disastrous for the viability of the mining industry as a whole. Standardization of components would reduce costs, and allow price comparisons to be made. But this cannot be achieved by Quadrem-style e-business but by collaboration between suppliers and buyers in engineering design.

Figure 1.4

The future of e-business in the mining industry (source: Mining Magazine, Aug. 2001).

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Mineral resources management and the environment

Mining industry suppliers are faced with a big dilemma involving risks and costs. They have to balance the risks and costs involved in doing e-business, or losing the competitive edge by not doing e-business. Whatever might be the prognosis, there is little doubt that Quadrem will have a powerful impact on all facets of the mining industry. Time only can tell whether Quadrem will remain unchallenged or whether new, more complex and more heterogeneous e-marketplaces will emerge.

CHAPTER 2

Mining methods and the environment

2.1

INTRODUCTION

A mineral is mined only when it is profitable to do so (in terms of goods and services it could provide). Also, it has to be mined where it is found. The Chapter provides a brief account of various mining methods, and seeks to elucidate how the adverse environmental impact of a given mining activity can be minimized through an understanding of the method of mining, equipment used for mining, haulage and transport, quantum of mineral production, disposal of wastes, etc. Coal is chosen as a type case to examine the environmental impacts of different methods of mining, for the following reasons: (1) The annual production of coal in the world (⬃4600 Mt in 1998) is higher than any other metallic and non-metallic mineral, (2) Its use is widespread because of its versatility as a fuel and industrial raw material, (3) It is mined both by opencast and underground mining, or combinations of both, (4) Transport of coal is expensive. Hence, industries using large quantities of coal, such as, thermal power stations, iron and steel complexes, etc. tend to be located near the coalmines. Consequently, coal-mining areas tend to be the foci of a wide range of environmental stresses, arising not only from the coal mining industry itself, but also from coal-using industries, (5) Coal has a variable composition (e.g. rank of coal, calorific value, sulphur content) depending upon its geologic setting and burial history. It may have to be preprocessed (e.g. washed), depending upon the requirements of the user. Depending upon the composition of coal (such as sulphur content), mining of coal may have consequences such as acid mine drainage (AMD) and burning of coal could cause acid rain, (6) the environmental impacts associated with the coal cycle are complex and interactive. They may be instantaneous (e.g. land clearance), accumulative (e.g. spoil deposition), or progressive (pneumoconiosis). The following account is largely drawn from Chadwick et al. (1987). The special feature of this excellent work is its particular reference to the mining problems of the developing countries. In most cases, mining is preceded by exploratory diamond drilling (Fig. 2.1; source: UNEP Tech., Rept., No. 5, 1991, p. 10) in order to get samples of the subsurface, and build a three-dimensional structure of the ore body.

26

Mineral resources management and the environment

Figure 2.1 Diamond drilling, and collection of sludge samples (source: UNEP Tech. Rept., No. 5, 1991, p. 10).

2.2

MINE DESIGN PROCESS

A large coal mining project is bound to have a profound effect on the economy of an area or region, in terms of investment, use of natural resources, employment, environmental impact, etc. The Design Process of a coal mine is a part of the Coal Project Development Cycle. The trickiest part of the exercise is the choice of technology to be adopted in mining, as considerations of national policy are involved – whether to go in for the most advanced and productive technology, or whether to opt for low-cost, low-productivity, labour-intensive technology. Figure 2.2 (source: Chadwick et al., 1987, p. 72) shows the relationship between the planning stages of a coalmine, and expenditure during a typical coal project development cycle. There are four phases of mine planning – Pre-feasibility studies, Conceptual planning and Full feasibility, Preliminary Design and Final Design. The expert geotechnical assistance needed at various phases of mine planning, is shown in Table 2.1 (source: Chadwick et al., 1987, p. 75). Chadwick et al. (1987, p. 76) showed diagrammatically how the various inputs are to be integrated to decide upon the design of the combination of opencast and underground mine. 1. On the basis of the geophysical data, basic drillhole data and topographic and existing status data, the coal seam (chemical and physical properties, reserve

Figure 2.2

Relationship between the planning stages and expenditure during a typical coal development cycle (source: Chadwick et al., 1987, p. 72).

Mining methods and the environment 27

28

Mineral resources management and the environment

Table 2.1 Geotechnical expertise needed at different stages of mine planning (Chadwick et al., 1987, p. 75). Geotechnical input

Coordinators

Expert assistance needed

General site

Mining engineer-geologist, Structural geologist

Photogeologist, Geotechnical engineer, Hydrologist, Geochemist, Petrologist, Seismologist

Site-specific

Mining engineer-geologist, Geotechnical engineer, Hydrogeologist

Geophysicist, Photogeologist, Structural geologist, Geochemist, Petrologist

Geotechnical designs

Geotechnical engineer, Hydrogeologist

Mining engineer-geologist, Geophysicist, Structural geologist, Engineering geologist

estimations, etc.) and overburden (specific gravity, hardness, diggability, etc.) are evaluated. 2. Choice of underground methods (select mining areas and design the layout of the mine), and/or opencast methods (layout of the strip plan). 3. Projection of the problems of hydrology, subsidence, spoil characteristics, safety, economics, etc. 4. Schedules of underground mining, open cut mining, mine production, and waste disposal. 5. Infrastructure, manpower requirements, operating costs, financial evaluation, sensitivity data, etc. Figure 2.3 (source: Chadwick et al., 1987, p. 78–79) is a matrix diagram indicating the linkages between and the importance of, the various investigations needed for, the design of the underground mining, surface mining and surface facilities. The mine planning process requires a large volume of information, starting with the nature, location and extent of coal deposit, and features that may affect the economic extraction of coal. Before drawing up the programme of exploitation, it is necessary to establish whether the reserves and quality of coal justify the development of a new mine. Thereafter a study will have to be made of the factors (largely geotechnical), which affect the design and layout of the mine. The factors which have a bearing on the location, design and layout of any kind of mine (coal or others) are briefly described as follows: 2.2.1

Geographical factors

Terrain: The nature of the terrain (rough, rolling, flat, etc.) has an obvious bearing on the mine location and layout. The land contours and the elevation of an area have to be determined precisely. The relative topographic data is needed to determine the exact location of the drillhole collars, to calculate the volumes of the overburden to be removed, to decide upon the specifications for site accesses, coal preparation and overburden stripping equipment, etc. Even for areas for which topographical maps are available, it is prudent to resurvey the area because of the crucial importance of

Mining methods and the environment 29

the topographic data. It should be borne in mind that high altitudes (such as those characterizing the mines in the Andes in South America) affect the performance of the mining machinery. Land ownership: A map of the land has to be drawn up, indicating the mineral ownership (government, public institutions, private companies, individuals, reservations, etc.). Surface features: such as heavily forested areas, desert terrain, seasonal depth and rate of flow of surface bodies of water (such as streams and ponds), presence of monuments or structures of archeological, religious or cultural importance, burial areas, settlements, etc. are to be recorded. Natural hazards: Some areas may be subject to natural hazards, such as, earthquakes, volcanoes, floods, avalanches, bush fires, insect plagues, etc. Their frequency and intensity need to be ascertained and recorded. 2.2.2

Meteorological factors

The following meteorological factors have to be taken into account in the design of the mine: Rainfall: 10-, 20- and 100-year maximum and minimum rainfall data (daily, monthly, yearly) are necessary for the design of the capacity of pumps, haulage roads, water handling and conservation facilities, etc. In monsoon climates, heavy rains occur in 3–4 months in a year, while it is almost dry for the rest of the year. Temperature and humidity: Data regarding the daily maximum and minimum temperatures and humidity are needed to design the ventilation in the mine, and airconditioning in the office buildings. Winds and extreme weather conditions: 10-, 20- and 100-year data regarding wind direction and velocity are needed for the design of the buildings, headframes and other structures. Extreme weather conditions (hurricanes, heavy snowfall, etc.) affect the number of working days and productivity of mining (particularly opencast mining), and have to be taken into consideration in the design of the excavation equipment. 2.2.3

Geological and structural setting

This is the first and most important step. As much data as possible about the geological and structural setting should be gathered from geological maps, aerial photographs and space images, published papers, reports and theses, personal discussions with individuals who have knowledge of the area and who have worked in the adjacent areas, etc. On the basis of the regional geologic setting, the structure and configuration of the strata in the area are delineated. Information on the frequency, and geometry of faults (and in some cases, dykes) is of crucial importance, because it has a profound effect on the minability and the economics of coal mining. The three-dimensional configuration, size and structure of the deposit are delineated on the basis of the following studies (Chadwick et al., 1987, p. 81): field mapping, subsurface geophysics (gravity, magnetism, electrical resistivity, electromagnetism,

30

Mineral resources management and the environment

(a)

Figure 2.3(a, b) Matrix diagram showing how the investigation techniques are linked to the mining considerations (source: Chadwick et al., 1987, p. 78–79).

Mining methods and the environment 31

(b)

32

Mineral resources management and the environment

seismic reflection/refraction, etc.), trenching and pitting, drilling (non-core drilling, core drilling, geophysical borehole logging), exploration shafts and drifts, etc. The mine is designed on the basis of the following data derived from the above surveys: (1) Stratigraphy of the deposit, (2) Three-dimensional configuration, size and structure of the deposit, (3) Location and nature of the faults, dykes and washouts, (4) Depth of the deposit, (5) Thickness and dip of the different coal seams, etc. 2.2.4

Techno-economic viability

The techno-economic viability of the mine is evaluated on the basis of the following parameters: 1. Quantity of coal available for extraction under the present economic and technical conditions: The system used in the assessment of coal reserves is given Figure 2.4

Figure 2.4

System used in the assessment of coal reserves (source: Chadwick et al., 1987, p. 83).

Mining methods and the environment 33

(source: Chadwick et al., 1987, p. 83). Reserves are classified as Inferred, Indicated, Measured, Assessed, on the basis of increasing confidence (see Table 2.2 about the reliability and economic limits for coal resources assessment – source: Chadwick et al., 1987, p. 84). As should be expected, the degree of geological certainty and confidence in regard to the reserve estimates depend upon the density of sample points (such as boreholes, trenches, outcrops). The size of the reserve is not static – it keeps on changing depending upon the method of mining chosen, the market conditions, and emerging technologies. 2. Quality of coal: The possible laboratory preparation flowsheet for the bore core is given in Figure 2.5 (source: Chadwick et al., 1987, p. 89). The following parameters generally define the quality of coal: calorific value, rank and type of coal, ash content, sulphur and chlorine contents, etc. High rank coals (e.g. anthracite and bituminous coal) are characterized by high calorific value, and low contents of ash, sulphur and chlorine. On the basis of such preliminary measurements on the samples of drillhole cores, the general market for which the given coal is best suited (e.g. steam coal, metallurgical coal, etc.) is determined. Table 2.2 Reliability and economic limits for coal resources assessment (source: U.S. Geological Survey, 1976, as quoted by Chadwick et al., 1987, p. 84). Term

All coals

Measured

0–400 m* around data points or inside well controlled outcrop belt, or area with data points upto 800 m apart.

Indicated

400–1200 m around data points or inside well-controlled outcrop belt, or area with data points 800 m to 2.4 km apart.

Inferred

1.2–4.8 km around data points or inside well controlled outcrop belt, or areas with data points 2.4–9.6 km apart.

Hypothetical

Greater than 4.8 km around data points or well controlled outcrop belt, or area with data points greater than 9.6 km apart.

* Presently, the commonly used interval between data points is 100 m, and in some cases, even 50 m.

Bituminous coal and anthracite

Lignite and sub-bituminous coals

Reserve base*

Seams
70 cm, Depth 300 m

Seams
150 cm, Depth 300 m

Sub-economic

Seams 35–70 cm

Seams 75–150 cm

Resources

Depths 1800 m, or Seams
35 cm, depth 300–1800 m

Depths 1800 m, or Seams
75 cm, depth 300–1800 m

Resources

Seams
15 cm, Depth 1800 m

Seams
75 cm, Depth 1800 m

* Equivalent to in situ reserves. Notes: (1) “Sub-economic” seams may be included in the “Reserves” or “ Reserve base” if it is possible to mine them in conjunction with thicker seams, such as in a multi-seam open-cut operation. (2) Coal with ash content of more than 33% is excluded in all calculations.

34

Mineral resources management and the environment

Figure 2.5 Possible laboratory preparation flowsheet for the examination of the drill core (source: Chadwick et al., 1987, p. 89).

The following is the outline of the ply-by-ply analysis of coal seams in an exploration area (source: Chadwick et al., 1987, p. 86–87): 1. Non-destructive testing of whole seam 1.1 gas emission characteristics, 1.2 geological (including macropetrographic) logging, 1.3 X-radiography, 1.4 Apparent relative density determination. 2. Selection of plies for analysis on an engineering and geological basis, 3. Analysis of each ply (including dirt bands) for determining 3.1 volumetric recoveries, 3.2 true relative density, 3.3 ash and inherent moisture (or full proximate analysis), 3.4 total sulphur, 3.5 swelling index. 4. Crush each ply or sub-section to specified size with minimum percentage of fine particles. 5. Float-sink tests for each ply, then for each R.D. fraction, determine 5.1 yield, 5.2 ash and moisture content, 5.3 total sulphur, 5.4 swelling index, 5.5 specific energy.

Mining methods and the environment 35

6. Select optimum working section from coal quality and engineering properties. 7. Combine appropriate “clean coal” fraction of each ply of subsection involved, to prepare simulated washed coal product or products. 8. Analysis of simulated washed coal product for coking properties, by determining 8.1 proximate analysis, 8.2 ultimate analysis, 8.3 swelling index, 8.4 Gray-King assay and coke type, 8.5 phosphorus content, 8.6 maceral analysis, 8.7 vitrinite reflectance, 8.8 Gieseler plastometer characteristics, 8.9 Arnu-Audibert dilatometer characteristics, 8.10 mineral matter determination and analysis. 9. Analysis of simulated washed coal product or middlings from coking product to test potential value as steaming coal, by determining 9.1 proximate analysis, 9.2 specific energy, 9.3 ash fusion temperature, 9.4 Hardgrove grindability index, 9.5 ash analysis. Notes: (1) Some tests may be omitted, depending upon the projected use of coal. For instance, if the coal is to be sold as steam coal after washing, step no. 8 may be omitted. (2) Non-coal beds within the seam may be omitted from float-sink tests 5–9 in ply-by-ply analysis, and counted directly as a part of the reject material. The mass of these present should, however, be included in the assessment of yield of clean coal or middlings, (3)When once the working section is established, float-sink test (no. 5) may be performed on that alone. It is always cheaper to undertake detailed analyses of coal samples, in the beginning itself, rather than redrilling at a later date to get the samples to determine the parameters that may be needed in the light of the emerging market conditions. This does not mean that every foot (⬃0.3 m) of the core should be examined for all the parameters. This would produce huge quantities of redundant data, which is not worth the expense. The most important commercial data relate to the final ROM (run-of-mine) product and the final saleable coal. It follows that the investigation of detailed properties should be confined to the coal sections that are proposed to be mined. Hence coal bands that will not be mined, may be excluded from the detailed analyses, whereas the dirt partings and interburden that will form the ROM product should be included. A practical arrangement would be for the geologists, mining engineers, mineral technologists, marketing experts and laboratory personnel to meet together and decide upon the analytical programme which is most costeffective.

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Mineral resources management and the environment

Where alternatives exist for the extraction of coal, the quality data based on plyby-ply analysis should be examined in conjunction with geomechanical properties to select the most favourable working section of the seam. Often, the ROM coal may have to be beneficiated to satisfy the market specifications. In order to establish the techno-economic feasibility of the beneficiation, the ROM coal is subjected to simulated preparation plant processes, such as float-sink tests and froth flotation. The marketable (“clean”) coal fraction is subjected to detailed tests, such as calorific value, coking characteristics, trace elements, liquefaction characteristics, etc. Such data will be useful to determine the percentage of the ROM coal that is saleable. Thus, knowing the quantum of demand for saleable coal, one can calculate the amount of ROM coal that needs to be produced in order to satisfy the market demand. After the relevant data are assessed and refined, in progression with increasingly precise and detailed data, final decisions are taken in regard to the following: (1) whether the mining is to be opencast or underground or both, (2) the size of the mine, and the rate of annual production, (3) the seams or sections of the seams that are to be mined, and (4) costing. Whether a given deposit is to be mined by opencast or underground methods, is critically dependent upon the geology and geometry of the deposit. For instance, underground mining is virtually the only option to mine a 3 m thick seam occurring at a depth of (say) 500 m. On the other hand, if the same seam occurs at a depth of 15 m, opencast mining would be the evident choice. A combination of opencast and underground methods may have to be used to mine the same seam occurring at a depth of (say) 50 m, and dipping from the surface at an angle of (say) 10 °. 2.2.5

Geotechnical considerations in mining

The design, safety and techno-economic viability of a mine are critically dependent upon the geotechnical characteristics of the rock strata. In the case of the underground mines, geotechnical data are needed to decide upon the following (Chadwick et al., 1987, p. 88–89): (1) pillar sizes and extraction ratios, (2) ways and means of controlling the subsidence and ingress of water, (3) most economical method of excavating coal and waste rock, (4) where to locate the accesses to the mine, (5) where to locate the surface structures and tips. In the case of opencast mining, geotechnical considerations are taken into account for (1) determining the pit slope and bench angles, (2) choice of excavation technique, and the equipment to be used for the purpose, (3) location of the surface structures and tips. Some geotechnical tests are performed in situ (Table 2.3) while some are performed in the laboratory (Table 2.4). Special rock mechanics tests that are performed in trenches, shafts and adits are given in Table 2.5 (Chadwick et al., 1987, p. 91–96).

Table 2.3

Rock mechanics in situ tests (source: Chadwick et al., 1987, p. 91–93).

In situ mechanical tests 1. Deformability tests 1.1 Static method 1.1.1 Plate bearing (flat jack; hydraulic jack; cable jacking) 1.1.2 Pressure tunnel (water loading; radial jacks) 1.1.3 Pressure borehole (dilatometer) 1.2 Dynamic method 1.2.1 Measurement of Longitudinal waves velocity (geophones) 1.2.2 Measurement of the velocity of the longitudinal and transversal waves (Rayleigh’s vibrograph) 1.2.3 Measurement of direct longitudinal waves velocity in a borehole (sonic coring) 1.2.4 Detailed stratigraphic surveys 2. Natural rock mass stresses tests 2.1 Rock surface tests 2.1.1 Measurement of deformation after overcoring or bond removal (by strain rosette) 2.1.2 Measurement of pressure to balance natural stresses (by flat jack) 2.2 Test inside borehole 2.2.1 Measurement of core deformation after overcoring 2.2.2 Measurement of borehole wall deformation after overcoring 3. Strength tests 3.1 Compression 3.1.1 Triaxial tests 3.2 Shear 3.2.1 Rock block test along discontinuity surface 3.2.2 Concrete block test along interface 4. Permeability 4.1 Inside borehole (Lugeon) 4.2 In a joint pumping test 4.3 Piezometric levels and groundwater flow 5. Rock anchor tests 6. Rock movement monitoring 6.1 Long base extensometer 6.2 Inverted pendulum 6.3 Slope indicator 6.4 Blast and ground motion monitoring 6.5 Rock noise monitoring

Large Tunnels, shafts, underground underground works mining nDC (n)DD

Open air mining, quarries, large surface excavations

nDC

(n)DD aF; (n)DD aF; nDC aF

oiDC nDC nDC

nDD aDC nDC aF; nDD (n)F a(F) nDD nDD nDD

aDD nDD nDD

aDD aDD

aDD aDD oiF

nF nF

nF

oiF

aDD

aDD

aDC

nAC aAC nF; nDC

nF; nDC OiAC

Test importance: n – necessary, a – advisable, oi – of interest, ( ) – alternative. Stages of work: F – Feasibility, DD – Detailed design, DC – During construction, AC – After completion.

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Mineral resources management and the environment

Table 2.4

Rock mechanics laboratory tests (source: Chadwick et al., 1987, p. 94). Large underground works

Rock mechanics laboratory tests 1. Uniaxial test 2. Biaxial triaxial test 3. Poisson’s ratio 4. Sound velocity – pulse and resonance 5. Direct shear 6. Tensile (Brazilian) test 7. Hardness (Rockwell indentation, Shore scleroscope, Schmidt rebound hammer) 8. Triaxial chamber for determining body forces due to interstitial pressure 9. Density 10. Water content 11. Porosity 12. Absorption 13. Permeability

aDD oiF; aDD aDD aF aDD nDD

Tunnels, shafts, Open air mining, underground quarries, large mining surface excavations

oiF aDD nDD nDD aDD aDD aDD aDD

Test importance: n – necessary, a – advisable, oi – of interest, ( ) – alternative. Stages of work: F – Feasibility, DD – Detailed design, DC – During construction, AC – After completion.

2.2.6

Stripping ratio

For all practical purposes, it is the economics of mining, in the form of stripping ratio, that would determine whether a coal seam is better mined by opencast or underground methods (Chadwick et al., 1987, p. 101–102). The stripping ratio (S) is the ratio between the volume of overburden removed to the volume of coal recovered. Maximum Stripping Ratio (Se) 

(U  M  A) O

(2.1)

where U  total production cost per unit volume of coal mined by underground methods (ROM), M  Cost of excavating and transporting a unit volume of coal, A  Total fixed charges for mine development, overheads administration, and financing per unit volume of ROM coal, O  Cost of excavating, transporting  disposing of unit volume of overburden/ waste. If, as is possible, the operation of a surface mine under conditions of maximum stripping ratio is uneconomic, a cut-off stripping ratio (Sc) may be calculated as follows: (Sc) 

(D ((P  R)  (B  P  R))  M  A) O

(2.2)

Mining methods and the environment 39 Table 2.5 Geotechnical tests in trenches, shafts and adits (source: Chadwick et al., 1987, p. 95–96). Object of investigations (rock properties, and engineering aspects) System of spacing of joints, faults, etc. Nature of surfaces of joints, faults, etc. Contact of different rocks Observation of deep weathered zone Observation of hydrothermal altered zone Trace of very important faults Observation of permeable strata Study of improvements of rock masses Study and arrangement of volume of explosives Ascertain the effects of grouting Ascertain the constructional techniques for underground work Shearing strength tests in situ Permeability tests in situ Stress state tests in situ Rock hardness tests in situ Taking samples for identification or lab. tests In situ stress – strain determinations Measurement of rock temperatures Identification of noxious gas emanations Measurement of rock hardness Measurement of physical properties using geophysical methods Protection against inflow and pressure water Construction of improvement of dispositions of rock masses

Tunnels, shafts, Rock underground mining, slopes – natural large underground or artificial openings

Open air mining, quarries, large surface excavations

nF; nDD; nDC nDD; nDC nF; nDD nDD nDD nF nF nDD nDD; nDC

nF; nDC nDC nF; nDD nF; nDD nF nF nF nF; nDD nDD; aDC

nF; nDD oiDC aDC oiDC aDD oiF – – nDD; nDC

nDC

NDC nF; nDD

–

aF – nF; nDC – aF

nF aF nF; nDC nF nF; nDC

– – – –

nDC; nAC – – – aAC

nF; nDC aDC nDD NDD aF; aAC

– – – nDD –

aDC

aDC

–

OiDC

–

–

Test importance: n – necessary, a – advisable, oi – of interest, ( ) – alternative. Stages of work: F – Feasibility, DD – Detailed design, DC – During construction, AC – After completion.

Where R  Recovery of coal for sale from ROM material (i.e. after beneficiation), D  Density of ROM coal, B  Unit cost of transport of coal from pit limits to the preparation plants  cost of preparation  cost of waste disposal  cost of loading out per tonne of ROM coal, p  Minimum acceptable profit per tonne of saleable coal, P  Selling price of saleable coal per tonne. These simple formulae are helpful in getting a feel of the problem. Now-a-days, computers are extensively used to figure out Se and Sc by considering and optimising

40

Mineral resources management and the environment

all the variables involved, such as geology, topography, geotechnical characteristics, mining methods, economics and cost information, NPV (Net Present Value), etc.

2.3 2.3.1

OPENCAST MINING Advantages

The following are the advantages of the opencast mining (Chadwick et al., 1987, p. 100–101): (1) high productivity per man-hour, and high output per mine, (2) low annual capital costs and operating expenses per tonne of mineral mined, (3) easy to manage the equipment and the workforce, (4) further exploration can be carried out relatively cheaply, and would yield data of greater confidence, (5) allows the use of large-capacity machines, (6) better safety record (relative to underground mines), (7) labour prefers the opencast mines, relative to underground mines, (8) few problems with seam gases, heat and roof collapse, and subsidence, (9) shorter lead time, relative to underground mining. Because of these advantages, opencast mining is the most prevalent form of mining, accounting for 60% of the large mines (i.e. those with production of more than one Mt/y), and 69% of the production. Sengupta (1993) gave a detailed account of dragline operations to undertake surface coal mining coupled with reclamation. The dragline initially cuts a trench called as keycut, adjacent to the newly formed highwall. The length of the block is the distance between the previous keycut position and the present keycut position. The keycut material is dumped in the bottom of the mined-out pit. The operating cycle of the dragline consists of five steps: (1) The empty bucket is placed in a position ready to be filled, (2) the bucket is dragged towards the dragline in order to get filled, (3) the filled bucket is hoisted up, and the boom is swung towards the spoil pile, (4) the bucket dumps the spoil material it is carrying, (5) the bucket is lowered, and the boom swings back to the cut. The width of the panel is an important consideration in the dragline operations. It is chosen on the basis of the following considerations: (1) coal loadout: the practical minimum width is 28 m; any width less than 28 m hampers maneuverability of the coal trucks, (2) slope stability: wide pits are safer for mine and equipment, (3) Cycle time: depends upon the swing of the dragline; for medium and large draglines, wide panels give better productivity, (4) spoil regrading: the wider the panel, the greater would be the amount of dozing to be done to level the spoil piles, (5) walking: the wider the panel, the less would be the walking needed for the dragline, (6) spoiling at entryways: the narrower the panel is, the shorter would be the spoiling radius. The cycle time for a small dragline increases significantly if the panel width is increased, but if large draglines are used on the same depth of overburden, the increase in the cycle time will only be marginal. For instance, when a large dragline

Mining methods and the environment 41

is used, the cycle time increases by only 1.6% even though the panel width has been increased from 75 ft. (22.8 m) to 175 ft. (53.3 m) (Sengupta, 1993, p. 39). 2.3.2

Mine layouts

When coal measures are in the form of flat, tabular deposits, they can be conveniently mined by strip or area mining (Fig. 2.6; source: Chadwick et al., 1987, p. 111). Excavation is started in the area at or close to the surface where the thickness of overburden is at a minimum. The overburden is first removed in order to expose the first strip of coal, and this overburden is deposited outside the proposed pit area. After coal is removed from the first strip, a second strip of overburden is then excavated along the downdip side of the first. “The material taken from this cut is cast directly into the void created by the first strip” (Chadwick et al., 1987, p. 110). This process of stripping is continued, until the overburden to be excavated is found to be too thick to be stripped economically or when the excavation has reached its maximum depth or when some other boundary condition is reached. Contour mining which is a variant of strip mining, is used to mine flat or gently dipping coal seams exposed on steeply sloping hillsides (Fig. 2.7; source: Chadwick et al., 1987, p. 111). “Overburden is removed from above the seam outcrop and placed below the exposed coal on the downhill side” (Chadwick et al., 1987, p. 112). Successive cuts are made on the hillside until a situation arises whereby the high-wall height is such that further excavation is no longer economic. The excavation process leaves behind a long, narrow bench which follows the contours of the hillside. Open pit mining is best suited to excavate coal measures which are large, thick, and irregular, or which are multi-seam and steeply dipping. If a seam is too thick to be mined from a single face either because of the limitations of the reach of the mining equipment or because of the possibility of slope failure, recourse is taken to the development of several smaller faces. Similar conditions hold good for multi-seam measures – faces or benches may be developed for individual seams in such a manner that some faces are used for the removal of overburden and interburden, and

Figure 2.6

Principle of strip mining (source: Chadwick et al., 1987, p. 111).

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Mineral resources management and the environment

Figure 2.7 p. 111).

Strip-mining in steeply sloping terrain (contour mining) (source: Chadwick et al., 1987,

Figure 2.8 Schematic diagram illustrating the layout of an open pit mine (source: Chadwick et al., 1987, p. 113).

some for winning coal. A possible layout of a open-pit mine is shown in Figure 2.8 (source: Chadwick et al., 1987, p. 113). In this arrangement, the excavated overburden is deposited outside the pit, until a suitable area becomes available within the pit area itself. Only when the excavation is started on the lowest bench, will it become possible to emplace the overburden material to fill the previously created voids. A variety of machines are used in opencast mining. It is convenient to use scrapers to remove the top soil, subsoil and unconsolidated overburden. Though stripping shovels and bucket wheel excavator with boom stacker are used in strip mining, the walking dragline is the most widely used equipment for strip mining of regular, flat coal deposits. It strips the overburden and casts it directly into the void. In some situations, such as when the overburden strata are composed of resilient

Mining methods and the environment 43

Figure 2.9 Opencast mining with dragline with progressive restoration. 1. Carbonaceous sediment, 2. Overburden, 3. Topsoil (source: Chadwick et al., 1987, p. 159).

material, it may be necessary to drill the strata, and then break it up with explosives. Coal is won in a second drilling and blasting operation. Coal is loaded out either by power shovel or front-end loader into trucks for being hauled away. Where the ground is sufficiently hard, combination of power shovels, hydraulic excavators and front-end loaders are commonly used to remove both the overburden and coal from multi-bench systems. Where the ground is soft, the usual practice is to use combinations of bucket wheel and bucket chain excavators with railcar or conveyor belts. Figure 2.9 (source: Chadwick et al., 1987, p. 159) shows how opencast coal mining with progressive restoration can be carried out using a dragline. A bird’s eye of opencast mining and progressive restoration using a dragline is given in Figure 2.10 (source: Chadwick et al., 1987, p. 160). In some open pit mines in Indonesia, mining operations have been abandoned in the past when they developed long high walls. Matsui and Shimida (2001) developed a high wall mining system to extract coal from exposed seams at the base of the open cut or stripping operations. The equipment used in high wall mining is analogous to the machinery used in underground mining. Figure 2.11 (source: Matsui & Shimida, 2001) shows how the high wall mining is carried out with the Addcar system. After making a small bench, mining can be started from the outcrop with minimum environmental disturbance. As only a narrow bench is required to gain access to the coal

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Mineral resources management and the environment

Figure 2.10 A bird’s eye view of the opencast coal mining and progressive restoration, using a dragline (source: Chadwick et al., 1987, p. 160).

Figure 2.11

Highwall mining using the Addcar system (source: Matsui & Shimida, 2001, p. 488).

seam, there is minimal disturbance to the surrounding land, and there is no need to worry about failures of waste rock spoils. 2.3.3

Projected advances

The following are the projected advances in open-pit mining (Hustrulid, 2000): 1. Increase in mining geometry, steeper slopes, deeper pits 2. New, large production machines/techniques 2.1 400t capacity trucks, 76.5 m3 shovels and 381–432 mm drill holes 2.2 continuously variable explosives with respect to energy and other properties 2.3 electronic blasting caps

Mining methods and the environment 45

3. Mechanization/automation 3.1 very high accuracy GPS on all machines 3.2 driverless trucks 3.3 remotely-operated drills 3.4 remotely-operated shovels 4. MARC in place, guaranteed availability. Advanced condition monitoring and prediction 5. Few working places, with high utilization 6. Short time between stripping and production 7. Automatic sampling of drill cuttings, remote after blast sampling 8. Automatic sampling in the dipper/truck bed or along the route. Automatic destination assignment 9. Simulation is extensively used to plan production. The projected advances in open-pit mining are realisable only in the context of the following considerations (Hustrulid, 2000): 1. The very large automated machines and techniques require precision cutting of bench faces and maintenance of bench widths, 2. The production would be coming from a limited number of working places, and the plant should be able to handle the feeds in such a situation, 3. It may be necessary to maintain several stockpiles, and rehandle the ROM, 4. A great number of safety factors may have to be considered, to take care of the mixture of automated and non-automated jobs. Presently, even the least expensive underground mining method (say, by panel caving) costs 3–5 times more per tonne than the material handled by the open pits (Hustrulid, 2000). 2.4 2.4.1

UNDERGROUND MINING Advantages

The following are the advantages of the underground mining (which can also be thought of as the disadvantages of the opencast mining): (1) mining can be carried on round-the-year, and round-the-clock, unaffected by weather conditions, (2) minimal environmental disturbance of the surface, (3) relatively small amount of spoil is generated, with the implication that less land is disfigured and contaminated, and the expense of rehabilitation of the mined land is correspondingly limited, (4) oxidation problems at the outcrop are less likely, (5) mining can be done selectively – specific sections of seams can be mined to maintain quality, and to relieve breakdowns, (6) the working environment can be adjusted, etc. An underground mine may be a drift mine or slope mine or vertical shaft mine, depending upon the inclination of the access to the seam. The choice is determined by the position of the seam relative to the surface and the economics of mining. Where a seam outcrops at the surface and is more or less horizontal, it can be conveniently mined as a drift mine (Fig. 2.12 ; source: Chadwick et al., 1987, p. 115).

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Mineral resources management and the environment

Figure 2.12

Schematic diagram of a drift mine (source: Chadwick et al., 1987, p. 115).

Figure 2.13

Schematic diagram of a slope mine (source: Chadwick et al., 1987, p. 115).

Access by inclined tunnel is limited to seams which occur at shallow depths. This is so because the length of the tunnel tends to be about four times that of the vertical depth of the seam (Fig. 2.13; source: Chadwick et al., 1987, p. 115). A vertical shaft mine is necessary to mine deep seams. For purposes of ventilation, and to provide means of egress, all underground mines should necessarily have at least two accesses from the surface. For this reason, most mines contain vertical shafts and inclined tunnels. Table 2.6 (source: Chadwick et al., 1987, p. 116–117) gives a comparison of the engineering aspects of shaft and drift types of mines. In the past, tunnels were constructed through a cycle of drilling, blasting, loading and haulage of the broken rock and installation of supports. The current practice is to use tunnel boring machines with multiple cutting heads to drive the tunnels continuously, without using explosives. The shafts are usually circular in outline, and are lined with concrete. Just as happened in the case of tunnels, shafts are nowa-days sunk using large diameter shaft boring machines, thereby avoiding blasting.

Mining methods and the environment 47 Table 2.6 A comparison of the engineering aspects of shaft and drift mines (source: Chadwick et al., 1987, p. 116–117). Shaft

Drift

Mineral

(a) Limited to between 2.2 and 4.4 M tonnes/annum/shaft. (b) Intermittent feed to coal preparation plant evened out by surface bunkers or stockpiles. (c) Adequate pit bottom bunkerage essential. (d) Inspection and maintenance carried out from the winding system.

(a) No significant limit on capacity; upto 12 M tonnes/annum is achievable. (b) Continuous feed to coal preparation plant but stockpile are still required to even out peaks and cover breakdowns. (c) Drift bottom bunker desirable for smooth flow and to cover belt stoppages. (d) Haulage system required for men and materials access for conveyor and drift inspection and maintenance.

Labour

(a) High capacity and shortest time between surface and pit bottom. (b) Capacity of second egress at mineral shaft limited to around 30%/40% of man shaft.

(a) Capacity similar to shaft but time between pit top and seam level is greater. (b) Maintenance haulage in conveyor drift may only give limited second egress facility but conveyor could be equipped for man-riding if speeds are appropriate, or men could walk out on a power failure.

Material

(a) Large equipment can be accommodated but this cannot always be fully utilized due to restrictions of underground roadways. (b) Speedier transport of materials to pit bottom.

(a) Equipment size limited by drift dimensions but this will commensurate with underground roadways. (b) Slower transport of materials to drift bottom but problems of transfer to underground haulage systems may be less.

Ventilation Resistance is relatively less

Resistance is relatively more

Services

Arrangement of electric and other cables, water and compressed pipes, is relatively less convenient

Allows a better arrangement of electric and other cables, water and compressed air pipes

Other considerations affecting the choice between shat and drift are: construction time, extra distance of drift, geological factors, weak/wet strata, and the nature of the reserves.

Figure 2.14 (source: Chadwick et al., 1987, p. 118) gives a schematic diagram of a vertical shaft mine. The design of a major access underground has to take into account the geotechnical and hydrological characteristics of the rock strata through which the entry structure is to be driven. A weak or unconsolidated ground may lead to roof collapse, and large quantities of groundwater may flood the mine. Dewatering at shallow depths can no doubt be accomplished by pumping, but this may not always be possible in the case of deep strata. Grouting with cement or chemical solutions to fill the voids in the rock mass, is the only remedy in such a situation – grouting not only reduces the permeability of the rock mass, but also increases its strength. An

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Mineral resources management and the environment

Figure 2.14 Table 2.7

Schematic diagram of a vertical shaft mine (source: Chadwick et al., 1987, p. 118). Underground mining methods (source: Cummins & Given, 1973).

I – Self-supporting opening

II – Supported openings

III – Caving methods

A. Open-stope mining 1. Isolated openings 2. Pillared open stopes a. Open stoping with random pillars b. Open stoping with regular pillars B. Room-and-pillar mining C. Sub-level stoping D. Shrinkage stoping E. Stull sloping

A. Cut-and-fill stoping B. Square-set-and-fill stoping C. Longwall mining D. Shortwall mining

A. Sub-level caving B. Block and panel caving

E. Top slicing

alternative is freezing the water in the voids of the rock mass, by the circulation of the coolants. This has the same effect as grouting, but this technique is seldom used in the developing countries. 2.4.2

Room-and-pillar method, and Longwall mining

There are three types of underground mining methods: Self-supporting openings, Supported openings, and Caving (Table 2.7; source: Cummins & Given, 1973). The room-and-pillar method, and longwall mining are the two common methods of underground mining of coal. The room-and-pillar method is best suited to mine

Mining methods and the environment 49

Figure 2.15 Schematic diagram showing the operation of the room-and-pillar method (source: Chadwick et al., 1987, p. 121).

relatively thick coal seams which occur at shallow depths, and have reasonably strong roof and floor strata. In the first stage, a series of intersecting openings are driven through the seam. At this point, solid pillars of coal support the roof. The size of the pillars needed depends upon the depth of the seam – at shallow depth, small pillars would suffice, but at greater depths, the pillars have to be thick. Thus, in the first stage, the percentage of recovery of coal decreases with increasing depth. In the second stage, the pillars are mined, allowing the roof to collapse into the abandoned area. Figure 2.15 (source: UNEP Tech. Rept. No. 5, 1991, p. 11) depicts an open stope with regular pillars. The sub-level stoping longitudinal slopes in narrow veins is shown in Figure 2.16 (source: UNEP Tech. Rept. No. 5, 1991, p. 12). The process of cut-and-fill mining operation is depicted in Figure 2.17 (source: UNEP Tech. Rept. No. 5, 1991, p. 12). In the past, the cycle of winning coal used to be through drilling and blasting the seam, loading the coal and hauling it to the surface. The present practice in most mines is to mine coal continuously with a cutting head, and load the coal to a shuttle car or an extensible conveyor system. Such a system has a much higher productivity than the conventional cycle.

50

Mineral resources management and the environment

Figure 2.16 Sub-level stoping longitudinal slopes in narrow veins (source: UNEP Tech. Rept., No. 5, 1991, p. 12).

Figure 2.17

Cut-and-fill process in mining (source: UNEP Tech. Rept., No. 5, 1991, p. 12).

Longwall mining is characterized by a greater flexibility. It is the preferred method for mining deep, thin seams, where the dips are steep, and the roof strata are weak. This method involves mining coal along a single face about 100–200 m long, using a rotary trim shearer, a trepanner or a coal plough which traverses along the face. The broken coal is loaded onto a series of conveyor systems. The working area is protected by self-advancing, hydraulic roof supports. As the working face advances, the roof supports move synchronously. As should be expected, the

Mining methods and the environment 51

Figure 2.18 p. 123).

Schematic diagram showing the longwall retreat mining (source: Chadwick et al., 1987,

removal of the roof supports will result in the collapse of the roof in the area from where coal has earlier been removed. There are two basic variations of longwall mining – longwall advance where the face is moved into the seam away from the entry area, or longwall retreat, where the face is opened up at the boundary of the seam, and worked backwards towards the original entry point. Figure 2.18 (source: Chadwick et al., 1987, p. 123) is a schematic diagram of longwall retreat mining. The principal advantages and disadvantages of the longwall mining vis-à-vis room-and-pillar method, are summarized as follows (source: Chadwick et al., 1987, p. 124). Advantages (1) Higher overall recovery of in situ coal reserves, (2) Lower cost of timber supports, roof bolts, etc., (3) Greater productivity since fewer personnel are needed for equivalent coal production, (4) Improved efficiency in ventilation as an extensive system of “first workings” is not needed, (5) Can cope with weak strata and with mining at great depths, (6) Better protection for operating personnel at the working face. Disadvantages (1) The equipment needed for the purpose is expensive, and needs a large capital outlay, (2) Since the working mine faces are large and few in number, the stoppage of work at a single face may mean a large drop in the total mine output, (3) Large

52

Mineral resources management and the environment

haulage capacity is needed over a single line to transport coal from the mine face to the top, (4) Cannot cope efficiently with thick seams, or geological irregularities in the seam, (5) Will always produce subsidence at the ground surface. Irrespective of the method of mining used, a mine should have good ventilation. The purpose of the ventilation in a mine is not only to provide fresh air to the work force, but also to cool the work face and remove dust and noxious gases. Ventilation is generally provided by powerful fans (pressures upto 6 kpa) located at the surface. Fresh air is circulated through the mine from one entry, and the exhaust is removed through another entry. Surface subsidence invariably accompanies longwall mining. Similarly, surface subsidence can be expected to take place when most or all the pillars in the roomand-pillar method are moved. Surface subsidence can, however, be minimized by sand stowing under pressure or back filling with gangue material or the new technique of emplacement of paste. Tailings are being increasingly used for mine backfill or surface stackings. This would require a very high solids content. Previously, tailing dams have been used for water recovery and solids disposal. Paste thickeners have long been used by the alumina industry and the thickener technology is being applied to mineral industry as a whole. Deep cone thickeners are used to produce pastes with over 70% solids, suitable for backfill and stacking. 2.4.3

Special problems of underground mining of coal

The underground mining of coal has some special problems of critical importance: 1. Seam gas: Coal measures may have large contents of methane (also called “fire damp”). Historically, methane explosions have caused several of the worst mining disasters in the world. The methane hazard can be minimized by the appropriate design of the workings and equipment, sufficient ventilation and drainage of methane gas. Continuous monitoring of the gas emissions is necessary to alert the workers before the gas concentrations reaches dangerous levels. On the basis of in situ gas pressure, flow rate (in terms of m3 per tonne of ROM coal), and the chemical composition of coal, it is possible to predict the likelihood of gas emissions, and incorporate this aspect in the mine design. 2. Cleat of coal: Cleat refers to the fractures in the coal seam. The existence of cleats in a seam can assist in the winning of coal in the course of longwall mining. Cleats have a bearing on porosity and permeability. Consequently, underground openings driven parallel to the orientation of cleats, may be characterized by higher rates of water and gas seepage. 3. Roof and floor of the seam: If the roof of a seam is composed of thick strata of strong, well-cemented, unfissured sandstone, it may not cave. This is an important consideration in longwall mining. 4. Liability of coal for spontaneous combustion: In the presence of air, coal may get oxidized, releasing energy. If the air flow is sufficient to oxidize coal, but not sufficient to remove the heat generated, spontaneous combustion may take

Mining methods and the environment 53

place. Spontaneous combustion may occur underground, or on the surface (such as stockpiles, storage bins or spoil tips). It can be prevented by isolating the broken coal from air flow or by compaction. The tendency of a given coal for spontaneous combustion could be assessed from the degradability of coal, and rank of coal. 5. Swell factors: A unit mass of coal will occupy a greater space after excavation. The density of mined coal will hence be lower than the same coal in situ. This factor has to be taken into consideration in the transportation and storage of coal, and in backfilling the excavations. 2.5

MASS MINING

The methods of opencast (Chap. 2.3) and underground (Chap. 2.4) mining have been explained in terms of coal. In contrast, the mass mining method (Chap. 2.5) is unrelated to coal – it is essentially used for mining metallic minerals. The method of mining through block caving is shown in Figure 2.19 (UNEP Tech. Rept. No. 5, 1991, p. 13).

Figure 2.19

Mining by block caving (source: UNEP Tech. Rept., No. 5, 1991, p. 13).

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Mineral resources management and the environment

Mass mining is underground mining by caving. Table 2.8 (source: Mining Mag., July, 2001) lists the important mines in the world where different kinds of caving operations (block caving, panel caving, sublevel caving, sublevel and longhole stoping and vertical crater related) are practised. As in the case of open-pit mining, advances in underground mining are predicated to the achievement of the following: (1) With increase in the scale of production, the output will have to come from limited number of places, (2) There should be minimal time-lag between the development and extraction (just-in-time delivery), (3) Increasing dependence on a small fleet of sophisticated machines, (4) In view of the large scale of the mining operations, the consequences of misjudging the geologic environment can be severe and extremely expensive. Hence it is critically important that the geological structure, and the geotechnical characteristics of the rock strata should be clearly understood beforehand. According to Hustrulid (2000), any mining system should satisfy the requirements of high production, competitive cost, safety and teamwork. The choice of an appropriate cost-effective mining system would depend upon the scale of mining, mine design/layout, equipment selection, sequencing, etc. Technology is no doubt a powerful tool to reduce costs, but as new technologies tend to spread fast, everybody has access to the same technology sooner or later. In order to stay competitive, the mining engineer should understand his deposit more closely, and customize the tools/techniques employed/employable to suit the specific conditions in his mine. 2.5.1

Equipment automation

Though mobile mining equipment represents only a small portion (about 10%) of the costs of a mining project, the mine’s performance and profitability are critically dependent upon the choice of the mobile equipment technology. Mass mining is different from small-scale mining or artisanal mining in that it has to provide for the efficient and continuous movement of large quantities of material produced (say) through block caving. Automation is hence an inevitable concomitant of massive mining. In order to get the best out of the automated mobile equipment, it needs to have trained personnel, supportive infrastructure, monitoring and information transfer systems, established working procedures, etc. Puhakka (2000) gave an account of the OPTIMINE simulation tool for the selection of mobile fleet. The tool combines the performance capabilities of the machines with operational knowhow and the mine environment, to optimize the performance of the mobile fleet, scheduling of work, and fine-tuning the layout of the mine. OPTIMINE can be used to identify the effect of a particular change (say, one additional turn in a continuous loading cycle) to the daily capacity. Pukkila and S
arkká (2000) developed the software for Intelligent Mine. This includes the mine-wide information and data acquisition system, high-speed two-directional mine-wide communication network for monitoring and control, mine planning, automated, and tele-operated machinery connected to the information network, etc.

Mining methods and the environment 55 Table 2.8

Mines/projects included in Massmin proceedings (source: Mining Mag., July, 2001).

Mine

Country

Product

Block cave Bingham Canyon Bulfontein Didipio DOZ Ertsberg Henderson Kings (Gaths) Mont Porphyre Nothparkes Palabora Premier Salvador Sao Tomas II Shabanie Tongkuangyu

US South Africa Philippines Indonesia Indonesia US Zimbabwe Canada Australia South Africa South Africa Chile Philippines Zimbabwe China

Copper Diamonds Copper Copper/gold Copper/gold Copper/molybdenum Asbestos Copper/molybdenum Copper/gold Copper Diamonds Copper Copper Asbestos Copper

Panel cave Premier El Teniente

South Africa Chile

Diamonds Copper

Sublevel caving Big Bell Kiruna Obuasi Perseverance Shabanie Trojan

Australia Sweden Ghana Australia Zimbabwe Zimbabwe

Gold Iron ore Gold Nickel Asbestos Nickel

Sublevel and longhole stoping 777 Anqing Brunswick Cannington Enterprise George Fisher Golden Grove Jinchuan Mount Charlotte Mount Isa Obuasi Olympic Dam Target

Canada China Canada Australia Australia Australia Australia China Australia Australia Ghana Australia South Africa

Copper/Zinc Copper Pb/Zn/Ag/cu Ag/Pb/Zn Copper Pb/Zn/Ag Copper/zinc Nickel Gold Copper Gold Copper Gold

Vertical crater retreat Mindola

Zambia

Copper

56

Mineral resources management and the environment

The lessons learned through the use of Intelligent Mine software have been used in Outokumpu’s Kemi chrome mine in Finland. Kay (2000) explains how the digital blasting technology developed by M/S Orica can revolutionize mass mining. The new technology allows large and complex blasts to be fired routinely and with minimum of risk. 2.5.2

Case histories of mass mining

Block caving is most suitable to mine large, low-grade deposits where high production is needed to maintain profitability. It has both advantages and disadvantages. It has emerged as the lowest cost underground mining method, but it is characterized by high technical, social, political and environmental risks, and high up-front capital and development costs (ranging from USD 100 to 1000 million). Thus, a decision for block caving has to be taken after a detailed consideration of the risks involved (Heslop, 2000). Block caving is like an elephant. An elephant eats a lot, but can do a lot (such as, transporting large logs of wood in inaccessible forest areas). Wisdom therefore lies in making use of the elephant most efficiently. The Northparkes copper – gold porphyry deposit in New South Wales, Australia, comprises two open pits, Endeavour 22 (E22) and 27 (E27). E26 is the first mine in Australia to employ block caving, and is said to be the most productive underground mine in the world (the Endeavour 26 mine achieved the phenomenal productivity of 42,600 t of copper/gold ore per underground employee, including the contractors!). The orebody comprises a moderately to well-jointed rock mass. The top 480 m of orebody is currently being exploited by block caving, with the undercut having dimensions of 196 m in length and 180 m in width. When cave inducement was needed to maintain caving, hydraulic fracturing was used as a cave inducement tool, using the exploration boreholes located midway up the current lift. This proved highly successful, and yielded more than 7 Mt of ore at a significantly lower price than for conventional cave inducement techniques. More importantly, this led to a better understanding of how to use the geometry, growth and influence of hydraulic fracture networks to induce caving. Construction of the second block cave (Lift 2) of Northparkes is due to be completed in 2003/2004. It will produce about 5 Mt/y for 6 years. Block caving minimizes the operating costs, and maximizes the mine value. Lift 2 continues the same design philosophy as lift 1, namely, low maintenance, continuous flow of ore, constructability, and minimized capital. Some design changes have been made for lift 2 to improve the caving response. These include “enforced regular-shaped, undercut footprint, and the implementation of a narrow inclined advanced undercut”. There are technical and capital cost benefits in having a single lift cave (rather than a dual lift cave) for the remaining reserves of E26. Besides, the higher lift promotes greater secondary fragmentation, and haulage by inclined conveying layout is more economical than shaft construction alternative (Duffield, 2000).

Mining methods and the environment 57

The Premier Mine in South Africa is a well known kimberlite-hosted, diamond mine. It is one of the great cave mines in the world. The kimberlite pipe is emplaced in a sequence of quartzites and norites. The greatest risk facing the mine is the geotechnical challenge of mining a weak rock at great depth. The new block cave will be at a depth of 1000 m, about 300 m deeper than the current operations. The geotechnical considerations which were taken into account in mine planning and layout, include the “hydraulic radius needed to initiate caving, fragmentation, drawpoint spacing, secondary blasting, and possibilities of seismicity” (Bartlett & Croll, 2000). Mont Porphyre in Quebec, Canada, is a large tonnage, low-grade coppermolybdenum, porphyry deposit. It is located at a depth of 1–1.7 km below the surface. As it is characterized by a very competent rock mass, it was felt that caving mining is not a viable option. But the present view is that any thing will cave if sufficient area is available for undercutting. Noranda which owns Mont Porphyre property has sponsored an International Caving Study to assess the techno-economic viability of cave mining of competent orebodies. The El Teniente copper mine, Codelco, Chile, is a good example of the use of panel caving (Diaz & Tobar, 2000). Mass caving methods are employed to produce 95,000 t/d of ore to the mill from a number of sectors underground, each sector being virtually a large mine. The current panel caving method faces problems of high seismicity level, coarse fragmentation and ore pass damage. Caving is initiated by undercutting the base of the block or panel by blasting. Instead of incorporating massive areas as in block caving, the panel caving is accomplished by continuous blasting. Caving is followed by the excavation of the drawbells, which are designed on the basis of geometry, dimensions and sequence of excavation, the size of the fragmented ore, etc. The drawbells are suitably adjusted to take care of mining problems that may arise, such as major rock bursts, and collapse of the production facilities. Caving operators are mortally scared of the hang-ups, because of the devastating air blast that they could trigger when they collapse. On Dec. 5, 1999, a planned collapse of 15,000 m2 arch that was formed in Codelco’s Salvador division produced a massive air blast. The damage from the air blast was minimized by maintaining the drawpoints and their drifts full and covered with ore, maintaining permanent seismic monitoring networks, and instant communication with personnel. In the Henderson molybdenum mine in Colorado, USA, mining has to be done about 2 km below the ground, with attendant problems of rock stress. The production of 36,000 t/d of ore through caving, involved a number of challenges: finding experienced staff, rock bursts, poor mining conditions, inflow of 50 °C water, raise boring and muck handling, etc. Apart from installing a conveyor system, Henderson was the first mine in the world to use the 100 t Sandvik Tamrock Supra 0012H trucks. The trucks have high productivity, long life and can accommodate both pullthrough and back-in chutes. The maintenance costs can be minimized through good haul roads, and traffic control to minimize queuing delays will enhance the productivity of the trucks.

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Mineral resources management and the environment

A chrome deposit in Zimbabwe has been mined to a depth of 80 m by what has been termed as vertical pit mining (Redford & Terbrugge, 2000). This is an alternative mining method for the exploitation from surface of small, vertical or near vertical orebodies. A conventional open pit is uneconomic due to the high waste: ore ratios. Reduced environmental impact and rehabilitation requirements constitute additional benefits. The sides of the vertical pit are maintained by systematic lateral support. 2.6

OFFSHORE MINING

Table 2.9 (source: G.J.S. Govett and M.J. Govett, World Mineral Supplies, Elsevier, Amsterdam, 1976) lists the various minerals obtained from the oceans, and their value in (millions of USD), also expressed in terms of the percentage contribution from the ocean supplies. Lime shells, titanium sands and tin are mined from shallow coastal, often estuarine waters. Offshore mining is related to the mining of heavy mineral placer deposits occurring on the beaches, lagoons, inshore sediments, etc. Manganese nodules (which contain Mn, Cu, Ni, Zn, Pb, etc.) occur in deep-sea areas, and their mining has not yet become commercially viable. India has staked claims over an area of 150,000 km2 of manganese nodules in the central Indian Ocean. The richest site here contains 21 kg of nodules per sq.m. as against 3.5 kg in the Indian Ocean elsewhere. Various Indian organizations are currently evaluating the techno-economic feasibility Table 2.9

Minerals from the oceans. Production value (in millions of USD), 1972

Percentage from oceans

10,300 4,200

18 33

Surface deposits Sand and gravel Lime shells Tin Titanium sands Iron sands Barite

100 35 53 76 10 1

1 80 7 20 1 3

Subsurface bedrock Coal Iron ore

335 17

2 1

Extraction from seawater Salt Magnesium and compounds Bromine Heavy water

173 116 19 27

29 51 30 20

Subsurface Petroleum Gas

Mining methods and the environment 59

of mining the nodules. It has been estimated that the hydraulic mining of Mn nodules at the rate of 1000 tpd, would entail the disposal of about 9000 tpd of sediments. Placer deposits form when heavy minerals get concentrated in detrital materials due to the action of moving water, waves, or wind. Some of the important heavy minerals, which form placers, are: gold, diamonds, cassiterite (SnO2, with 78.6% Sn), ilmenite (FeTiO3, containing 48.6 to 57.3% TiO2), rutile (TiO2), Zircon (ZrSiO4, with 67.2% of ZrO2), monazite (Ce, La, Di, PO4, with Th and U), etc. The main methods used in the mining of placers are the following: (a) Land-based plants: (1) Bucket scraper and wire-line, (2) mobile equipment such as dozers, draglines, shovels, bucketwheel excavators and trucks, (3) Hydraulic mining, where water under high pressure is used in loosening in situ material, (b) Floating plant: (1) dragline and washing plant, (2) hydraulic dredging, (3) bucket line dredging Marine mining of heavy minerals (ilmenite, monazite, etc. in India, cassiterite in Malaysia, and diamonds in Namibia, etc.) involves dislodgement, lifting, shipboard processing and/or overflows). Strip mining on the sea floor brings about changes in the bathymetry of the sea floor, coastal erosion, physical removal of organisms, changes in the particle size, depletion of oxygen, and formation of free sulphides. The environmental impact of discharge of slurry of fines and tailings from a mining vessel is indicated in the form of matrix diagram (Table 2.10; source: “Marine mining of the Continental Shelf ”). Marine mining causes coastal erosion, and hence no mining is allowed near the coast (in the case of U.K., it is 5 km from the coast). In the coastal area of the tropics (e.g. coast of Gujarat, western India), salt is produced by the solar evaporation of seawater. The saltpans are developed over the tidal flats which have hard impervious substratum or semi-consolidated clayey Table 2.10 vessel.

Environmental impact of the discharge of fines and tailings from the offshore mining

Potential direct or indirect impact

Water quality

Phytoplankton

Zooplankton

1. Suspended solids and turbidity dispersion 2. Reduction of sunlight in the water column 3. Oxygen demand from sediment dispersion 4. Release of nutrients 5. Release of pesticide 6. Interaction of fines with the marine organisms

D

D

D

D

D

D

D – Detrimental; B – Beneficial

D B D

Benthos

Shell fish

B D

Adult fish

D

D B D D

Juvenile fish

B D

B D D

D

D

B D

B D

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Mineral resources management and the environment

deposits. The saltpan development has the following environmental impacts: (1) only common salt (NaCl) is recovered. The supranuant fluids containing the chlorides and sulphates of magnesium, chloride of calcium, and bromide of potassium, etc. are discharged back into the coastal waters, thus affecting the marine biota, (2) the soil around the salt pans gets salinised, (3) agricultural land near the coast is brought under salt pan development, (4) the estuaries and creeks may get polluted due to toxic industrial effluents (containing cadmium, chromium, mercury, etc.), or pathogens from municipal sewage which are discharged into the sea at high tide. Since seawater for making salt is pumped from the sea at high tide, the pollutants may find their way into the extracted salt (Wadhwan, 1988). Gravel and sand are bulk commodities of low unit cost. It is hence not economic to transport them for long distances. Mining of gravel and sand from the beaches and barrier bars for use in construction in the nearby towns (say, in Gujarat referred to above) disturbs the shoreline equilibrium and beach nourishment, and causes severe beach erosion. Even as it is, the damming of the rivers and streams on the upstream side has reduced the discharge of sediment into the sea, and when this is compounded by the mining of the beach, the consequences can be disastrous and irreversible. 2.6.1

Mining of diamonds in the inshore sediments of the SW coast of Africa – a case study

The erosion of the diamondiferous kimberlite pipes of South Africa have led to the dispersal of diamonds, which now occur in the form of placers in the alluvial, aeolian and beach and inshore sediment environments. Along the southwest coast of Africa (e.g. Namibia), diamonds occur along the so-called “oyster line” (though the diamonds have nothing to do with oysters, they happen to occur in the shallow zone where the oysters also occur). The barge-mounted diamond recovery plants custom-designed by M/S Bateman, Boksburg, Republic of South Africa, have proved reliable and efficient. The plant consists of four modules – primary screening, dense media separation (DMS), preX-ray treatment, and final diamond recovery. The DMS plant for the separation of diamonds uses water-ferrosilicon (FeSi) suspension as the flotation medium. The density of the ferrosilicon-water mixture in the units is accurately controlled by the use of nuclear density control systems. The recovery module utilizes a wet X-ray sortex machine for the size range of 2 mm to –16 mm gravel. The use of wet X-ray sorting avoids the need to dry the concentrate before feeding it into the recovery plant. The 2 mm gravel is treated over a vibrating grease table. The 16 mm material is hand sorted in glove boxes. The material on the seabed is composed of a mixture of clay, boulders, sand, gravel, heavy minerals, foam and diamonds. It is airlifted as a slurry containing between 1% and 3% solids, which is then fed into the primary screening module. Some plants (e.g. Kovambo which operates along the Lauderitz coast off Namibia)

Mining methods and the environment 61

has a capacity of 3800 m3/h of slurry. The multistage vibrating screens allow most of the clay to be scalped off and discharged back into the sea. It is critically important to remove as much clay as possible – otherwise it can clog up the screens, trap the diamonds which may be rejected with the floats in the DMS circuit, increase FeSi consumption in the DMS unit, and make materials handling difficult. The sized gravel produced by the screens is pumped to the surge bins by means of a jet pump. In the process of pumping, much of the remaining clay gets removed. The scrubber-mill is so programmed as to retain the grinding charge (autogenous, using ceramic balls), while allowing the diamond bearing gravels to be quickly flushed through the system. Such a process avoids the exposure of diamonds to high energy impact, or long retention times which could damage the diamonds. The scrubber mill gets rid of the small quantities of clay that may still be in the system. The recovery plant is the heart of any diamond process plant, and the following security measures are incorporated into the system to prevent theft of diamonds: TV monitoring system, air transportation of the X-ray concentrate into the sort house, card access system coupled with lie detectors, and sealed glove boxes. 2.6.2

Offshore exploration for cassiterite in Thailand – a case study

When exposed to humid tropical weathering, the cassiterite-bearing granitic rocks disintegrate into quartz sand, kaolinitic clay, and unbroken grains of cassiterite. Rain-wash and fluviatile action transport the weathering products over distances, which are determined by topography of the land, grainsize and specific gravity of the minerals. Cassiterite grains get concentrated at the valley bottom. When the river valleys are drowned by sea level rise, the cassiterite-containing sands are reworked by wave action and concentrated. Evidently, the tenor and dimensions of a deposit depend upon the mode of formation of a deposit, which in its turn determines the method of exploration of the deposit. There are four types of cassiterite deposits in Thailand: (1) The Valley bottom type – this is most common. (2) The more truly residual type, with very little horizontal transport of heavy minerals (e.g. offshore at Thai Muang), (3) The Colluvial type, with little transport and little outwash, giving rise to small deposits with limited concentration of heavy minerals, e.g. Phuket Island and offshore, (4) The sheet flood or avalanche type, with long transport distance and reworking by fluviatile and marine action, e.g. Ramong area. For purposes of exploration, a platform on a pontoon and a drilling unit are needed. The pontoon may be built in a variety of ways: bundles of bamboo poles, and horizontal oil drums, two fishing boats, connected by wooden beams, steel floats interconnected by steel beams, twin-propeller elevation pontoon, commercial vessel with schottel propeller, or twin-propeller pontoon. In thin sediment layers (1 m), hand-bailed Banka drill is used. For sandy layers 5 to 25 m in thickness, the rammed-down casing of the Becker drill is most efficient (Aleva, 1978).

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Mineral resources management and the environment

ARTISANAL MINING The contribution of small-scale or artisanal mining to the overall mining output in the world is estimated to be 10–16%. In general, the percentage contribution with respect to industrial minerals is higher than for metallic minerals. Estimates vary widely about the number of persons involved in artisanal mining (upto 16 million). In some countries, the contribution of artisanal mining is of considerable economic significance. For instance, Peru has about 3000 small-scale mines which produce 100% of the antimony, 90% gold, 15% tungsten, etc. of the national production (Gocht, 1980, Natural Resources and Development, v. 12, p. 7–18). About 90% of Brazil’s gold production is attributable to artisanal mining. Capital-intensive, mechanized mining is not cost effective for the exploitation of small deposits, even of high grade. Such a deposit is amenable to small-scale mining, particularly where the deposit occurs at or close to the surface, and where the mineral could be won by simple methods, such as hand-picking, panning, sluicing, etc. It therefore follows that artisanal mining may be a cost-effective option in the case of several economic minerals occurring in the soil. For instance, by the nature of its occurrence and its properties, opal can only be mined manually. Small-scale mining has several advantages: it is labor intensive, can be initiated on any scale, with simple technology, at low capital cost, low consumption of energy, and short lead time, and without expensive imported equipment. It can also promote local industries. This, however, does not mean that small-scale mining is the panacea for the problems of the developing countries. Artisanal mining suffers from the following serious disadvantages: (1) it tends to be haphazard, since in most countries there is no systematic exploration activity to support small-scale mining; (2) destructive exploitation by the gouging of rich pockets; (3) low recovery rates; (4) low labor productivity (about 4% of highly mechanized mines); and (5) non-extraction of valuable byproducts which are therefore irretrievably lost to the country. In future, vegetative methods of reclamation of mined land may emerge as a significant, economically viable, and employment-generating activity. 2.7.1

Mercury pollution due to artisanal gold mining

Artisanal gold mining using mercury amalgamation has serious adverse implications for human health, and the integrity of the ecosystems. Usually, 6–8 kg of mercury is used for amalgamation to extract one kg of gold. Simple squeezing and sublimation recover most of the mercury, but about 1.5 kg of mercury is irretrievably lost to the environment per kg of gold extracted (the Brazilian average is 1.32 kg of mercury). This leads to mercury pollution in soils, sediments, waters, and biota. The bacteria (such as, Enterobacter aerogenes and Escherichia coli) present in the soils, sediments, human faeces, etc. convert the metallic mercury to the highly toxic form of methyl mercury. Mercury compounds may enter the human body through inhalation, ingestion of food and water, and transfer through the skin.

Mining methods and the environment 63

The intake and uptake of mercury is highly species sensitive. The organomercury, particularly methyl mercury, CH3 Hg, is more easily absorbed and is far more toxic than elemental mercury (Hg0) and divalent inorganic mercury (Hg2). In the food chain, methyl mercury gets concentrated in fish (about 80% of mercury in fish is in the form of the more toxic methyl mercury). The FAO/WHO permissible tolerable level of mercury exposure has been set at 0.3 mg/week, with methyl mercury constituting not more than two-thirds of it (i.e., 0.2 mg). Artisanal gold mining using mercury amalgamation has increased markedly in developing countries, such as Brazil, Tanzania, Zimbabwe, Philippines, Indonesia, China, Vietnam, etc. involving about 10 million people. According to Akagi (1998), there are 2000 goldfields (or “garimpos”) in the Amazon Basin in Brazil, involving about 650,000 gold miners (or “garimpeiros”) according to official reports. Since many of the garimpeiros are illegal miners, the actual number may be 1–1.2 million. The amount of mercury released into the environment annually is of the order of 130 t – about 45% of it is released into the river systems, and 55% into the atmosphere. The total amount of mercury released to the environment since 1980s is a mind-boggling figure of 2000–3000 t. There are two types of garimpos: the lowland garimpo where the garimpeiro digs a large hole in the ground to excavate the auriferous alluvium, and the raft garimpo where a motorized suction pump collects the god-bearing sediment from the river bed. There are two main pathways of mercury to man – in the gold mining areas, gold miners and gold shop workers are exposed to metallic mercury through inhalation. In the secondary environments, the metallic mercury would get methylated, and enters the food chain (say, fish) as more poisonous methyl mercury. The fish-eating populations who may have nothing to do with artisanal gold mining, are hence at risk. Akagi and Naganuma (2000) reported the mercury concentrations in hair, blood and urine of persons in Jacareacanga and Vila Novo Sitio, which are fishing villages, and Alta Floresta, which is the main trading centre in the Tapajos River basin in Brazil. (Table 2.11; source: Akagi & Naganuma, 2000).

Table 2.11 Concentration of methyl mercury in the hair, blood and urine of the inhabitants of the Tapajos River Basin, Brazil. Origin

Sample

Me-Hg (ng/mg)

Total Hg (ng/mg)

Me-Hg/ Total Hg (%)

Jacareacanga

Hair (ppm) Blood (ppb) Hair (ppm) Blood (ppb) Hair (ppm) Blood (ppb) Urine (ng/g, creatinine)

24.1 90.0 27.3 131.9 4.2 9.0 0.4

24.6 90.4 28.8 130.7 5.2 12.2 165.7

96.0 97.2 95.7 98.8 86.0 72.2 0.3

Vila Novo Sitio Alta Floresta

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Mineral resources management and the environment

In the Tapajos River, the mercury levels in fish ranged from 0.08 to 3.82 ppm (the permissible level in Brazil is 0.5 ppm). In the case of fish-eaters, mercury present in hair and blood is almost wholly in the form of methyl mercury. There is clear evidence that the inhabitants of fishing villages have been exposed to abnormally high methyl mercury levels due to the consumption of fish. On the other hand, the ingestion of metallic mercury by gold miners and gold shop workers shows up in urine. Levels of mercury in hair samples were more for males than females. Since hair grows fast at the rate of about one cm per month, the longitudinal analysis of mercury along a strand of hair provides timing of the exposure of individuals to methyl mercury. Such a study of the long hair of the women showed that they were exposed to methyl mercury during the fast few years, with an increasing trend with time. East Africa is another major area concerned with artisanal gold mining (van Stratten, 2000 a, b). Tanzania and Zimbabwe produce about 5 t of gold each from artisanal mining. It has been estimated that 200,000 to 300,000 persons are involved in small-scale gold mining activities in Tanzania, and more than 200,000 persons in Zimbabwe. For every 1 g of gold recovered, 1.2–1.5 g of mercury is lost to the environment (about 70–80% of Hg is lost to the atmosphere due to processing, and 20–30% in tailings, soils, stream sediments, etc.). Approximately 3–4 t of Hg is released to the atmosphere in the Lake Victoria goldfields, and
3 t in Zimbabwe. Mercury in soils and sediments is in the form of metallic mercury. The dispersal of Hg in soils and sediments is limited (laterally 260 m, and vertically 20 cm). Urine analyses show that about 36% of the gold miners working with amalgam exceeded the WHO limit (of 50 g/g creatinine). Concentrations in fish were low, and
90% of the hair samples from the fish-eating populations showed 2 g/g T-Hg. Highest Hg concentrations were found in the fish caught in the rivers draining the gold mining sites, and southern shores of Lake Victoria. Among the fish, lungfish species (Protopterus aethiopicus) have the highest concentrations, and tilapia (Oreochromis niloticus) the least. The amount of mercury pollution in Tanzania is estimated to be of the order of one mg/m2 annually (Aswathanarayana, 1995, p. 177). The critical organs affected by mercury intoxication are the lungs, kidneys and the brain. The effects of mercury on the respiratory tract are coughing, bronchial inflammation, chest pain, and in severe cases, respiratory arrest. Methyl mercury causes the disintegration of cells within the brain, and consequently affects the sensory, visual, auditory and coordination control functions of the brain. This leads to loss of coordination in walking, slurred speech, loss of hearing, blindness, coma, etc. (Fergusson, 1990, p. 542). 2.7.2

Innovative technologies suggested

It is possible to improve the efficiency of small-scale mining, while concomitantly reducing its deleterious consequences, by the adoption of the following innovative

Mining methods and the environment 65

approaches: 1. Developing simple techniques of prospecting which could be used by semiskilled labor, e.g. use of smoky quartz as indicator of cassiterite-lepidolite pegmatites, and looking for cassiterite resistate in the soils near pegmatite. Training of miners on-site about simple methods of mineral search and extraction. Using a portable X-ray fluorescence analyzer, it is possible to make a quick and fairly accurate on-site assay of several ore metals in the material mined or to be mined by a miner. Such an assay can serve two purposes: (1) to make the miner aware of the economic value of the material already mined by him (through a knowledge of what kind of ore metals and in what concentrations occur in the material mined by him), and (2) to advise him as to what kind of material he should be mining in order to get greater returns. 2. Research and development to design improved methods of ore search and ore extraction relevant to small-scale mining. Placer gold is a case in point. An artisanal miner can extract gold only if it is coarse grained (say, 30 m) and high grade (say, about 25 g/m3). He uses the mercury amalgam method of extraction which is highly polluting. New carbon-in-pulp and carbon-in-leach technologies have several advantages: (i) they are capable of extracting fine-grained gold (about 10 m) and at low concentrations (about 2 g/t); (ii) they are environmentally benign. These technologies need to be adapted for small-scale operations. In extremely dry areas, pneumatic methods of gold separation have to be developed. 3. Using mobile units for preconcentration and extraction on site: truck-mounted, diesel-powered, self-contained, ore-dressing modules are taken to the site of the artisanal mining and the ore is concentrated/extracted on site. The mobile unit can be owned and operated by a cooperative or a private company. A part (say, one-third) of the output could be collected in kind towards service charge due to the mobile unit and the royalty due to the government. As the recovery rates by the mobile unit are at least 2–3 times higher than by manual methods, the artisanal miner is still left with considerably more saleable material than he would have been able to recover on his own. 4. Through the use of the mercury amalgam method, artisanal gold mining industry in Tanzania has severely contaminated the waters and soils. About 78% of the water samples analyzed contained concentrations of mercury higher than the permissible level of 1 g/l. Mercury levels in the mine tailings range from 1.31 to 18.7 g/g. The Institute of Production Innovation of the University of Dar es Salaam, Tanzania, has developed a rugged, easy to handle, highly portable and locally manufactured, and inexpensive (eq. USD 50) retort which has efficiency of 99.6 –100%. The use of such a retort is the most effective way to reduce the pollution of airborne mercury produced by the firing of the Au–Hg amalgam (Mpendazoe, 1995). 5. The “Portable” gold plant developed by Libenberg, Rundle and Storey of San Martin mining company (Mining Magazine, July 97, p. 8–10) is a veritable

66

Mineral resources management and the environment

godsend for small-scale gold miners. The salient points of the plant are as follows: San Martin’s claims encompasses two dumps around Bonda, Kenya, with 250,000 t of material, grade: 1–3 g/t. Carbon-in-pulp/carbon-in-leach technique; Capacity of the plant: 10,000 t/month; production cost: USD 150/oz. The total steel requirement (12 t) for tanks, baffles, agitator mountings, and the pumps and piping, were brought from South Africa in one container and erected on site. Dump material is reclaimed by high-pressure water. In the first leach tank, lime (5 kg/t) and sodium cyanide (0.5 kg/t) are added. The residence time in each of the absorption tanks is approximately 1.3 hr at a throughput of 10,000 t/month, and carbon concentration of 15–20 g/l. The eluate is heated in a diesel-fired cast iron burner. Gold is recovered onto steel wool cathodes. Security is ensured by having the recovery cell protected by a 220 V inner cage, and 15,000 V outer cage (powered by solar cells). Doré is 80% pure. Total power consumption: 145 kw (diesel generators). Water is pumped from the Yala River (3 km from the plant). The plant has been in operation for more than a year and has the following advantages: environmentally-benign as no mercury is used; can be erected even in remote areas, and shifted and reassembled without much problem; can be operated with minimal expatriate assistance; economically viable. This technology can be used in two kinds of situations: (1) as a private enterprise, for treating dumps, where they exist, and (2) as a cooperative, by setting up the plant at a central place where a number of artisanal miners (50–100) operate. 6. The modular plants designed by M/S Bateman Project Holdings Limited, Boksburg, South Africa, have revolutionized the recovery efficiencies in artisanal mining of a number of minerals (such as, modular process plants for prospecting, sampling and small scale production of diamonds). The heart of the equipment is the Dense Media Separator (DMS) plant, which uses water-ferrosilicon mixture as the flotation medium. The density of the medium is automatically controlled. The smallest unit has a capacity of 1 t/h of diamondiferous gravel in the size range of 1–8 mm. The modular unit which has become very popular is 5 t/h DMS unit, which weighs only 4.5 t, and can fit into a standard 12 m container, with all the spares. It is custom-designed depending upon the kind of feed, assembled and tested. It is then dismantled and shipped to site. It can be erected on site in a day or two. The DMS modules are skid mounted and has built-in spillage pumps, and no concrete foundations are needed (see section 2.6.1 for further details).

2.8

LKAB IRON ORE MINE IN KIRUNA, SWEDEN – A CASE STUDY

The LKAB iron ore mines in Kiruna, Sweden, are located above the Arctic Circle. Two underground mines, located at Kiruna and Malmsberget, employ sublevel caving method, to produce 30 Mt/y of iron ore. Much of the mining operation is automated – for instance, the production drilling rigs, loading machines and transport systems on the new main haulage level are remote-controlled. The magnetite

Mining methods and the environment 67

ore is crushed, ground, screened and upgraded by magnetic separation techniques. The iron ore concentrate is pelletised using bentonite as a binder. The LKAB complex demonstrates how continuous improvements in technologies could bring about high productivity, while at the same time reducing water and air pollution (Nordstrom, 2001, p. 604–614). Mining and process water goes through large pond systems, to facilitate the removal of the sludge by sedimentation. The water is then pumped to the clarifying ponds from which the process water is recirculated. Since 1980, LKAB’s atmospheric emissions have been halved, while the production of pellets has doubled. The external energy consumption in the pelletising plants which was 639 MJ (million joules)/t of pellets in 1970 has been brought down to 250 MJ/t in 2000. The following air pollutants are produced in the process of pelletisation: 1. Fine dust, mainly composed of iron oxides, before induration, 2. Sulphur dioxide, from sulphur in the fuel, and sulphides in green pellets, 3. Hydrogen fluoride and hydrochloric acid from apatite residues in green pellets, 4. Nitrogen oxides, from nitrogen in the fuel and in the atmosphere. That the emissions in the pelletising plants in Kiruna are less than the statutory limits is evident from the following information: Parameter Particles Sulphur dioxide Hydrogen fluoride Hydrochloric acid

Statutory limit (g/t of pellets) 100 15 6 6

Emissions in Kiruna (g/t of pellets) 60 13 2 2

Noise is generated by ventilation fans, mining and transport equipment. The maximum noise level nearest to the dwelling should not exceed 40–45 dB (A). Blasting in mines produces vibrations in the bedrock in the surrounding areas. Noise and vibrations are measured continuously to minimize the inconvenience to property owners in the neighbourhood.

CHAPTER 3

Mode of occurrence of mineral deposits

The environmental impact of a given mineral industry depends upon the geologic setting, genesis and mode of occurrence of the mineral deposit, which in turn determines how the mineral is to be mined, and processed and how the wastes are to be disposed. This concept can be illustrated with two examples. Because of the nature of its genesis, bauxite, the ore of aluminium, is invariably a surface deposit, which is therefore mined by opencast methods. The major environmental impact of the bauxite industry arises from the need to dispose of the large quantities of red mud that are generated during the chemical treatment of bauxite to produce alumina. The mitigation of the adverse environmental impact consists in using the red mud to make useful products, and the rehabilitation of the mined land. On the other hand, underground methods are employed to mine vein deposits of (say) primary sulphide ores of base metals. Ore concentrates are produced from ROM through processes such as flotation. The adverse environmental impact arises from acid mine drainage (AMD) from the mine and waste piles, and SOx emissions and acid rain. These are mitigated by the use of scrubbers, and through the prevention and control of AMD, and by passive treatment of AMD through natural or constructed wetlands.

3.1

METALLIC MINERALS

The metallic minerals are divided into the following categories: 1. Precious metals: Gold, silver, Platinum group metals (PGM) 2. Ferrous metals: Iron, manganese, chromium, titanium, vanadium, 3. Non-ferrous metals: Molybdenum, copper, lead and zinc, tin, nickel, aluminium (some authorities designate a sub-group, copper, lead and zinc, as base metals) 4. Radioactive elements: Uranium and thorium For each metal, the following particulars are provided: principal ores and their composition, processes of concentration of ore elements needed to form ore deposits, and the important geological environments and locations in which the ore deposits occur in the world (Tables 3.1 to 3.9, partly after Smirnov, 1983).

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Table 3.1

Gold and Silver. Processes of concentration of ore elements to form ore deposits.

Element

Important ore minerals, and Processes of concentration to form ore deposits

Important geologic environments

CA: 4.5 ppb, CC: 2000.

Archaean greenstone belts (
2.5b.y.)(e.g.Yellowknife (Canada); Proterozoic, palaeoplacers (
2.2.b.y.), reworked and mobilized (e.g. Witwatersrand, South Africa), Subduction-related, island arc volcanism (e.g. Bougainville, PNG), Laterites in the greenstone belts (e.g.Tanzania); Placers (e.g. Nome, Alaska, USA).

Gold

The most important commercial mineral of gold is native gold. Though several intermetallic compounds with Ag (electrum – Au, Ag), Sb, Pt, Te, etc. are known, they have no significant role in Au production. Mantle-derived mafic-ultramafic rocks have the highest gold contents (upto 10 ppb). In the endogenous environments, gold may be mobilized and transported in the form of thiosulphate complexes [Au(S2O3)]3, which result in coarsely crystalline gold alloyed with 50–75% Ag, and  chloride complexes (AuCl 2 and AuCl2 ) which tend to be reprecipitated with concretionary Fe oxides with 0.5 wt.% of Ag. In the exogenous environments, Au may be transported as Au-humate complexes, and may end up as very fine lateritic gold. Alluvial placers of gold are of considerable economic importance and are the mainstay of artisanal gold mining Silver

CA: 50 ppb, CC: 1000. Native silver (80–100% Ag, with upto 10% Au), Argentite (Ag2S – Ag: 87.1%), Pyrargyrite (Ag3SbS3 – 59.8%), Proustite (Ag3AsS3 – 65.4%), Polybasite (Ag, Cu) 16 Sb2 S11; 62.1–84.9%), and Stephanite (AgSbS4 – 68.3%)

Volcanogenic hydrothermal deposits: Ag-Au Comstock (USA), Ag sulphide: Casapaslca (Peru); Ag-Sn: Potosi (Bolivia); Ag-As: Gowganda (Canada)

Insignificant variation in abundance from acidic to basic rocks (50–70 ppb). Commercial concentrations through post-magmatic thiosulphate and chloride complexes. Under exogenous conditions, silver sulphate or thiosulphate may be redeposited at depth as native silver or halides. Placers are unimportant. CA.: Crustal Abundance; CC * Concentration Coefficient.

3.2

INDUSTRIAL MINERALS

The industrial minerals have some common features: (1) Most of the industrial minerals are of secondary origin, and are mined by opencast methods, with the exception of some minerals such as fluorite and rock salt, which are unstable in the surficial environment, (2) They are produced in large quantities – their world production (about 2.5 billion tonnes, not counting the huge quantities of building stones, for which the records are rarely kept in many countries) is more than double that of

Table 3.2 PGM

Platinum Group Metals (PGM).

Platinum Group Metals (PGM) include Pt, Pd, Ir, Rh, Os, and Ru. CA: varies from 5 ppb for Pt to 50 ppb for Os. CC: varies from 1000 for Pt to 50 for Os. PGM form native elements, disordered solid solutions, intermetallic compounds, arsenides and sulphides, such as, Polyxene – Pt, Fe: 77–89% Pt), Sperrylite PtAs2 (56.5% Pt), Laurite (RuS2: 61–65% Ru), etc. Closely associated with mafic and ultramafic igneous rocks. Separation of PGM due to liquation and fractional crystallization. Hydrothermal deposits of PGM are rare. Pt forms disordered solid solutions and intermetallic compounds, arsenides and sulphides. In the ultramafic rocks, PGM concentrations are directly related to the abundance of ortho- and clino-pyroxenes. Besides, the Pt/Ir ration is controlled by CPX/OPX ratio.

Early magmatic deposits – e.g. Merensky Reef within the Bushveld Complex, South Africa; Late magmatic deposits – e.g. dunites of Nizhni-Tagil, Russia; Placer deposits in Columbia (South America), Zimbabwe, Zaire, etc.

Table 3.3 Iron and Manganese. Iron

CA: 4.65%; CC: 10. Economic minerals, with Fe%: Magnetite (Fe3O4 – 72.4), haematite (Fe2O3 – 70), limonite – hydrogoethite (FeO.OH.nH2O) admixed with siliceous ingredients – 48–63, siderite FeCO3 (48.3), chamosite – iron silicate (27–38). Fe as Fe2 (ferrous) in endogenous processes, and as Fe3 (ferric) in exogenous processes. Exogenous concentrations of Fe in basic and intermediate rocks. Exogenous concentrations in sedimentary rocks and weathering crusts in ultrabasic rocks. Precambrian banded iron formations (BIF) are economically the most important. Manganese CA: 0.1%; CC: 300. Economic minerals, with Mn%: Pyrolusite MnO2 (55–63), braunite Mn2O3 (65–72), hausmanite Mn.Mn2O4 (65–72), manganite MnOOH (50–62), psilomelane MnO.MnO2.nH2O (40–60), rhodochrosite MnCO3 (40–45), mangano-calcite (Ca, Mn)CO3 (7–23), mangano-siderite (Mn, Fe)CO3 (23–32). Mn2 substitutes for Fe2 in endogenous processes, resulting in the enrichment of Mn in ultrabasic and basic rocks (0.15%). Endogenous deposits have no commercial value. Mn4 substitutes for Fe3 in exogenous processes. Iron precipitates under higher oxidizing conditions near the coast, whereas Mn precipitates in less oxidizing conditions away from the coast. Exogenous concentrations include sedimentary rocks, volcanogenic sedimentary rocks, and weathering crusts of metamorphic rocks.

Lower Proterozoic, ferruginous quartzites of Labrador (Canada), Lake Superior (USA), Madhya Pradesh, Bihar and Orissa (India), Minas Gerais (Brazil), Hammersley (Australia), Krivoi Rog (former USSR)

Coastal marine and lagoonal, Oligocene sediments of Nikopol (former USSR), Chiatura (Georgia); Archaean-Proterozoic Gondites (Madhya Pradesh, India); ferruginous quartzites of Minas Gerais (Brazil), etc.

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Table 3.4

Chromium, titanium and vanadium.

Chromium

CA: 83 ppm; CC: 4000. Chrome-spinellids have all the same formula: (Mg, Fe)O. (Cr,Al,Fe)2O3, with Cr2O3, 18–65%, FeO upto 18%, Fe2O3 upto 30%, Al2O3 upto 33%. Chromium gets segregated at the high temperature magmatic stage. Higher concentrations of Cr in ultrabasic (0.2%) and basic rocks (0.02% Cr2O3).Cr3 compounds are most stable. They form oxides with ions of Al3, Mg2, Fe2 and Fe3. Chromite is stable under exogenous conditions and forms placers. Cr in the form of hydrolysate suspensions may end up in sands and clays. Cr6 compounds form only under extremely high Eh and pH conditions.

Early magmatic deposits in the Bushveld Massif (South Africa) and Great Dyke (Zimbabwe); Late magmatic deposits in Kempirsai (former USSR); Placer deposits in Cuba, Phillippines, New Caledonia, etc.

Titanium

CA: 0.45%; CC: 20. Ilmenite (Fe.TiO3, 31.6% Ti), Rutile (TiO2, 60% Ti). Leucoxene, which is the altered product of ilmenite, contains 96% TiO2. Titanium gets concentrated in gabbros, pyroxenites and alkali rocks. Concentrations in basic rocks (0.9%) and in intermediate rocks (0.8% Ti).Ti2 compounds (as TiO2) are most stable. Titanium minerals are resistant to weathering and form placers of ilmenite and rutile.

Large deposits of coastal-marine placers of ilmenite-rutile-zircon, occur along the SW coast of India (Chavara), coasts of Mozambique (Xai-Xai), Sri Lanka, (Pulmoddai), Sierra Leone, east Brazil.

Vanadium

CA: 90 ppm, CC: 30. Economic minerals of vanadium, with V%: Roscoelite KV2AlSi3O10 [OH]2 – 19–29; carnotite K2U2 [VO4] 2 O4.3H2O (20), vanadinite Pb5 [VO4] 3 Cl (19), desclozite (Zn, Cu) Pb [VO4] OH (20–23), and patronite VS4 (29%). In hypogenic processes, V3 substitutes for Fe3 and Ti4, gets concentrated in Fe-Ti minerals, and thus gets enriched in the early-formed magmatic rocks (200 ppm of V). In the hydrothermal stage, V is transported in the form of V3, V4 and V5 complexes with halogens. Under exogenous conditions, V forms complexes such as VCl3, VCl4, VCCl, VOCl3, moves as suspensions or in solution, and gets adsorbed on the hydroxides of Fe and Al, and organic substances. This explains the presence of V in high-sulphur crudes, pitch and coals.

Highest contents of vanadium (up to 0.22%) occur in the Permian phosphorites of Rocky Mountains (USA), Oxidation zones of poly-metallic ores (Broken Hill, Australia), coastal marine placers of New Zealand, high-sulphur crudes of Venezuela and Iran.

Mode of occurrence of mineral deposits 73 Table 3.5

Molybdenum and Copper.

Molybdenum

CA: 1.1 ppm, CC: 5000. Molybdenite (MoS2) with an isomorphic admixture of Re, is the principal ore mineral. Molybdescheelite Ca(Mo, W)O4 (0.5–15% Mo) is subordinate.Mo exists in Mo4 form in endogenous environments, and in Mo6 form in exogenous environments. Mo gets concentrated in the end phase of the magmatic cycle, i.e. in acid and alkali earth magmas, post-magmatic and hydrothermal solutions. Thus granites contain 2 ppm of Mo, whereas the basic rocks have only 0.2 ppm. In the endogenous environments, Mo gets transported in the form of heteropolysilicic acid complexes (SiO2.12MoO3.nNa2O.H2O types) in acid and weakly acid solutions. Drop in temperature and the presence of H2S result in the disintegration of such complexes, with the formation of MoS2 and silicification of the host rock. Under exogenous conditions, MOS2 gets oxidized into easily soluble compounds of MoSiO2, and H2MoO4 types, and may form molybdenorganic compounds (e.g. bituminous oil shales).

Precambrian, quartz-molybdenitesericite veins of Climax, Colorado, USA; Skarn deposits in Turnyauz, northern Caucasus (former USSR); Greisen deposits of Eastern Kounrad, Kazakstan (former USSR), etc.

Copper

CA: 47 ppm; CC: 200. Principal copper ores, with Cu%: Native copper (92), Chalcopyrite CuFeS2 (34.6), bornite Cu5FeS4 (63.3), cubanite CuFe2S3 (22–24), chalcosine Cu2S (79.9), covellite CuS (66.5), tennantite 3Cu2S.As2S3 (57.5), tetrahedrite 3Cu2S.Sb2S3 (52.3), enargite Cu3AsS4, cuprite Cu2O (88.8), tenorite CuO (79.9), malachite CuCO3.Cu(OH)2 (57.4), azurite 2CuCO3.Cu(OH)2 (55.3), Chalcanthite CuSO4.Cu(OH)2 (31.8), brocanthite CuSO4.3Cu(OH)2 (56.2), atacamite CuCl2.3Cu(OH)2 (59.5), chrysocolla CuSiO3.nH2O (36.0). Copper is polymagmatogenic. In the basaltic magmatism, it is concentrated in the plutonic stage to form liquation deposits, and at the volcanic stage to form post-volcanic, massive sulphide deposits. Post-magmatic, hydrothermal ores of copper come into existence due to the transportation of copper in the form of thiosulphate and chloride complexes. Supergene enrichment of copper takes place under exogenous conditions. Copper also gets concentrated in the “sabkha” environment.

Plutonogenic, hydro-thermal porphyry copper deposits of El Teniente (Chile), Bingham, Utah (USA), Vein deposits (Butte, USA; El Cobre, Cuba), Volcanogenic, massive sulphide deposits (Rio Tinto, Spain); Cupriferous sandstones and shales of Nchanga and Roan Antelope (Zambia).

Table 3.6

Lead and zinc.

Lead & Zinc For Pb: CA: 16 ppm, CC: 2000; For Zn: Skarn deposits (El Potosi, CA: 83 ppm, CC: 500. Mexico); Metasomatic Principal lead minerals, with Pb%: Galena PbS deposits of pyrite-galena(86.6), Jemsonite Pb4FeSb6S14 (40.16), sphalerite in carbonate rocks Boulangerite Pb5Sb4S11 (55.42), bournonite (Freiberg, Germany; CuPbSbS3 (42.6), with cerrusite PbCO3 (77.6), Agnigundala, India, Leadville, anglesite PbSO4 (68.3) in the oxidizing zone. USA); Carbonate-hosted, Principal Zn minerals, with Zn%: Sphalerite stratiform deposits (Mississippi – ZnS (67), wurtzite ZnS hex. (63), smithsonite Missouri, USA), Massive ZnCO3 (52), calamine Zn [Si2O7] (OH)2 (53.7). sulphide deposits (Bawdwin, Pb & Zn gets concentrated in the residual portion Burma; Rio Tinto, Spain); of the differentiates. Pb is enriched in acid rocks Chacopyrite-sphalerite-pyrite (20 ppm) relative to the ultrabasic rocks (0.1 ppm). in volcanogenic deposits of the Variation in Zn content is irregular (ultrabasic: Kuroko type, Japan; 30 ppm, basic: 130 ppm, Acid: 60 ppm). The Metamorphosed deposits complexation of Pb and Zn depend upon pH, (Broken Hill, Australia) temperature and the presence of H2S. In H2S-free solutions, Pb is transported in the form of complexes such as, (PbCl), (PbSO 02), (PbF), and (PbCO 30). In the H2S-bearing solutions, Pb is transported in the form of Pb(HS) 02, and Pb(HS)3 . Zn is transported in the form of chloride (ZnCl02) and sulphide complexes (ZnHS 2 ). In exogenous conditions, Pb and Zn sulphides are oxidized to sulphates. Zn sulphate is soluble and mobile, whereas lead sulphate is insoluble and immobile.

Table 3.7

Tin.

Tin CA: 2.5 ppm, CC: 2000. Tin pegmatites are known in Cassiterite SnO2 (with 78.6% Sn) is the principal ore. Bastar Dt., M.P. (India), Stannine Cu2FeSnS4 (27.7), tillite PbSnS2 (30.4), frankeite Silver Hill (USA), Skarn Pb5Sn3Sb2S11 (17), Cylindrite Pb3Sn4Sb2S14 (26) are not deposits (Lao Chan, China), important commercially. The large ionic radius and high Plutonogenic, and hydrothermal charge of Sn4 prevents its entry into early-formed magmatic deposits of Yakutia (Russia). rocks. The concentration of tin in magmatic rocks increases Tin-bearing placers are known with increasing acidity – from 0.5 ppm in ultrabasic rocks, in Yakutia (Russia), Kinta, Perak 1.5 ppm in basic rocks to 3 ppm in acidic rocks. It follows (Malaysia), Chanwat (Thailand), that tin ores should be looked for in granites and Tin-Tuk (Vietnam), etc. granodiorites. Tin-bearing granites are usually late-stage, S-type granites, which show distinct evidence of having been generated in the upper continental crust. When granite is remobilized, tin probably gets transported in the form of complexes such as [Sn (OH, F)6] in alkaline solutions. When pH decreases to 7–7.5 (say, due to the presence of carbon), the complex dissociates into hydrofluoric acid and tin hydroxide. The latter, on dehydration, becomes tin oxide (cassiterite). Cassiterite is stable under exogenous conditions, and forms eluvial, alluvial and diluvial placers.

Mode of occurrence of mineral deposits 75 Table 3.8 Nickel

Nickel and Aluminium. CA: 58 ppm, CC; 200. Sulphide ores, with Ni%: Pentlandite (Fe, Ni)S (22–42), millerite NiS (65), nickeline NiAs (44), chloanthite Ni As3–2 (4.5–21), polydymite Ni3S4 (40–54), gersdorffite NiAsS (26–40). Silicate ores, with NiO%: garnierite NiO.SiO2.H2O (46), nepouite 12NiO.3SiO2.2H2O (20–46), redvinskite 3(Ni,Mg)O.2SiO2.H2O (46%). As Ni2 can substitute for Mg2, nickel tends to get concentrated in the early-formed magmatic minerals like olivine. Consequently, ultrabasic rocks have the highest concentrations of Ni (2200 ppm), followed by basic rocks (160 ppm), with acid rocks having negligible concentrations of Ni (8 ppm). It follows therefore that commercial concentrations of Ni can only be found in mantle-generated ultrabasic – basic rocks. The tropical weathering of the ultrabasic rocks leads to the release of nickel contained in the olivine and other ferromagnesian minerals. Ni and Co thus released gets transported to the lower part of the weathering crust. The infiltrating solutions become more alkaline with depth, leading to the precipitation of secondary, Ni-containing minerals, such as garnierite. Ni gets concentrated 10–30 fold in the process of lateritisation of serpentine or peridotite.

Important deposits of segregated magmatic Cu-Ni ores are: Sudbury (Canada), Bushveld and Insizwa (South Africa), Kola Peninsula and Norisk Traps (Russia). Deposits of weathering with silicate ores of nickel occur in New Caledonia (island in the Pacific, under French control), Indonesia, Brazil, Russia, Albania, Greece, etc.

Aluminium Ca: 8.05%; CC: 5. Bauxite is the principal ore of aluminium. It is composed of gibbsite [Al(OH)3] (with 65.4% Al2O3), boehmite (-AlOOH) and diaspore ( -AlOOH), with 85% Al2O3. The abundance of Al is next only to that of Si, but because of the strong oxyphilic tendency of Al, it is not economic to extract Al from primary rocks. The principal ore of aluminium is bauxite. Formation of laterites and bauxites is facilitated by a combination of high rainfall (
1000 mm), high temperature (
20 °C), intense leaching, strongly oxidizing environment, subdued topography, long duration of weathering and chemically unstable rock. Autochthonous bauxites on igneous, metamorphic and sedimentary rocks may be primary, or they may be fossil, polygenetic, altered bauxites. There are also autochthonous karst bauxites in limestone terrains.

Residual lateritic deposits of Boke (Guinea), residual redeposited deposits (sheet deposits of Northern and SW Australia); Allitic latosols of Gujarat (western India), Surinam (South America), Arkansas (USA), equatorial Africa; Ferrallitic latosols: Galikonda (South India), bauxites on the alkaline syenites of SE Brazil, etc.

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Table 3.9

Uranium and Thorium.

U & Th For Uranium: CA: 2.5 ppm, CC: 400; Important ores of U, with U3O8%: Uraninite (or pitchblende) UO2 (92)- amorphous varieties may contain 60%). Brannerite (U, Ca, Th,Y) [Ti, (Fe)2O6] (28–44), davidite (Fe, U) TiO3 (20), uranothorite (Th, Fe, U) SiO4.nH2O (upto 17), uranophane CaH2 [UO2 (SiO4)2] 5H2O (67), coffinite U (SiO4)1x. (OH)4x (68), autunite Ca [UO2.PO4]2.10–12 5H2O (60), torbernite Cu [UO2.PO4]2.8–12 H2O (61), zeunerite Cu [UO2.AsO4]2, 10H2O (56), Carnotite K2 [(UO2)2.V2O8].3H2O (64). For Th: CA: 15 ppm, CC: 200 (?). Important ores of thorium, with ThO2%: Thorianite ThO2 (88%), bröggerite (U, Th) O2 (6–15), thorite ThSiO4 (81.4), uranothorite (Th, U)SiO4 (50–70), ferrithorite (Th, Fe)SiO4 (45–65), thorogummite (Th, U)[(SiO4) OH] 4 (45–65), Priorite (Y, Th) (Nb, Ti)2O6 (8), thorium-bearing monazite (Ce, Th) [(P, Si)O4] (3.5 to 10, upto 40). U4 (radius: 1.05 Å) and Th4 (radius: 1.10 Å) go hand in hand in the magmatic environment. They get enriched in acid rocks (Th:12 ppm, U: 3 ppm), relative to the basic rocks (Th: 3 ppm; U: 1 ppm), and their contents are largely in the form of accessory minerals, like allanite, monazite, etc. In the late stage granitic magmas and hydrothermal solutions, U4 gets oxidized into highly soluble uranyl ion (U6O2)2, while Th4 remains unchanged and immobile. In the exogenous conditions, uranium gets transported in the form of uranyl tricarbonate [UO2(CO3)]4 and hydroxide [UO2(OH)2], uranyl humate, phosphate, etc. complexes, and gets precipitated when reducing conditions (due to the presence of H2S, organic matteretc.) are encountered. This accounts for the close association of uranium ores with organic matter (e.g. sooty pitchblende). Th-bearing minerals are resistant to weathering, and form placers (e.g. monazite placers). Uranium minerals never form placers.

Deposits of uraninite-sulphide deposits of Marysvale, Utah, USA; Uraninite-arsenide deposits of Great Bear Lake, Canada; Uraniferous conglomerates in the Proterozoic metamorphic rocks of Blind River (Canada); Triassic Sandstones of the Colorado Plateau (USA); refractory brannerite – davidite deposits of U–Ti; uranium-bearing phosphorites of Florida, USA; Placer deposits of thorium-bearing minerals (such as, monazite) occur along the SW coast of India (Chavara) and the coasts of Sri Lanka and Mozambique (Deia), etc.

ppm  parts per million  1 g/106 g  1 g of ore element per tonne of rock. ppb  parts per billion  1 g/109 g  1 mg of ore element per tonne of rock. * Factor of concentration of crustal abundance needed to form an economic deposit.

metallic minerals (about 1.2 billion tonnes), (3) Several of the industrial minerals (notably sand and gravel) are of low unit cost, and hence it is not economical to transport them for long distances, (4) their existence is widespread. Far from creating environmental problems, several industrial minerals (such as, bentonite) are highly useful in the mitigation of the environmental problems.

Mode of occurrence of mineral deposits 77

All world production figures (in Mt – millions of tonnes) given below refer to 1998. In this section, industrial minerals are described mineral-wise, as a given mineral may have several uses – for instance, clays are used in ceramic, refractory, filler and other industries (see, the classic textbook, Economic Mineral Deposits, by Jensen & Bateman, 1979, for details). Asbestos: The term, asbestos, is applied to a group of silicate minerals which can be separated into fibres. There are two main groups of asbestos minerals – chrysotile asbestos which occurs in serpentine that has been altered from igneous rocks such as peridotite and dunite, and amphibole varieties (amosite, crocidolite, tremolite, actinolite and anthophyllite) which are associated with schists and banded ironstones. The fibres of chrysoltile are fine, silky and strong. About 4350 m of thread can be spun from 1 kg of the mineral. It can withstand temperatures upto 2750 °C. Asbestos is separated from the parent rock, fiberized and classified by length. Asbestos as spinning fibre is used in the manufacture of asbestos cloth, heat insulators, etc., whereas the non-spinning fibre is used for the manufacture of millboard, asbestos cement sheets and shingles, and various composites. As the inhalation of asbestos fibres can cause pleuro-pulmonary cancer, stringent limits have been put on the concentration of asbestos fibres in room air, and the use of asbestos is hence strongly discouraged. Consequently, the world production has gone down steeply during the last two decades, and now stands at 1.84 Mt (1998). Asbestos is probably the only industrial mineral in the world whose production has decreased. Barite (BaSO4): Commercial barite is formed as fissure and cavity fillings, breccia fillings, bedded deposits and residual deposits. It is the principal constituent of lithopone paint (barite and ZnS). It is used as filler in drilling muds, rubber, glass, lineoleum, etc. For being used in drilling mud, barite is ground finely (ten percent, minus 325 mesh) – it cools the drill bit and confines the high oil and gas pressure at depth. The world production of barite is 5.89 Mt. Boron: Borax (Na2B4O7.10H2O) is the principal mineral of boron. It is obtained from bedded deposits beneath old playas, brines of saline lakes and marshes, encrustations around playas, and hot springs and fumaroles. Chemically refined borax is an ingredient of baking powder and medical products. It is used in the manufacture of glass, and ceramics, etc. Its world production is about 4.44 Mt. Clays: Three types of clays, namely, bentonite, Fuller’s Earth and kaolin, are described. Bentonite: is a clay composed essentially of montmorillonite. It is a product of devitrification and alteration of volcanic ash or tuff. There are two classes of bentonite: the “sodium” type that swells and increases its volume 15–20 times when wetted, and the “calcium” type that does not swell. The importance of Na-bentonite in the waste disposal industry, arises from the following considerations: (1) its high baseexchange capacity and large surface area (600–800 m2/g) enables it to capture and attenuate the waste elements, particularly, the heavy elements, (2) because of its small particle size distribution, it can plug even the smallest voids against seepage, and (3) its high liquid and plastic limits make it a very flexible structural component

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(Tewes, quoted by Attewell, 1993, p. 92). A major use of bentonite is for binding iron ore pellets. Its annual world production is 9.33 Mt. Fuller’s earth: is composed predominantly of palygorskite. It is a soft abrasive for grease removal, and high-grade polish for silver and chromium wares. Its world production is 3.32 Mt. Kaolin: Al2Si2O5(OH)4. The word kaolin is derived from Kaoling in China – fine chinaware has been made in Kiangsi province in China since A.D. 220. The physical properties of importance are: plasticity, transverse strength, shrinkage, and fusibility. Kaolins are used not only in ceramics, but also as a filler and paper coater, and in medicines, cosmetics, building industry. The world production of kaolin is 39.8 Mt. Diatomite: It is also known as diatomaceous earth or kieselguhr. It is composed of microscopic siliceous tests of diatoms. It is friable and light, and when dry, floats on water. It is used as a filler and filter. Its main use is in filtration of oils, juices, wastes, medicines, etc. Its world production is 2.15 Mt. Fluorspar (CaF2 ): occurs as disseminated and replacement deposits in igneous rocks, such as rhyolites and carbonatites, in association with volcanoclastic sedimentary rocks, and in hydrothermal deposits. It finds its most important use in steel industry (to facilitate fusion in the basic open hearth furnace). It is used to make hydrofluoric acid, from which synthetic cryolite used in aluminium industry, is made. Other uses are in glass and enamel industry. Its world production is 4.7 Mt. Gypsum (CaSO4.2H2O): is an evaporite mineral. As it occurs in flat and gently inclined beds, it is generally mined by open pit methods. Its main uses are in construction industry and agriculture. It is used as a retarder in setting time in Portland cement, and as a soil conditioner and fertilizer in agriculture. It is used for the manufacture of wallboards used in the building industry. Plaster of paris is produced by calcining gypsum at 300 to 350 °F, during which part of water of crystallization is removed. The world annual production of gypsum is 107 Mt. Magnesite (MgCO3): occurs both in crystalline and amorphous forms. It has three modes of occurrence: as replacement of dolomite or limestone, as veins, and in sedimentary rocks. Magnesite in commerce refers not only to MgCO3 but also its sintered products, such as, caustic magnesite (700–1200 °C) and dead-burned magnesite (1450–1500 °C). Caustic magnesite is used for sorel cements, and in the manufacture of high-quality floor tiles and wallboard. Dead-burned magnesite is a high-grade refractory. The world production of magnesite is 10.7 Mt. Phosphate rock: Phosphate rock is the principal raw material for the production of industrial phosphatic fertilizers. The principal phosphorus mineral is apatite, Ca5(PO4)3 (F,Cl,OH). Apatite in magmatic and metamorphic rocks is in the form of crystalline fluorapatite or chlorapatite Ca5(PO4)3 (F,Cl), with P2O5 content in the range of 42.3–41.0%. In sedimentary phosphates (phosphorites), phosphate may occur in the form of cement in sandstones, or as oolites and concretions. Phosphorites should contain at least 20% P2O5 in order to be commercially usable. Raw sedimentary phosphate (phosphorite) invariably contains some amount of cadmium, which ends up in industrial fertilizers. When such industrial fertilizers are applied,

Mode of occurrence of mineral deposits 79

cadmium is taken up by plants and enters the food chain. Some guano phosphorites (as those of Minjingu, Tanzania) have high contents of uranium (about 200 ppm). The local farmers directly apply the crushed phosphorite to their crops. The addition of bentonite to the crushed phosphorite at the time of application, markedly reduces the loss of nutrient elements through leaching of P (and of U and F as well) by rainwater, thus preventing the pollution of streams by U and F (Aswathanarayana, 1988). The world production of phosphate rock is 145 Mt. Salt: Commercial salt is obtained from sedimentary-bedded deposits, brines, seawater, surface playa deposits, and salt domes. It is the most familiar of all minerals. In ancient times, in countries where salt was scarce, salt was as precious as gold, and was even used as currency (“salt of the earth”, “is he worth his salt?”). On an average, a person consumes 5–6 kg of salt per year. This works out to about 30 mt/y for the world population of about 6 billion. Considering that the world production of salt is 192 Mt/y, it is obvious that the industrial uses of salt are far larger than human consumption. Salt is used in (1) industries: metallurgical industries (treating and refining of ores), chemical industries (soaps, dyes, wood preservatives, bleaching), ceramics, refrigeration, (2) agriculture (cattle feed, fertilizer, soil amenders) (3) medicine, and (4) home. Sulphur: Sulphur is by far the most important chemical mineral. It occurs both in the native form, and also as sulphides and sulphates. Sulphur occurs as (1) elemental sulphur deposits in evaporite rocks, (2) hydrogen sulphide contained in sour natural gas, (3) organic sulphur compounds found in petroleum, (4) massive deposits of pyrite, (5) elemental sulphur deposits in volcanic rocks, (6) ores of metallic sulphide minerals (Jensen & Bateman, 1979, p. 562). Sulphur is used in the manufacture of soluble fertilizers, synthetic fibres, pigments, explosives, drugs, insecticides, etc. The world production of sulphur in all its forms is 57.8 Mt.

3.3

COAL

Coals are formed from the accumulation of vegetable debris in specialized environments. They range in age from Upper Palaeozoic to Recent. The rank of coal (peat, lignite, sub-bituminous coal, bituminous coal, semi-anthracite and anthracite, in order of increasing rank) and the degree of structural complexity are determined by the synsedimentary and post-sedimentary processes to which the vegetable matter has been subjected. The coal-bearing sequences tend to be so similar that when once a lithofacies (say, a sandstone) of a particular sequence (say, a Gondwana cyclothem) are met with, it is possible to predict the existence of coal of a particular rank. The greater the depth of burial, and the longer the length of burial, the higher would be the rank of coal. As Hilt’s law states, “In a vertical sequence, at one locality in a coal field, the rank of the coal seams rises with increasing depth”. The rate of rank increase depends upon the geothermal gradient and heat conductivity of rocks. Where the geothermal gradient is high (70–80 °C/km), coal attains bituminous rank at depths

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Mineral resources management and the environment

of 1500 m (as in Upper Rhine graben, Germany), whereas in an area of lower gradient (40 °C/km), coal is bituminous only at a much greater depth of 2600 m (Thomas, 1992, p. 21). Thus, Palaeozoic coals tend to be bituminous and anthracitic, whereas Tertiary coals are generally lignitic. Coal is formed in fluvial, deltaic and coastal barrier systems. The palaeodepositional environments of coal are reconstructed on the basis of the study of the relationships between the changes in the lateral and vertical sequences and the depositional settings in the modern analogues of fluvial, deltaic and coastal barrier systems (Thomas, 1992, p. 55–95). 3.3.1

Coal-bearing sedimentation sequences

Coastal barrier and back-barrier facies: The clean barrier sandstones become finegrained in the seaward direction and grade landwards into dark grey lagoonal shales, and marginal swamp areas on which the vegetation was established. As the barrier sandstones have been constantly reworked, they tend to be more quartzose than the sandstones in the surrounding environments. In this sequence, upwardscoarsening, organic-rich grey shales and siltstones are overlain by thin, discontinuous coals, with bands and concretions of chemically precipitations of sideritic ironstones. The sequences are generally 20–30 m thick, and 5–25 km in width. Lower delta plain facies: The lower delta plain deposits are composed of mudstones and siltstones, ranging from 15 to 55 m in thickness and 8 to 110 km in lateral extent. Sandstones are common in the upper part of the sequence, indicating shallow water deposition. As the bays filled, plants grew abundantly, and these provided the vegetable debris needed for coals. Thick organic accumulations in the abandoned distributary channels resulted in the formation of lenticular coal deposits. Upper delta and alluvial plain facies: Linear, lenticular sandstone bodies upto 25 m in thickness and width of 11 km, are characteristic of upper delta and alluvial facies. The massively bedded sandstones are overlain by siltstones. Coal seams in the upper delta plain facies are more than 10 m in thickness, but are of limited areal extent. A special characteristic of the transition zone between the upper and the lower delta plain facies is the formation of peat mires on a widespread platform. The platform was cut by numerous channels, and there was development of crevasse-splay deposits. The coals formed on such a platform are thicker and more widespread than the coals of the lower delta plains (Thomas, 1992, p. 63). As should be expected, the variations in the thickness of the coal seams are closely related to the pre-existing topography. The environment of deposition of, and synsedimentary and post-sedimentary changes in, a coal seam has a direct bearing on the thickness, quality and minability of the seam. Any rise in pressure (due to say, folding or faulting) or temperature (such as, due to igneous intrusions) could have the effect of raising the rank of coal. Syndepositional changes: The combination of thick sediment accumulation and rapid basin subsidence could lead to slumping and loading structures and liquefaction

Mode of occurrence of mineral deposits 81

effects. Under such loading, coaly material may be squeezed into the overlying strata. Growth-faulting is common in the coal-bearing basinal sediments. The basement faults may continue to be active in the sedimentary basin, and their effect may be compounded by faults which owe their origin to gravity sliding within the sedimentary pile. The jointing or “cleat” in the high-rank coals, is a consequence of the reduction in porosity and permeability brought about by the burial, compaction and continued diagenesis of the organic constituents of coal. Post-depositional changes: Folding of coal seams has a profound effect on their minability. Steeper dipping strata may result in unfavourable overburden stripping ratios, and may lead to the cancellation of the project. Similarly, in the underground operations, if the dip of the coal seam is too steep, it can make further working of coal difficult, and in the case of longwall mining, extraction of coal may have to be given up. The heat associated with the intrusion of dykes and sills may some times have the beneficial effect of raising the rank of coal, but the intrusions may also cause problems in mining. The dykes and sills are generally doleritic. They are extremely hard, and by their baking effect, they render the surrounding area hard. Such intrusions are particularly common in the South African coalfields. They need to be carefully mapped, and their disposition has to be taken into account while planning the mining operations. A common feature of the coal-bearing sequences is the presence of iron stone (siderite – FeCO3) which is extremely hard. This creates problems in mining, because of the difficulty in separating coal and siderite. Iron sulphide (pyrite – FeS2) may be precipitated along with coal as disseminations or as thin bands. This gives rise to the extremely troublesome acid mine drainage (see section 8.1 for details).

3.4

OIL AND NATURAL GAS

Customarily, drilling for oil and water is not included under mining industry. There is a vast body of literature on all aspects of oil – its mode of occurrence, distribution, extraction, environmental impact, economics, politics, etc. Only the barest outlines of the oil and natural gas industry is given in this section (just for purposes of completion). It is generally accepted that petroleum is derived by the slow decomposition of the remains of marine and brackish water organisms (such as, plankton and algae) in an oxygen-free environment. Carbon-14 studies indicate that the process could take place in less than 10,000 years. The bacteria that exist in seafloor muds are believed to have converted the organic matter into protopetroleum. Petroleum is composed of a variety of compounds of carbon and hydrogen, with minor amounts of oxygen, nitrogen and a little sulphur. There are broadly two kinds of crudes – paraffin-based light crudes (with specific gravity of about 0.8), and asphaltic-based heavy crudes (with specific gravity nearer to 1.0). Oil is a fugitive mineral – it may migrate from the source rock, and accumulate in structural traps (e.g. anticlines) or stratigraphic traps (e.g. unconformities) in the reservoir rocks. The presence of

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impervious caprocks prevents the escape of petroleum. The migration might be caused by the compaction of muds, capillarity, buoyancy, gravity and currents. The differences in the composition of the crudes in different parts of the world are attributed not so much to the differences in the source material, but due to the post-depositional processes to which the source material has been subjected. The age distribution of the known reserves of the world’s oil and gas are as follows: Cenozoic – 29%, Mesozoic – 59%, Permian – 8%, Precambrian – 6%. The depth versus production of the oil fields in the world is as follows: Depth (in m)

Production (per cent of total volume)

500 500–1000 1000–1500
1500

6.9 32.3 26.1 34.7

Though some oil wells are deeper than 10,000 m, the most productive wells are less than 3300 m deep. Some authorities even hold that the best possibilities exist for wells less than 2000 m deep. Oil reserves are expressed in terms of billions of barrels (b bbl; one barrel is equivalent to 42 US gallons 162.75 l). The largest reserves of oil in the world are in the Middle East and North Africa (391 billion barrels), with Saudi Arabia (137), Kuwait (74), Iran (62), Iraq (33), Libya (24), etc. having large reserves. Other important oil-producing countries are: Former Soviet Union (FSU) (42), USA (36), Venezuela (13), Nigeria (13), Indonesia (11), etc. The oil producing and exporting countries have formed a cartel called OPEC (Oil producing and Exporting countries), with headquarters in Vienna, Austria.

CHAPTER 4

Environmental impact of mineral industries – industry-wise

Environmental impacts of any industry cover two broad categories – harmful effects on human health and environment which can be studied objectively, and social perceptions in regard to unpleasantness and annoyance arising from a particular environmental situation, which could be highly subjective. History shows that what is considered unacceptably unpleasant to one group of people enjoying a high standard of living, may be acceptable to less favoured groups which may be dependent upon the particular activity for their living. This chapter is confined to changes in the natural biophysical environment arising from the mineral industries. Though several of the environmental, safety and health issues are common to all the minerals, each mineral industry has certain specific environmental impacts, which are unique to it (e.g. red mud in aluminium industry). This chapter deals with such unique environmental impacts, industry-wise. 4.1

STEEL INDUSTRY

The iron and steel industry is broadly divisible into two types, depending upon the raw materials used: Integrated steel mills, starting with iron ore, and mini mills, based on iron and steel scrap. This categorization is of course an over-simplification, because integrated mills also remelt scrap, and some mini mills include facilities for the pre-reduction of iron ore. The following are the principal sectors of the integrated steel works, with each sector being characterized by a particular kind of environmental impact: 1. Stocking and handling of the basic raw materials, namely, coal, iron ore and limestone fluxes, 2. Coking, where raw coal is carbonized in coke ovens, to form metallurgical coke which is used to produce pig iron in the blast furnace, with the recovery of highenergy, coke-oven gas, 3. Sintering: where the crushed iron ore, and coal fines and coke breeze, are combined together at high temperature to form a product (called sinter) with appropriate

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Mineral resources management and the environment

mechanical strength and porosity to be used in blast furnace. When the limestone fines are added to the mixture at the outset, a self-fluxing sinter can be obtained. Pelletizing is a related process – iron ore fines are hardened as pellets in a rotary furnace at a high temperature, 4. Blast furnace: This is charged with iron ore, coke and limestone flux, or sinter or pellets and coke. In the blast furnace, the iron ore gets melted and reduced to liquid iron. The pig iron and slag are drawn out by tapping, and the gas is recovered from the “throat”, 5. Oxygen converter: This refines pig iron into steel, through the removal of the impurities in pig iron, such as, C, Si, P, Mn, etc. Some countries use open hearth furnace for refining pig iron to steel – these are more flexible, and could be charged with scrap also, apart from pig iron, 6. Casting: to solidify liquid steel in the form of ingots, billets or slabs, 7. Rolling mills: for hot forming solid steel, or cold working of thinner products, 8. Processing units: for ingot scarfing, acid pickling, tinning, galvanizing, lead coating, etc. The building costs of steel works are schematically shown in Figure 4.1 (source: UNEP Tech. Review, 1986, p. 14). It may be noted that investments costs (per t of steel) in the case of large steel works of high productivity in industrialized countries are much lower than small, integrated works in developing countries.

Figure 4.1

Building costs of steel works (source: UNEP, 1986, p. 14).

Environment impact of mineral industries – industry-wise 85

Presently, there are two main processes of steel making: processes based on reducing gases (CO, H2) via shaft furnaces or fluidized bed, and processes based on coal. Gross energy consumption in integrated works (in terms of G cal/t of liquid steel) is as follows: solid fuel (0.56), coke (2.08), hydrocarbons (0.85), electricity (0.4), total (3.89). Energy constitutes an important component of the cost of steel making – for instance, energy accounts for 25% of the cost of steel making in integrated steel works. The structure of the price of a tonne of rolled steel in the case of integrated steel mill (flat product works, based on blast furnace and oxygen converter), and mini bar mill (based on scrap melting with electric furnace), are summarized in Table 4.1 in terms of percentage costs (source: UNEP Tech. Review, 1986, p. 12). The UNEP document (1986) quotes the production costs of steel in terms of French Francs in 1978 – FF 1081/t for integrated mill, as against 971 FF/t for mini bar mill. As the market value of the currencies tend to change, the cost figures for various components are shown in terms of percentages, which are likely to remain relatively more valid. 4.1.1

Air pollutant discharges in the steel industry

The steel industry has a bad reputation as a dirty industry. Thanks to the technological improvements that have been made all over the world to reduce the emissions, modern installations, such as, coke ovens, sintering plants, blast furnaces, steel making shops and rolling mills, can be made reasonably dust-free, if properly operated. It is not, however, possible to eliminate the pollutants altogether. The steel works produce particulate emissions (i.e. dust) and gaseous pollutants. The particulate emissions are of two types: (1) coarse dust particles of larger grainsize (known as grit or coarse dust) which tend to be deposited on the ground in the vicinity of the installation concerned, (2) Fine dust particles (of micron and submicron size) or “suspended dust” which can be carried for long distances in the air. The gaseous pollutants are: sulphur dioxide (derived from sulphur present in the Table 4.1

Structure of the price of rolled steel. Integrated steel mill

Mini bar mill

Iron ore (0.8 t iron) Scrap

14.4%

–

Power (coal, hydrocarbons, electricity, etc.– 700 kg of coking coal) Electricity (600 kwh)

25.4%

Miscellaneous supplies

13.9%

13.4%

Manpower

18.5%

16.5%

Depreciation

27.8%

24.2%

Total

100%

100%

36%

9.9%

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Mineral resources management and the environment

Table 4.2

Emission of fine particles (in terms of aerodynamic diameter).

Operation

30 m 15 m 10 m 5 m 2.5 m Units

Emission fraction rating *

Continuous drop – Conveyor transfer sites – Sinter

13

9.0

6.5

4.2

2.3

g/Mg

D

1.2 0.15 0.055

0.75 0.095 0.034

0.55 0.075 0.026

0.32 0.040 0.014

0.17 0.022 0.0075

g/Mg g/Mg g/Mg

B C E

Batch drop – Front and loader track High silt slag 13 Low silt slag 4.4

8.5 2.9

6.5 2.2

4.0 1.4

2.3 0.80

g/Mg g/Mg

C C

Vehicle travel on unpaved roads Light duty vehicle 0.51 Medium duty vehicle 2.1 Heavy duty vehicle 3.9

0.37 1.5 2.7

0.28 1.2 2.1

0.18 0.70 1.4

0.10 0.42 0.76

kg/VKT C kg/VKT C kg/VKT B

Vehicle travel on paved roads Light/heavy vehicle mix 0.22

0.16

0.12

0.079

0.042

kg/VKT C

Pile formation – Stacker Pellet ore Lump ore Coal

* Definition of Emission Factor Rating (see Supplement no. 10, Air Pollutant Emission Factors, Third Edition, AP-42, US EPA – PB 80-199045): A – Excellent, B – Above average, C – Average, D – Below Average, E – Poor.

fuels or iron ore), nitrogen oxides (arising from combustion processes involving coke in the blast furnace and coke breeze in the sintering plant, and fuel oil in the blast furnace), carbon monoxide (from sintering fumes) and HF and HCl (from ores used in sintering, or from fluorspar that may be charged in the steel melting shop). Sintering plant is a major source of emissions. For instance, pollutants from sinter contain 1% carbon monoxide in a discharge of 2500 Nm3 per tonne of sinter. Sintering plant is a major emitter of sulphur oxides and sulphuric acid aerosol. The quantities of the open dust from various sources (in terms of particle size range) are listed in Table 4.2 (source: UNEP Tech. Review, 1986, p. 22). These are indicative of the order of magnitude – the actual quantities of dust may vary depending upon the composition of the raw materials, and the nature of the technology used. The following qualitative conclusions can be drawn from Table 4.2: (1) Conveyor transfer sites at sinter plant are a major source of fine particulates, (2) the emissions from pellet ore are more than for lump ore and coal, (3) the emissions from high silt slag are invariably higher than the low silt slag, in all size ranges, (4) dust from vehicle travel on unpaved roads is far higher than the travel on paved roads, and (5) dust from heavy duty vehicles is about seven times more than that from light duty vehicles, etc. The standard emission factors of gaseous pollutants (as proposed by OECD) are given in Table 4.3 (source: UNEP Tech. Review, 1986, p. 23).

Environment impact of mineral industries – industry-wise 87 Table 4.3

OECD Proposed standard emission factors for gaseous pollutants.

Sinter plant Coke oven Hot metal production Steel production converter Electric arc furnace Rolling mills

4.1.2

Unit

CO

SO2

NO2

kg/t sinter kg/t coke kg/t pig iron kg/t steel

30 1 10 15 10 –

2 0.5–2 0.2 – – –

0.3 0.65 0.5 0.3 – 1.1

Kg/t product

Water pollutant discharges in the steel industry

Water pollution arising from the steel industry is assessed in terms of the following parameters: COD (Chemical Oxygen Demand), BOD5 (Biochemical Oxygen Demand after 5 days), SS (Suspended Solids), Hydrocarbon content, Conductivity (which is linked to salinity), Toxic substances (inorganic substances, such as Cd, Cr, Cu, Pb, Ni, Tl, Zn, cyanide, fluoride, sulphide, and organic compounds, such as, Polynuclear Aromatic Hydrocarbons (PAHs). Table 4.4 (source: UNEP Tech. Review, 1986, p. 25) gives the orders of magnitude of potential pollution). Waste dumps are likely to get leached, and this process may go on for a long time. The toxic constituents of the leaching effluent may contaminate the watercourses, and could end up in the food chain (e.g. vegetables). The pollution potential of the dumps will be considerably reduced if the deposits have pH value nearer to 7–8, and they contain carbonate. At the level of neutral pH, wastes from the steel industry are likely to be insoluble (solubility: 106 mols/l). However, complexation with organics may render such substances soluble. 4.1.3

Solid wastes in the steel industry

Steel industry generates the following types of solid wastes: 1. Slag: related to the gangue compounds from the blast furnace and steel melting shop, 2. Dust and sludge: arising from the screening of raw materials, dry scrubbing of gases, liquid waste treatments or works cleaning, 3. Used refractories, 4. Oil and gas residues, 5. By-products from coking or from recycling treatments. The extent of the waste generated depends on the raw materials and the production process. If the original ores are of low grade, and contain impurities, that will be reflected in the quantity and the composition of the blast furnace slag. In the case of electric furnace-based mini mills, little waste is generated. The order of fugitive dust emissions from an oxygen steelmaking plant is as follows: (in terms of g/t of steel): Rehandling of pig iron (19), desulphurization of pig iron (16), converter charging (140), converter blowing (24), miscellaneous (8), total (187).

0

1–3

0.6

0.06

0.05–0.1

0.5

0.1–0.2

0.05

Sintering, pelletising

Coke oven plants

Blast furnace

Oxygen converter

Continuous casting hot rolling mills

Pickling

Cold rolling mills

Surface treatments

Inhibited by toxics

0.1–0.15

20

0

inhibited by toxics

0

COD (kg/t) BOD5 (kg/t)

0.1–1

0.1–0.4

0.1

0

Hydrocarbons (kg/t)

Extent of the water pollution potential of steel industry.

All cooling circuits

Area

Table 4.4

0.005

Increase by concentration and treatment products

Conductivity (mRO/cm3  m3t)

Zn, H , Cl, Sn, Cu, etc.

0.1–0.15

0.2–0.4

7–9

H; 2/3 mols/t – various 

0–30

3–40

1.2–6

0.32

0.01 0.140

Scant (coolant)

SS (kg/t)

0

Cn 0/2

NH4: 0.4/2.5, Phenol: 0.4/08 CN: 5  105, Cl: 1.5

Ore impurity, Zn, As, F, S, Cu

Products

Toxic substances (mg/l)

According to type

Dry dust cleaning Wetdust cleaning

Remarks

88 Mineral resources management and the environment

Environment impact of mineral industries – industry-wise 89

4.1.4

Fumes collection in the steel industry

Stockyards and handling areas: In the steel industry, unloading, storage, recovery and transfer operations in the case of iron ore, coal, coke, limestone, lime and also slag, take place all the time, creating dust pollution. The following techniques can be made use of to collect and clean the dust (UNEP Tech. Review, 1986, p. 49–51): (1) installation of hoods above the conveyor belts to suck in the air, and extract the dust from it (on the analogy of a vacuum cleaner), (2) dozing the coal in the stockyard for smoothing and compacting of coal, (3) spraying the stockpiles with water, with or without surfactants, (4) covering the stockyards with a roof, and (5) building walls to serve as wind-breaks. Coke ovens: Pollution occurs during the preparation of the coal, charging the coal into the oven, the coking process itself, removal of the coke from the oven, quenching it, screening and handling. Dirty, black dust is visible all around. The quantities of dust produced are highly variable, and are dependent upon the properties of coal, the design of the coke oven, and operational procedures. The progress that has been made in the techniques of reducing the dust pollution, is illustrated with two examples from coke pushing and the coke quenching operations. For instance, there are three possible ways of recovering waste gases and extracting dust from them in the case of coke pushing operations: a wholly mobile technique, with a mobile hood and dust cleaner coupled to the coke car, a wholly stationary technique, in which stationary dust cleaner in a covered bay cleans up the dust, and a combination technique, with a mobile hood connection running along the length of the battery, and linked to a stationary dust extraction system on the ground. Similarly, there are wet or dry methods of limiting the emission of particulates in the coke quenching tower. In the case of wet methods, the quantity and quality of cooling water, and the system of baffles have to be carefully controlled. To avoid the hassles of treating large quantities of used water, dry techniques of quenching are being increasingly used. The dry techniques have two merits: they not only avoid the emission of particulates and gaseous pollutants, but also allow the recuperation of heat from the hot coke. The extent of generation of pollutants in the earlier coke ovens, and how the installation of modern cleaning equipment can drastically bring down the dust pollution in the coke oven are indicated in Table 4.5 (source: UNEP Technical Review, 1986, p. 51). Sinter plant: The dust collection system in the case of the sinter plant consists of electrostatic precipitator for the main waste gases, and bag filters for the collection of dust in the premises. Two 700 kW ventilators are needed to take care of air flow of 2 million m3/hr over a 400 m2 grid surface. Blast furnace: Blast furnace has always been regarded as a major source of pollution. The top gas is highly noxious, with 25% content of carbon monoxide, and it is discharged with 40 kg of dust per tonne of hot metal. Top gas is, however, a source of energy, and the current practice is to recover the energy in the top gas,

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Mineral resources management and the environment

Table 4.5

Effectiveness of cleaning equipment in the case of coke ovens.

Operations

Dust pollution before treatment, in g/t of coke

Dust pollution after treatment, in g/t of coke

Coal charging Coke pushing Coke quenching Coke handling

150 400 350 1500

10 10 5 50

Total

2400

50

and remove the dust contained in it, so that the top gas is never discharged into the atmosphere. Pig iron refining plants: Pig iron is refined into steel by the removal of impurities contained in it, such as, silicon, carbon and phosphorus, through the Bessemer process or open hearth furnace. Bessemer process is obsolete, and the importance of open hearth furnace is decreasing. Currently, steel refining is mostly done through oxygen converters. The emissions at the mouth of the converters are composed of CO, and lesser amounts of CO2, and substantial concentration of fine particles of iron and oxides, called “red fume” (about 150 g/Nm3). There are two environmentally acceptable ways of handling the emissions: (1) recovery without involving the combustion of CO, with the combustible gas being recycled into the energy circuit of the works, and (2) recovery with the air combustion of CO, whereby the energy is extracted in the form of steam. Dust cleaning is usually done by the wet method involving Venturi scrubbers using high or low pressure drop. Electrostatic precipitators can bring down the dust content from 120 mg/Nm3 to 10 mg/Nm3. As considerable progress has been made in the extraction of dust from the waste gases, the focus is now on the fugitive emissions in the oxygen steel making plant. The order of fugitive dust emissions from an oxygen steelmaking plant is indicated below (in terms of g/t of steel): Rehandling of pig iron (19), desulphurization of pig iron (16), converter charging (140), converter blowing (24), miscellaneous (8), total (187). The problem in the case of fugitive gases is not so much the extraction of dust from them (which is a standard procedure), but the difficulty in forcing the waste gases into a hood at the front of the converter. Extremely high suction velocities (e.g. 15 m/s) and throughput (e.g. 300,000 Nm3/h) are needed to achieve this. Dust cleaning does not come cheap. The cost of investment of dust cleaning facilities is about 15% of the cost of the steel works itself, and the operating costs are high. Scrap melting plants: There are essentially two kinds of scrap melting methods – open hearth process, which takes its heat input from the burners, and the electric arc method, which uses electricity. In the case of the open hearth furnace, if the intensity of steel making is low, the rate of emission of fumes would be limited, and it may not be necessary to install cleaning systems. However, if high top blow technology is

Environment impact of mineral industries – industry-wise 91

used, the red fume emission would be high, and cleaning systems, such as electrostatic precipitators, will have to be installed. In the case of electrical furnaces, there are two methods of fume collection: (1) “direct” collection of fumes from the fourth hole into the furnace roof (three holes are taken up by electrodes), and (2) secondary collection of fumes to capture those gases which are emitted in charging the furnace, and tapping from it. In the case of a 80 t furnace, the throughput rates are about 1000 Nm3: h/t for the collection from the fourth hole, and 4000 Nm3/t for secondary fumes. Dust cleaning is done by bag filter, fitted with needle felts. High-energy scrubbers have been developed for direct collection only. Reheating furnaces used in rolling mills are energized by blast furnace or coke oven gas, or natural gas or fuel oil. Particulate pollution is minimal, and hence no dust cleaning is needed. 4.1.5

Techniques for reducing gaseous pollutants in the steel industry

Control techniques have been installed in most steel mills to reduce the particulate emissions. The emphasis now is on the reduction of gaseous pollutants. Desulphurization and denitration constitute the most important techniques for the elimination of gaseous pollutants in the iron and steel industry (source: UNEP Technical Review, 1986, p. 54–55): Desulphurization: can be effected in two ways, by chemical treatment through alkaline products, such as, calcium, sodium, magnesium, ammonium products, etc. or by physical treatment involving adsorption using activated carbon. Japan achieved desulphurization of 90% using the milk of lime for desulphurization. The gases are scrubbed with calcium (milk of lime or calcium chloride solution) or ammonium based liquid, to recover SO2 and SO3 in the form of calcium and ammonium sulphate. The new practice is to link several physical purification processes together – for instance, it is possible to capture residual dust and SO2 together by using bag filters charged with lime. Denitration: Since nitrogen oxides are formed in the course of combustion, denitration is effected by limiting the formation of nitrogen oxides or removing them as they form: (1) modification of the combustion process (by lowering the temperature of the flame, reducing the excess air, cutting down the time spent in the combustion chamber, and technological modifications in the chamber), (2) modification of the fuel (high-temperature denitrating of the coke beforehand), (3) by the addition of lime to the sinter burden, nitrogen oxides formed are immediately recovered, (4) waste gas is denitrated by chemical reaction with a base, catalytic reduction of nitrogen oxides to molecular nitrogen (by ammonia in the presence of the catalyst Fe2O3 – Al2O3 or V2O5 – Al2O3 at temperatures of 200–400 °C) and consolidation in the form of dust (to be removed by simple dust collectors). Dust extraction systems need to be modified continually in response to changes in steel-making technologies, nature of the feedstock, environmental regulations (which generally tend to be more and more stringent as time goes on), and markets.

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The directions in which progress could be expected in dust collection are as follows (UNEP Tech. Review, 1986, p. 59–61): 1. Electrostatic precipitators are used extensively in the steel industry for dust collection (main gases in the sinter plants, detarring in coking plants, oxygen cutting and scarfing), as they are economical to use in terms of energy. The performance of the electrostatic precipitators is being enhanced by adopting higher voltages (e.g. 150,000 V at the sinter strand), improvements in the design of the emitting and collecting electrodes, introduction of partitions in the precipitators to minimize the quantity of particles that fly off on impact, improving the efficiency of wet precipitators by improving the spraying action of the liquid through the use of an electrostatic device, etc. 2. Use of ring-shaped wet precipitators which operate at high speed (e.g. 20 m/s). 3. Dust collection at high temperatures (say, 600–1000 °C) through the use of fabrics woven from stainless steel fibres, or refractory fibres (e.g. aluminium oxide). 4. Increasing filtering speed through the use of needle felts, to be able to achieve throughput rates of the order of millions of m3/h. 5. Use of ceramic “sponges” which can be used both for dust collection and water treatment. 6. Energy efficiency: The dedusting operations generally use high energy scrubbers of the Venturi type for fine-spraying of water into the gas. A more efficient energy option is the use of convergent jets, whereby a mist of very fine droplets is formed by making two jets of water under pressure to converge. 7. The new trend is to combine several physical processes in the same appliance, (e.g. bag filters charged with lime, which could capture both dust and SO2 gas in one go). 4.1.6

Noise pollution in the steel industry

In the case of steel industry, large capacity blast furnaces (say, 9000 t of pig iron/d) are a major source of noise. The noise may arise from multiple sources, such as, balance of high top pressure, charge in the throat, hydraulic drive, blowers, snort valves on the blast, inversion of hot-blast stoves, safety valves on the top gas ducts, cleaning of top gas, water cooling pumps and circuits, etc. Electric arc furnaces may emit upto 120 dB(A) of noise, which could be reduced by the installation of a system of sliding doors to insulate the furnace from the rest of the bay. The noise emissions could be reduced by changing from A.C. arc (which is the source of noise on 100 Hz) to D.C. arc. Induction furnaces are recommended to be used, as they are noiseless. 4.2

ALUMINIUM INDUSTRY

Berthier gave the name “bauxite” to the aluminous sediments in the Les Baux area in France. The term, Bauxite, is now used to designate the Al-rich varieties

Environment impact of mineral industries – industry-wise 93

of weathering products, composed largely of gibbsite [Al (OH)3], boehmite ( -AlOOH), and diaspore ( -AlOOH). Bauxite is the principal ore of aluminium. It should preferably contain not less than 45% of Al2O3, and not more than 20% Fe2O3, and 3–5% combined silica. As bauxite is a surficial deposit, it is invariably mined by opencast mining. The overburden is stripped, and the ore is mined by draglines and shovels. An ugly scar in the landscape will be left behind, unless steps are taken to reform the arable layer through appropriate revegetation methods. Open-pit mining of bauxite produces large amounts of dust. Other operations, such as transportation of the ore, grinding, sorting, etc. also produce large quantities of dust. Knowledge of the wind patterns is necessary to design control measures. Other environmental pollutants are coal dust from steam generators, alumina dust from calcining stacks, emissions of fluoride and other gases from the refinery, etc. During the calcination of aluminium hydrate to anhydrous alumina, dust comes out at both the ends of the kiln. Electrostatic precipitation at one end of the kiln, and bag filters at the other end help to reduce dust emission. The ash and dust particulates that are emitted by the steam plants along with fine gases are passed through cyclones before being discharged through high chimneys. 4.2.1

Red mud

Huge quantities of red mud waste are produced in the process of treating bauxite to produce alumina by the Bayer process. Red mud is by far the most serious environmental problem associated with aluminium industry. It is composed principally of the oxides of aluminium, iron, titanium and silica, with minor quantities of vanadium, gallium, calcium, magnesium, etc. The range of composition of red muds is as follows: Al2O3: 15–30%, Fe2O3: 20–50%, TiO2: 5–28%, V2O5: 0.1–0.4%, etc. The amount of red mud produced per tonne of alumina varies from about 1.06 to 1.33 t in India, to as high as 3.5 t in Australia, though 2 t may be taken as typical. For each tonne of alumina, about 1 to 1.3 t of red mud is produced, depending on the composition of bauxite. It has been estimated that from one million tonnes of red mud, about 300,000 t of iron, 60,000 t of titania, and 900,000 liquid alum could be recovered (source: Monograph no. 5 on Bauxite, 1977, Indian Bureau of Mines, Nagpur). Red mud has a coarse fraction (sand) and a fine fraction containing iron oxides, sodium-aluminosilicates, titanium oxide, etc. The slurry consisting of the insoluble residue from the caustic liquor is pumped to storage areas, called red mud ponds. It has been estimated that the disposal of one tonne of red mud requires a space of 0.4 m3. These ponds cause a number of problems: they are ugly to look at, they occupy a large area, make the surroundings dusty as they dry up, contaminate the surface water through overflow or rain wash, and the groundwater through seepage, etc. Extensive R&D studies are going on to ameliorate the red mud problem, through (1) extraction of valuable metals, such as vanadium, and gallium, and (2) use of red mud to ameliorate the wastewater, and for making bricks and as a filler.

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Gallium is extensively used in the electrical (e.g. vapour arc lamps, electrodes) and electronics (e.g. rectifiers, transistors, lasers) industries. As the electronics industry is growing exponentially, there is bound to be an increasing demand for the metal which fetches a good price in the market (USD 600/kg in 1980). The most convenient way to recover gallium is from the sodium aluminate liquor obtained in the Bayer process – the liquor has a high content of gallium in a readily available form, and gallium could be recovered without any preliminary processing. Vanadium is used in iron and steel industry, to make the steel fine-grained and uniform, and to improve the ductility and hardness of steel. Other applications of vanadium are as a colouring agent in the ceramic industry, and as a catalyst in chemical industries. Vanadium is recovered from the vanadium sludge. Some companies process the red mud in the form of semi-dry and impermeable cake, and dump it in the open. The cake gets dried in a week’s time, and can be dozed. Since the material is dry, seepage would not be a problem. Another option is washing the red mud to reduce the caustic soda content from about 65–70 g/l to 2–3 g/l, and then transporting the mud in the form of slurry. The critical aspect here is the prevention of seepage. Either the pond should be sited in an area of low permeability, or it should be having layers of compacted clay, or a geosynthetic liner should be used. Additionally, a series of underdrains could be built to collect any seepages. 4.2.2

Pollutants from aluminium smelters

The principal pollutants from the smelters are summarized in Table 4.6 (source: The World Aluminium Industry, v. 1, 1982, Sydney). Table 4.6

Principal pollutants from Aluminium smelters.

Type of pollution

Material produced

Gaseous emissions

Carbon monoxide, carbon dioxide, hydrogen fluoride, sulphur dioxide, carbon disulphide, silicon tetrafluoride, hexafluoroethane, water vapour

Solid emissions

Alumina, cryolite, aluminium fluoride, calcium fluoride, carbon, iron oxide

Liquid effluents

Fluorine compounds, hydrocarbons (from soderberg plants entrained water)

Smelter waste

Spent potlinings, anode butts from prebaked pots, dust from gas cleaning, sludges from cleaning scrubbing water, material from pot skimming, spills

Paste preparation emissions and wastes

Coke dust, coal dust fines, hydrocarbon fumes

Anode baking emissions and wastes

Hydrocarbons, fluorides, sulphur

Cast house emissions and wastes

Fluxing flumes (primarily aluminium chloride), trace fluorine, sulphur dioxide

Ancillary operations emissions and wastes

Dust from material handling, demolition of old pots, and cleaning of pre-baked anode butts to recover carbon

Environment impact of mineral industries – industry-wise 95

Aluminium smelters emit approximately 780 m3 of gases per tonne of aluminium from the cryolite, aluminium fluoride, calcium fluoride and sodium fluoride used in the electrolytic process. Gas cleaning plants remove tar vapours, carbon monoxide and other gases. Dust (96–97%) and tarry substances (∼70%) are removed through the use of electrostatic precipitators. Scrubbing with soda solution traps 98% of HF and SO2 gases in the form NaF and Na2SO4. After the noxious gases are released, the emissions are let out through a high chimney. Cryolite is recovered from the scrubbed solution in the Cryolite Regeneration Plant. The residual mud after the recovery of cryolite, is neutralized with lime and sent to the mud pond. The soda solution is also recycled. An oil-water emulsion is used for cooling and lubrication purposes. As should be expected, water used for washing and cooling in the fabrication plant gets contaminated with oil. The contaminated water is collected into a sump, and the oil which comes to the top is skimmed off. The water is chemically treated, before being reused in the process line. The emulsion waste is treated in an emulsion waste disposal plant. The recovered oil is purified, and stored in drums. The water is neutralized, and disposed. Air quality is measured at the anode paste plant, steam plant, and gas cleaning plant. Fugitive emissions are measured at the ropeway, bauxite crusher, coal crusher, alumina silos, weighing bridge/wagon tippler, calcinations/caustic drum storage yard, foundry pig yard, cell houses/smelter silos, etc. The permissible threshold for humans set by US National Academy of Sciences in 1971 was 2.45 g/m3 for hydrogen fluoride, and 2.15 g/m3 for particulate fluoride. Ingestion of large quantities of fluoride (say, 20–80 mg/d) over a long period (say, 10–20 years) is known to cause skeletal fluorosis in humans and animals. Cattle may ingest fluoride when they graze plant leaves covered with fluoride-rich dust from aluminium refineries. Studies in Japan (source: Tsunoda) have shown that if the atmospheric fluoride level is 1 ppb, the fluoride content of the vegetation in the area around the aluminium refinery reaches about 30 ppm (dry weight basis). There is considerable variation in the tolerance of plants for fluoride toxicity. In Hungary, an oak pine forest has been destroyed to a distance of 800 m from the aluminium smelter. Scotch pine forests have been seriously affected upto a distance of 10–13 km from the fluoride source. 4.3

BASE METALS INDUSTRY

This account about base metals is drawn largely from the UNEP Tech. Report no. 5, 1991. Base metal ores represent about 15% of the tonnages of minerals extracted globally. The specific environmental problems of the base metals arise from the compositional nature of the ores, the reagents used for the beneficiation process, and the potential toxicity of the metals and compounds extracted.

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The important sulphide and oxide ores of Cu, Ni, Pb, and Zn are given in Table 4.7. The metal content of ROM (Run-of-Mine) ores of non-ferrous metals is usually low (e.g. 1.014% Cu in El Teniente, Chile; 0.87 g/t of Au in Cortez, Nevada, USA). Hence it is necessary to concentrate the ores at mine site, and then send the concentrates to a smelter or a hydrometallurgical plant for the extraction of metal concerned. Table 4.8 lists the common beneficiating processes. Unlike the iron ore whose Fe content is generally of the order of 60%, the content of metal in the base metal ores is usually of the order of a few per cent. The gangue minerals most frequently present are silica, silicates, carbonates and pyrite. Occasionally, fluorite and barite may also be present. Acid Mine Drainage (see section 8.1 for details) is caused by pyrite and pyrrhotite which may be the principal gangue minerals in the sulphide ores of base metals. Table 4.7

Ore minerals of Cu, Ni, Pb and Zn.

Metal

Sulphides

Oxidized minerals

Copper

*** Chalcopyrite CuFeS2 ** Bornite Cu5FeS4 ** Chalcocite CuS * Tetrahedrite (Cu, Fe, Zn, Ag)12 (Sb,As)4S13

** Malachite Cu2(OH)2CO3 * Azurite Cu2O * Cuprite Cu3(OH)2(CO3)2

Nickel

*** Pentlandite (Fe,Ni)9S8 *** Millerite NiS

** Garnierite 3SiO2.4(Mg,Ni)O.6H2O *** Lateritic nickel ores

Lead

*** Galena PbS

** Cerussite PbCO3 * Anglesite PbSO4 * Pyromorphite Pb5(PO4,AsO4)3Cl

Zinc

*** Sphalerite ZnS

** Smithsonite ZnCO3 * Calamine SiO2.2ZnO.H2O * Zincite ZnO * Willemite ZnSiO4 * Franklinite (Fe,Mn,Zn)O.(Fe,Mn)2O3

*** Most important, ** Occasional ore, * Rare.

Table 4.8

Common beneficiation methods (source: UNEP, 1991, p. 16).

Metal

Sulphide ore

Oxide ore

Copper Nickel Lead Zinc

Gravity, Flotation Flotation, Magnetic separation Gravity, Flotation Gravity, Flotation

Gravity, Flotation, Leaching – Gravity, Flotation Gravity, Flotation

Gold is beneficiated using gravity, flotation and leaching methods.

Environment impact of mineral industries – industry-wise 97

4.3.1

Pollution of water by base metals

The chemical characteristics of raw mine water in the lead and zinc mines are given in Table 4.9 (source: Hustrulid, 1982). Some base metals, such as zinc and copper, are necessary for human health. Zinc and copper serve the physiological function as metallo-enzymes, and their Recommended Daily Intake is 15 mg/d and 0.15–0.5 mg/d respectively. But in high concentrations, they are toxic to humans and aquatic biota. Heavy metals can prevent the reproduction in fish, and could enter the human food chain by getting concentrated in the fish tissue. The toxicity of heavy metals in fresh water depends not only on the concentration of metals, but also on factors such as pH, water hardness, presence of other metals and chelating agents, etc. Table 4.10 shows that at low levels of water hardness, even small concentrations of copper and zinc could be toxic to the fish (source: EEC Council Directive no. 78–659). Table 4.9 Range of chemical characteristics of raw mine water from lead and zinc mines (source: Hustrulid, 1982). Parameter

Mines with acidic characteristics (concentrations in mg/l)

Mines without acidic characteristics (concentrations in mg/l)

pH (units) TSS * COD ** Oil & grease P Ammonia Hg Zn Cu Cd Cr Mn Fe Sulphate Chloride Fluoride

3.0 to 8.0 2 to 5.8 15.9 to 95.3 0 to 3 0.002 to 0.075 0.05 to 4.0 0.0001 to 0.0013 1.38 to 38.0 0.02 to 0.04 0.016 to 0.055 0.17 to 0.42 0.02 to 57.2 0.12 to 2.5 48 to 775 0.01 to 220 0.06 to 0.80

7.4 to 8.1 2 to 138 10 to 631 3 to 29 0.03 to 0.15 0.05 to 1.0 0.0001 to 0.0001 0.03 to 0.69 0.02 0.002 to 0.015 0.02  0.02 to 0.06  0.02 to 0.90 37 to 63 3 to 57 0.3 to 1.2

* Total Suspended Solids, ** Chemical Oxygen Demand.

Table 4.10

Effect of water hardness on the toxicity of Cu and Zn for fish.

Water hardness (mg/l CaCO3)

Cu (mg/l)

Zn (mg/l)

10 50 100 500

0.005 0.02 0.04 0.11

0.3 0.7 1 2

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Mineral resources management and the environment

Acidity causes the solubilization of heavy metals, and thereby increases the toxicity of water. Cyanides are lethal to fish even at extremely low concentrations of 0.04 mg/l. Some of the organic reagents used in ore beneficiation may be toxic. Oil forms a thin film over water, and could impede oxygenation of water by the atmosphere. It may also coat the gills of fish. Nitrogen contributes to the eutrophication of water bodies. 4.3.2

Pollution due to flotation reagents

The flotation reagents used in the concentration of base metals are listed in Table 4.11 (source: Environment Canada, quoted in UNEP Tech. Report no. 5, 1991, p. 23). Flotation processes for the beneficiation of base metals are generally carried out under alkaline medium. The solubility of heavy metals in water under conditions of basic pH is low. The limited amount of heavy metals present in the process water is precipitated with the solid tailings (as in Swedish mines, item I of Table 4.12). However, if iron sulphides are present in the tailings, and such tailings are used to build tailings dam, low pH seepage water, similar to acid mine drainage, may get generated (as in Canadian mines, item II of Table 4.12). Table 4.11

Typical ore processing reagents (source: Environment Canada, 1987).

Reagents

Comments

Acids (H2SO4, HCl, HNO3) Alkalis (CaO, Ca(OH)2, CaCO3, Na2CO3, NaOH, NH4OH, NH3) Frothers and collectors

Surface active reagents

Modifiers

Surface active organics and various inorganics, such as NaCN, Na2SO3, CuSO4, ZnSO4, Na2S, AlCl3, Pb(NO3)2, silicates and chromates

Sodium Cyanide

Used for the cyanidation of precious metals, and as depressants in the flotation of copper, lead and zinc ores

Flocculants, Coagulants

Aluminium and iron salts, and organic polymers

Table 4.12

Wastewater quality of tailing ponds at base metal mills.

pH Turbidity (mg/l) Conductivity (S/cm) Cu (mg/l) Fe (mg/l) Zn (mg/l) Pb (mg/l) SO4 (mg/l) Thiosalts (mg/l S2O3)

Cu-Pb-Zn Swedish mines

Cu-Pb-Zn Canadian mines

7.5–8.1 1– 600–1700 0.01–0.003 0.11–0.23 0.14–0.32 0.013–0.026 190–330 n.a.

6.5–9 8 0.1 1.0 0.5 0.1 n.a. 50

Environment impact of mineral industries – industry-wise 99

Thiosalts form in the course of flotation of sulphides under alkaline conditions. If such thiosalts (even at concentrations of few hundred mg/l) find their way to the tailings pond effluents, they can get oxidized into sulphuric acid, and create serious environmental problems. When flotation is carried out properly, most of the process chemicals used in the process, with the exception of the pH modifiers, get adsorbed on the surface of the minerals. However, if some reagents are used in excess, they may remain in solution in the mill tailings. When once the reagents reach the tailings ponds, they will get oxidized, and will therefore not appear in the final effluent. The kinetics of oxidation is temperature-dependent. In the cold season, oxidation may not be able to completely destroy the excess reagents which may therefore persist in the final effluent. Cyanide at low concentrations is used in the flotation of lead-zinc ores. The content of cyanide in the flotation tailings is low enough to be removed by natural degradation, through the process of volatilization of hydrogen cyanide. Large quantities of cyanide are used in the gold processing, and the mode of removal of cyanide has been described elsewhere (see Section 7.6).

4.4

COAL INDUSTRY

Coal is a critically important mineral in the industrial productivity of any country. It is used to generate electricity, power the steam engines, smelt iron ore, and produce a variety of chemicals. No wonder the production of coal (4600 Mt.) far exceeds other minerals. In the case of countries like USA, coal contributes about one-third of the energy production. As against this, the contribution of coal to energy production far outweighs that of oil and natural gas in the case of countries, such as China and India. The environmental impact of coal industry arises from the mining and transportation of coal, washing of coal, combustion of coal, etc. (see Das & Chatterjee, 1988, for a good summary of the topic). It has been estimated that the progressive disintegration of 1 cm3 lump of coal may form 1012 particles, and could spread over 283 m3 of working ambient. Because of their extremely small size (0.2–10 m), they are invisible to the naked eye, and could remain suspended in the air for a long time. For this reason, the ambient air loaded with these dust particles appears deceptively clear. But this dust is respicable and could cause pneumoconiosis, bronchitis and severe dyspnea (shortness of breath). The coal mine dust contains a wide range of non-coal particles, such as silica, naphthalene, and several Polynuclear Aromatic Hydrocarbons (PAHs). It has been estimated that a mine producing one million tonnes of coal annually, about a tonne of toxic elements such as, arsenic, beryllium, cadmium, fluorine, lead, mercury, etc. are liberated as dust or gas where coal is cut from the working face. The dust problem is greater in arid and tropical climates.

100 Mineral resources management and the environment

Coal is mainly transported by rail and truck. In countries, which have canals and navigable rivers, coal is transported by towed barges. Coal is also transported by sea. The transport of coal involves emission of fugitive dust. It has been estimated that 0.2 kg/t each is emitted during loading and unloading operations, and the loss in transit may be 0.05–1% of total coal (excluding loss to spillage and pilferage). Szabo (1978) made the following estimates of the atmospheric emissions from a unit train carrying 1143 t of coal making a round trip of 985 km (in terms of kg/trip): Particulates: 345; SO2: 780; NO2: 4855; Hydrocarbons: 2075; CO: 935; Particulates during loading: 2285; Particulates during unloading: 2285; Fugitive emissions in transit: 5700. Coal is beneficiated to improve the heat content, while at the same time reducing the content of mineral matter, including pyrite. In the case of the Gondwana coals, which are of drift origin, the mineral matter is intimately interspersed in coal, and it is virtually impossible to remove all sulphur and other mineral impurities present in the coal. All the steps involved in the beneficiation process, namely, comminution, sizing, cleaning, dewatering, drying, etc., all contribute to pollution. Huge quantities of water used in washing, get polluted, and need to be treated before recycling. Coal is carbonized in coke ovens to produce hard coke suitable for the steel industry. The process produces a series of primary byproducts, such as coal tar, ammonia liquor or ammonium sulphate, crude benzole and coal gas. Coal tar itself is a complex mixture of aromatic hydrocarbons, such as benzene, naphthalene, anthracene, pheanthrene and their homologues. Figure 4.2 (source: UNEP, 1986, p. 83) gives the treatment models summary of the byproducts of coke making. Carcinogenicity of coal tar derivatives depends upon the temperature of carbonization. Distillation products of tar at high distillation temperatures of around 800–850 °C, are composed of Polynuclear Aromatic Hydrocarbons (PAHs) (such as BP – benzo( )pyrene, DBA – dibenzo( )anthracene, or DBP – dibenzo( )pyrene), which are known carcinogens. It has been observed that roofing workers who routinely handle coal tar and pitch products, contracted skin cancer four times, and lung cancer fifteen times, more than the control group. The carcinogenicity of anthracene fraction of coal tar arises from its high content of benzo pyrene (27 g per kg). The combustion of coal leads to the production of a variety of pollutants, such as the oxides of sulphur, nitrogen and carbon, as well as particles of ash that get entrained in flue gases. Sulphur dioxide is by far the most serious pollutant, because it has impacts on human health, and it causes acid rain, which damages vegetation and buildings, etc. In the atmosphere, sulphur oxides get converted into highly corrosive sulphuric acid. Sulphur may be present in coal in two forms: (1) organic sulphur, and (2) pyritic sulphur. About 70–80% of sulphur present in the Indian coals is said to be in the organic form. When coal is subjected to combustion (as in thermal power stations), organic sulphur is more readily converted to SO2 than pyritic sulphur. Stationary combustion sources account for 70% of the sulphur emissions. The sulphur emissions from the

Figure 4.2

By-products of coke making – treatment models summary (source: UNEP, 1986, p. 83).

Environment impact of mineral industries – industry-wise 101

102 Mineral resources management and the environment

coal industry exceed the emission of sulphur compounds from natural processes world wide. Nitrogen oxides (NOx) are produced when nitrogen naturally present in coal reacts with oxygen in the combustion chamber. In the atmosphere, NO gets readily converted to more toxic NO2, and the production of highly corrosive nitric acid. Nitrogen oxides can have health effects, can damage crops, and lead to the production of secondary pollutants. Fossil fuel combustion accounts for about 95% of the anthropogenic production of NO2. Los Angeles type of smog is produced when NO2 and hydrocarbons react photochemically under conditions of atmospheric inversion. NOx is a radiatively active gas, and has a role in global warming and the depletion of the ozone layer in the atmosphere (“Antarctic Ozone Hole”). Two main groups of hydrocarbons are emitted during coal combustion: (1) Low molecular weight species, derived from the volatile matter present in the raw coal, and (2) High molecular weight species which are emitted as fine particles, or more commonly adsorbed on fie particles. In moderately large boilers (say, 25 MW), the volatile fraction (measured as CH4) and particulate fraction (measured as benzene soluble organics) is of the order of a few milligrams per m3 of flue gas. Pre-treatment of coal, fluidised bed technologies and the advanced, low-polluting coal combustion system, called Low NOx Concentric Firing System (LNCFS), are making it possible to make efficient use of high-ash coal, with reduced emission of gases.

4.5

INDUSTRIAL MINERALS

The following account is drawn from an excellent study of Saxena and Chatterjee (1988) about the environmental impact of mining of some industrial minerals in the state of Rajasthan, India. This study has been chosen as a case history, as quantitative data has been reported about the degree of loss of biodiversity, and reduction in the biomass productivity, as a consequence of mining of industrial and other minerals. It has been estimated that wasteland constitutes about 27% of the land area of Rajasthan. Though exact figures are not known, mining is undoubtedly the principal cause of degradation. In western and southern Rajasthan, mining has resulted in vast areas of land becoming barren, unproductive, and deeply pitted. Gypsum: Gypsum is mined after the removal of the overburden (60–120 cm). There are mounds of 2–11 m height. Excavation brings up salts from lower depth. Desmostachya bipinnata (dab) grass is the preponderant vegetation, and is probably an indicator for gypsum, while Peganum harmala (harmal) appears to be an indicator of crystalline gypsum (CaSO4.2H2O). Unmined sites show 3–4 species of trees and shrub, while the mined sites have none. The herbage yield from the mined sites varies from 0.92–2.5 t/ha, as against zero to 0.09 t/ha for the mined sites. Fuller’s earth and bentonite: The inhospitable habitat conditions coupled with the removal of vegetation by the labourers for fuel wood, has severely degraded

Environment impact of mineral industries – industry-wise 103

the vegetation. Only a few stray, deformed, cushion-shaped tree species stumps (5–10 plants/ha) of kumut (Acacia Senegal), jal (Salvodora oleoides), kangkera (Maytenus emarginata) are observable. The ground vegetation of the unmined sites includes bui (Aerva psuedotomentosus), sannia (C. burhia), tantia (Elesine compresa) and several grass species. The mining sites and mine spoils areas do not support any shrub or tree species. Old mining waste dumps support a few pioneer colonizer species, such as dhamsa (Gagonia cretica), bhoorangni (Solanum surattense), chamkas (Corchorus depressus), etc. Ochre and china clay: Red and yellow ochres are mined after the removal of 60–90 cm of the overburden soil of the pediment plains. The excavation has been continued, resulting in a huge pit of 200  300 m which could serve as a water reservoir or a fishpond. Almost all the firewood material has already been removed, as evidenced by tree stumps. The natural vegetation surrounding the mine includes Phoenix sylnestris, Delonix elata, Acacia nilotica, Cassia auriculata, etc. All the pits are devoid of any vegetation. China clay is mined after the removal of top soil (60–100 cm). The mining site does not support any perennial vegetation except a few short-lived annual species which are capable of serving as pioneer colonizing species on disturbed substratum. As usual, firewood and shrub species have been severely exploited. Marble: Marble is mined after the removal of thin overburden of 90–150 cm of soil overburden. Tree density varies from 24–40 plants/ha, whereas grass clusters range 15–20/ha. The ground flora includes dab (D. bipinnata), tantia (Eleusine compressa), beoni (Tephrosa purpurea), etc. Old mine spoils with good soil cover gets easily established by trees and shrubs like vilayati babool (P. juliflora), ak (C. procera), munj (Saccharum bengalense), etc. These exhibit a density of 6– plants/1000 m2, with 2–5% crown cover. During monsoon, colonization of annual species takes place. Sandstone: Sandstone is mined in large-scale quarries. Heaps of overburden 5–10 m high are scattered haphazardly. They occupy a much larger area than the actual area of mining. Unmined hilly part provides 20–55 shrubs/ha with 6–9% crown cover, and above ground biomass of 1.0 t/ha. Some sandstone pits are quite large and deep, and could be developed for fish culture. Scrubby vegetation, such as thor (Euphorbia caducifolia) and gangeran (Grewia tenax) community (60–90 shrubs/ha) is characteristic of unprotected hillocks. Soapstone, pyrophyllite, wollastonite and calcite: The minerals are mined after the removal of 120–150 cm soil overburden. Heaps 3–5 m high are scattered all over the area. Due to fifty years of mining activity, the vegetation as a whole is in a highly degraded condition, whereas the mining areas are completely bare. The degraded and deformed trees and shrubs pertain to rehonja (A. leucophloea), dhak (Butea monosperma), anwal (Cassia auriculata), etc. with a density of 15–20 plants/ha. In the case of calcite mining area, the luxuriant vegetation in the unmined area is in sharp contrast with the mined area which is devoid of vegetation. In the unmined area, there is tree density of 15 plants/100 m2, with more than 50% crown cover. The important tree species are, jamun (Syzygium cumini), baheri (T. bellerica), gular

104 Mineral resources management and the environment

(Ficus glomerata), etc. The stone debris of mining does not support any vegetation as there is no soil cover. Limestone: This is mined by mechanized methods, to provide the raw material to the cement factories. As a consequence of cutting down of vegetation for fuelwood, the vegetation in the area is generally degraded. Deformed stumps of dhokra (Anogeissus pendula) and salaran (Boswelia serrata) could be seen at a density of 60–90/ha. The gravelly and bouldery muck dumped in the valley is completely devoid of any vegetation. At one point, excavation created a large, deep (27 m) pit, which could later serve as a water reservoir or a fish pond. Rock phosphate: The rock phosphate is mined on a large scale using heavy equipment. Mine spoils, 20–50 m high, could be seen all over the place. The unmined area supports an open plant community of Butea monosperma and Wrightia tinctoria. The associated shrub vegetation is anwal (Cassia auriculata) and neel (Indigofera argentea). Annual grasses grow in profusion during the monsoon time. Propopsis juliflora is a pioneer colonizer on the tailings dump. Mica: This is the only industrial mineral which is mined by underground mining. Colourful flowering of Saccharum during winter is an indirect indicator of the existence of mica, but needs to be confirmed by drilling. The mica mining areas support plant community of Acacia nilotica, and C. deciduas (35–60 plants/ha). Very old mica dumps (2.4 m high) support a few perennial species such as dhak (Butea monosperma) and khemp (Leptadenia pyrotechnica). The following plant species are suitable for being used for revegetating mining spoils/tailings of gypsum, bentonite, Fuller’s earth, and clays (Saxena & Chatterjee, 1988). Trees: Prosopis juliflora (vilayati babool), Acacia tortilis (Israeli babool), Salvadora Oleoideas (jal). Shrubs: Sueda fruticose (kala lana), Haloxylon salicomicum (jeriolena), H. recurvum (sajilana), Indigofera oblongata (goila). Undershrubs: Aerva persica (bul), Crotalaria burhia (sannia). Grasses: Dichanthium annulatum (kerac), Sporobolus marginata (dave), Chloris virgata (kalia), Cynodon dactylon (doob), Desmostechya bipinnata (dab). Apart from the nutritional and other deficiencies of the mine dumps, any revegetation of the mined land has to take into account the fact that the area is arid. So the local hardy species together with the introduced successful exotics should be tried. For instance, Dichrostachys (kolai) and Balanites aegyptiaca (hingola) produce root suckers in course of time. Large-sized pits are produced as a consequence of the mining of limestone and sandstone. These get filled during the monsoon time, and water remains in them for about six months. Fish can be grown in these ponds during these periods. By stocking the ponds with selective breeds, by giving the fish supplemental feed and by adopting a cycle of harvesting by which only adult fishes are caught, and the fingerlings left behind, it is possible to get good returns from the ponds. During years of excessive rainfall, the pond water could be used for sprinkler irrigation. Some unsuitable quarry pits could be filled by rock debris and used for groundwater recharge.

CHAPTER 5

Impact of mining on the environment – waste-wise

5.1

INTRODUCTION

Almost all the mining involves the penetration of the lithosphere through quarries, opencast mines and the underground mines. Hydrosphere comes into the picture in the process of working the river placers and extracting minerals (usually heavy minerals, but in the case of Namibia, diamonds) from the seabed. Mining and extraction of minerals have impacts on rocks, soils, water, air and the biota. Three types of changes may be expected as a consequence of mining: (1) Change in the natural topography, and the consequent disturbance in the suitability of land for various uses, such as, agriculture and forestry, (2) Change in the hydrogeological condition, affecting groundwater and surface water, and (3) Change in the geotechnical conditions resulting in the deformation of the natural conditions of the rock mass, including dislocations the surface (Vartanyan, 1989, p. 39). The impact of mining in a given district is determined by the geological characteristics of the rocks, such as, age, lithology, structure and tectonics, geomorphic setting, weathering, etc. Most of the Archaean belts have undergone polyphase metamorphism and deformation. On the other hand, some of the younger formations may be flat-lying and unmetamorphosed. Igneous and metamorphic rocks are generally much harder than the sedimentary rocks. In the tropical countries, weathering can go very deep. Surface mining usually involves the removal of the soil cover and the detritus through the use of scrapers, bulldozers or digging machines, followed by the drilling and blasting of the rock below it. The mined material is crushed, stored, dressed and concentrated in various ways. These operations have the effect of changing the stress balance in the rock, hydrostatic pressure in the pores and aquifers, and releasing dust and gas into the atmosphere. The resulting vibrations, landslides, and contamination of soil, water and air may adversely affect people, animals, vegetation and engineering structures. The response of the rocks to drilling and blasting depends upon the geotechnical properties of the rocks (Johansson, 1986; Zhu, 1986; Nilsen, 1986; Lappalainen, 1986,

106 Mineral resources management and the environment

quoted by Vartanyan, 1989). For instance, the strength index in uniaxial compression of some granites have been found to vary from 38 to 275 Mpa depending upon the modal composition and stress orientation of a granite. The uniaxial compression strength of a sandstone may vary from 58.3 Mpa in dry state to 29.1 Mpa when wet; shearing strength perpendicular to the bedding is 4.1 Mpa and parallel to it, 2 Mpa, and so on. The stability of rock masses is determined by the presence of fractures, folds and faults. Intrusive rocks generally have three main conjugate system of joints, which intersect each other, leading to cubical joints. Folding determines the kind of jointing in gneisses and shales. Some rocks have cavities in the fractures, which are often filled with clays that swell when moistened. The swelling could be as high as 80%. This results in strong pressure leading to rock displacement. In the solid rock, permeability is generally low. Rock stress changes as mining progresses. Hence, it is essential to monitor the stress. Vertical stress is about one-third to one-half of the main horizontal stress. Some studies show that the horizontal stress in the bedrock could increase from 5 Mpa at the surface to about 50 Mpa at a depth of 700 m.

5.2 5.2.1

IMPACT OF MINING ON THE GEOENVIRONMENT Impact of mining on the lithosphere

Mining involves the extraction of large quantities of rocks, liquids and gases from the depths of the earth, and therefore causes damage not only on the surface but also to depths of hundreds and thousands of metres. In the case of surface mining, the extent of geomorphic change is conditioned by the thickness of the overburden covering the deposit, the quantity of barren rock that needs to be excavated per unit of the extracted mineral and the area of the mine. Underground mining may lead to surface subsidence with consequent disturbance to surface runoff, formation of water-filled depressions, and flooding in the coastal areas or near lakes. When the horizontal layer deposits are mined, waste banks are left behind in the worked out area as the mining front advances. This leads to the formation of alternating ridges and depressions of the waste rock. In the case of steeply-dipping lodes, big cone-shaped excavation pits form. Wind-blown dust, spontaneous combustion and contamination of precipitation are some of the adverse consequences of the waste dumps. Also, the waste dumps use and degrade land that could be used for farming or forestry. For instance, in the former East Germany, the mining of brown coal decreased the farm land by 320 km2, and forest land by 90 km2 (these degraded lands have subsequently been ameliorated). Mining under water generally involves dredging of loose sediments under water. If the sediments involved are alluvial sediments, then the river beds, flood plains

Impact of mining on the environment 107

and river terraces will be affected. Dredging may leave behind waste dumps and small valleys. The mining of the estuaries and intertidal zones (usually for heavy minerals) disturbs the balance between the land and sea, and may trigger beach erosion. Cavities are formed underground when geotechnical methods of mining (such as, leaching, dissolution, fusion) are used. This leads to increase in porosity and decrease in the strength of the rocks. The area becomes prone to collapse of roofs and subsurface subsidence. Instances are known of collapse of rock-salt mines when water entered the abandoned mine and dissolved the salt pillars left there for roof support. Underground gasification of coal in the Angren coal basin in the former Soviet Union (involving a coal seam 5–15 m thick at a depth of 100–130 m, in an area of about 1 km2) gave rise to one of the biggest landslides in the world, with a volume of 0.8 km3 spread over an area of 8 km2 (Vartanyan, 1989, p. 42). Landslides and rock and mud flows are common in the mining areas, especially when the wastes are dumped on the hillsides. For instance, the volume of the mudflow arising from the Yimen copper mine in China, was of the order of 200,000 m3. Another mudflow of the volume of 100,000 m3 from a mine in Yunnan, China, destroyed 6.2 km2 of the fertile land on the plain. The mining of limestone and dolomite over a length of 40 km in Mussorie Hills in U.P., India, had disastrous environmental consequences. The mine owners picked up only the very high-grade material (50 mm size stones which are in demand for the sugar industry) and more than 30% of the ore (50 mm size material) was cast off to slide down the 30–50° slope. When heavy rains saturate the loose material, the debris flow cascades into the valley, clogs the river channels and gets spread over agricultural fields. The vibrations caused by the blasting operations destabilized the hill slopes, by opening out joints, fractures, fissures and cracks. This triggered mass movements, and reduced the discharge of springs (e.g. Shahastradhara, which means thousand discharges) which feed the streams. Consequently, many streams dried up (quoted from K.S. Valdiya, in Environmental Geology, 1987). 5.2.2

Impact of mining on the hydrosphere

Mining profoundly affects the hydrosphere in the following ways: (1) Groundwater table is lowered for mining to take place, (2) Mine water is discharged into the river systems, (3) Seepage from the settling tanks and evaporators adversely affect the quality of groundwater, and (4) Water is pumped into the ground for the extraction of a mineral (say, salt). Figure 5.1 (source: Vartanyan, 1989, p. 43) illustrates how the water drawdown in the course of the mining affects the hydrological processes. It shows how with the increase in the volume of mining activities and water pumping, a cone of depression comes into existence rapidly, the transient ground flow is reduced, and the mineralization of mine water and river water increases, with time. As a consequence of the surface mining, all the aquifers above a mineral deposit may be drained. In the case of the aquifers below a mineral deposit, water pressure

108 Mineral resources management and the environment

Figure 5.1 Diagram illustrating how the water drawdown in the course of mining affects the hydrological processes (source: Vartanyan, 1989, p. 43).

will be reduced, resulting in the formation of cones of depression. Also, surface mining involves the placement of large waste water ponds, seepage from which can pollute both surface water and groundwater. Underground mining results in the dewatering of rock and reduction in the hydraulic head. The consequences of removal of large quantities of groundwater are the compaction of sand and clay, development of major jointing, surface subsidence and damage to mine shafts and other installations. For instance, coal mining in the Upper Silesian basin of Poland at a depth of 400 m, adversely affected the hydrological regime in an area of 1200 km2. Coal mining in the Guishou province

Impact of mining on the environment 109

of China has caused the subsidence of 0.1–0.3 m over an area of 93,000 km2. Gold mining at a depth of 3000 m in the Western Rand area of the Republic of South Africa, has resulted in the formation of karstic sinkholes with depths of about 60 m and diameter of 90 m. In one district in the karstic region in the Urals in the former Soviet Union, the mine drainage increased the groundwater discharge from 3000 to 20,000 m3/h. The depression of groundwater levels and piezometric cones may sometimes lead to complete dewatering of the aquifers in the mining area. The size of the cones of depression depends upon the geological structure of the area and the type of mining. It may vary in radius from a few hundred metres to tens of kilometers. In districts where there is extensive mining, the cones may link up and cover the whole region, As a consequence of mining, huge cones of depression with a radius of 10–15 km have formed. Computer simulation has indicated that by the beginning of the twentyfirst century, the groundwater level in the European part of Russia may get lowered by hundreds of metres, and piezometric cones of more than 200 km may develop. As is well known, groundwater resources are depleted within the limits of the cones of depression. The water wells may go dry, and serious shortages of water may occur. Surface water resources may also be affected. The direction of movement of groundwater may change, and the springs feeding the streams may dry up. Swamps fed by groundwater seepages and fertile paddy soils (like gleysols and fluvisols) in the low-lying areas may be drained, thus affecting the productivity of land and the ecosystems. Small rivers and streams are particularly susceptible to the adverse consequences arising from mining, such as the inflow of highly mineralized waters and the reduction in the runoff. When water under pressure is used for mining, the hydrological consequences are exactly the reverse of normal mining – the groundwater level may rise, artificial springs may come into existence, and the groundwater recharge and rise in the water level may occur in the vicinity of settling, tailing and clear water ponds, etc. Mining has a profound effect on the geochemistry of both surface waters and groundwaters. The chemical composition of mine waters may range from freshwater to brine, depending upon the chemical composition of the pore water in the drained layers, and the content of the soluble salts in the formations. The water–rock interaction, particularly in the oxidation zone created by the mine workings, renders the waters highly acidic and capable of taking into solution a variety of toxic and heavy metals, such as, lead and cadmium. Where the mine water is discharged into streams, seepage invariably occurs, contaminating the groundwater. The stream water and the groundwater thus polluted become unfit for human consumption or even for irrigation, unless and until it is cleaned. A case history of coal mining from Guandong and Guizhon areas in China, illustrates how serious the hydrogeochemical consequences could turn out to be. The coal seams have a high sulphur content, and as expected, the mine waters have a highly acid pH, as low as 2 to 3. The mine waters from Guizhon contained ten times

110 Mineral resources management and the environment

the allowable concentration of contaminants. When the mine water was discharged into the streams, there was a marked decline in the catch of the fish and shrimp. When the water was used for irrigation, the yield of farm crops declined. It has been estimated that the polluted waters contaminated an area of 47,000 ha of rice paddies (Mengxiong & Alsong, 1989). 5.2.3

Impact of mining on the atmosphere

Dusts and gases are emitted in the course of working of the mineral deposits, or from dumps of coal and ore, waste tips, tailings, etc. In the opencast mines, dust may be released in the course of blasting. Escaping gases from rock and mineral masses, exhausts from the internal combustion engines in the mining machinery, gases released from the waste tips, etc. contribute to the gaseous emissions from the opencast mining. In the case of underground mining, air released from the underground workings, and rock masses, pollute the atmosphere. Methane, carbon monoxide, nitrogen oxide, and sulphur compounds may be released to the atmosphere in the process of mining. For instance, huge quantities of methane are released during coal mining in the Donetsk Coal Basin in the former Soviet Union (2.5 billion m3 of gases, of which methane constitutes 32%). The extracted gas is used as boiler fuel. Burning waste tips discharge noxious gases into the atmosphere. A medium-sized burning waste tip, can emit annually: 620–1280 t of SO2, 11–30 t of NO2, 330–500 t of CO, and 230–290 t of H2S. There were instances where a burning waste tip polluted the air for about 2 km around. As coal contains sulphur in the organic form of pyrite (FeS2), the burning waste tips of coal mines discharge large quantities of SO2 and H2S. It has been estimated that a total of 175 million tonnes (Mt) of gases are discharged from all the waste tips of the coal mines in the world. This amount includes 23 Mt of CO, 2 Mt of SO2, 0.9 Mt of H2S and 0.3 Mt of NO2. Blasting operations in quarrying and opencast mining pollute the atmosphere through dust and gases. For instance, if 200–300 t of explosives is used for blasting in a particular operation, the volume of the dust generated may be of the order of 20–25 million m3. Blasting operations also discharge nitrogen compounds, such as NH3 and NO2, into the atmosphere. One tonne of explosives produce 40–50 m3 nitrogen oxides. The discharge of dusts and gases into the atmosphere is bound to have health effects. It has been reported that in the highly industrialized Ruhr District of Germany, the incidence of respiratory diseases is 60% above the national average. High intensity noises, which are generated during blasting and the operation of the mining machinery, are hazardous to human health. It is now a common practice in most of the mining areas in the Industrialized countries to monitor the air continuously, for (1) the discharge, content and precipitation of dust and the concentration of heavy elements like cadmium, lead, etc. in air (pg/m3), and (2) the concentration of gases such as, SO2, CO2, H2S, NOx, NH3

Impact of mining on the environment 111

etc. in the air. When the ambient levels rise beyond the prescribed loads, corrective action is taken promptly to bring down the concentrations to the acceptable levels. To prevent loss and minimize pollution in the course of long rail transportation from the mine to the smelter, ore concentrates (e.g. Pb–Zn) are packed in heavy duty polythene bags. When the concentrates are transported by open trucks for short distances (say, less than 50 km), a minimum moisture content of 8% is maintained. 5.2.4

Impact of mining on the biosphere

Mining activity adversely affects the biosphere through the loss of the farming land, and through the degradation of the ecological systems. Microclimate in the mining area is also affected. Land subsidence in the areas of underground mines, and the creation of waste tips lead to the destruction of the vegetation, and the death of animals and birds. It should not be forgotten that man is a part of the biosphere, and he cannot avoid being adversely affected when the vegetation and the animals are degraded. Acid mine drainage from mining areas contains toxic substances, and pollutes the soil and water. Numerous instances are known from all over the world whereby the rivers down stream of mines have been rendered virtually devoid of life. In Feb. 2000, leachates from the cyanide wastes of an Australian-operated gold mining company in Romania entered the Danube river through the Tizsa (a tributary), and caused an ecological disaster. For several tens of kms. of the stretch of the Danube river in Hungary, and Yugoslavia, hundreds of tonnes of dead fish were found floating in the waters, and the birds which ate the fish also died. The wastes from the Outukumpu copper mine in Finland killed fish in the Ruutunene River and Sismaervi Lake 10 km downstream. Fish appeared again when the pollution has been cleaned up. In the northern areas of the Russian Republic, fish have stopped spawning near mines, and polar foxes, lemmings and willow grouse have left the mining areas. Wild reindeer evidently dislike the pollution so intensely that there are instances of their going 150–200 km away from the mining areas. When the lakes in the mining areas are polluted, birds are known to desert their traditional nesting sites on the lakes. Coal mines generally use timber for roof support. Experience shows that a coal mine with a production of (say) 400,000 tonnes per annum, uses 9000 to 12,000 m3 of timber, which is usually obtained from the local forests. Thus, local forests tend to disappear unless tree crops are grown to provide the wood needed on a continuing basis. Dewatering of the mines may lead to significant changes in the vegetation in the mining area. Plants are particularly susceptible to atmospheric pollution. The intensity of photosynthesis is adversely affected by pollutants such as, sulphur dioxide, carbon monoxide and hydrocarbons, which cause necrosis of leaves, inhibition of growth and early leaf fall. Eventually, the plants wither and die. Space photographs clearly show the devastation of the vegetation caused by mining in different parts of the world (e.g. nickel mining in Sudbury, Canada, and zinc mining in Norway).

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5.3

HYDROGEOLOGICAL AND GEOTECHNICAL FORECASTING

In any branch of human activity, wisdom lies in anticipating the shape of things to come, and being prepared to face the eventualities that may arise. This philosophy holds good for the mining industry as well. The principles of hydrogeological and geotechnical forecasting are summarized as follows (Vartanyan, 1989). Hydrogeological forecasting: Hydrogeological forecasting involves (1) forecasting the cones of depression during the dewatering of the deposits, (2) evaluation of the effects of dewatering on the existing and proposed water abstractions, (3) forecasting the effects of dewatering on the surface run-off, (4) forecasting changes in the quality of the drainage, (5) forecasting the groundwater pollution from the mining effluent ponds, etc. Hydrodynamic, balance and hydrogeological analogue methods, etc. are used for the purpose. The hydrodynamic methods, which are based on the resolution of the infiltration continuity equation for various initial and boundary conditions, yield satisfactory results if the rock structures are fairly homogeneous. The hydrogeological analogue method makes use of the similarity in the hydrological settings between a mining situation for which considerable operating data is available, and the mine to be studied. It is not necessary that the two mines should be of similar size; it is enough if the hydrological settings are similar (Vartanyan, 1989; Wood, 1981; Day et al., 1984). Forecasting geotechnical conditions: Forecasting geotechnical conditions involves the evaluation of the “possibility and extent of subsidence, displacement and caveins at the ground surface; land-slides and collapses of natural and man-made slopes; evaluating the weathering qualities of rocks, their ability to withstand long-term loading (for the siting of the waste tips and tailings storage), future compaction of rocks, change in the strength characteristics, development of karst, bulging, deformation of waste tips, etc.” (Vartanyan, 1989, p. 82). Evidently, the forecasting has to take into account the mining practices, such as roof caving, back filling, leaving pillars behind, etc. The analogy method is widely used to forecast geotechnical changes, i.e. whatever happened in a similar kind of mine under similar geotechnical conditions, is likely to happen in the mine in question. Apart from mathematical simulation, mechanical simulations using materials similar to those in the mine can be used to forecast the safe excavation angles and the ground surface effects. The strength of the rock determines its susceptibility to slide, to undergo dislocation, to be fractured and to resist weathering. It is estimated on the basis of the following parameters: uniaxial compressive strength (Cu or c), the uniaxial tensile strength (T or T) in the dry and water-saturated state; peak or residual shear strength ( ); the ultimate strength in bending (bend) and the rock hardness ratio (Sergeev, 1984, quoted by Vartanyan, 1989; Farmer, 1983). Hazard zoning is a part of the Preparedness Systems for the mitigation of hazards (see Aswathanarayana, 1995, Chap. 9 of “Geoenvironment: An Introduction”). Hazard maps may be prepared on the basis of the geotechnical properties of rocks,

Impact of mining on the environment 113

and the ways in which the rocks are likely to react to mining. It is possible to predict the sites which are prone to rock bursts, landslides, cave-ins, etc.

5.4

SOLID WASTES FROM MINING

Mining industry produces more solid wastes than any other industry. The aggregate volume of mine tailings produced in the world has been estimated to be 18  109 m3/y (Förstner, 1999, p. 1–3). Certain kinds of solid wastes, such as, waste products of quarrying for building stone, lime for cement and agricultural use, filters (e.g. gypsum, barytes), and roadstone, are generally inert. Consequently, water percolating through them does not undergo any significant chemical changes. If the waste contains crushed material, the Total Suspended Solids (TSS) content of the percolating water could increase. When the soil or sediment cover is removed in the process of quarrying, their filtering and attenuation capabilities would have been lost, thus exposing the groundwater to greater risks of pollution. Groundwater could also be contaminated due to some ancillary activities associated with quarrying, such as, accidental spillages of fuel oil, leakages from storage tanks or toilets for workers, or draining of water from the surrounding areas into the quarry, etc. Solid wastes arising from the mining of coal, lignite, metallic sulphides, uranium, etc. tend to contain pyrite (FeS2). Under oxidizing conditions, and in the presence of catalytic bacteria, such as Thiobacillus ferrooxidans, pyrite gets oxidized into sulphuric acid and iron sulphate. Thus, surface runoff and groundwater seepages associated with waste piles tend to be highly acidic, and corrosive, and contain high concentrations of iron, aluminum, manganese, copper, lead, nickel and zinc, etc. in solution and suspension. The discharge of such waters (known as Acid Mine Drainage or AMD) into streams destroys the aquatic life, and the stream water is rendered non-potable. The ubiquitous gangue minerals, such as calcite and quartz, are less soluble and reactive (ways and means of ameliorating AMD have been discussed in detail under section 8.1). The solid wastes produced in mining activities which could contaminate water resources through leaching and effluent production, are listed in Table 5.1 (source: Laconte & Haimes, 1982). Figure 5.2 (source: Laconte & Haimes, 1982, p. 4) is a schematic depiction of how mining activities could contaminate the water resources. Fly ash is reactive because of its high surface area to volume ratio. Leaching of the fly ash may produce effluents containing toxic elements, such as, Mo, F, Se, B and As. Low pH leachates from fly ash may give rise to problems of iron floc formation in surface waters. When the flue gases are scrubbed, the resulting sludge will typically contain cyanide and heavy metals. Its pH will be low, unless neutralized by lime. It has been reported that mixtures of sludge, lime and fly ash will set rapidly to a load-bearing, low-permeability, solid which is not easily leachable. Two benefits accrue from this

114 Mineral resources management and the environment Table 5.1

Solid wastes from mining (source: Water Resources and Land Use Planning). Rate of effluent or solid waste production

Source

Potential characteristics of leachate/effluent

Coal-mine drainage

High total dissolved solids. Suspended solids. Iron. Often acid. May contain high chlorides from connate water

105–107 m3/y

Colliery waste

Leachate similar to mine drainage waters

105–107 t/y of wastes per colliery. Quantity of leachate depends on climate

Metals

High total suspended solids. Possibly low pH. High sulphates from oxidation of sulphides. Dissolved and particulate metals. Washing and mineral dressing waters may contain organic flocculents

105–107 t/y of wastes per mine. Quantity of leachate depends on climate

Power generation (thermal)

Pulverized fuel ash. Upto 2% by weight of 104–106 t/y soluble constituents, sulphate. May contain concentrations of Germanium and Selenium. Fly ash and flue gas scrubber sludges. Finely particulate, containing disseminated heavy metals. Sludges of low pH unless neutralized by lime addition.

Leaching from spoil

Infiltration of mine discharge

Leakage through quarry floor

Leakage from stockyards and cesspits, contaminate shallow wells

Release of Spreading nitrate by fertilizers, ploughing pesticides, etc.

Unprotected watering holes

AQUICLUDE

Pumping saline groundwater from mines

Figure 5.2 Schematic depiction of how mining activities can contaminate the water sources (source: Laconte & Haimes, 1982, p. 4).

process – on one hand we will have a useful construction material, and on the other, we would have minimized the pollution risk. An environmentally-sound, and technoeconomically viable approach to minimize the contamination potential of the wastes, such as fly ash and red mud, is to put them to some useful purpose soon after they are produced (see section 9.4, Beneficial use of mine wastes).

Impact of mining on the environment 115 Table 5.2

Characteristics of the waste effluents from different mineral-based industries.

Industries

Characteristics of the waste effluents

Petrochemicals

High BOD, toxic sulphur compounds and phenols

Metallurgical & metal finishing

Characteristically acid, with high suspended solids; metal finishing wastes additionally contain heavy metals, phenols and oils

Thermal power production (cooling water)

Suspended matter in cooling water will not increase as it does not come into contact with any particulate matter during circulation. It may, however, get reduced in volume due to evaporation, and raised in temperature by about 10 °C. Consequently, the concentration of dissolved constituents will increase four-fold, and carbonate minerals may be partly precipitated due to loss of dissolved carbon oxide because of increasing temperature. Loss of dissolved oxygen may also occur. The disposal of such oxygen-depleted, heated water to the ground may have the following consequences: (1) soil or aquifer material may be leached, (2) when the warm water cools down as a result of contact with cooler, less mineralized groundwater, some components may be reprecipitated within the rock pores, thus reducing the permeability of the rock, and sequestering the recharged waters within an oxygen depleted zone. If the heated water is recharged via boreholes, microbial growth may take place, and clog the wall screens.

Production of gas by coal distillation (by, say, horizontal retort method)

Crude tar oils with significant content of phenolic compounds are produced. When hydrated ferric oxide is used to purify the raw gas, it may be contaminated with sulphides, free sulphur and cyanides. Impurities in the gas itself may dissolve in water. Leaching of these wastes could contaminate the groundwater with phenols and cyanide.

5.5

LIQUID WASTES FROM MINING

The waste effluents from different industries are listed in Table 5.2. Liquid wastes from mining industries are given in Table 5.3. An estimate of the quantum of production of contaminants from mineral industries is given in Table 5.4. Drainage waters from coal collieries tend to have high suspended and dissolved solids of iron and sulphate (derived from the oxidation of sulphates), and chlorides (derived from connate water trapped within the sedimentary rocks). Discharge of such waters on the surface and their subsequent percolation could contaminate the groundwater seriously (in the early part of the last century, the discharge of mine drainage water severely contaminated about 13 km2 of Chalk aquifer in southern England). The drainage waters from metallic mines tend to be acidic, and have higher concentrations of dissolved metals. The drainage waters may also contain organic flocculents used in the screening and dressing of metallic ores. Oil deposits are often associated with hot brines carrying traces of hydrocarbons. In the early phases of development of the hydrocarbons, it is not uncommon for the hydrocarbon/water systems to be under artesian conditions. In such a situation, the

116 Mineral resources management and the environment Table 5.3 Contaminants resulting from liquid wastes from mining (source: Water Resources and Land Use Planning). Source

Potential characteristics of leachate/effluent

Rate of effluent/leachate production

Oil and gas well brines

High total solids (103–105 mg/l), High Ca2 and Mg2 (103–105 mg/l) High Na and K (⬃104 mg/l), High Cl (104–105 mg/l), High SO42 (10–103 mg/l), Oil, upto 103 mg/l, Possibly high temp.

103–104 m3/d per well

Saline intrusions, due to overpumping close to coastlines

Na (103–104 mg/l), Mg2 (102–103 mg/l), Ca2 (102 mg/l), K (10–102 mg/l), Cl (103–104 mg/l), SO42 (102–103 mg/l), Alkalinity (as CaCO3) 102 mg/l

Rate of landward movement of saline incursion varies with pump ing regime and aquifer type (example: 4 km in 40 y along the estuary of River Thames in England)

Table 5.4 Quantum of production of contaminants from mineral industries (source: Paper 1.1 in Laconte & Haimes, 1982). Petroleum and petrochemical refining process

High BOD, chloride, phenols, sulphur comp. High BOD, Suspended solids, chlorides, variable pH

106–108 m3/y

Thermal power

Increased water temperature. Slight increase in dissolved solids by evaporation of cooling wastes

103–104 m3/y/megawatt

Engineering works

High suspended solids, soluble cutting oils, trace heavy metals, variable BOD, pH

104–107 m3/y

Foundries

Low pH, high suspended solids, phenols, oil

107–109 m3/y

Plating and metal finishing

Low pH, high content of toxic heavy metals, sometimes as sludge

107–109 m3/y

Deep well injection

Various concentrated liquid wastes, often toxic. Brines. Acid and alkaline wastes. Organic wastes

104–106 m3/y

Leakage from storage tanks and pipelines

Aqueous solutions, hydrocarbons, petrochemicals, sewage

Accidental spillages

Various liquids in transit, hydrocarbons, petrochemicals, acids, alkalis, solvents. Liquids may enter surface drains or soakaways

Generally 10 m3 per incident

contaminated water may spill on the ground and percolate into shallow aquifers, or it could leak upwards into a incompletely grouted production well. When hydraulic mining is employed to mine evaporite deposits, care should be taken to ensure that the brines do not contaminate the groundwater through surface spills and pipeline leakages.

Impact of mining on the environment 117

The heavy withdrawal of groundwater in the coastal regions and estuaries could lead to the incursion of saline water into the coastal freshwater aquifers, thereby degrading them. There have been several instances of giant tidal waves generated by tropical cyclones, salinizing the arable land, surface water and the groundwater (On Oct. 29, 1999, a 10 m high tidal wave generated by a super-cyclone swept across a stretch of 150 km along the coast of Orissa province in eastern India, destroying every thing in its path, and rendering the surface and groundwaters saline). Mineralized waters may sometimes occur at depth – in the form of connate water trapped below the zone of natural groundwater circulation, or they may arise from the leaching of evaporite beds terminating against an aquifer. Salinization of fresh groundwater can occur in inland areas due to upconing of such mineralized waters. Overpumping of the groundwater may result in the lowering of the water table below the streambed levels. If the river concerned is perennial or seasonally influent, and if the river water is already contaminated, this would inevitably induce undesirable recharge of the aquifer with the contaminated water of the river. There may be accidental spills when liquid wastes stored in tanks are transported by road or rail. Also, there may be leakages when the wastes are transported by pipeline. Such spills or leakages could contaminate the groundwater, particularly in the case of shallow water-table aquifers. The magnitude of such contamination may have an enormous range – while the leakage of a few cubic metres of oil from a domestic tank may contaminate a water well nearby, an undetected leak of several thousand cubic metres of oil from a pipeline could jeopardize a whole aquifer. 5.5.1

Industrial effluents arising from coal mining in the Damodar river basin, India – a case study

Damodar river basin in eastern India contains about 46% of the coal reserves of India. Apart from underground and opencast mines of coal, the area has numerous coal-based industries, such as, steel, chemical and fertilizer plants. Fortunately, the pyrite content of coal is not high. The water of the Damodar river is contaminated by (1) huge volumes of polluted water from underground mines – for instance, Bharat Coking Coal Limited (BCCL) mines in Jharia pump out ⬃300 million gallons (⬃1.364 M m3) of mine water daily, (2) runoff water leaching the overburden dumps, (3) industrial effluents from coal-based plants. Large amounts of fly ash and fine coal particles discharged by the thermal power plants and washeries settle down to the bed of the river and hinder the growth of the biota. About 25 million tonnes of coal is washed annually in the area, involving the use of about ⬃2000 t of pine oil. Large amounts of suspended solids, oil and grease arising from the washeries are discharged into the river. The coke oven plants serving the steel industry, release highly toxic substances like phenols and cyanides. The low DO contents, and high content of heavy metals in the effluents make it almost impossible for the biota to survive in the river water.

118 Mineral resources management and the environment Table 5.5 Physico-chemical characteristics of the industrial effluents in the Damodar river basin, eastern India. Parameter

IS:2490

Coke oven plant

Thermal power plant

Coal washery

Steel plant

Flow rate (m3/hr) pH Temp. (°C) TSS TDS DO BOD COD Phenols Cyanide Oil & Grease Fe Mn Cr Pb As Cd

– 5.5–9.0 40.0 100 2100 – 30 250 – 0.2 10 – – 2.0 0.1 0.2 2.0

10.8–72 7.67–8.62 29.2–40.0 447–636 486–581 0.5–2.2 7.8–81.0 208.3–331.2 0.1–0.2 0.002–0.2 0.98–1.26 2.89–6.54 0.28–0.45 BDL–0.05 0.0–0.5 BDL BDL

81–33768 7.98–8.46 28.0–39.0 780–20400 206–398 3.98–5.89 3.0–22.0 359–5192 Nil Nil 0.7–1.8 5.61–83.6 0.08–1.19 BDL–0.17 BDL–0.09 BDL BDL

30–810 7.31–7.49 29.1–31.2 160–83560 304–775 2.61–3.84 4.0–10.0 2073–63848 Nil Nil 0.4–32.5 0.11–181.3 0.06–6.20 0.18–0.43 020–0.75 BDL–0.02 BDL–0.2

112–7245 2.98–7.3 20.0–36 334–1465 16–186 2.86–7.52 8.0–32.0 55–1098 0.02–1.13 0.01–0.07 0.86–112.4 2.17–37.0 0.14–0.41 BDL–0.34 BDL–0.06 BDL BDL–0.12

BDL – Below Detection Limit All parameters are expressed in mg/l, except for flow rate, and pH

Table 5.5 (source: Tiwary et al., 1995) summarises the physico-chemical characteristics of the industrial effluents in the Damodar river basin. The quality of the water in the upstream part of the Damodar river is fairly good with TSS in the range of 18–168 mg/l. But serious deterioration of water quality occurs when the industrial waters from Patratu thermal power plant, and the steel plant at Durgapur are discharged into the river. But people who live in the area have no option except to drink the contaminated water. A health survey conducted in 1993–94 showed high incidence of water-related diseases, such as, dysentery, diarrhea, skin infections, jaundice, typhoid, etc. (Tiwary et al., 1995).

5.6 5.6.1

EMISSIONS DUE TO MINERAL INDUSTRIES Modeling of particulate emissions

Particulate matter is the major pollutant of concern for most surface mining operations. The US EPA regulates the particulate matter less than 10 m (PM10) with recent emphasis on particulate matter less than 2.5 m. The dispersion of air emissions is modeled using the Industrial Sources Complex Short Term Model (ISC3) developed by US EPA. A hypothetical quarry with the following characteristics is

Impact of mining on the environment 119

Figure 5.3 Diagrammatic sketch of a hypothetical quarry (source: Reed, Westman & Haycocks, 2001, p. 694).

used for the modeling (Fig. 5.3; source: Reed, Westman & Haycocks, 2001, p. 694): The area surrounding the quarry is flat, with an elevation of 500 m above MSL. The quarry benches are 15 m in height, with 15 m catch benches. The pit slopes thus created have inclination of 45 °. The haul road into the quarry is based on a 10% grade with a width of 40 m. The surface where the crusher is located has an elevation of 15 m above the ground level. The quarry is assumed to be working 8 h/d, for 250 days a year, producing 900,000 tonnes per year of stone. The material is assumed to have a silt content of 10%, moisture content of 1.0%, and specific weight of 2.0 t per cubic yard (2.658 t/m3). Meteorological data are obtained from US EPA website. The amount of PM10 produced by individual quarry operations is calculated using the emission factors published by US EPA under AP-42 (1995) for various quarrying operations, such as drilling, truck loading, haulage, stockpiles, crushing, screening, conveyance, etc. In actuality, it has been found that the major contributors to PM10 emissions were truck hauling on unpaved roads, and loading of stockpiles and trucks. The ISC3 model proposed by US EPA is no doubt applicable to gases such as CO, NOx, SOx, etc., but has been found to over-predict values for PM10. This is probably so because the dust particles have larger particle sizes, and higher particle densities than the gases. Also, the dust created in the operation does not consist of PM10 only, and they settle in different ways. In the light of these observations, ISC3 model is being refined using the terminal velocity settling approach. 5.6.2

Gaseous pollutants

Energy industries (particularly coal-fired, thermal power stations) produce huge quantities of gaseous pollutants (Table 5.6; source: El-Hinnawi, 1981). The global

120 Mineral resources management and the environment Table 5.6 Average emissions from 1000 MW coal-fired and oil-fired stations (in tonnes) (source: El-Hinnawi, 1981).

Sulphur dioxide Nitrogen oxide Particulates Carbon monoxide Hydrocarbons Ash

Table 5.7

Coal-fired station

Oil-fired station

110,000 27,000 3,000 2,000 400 360,000

37,000 25,000 1,200 710 470 9,000

Heavy element emissions from coal and oil combustion (109 g/y).

Element

Total

Coal

Oil

As Se Cd Hg Pb

23.6 1.1 7.3 2.4 449

0.7 0.42 – 0.0017 3.5

0.002 0.03 0.002 1.6 0.05

Table 5.8 Atmospheric emission of trace metals from natural and industrial sources (109 g/y) (compilation from Salomons & Förstner, 1984, p. 99). Metal

Natural source

Industrial source

Cd Cu Ni Pb Zn

1.23 18.48 26.04 29.5 53.5

7.3 56 47 449 314

emissions of heavy elements and the contribution by the combustion of coal and oil (in terms of 109 g/y) are given in Table 5.7 (compilation by Fergusson, 1990). There exist both natural and industrial sources of particulates in the atmosphere. The contribution from various sources (in terms of 1012 g/y) is: windblown dust (5000), forest fires (36), volcanic particles (10), vegetation (75) and seasalt sprays (1000). Though the contribution from the industrial activities is much less (200) in global terms, the contribution of atmospheric particulates by industrial activities is far more than natural sources near industrial centers. Atmospheric emissions of trace metals arise both from natural sources as well as industrial sources. The predominance of industrial sources relative to natural sources can be understood from Table 5. 8 (data in terms of 109 g/y).

Impact of mining on the environment 121 Table 5.9

Plant communities in disturbed sites in Jharia Coalfields, Bihar, India.

Site

Plant communities and their abundance (%)

Total plant biomass (g/m2)

Unmined Mandman Mudidih

Andropogon (40), Eleusine spp. (20) Ergrostis (30), Andropogon spp. (26)

380 456

Mined Mandman Mudidih

Ergrostris (24), Panicum (22), Tridex (14) Saccharum (25), Eupatorium (22), Leonotis (22)

230 270

Three approaches have been attempted to assess the extent of anthropogenic impact on metal emission rates (Salomons & Förstner, 1984): 1. Comparison of the actual emission rates of the natural and anthropogenic processes. For instance, the natural and anthropogenic emissions (in terms of 108 g/y) of lead are 40 and 4000 respectively. The Mobilization Factor (anthropogenic/natural emission) is therefore 100 (4000/40). In contrast, the mobilization factor of chromium is 1.6 (940/580). 2. Comparison of atmospheric concentrations to those in natural concentrations (say, crustal abundance) contributing to it. Aluminium is used as a reference element. Enrich factor is computed from the ratio (X/Al)air/(X/Al)crust. 3. Delineate the temporal variation in the composition of the metals by the study of the metal in the cores of the lake sediments.

5.7

LOSS OF BIODIVERSITY

Large scale mining disturbs the biodiversity and productivity of the ecosystem. The huge accumulations of overburden dumps at Mandman and Mudidih areas in the Jharia Coal Field, Bihar, India, reduced the vegetation cover from 65% to 39% and the fallow land and pasture from 9.1 to 3.1%, during the period, 1925 to 1993. Table 5.9 (source: Tewary, Singh & Dhar, 1995) shows how these dumps affected the composition of the plant species and their biomass.

CHAPTER 6

Mining and health hazards

6.1

INTRODUCTION

Mining is undoubtedly the most hazardous industrial occupation. For instance, during the period 1980–89, mining ranked as the number one in USA with respect to the average annual rate of traumatic fatalities (with the rate of 31.91 for 100,000 workers), as against 25.61 for the construction industry, 23.30 for the transportation/ communications/public utilities industries, and 18.33 for the agriculture/forestry/ fishing industries. There are two kinds of health impacts associated with mining: immediate impacts such as accidents, and accumulative and progressive impacts such as stress and pneumoconiosis. Opencast mining is generally less hazardous than underground mining. Industrialised countries tend to use highly automated mining systems, which not only employ lesser number of workers (who have to be highly skilled), but also have the effect of drastically reducing the hazards to which they are exposed. Developing countries cannot afford such high-tech mining systems, so much so that mining accidents are a common occurrence in developing countries such as China and India. Health hazards in mining are described with reference to coal mining. There are four types of health hazards (see the excellent account by Chadwick et al., 1987, p. 203–236, from which the following account has largely been drawn). 1. Physical hazards, e.g. coal dust, silica dust, excessive heat, noise, heavy physical work, contorted body posture, 2. Chemical hazards, e.g. carbon dioxide, carbon monoxide, methane, nitrogen oxide gases, 3. Biological hazards (applicable in some developing countries), e.g. fungus, hookworm, 4. Mental hazards, e.g. shift work, constant danger. The 3 km deep, Kolar gold mines of south India, constitutes an unusual case where all the above problems are evident at one place, namely, rock bursts, high thermal stress, gas and dust explosions, fires, inundations, hookworm infection, etc. (Pai & Shenoi, 1988).

124 Mineral resources management and the environment

6.2

DUST HAZARDS

Dust is the cause of the many of the cumulative health hazards in the mineral industries, and is hence dealt with in some detail. The main sources of dust in the mining operations are: Point sources: (1) Ore and waste loading points in trucks, railroad cars, etc. (2) Ore chutes in the haulage systems (bin, conveyors), (3) Screens in outdoor crushing plants, (4) Exhaust from dedusting installations, and (5) Dryer chimneys. Dispersed sources: (1) Waste dumps, (2) Ore stockpiles, (3) Haul roads, (4) Tailings disposal. The main natural and artificial dusts, associated sources and possible health disorders are summarized in Table 6.1 (source: Archer et al., 1987, p. 171). Table 6.1 Main natural and artificial dusts, associated sources and possible disorders (source: Archer et al., 1987, p. 171). Dust type

Possible source

Possible disorders

Silica (crystalline and amorphous) Coal

Mining, quarrying, sand blasting, abrasives, glass making, etc. Mining, transportation and use, smoke from the burning of arsenious coal for domestic cooking Asbestos cement, insulation, friction materials (brakes, clutches, etc.), floor-tiles Volcanic tuff Quarries, drilling mud, pharmaceutical industry Mining, rubber industry, lubricants, pharmaceutical industry Quarrying, ceramic industry Quarrying, drilling Bauxite mines, ceramics, abrasives, paint, metallurgy Mining, metallurgy, pharmaceutical industry

Silicosis

Asbestos Fibrous zeolite Fibrous clays Talc Kaolin Bentonite Aluminium, alumina Barytes Beryllium compounds Iron oxides Nickel Chromium Cadmium Manganese Titanium, tantalum, wolfram carbides All metals Synthetic mineral fibres Airborne ash Volcanic ash

Metallurgy, aeronautics industry, nuclear industry, solid fuel Iron mines, foundries, steel plants Mining, polishing Mining, polishing, electrochemistry Mining, polishing, electrochemistry Mining, polishing, foundries Polishing Welding Thermal and acoustic insulation, composite materials Coal and oil fired plants, incineration of household and industrial wastes Volcanic eruptions

Silico-anthracosis, coal worker pneumoconiosis, arseniasis Asbestosis, and pleuropulmonary cancer Pleural cancer Fibrosis Talcosis Kaolinosis Fibrosis Fibrosis Barytosis (pneumoconiosis due to accumulation) Beryllosis (granulomatosis) Silico-siderosis, siderosis Fibrosis, lung cancer Fibrosis, lung cancer Fibrosis, urinary tract cancer Fibrosis Fibrosis, lung cancer Fibrosis, lung cancer Fibrosis? Fibrosis? Cancer?

Mining and health hazards 125

6.2.1

Aerosols

Aerosol particles range in size from sub-microscopic to almost visible, and they are characterized by a wide variety of chemical compositions. They are mainly responsible for the haze, which affects the visibility in the industrial areas in Europe and North America. The distribution of the size of the aerosols is log-normal. Consequently, most of the aerosols are in the 0.01–10 m range, with the mean around 1 m. Depending upon the size and nature of the particles, an aerosol may be called “dust” (diam.
1 m) or “fume” or “smoke” (0.01–1 m). Mists (d
40 m) and fogs (d  5–40 m), are liquid droplets. Aitken nuclei (d  0.2 m) are small hygroscopic particles or condensation nuclei. The size ranges of different aerosols are given in Figure 6.1 (source: Fergusson, 1990, p. 208). Iron, aluminium, manganese and chromium are generally found in the form of coarse particles (around 1.5 m), whereas cadmium, lead, zinc and antimony occur in the form of smaller particles (d  0.25 m). The particle size distributions in respect of trace metals are customarily expressed in terms of Mass Median Diameter (MMD), which is defined as the particle size for which 50% of the mass occurs on larger, and 50% occurs on smaller, particles. For copper, MMD for marine air is 0.8 m, and general (rural to urban) air is 1.8 m.

Figure 6.1

Size ranges of different aerosols (source: Fergusson, 1990, p. 208).

126 Mineral resources management and the environment

Coarse particles are generally produced by mechanical processes (such as, disintegration of minerals). On the other hand, fine particles are produced by condensation processes. The fine particle mode can be subdivided into nuclei mode and accumulation mode. 0.3 m: Nuclear mode, involving condensation nuclei, secondary particles. Brownian motion is the principal controlling force. The particles get removed by adsorption on larger particles. 0.3–3.0 m: Accumulation mode. Important for fly ash. Small-sized particles (0.1 m) coagulate to form larger particles, the movement and contact being controlled mainly by Brownian motion. The number of particles decreases as a consequence of coagulation. For particles 0.01 m, the decrease is 50% in an hour, and for 0.05 m, it would take a day to bring the number down by 50%. Both soluble and insoluble types adhere to the surfaces.
3.0 m: Coarse particle mode, involving large dust particles. Gravitational settling and particle motion are the principal controlling forces. Anthropogenic aerosols are dominated by comparatively finer particles (2 m). In contrast, natural particles such as wind-blown or re-entrained dust is typically
2 m. Aerosols can be transported for long distances, of the order of hundreds of kilometers. In the ice-cores of Arctic and Antarctic, the lead level for 1965 (0.15–0.42 ng/kg) is markedly higher than the pre-1940 levels (0.08 ng/kg). This is attributed to the transport of lead from distant industrial sources. The concentration of a trace metal in air, Ca, is related to the condensation nuclei by the following equation: Ca  ken /L

(6.1)

where k  transfer constant, whose value ranges from 1.0 to 6.0 g/m , en  mass fraction of the aerosol used in condensation nuclei,  a factor linked to the evaporation below the cloud, and L  Liquid water content of the cloud. The total emission of particles in the atmosphere has been estimated to be 2608 million tonnes per year. Out of these 89% (2312 Mt/y) are of natural origin (derived from sea salt; soil dust; gas particle conversion from hydrogen sulphide, nitrogen oxides and ammonia; photochemical, from terpenes, etc.; volcanoes; and forest fires). The emissions from man-made sources are estimated to be 11% of the total emissions, (about 296 Mt/y), distributed as follows: 3

Particles: Gas particle conversion: sulphur dioxide Nitrogen oxides Photochemical, from hydrocarbons Total

92 Mt/y 147 Mt/y 30 Mt/y 27 Mt/y 296 Mt/y

The circulation of the particles in the atmosphere would depend upon their size and the altitude at which they are generated. Particles may remain in the lower

Mining and health hazards 127

atmosphere for about 5 days, in the troposphere for a month, and in the stratosphere for 2–3 years. This enables them to travel for long distances. 6.2.2

Dust hazards in coal mining

Dust is a serious hazard in coal mining. Coal and some stone dust are produced in the process of drilling, cutting, crushing and blasting of the coalface. The dust gets airborne due to ventilation, shoveling, transport and human movement. Only fine dust particles of diameter 0.5–5 m are respirable. Anthracite (hard coal) particles are more hazardous than particles of soft coal (e.g. lignite). Respirable coal particles pass through the upper airways, and finally settle down in the respiratory branchioli. There they accumulate and form nodules. Exposure to respirable coal dust over a period of years leads to the incidence of Coal workers’ Pneumoconosis (CWP, also known as Anthracosis or Black Lung). X-ray examination is the principal method of diagnosing CWP. Simple CWP will not progress when once there is no more exposure to coal dust. But the complex CWP keeps on getting progressively more and more serious, leading to emphysema and heart failure. Silicosis is caused by the respiration of free silica (quartz) particles in the dust. The respirable particles have diameters of less than 5 m. Although small quantities of free silica particles may occur in the dust in the underground mining, the risk from them is greater in the opencast mining. When the silica particles reach the lung alveoli, they are attacked by microphages, leading to the formation of fibrotic nodules (“simple silicosis”). In due course, the nodules coalesce to form large fibrotic masses called conglomerates. Simple silicosis may not show any clear symptoms, but patients suffering from conglomerate silicosis invariably suffer from shortness of breath. X-ray examination of the lungs is the standard procedure for the diagnosis of silicosis. The Kolar gold mines in southern India, and the Rand gold mines in South Africa began production at about the same time, around 1880s. The nodular type of silicosis which was highly prevalent in the Rand mine workers, had minimal incidence in the case of Kolar mines. This is attributed to the extent of exposure to silica dust (Pai & Shenoi, 1988). In the case of Rand, both the lode and host rock was quartzose, whereas in the case of Kolar, only the lode is quartzose, whereas the host rock is amphibolitic. The free silica percentage of the quartz reef averages about 90%, and that of amphibolite, about 50%, with the aggregate having a free silica percentage of 52–55%. There is therefore sharp difference in regard to the aggregate free silica percentage between Rand (⬃90%) and Kolar (52–55%). The International Labour Organization (ILO), Geneva, has developed elaborate classifications for pneumoconiosis and silicosis, for clinical and epidemiological purposes. The characterization of the lung function is based on the parameters of Forced Vital Capacity (FVC) and Forced Expiratory Volume in one second (FEV1). If unchecked, the conglomerate silicosis may lead to emphysema and heart failure.

128 Mineral resources management and the environment

The composition of the dust varies from mine to mine. Anthrcosilicosis is a mixed disease caused by the inhalation of both coal and silica dust. Simple anthrocosis may degenerate into Progressive Massive Fibrosis (PMF). Workers suffering from silicosis become highly susceptible to the dreaded disease of tuberculosis. Such an infection is hard to treat, as the fibrous and scar tissues impede the penetration of antituberculostatica. No wonder that 25% of the silicosis deaths are attributable to silicotuberculosis. Bronchitis among the mine workers is attributable to the inhalation of relatively coarse dust particles of the diameter 5–15 m. Such particles are too large to go into the lungs. When inhaled, these particles get stuck in the upper airways. Constant irritation by such particles leads to infection, coughing and production of sputum. Statistics show that in a number of countries one out 8 workers suffers from CWP and silicosis, and one out three workers suffer from bronchitis. In USA, during the period, 1970–77, Federal Black Lung Compensation was awarded to 420,000 coal mine workers who were totally disabled because of CWP. A survey during 1974–77 by the National Coal Board of U.K. found that about 7% of the British Coal Miners were suffering from CWP. It has been reported that the incidence of CWP in India may be as high as about 16%. 6.2.3

Dust in steel industry

The steel industry is notorious for the large quantities of visible fumes and clouds of dust. The problem here is one of quantity of dust, rather than the toxicity of dust. Two categories of dusts can be recognized in the steel industry (UNEP, 1986, p. 36): 1. Coarse particles (diam. 10–100 m) produced in the course of mechanical operations, such as crushing, screening, and charging of raw materials – these settle down fairly rapidly. 2. Particulates (less than 1 m diam.) produced in the course of high temperature metallurgical processes such as, blast furnaces, steel making, oxygen scarfing. These remain suspended in air for long periods. 6.2.4

Pathological effects of mineral dusts

Toxic particles, such as silica, can cause severe fibrogenic reaction. In industrialized countries, the incidence of pneumoconiosis has been kept under control by improved dust control techniques. Asbestosis and pleuropulmonary cancer arising from exposure to asbestos particles in the construction materials, have emerged as the principal health hazard arising from mineral dusts. In USA, there have been cases of whole school buildings being completely demolished because asbestos products have been used in their construction. Soot or carbon black, which is the waste product of incomplete combustion in private or industrial buildings and incinerators, is the most visible dust, although not necessarily the most harmful. Air near the industrial areas may contain particles of metal oxides, silicate and inert dust. Exposure to fibrous minerals, such as, chrysotile,

Mining and health hazards 129

amphiboles, attapulgite, diatomaceous earth, bentonite, sillimanite, etc. in the course of their mining, fabrication and use, leads to the development of various kinds of fibroses. 6.2.5

Fibrogenetic effects

The biological activity and hence the pathological effect of mineral dust particles depend upon the extent of their penetration, retention and clearance. Some mineral particles, such as those of carbon, iron and barium, have limited biological effect. When inhaled in large quantities, they accumulate and cause pneumoconiosis around the terminal repository bronchioles. On the other hand, the inhalation of fibrous mineral particles causes pulmonary fibrosis. Fibrogenic pneumoconiosis is caused by the inhalation of fibrous minerals such as silica, and asbestos, and metals such as beryllium, aluminium, nickel, cadmium and manganese. In the case of mixed dusts, the more the content of silica, the more pronounced is the fibrosis. Electron microscopic images (300) allow us to distinguish between the interstitial fibrosis of the lung associated with pleural fibrosis, and the nodular or massive hyaline fibrosis found in silicosis. This may be a manifestation of the difference in the penetration and clearance of the two kinds of dusts. It has been observed that fibrous particles lodged in the lung tend to be surrounded by a ferrous protein sheath. This probably represents an effort by the body to detoxify the toxic fibres. 6.2.6

Carcinogenic effects

Several epidemiological and experimental studies have indicated that asbestos is the direct cause of pleural or peritoneal mesotheliomas, besides being a co-factor in inducing bronchopulmonary or gastro-intestinal cancer. There is epidemiological evidence to suggest that chromium, nickel, arsenic and cadmium and their complexes are carcinogenic in man. It has been reported that the toxic and carcinogenic effects of the fibres are not only dependent upon their type and size, but also on their chemistry, particularly surface chemistry. Experiments with animals suggest that the carcinogenicity of metals depends upon their crystal structure and state of ionization. Table 6.2 (source: Chen et al., 1999) summarizes the health effects of arsenic in mineral dusts as observed in some countries. Low-rank coals invariably contain pyrite. Arsenic may substitute in pyrite (FeS2) or may be found in the form of a separate mineral, arsenopyrite (FeAsS). In Guizhou province of China, coals have very high arsenic content (9600 mg/kg). When such high-As coal is used for cooking, keeping warm, and drying of grain, arsenic content of the ambient kitchen air rises to 0.003–0.11 mg/m3. Exposure to this environment leads to the absorption of arsenic by the respiratory tract, skin, and digestive tract (Zheng et al., 1994, quoted by Sun et al., 1999). About 30,000 workers in the copper smelting and arsenic mining industries are exposed to high-As aerosols. The tin mine workers in the Yunnan province are exposed to high-As aerosols – the cancer incidence among these workers is 716.9 per 100,000,

130 Mineral resources management and the environment Table 6.2

Health hazards due to exposure to arsenical dusts.

Area

Source

Guizhou province, China Yunnan, China Toroku/Matsuo, Japan Ronpibool, Thailand

Burning of high-As coal Metal smelting Metal smelting Tin mining

Population at risk

Non-cancer manifestations

Cancer manifestations

200,000

M/K, G, P

S, Li

100,000 217 patients 1000 patients

M/K, D, G, B, P M/K

S A, S, Lu, U, K A

M/K – melanosis/keratosis; D – dermatitis, G – gastroenteritis; B – bronchitis; P – polyneuropathy; A – all sites; S – skin; Li – liver; Lu – lung; U – urinary bladder; K – kidney; P – prostate.

which is 82 times that of the controls. The average As content in the lungs of the cancer patients was found to be 43.33 mg/kg. Carcinoma of the lung is associated with inhalation of arsenic dusts. Instances are known from Southeast Asia where lung cancer is attributed to As in drinking water. In the Xinjiang province of China, both arsenic and fluoride contents are high in the drinking water as well as in the coal used for burning. This led to the concurrent endemicity of arseniasis and fluorosis among the populations. Coal is the principal source of energy in China. China is the largest producer of coal in the world (1235 Mt in 1998). With increased industrialization, and with people aspiring for a higher standard of living, consumption of coal-fired thermal energy as also the use of coal in home heating, has been growing rapidly. There is a price for this. It has been said that nine out of ten most polluted cities in the world are in China, and one out of three deaths in China is due to contaminated air and water (Time, USA, Nov. 8, 1999). Two or more mineral substances may interact together, some times antagonistically, and more often synergistically. The inhibition of quartz by carbon, aluminium or polymers is an example of the antagonistic interaction. When sulphur dioxide is adsorbed on soot particles in the atmosphere, the toxic effect of sulphur dioxide gets intensified due to synergism. A possible mechanism for the operation of synergism is as follows: when the solid particles are lodged in the lung tissues, the adsoptive capacity of the solid particles allows them to retain the gaseous or soluble substances adsorbed on them. It is also possible that through their surface properties, the solid substances act as catalysts, accelerating or facilitating some processes. They may also serve as vectors of toxic substances, penetrating the cells more readily. 6.2.7

Analytical methods

As the mineral dust particles tend to have a size range of 1 mm to 1 m, the usual practice is to study the individual particles for their size (which determines their aerodynamic properties, and respirability), shape (whether the particle is fibrous), mineralogy, chemical composition and speciation, isotopic characteristics, etc. At least two characteristics of a mineral dust particle, namely, morphology and chemistry, need to be determined.

Mining and health hazards 131 Table 6.3

Characterization of dust particles.

Parameter

Mode of measurement

Mineralogy

Polarised transmitted light microscopy, and polarized reflected light microscopy (for particles
1 m in diam.), dark field microscopy (for particles of more than 0.01 m) Electron microprobe (for mineral particles 0.1 m, and atomic number
5). Scanning electron microscopy (of particles with diam.
500 Å) Automatic image analyzer (for geometrical characterization)

Microanalysis Morphology Textures

The parameters to be measured and methods of measurement are summarized in Table 6.3. Dust is monitored in the following ways: 1. Air samples are regularly analysed for their dust content. Automatic air samplers at fixed locations analyse the air, and feed the information to the central control point. Besides, personal samplers worn by the workers are also analysed. The Threshold Limit Values (TLV) for the total dust are 10 mg/m3, for silica dust, 0.2 mg/m3, and for coal dust, 2 mg/m3 (incidentally, this implies that the silica dust is ten times more hazardous than coal dust), 2. Workers must undergo regular medical checks (X-ray photographs of the lungs, lung-function tests, etc.), and records should be kept. Workers with dust-related illnesses may be shifted to dust-free jobs. 6.2.8

Regulation

Asbestos has been the most widely studied particulate pollutant. Ambient air is monitored inside buildings that have materials containing asbestos, such as sprayed insulation materials and certain types of floor tiles. During the on-site inspections, the fibre count in the ambient air is measured using the membrane filter method. In 1983, the European Commission set the limit of the maximum concentration for occupational health at 0.2 fibre per ml. of air for crocidolite and 1 fibre per ml. for other asbestos fibres (with an averaging time of 8 hours). USA prescribed that the maximum pollution level of asbestos in air should not exceed 30 ng/m3 of air. Biological monitoring involves the direct measurement of the pollutants in human biological samples. In the case of asbestosis, asbestos body counts are made in the lung parenchyma and sputum or bronchioalveolar washing fluid.

6.3 6.3.1

OTHER PHYSICAL HAZARDS Noise

Workers in mining industry are exposed to noises from drilling equipment, loaders, scoop-trams, diesel locomotives, trucks, etc. in the mines, and from grinding mills and air compressors in the beneficiation plants. Continuous exposure to intense

132 Mineral resources management and the environment

noise causes hearing loss. While temporary loss of hearing or auditory fatigue may last for a short period of time, the loss of hearing due to prolonged exposure to high noise levels may be permanent and irreversible. Noise is measured by sound level meter, noise dosimeter, frequency analyzer, impact or impulse noise meter, calibrator, etc. (UNEP, 1991, p. 64). The frequencies which are audible to the human ear, range from 20 Hz to 20 kHz. There is a threshold of audibility below which we cannot hear anything. At the other extreme, there is a maximum pressure level (threshold of pain) beyond which the eardrum will get irreversibly damaged. For instance, at the frequency of 1 kHz, the threshold of audibility is 2  104 Pa, whereas the “threshold of pain” is in the region of 102 Pa. Hearing losses are most prominent in the frequencies around 4000 Hz. Figure 6.2 provides the classification of sound frequencies. The threshold of audibility and pain in the human ear is depicted in Figure 6.3 (source: Environmental aspects of iron and steel production, UNEP, 1986, p. 42). The acoustic levels are customarily expressed in terms of decibels. Noise regulations cover two kinds of situations: regulations for workers within an industrial establishment, and regulations for the population living near the works. The ISO standards evaluate the risk of deafness incurred by workers in two ways: (1) Danger exists if in an 8-hr day, the level of noise to which a worker is continuously exposed is over 90 dB(A), (2) If the noise is not constant, the figures taken must be weighted to take into account both the length of exposure to each noise level, and the corresponding threshold. On this basis, an estimate is made of the equivalent acoustic level (i.e. “the level which, were it present for 40 hours per week, would give the same index of exposure to noise as the various acoustic levels measured during the week”). Figure 6.4 (source: Environmental aspects of iron and steel production, UNEP, 1986, p. 99) shows the relationship between years of exposure and percentage risk of loss of hearing for various noise levels, ranging from 85 dB(A) to 115 dB(A). Besides deafness, high noise levels could cause cardiovascular and respiratory diseases.

Figure 6.2 Classification of sound frequencies (source: Environmental aspects of iron and steel industry, UNEP, 1986, p. 42).

Mining and health hazards 133

The regulations about environmental noise prescribe a limit of 10 dB(A) in the neighbourhood of the works, with a lower figure during the night. The rules are stricter for the residential areas than for industrial zones. Noise levels from plants, and from mobile equipment are stated in Tables 6.4 and 6.5 respectively (source: Dowon & Stocks, 1977). It is not possible to avoid noise in mining – air drilling and pneumatic picks typically produce noise of the order of 100 dB(A) (decibel equivalent). Blasting produces a strong impulse noise. Ventilation blowers, graders and crushers, etc. produce noise levels, which do not allow normal conversation. According to health experts, exposure to noise levels greater than 85 dB(A) or more for 8 hours a day over a long period will irreversibly damage the ciliated nerve cells in the hearing organ, and cause occupational deafness (this is different from natural loss in hearing which occurs in old age, called presbyakusis). A person suffering from occupational deafness may not notice it when he is young, but as he grows older (beyond, say, 50 years) the occupational deafness may get compounded by presbyakusis, resulting in total loss of hearing. Audiography is used to evaluate occupational deafness, which is indicated by a loss of perception in the range 4000–6000 Hz. Workers should undergo periodical audiography test, and the records of audiograms should be kept for monitoring the situation. EEC regulations allow a noise level of 85 dB(A) for daily exposure level with no peak sound in excess of 140 dB(A). Most countries allow noise levels of 85–90 dB(A) for an 8-hr day, with higher levels allowed for short periods. In the case of steel industry, large capacity blast furnaces (say, 9000 t of pig iron/d) are a major source of noise. The noise may arise from multiple sources, such as, balance of high top pressure, charge in the throat, hydraulic drive, blowers, snort

Figure 6.3 Threshold of audibility and pain (source: Environmental aspects of iron and steel industry, UNEP, 1986, p. 42).

134 Mineral resources management and the environment

Figure 6.4 Relationship between years of exposure versus percentage risk of loss of hearing for various noise levels (source: Environmental aspects of iron and steel industry, UNEP, 1986, p. 99).

Table 6.4

Noise level from plant installations (source: Dowon & Stocks, 1977).

Equipment

Noise level (dB(A))

Measurement location

Electrical ventilation fans Compressed air fans Jaw crusher Cone crusher Compressed air hammer Drill sharpeners Ball mill Flotation equipment

90–100 Upto 110 90–100 92–98 104–112 102–112 Upto 100 63–91

At 5 m At 5 m Operator position Operator position Operator position Operator position Operator position Inside flotation building

Mining and health hazards 135 Table 6.5

Noise levels from mobile equipment (source: Dowon & Stocks, 1977).

Equipment

Noise level (dB(A))

Measurement location

Compressed air rock drill

110–115 98 80 81 90–92 74–109 88 78–101 76–104 84–107 87 75–95 72–100 83–101 92–104 88

At 1 m (3 ft) At 15 m (50 ft)* At 7 m (23 ft) At 15 m (50 ft)* Operator’s cab Driver’s cab At 15 m (50 ft)* Operator’s cab Operator position Operator position At 15 m (50 ft)* Driver position Operator position Operator position Operator position At 15 m (50 ft)*

Large portable compressor 7 m3 (10 yd3) dragline Diesel trucks Electric shovels Graders Dozers Locomotives Rotary drills Front end loaders Scrapers * Figures used by the US EPA.

valves on the blast, inversion of hot-blast stoves, safety valves on the top gas ducts, cleaning of top gas, water cooling pumps and circuits. Electric arc furnaces may emit upto 120 dB(A) of noise, which could be reduced by the installation of a system of sliding doors to insulate the furnace from the rest of the bay. The noise emissions could be reduced by changing from A.C. arc (which is the source of noise on 100 Hz) to D.C. arc. Induction furnaces are recommended to be used, as they are noiseless. There are two ways of reducing noise – sound proofing where possible, and redesigning of equipment so as to produce lesser amount of noise. As it is difficult to reduce the noise of the machines, a practical way-out is for the workers to protect themselves from noise by using ear muffs. The ambient noise levels at various working points in the mine are regularly monitored, to ensure that they are within the statutory limits. 6.3.2

Heat

The four environmental factors which determine the heat stress are: temperature, humidity, velocity of the air and radiant heat. Mine workers are exposed to combinations of these stresses, apart from producing large amounts of body heat when they perform heavy work. In the opencast mines, if the rocks are lightcoloured (such as quartzites), there is radiant heat load from the sun and from reflected infrared radiation. If the rocks are dark coloured (such as, basalts), they absorb the sun’s heat, and act as an additional heat source. As is well known, it gets warmer as we go deeper into the earth, at the rate of ⬃2 °C per 100 m. Thus, if the mining is taking place at a depth of (say) 300 m, the ambient temperature at the mine face would be 6 °C more than the surface

136 Mineral resources management and the environment

temperature. Added to this is the heat produced by the operation of the mining and transport equipment, and rise in body temperature due to heat-producing muscular activity. Under these conditions, the body temperature of a worker may rise to 40 °C or more, leading to heat collapse or syncope. If the intake of water is not commensurate with heat, the worker may suffer dehydration. The problem may be treated by transferring the worker to a cool environment, and by increasing the fluid intake. In some coal mines, one may have to do heavy physical work in narrow confined spaces in a cramped position. This would lead to muscle and joint disorders, such as sprains, myositis, tendonitis, lumbago, etc. The problem of heat stress is best understood with the example of the Kolar gold mine in south India, which at the depth of 3 km, is one of the deepest, if not the deepest, mine in the world. The virgin rock temperatures at that depth are exceedingly high (⬃68 °C). In 1930s when the working depth was about 1500 m, heat collapse cases were rare. As the mine became deeper, the heat stress problem became more evident. Heat collapse cases occurred if the dry bulb temperatures was in the neighbourhood of 110 °F, and the wet bulb temperature was around 93 °F. Experience has shown that dry bulb temperatures of 110–120 °F and wet bulb temperatures of 90 °F or less, indicates good ventilation. A wet bulb temperature of 94–95 °F is indicative of poor ventilation, and heat collapse should be expected if the temperature is above 96 °F. With improved ventilation, installation of air cooling plants underground, and the provision of cool drinking water, the heat stress problem in Kolar has been controlled (Pai & Shenoi, 1988). 6.3.3

Vibration

In the mineral industries (e.g. iron and steel industry), three major categories of vibration can be distinguished: mechanical vibration, vibration by combustion, and aerodynamic vibration. The international standard ISO 2631 fixes the orders of magnitude of tolerance limits. Thus, the vertical vibration with frequencies between 4 and 8 kHz is the least tolerated, particularly when the vertical acceleration exceeds 6 m/s2. Besides, vibration causes noise pollution. Workers using mining and pick-hammering equipment are exposed to vibrations in the 40–300 Hz range. Exposure to such vibrations over a long period of time affects the hands, joints of hand, forearm, arm and shoulder, and may give rise to microtraumata, peripheral nerve stimulation, spasm of the arterioles, etc.. Starting with numbness of hand (pasraesthesia), the affected person may develop vascular disorders spread over the whole body. Such a condition is known as Raynaud’s disease. Avoidance of the use of hand-held equipment (by the mechanization and automation of the equipment), and routine use of shock absorbers and gloves by the workers are some of the ways of mitigating the vibration-caused diseases. The hazard can be monitored by regular X-ray examination of the hands and arms of the workers, and the analysis of the records. The localized vibration arising from the use of hand pneumatic tools in mining exposes the workers to: neurovascular alterations in the hands, including Raynaud’s

Mining and health hazards 137

phenomenon (i.e. “dead hand”, “white fingers”), bone alterations, including cysts on the some of the bones of the hand, muscular atrophy, degenerative alterations in ulnar and median nerves, tenosynovitis (UNEP, 1991, p. 62). 6.3.4

Falls and explosions

Most of the serious accidents in mining arise from falls from the roof or walls in the underground mining, and falls from side-walls in the opencast mining. The falls may seriously or fatally injure the workers, and may entomb and suffocate them. Explosions constitute a serious hazard in mining. They may be caused in the following ways: (1) poor timing and misfiring of charges in blasting, (2) methane gas released by drilling and blasting, may explode when it is mixed with air in a proportion of 5–15%, (3) fine particles of coal dust may explode, following a methane gas explosion. Dust explosions have a multiplier effect – one explosion triggering another. The effects of these explosions are invariably very serious, and may consist of severe burns, asphyxiation, intoxication caused by carbon monoxide gas, pulmonary oedema, and physical injuries. 6.3.5

Mine flooding

Flooding of coal mines may cause hundreds of deaths, as has happened in the Damodar Valley coal fields in eastern India. If an underground mine is in the proximity of a river, and if the river and the coal mine are separated by a relatively porous rock, the water in the river may leak into the mine and flood it. Some times water from a flooded mine may leak into a nearby working mine. Such flooding can be avoided by the construction of underground grout barriers, called hydrocurtains.

6.4

CHEMICAL HAZARDS

Methane problem is particular to coal industry, and fluorine problem is a special feature of steel industry. Other gases, such as, CO, CO2, SOx, NOx, etc. are common among several mineral industries. Methane gas is easily the most serious chemical hazard in the underground mining of coal. It is naturally present in the layers of coal, and gets released when the layers are drilled through or blasted. It is non-toxic when inhaled. However, methane dilutes the oxygen in air, and thus causes oxygen deficiency, and asphyxiation. The symptoms of methane intoxication are nausea, unconsciousness and convulsions. The principal hazard due to methane arises out of its high flammability, and the consequent ability to cause explosions. Hence great care has to be taken to ensure that there is no build up of the methane concentration in the air in the mine. It is necessary to check methane concentrations frequently using the methane detectors. As a rule, the methane concentrations should invariably be checked before and after drilling and blasting. Now-a-days, in the highly mechanized mines, the methane concentrations

138 Mineral resources management and the environment

are routinely monitored using remote registration. Methane concentrations in the air should not exceed 0.5–1.0 vol. per cent. Ventilation can be used to dilute the methane concentrations to safe levels. An innovative approach that is followed in some countries is to collect the methane gas from the mines, and use it as a fuel for boilers. 6.4.1

Health hazards from chemical pollutants in air

Carbon monoxide is an odourless, highly toxic and extremely flammable gas. Incomplete combustion produces the gas, which is therefore to be found in the exhaust fumes of combustion engines and in methane or coal dust explosions. Carbon monoxide has 200 times more affinity than oxygen for haemoglobin in the blood, and hence causes acute intoxication of all body cells. The symptoms of carbon monoxide intoxication are headache, weakness and shortness of breath. If not treated promptly, carbon monoxide poisoning may result in collapse and death. Treatment consists of artificial respiration and supply of oxygen. The level of carboxyhaemoglobin is linked not only to the concentration of carbon monoxide in the air, but also to the duration of exposure, the volume of air passing through lungs, and the blood volume circulation. In healthy individuals, carboxyhaemoglobin levels of 5% impair the vision, but in the case of individuals with heart or lung diseases, levels of 2.5% can be harmful. Hence the average atmospheric monoxide levels should not exceed 11.5 g/m3 (UNEP, 1986, p. 37). Oxides of sulphur (SOx ) Sulphur dioxide (SO2 ) gas is a respiratory irritant. It causes respiratory diseases, particularly in the elderly people and in young children. The health effects of various levels of atmospheric concentration of SO2 are summarized as follows: At 2.1 mg/m3, early reduction of pulmonary function occurs, At 10 mg/m3, the pungent odour becomes easily identifiable, From 17 to 35 mg/m3, irritation of the throat and nose occurs, At 58 mg/m3, it causes the irritation of the eyes. At high concentrations, inhaled SO2 causes the oedema of the larynx. SO2 levels in the air should not exceed 24 hr mean values of 0.10–0.15 mg/m3, with approximately 50% of these values for annual mean exposure. Sulphur dioxide concentration in the air causes cankers in the flora, and corrodes the building materials. Sulphur trioxide (SO3) gets converted in the atmosphere to highly corrosive and toxic sulphuric acid. SO3 is more toxic than SO2 and affects the respiratory functions at levels of 0.35 mg/m3. Oxides of sulphur become more harmful when combined with particulates. Nitrogen oxides (NO and NO2). NO gets readily oxidized to NO2 in the atmosphere, and therefore the consequences of NO2 are more important. Nitrogen oxides are akin to carbon monoxide in that both are products of incomplete combustions, and are found in the same kinds of situations. At concentrations of 1.3–3.8 mg/m3, respiratory functions are affected. Short term exposure (1 hr) to 47–140 mg/m3 can cause bronchitis and pneumonia, and at 560–940 mg/m3, fatal pulmonary oedema can occur.

Mining and health hazards 139

The guideline value is in the region of 0.19–0.32 mg/m3. The intoxication by NO2 may be treated preliminarily by the supply of oxygen, and antitussive medication. Fluorine compounds. Fluorosis is caused by the ingestion of fluorides, and affects bones and teeth of humans and animals. The principal pathway (80%) of fluoride to man is through drinking water, but ingestion could occur through inhalation also. Daily intake of more than 8 mg/d of fluoride causes dental mottling and skeletal fluorosis. Fluorosis has been noted in the animals in the vicinity of steel complexes. Fluorine poisoning of plants manifests itself in the form of canker of the needles of fir, spruce, pine trees, deformation of the leaves of cherry, peach and almond trees, and blight in the case of tulips and gladioli. Carbon dioxide is produced in the process of breathing. The inspiration (ambient) air contains 21% oxygen, and very little carbon dioxide. The expiration air contains 17% oxygen, and 4% carbon dioxide. If the ventilation is inadequate, i.e. there is no supply of fresh air, the percentage of oxygen in the ambient air gets reduced, while the percentage of carbon dioxide increases. If the oxygen concentration in the breathing air becomes less than 10–12%, a person becomes unconscious. This condition can be treated by administering oxygen. 6.4.2

Health hazards from chemical pollutants in water

The principal water pollutants are: suspended particulate matter, hydrocarbons, oxidisable substances and toxic substances. Suspended particulate matter in polluted water can reduce the transmission of sunlight, and thereby adversely affect the ability of the organisms living in it to perform photosynthesis. This in its turn may affect the ecological cycle. The soluble particulate matter could change the chemical characteristics of the aquatic environment, and thereby affect the flora and fauna. Hydrocarbons impede the transfer of oxygen from air in water, and could render the environment anaerobic. This could strongly impede the growth and reproduction of the organisms most of which are aerobic, leaving only a few resistant strains to survive. Oxidisable substances use up the oxygen present in the water, and could bring about a rapid and severe depletion of oxygen in water. The water will become anaerobic, and degrade the ecosystem. However, if the oxidisable substances are biodegradable and are present in limited quantities, they may actually improve the productivity of water courses (with increase in algae and fish populations). Living organisms best function at neutral pH of 7. Most organisms can function only within the pH limits of 4–9. Highly acid or alkali effluents which have the effect of changing the pH beyond the limits, degrade the ecosystem. Similarly, pollution by heavy metals (such as, Cd, Pb, Hg, Ni, etc.) intoxicate the organisms and destroy them. 6.4.3

Health hazards from chemical pollutants in solid wastes

In some mineral industries (such as, steel industry), the wastes are recycled, or sold. Recycling could lead to the danger of accumulation of toxic substances – as has been found to be the case with thallium in the cement industry. Recycling of wastes

140 Mineral resources management and the environment

containing lead and cadmium, could produce a product with unacceptably high content of these toxic metals. This should hence be guarded against. The leachates from the wastes could contaminate the soils and groundwater. 6.5

BIOLOGICAL HAZARDS

Biological hazards are those caused by living organisms. These tend to be common among the mine workers in the developing countries because of poor standards of hygiene and sanitation. Tinea pedia is a fungus, which causes interdigital mycosis of the feet of the mine workers. The hot and moist climate of the tropical countries promotes the propagation of the fungus inside the boots. The fungus spreads by skin contact with infected waters in the shower rooms. Coccidiodmycosis is a disease caused by the fungus, Coccidiodes inmitis. The fungus can survive in the soil in a cyst form for many years. When the soil is exposed because of mining, the fungus may get released into the air. The inhalation of the spores may cause pulmonary symptoms, similar to tuberculosis. Ankylostoma duodenalis is a disease caused by the parasite, hookworm. The victim develops hypochromic anaemia. Weil’s disease (leptospirosis icterohaemorrhagica) is spread by a bacillus in the urine of rats. The disease is marked by jaundice and internal haemorrhage. Workers may get exposed to this disease in mines, which use wooden props for roof support. 6.6

MENTAL HAZARDS

A person working in an underground mine is always aware that falls of the ground, roof collapse, blasting and explosions of dust and gas, could injure or kill him any time. Such an environment may provoke feelings of anxiety, tension, irritability and fatigue. A person working alone in a mine may develop feelings of claustrophobia. If the management makes it known to the worker the various precautions that have been taken to provide security and comfort to him, the worker will feel less anxious, and more cheerful. Almost always, the mines are operated on a shift basis (of, say, eight hours). The shift work has an adverse effect on the circadian rhythms of the body, leading to sleep disorders, stomach ailments and social stress. Some companies find that operation in 4-hr shifts, or 12-hr shifts on a 4-day rotation basis, may be less disruptive of the circadian rhythm. 6.7

COAL CYCLE AND ENVIRONMENTAL HEALTH

The major environmental and health impacts of the coal cycle are summarized in Table 6.6 (Chadwick et al., 1987, p. 135–136).

Destruction and disruption of vegetation, natural drainage patterns and land use in the area of the mine. Erosion of cleared areas and soil and overburden dumps leading to sedimentation and pollution of water courses. Possibility of acid mine drainage. Dust created during operations causing visibility problems and loss of agricultural production. Water consumption effects in arid areas.

Surface mining Many variations (contour stripping, mountain top area mining, open pit), and machinery-use options (shovel-truck, dragline, continuous mine). All basically involve removal of vegetation, top soil and overburden to expose coal. Usual depth limit ⬃300 m.

Utilization Coking, direct combustion, coal conversion.

Coal transport and storage Conveyor, slurry pipeline, truck, railway, barge, ship.

Coal preparation and beneficiation Coal crushing and grinding for different end-uses, and washing to reduce ash and sulphur contents.

Emissions from all processes of particulates, nitrogen and sulphur dioxides, carbon monoxide, hydrocarbons and trace elements. Disposal of liquid effluents, e.g. ammoniacal liquor from coking. All processes produce large amounts of solid waste which can pose problems of erosion, runoff, toxicity and contamination of water courses.

Dust effects particularly during transit and at transfer points. Water pollution from disposal of untreated slurry water.

Dust effects. Water consumption effects in arid areas. Air pollution from emissions from coal drying after washing. Solid waste heap disposal – erosion, runoff and spontaneous consumption. Aqueous waste disposal – slurry lagoons, pollution of ground and surface water.

Production of surface spoil heaps with potential erosion effects such as sedimentation and acidification of water courses. Possibility of spontaneous combustion of spoil heaps causing air pollution and tip instability. Mine drainage adversely affecting the water quality of a large area by removing soluble minerals from aquifers and by the acidification of surface water courses. Loss of agricultural productivity over large areas caused by subsidence. Water consumption effects in arid areas.

Environmental impact

Operation

Deep mining Basically two types – longwall, and board-and-pillar, but many variations and degrees of mechanization. Access to seams by vertical shaft or drift.

Major environmental and health impacts of coal cycle (source: Chadwick et al., 1987, p. 135–136).

Table 6.6

Emissions of noxious gases, heat and dust. Process and end-product related to occupational health risks.

Dust effects.

Dust effects. Emissions from coal drying. Noise and vibration effects.

Noise, vibration and blast effects. Pneumoconiosis and other respiratory problems from dust. Effects of mine gases. Poor working environment – high temperatures, wet conditions, inadequate light. Hard physical work. High accident rate.

Noise and vibration effects from machinery. Blast effects. Potential silicosis and respiratory problems.

Health impact

142 Mineral resources management and the environment Table 6.7 Severity estimates for underground and surface mining by sector (data for USA in 1995) (source: Grayson, 1999, p. 94). Sector

Fatalities

Fatal-IR

NFDL

NFDL-IR

Total-IR

Overall SM

Coal underground Coal surface Metal underground Metal surface Nonmetal underground Nonmetal surface Stone underground Stone surface Sand/gravel surface Sand/gravel dredge

25 10 3 5 3 3 0 11 4 2

0.05 0.03 0.04 0.03 0.08 0.05 0 0.04 0.02 0.04

5426 942 422 469 146 137 75 1201 881 182

10.57 2.75 5.79 2.52 3.83 2.41 3.71 4.15 3.56 3.77

13.50 4.06 9.75 4.23 6.34 4.19 5.53 6.86 5.62 6.10

772 288 498 290 712 433 122 345 269 335

IR – incident rate; NFDL – non-fatal days lost; SM – severity measurement (the number of lost and restricted work days, multiplied by 200,000 and divided by the number of employee-hours worked).

Table 6.8

Occupational illnesses in mining by sector (US data, 1995) (source: Grayson, 1999, p. 95).

Type/sector

Coal

Metal

Nonmetal

Stone

Sand/gravel

Skin diseases Dust diseases – lung Respiratory – toxic agents Poisoning Disorders – nontoxic physical agents Disorders – repeated trauma All others Total

3 207 8 3 2 214 21 458

4 8 1 1 12 109 2 137

1 5 2 0 3 32 3 46

12 9 1 3 15 49 5 94

3 2 0 0 5 22 1 33

An examination of the statistical data (for USA, 1995) in regard to fatalities, nonfatal days lost (NFDL), total accident incident rate, and severity measurements (SM) for underground and surface mines by sector (Table 6.7, source: Grayson, 1999, p. 94) leads to the following conclusions: (1) Among all the mining activities for various minerals, the most hazardous is the underground mining of coal, (2) The underground mining of coal, metal and nonmetal has higher severity measure than the corresponding figures for surface mining for the same minerals, (3) Surface mining of stone has a greater SM than underground mining of stone. On the basis of such analyses, the Mine Safety and Health Administration (MSHA) targets sectors, mines and jobs to enforce the regulations. Table 6.8 (source: Grayson, 1999, p. 95) indicates that coal mining leads mining for other minerals in regard to dust diseases of lungs and trauma disorders. By improving the working conditions in the mines, the number of silicosis cases per year came down from 857.4 during 1968–78 to 284.5 in 1991–92 in USA. Similarly, the number of cases of pneumoconiosis per year, which was 2374.8 in 1968–78, was brought down to 1852.0 per year in 1991–92.

Mining and health hazards 143 Table 6.9

Hazard prevention measures (source: Chadwick et al., 1987, p. 223).

Hazard

Principle of prevention

Preventive measure

Dust

Wetting the coal face, ventilation, surfactants on the floor

Noise Heat Heavy work

Suppression at the source, dilution in the air, suppression in the environment Substitution Reduction Elimination, substitution

Vibration Falls of ground Dangerous machines

Elimination Elimination Substitution, segregation

Blasting

Suppression at source, dilution of air Disposal, dilution

Gases

Other machinery Ventilation and air-conditioning Mechanization/automation, ergonomic design work Remote control Support to roof and walls Maintenance/replacement, machine guarding Wet methods, ventilation Extraction, ventilation

There are three E’s of mitigation: Education, Engineering and Enforcement. The goal of the mining industry should be to ensure that the workers could work their entire career without incurring death, disability or serious injury. Table 6.9 lists the hazard prevention measures in the case of the coal cycle (source: Chadwick et al., 1987, p. 223).

CHAPTER 7

Process technologies and the environment

The Run-of-Mine (ROM) economic mineral is rarely saleable as such. In the olden days, the saleable material used to be handpicked. Now a days, we have a whole array of technologies to process the ROM to suit the specifications of the consumer. The beneficiation process has to take into account (1) the market specifications, (2) techno-economic viability and minimum costs, (3) ecological sustainability, (4) national policy, and government regulations, etc.. If the ore is polymetallic, the flowsheet is adjusted so as to produce more of the metal for which there is a strong current demand. For instance, due to demand in high-tech applications, particularly the cell phones, the market price of tantalum has shot up from USD 66 to 264/kg. Thus, when tantalum ores, such as fergusonite, samarskite, euxenite, etc. are to be processed, the flowsheet should be so designed as to be able to achieve the maximum recovery of tantalum, in preference to other associated elements such as cerium earths, thorium, etc. The Chapter elucidates how the environmental impacts of mineral processing could be minimized through an understanding the scientific basis of the process technologies.

7.1

PREPARATION OF COAL

Good part of the global production of coal (about 4600 Mt/y) undergoes some form of preparation before it is used directly (say, in a pit-mouth thermal power station) or sold. Consumers demand a high degree of consistency in the product sold to them, and the environmental regulations need to be adhered to. To start with, the ROM coal and the associated refuse material are analysed for their mineralogy, size distribution, hardness, calorific value, coking properties, etc. in order to determine their treatability by the main separation techniques available. ROM coal is crushed using jaw, gyratory or roll crushers, and then screened to produce different size fractions. “Clean” coal is lighter, because of its lower ash content. Hence coal separation is effected using the density criterion. Jigging using the water medium is by far the

146 Mineral resources management and the environment

oldest and the simplest method of separation of clean coal. The density of the medium can be raised to the desired level by making use of water-based suspensions of sand, shale, barite, magnetite, etc. The lighter clean coal particles float to the top of the washery cell, whereas the higher density waste particles accumulate at the bottom, with middlings in between. The cycle is repeated until the needed separation is effected. Separation of coal and waste material can also be effected using cyclones, which may make use of water or some other appropriate (heavier) medium. Occasionally, shaking tables, launders and spirals are used. Froth flotation could be made use of to clean coal fractions with a maximum diameter of 0.5 mm. In the flotation cell, air is bubbled through the coal slurry, which contains the collector reagents. The aerophyllic coal particles rise to the surface, while the hydrophyllic shale and pyrite particles sink to the bottom of the cell.

7.2

PREPARATION OF METALLIC ORES

The metal content of ROM ores of non-ferrous metals is usually low (e.g. 1.014% Cu in El Teniente, Chile; 0.87 g/t of Au in Cortez, Nevada, USA). Hence it is necessary to concentrate the ores at mine site, and then send the concentrates to a smelter or a hydrometallurgical plant for the extraction of metal concerned. The marketable mineral species in the ore have to be separated from the undesirable and valueless gangue. This invariably involves a size reduction operation, called comminution. Thus comminution has to precede the processes of beneficiation or leaching. The size distribution of ROM may range from a few microns to several hundred millimeters, whereas the liberation size of the sulphide minerals is usually less than 100 microns. Thus ROM has to be ground down to about 100 microns or lower, depending upon the grain size of the ore metal that needs to be liberated. Research and Development in the process technologies is aimed at not only making the processes efficient, but also environmentally benign. The following techniques are used for the reduction of the grainsize: (a) Crushing–grinding: Size reduction of dry solids of ore particles to about 10 mm size is accomplished through primary crushing using a jaw crusher or gyratory crusher, followed by one or two stages of secondary gyratory crushers. At each stage, vibrating screens are employed to obtain materials of desired size. Water is added to the size of the crushed material whose size is to be further reduced by grinding in rod mills and/or ball mills. (b) Autogenous grinding: After primary crushing, the ROM ore is made into a slurry and fed to an autogenous (or semi autogenous) grinding mill. Further fine grinding can be accomplished using pebble mills or conventional ball-mills. (c) Classification: There could be upto three grinding stages, depending upon the grainsize required and the capacity of the processing plant (ROM in some large mines may be of the order of 100,000 tpd). Classifiers, including hydrocyclones,

Process technologies and the environment 147

rake classifiers, and spiral classifiers, are coupled with each grinding stage to remove the ore grains of desired size dimensions. Two innovative developments in comminution technology are summarized as follows: Microwave heating is being used for the liberation of minerals from the refractory ores of gold, copper and other metals (Wang & Forssberg, 2000). This technology has tremendous potential for use with sulphide flotation concentrates to replace processes such as autoclaving, roasting and smelting. More importantly, the technology is environmentally benign. The microwave heating behaviour and the grindability of materials depend not only on the microwave energy intensity and exposure time, but also on the grainsize. Dry milling of the microwave treated coarser particles (9.50 mm, 4.75 mm) of limestone and quartz greatly improved their fineness. When copper ores are subjected to microwave treatment (energy intensity
7 kw, and exposure time 30 mins.), thermal stress fractures occurred readily, resulting in better and cleaner separation of sulphide minerals from the ore matrix. On the other hand, microwave heating did not induce stress fractures in silicate and carbonate minerals, possibly because of their transparency to microwave radiation. Namdeb Diamond Corporation in Namibia (SW Africa) has a floating treatment plant for the screening and concentration of diamondiferous gravels from an overburden dredging operation. The installed trommel screens were not effective in achieving primary screening requirements at 2 mm apertures. If conventional screening techniques are to be employed, a separate screening barge would have been needed. This option has been ruled out as it is prohibitively expensive. McDougall and Cooke (2000) used the principle of elutriation innovatively for solving the screening problem. The flow in the feed pumping system is split in such a way as to remove part of the 90% fines in the feed, thereby reducing the duty required of the trommels. In the elutriator column, the overflow stream flows vertically upwards. Thus, the feed from the dredge is split into two streams – the underflow of coarse material goes to the trommel screens, whereas the overflow of fine material bypasses the trommel screens and goes directly to the screen underpans. A magnetic flow meter is used to monitor and control the upward velocity of the stream in the elutriator column.

7.3

FLOTATION

Flotation is the most commonly used process for the beneficiation of the sulphide and oxide ores of base metals, and ores of gold associated with sulphides (with the exception of the oxide ores of nickel). It is a complex physico-chemical process, but its basic principle can be explained as follows: In froth flotation, air is blown through the solution containing flotation reagents. The particles with water repellent surfaces stick to the air bubbles, and rise to the

148 Mineral resources management and the environment

surface, where they are collected. Particles, which are wettable, remain in suspension or settle down. In the case of dispersed air flotation, gas bubbles are generated by introducing the air by mechanical agitation. In the case of dissolved air flotation, bubbles are produced when air is released from a supersaturated solution under a relatively high pressure. In vacuum flotation, wastewater is saturated by air, directly in an aeration tank. A typical vacuum flotation unit consists of a covered cylindrical tank under partial vacuum, with mechanisms for scum and sludge removal. The floating material is got swept into scum trough, where from it is pumped out under partial vacuum. Finely ground ore is pulped with water and appropriate chemicals (or flotation reagents). Flotation separation takes place in a series of cells or columns, which are agitated by air to promote dispersion. The hydrophobic minerals (such as, sulphides) are carried piggy-back on the bubbles formed in the cell, and rise to the top as scum. The scum, which contains the minerals of value, is skimmed off. Often several stages of flotation may have to be employed in order to obtain the desired concentration. On the other hand, the wettable gangue minerals (such as magnetite and quartz) sink to the bottom of the cell. They are collected and sent to disposal ponds. Flotation has a number of advantages: the energy requirements are not high, and the airflow can be controlled depending upon the characteristics of the wastewater. The disadvantages are that chemicals are needed to be added to enhance process performance, the operators have to be properly trained and attentive, and large quantities of solid wastes are generated. Ultrafiltration involves the use of pressure and semi-permeable polymeric membranes, which allows the passage of water and low molecular weight materials, while retaining emulsified oil droplets and suspended particles. A major limitation of ultrafiltration is that for satisfactory operation, it has to be used in the narrow temperature range of 18–30 °C. Higher temperatures increase the flux, but reduce the life of the membrane. So a trade-off is inevitable. Strong oxidizing agents, solvents and some organic compounds can dissolve the membrane, and hence wastewaters containing them cannot be treated by ultrafiltration. Also, large particles are capable of puncturing the membrane, and must be removed by gravity settling or filtration, before the wastewaters are subjected to ultrafiltration. The membranes must be periodically changed, and detergent solutions should be passed through the system to remove oil and grease films that may accumulate on the membrane. The chemicals (flotation reagents) used in the flotation process serve different purposes: acids and alkalis (for pH control), frothers (for producing froth), collectors (to collect the ore mineral by facilitating their separation from gangue minerals) and modifiers (to modify the characteristics of the pulp), etc. The following flotation agents are used in Base Metal Concentrators: 1. Acids: Sulphuric acid, 2. Alkalis: Lime, Sodium Carbonate, Sodium hydroxide. 3. Modifiers: Copper sulphate, Sodium cyanide, Zinc sulphate, Sodium sulphide, Sodium silicate, Sulphur dioxide, Starch.

Process technologies and the environment 149 Table 7.1

Typical ore processing reagents (source: Environment Canada, 1987).

Reagents Acids (H2SO4, HCl, HNO3) Alkalis (CaO, Ca(OH)2, CaCO3, Na2CO3, NaOH, NH4OH, NH3) Frothers and collectors Modifiers

Sodium Cyanide Flocculants, Coagulants

Comments

Surface active reagents Surface active organics and various inorganics, such as NaCN, Na2SO3, CuSO4, ZnSO4, Na2S, AlCl3, Pb (NO3) 2, silicates and chromates Used for the cyanidation of precious metals, and as depressants in the flotation of copper, lead and zinc ores Aluminium and iron salts, and organic polymers

4. Collectors: Potassium amylxanthate, Potassium ethylxanthate, Potassium isopropylxanthate, Aniline Dicresyldithiophosphate, Diesel oil, Amine. 5. Frothers: Dowfroth 250, Hexylic Alcohol, Pine Oil, HBTA frother. Depending upon the composition of the ore, and the component to be concentrated, suitable combinations of flotation reagents are chosen (Table 7.1). Typical consumption of flotation reagents is given in Table 7.2 (source: UNEP, 1991). The concentrates are then dewatered in thickeners and filters. Figure 7.1 (source: UNEP, 1991) gives the flow sheet of the Pb–Zn concentrator. Wastes are sent to the disposal ponds through ditches, launders and pipe systems. Water in the disposal ponds is recovered by decantation – it is either recycled in the processing plants or released to the environment. While the reagent suite is chosen on the basis of surface chemistry considerations, the overall efficiency of the system of beneficiation would also depend upon engineering aspects of the system, such as the type, design and operation of the machines used in flotation, pre-classification of the flotation feed, and the application of magnetic field to the flotation cells, etc. Problems arise when concentrates of copper, lead and zinc are to be obtained selectively from complex ores of these metals. Most often, the concentrates are produced from low-grade ores, and are characterized by low recoveries. There will be penalties if the concentrates of one metal (say, copper) are contaminated with excessive amounts of other metals (say) lead and zinc, because of the consequent problems in smelting. Electrochemical techniques have been developed for the collectorless flotation of sulphide minerals of copper from their gangues. These methods have dual advantages of being cost-effective and environment-friendly. For instance, in the case of pulp containing chalcopyrite and galena, flotability of chalcopyrite reaches the highest level of 73%, at pH 10 and pulp electrochemical potential between 100 mV and 120 mV. Flotation was depressed significantly if the electrochemical potentials are outside the above range. Galena showed good flotability at pH 8, and

150 Mineral resources management and the environment Table 7.2 Typical consumption of flotation reagents in Non-ferrous metal mills (g/t of ore) (source: Weiss, 1985; McQuiston & Shoemaker, 1975, 1980). Concentrator Acids H2SO4 Alkalis Lime Sodium carbonate Sodium hydroxide Modifiers Copper sulphate Sodium cyanide Zinc sulphate Sodium sulphide Sodium silicate Sulphur dioxide Starch Collectors X-Amylxanthate X-Isopropyxanthate X-Ethylxanthate Diesel oil Amine R-242 * Frothers Dowfroth 250 Hexylic alcohol Pine oil HBTA frother Carbon

(1)

(2)

(3)

(4)

(5)

(6)

500–600 1000 550 246 200 10 60

120 13 91 2800 2700

2500 3300

225–400

815

35–60

(7) 5000 #

1100

1200

3150

550

330 28 1450

700 100 45

130

5

20 69 250 60

270

60–85

35 30

20–25

14

220

40 20 85 30

(1) Pb–Zn sulphides – Les Malines (France); (2) Pb–Zn (oxide sulphides) – Zellidja (Morocco), (3) Cu–Pb–Zn Brunswick Mining and Smelting (Canada), (4) Ni (sulphide) – Falconbridge (Canada), (5) Cu (sulphide) – Lornex (Canada), (6) Au (Cyanidation  CIF) – Homestake (USA), (7) Cu–Zn pyrite – Pyhasalai (Finland). * R242: Aniline Dicresyl dithiophosphate  thiocarbonilide #: Sulphuric acid is used for pyrite recovery

electrochemical potential between 190 mV and 230 mV. At pH 8, addition of ferric nitrate minimized the flotation to about 3%. Rutile and ilmenite are usually separated through a combination of gravity and electromagnetic techniques. These techniques achieve their purpose if the particles are coarser than 100 mesh. If the particles are fine (less than 45 microns), these techniques are ineffective and uneconomical. Froth flotation techniques have been developed to get over the problem. In the presence of 7.5  106 M of the cationic collector Hydrogenated Tallow Amine Acetate (HTAA), pH 12 and temperature of 25 °C, the flotation recovery of ilmenite reached 84%, while that of rutile remained at only 16%.

Process technologies and the environment 151

Figure 7.1

A typical Pb–Zn concentrator flowsheet (source: UNEP Tech. Rept., no. 5, 1991, p. 18).

The iron-ore mining industry in USA faces stiff competition from high-grade imported iron ores. Cationic silica flotation of magnetic concentrates is a low-cost, environmentally-benign flotation process which is capable of yielding a concentrate which satisfies the increasingly stringent specifications for the raw feed materials for blast furnaces and direct reduction processes (Iwasaki, 2000). While the reagent suite is chosen on the basis of surface chemistry considerations, the overall efficiency of the system of beneficiation would also depend upon engineering aspects of the system, such as the type, design and operation of the machines used in flotation, pre-classification of the flotation feed, and the application

152 Mineral resources management and the environment

of magnetic field to the flotation cells, etc.. This approach may be illustrated with an example. In southern Sardinia, gold ores occur with enargite, which contains arsenic. Alkali leaching of enargite in the sodium sulphide medium, achieves more than 90% efficiency, with significantly higher extraction rates if the ore is finely ground. The solid leach residue has the composition of covellite, which can be subjected to pyrometallurgical treatment. Maelgwyn Mineral Services developed more efficient techniques of Imhoflot pneumatic flotation for improved coal recovery. The key element in the flotation process of coal is the bubble adhesion in a coal slurry and the nature of the bubble– particle interaction. The Imhoflot process makes use of intense pre-aeration using a self-aspirated, multijet device to promote the interaction. The mineralized bubbles are recovered in a relatively quiescent separator cell. The stage residence times are generally less than three minutes. This process achieves high selectivity and the consequent production of high grade concentrates in the primary flotation stages. Multiple stages may be needed in the case of coal types with slow time recovery response. This technique has been used successfully in coal and tailings processes with unit feed capacities of 80 t/h or (800 m3/h) and cell sizes of 5 m diam. The recovery efficiency may be optimized by adjusting the barometric conditions and jet configurations in the self-aspirated aerator, the pulp level, froth height, dispersion characteristics of the distributor and jet nozzles, etc. Enhanced Gravity Separation (EGS) involves the use of mechanically applied centrifugal field to increase the efficiency of conventional gravity-based devices, such as jigs, riffle tables, teeter-beds, and flowing film devices. The cleaning of 1000  44 micron coal through EGS can be considerably improved by use of a dense medium comprising an ultrafine magnetite suspension. The EGS technology helped in the reduction in the ash content from 16.9% to below 5% of fine no. 6 Illinois coal, while achieving organic efficiency value as high as 95%. High process efficiencies are achievable over a whole range of particle sizes of coal from the coarsest particle sizes (1000  600 microns) to the finest fraction (150  44 microns). In the case of low-rank coal of El-Maghara, Egypt, it has been found that the use of pine oil in the emulsification of the fuel oil collector resulted in better recoveries, particularly of fine coal particles. Cyclones have been traditionally used for classification in the 50–200 micron range. Maelgwyn Mineral Services have developed a new kind of technology to improve the efficiency of classification. The new technology developed by Maelgwyn Mineral Services makes use of traveling pans each containing precisely woven slotted mesh panels. The slurry bed is mobilized with fine, high velocity water sprays above and below the mesh. The new process consumes less energy, and provides for high process efficiency. In the past, many process applications, including those for coal, have involved two stages of flocculation, using first an anionic flocculant, followed by a cationic flocculant. Ciba Speciality Chemicals has come up with a two-in-one flocculant, TWINTEC, in which the anionic and cationic species exist together. TWINTEC is

Process technologies and the environment 153

said to have the advantages of reduced filter cake moisture, improved throughput, reduced pH sensitivity, and increased life of the expensive filter cloth.

7.4

HYDROMETALLURGY

As the name indicates, hydrometallurgy is an industrial process for recovering metals using solutions, as against pyrometallurgy, which uses heat for the purpose. Hydrometallurgical extraction is fast replacing pyrometallurgical extraction, as it is environmentally less polluting, and involves lower energy consumption. A number of case histories are cited to illustrate the trend. For instance, when gold-bearing refractory ore, stibnite, is treated pyrometallurgically, toxic gases are generated. Ubaldini et al. (2000) found that pretreatment of stibnite by chemical alkaline leaching followed by the cyanidation of residues, permits the extraction of 75% of antimony in a high purity and quality form, and 80% of the gold. Further efficiencies could be achieved by incorporating the gold purification/gold electro-deposition step to the circuit. Tungsten in the form of pure WO3 is usually recovered from scheelite and wolframite concentrates through a multi-step alkaline-based leaching process. Although WO3 is acidic in character, it can be dissolved in the form of poly-tungstate ions by changing the ligand mantle of WO3. Extraction efficiencies of 93% have been achieved through chelate-added acid leach of concentrates below 325 mesh at 70–80 °C using 2M hydrochloric acid at solids to liquids ratio of 1 : 5. It has become a common practice to extract gold from oxidized ores through the heap leaching of cyanide solutions. The gold cyanide complex is adsorbed on activated carbon, and the solutions are then electrolysed using steel wool as cathode. New flowsheets have been proposed whereby gold is directly won from pregnant heap-leaching solutions, thus eliminating gold adsorption and desorption steps. It has also been found that higher gold recoveries are achieved with a steel mesh cathode relative to steel wool cathode. The superior performance of the steel mesh cathode is attributed to its better surface area distribution and homogeneity, which facilitates a better flow of electrolytic solutions. The extraction of several metals involves Leaching, Solvent Extraction and Electrowinning (LX–SX–EW) sequence. The overall objective of the LX–SX–EW process is the maximization of the net revenue on the basis of the production of commercial cathode of the prescribed quality. The performance of the various units is optimized on the basis of the properties of the raw ore (mineralogy, geochemistry, content of ore metals and their speciation, solid-state chemistry, nature of the gangue minerals, etc.), feed rate, energy and reagent costs, metal market prices. Cognis has developed a full range of Solvent Extraction (SX) reagents, which could be custom-blended to optimize metallurgical and physical performance regardless of the operating conditions. A good example of the application is the Cawse

154 Mineral resources management and the environment

Figure 7.2

Cawse flowsheet for nickel SX extraction (source: Mining Mag., Sept. 2001).

Nickel Operations in Queensland, Australia. Before the application of the new flowsheet involving LIX reagents of Cognis, the ore pretreatment involved gravity concentration, cycloning and scrubbing. The new Cawse flowsheet is based on High Pressure Autoclave Acid Leaching (HPAL), followed by the ammonia leach of a base metal hydroxide intermediate filter cake and nickel solvent extraction with LIX 84-I. An important advantage of the Cawse flowsheet is that the process employs only one SX circuit and extractant type. The process produces a high purity electrowon cathode and cobalt sulphide. By recycling ammonia and metal containing intermediates,

Process technologies and the environment 155

the consumption of ammonia could be kept low, while ensuring very high metal recovery (Fig. 7.2; source: Mining Mag., Sept. 2001). Mintek had developed a plant-wide control system called Plantstar. This is powerful software, which incorporates the milling and flotation control strategies. It has a built-in Interpreting Expert System (IES). This constitutes Artificial Intelligence solution, which provides on-line training to plant operator, by translating the numerical results of the various algorithms used in the system in the form of understandable human sentences. This way, the operator becomes familiar with the Plantstar system (Houseman et al., 2000).

7.5

BIOLEACHING

Bioleaching makes use of naturally occurring bacteria to facilitate the extraction of precious metals (Au, Ag) and base metals (Cu, Pb, Zn) from sulphide ores or concentrates. In effect, bioleaching accelerates the natural processes of breakdown of sulphides into oxides. For a given level of production, bioleaching has minimal energy consumption, pollution and waste generation. The bacteria involved do not affect people, they feed on minerals, and they can be transported safely, they are resistant, and can operate in temperatures ranging from freezing to 80 °C. Bioleaching is not only environmentally benign but also cost-effective. No wonder, it is fast replacing the traditional technologies such as roasting, autoclaving and smelting which are not only energy intensive but also cause environmental degradation, as they are associated with the emission of noxious gases (such as SOx), toxic residues and acid rain (see the excellent update by Adiana Potts, Mining Mag., Sept. 2001, p. 128–134, from which this account is drawn). The bacteria, Thiobacillus ferrooxidans, were earlier thought to be the only factor involved in the bioleaching of sulphides (each bacterium is 1.5 m long, and 0.4 m diam.). While this bacteria is undoubtedly the most important, subsequent studies have brought to light a new group of organisms, called archae. Some archae are mesophiles (requiring a moderate amount of heat to grow) and some are thermophiles (which need higher temperatures to grow). Iron and sulphur-reducing archae are widely used in the tank leaching processes, and in the extraction of base metal sulphides. The microorganisms that are used in bioleaching are no different from those that occur in nature – only, we choose those organisms that serve our purpose best. Some organisms require the availability of iron and sulphur, particular temperature, and particular pH (say, 2.5). Since such extreme conditions are rare in natural environments, these organisms have no adverse effect on ecosystems. The BHP Billiton-Codelco and BacTech–Mintek are leaders in bioleaching technologies. Treatment of refractory ores by the traditional methods is not only expensive but also polluting. Gencor of South Africa pioneered commercial tank bioleaching of

156 Mineral resources management and the environment

refractory gold-bearing sulphide ores. It was implemented in 1986 in the Fairview goldmine of the Barberton gold fields of South Africa. Ten years of in-house research, and a 750-kg/d pilot plant, led to the development of the patented process, BIOX™, which proved to be technically and commercially viable. Plants using this technology were set up in Australia, Ghana, Brazil and Peru. In 1994, the Ashanti gold mine in Ghana has switched over to BIOX™ technology, and presently, the 550,000 oz (17.106 t)/y plant employs the new technology (after decommissioning the old Pompora gold recovery plant). In 1997, the Gencor non-precious metals assets have been taken over by Billiton, and in 1998, the Gencor gold assets have been merged with Gold Fields Limited, which continues to market the BIOX™ technology. BacTech’s bioleaching technology for gold, BACOX®, has been used in Australia. Youanmi mine in western Australia (60,000 oz or 1.87 t/y) improved its gold recovery from refractory ores from 40 to 92%. The 65,000 oz (or 2.02 t/y) Laizhou plant in Shandong province in China is in the process of being commissioned. Three more plants using BACOX® technology, are being set up. Newmont is making use of its patented bioleaching process, BIOPRO™, to recover refractory gold at the Carlin mine in Nevada, USA. The USD 8 million facility will treat 10.6 Mt stockpile of low grade (1.90 g/t) sulphide ore, and gold-bearing liquor from a 150-day heap leach biooxidation cycle, to produce 645,000 oz or ⬃20 t/y. While the technical and commercial viability of bioleaching of gold is now firmly established, the prospects of using bioleaching for base metals and molybdenum is even more exciting. Codelco, which is the state-owned mining company of Chile, not only produces the largest quantity of copper (1.614 Mt in 1999), but at the lowest price (USD 0.47/lb or 1.034 /kg) in the world. At Mansa Mina, Codelco is inserting a bioleach plant between the existing flotation module producing copper sulphide concentrates and the existing Solvent Extraction–Electro Winning (SX–EW) unit. Copper-bearing liquid from the bioleach plant and the liquor from the heap leach operations, feed into the SX–EW unit to produce cathode copper (Fig. 7.3; source: Mining Mag., Sept. 2001). Apart from avoiding smelting, the bioleach process takes care of a problem peculiar to Mansa Mina. The ore contains significant quantities of arsenic in the form of enargite. BIOX™ technology precipitates arsenic from the gold-bearing arsenopyrite concentrates in the form of a stable, environmentally-acceptable compound of arsenic. While the viability of bioleaching of secondary sulphides is now firmly established, considerable amount of research is going on to improve the economic viability of bioleaching of refractory chalcopyrite. The copper recovery rates from chalcopyrite using conventional bioleaching technologies at atmospheric pressures, are low (20–40%) and hence uneconomic. Bioleaching employing thermophilic microorganisms operating at temperatures of 60–85 °C in stirred tanks, holds great promise for enhancing the recovery rates to economic levels. BHP Billiton is experimenting with bioleaching involving thermophilic microorganisms in stirred tanks, for copper-nickel and zinc concentrates.

Process technologies and the environment 157

Figure 7.3 Integration of bioleaching with Solvent Extraction (SX) and Electrowinning (EW) processes (source: Mining Mag., Sept. 2001).

There is little doubt that bioleaching will be increasingly put to use because of the techno-economic and environmental benefits. Nalco has developed a new line of polymers for water clarification. The strong points of OPTIMER® mineral processing flocculent are high settling rates of suspended solids, superior overflow clarification, and maximum underflow compaction and pumpability. The Nalco 98DF063 is a liquid polymer system which is custom-made for the flocculation of red mud in the bauxite industry. The Nalco patented TRASAR technology has four components of tracer chemicals, control equipment, diagnostic capabilities and on-site services. The system provides not only protection against scale formation but the inert tracer allows continuous diagnostic monitoring of the system volume, mixing studies, system flow, residence time/water travel time and environmental compliance. Such a system not only helps in the efficient operation of the process, but also allows remedial action to be taken before a problem becomes serious. 7.6 7.6.1

GOLD PROCESSING TECHNOLOGY – A CASE STUDY Introduction

Gold is one metal for which there has never been a diminishing of demand. The world production of gold was about 1400 t in 1980s, and about 1800 t in 1990s. The present world production of gold is about 2500 t, worth about USD 25 billion. More countries are producing larger quantities of gold. 7.6.2

Where to look for gold

Gold occurs as (1) free gold ores, (2) gold with iron sulphides, (3) gold with arsenic and/or antimony minerals (e.g. arsenopyrite), (4) gold tellurides, (5) gold with

158 Mineral resources management and the environment

copper porphyries, (6) gold lead and zinc minerals, (7) gold with carbonaceous minerals, etc. The processes of concentration of gold to form economic deposits are summarized in Table 3.1. Gold particles may range in size from dispersed (upto 10 m), small (upto 0.1 mm), medium (upto 1 mm) and large (upto 5 mm). Pure gold is said to have fineness of 1000 (or 24 Karats). The generally lower fineness of gold in the greenstones (600–900) is attributed to Au–Ag alloy (electrum). Gold occurs in a large variety of environments (Hutchinson, 1987). Igneous: Basalt–ubiquitous, iron-tholeiitic; commonly found pillowed and variolitic-spheruliitic, also magnesian and komatitic; Thin fragmental-pyroclastic rock, Quartz and/or feldspar porphyritic stock. Sedimentary: Polymict conglomerate, Turbiditic greywacke, Iron formation, any facies, Carbonaceous graphitic-(pyritic) sediment. The most important, numerous and largest major districts are of Archaen age. The environments which are characteristic of large deposits of gold, are summarized as follows (Cox & Singer, 1986): 1. Porphyry Cu–Au (Model 20 c): Central Cu, Au, Ag. Peripheral Mo. Peripheral Pb, Zn, Mn anomalies may be present if late sericite pyrite alteration is strong. Au (ppm): Mo (%)  30 in ore zone. System may have a magnetic high over intrusion, surrounded by magnetic low over pyrite halo (e.g. Copper Mountain, Canada). 2. Hot Springs Au–Ag (Model 25 a): Au  As  Sb  Hg  Tl higher in the system. Increasing Ag with depth. Locally NH4, W (e.g. McLaughlin, California, USA). 3. Creede epithermal vein (Model 25 b): Bleached country rock, goethite, jarosite, alunite; supergene processes often an important factor in increasing the grade of the deposit (e.g. Pachuca, Mexico). 4. Comstock epithermal vein (Model 25 C): Au  As  Sb  Hg higher in the system. Also Te & W (e.g. Comstock, Nevada, USA). 5. Epithermal quartz–alunite Au: Au  As  Cu higher in the system. Increasing base metals with depth. Also Te & W (e.g. Iwato, Japan). 6. Carbonate hosted Au (Model 26 a): Light brown to reddish brown iron oxide stained jasperoid. Au  As  Hg  W  Mo. NH3 important in some deposits (e.g. Carlin, Nevada, USA). 7. Quartz pebble conglomerate, Au–U (Model 29 a): Braided stream channels in broad unconformity surfaces in alluvial fans. Gold gets concentrated at the base of the mature conglomerate beds deposited on an erosion surface. Anomalous radioactivity (e.g. Witwatersrand, South Africa). 8. Low sulphide Au–Qz veins (Model 36 a): Arsenic best pathfinder. Association with Ag, Pb, Zn and Cu. Abundant quartz chips in the soil. Gold may be recovered from the soil by panning (e.g. Ballarat Goldfield, Australia). 9. Homestake Au (Model 36 b): Volcanogenic gold, iron formation – hosted gold. Archaean lode gold. Au  Fe  As  B  Sb (PGE in mafic volcanic terrains). Bi, Hg and minor Cu  Pb  Zn  Ag  Mo (e.g. Vubachikwe, Zimbabwe).

Process technologies and the environment 159

10. Placer Au–PGE (Model 39 a): Anomalously high amounts of Ag, As, Hg, Sb, Cu, Fe and S. Heavy minerals, magnetite, chromite, ilmenite, haematite, pyrite, zircon, garnet and rutile. Au nuggets have decreasing Ag content with distance from the source. 7.6.3

How to look for gold

Since pyrite is a precursor for mineralisation of metals, such as gold, it follows that the higher the content of pyrite in the host rock, the greater the possibility of gold mineralisation. A 1:1 correlation has been found between the pyrite content of the host rock and its Au content (Ferrow, 2001). Mössbauer spectroscopy (MES) and Raman spectroscopy have emerged as useful tools in looking for gold (Ferrow, 2001). MES is useful in determining the valence state, coordination number, spin state, magnetic properties and structure of the minerals. For instance, the MES spectra of Au-poor pyrite samples are characterized by low-spin doublet, while Au-rich samples contain an additional magnetic sextets (produced by the oxidation of pyrite substrate during the simultaneous reduction and sorption of Au.) (Fig. 7.4; source: Zhenru et al., 1989). The Raman spectrum of Au-rich quartz is markedly different from the spectrum for Au-poor quartz – the intensity of Raman emission for Si–O–Si and for crystal lattice vibrations is higher for Au-rich quartz than for Au-poor quartz (Fig. 7.5; source: Zhenru et al., 1989). The most serious problem that hindered the prospecting for gold has been the great difficulty and expense in determining the gold content in situ at ppm and subppm levels. The usual practice has been to pan for gold (which requires water) and look for grains of gold visually. Fire assay of gold is accurate, but it cannot easily be done in the field. Portable XRF devices are available for the geologist to check the ore grade in the drill core, or this could be done automatically. Niton’s new XL-500 Prospector can assay ore samples directly in situ (rock face or drill core). It is a single-piece, handheld analyzer weighing only one kg, including the battery. Typical in situ measurements range from 30–60 sec., and 500–1000 measurements can be made per

Figure 7.4

Mössbauer spectra of Au-poor and Au-rich pyrite (left) (source: Zhenru et al., (1989).

160 Mineral resources management and the environment

Figure 7.5

Raman spectra of Au-poor and Au-rich quartz (right) (source: Zhenru et al., 1989).

day. About 1000 measurements can be stored in the instrument internally, and can be downloaded as needed for mapping, grade control and other kinds of analyses. Niton also markets a special device for precious metals (called Precious Metals Analyser), for the analysis of Au, Ag. Pt, Rh, Ru, Ir, Pd, Cu, Zn, Ni, Co and Fe in ores, and fire assay can be avoided. Details about Niton instruments can be had from www.niton.com. 7.6.4

How to extract gold

McNulty (2001) gave an excellent update on cyanidation. The cyanidation process was patented in UK on October 19, 1887 by J.S. MacArthur and two brothers, W. and R.W. Forrest. Cyanidation changed for ever the economics of gold industry. For instance, the application of cyanidation process in the Rand goldfields of South Africa, led to a thousand-fold increase in gold production in a matter of just three years – from 300 oz (9.33 kg) in 1890 to 300,000 oz. (9331 kg) in 1893. During the past 20 years, cyanidation accounted for about 92% of the total world production of gold. Cyanidation has the following advantages: (1) it requires only dilute solutions containing typically 300–1000 ppm (0.3–1.0 g/l) of sodium cyanide, (2) the pH range used (9.5–11.5) is such that only gold and silver get mobilized, and (3) it is simple to operate and control. Figure 7.6 (source: UNEP Tech. Rept., no. 5, 1991, p. 20) shows the gold concentrator flowsheet (used by Hecla Mining Co.) which combines flotation with cyanidation. Heap cyanidation of low grade ores has proved to be efficient and inexpensive, and is extensively used all over the world. The great advantage of cyanide heap leaching is that there would be no discharging of process solutions, and minimum recycling of water. Treatment and discharge of process solutions would not be needed during the operation. In effect, there would be a single permanent large heap leach pad. Percolation of pregnant cyanide solutions downwards through hundreds of metres of leached ore can take place, without the solutions undergoing chemical

Process technologies and the environment 161

Figure 7.6 p. 20).

Gold concentrator flowsheet (Hecla Mining Co.) (source: UNEP Tech. Rept., no. 5, 1991,

change. On the other hand, other lixiviants (such as, sodium hypochlorite stabilized by sodium chloride, Bromine stabilized by sodium bromide, Ammonium thiosulphate stabilized by ammonia, and catalyzed by cupric ion, and Acidic thiourea) require rigorous control of pH and Eh, and there is always the possibility of side reactions and precipitation of gold.

162 Mineral resources management and the environment

Figure 7.7 Gold recovery flowsheet (Ortiz gold mine) (source: UNEP Tech. Rept., no. 5, 1991, p. 21).

Cyanidation may be used to extract gold from almost any kind of gold ore. It may be done in different ways: (1) leaching of the ROM or crushed ore, (2) vat leaching, and (3) leaching of ground ore, flotation concentrate, etc. in agitated tanks. Activated carbon is being increasingly used to recover gold dissolved by cyanide in ore pulps (carbon-in-pulp process) or in clear pregnant solutions (carbon-in-column process). Figure 7.7: (source: UNEP Tech. Rept., no. 5, 1991, p. 21) depicts the flowsheet used by the Ortiz gold mine to recover gold from heap leaching solutions using Carbon-in-pulp process. The methods of treatment applicable for different kinds of gold associations are summarized as follows (Weiss, 1985): Alluvial gold: (1) Gravity concentration, (2) Amalgamation. Free milling lode ores: (1) Gravity concentration, (2) Amalgamation, (3) Direct cyanidation, activated carbon in pulp.

Process technologies and the environment 163

Free milling sedimentary ores: (1) Direct cyanidation, (2) Treatment of refractory carbon, direct cyanidation. Gold tellurides: (1) Bulk flotation-roasting cyanidation, (2) Direct cyanidation – SO2 roasting of concentrate cyanidation, (3) Flotation – cyanidation of concentrateroasting of residue – recyaniding, (4) Direct cyanidation, with added bromocyanide. Gold with pyrite and marcasite: (1) Flotation – smelting of concentrates, (2) Flotation – cyanidation of concentrates. Gold with pyrrhotite: (1) Direct cyanidation with pre-aeration at low lime alkalinity, (2) Direct cyanidation – flotation of cyanide tailings – regrind and recyanide flotation concentrate or roast and recyanide. Gold with arsenopyrite: (1) Direct cyanidation, (2) Flotation – roasting of concentrates, (3) Roasting ore – washing – cyanidation, (4) Autoclaving, (5) Nitric acid oxidation. Gold with copper ores: (1) Flotation – smelting of concentrates – recovery during electrolytic refining, (2) Flotation – cyanidation of molybdenum. Gold in refractory: (1) Roasting – cyanidation carbonaceous ores, (2) Chlorination of ore – cyanidation, (3) Flotation of graphitic material – cyanidation of tailings. Gold with lead-zinc ores: (1) Flotation – smelting of concentrates, (2) Jigging – amalgamation – retorting. Butyl diglyme extraction (developed by Ferro Corp., Louisiana, USA) is an environment-friendly process to extract gold (III) from ores, concentrates, anode slimes, cathode sludges, electrolytic plating operations, etc. Four steps are involved: (1) oxidative leaching crude metallic gold or gold (I) to an aqueous solution of gold (III) chloride, (2) solvent extraction of gold (III) chloride into the butyl diglyme phase, (3) Reduction of gold (III) into metallic gold, which is collected and cast into ingots, and (4) recycling butyl diglyme. Degussa-Hüls of Germany has developed proprietary technologies which has the effect of making the gold recovery more efficient, while at the same time ensuring minimum or nil adverse impact on the environment: PAL – Peroxide-assisted leach to increase gold recovery, CCS – Cyanide control system to optimize cyanide consumption, DETOX – Cyanide detoxification technology to meet the environmental standards. From the environmental point of view, the peroxide-based detoxification technology is most relevant. The detoxification technology can be custom-made for any kind of mining effluent. The chemistry of the detoxification process and the benefits arising therefore are summarized in Table 7.3 (source: Degussa-Hüls brochure). A Nobel Prize winning concept has led to the development of a revolutionary technology, called Molecular Recognition Technology (MRT), for the rapid, selective extraction and recovery of cations and anions from process and waste streams. In specific cases, complete recovery of high purity (99.95–99.99%) marketable metals is possible after a single-pass process. MRT involves the use of custom-designed organic crown molecules or other chemical ligands, which

164 Mineral resources management and the environment Table 7.3

Chemistry of detoxification technologies.

Application

Process

Chemistry

Benefits

In-situ pond Conventional CN  H2O2 → OC N  H2O detoxification H2O2

Ease of use, Environmentally safe, Economic reagent costs with low capital costs

Heap rinse solutions

SILOX TM process

| | H2O2  SiOH → SiOOH  H2O | | CN  SiOOH → OCNSiOH CN  H2O2 → OCN  H2O

Reduces H2O2 usage, Enhances reaction kinetics, In-situ formation of peroxy silicate resulting in increased cyanide destruction efficiency

Barren Bleed Solutions

Activated H2O2

Activator CN  H2O2 → OCN  H2O

Peroxygen-based activator reduces treatment costs, Can be used for pulps

High metal cyanide solutions

HOSO

2H2O2 → O2  H2O CN  O2  H2 SO4 → OCN  HSO4

Excellent for pulps, Superior reaction kinetics over SO2/Air, Low operating costs with no royalty fee

C.I.P. & C.I.L. slurries

Caro’s acid with Degox equipment

H2O2  H2SO4 → H2SO5  H2O CN  H2SO5 → OCN  H2O

Excellent for pulps, min. retention time required, Extremely fast kinetics, often 30 sec, Normally no additional catalyst is required

selectively target specific metals. When such molecules are bonded to solid hydrophilic supports (such as, silica or polyacrylate) and incorporated into resin beads, porous membranes and gels, they are capable of extracting various metals (such as, copper, gold, zinc, nickel, etc.) from bleed streams, acid mine streams, etc. MRT has been used for the efficient treatment of copper-gold ores (source: BATEMAN brochure). 7.6.5

Cyanidation without tears – case study of Boliden, Sweden

Gold was discovered in Boliden, Sweden, in 1924. Boliden is currently using the most advanced cyanidation process under the extremely stringent environmental constraints of discharge of cyanide prescribed by the Environmental Court: (1) The content of cyanide and hydrogen cyanide (as CN) should not exceed 5 mg/m3, (2) the content of total cyanide (as CN) in the processed slurry from the cyanide destruction process may not exceed 2 mg/l over 14 days, and (3) the content of cyanide in the discharge from the clarification pond may as a guiding value for free cyanide not to exceed 0.5 mg/l at each sampling occasion and not to exceed 0.2 mg/l as a monthly mean. The gold process flowsheet used by Boliden is shown in Figure 7.8 (source: Lindstrom et al., 2001, p. 442). Boliden uses the INCO SO2/Air technology (Robbins et al., 2001) to achieve the destruction of cyanide from waste streams (Fig. 7.9; source: Robbins et al.,

Process technologies and the environment 165

Figure 7.8

Gold process flowsheet of Boliden, Sweden (source: Lindstrom et al., 2001, p. 442).

Figure 7.9 INCO SO2/Air technology for the destruction of cyanide in waste streams (source: Robbins et al., 2001, p. 726).

166 Mineral resources management and the environment

2001, p. 726). The chemistry involved in the technology may be briefly described as follows: 1. Oxidation: Weak Acid Dissociable cyanide (CNwad), which includes free cyanide and weakly complexed metal cyanides, is oxidized to produce cyanate (OCN) and sulphuric acid, 2. Neutralisation: Acid produced during oxidation is neutralized with lime in the pH range of 7–10, 3. Precipitation: Iron cyanide is precipitated as insoluble salt, along with metals which were dissociated during the oxidation reactions. Stoichometrically, the reactions require approximately 2.5 g of SO2 per gm. of CNwad to be oxidized.

CHAPTER 8

Control technologies for minimizing the mining environmental impact

8.1

ACID MINE DRAINAGE (AMD)

Acid Mine Drainage (AMD) is also called Acid Rock Drainage (ARD). All aspects of the mitigation of the environmental impact from mining waste, have been comprehensively dealt with in a state-of-the-art report by MiMi (1998), a Swedish organization devoted to the study. MiMi stands for the Mitigation of the environmental impact from Mining Waste. 8.1.1

What is acid mine drainage?

Acid Mine Drainage (AMD) gets generated due to the oxidative dissolution of the iron-containing sulphide minerals, such as pyrite. Both purely chemical reactions as well as microbially catalyzed reactions are involved. AMD may arise from the mining of coal, lignite, metallic sulphides, uranium, etc. Under oxidizing conditions, and in the presence of catalytic bacteria, such as Thiobacillus ferrooxidans, sulphides are oxidized into sulphuric acid, as per the following equation: 4 Fe S2  15 O2  2 H2O  2 Fe2 (SO4)3  2 H2SO4 Pyrite  Oxygen  Water  Iron sulphate  Sulphuric acid

(8.1)

Surface runoff and groundwater seepages associated with waste piles tend to be highly acidic, and corrosive, and contain high concentrations of iron, aluminum, manganese, copper, lead, nickel and zinc. etc. in solution. The discharge of such waters into streams destroys the aquatic life, and the stream water is rendered non-potable. An understanding of the physical, chemical and biological processes that lead to the production of AMD is necessary for the following purposes: (1) to minimize the production of AMD, (2) to dispose of AMD from the operating mines or for the decommissioning of waste piles, as required by law, and (3) to ameliorate AMD to allow it to be used for beneficial purposes, such as irrigation, industrial and domestic purposes.

168 Mineral resources management and the environment

8.1.2

Element recycling in the sulphidic mine tailings

Apart from the primary mineralogy (e.g. sulphide/carbonate contents, alterations), climate has a direct influence on the composition of the secondary minerals and hence on the availability of certain metals for remobilization. Dold and Fontbote (2001) gave schematic models for element recycling in porphyry copper mine tailings for precipitation-dominated and evaporation-dominated climates (Figure 8.1; source: Dold & Fontbote, 2001, p. 150). Model A represents the precipitation-dominated climate such as that La Andina (alpine climate, 700 mm/y of rainfall). Under these conditions, sulphide oxidation leads to the liberation of bivalent cations (e.g. Fe2, Cu2, Zn2), oxyanions (e.g.  2  HMoO 4 , H2AsO4 and SO4 ), as well as protons (H ). with downwards mobilization of the liberated elements to more reducing conditions.  FeS2  7/2 O2  H2O → Fe2  2SO2 4  2H

(8.2)

Fe 2  1/4 O2 H ↔ Fe3  1/2 H2O

(8.3)

(this process goes on much faster, in the presence of bacteria, e.g. Thiobacillus ferrooxidans) FeS2 14 Fe3  8 H2O → 15 Fe2  2 SO42  16 H

(8. 4)

Model B represents Evaporation-dominated climates (such as those of El Salvador, with precipitation of 20 mm/y) with upward mobilization to oxidizing conditions.

Figure 8.1 p. 150).

Element recycling in mine tailings in different climates (source: Dold & Fontbote, 2001,

Control technologies for minimizing the mining environmental impact 169

8.1.3

Leaching tests

Irrespective of whatever technology is used to mitigate the problem of acid mine drainage, it is necessary to study the focuses of oxidation and flow-pattern of waters in the mine, identification of sources of acid mine water, and the pattern of spreading of mine water. Whole-rock analyses and leaching tests can be used to predict the nature and extent of AMD that could develop in a given mine or from a waste pile. Rock samples are leached with water, and the leachate is analyzed for parameters, which indicate the pathways of weathering, namely, pH, specific conductance and sulphate. The mineralogical and chemical composition of the rock, the pyrite content and the presence or absence of calcareous material are the determining factors (Table 8. 1). Several countries have prescribed the allowable concentrations in mine effluents: pH: 7, SS (Suspended Solids): 30 mg/l; BOD (Biochemical Oxygen Demand): 30 mg/l; Pb: 0.2 mg/l; Fe: 0.1 mg/l; Cu: 0.1 mg/l. In other words, the mining companies are expected to treat the mine water in such a manner that the discharge stays within the prescribed limits. In many countries, a company responsible for noncomplying discharges is issued a Notice of Violation by the Environmental Agency of the government concerned. If the company does not take prompt remedial action, it is penalized. The US Bureau of Mines has developed a simple, low-cost, portable and highly efficient system to neutralize the acid mine drainage on site. The only drawback of the system is that it requires at least 130-kPa water pressure, and may not be able to remove manganese if the iron content is low. Apatite can be used to ameliorate AMD. Apatite is soluble only in acid conditions. So it will act only when the AMD becomes sufficiently acid. The phosphate ion can sequester and precipitate Fe3, Al3, Mn2, etc. 8.1.4

Decision making about AMD amelioration

The Pennsylvania Department of Environmental Protection divided mine drainage into five sub-categories based on the net acidity (acidity minus alkalinity) or alkalinity (alkalinity minus acidity) of the untreated mine drainage: 1. Very acid: net acidity
300 mg/l as CaCO3 2. Moderately acid: net acidity ⬃300 mg/l as CaCO3 Table 8.1

Guidelines for the choice of tests for acid mine drainage.

Pyrite content

Leachate characteristic

Method recommended

1% (C. M. absent) 1–1.5% (C. M. absent)
1.5% (C. M absent) 1% (C. M. present) 1–1.5% (C. M. present)
1.5% (C. M. present)

Slightly acidic, low SC Acidic Acidic Alkaline, low SC Alkaline, high SC Slightly acidic

WR or LT WR or LT WR or LT WR or LT LT LT

C.M.  Calcareous Material; SC  Specific conductance. WR  Whole rock; LT  Leaching tests.

170 Mineral resources management and the environment

3. Weakly acid: net acidity100 mg/l as CaCO3 4. Weakly alkaline: net alkalinity80 mg/l as CaCO3 5. Strongly alkaline: net alkalinity ⬃80 mg/l as CaCO3 Conventional treatment is the best available treatment for discharges of subcategory 1. For the rest, the best available technology is wetlands treatment, which is to be custom designed on the basis of chemistry and loading. Figure 8.2 (source: Hedin et al., 1994, quoted by Hellier, 1999, p. 109) gives the decisionmaking chart about the design of mitigation measures for AMD.

Figure 8.2 Decision-making about AMD amelioration (source: Hedin et al., 1994, quoted by Hellier, 1999, p. 109).

Control technologies for minimizing the mining environmental impact 171

Alkalinity is imparted to acid discharge by passing it over and through limestone channel under aerated conditions. Anoxic limestone drains (ALD) are most effective when there is no dissolved [O2], [Fe3], and [Al3] in the influent. Figure 8.3 (source: Hellier, 1999, p. 113) gives the design of the anoxic limestone drain,

Figure 8.3

Design of anoxic limestone drain and other structures (source: Hellier, 1993, p. 113).

172 Mineral resources management and the environment

aerobic wetland, horizontal flow anaerobic wetland, and vertical flow anaerobic wetland. 8.1.5

Principles of mitigation of acid mine drainage (AMD)

Since the supply of both oxygen and water is necessary for the generation of AMD, an obvious way to prevent the formation of AMD is to block the entry of oxygen and water to the mine or waste pile. This is easier said than done, for the simple reason that Fe (III) that may be present in the partly oxidized waste, could serve as an oxidant and still generate AMD. Also, if the pore water in the mine waste is acidic, the mobility of heavy metals gets strongly increased due to their higher solubility and lower tendency for sorption. Thus, if the waste dump contains buffering substances such as calcite, or if lime is added, the development of acid drainage, and the release of heavy metals could be substantially mitigated. Figure 8.4 (source: Höglund, 2001, p. 283) is a schematic illustration of the causes of, and remedies for, acid mine drainage from sulphidic mine wastes. MiMi (1998) and Angelos and Niskanen (2001) described several rehabilitation options for the waste dumps. The common purpose of all of them is to limit the transport of oxygen and air into the waste: 1. Changing the chemical properties of the waste (such as, separation of pyrite or addition of a buffering substance, such as lime) or physical properties of the waste (such as, compaction to reduce porosity and permeability). This is expensive. 2. Flooding of the waste, such that the water table is established above the disposed waste, thereby limiting the transport of oxygen or air into the waste – this is by far the most cost-effective and efficient option, where it possible to implement. 3. Dry covering of the waste. 4. Treatment of the leachate with the objective of reducing the metal concentrations in the water that is discharged from the waste pile. 8.1.6

Biologically supported water cover (BSWC)

The water cover has been found to be the most effective in preventing and controlling AMD. This is so because he solubility of oxygen in water is quite low (11 mg/ l),

Figure 8.4 Schematic outline of the causes of, and remediation for, acid mine drainage(source: Höglund, 2001, p. 283).

Control technologies for minimizing the mining environmental impact 173

and the diffusion rate of oxygen through water is 10,000 times less than through air. The placement of an organic/soil cover between the waste rock and the water cover will not only reduce the oxygen infiltration into the waste rock, but also reduce the metal flux from the waste rock into the water column. Figure 8.5 (source: MEND, 1997) shows the processes affecting the sulphide oxidation. Eriksson et al. (2001, p. 220) evaluated the effectiveness of the water cover at the Stekenjokk tailings pond in northern Sweden using sulphate as conservative tracer for sulphide oxidation mass balance. The water balance for a pond is governed by the equation P  R  O  L  E  S

(8.5)

Where P is the precipitation on the pond surface (1187 mm), R is the recharge through surface and subsurface flow (0.9 M m3), O is the outlet discharge (1.5 M m3), L is the dam leakage (⬃0.35 M m3 /y), E is the potential evaporation from the pond surface (321 mm/y), and S is the net change in the stored volume (which is essentially zero on an annual basis). After the project was decommissioned, the sulphate concentration in the pond effluent decreased steadily during 1992 to 2000 (Figure 8.6; source: Eriksson et al., 2001, p. 220). The pronounced seasonal variations in the sulphate concentrations have been attributed to freezing effect. Based on the mass balance calculations, it has been found that the resulting oxygen flux through the water cover to the sulphur-rich tailings is less than 1  1010 kg O2/m2/s. This is an order of magnitude less than the oxygen flux of dry cover which is about 109 kg O2/m2/s. The study confirms the effectiveness of the water cover in impeding the formation of ARD. Besides, the water cover cost of USD 2/m2 is much cheaper than dry covers which cost USD 12/m2.

Figure 8.5

Processes affecting the sulphide oxidation (source: MEND, 1997).

174 Mineral resources management and the environment

Figure 8.6 Seasonal variation in the sulphate concentrations in the pond effluent (source: Eriksson et al., 2001, p. 220).

Table 8.2

Types of soil covers and their functions (source: MiMi, 1998).

Cover type

Primary function

1. Oxygen diffusion barriers

To limit the transport of oxygen by acting as a barrier against the diffusion of oxygen to the waste To limit the transport of oxygen by consuming it before it could reach the waste To limit the transport of oxygen and the formation of leachate by acting as a barrier against the diffusion of oxygen, as well as the infiltration of precipitation To provide a favourable environment to limit reaction rates and metal release

2. Oxygen consuming barriers 3. Low permeability barriers

4. Reaction inhibiting barriers

8.1.7

Soil or dry covers

There are four types of soil cover depending upon the function (Table 8.2; source: MiMi, 1998). Experience in Sweden shows that a single layer cover of thickness of 1.0 m results in the reduction of pyrite weathering rate and metal release, in the region of 80–90%. A cover of 2 m of organic waste or lime stabilized sewage sludge can be used as an oxygen-consuming barrier. Clean (i.e. non-acid generating) wastes from other industries, which are moisture-retaining and oxygen-consuming, can be used as barriers. For instance, in the case of the Luikonlahti mine, magnesite tailings from talc industry, were proposed as soil/dry cover. Figure 8.7 (source: Angelos & Niskanen, 2001, p. 27) illustrates the principles of the soil cover types. Ayres et al. (2002) sought to evaluate three types of dry cover systems, namely, geosynthetic clay liner (GCL), a 0.45 m thick compacted sand-bentonite mixture,

Control technologies for minimizing the mining environmental impact 175

Figure 8.7

Types of soil covers (source: Angelos & Niskanen, 2001, p. 27).

Precipitation (PPT) Atmosphere Run

off (

Cover Material

Waste Material

RO)

Net Surface Infiltration (NSI)

(⌬S) Change in Moisture Storage

Actual Evapotranspiration (AET) Oxygen Ingress

La Perc teral olat ion

Net Percolation to Waste Material (PERC)

Figure 8.8

Parameters affecting the performance of sloped cover system (source: MEND, 2001).

and 0.6 m compacted silt/trace clay material, for acid-generating waste rock at Whistle Mine, Ontario, Canada. The waste rock (about 6.4 Mt) is essentially a mafic norite, with an average sulphide content of 3%, and the final contoured surface of the backfilled pit will have a slope of 20%. The parameters affecting the field performance of a sloped cover system are schematically shown in Figure 8.8 (source: MEND, 2001). A state-of-art monitoring system has been installed to monitor continuously various climatic parameters, gaseous oxygen/carbon dioxide concentrations, moisture/temperature conditions within the cover and the waste materials, and the quantity of net percolation through each test cover. The observational data obtained from the test plots will be made use of to determine the optimum design cover for the waste rock deposit.

176 Mineral resources management and the environment

8.1.8

Passive treatment of acid mine drainage

Passive treatment of AMD makes use of the naturally occurring chemical and biological processes to cleanse the contaminated mine waters, without requiring continuous chemical inputs. The principal passive treatment technologies include constructed wetlands, anoxic limestone drains (ALD), successive alkalinity producing systems (SAPS), limestone ponds, open limestone channels (OLC), etc. (Angelos & Niskanen, 2001, p. 27). There are numerous permutations and combinations of these techniques. An open limestone channel followed by a settling pond and filter system has been chosen for the Luikonlahti mine waters. AMD gets ameliorated when acid waters flow through limestone channels, or ditches lined with limestone. The design factors to be taken into consideration are the length of the channel, and the gradient of the channel, which affects the turbulence, and the buildup of coatings. Experience has shown that for channels with slopes of more than 20%, the flow velocities will be sufficient to keep the precipitates in suspension and allow aeration of water. Filter dams are built with materials with large capacities for the adsorption of heavy metals, such as Zn, Ni and Cu. The optimal absorption takes place at pH levels higher than 6. The purpose of open limestone channels and the settling pond is to remove as much iron as possible, so that the filter dam can take care of heavy metals other than iron. Gusek (1995) gave a lucid review of the techno-economic aspects of passive treatment of acid rock drainage. The conventional method of amelioration of acid rock drainage is the liming of the runoff. Liming neutralizes the water and chemically precipitates the metals. However, liming is expensive, leaves behind large quantities of sludge, and has to be continued long after the mine ceased operating. For this reason, much R. & D. effort has been concentrated in developing low-cost, low-maintenance, passive treatments of AMD. These involve the utilization of vegetation and sediment microbial communities found in wetlands to reduce the acidity and precipitate the metals. The techno-economic viability of the passive treatment is now well established. For instance, the Tennessee Valley Authority (TVA)’s Fabius Mine in Alabama, USA, replaced an earlier lime-treatment plant by a large, passive treatment system. The latter treats 126 l/s (about 2000 gpm) of coal mine drainage. It has been operating for several years and discharging compliant effluent. Interestingly, wetlands established for water quality improvement have been found to provide habitat for abundant development of herptofaunal wildlife (Lacki et al., 1992). It has been known that wetlands are capable of improving the water quality by reducing the contaminants through the precipitation of metal hydroxides, sulphides and carbonates and pH adjustments. Whether these reactions would occur under oxidizing (aerobic) conditions or reducing (anaerobic) conditions would depend on

Control technologies for minimizing the mining environmental impact 177

Figure 8.9

Design of constructed wetland (source: Kolbash & Romanovski, 1989).

the Eh of the environment, and the chemistries of soil and water. Where natural wetlands are not available, wetlands are constructed. The latter are engineered so as to optimize the biogeochemical processes that take place in the natural wetlands. Figure 8.9 (source: Kolbash & Romanovski, 1989) shows the design of a constructed wetland. The wetland plants that are most commonly used are Typha, Schoenoplectus, Phragmites or Cyperus. The important physical, chemical and biological mechanisms that operate in the passive wetland treatment are as follows: (1) hydroxide precipitation catalyzed by bacteria in the aerobic zones, (2) sulphide and carbonate precipitation catalyzed by bacteria in anaerobic zones, (3) filtering of suspended material, (4) metal uptake into live roots and leaves, (5) ammonia-generated neutralization and precipitation, and (6) adsorption and exchange with plant, soil and other biological material. The predominant mechanisms by which microorganisms remove soluble metals from solution are as follows: (1) volatilization – whereby microorganisms methylate metals, (2) extracellular precipitation – whereby metals are immobilized by the metabolic products produced by microorganisms. Sulphate-reducing bacteria reduce H2SO4 to H2S, which would readily react with soluble metals to form insoluble metal sulphide minerals, (3) extracellular complexing and subsequent application – whereby chelating agents (known as siderophores) synthesized by microorganisms have a high binding efficiency for some metals, resulting in the generation of metal-binding polymers, (4) binding to bacterial, fungal and algal cell walls, and (5) intra-cellular accumulation (Brierley et al., 1989). Studies made by White and Gadd (1996) showed that the most efficient nutrient regime for

178 Mineral resources management and the environment

bioremediation using sulphate-reducing bacteria required both ethanol as a carbon source and cornsteep as a complex nitrogen source. Brierley (1990) gave a detailed review of the techniques of bioremediation of metal-contaminated surface and groundwaters. Advances in biotechnology have made it possible to make use of nonliving microorganisms immobilized in polymer matrices to remove low concentrations (1 to about 20 mg/l) of heavy metal cations in the presence of high concentrations of alkaline earth metals (Ca2 and Mg2) and organic contaminants. The removal process is so effective that the effluent more than satisfies the requirements of U.S. National Drinking Water Standards. Davison (1993) describes a proprietary Lambda Bio-Carb Process which is an in situ bioremediation system utilizing site-indigenous, mixatrophic cultures hybridized for maximum effectiveness. Lambda has catalogued about 6000 microorganisms suitable for the purpose. The system is utilizable in conjunction with wetlands, and is capable of self-adjustment in response to influent changes. It has been successfully used to treat sites contaminated by heavy metals, hydrocarbons, organics, agricultural wastes and other hazardous compounds. The economics of the passive treatment can be illustrated with a case (Eger & Lapakko, 1989). Drainage from the Dunka mine in the mineralized Duluth complex in northern Minnesota, USA, has increased upto 400 times, the concentration of metals (Ni, Cu, Co and Zn) in the creeks in the proximity. This was naturally unacceptable to Minnesota Pollution Control Agency, and the company concerned had to give an undertaking to achieve the water quality goals. A feasibility study was made of the options for treating 6  108 l/y of mine water: 1. A full-scale treatment plant (lime precipitation with reverse osmosis): capital cost: $ 8.5 million, and annual operating cost: $ 1.2 million. 2. Passive treatment (combining infiltration reduction, alkaline treatment and wetland treatment): capital cost: $ 4 million; annual operating cost: $ 40,000. 8.1.9

In-pit disposal using sulphate reducing bacteria (SRB)

Sulphate Reducing Bacteria (SRB) has been found to be effective in reducing the metal and sulphate concentrations in the mine water. Liquid manure and press-juice from silage were used as nutrients. SRB was obtained from local lake sediments and was enhanced before application. The costs are very low, but the catch in the technology is that would take some years before the treated water is of quality that would permit discharge into local water ways. If a site is an abandoned one, in a remote area, and the costs have to be kept minimal, this technology may turn out to be appropriate (Angelos & Niskanen, 2001, p. 27). 8.1.10

Case history of pyritic uranium tailings sites of Elliot Lake, Canada

As a part of the mine waste management and decommissioning studies, Davé and Paktunc (2001) studied the hydrogeochemistry and mineralogy of the inactive and rehabilitated pyritic uranium tailings at Stanrock and Lower Williams Lake sites

Control technologies for minimizing the mining environmental impact 179

related to the Elliott Lake uranium mine, Ontario, Canada. The Stanrock sites holds about 8 Mt of pyritic uranium tailings spread over an area of 71 ha. The water table in the area fluctuated between 0.5 to 2 m., rising nearer to the surface in the central section. The water table goes down by about 2 m during the dry summer and winter months. The Lake Williams site is much smaller (⬃2 ha) and contains about 20,000 t of tailings (Figure 8.10, source: Davé & Paktunc, 2001, p. 129, gives a general view of the tailings site). The tailings contained 0.9 to 6.3% pyrite and 0.07 to 5.3% calcite. The pyrite content generally increased with depth. During 1976–77, limestone amendment was applied to the exposed tailings at the surface. The dry tailings were covered with ⬃1 m. thick layer of glacial sand/gravel and till, which was then vegetated with agronomic species of gases and legumes. The incoming treated water was discharged into the downstream water pond which also serves as a sludge-settling pond. The site was maintained till 1980, but was left on its own since then. Davé and Paktunc (2001) report that the site supports dense, lush vegetation. The Stanrock tailings essentially consist of quartz, K-feldspar, muscovite, and pyrite, with small quantities of rutile, La-Ce monazite, chalcopyrite, pyrrhotite and galena. The pyrite content of the tailings varied from 0.1 to 12.4%, depending upon the depth (Davé & Paktunc, 2001, p. 133). As the bulk of the unoxidised material which has high acid generation potential is below the water table, its ability to produce AMD is negligible. An examination of the geochemical characteristics of shallow groundwater along the central longitudinal direction, of the Stanrock tailings (vide Figure 8.11; source: Davé & Paktunc, 2001, p. 132) show that, except for one central site, the groundwater is characterized by low pH (between 1.8 and 4), high total acidity

Figure 8.10

Elliott Lake uranium mine tailings site, Canada (source: Davé & Paktunc, 2001, p. 129).

180 Mineral resources management and the environment

Figure 8.11 Shallow zone groundwater quality profiles at Stanrock tailings site (source: Davé & Paktunc, 2001, p. 132).

(1000–12,000 mg CaCO3/l), and high concentration of dissolved SO4 (2000– 14,000 mg/l) and Fe (500–6000 mg CaCO3/l). At the central site, near the surface water streams (between 381400 and 381600), the pH of the groundwater is high (6), and the concentrations of total acidity (⬃50 mg CaCO3/l), SO4 (⬃2200 mg /l), and Fe (⬃100 mg /l) are low. The pH, total acidity, Fe and SO4 contents of the groundwater in the longitudinal direction of the Lower Williams Lake site are shown in Figure 8.12 (source: Davé & Paktunc, 2001, p. 134). Compared to the Stanrock site, the pH of the Williams Lake site is much higher (⬃6.0–⬃8.0), and concentrations of total acidity, SO4, and Fe much lower. The saturated conditions that developed within the tailings substrate increased the pH, and the microbial degradation of the organic matter (caused by vegetative cover in the soil layer), besides increasing the total available groundwater alkalinity. Thus, the overall water quality has improved with time. Davé & Paktunc (2001) conclude that covering the tailings with a vegetated cover layer, and raising the water table can effectively suppress acid generation. 8.1.11

Remediation of acid lakes – case history from former East Germany

The extensive opencast mining of lignite in the former East Germany, has created a large number of acid lakes in the Lusatian mining district, after the mining was

Control technologies for minimizing the mining environmental impact 181

Figure 8.12 Surface water quality profiles at Lower Williams lake site (source: Davé & Paktunc, 2001, p. 134).

abandoned. The pH range in the mining lakes ranged from 2.6 to 3.8. These acidic water bodies were often toxic because of high metal concentrations. It was concluded that increasing the pH by neutralization measures was the most promising way to reduce the metal concentrations. Figure 8.13 (source: Klapper & Schultze, 1997, quoted by Stottmeister et al., 1999) illustrates the techniques for the abatement of acidification through in-situ technologies.

8.2

TAILINGS DISPOSAL

The most serious problem facing the mining industry presently is the enormous mass of the mine tailings (about 18 billion m3/y), which incidentally is the same order as the quantity of sediment discharge into the oceans. As progressively lower grades are worked, the mass of the mine tailings is expected to double in the next 20–30 years. It is not without significance that the failure of the tailings dams figures prominently in the list of major accidents related to mining (vide Appendix D). 8.2.1

Environmental risks from mine tailings

Ellis and Robertson (1999) gave a concise account of the environmental risks from mine tailings: 1. Chemical contamination: Tailings may cause acid rock drainage and other undesirable geochemical processes. They may damage the ecosystem and resource

182 Mineral resources management and the environment

Figure 8.13 Abatement of acidification of mining lakes (source: Klapper & Schultze, 1997, quoted by Stottmeister et al., 1999).

Control technologies for minimizing the mining environmental impact 183

2.

3.

4. 5.

6.

use downstream from site. Recovery from a degraded ecosystem is likely to be very slow (of the order of decades or more). Habitat smothering: The tailings may smother the living organisms and their habitats. This occurs when the deposition is made at a rate greater than the organisms could cope or grow through the deposits. Recovery of tree growth on land is measured in decades, whereas the recovery underwater may be quicker, i.e. 1–5 years. Catastrophic system collapse: Earthquakes or torrential rains may undermine the structural stability of the tailings deposit, and may cause sudden and extensive loss of life and property. Landform changes: Tailings may change the landforms and habitats. Water turbidity and siltation: The tailings adversely affect the use of rivers and lakes by changing the river channels and flood plains, biological productivity and fisheries resources. Water quality may recover in a matter of days, but the ecosystem consequences may last for years. Socio-economic changes: Tailings may cause changes in resource use, and thereby affect the quality of life of the people. The recovery may be complex.

8.2.2

Characteristics of tailings

Tailings can be considered as “man-made” soil with properties between those of sand and clay. The grainsize distribution of the coal colliery spoils determine their geotechnical properties, which in there turn influence the design of the tailings deposit. The particle size distribution of colliery spoils from different countries is given in Figure 8.14 (source: Skarzynska & Michalski, 1999, p. 185).

Figure 8.14 p. 185).

Grainsize distribution of colliery spoils (source: Skarzynska & Machalski, 1999,

184 Mineral resources management and the environment

Vermuelen, Rust and Clayton (2002) summarized the properties of the gold tailings from the literature: Slurry: “low plasticity, fine, hard and angular rock flour, slurried with process water in a flocculated, slightly alkaline state with soluble salts”. Rheology: (study of deformation and flow of matter): The rheological characteristics of the mine tailings are intermediate between a Bingham plastic and a Newtonian fluid. Mineralogy: Quartz is by far the most abundant mineral, with small quantities of phyllosilicates, pyrites and other sulphides. Specific gravity ranges between 2.5 and 3.0. Oxidation of pyrites (FeS2) leads to the production of sulphuric acid, and the acidification of the tailings water. The low pH water is capable of leaching toxic heavy elements from the tailings. Grading: Generally of silt size range, with small percentages of fine sand and clay-sized particles. Particle shape and texture: The coarser or sand fraction of the tailings range in shape from very angular to sub-rounded, whereas the fines are invariably angular, with very sharp edges. The surface textures are described as “ harsh”. 8.2.3

Methods of tailings disposal

Tailings from the beneficiation plants in the case of non-ferrous metals are generally in the form of slurry, which is discharged into specially constructed containment structures. The various tailing disposal methods are summarized as follows (source: UNEP Tech. Report no. 5, 1991): 1. Subaqueous discharge into the tailings ponds: The great advantage of the method is that transfer of oxygen to the tailings is impeded, thereby inhibiting acid production from the tailings. The disadvantage is that sub-aerial discharge involves lower in-situ densities, 2. Layered methods of tailings disposal: The tailings slurry is deposited in thin layers of uniform thickness (10–150 mm). The slope of the deposited slurry layers may vary from 0.5 to 1.0%, depending upon the characteristics of the slurry. The fresh tailings are allowed to settle down, and dry – this may take several hours or a few days. The consolidated, gently sloping mass of tailings composed of uniform layers, formed in this manner, will greatly facilitate the de-commissioning of the waste disposal site. Site preparation for this method involves high capital costs. 3. Thickened tailings disposal: Tailings may be deposited in the form of cones, with slopes ranging from 2 to 8%, if the tailings slurry is thickened and discharged from spigotting points within the tailings disposal area. For a slope of 6%, the solids content has to be in the range of 55 to 75%. This method allows larger volumes of tailings to be disposed in a small area, but the thickening process involves high operational costs. 4. Tailings disposal behind a dam: The dam is usually constructed from the coarse fraction of the tailings. The tailings slurry can be discharged from a single point

Control technologies for minimizing the mining environmental impact 185

through a series of spigots. Discharge of tailings through cyclones allows the sands from the tailings to be mechanically separated and used for dam construction. If the beneficiation process involved fine grinding of the ore, the tailings would not contain any coarse materials suitable for dam construction. In such a situation, the dam has to be built with borrowed material. In one sense, this is advantageous in that the quality of the materials and their properties can be controlled, but it carries with it extra operational costs for the excavation and placement of dam material. 8.2.4

Methods of construction of tailings dams

Figure 8.15 (source: UNEP Tech. Report no. 5, 1991, p. 37) shows different methods of constructing the tailing dams. 1. Upstream methods: Though this method was used extensively in the past, it is not much in vogue now. A typical upstream section incorporates slimes fraction

Figure 8.15 Different methods of construction of tailings dam (source: UNEP Tech. Rept. 5, 1991, p. 37).

186 Mineral resources management and the environment

in the dam structure, and the resulting heterogeneous dam is susceptible to failure, particularly under seismic conditions. 2. Downstream methods: Under this method, the dam is built of coarse tailings. When cycloned sand is used, the slope will be adequate, the sand will be properly drained, and the dam will retain its stability even under seismic conditions. The drawback of this method is that a large quantity of sand is required. 3. Centreline method: As in the case of the downstream method, the centerline is built with coarse fraction of tailings, but with the dam centre line being maintained in the same vertical plane as the dam height is increased. Downstream of the centre line, the dam will have the same characteristics as the downstream method, and therefore tends to be stable. Decant towers, siphon systems and barge-mounted pumps are used to release the supernatant water in the tailings disposal facilities. A tailings dam fails when the peak flow exceeds the hydraulic capacity of the spillways, decants and diversions. The resulting liquefaction and the release of the stored tailings can cause great damage to life, property and the environment. It is therefore essential that the design of the impoundment provides for the spillway and decant structures to take care of the statistical probability of the rainfall/runoff event occurring once in thousand years. If the risks are very high, it is better not to install the tailings disposal facilities where such risks could occur. 8.2.5

Disposal of coal mine tailings

Coal mining industry produces enormous quantities of wastes, considering that the world production of coal is ⬃4600 Mt/y. Apart from the solid wastes (shale rock, dolerite, burnt coal, etc.) produced in the course of coal mining, coal preparation plants produce large quantities of coarse and fine particles, and contaminated water. The usual practice is to impound the tailings and slurry in the lagoons. As breaching of the lagoons constitute some of the most serious environmental disasters associated with mining, great care should be taken in the design of the lagoons. The stability of, and control of seepage from, the lagoons can be ensured by keeping in mind the following design parameters: (1) Construction of the lagoon at or below the ground level, (2) the banks should have a slope of 34° on the lagoon side, and 26.5° on the outer side, (3) there should be a toe drain to allow the water table drawdown below the outer slope, (4) there should be a free board (water surface to the crest of the lagoon bank) of at least one metre, (5) the inner surface of the bank should be capable of withstanding erosion due to wave action, (6) there should be provision for drawing off the supernatant, as also rainwater due to abnormally heavy rainfall, etc. (Chadwick et al., 1987, p. 126–127). The supernatant water from the lagoons may be either recycled, or discharged into the natural waterways after treatment. In some countries, such as Germany and Poland, colliery spoils are tipped with domestic wastes (Figure 8.16; source: Skarzynska & Michalski, 1999, p. 189).

Control technologies for minimizing the mining environmental impact 187

Figure 8.16 Joint tipping of colliery spoils and domestic refuse (source: Skarzynska & Machalski, 1999, p. 189).

Figure 8.17

Design of trommel cutoff (source: Skarzynska & Machalski, 1999, p. 196).

Untreated coal colliery spoils are used as bulk material for various types of earth works, such as embankments of roadways, railways, rivers and dams. The water contained in the dumps and infiltrating through the dumps, is likely to be contaminated. In order to prevent such contaminated water from polluting bodies of freshwater, polyethylene sheeting or clay screens should be incorporated with drainage to remove the infiltrating water (Figure 8.17; source: Skarzynska & Michalski, 1999, p. 196). 8.2.6

Disposal of gold mine tailings

The mode of disposal of tailings is illustrated with the case history of gold tailings in South Africa (Vermuelen, Rust & Clayton, 2002). The Witwatersrand Goldfields occurring in the Johannesburg area in South Africa are the largest deposits of gold in the world. Despite the reduction in production during the last decade, South Africa has been and continues to be the largest producer of gold in the world. The mineral composition of the typical Witwatersrand gold reef is as follows: Quartz: 70–90%, Phyllosilicates (clays): 10–30%,

188 Mineral resources management and the environment

Pyrites: 3–4%, Other sulphides: 1–2%, Grains of primary minerals: 1–2%, Gold: ⬃45 ppm. The mean and the range of the mineral abundances in the Witwatersrand gold tailings (as determined by EDS and XRD analyses) closely follow those of the gold reef (Vermuelen, Rust & Clayton, 2002): Quartz: 75% (59–83%); Muscovite: 8% (7–19%); Pyrophyllite: 5% (1–17%); Illite: 5% (3–11%), with small percentages of clinochlore, kaolinite and pyrite. The specific gravity of the tailings is 2.74 Mg/m3. The coarse particles (sands) are almost wholly composed of quartz. The slimes also have a preponderence of quartz, with significant amounts of pyrophyllite, muscovite, illite, kaolinite and pyrite. Grading study of the tailings shows that about 2% are coarser than 200 m (limit of fine sand), 10% finer than 2 m (clay-sized), and at least 50% slimes. The median particle size (D50) ranged between 6 and 60 m. The behaviour of the tailings is largely dependent upon the fines fraction. The shape of the particles (such as angularity) is as important as the size in determining the engineering behaviour of the tailings. Under load, the angular corners break and crush and angular particles tend to resist displacement, whereas more rounded particles are less resistant to displacement, but may be less likely to get crushed depending upon the surface texture. The coarser tailings sands are characterized by highly angular to subrounded, bulky but flattened particles. In contrast, the slimes, which are composed of clay minerals, consist of thin and plate-like particles. The engineering behaviour of slimes is akin to that of clay of intermediate plasticity. Also, the slimes can be flocculated, indicating the effects of the surface forces. Electron micrographs of coarser or sand tailings show either smooth surfaces or rough or irregular surfaces. Some particles show the typical conchoidal fracture of quartz. Sand particles with irregular surfaces may have developed as a consequence of fines attaching themselves to these surfaces. Slime particles have invariably very smooth and flat surfaces. In South Africa, a typical gold tailings impoundment has two sections: the embankment or daywall and the interior or nightpan. The daywall is meant to provide sufficient freeboard to retain the accumulated water from the deposited tailings, besides taking care of storm water when it rains heavily. The daywall has a number of sections or paddocks. A delivery station fills each paddock starting with the midpoint. When the pulp is delivered into a daywall paddock during the dayshift, it gets distributed by gravity, with the excess or supernatant water being decanted into the nightpan. Since the pulp depth has to be closely controlled, the filling of the paddocks is invariably done during the daytime – hence the name daywall. During the night, the tailings are discharged into the nightpan, but this is done from delivery stations located inside the daywall. The next day, the clear supernatant water is pumped out or drawn off by penstock decant. A natural beach develops between the delivery point and the pond from which supernatant water is decanted. The paddocks are filled according to a cyclic system, to allow sufficient

Control technologies for minimizing the mining environmental impact 189

time for the desiccation, consolidation and densification of the embankment material (Figure 8.18; source: Vermuelen, Rust & Clayton, 2002, p. 47). As should be expected, the impoundment facility at Mizpah, which takes care of the gold tailings of the Vaal River Operations west of Johannesburg, is very large. It was commissioned in 1993 and receives about 5000 t of tailings per day. The dam was designed for a final height of 60 m, with a total surface area of 165 ha. The average rate of rise is 2.4 m per year, and one depositional cycle takes about ten days. The dam is of the upstream daywall – nightpan system. The soil-forming processes on the gold tailings lead to a pronounced vertical layering, with coarse layers (“sands”) alternating with fine layers (“slimes”). Besides, there may also be horizontal variability depending upon the properties of the slurry and the depositional programme. In South Africa, the gold tailings impoundments are usually constructed using the daywall-nightpan paddock system. Generally, the more competent coarser material tends to get deposited near the embankment, with

Nightpan Discharge Beach

Pond Penstock Decant

Daywall Paddock Daywall Discharge Delivery Main PLAN

Daywall Beach

Pond

Penstock Decant

Starter wall

Figure 8.18 Layout of typical gold tailings impoundment in South Africa (source: Vermuelen, Rust & Clayton, 2002, p. 47).

190 Mineral resources management and the environment

finer material in the central part of the impoundment. However, it has been observed in practice that a significant amount of fines are trapped in the daywall and settle on the beach. 8.2.7

Use of paste technologies in tailings disposal

Environmental and economic considerations demand a reduction in the volumes and sizes of the tailings dams. The dayfall – nightpan system described above is a case of manipulating the environment to accommodate the tailings. As against this, thickened tailings and paste technologies are being increasingly used to design the tailings disposal sites to suit the surrounding environment. Paste production process is suitable for solids volume of 40 to 55%. Equipment is commercially available (e.g. GL&V) to produce paste consistency material from mill tailings, for purposes of backfill. Tailings are introduced with a flocculent into a feedwell. A mechanical rake and helix concentrates the solid particles by inductive circulation in a compression zone while preventing ratholing. The paste-like material can be withdrawn from the bottom, and a clear liquid overflows into the launder at the top of the tank. The paste consistency material can be stored indefinitely (Figure 8.19; source: Technical brochure of GL& V). Nalco has developed a new line of polymers for water clarification. The strong points of OPTIMER® mineral processing flocculent are high settling rates of suspended solids, superior overflow clarification, and maximum underflow compaction and pumpability. The Nalco 98DF063 is a liquid polymer system is custom-made for the flocculation of red mud in the bauxite industry. The Nalco patented TRASAR technology has four components of tracer chemicals, control equipment, diagnostic capabilities and on-site services. The system provides not only protection against scale formation but the inert tracer allows continuous diagnostic monitoring of the system volume, mixing studies, system flow, residence time/water travel time and environmental compliance. Such a system not only helps in the efficient operation of the process, but also allows remedial action to be taken before a problem becomes serious. Figure 8.20 (source: Sofra & Boger, 2002, p. 132) shows the relationship between shear rate and shear stress for Newtonian and non-Newtonian fluids. The inelastic Newtonian fluids exhibit a linear relationship between the applied shear stress and shear rate (curve A). The flow in the case of the Newtonian fluids gets initiated as soon as the shear stress is applied. On the other hand, concentrated mineral tailings often exhibit a non-Newtonian behaviour, in that they are characterized by an yield stress ( y). Thus, flow will occur in non-Newtonian fluids only after the critical stress is exceeded (curves B, C and D). It can be seen from Figure 8.21 (source: Sofra & Boger, 2002, p. 133) that (1) the yield stress is a function of concentration for a number of industrial slurries, (2) though there is variation in yield stress for different mineral tailings, all materials exhibit an exponential rise in yield stress with concentration.

Control technologies for minimizing the mining environmental impact 191

Figure 8.19

Production of paste from mill tailings (source: GL & V Tech. Brochure).

It is hence necessary to have a thorough understanding of the rheological characteristics of the tailings for the planning, design, operation and optimization of the dry disposal systems including dry stacking, thickened tailings disposal and paste backfill (Sofra & Boger, 2002). The suggested approach for the determination of

192 Mineral resources management and the environment

Figure 8.20

Relationship between shear rate and shear stress (source: Sofra & Boger, 2002, p. 132). 1800 1600

Shear Yield Stress (Pa)

1400 1200 1000

Manganese Tailings Gold Tailings Nickel Tailings (165 µm) Nickel Tailings (135 µm) Red Mud - Brazil (1) Red Mud - Brazil (2) Red Mud - Pt Comfort Red Mud - Jamaica Red Mud - Kwinana Red Mud - Surinam Coal tailings - uncont. Coal tailings - controlled

800 600 400 200 0 20

30

40

50

60

70

80

Concentration (% w/w)

Figure 8.21

Shear yield stress versus concentration (source: Sofra & Boger, 2002, p. 133).

Control technologies for minimizing the mining environmental impact 193

the tailings disposal system and requirements is schematically shown in Figure 8.22 (source: Sofra & Boger, 2002, p. 131). A number of parameters have to be manipulated in order that the tailings to be deposited have the desired rheological characteristics: (1) material parameters, such as solids concentration, viscosity and yield stress, (2) operational parameters, such as the flow rate (which is determined by the pipe diameter and throughput), and the shear to which the tailings are subjected (which depends upon the pump type, flow regime, etc.). A tailings management system which is safe, environmentally-responsible and cost-effective, can be designed on the basis of the study of (1) the concentrations required to achieve the optimum spreading and drying of the deposited tailings, (2) the optimum conditions for pipeline transport, and (3) the optimum dewatering of the slurry (Sofra & Boger, 2002). The higher the angle, the greater the volume that can be filled per unit surface area for a constant dam height. A smaller surface area of a tailings disposal site has a number of benefits. If the tailings are capable of generating AMD, multi-layer capping may be needed, and the expenses for capping and decommissioning could be considerable. Also, a smaller area means less evaporation, which may be an important consideration in areas of water scarcity. Less water in the site improves the dam safety – many cases of dam failure are attributable to the presence of large amounts of water in the disposal area.

Figure 8.22 Suggested approach for designing the tailings disposal system (source: Sofra & Boger, 2002, p. 131).

194 Mineral resources management and the environment

Thickened tailings, when discharged at solids concentrations by mass of about 60%, are self-supporting enough to attain a slope of about 5°. Slope angles as high as 10° could be attained when pastes are used (a paste is a tailings mixture with extremely high solids concentration). Pastes have been used for backfilling in underground mines with underground transportation in pipelines and boreholes, and for the surface disposal of tailings of base metals and gold. A paste should contain more than 50% solids, in order to avoid drainage of water and segregation of particles. A small amount of water means less use of a binder for attaining high strength. The average particle size varies from 20 to 100 m, with more than 15% of the particles being smaller than 20 m. In order to attain high solids concentrations, conventional thickeners are used in conjunction with mechanical dewatering techniques. Centrifugal pumps are used for large flow rates and low to moderate working pressures, whereas positive displacement pumps are used for small flow rates and high pressures. 8.2.8

Paste technologies in mining backfill

Moellerherm and Martens (2002) gave an account of the use of the tailings as paste backfill in the copper mining industry. Out of the total copper ore production of about 2 billion tonnes in 1998, open pit mining and underground mining accounted for 81% and 19%, respectively. Because of their low costs, block caving and roomand-pillar mining have emerged as the most widely used mining methods. The scheme of the backfill process is shown in Figure 8.23 (source: Moellerherm & Martens 2002, p. 150).

tailings

processing plant

crude ore

pipeline

recycled water

thickener

settling pond

thickened tailings

transport

hydraulic or paste fill

shaft haulage overburden + waste rock transport

pipeline transport gravity fill

concrete

back fill plant

sand

transport

other additives

crusher overburden and waste rock

heap

Figure 8.23

Scheme of backfill process (source: Moellerherm & Martens, 2002, p. 150).

Control technologies for minimizing the mining environmental impact 195

The share of the backfill techniques in copper mines is as follows: Gravity fill (waste rock): 46%, Hydraulic fill (tailings): 28%, Paste fill (tailings): 16%, and sand fill (sand): 10%. Thus, almost half of the mines (46%) use gravity backfill involving waste rock because of the ready availability of overburden and waste rock due to combined open pit and underground operations. The parameters of the backfill techniques are summarized in Table 8.3 (source: Moellerherm & Martens, 2002). It may be seen from Table 8.2 that the paste backfill has two main advantages: (1) the cavity is filled to the extent of 85%, and (2) it makes use of the tailings from the processing plant, thus reducing the need for surface disposal of the tailings. Thus, the use of backfill techniques has the advantage of minimizing the use of land on the surface, but the disadvantage of higher operating costs because of energy consumption. 8.2.9

Underwater placement of mine tailings

The studies made under the Canadian MEND (Mine Environment Neutral Drainage) programme have shown that the placement of tailings underwater can prevent or reduce ARD (Acid Rock Drainage). The tailings disposal under river and lake water is infeasible in most situations as it may adversely affect the productivity of the intensively used ecosystems, and may come into conflict with traditional rights (such as, fishing) of the communities. CCORE (1996) study has shown that after defaunation events, the benthic diversity on the seabed may recover in about one year in the case of fine-grained deposits of muds/silts/clays, and within about five years in the case of coarse-grained deposits such as gravels. Thus deep seabed emerged as a possible site for the placement of mine tailings. The 1996 Protocol for the 1972 London Dumping Convention allows the dumping in the sea of “inert, inorganic geological materials”. The submarine placement of tailings is deemed to comply with this convention, because (1) the tailings constitute inorganic, geological material, and (2) they would be inert (i.e. would not be able to generate ARD) under submarine conditions. Table 8.3

Parameters of the backfill techniques.

Parameter

Gravity fill

Hydraulic fill

Paste fill

Solids content Water content Concrete content Compressive strength Density Fill grade (cavity utilization) Solid

75–90% 7–11% 3–12% 1–20 MPa 1.8–2.5 t/m3 ⬃80%

50–75% 25–35% 3–15% 0.5–3.0 MPa 1.4–2.3 t/m3 ⬃85% (tailings backfill); ⬃60% sand backfill Fine-, and coarse grained tailings, sand Neves Corvo, Myra Falls

65–85% 12–25% 2–5% 1–5 MPa 2.1–2.35 t/m3 ⬃90%

Examples

Overburden, waste rock (coarse grained) Kidd Creek, Norilsk

Fine-, and silt grained tailings Louvicourt, Brunswick

196 Mineral resources management and the environment

Figure 8.24

Risk management process in tailings dams (source: Alexieva, 2002, p. 296).

Ellis and Robertson (1999) made a detailed study of a number of case histories of underwater placement of tailings. Potentially acid generating tailings from the Island Copper Mine of Canada were discharged into a target basin within a fjord at a depth of 100 to 200 m. The bulk of the tailings remained within a basin, and the seabed recovered its biodiversity within 1–2 years. The company used an outfall design, which is now standard for submarine tailings placement. Where the tailings pipeline reached the edge of the sea, it discharged into a tank where it is deaerated and mixed with seawater. This has the effect of making the slurry denser and more coherent as it flowed on the seabed. The tailings from the Kitsault Molybdenum mine in Canada were discharged at 50 m depth, with the same outfall design as Island Copper. Here also recovery of moderate successional biodiversity took place in 1 to 2 years, though the species present were not identical to those at nearby reference stations. In the case of the Misima Gold and Silver mine, Papua New Guinea, the tailings were placed in a 1000 to 1500 m deep near shore basin in an area of tropical, open coast with coral reefs. The tailings were dispersed to ensure a slow rate of deposition so that the organisms are able to cope with it. Ellis and Robertson (1999) suggested the physical and risk assessments to be made to determine the viability of submarine tailings placement at coastal and island mines. 8.2.10

Tailing operations and risk assessment

Tailings and waste disposal which are critical components of mine operation, are associated with risks involving human health, loss of life and property, damage to the ecosystem and biodiversity, etc. It is obviously prudent on the part of a mining company to be aware of risks involved, to what extent they are acceptable, and how to manage the risks at least cost. The risk management process is schematically shown in Figure 8.24 (source: Alexieva, 2002, p. 296). In the case of mine tailings,

Control technologies for minimizing the mining environmental impact 197

Figure 8.25 Acceptability of risk in tailings dam failure (source: Australian National Committee on Large Dams).

the hazards are slope failure, contaminated seepage, overtopping due to insufficient dam freeboard, etc. The possibility of a given risk occurring is evaluated qualitatively, ranging from “Very likely” to “Very unlikely”, on a scale of, say, 1 to 5. Risk assessment involves deciding whether the estimated risk is tolerable. Figure 8.25 (source: Australian National Committee on Large Dams) presents the societal risk criteria curves for dam failure, indicating the limit of tolerability. Risk management has to be ongoing and proactive. Risk management strategy has to be updated when, for instance, the design capacity of the tailings storage facility is increased, or when a new depositional method, or embankment construction method is thought of, and so on.

8.3

DUST CONTROL

Dust is a problem in almost all mineral industries, though the degree of severity of the problem varies from industry to industry. Some generalizations may, however, be made (source: Mining Mag., Sept. 2001, p. 124): 1. Loss of valuable material: Wind erosion from stockpiles may lead to the loss of upto 5% of the stockpiles of (say) coal or mineral concentrates. 2. Environmental problems: Dust can cause air pollution. It can also enter soil and water environments and pollute them. 3. Health hazard: Inhalation of certain kinds of dusts is known to cause diseases, such as, silicosis and pneumoconiosis.

198 Mineral resources management and the environment

4. Reduced visibility: The haze caused by dust in the air can cause hazardous working conditions for vehicle drivers and plant operators. 5. Explosion/oxidation: Very fine (10–20 ③m) combustible particles are liable to explode. Stockpiles of coal can “oxidize” and undergo spontaneous combustion. 6. Machine maintenance: Dust particles can clog machinery parts such as bearings and air filters, and damage them. 7. Capital investment: Greater quantities of dust would require the use of expensive dust control equipment, such as spray bars, pumps and bowsers. 8.3.1

Types of dust control techniques

In the case of the iron and steel industry, dust is produced in the process of unloading, storage, recovery and transfer operations involving iron ore, coal, coke, limestone, lime, slag, etc. Dust can be controlled by installing hoods over the conveyor belts which suck in the air and extract dust from it, by smoothing and compacting of coal in the stockyard using a bulldozer, by spraying the stockpiles with water (with the addition of surfactants where available), enclosing the stockyards to prevent dust from being blown away, etc. Four types of dust control techniques are used in the mineral industries, including the iron and steel industry (UNEP, 1986, p. 48–49). 1. Mechanical dust catchers: These are based on the principle of precipitation of heavy particles by settling (dust catchers) or centrifugal action (cyclones). Mechanical dust produced in the handling of raw materials, particularly in conjunction with blast furnaces. 2. Electrostatic precipitators: These consist of electron-emitting electrodes, and electron-collecting electrodes, which are kept at a potential difference (say, 40,000 V). When the dust-laden waste gas circulates at low speed between these electrodes, the particles of dust are bombarded with electrons. If the particles are sufficiently conducting, they become negatively charged, and get precipitated onto the collecting electrode. From the collecting electrode, the dust particles are either knocked off (dry method) or washed off (wet method). Electrostatic precipitation is a well-established technique of dust control in the iron and steel industry (main gases in sinter plants, detarring in coking plants, oxygen cutting and scarfing). The efficiency of trapping of fine particles and particles with high resistivity has been improved by (1) adopting high voltages (Nippon Steel uses a voltage of 150,000 V in their sinter strand), (2) redesigning both emitting and electrode electrodes, (3) introducing partitions into precipitators, to minimize the quantity of particles flying off on impact, (4) operating at higher temperatures, and (5) in the case of wet precipitators, using an electrostatic device to improve the spraying action of the liquid and the use wet precipitators which operate at high speed (⬃20 m/s). The improvements in the dust control techniques may be illustrated with the example of iron and steel industry (UNEP, 1986). A dust collector, which can

Control technologies for minimizing the mining environmental impact 199

function effectively when a burden of good scrap is loaded into an electric arc furnace, may fail if the charge is oily scrap. But the steel maker may not be in a position to dictate the quality of scrap supplied by a merchant. So the steel maker should be in a position to modify the dust control system as needed. 3. Filter media: Bag filters are extensively used in for dust control in industries. For instance, the use of bag filters in the iron and steel industry have made it possible to reduce dust content to less than 10 mg/m3 N. However, the relative equipment is expensive, requires frequent maintenance and involves energy consumption of 45-kwh/t. Bag filters are used in electric steel plants, for treating the diffuse gases produced by sintering, in blast furnace cast-houses and in steel-making shops. Bag filters made of terylene cloth and felt are no doubt effective, but they can be used only at lower temperatures (say, less than 130 °C for terylene). If dust collection has to be done at high temperatures (say 600–1000 ° C), fabrics woven from stainless steel fibres or refractory fibres made up of (say) aluminium oxide, have to be used. 4. High-energy scrubbers: There are three ways of using water to trap the dust: by collision between water and the dust on the basis of either flow of water or droplets, condensation of water on to the dust (on the analogy of fog), trapping by diffusion (on the principle of Brownian motion involving very fine droplets of water and very fine particles). Dedusting through fine spraying of water into the gas can be achieved either by the gas (high energy scrubbers of, say, the Venturi type, involving a pressure drop of about 250 mb on the waste gas) or by the water (whereby is injected under high pressure, of the order of 15 bars). Aerodynamic profiling of the Venturis improves the efficiency of the scrubbers with a large pressure drop. A number of new techniques have been developed for bringing the gas or fumes into contact with water. These include a multicellular reactor which contains water gates which the gases have to cross, thus causing a small drop in pressure. In other cases, the classical Venturi device is replaced by a bulb-shaped combining nozzle. The new technique of using columns with perforated plates can be used both for dedusting and desulphurization in the sinter plants. Aluminium industry discharges huge amounts of fluoride-loaded particulates which can cause dental mottling and skeletal fluorosis in human being and animals. Aluminium plants produce cryolite mud (at the rate of 0.02 t of cryolite mud per tonne of cryolite used) which contains toxic heavy metals, such as, arsenic, cadmium, nickel, etc. A. Bernatsky in his book, Tree Ecology and Preservation strongly advocates the use of tree belts around industries to reduce particulate pollution, and noise. One ha of spruce can collect about 32 t of dust from the atmosphere, one ha of pine 36.4 t, and one ha of beech, 63 t. 8.3.2

Dust control chemicals

Cognis has developed a number of new surfactants to provide for improved dust control on mine haulage roads while being compatible with solvent extraction and

200 Mineral resources management and the environment

leaching processes. EnviroWet DC-100 is highly biodegradable, and has superior wetting properties relative to the traditional surfactants based on linear alkyl benzene sulphonate and similar compounds. Two reagents are now available commercially for dust control. 1. ALCOTAC® DS1 is a chemical binder or encrusting agent. When sprayed on fine particles of minerals such as coal, limestone, iron ore, etc., it forms an adherent film, and prevents the creation of airborne dust from the surface of the stockpiles, railcars and road wagons. The film is water resistant, and consequently, there will be no channeling or slumping on the stockpile when there is rain. The chemical also minimizes spontaneous fires in coal stockpiles. 2. ALCOTAC® 1235 is a chemical “wetting agent”. When added to water, it will drastically reduce the surface tension of water, and would thereby promote the wetting of fine dust particles. The chemical is so formulated that it has a residual effect after initial application. Consequently, the fine particles are kept wetter longer, thus reducing the frequency of application needed. This reagent has been found to be useful to control the dust at the entrance to crushers, conveyor transfer points or on unmade roads.

8.4

LOW-WASTE TECHNOLOGIES

The idea of low-waste technology originated with water – that it is better not to pollute the water during the manufacturing process rather than clean it up afterwards. Low-waste technologies are those that are the least environmentally-degrading, involving pollutants (dust, gas, odour), nuisance (noise, vibration), with least consumption of energy and the use of raw materials. Waste minimization techniques are schematically shown in Figure 8.26 (source: Anonymous). Low-waste technologies may be categorized into three types: (1) Internal action – this directly concerns the manufacturing process, whereby no waste is produced, and all products are saleable, (2) External action – whereby waste is transformed into saleable products, and (3) Recycling action, whereby waste materials, after intermediate treatment, are reusable as quality raw materials. Low-waste technologies in the case of iron and steel industry consist of the following processes (UNEP, 1986): 1. Pre-reduction or direct reduction of ores: By this method, coking/sintering/blast furnace stages can be avoided, thereby eliminating the generation of byproducts from the coking plants, blast furnace slag and dust and sludges upstream of the steel shop. Besides, the dusts recovered by gas cleaning can be directly recycled. In Sweden, PLASMARED (SKF) process uses a plasma reactor to reduce the ore. 2. Scrap preparation: Scrap can be recycled in the blast furnace and the melting shop without any problem. But the scrap may carry pollutants, such as oils,

Control technologies for minimizing the mining environmental impact 201

Figure 8.26

Techniques of waste minimization (source: Anonymous).

coatings and alloy elements, which are not environmentally acceptable. The scrap can be cleansed of its pollutants before recycling, by shredding with magnetic separation, cryogenic grinding and preheating to burn off oils and plastic coating (Ceretti process). 3. Continuous processing: The blast furnace technology can be considered to be low-waste technology if the slag, dust and sludge could be made use of. Continuous steel making by electrical and other methods, saves energy and is environmentally less polluting. In some iron and steel mills, silica, sulphur and phosphorus are removed in the pre-treatment processes in the blast furnace launder. In Sweden, liquid pig iron is produced by the pre-reduction in a fluidized bed of fine-grained concentrates, or injection of pre-reduced material by a hollow cathode electrode in an immersed arc furnace. If the furnace is operated by D.C. current, there is reduction in noise. 4. Low-pollution pickling: Wastes produced by acid pickling (by HCl or H2SO4 for ordinary steels, or HF-HNO3 for stainless steels) can be minimized in the following ways: (1) Ishiclean process, which is a mechanical-hydroprocess, is virtually pollution-free, (2) Nitric acid pickling could be replaced by fluonitric

202 Mineral resources management and the environment

pickling for stainless steels, as is done in Sweden. If the reheating before pickling is carried out in slightly reducing conditions, it will lead to the formation of scales. Such scales dissolve rapidly in acid and soil the pickling baths. The fouling of the pickling bath by scales can be avoided if the preheating done in an oxidized atmosphere. Common steels pickled in sulphuric acid produce ferrous sulphate (FeSO4.7 H2O) which is used in agriculture as a weed killer, and in the treatment of water (flocculation and dephosphorisation). In the hydrochloric acid pickling, ferrous oxide is obtained as a product. This may be recycled in the sinter plant in the steel works. 5. Blast furnace dust and sludge: The top gas off the blast furnace is dry dedusted, and then wet scrubbed. This leads to the production of dust and sludge rich in ferrous oxides and carbon, but also containing volatile elements such as zinc and lead. The previous practice has been to recycle the dust and the sludge in the sinter line. This led to operational difficulties due to recirculation of large quantities of zinc. The coarser particles which are generally zinc poor, can be recycled as before. Zinc which tends to be present in fine particles, can be recuperated by cycloning of the top gas before it is wet-scrubbed. It can be either dumped, or sent to the non-ferrous industry. 6. Remelting of waste materials for special steels: Valuable trace metals that may be contained in the waste materials (such as, dust, sludge and scale) may be recovered by a combination of the following processes: drying of sludge, blending and mixing with carbon, agglomeration (briquetting or palletizing), addition to an arc furnace. 7. Correction of the composition of the slag: To suit the specifications of the market, it may some times become necessary to adjust the mineralogical and chemical composition of the slag. This may be accomplished during the manufacturing process (e.g. slagging additions to the blast furnace) or by careful tapping or by operating the furnace in a particular thermal regime. 8.4.1

Recycling of scrap

The recycling of scrap is explained in terms of the iron and steel industry. Steel production in USA involves the use of 64% of scrap. Each tonne of steel scrap recycled saves 1.1 t of iron ore, 0.6 t of coal and 54 kgs. of limestone, apart from savings in energy. There are three types of scrap in the steel industry: (1) Scrap arising in the individual steel works, which can be recycled in the same steel mill, without being involved in any commercial transaction, (2) Process scrap produced in the manufacture downstream of steel products, (3) Commercial scrap which helps the steel industry to balance their scrap requirements. Recovery depends upon the useful life of a manufactured product made of steel (for instance, 9–12 years, in the case of automobiles). Figure 8.27 (source: UNEP, 1986, p. 109) shows the cycle of the three types of scrap.

Control technologies for minimizing the mining environmental impact 203

Figure 8.27

Cycles of three types of scrap (UNEP, 1986, p. 109).

The properties of different kinds of scrap, depending upon the source, are summarized in Table 8.4 (source: UNEP, 1986, p. 110). The waste is made use of in the works itself or is sold. Only a fraction of the tonnage (less than 10%) is dumped.

204 Mineral resources management and the environment Table 8.4

Composition of scrap from different sources.

Type of scrap

Fe(%)

C(%)

S(%)

Density

Rolling mill off cuts (angles) Demolition scrap (structure) Shredded scrap (classic process) Cryogenic scrap (shredded at low temperature)

99 99 95 97 92 80 82

0.40 0.25 0.50 0.17 1.9 0.25 1.3

0.025 0.045 0.045 0.040 0.050 0.110 0.070

1 to 1.5 0.6 to 1.4 0.9 to 1.1 0.8 2.6

Packets of used scrap

The ways in which the waste products in the iron and steel industry are recycled are summarized as follows: 1. Sinter dust: Dust is produced during the process of sintering, and related handling operations, at the rate of 30 kg/t of sinter. This dust can be recycled in the sinter grate. 2. Blast furnace slag: Apart from liquid pig iron, 300 kg of slag per ton of pig iron are produced. As the slag resembles a natural rock in its chemical composition, it is used for building roads, production of cement and to a lesser extent, for thermal and sound insulation. 3. Oxygen steel-making slag: Pig iron may be either high phosphoric (P  1.7%) or low-phosphoric, haematitic (P  0.2%). Phosphoric slag has good market, as a fertilizer in agriculture. The haematitic slag can be used as limestone adjuster in agriculture, and in road-making, but there is not much market for it. Its low value does not allow it to be transported for long distances. In such a situation, there is no option except to dump the haematitic slag. 4. Electric arc furnace dust and sludge: Electric arc furnaces can remelt coated scrap (e.g. galvanized or plastic-coated) and alloy scrap. The dust and sludge recovered from the electric furnace often contain volatile elements, such as Zn and Pb, and are hence useless in the case of steel industry. These elements can, however, be recovered in the non-ferrous industries by various methods, such as reduction in a rotating furnace, soda extraction, injection in a plasma, etc.

8.5

TREATMENT OF WASTEWATER

There are a number of ways of treating the large quantities of wastewater produced in the iron and steel industry, namely, recycling, removal of suspended solids, oil, and organic toxic pollutants, etc. (UNEP, 1986, p. 70–82). These are applicable to other mineral industries as well. 1. Recycle systems: Recycling will reduce the pollutant loads at low cost, besides reducing the volume of wastewater that is discharged. However, if the wastewater is recycled too many times, two problems may arise in the recycled water – build-up

Control technologies for minimizing the mining environmental impact 205

of dissolved solids and the rise of temperature. High concentration of dissolved solids in the water can cause plugging and corrosion. This can be controlled by treatment of wastewater prior to recycling through the addition of chemicals, which inhibit scaling, or corrosion. If the recycled water is too warm to be used for its intended purpose, it has to be cooled prior to use. This can be achieved by passing the water through mechanical draft cooling towers. Most recycle systems require simple pumping only. They do not need much attention, except routine maintenance. However, if the wastewater concerned has arisen from wet air pollution control devices, the maintenance costs will be high, as the recycled water has to be cleansed of the dissolved constituents, which can cause fouling and scaling. 2. Removal of suspended solids: Suspended solids in wastewater may be removed by settling, clarification and filtration. When a stream of wastewater is let into a large volume lagoon, the velocity of water is reduced, and the gravitational settling of particles takes place. Settling is a slow process and usually takes days. The process of settling can be speeded up by the addition of settling aids, such as alum and polymeric flocculants. Sedimentation is often preceded by chemical precipitation and coagulation. These enhance the settling process by converting the precipitates into coarser particles, which will settle down faster. The ability of the lagoon to remove the suspended solids (including metal hydroxides) depends on the rate of overflow, density and particle size of the solids, the effective charge of suspended particles and the types of chemicals used for pre-treatment, etc. By allowing sufficient time for retention, by the proper control of pH, and by the regular removal of sludge, it is possible to have an efficient, low-cost system of removal of suspended solids. Relative to settling lagoons, clarifiers can remove suspended particles faster and more efficiently. Besides, they occupy less space and provide for centralized sludge collection. They are, however, more expensive to build and maintain. Conventional clarifiers consist of a tank and an arrangement for sludge collection. The tank may be circular or rectangular. The sludge may be collected by a mechanical device, or the sludge may be allowed to accumulate along a sloping, funnel-shaped bottom. In the case of advanced clarifiers, which use inclined plates for sludge collection, it is necessary to prescreen the wastewater to eliminate any materials, which could clog the system. As in the case of settling lagoons, clarifiers use flocculants to speed up settling Filtration is a highly reliable method of wastewater treatment. It is used to remove suspended solids, oil and grease and toxic metals from steel industry wastewaters. It has a number of advantages – low initial and operating costs, small land requirement, no need to add flocculant chemicals which add to the discharge stream, and low solids concentrations in the effluent, etc. Filters may of pressure or gravity type, and may involve one or more media, such as sand, diatomaceous earth, walnut shells and others. Higher flow rates and efficiencies may be achieved by the use of dual or multiple media. In the filtration process, suspended solids and oil accumulate in the filter bed, and impede the movement of wastewater. In order

206 Mineral resources management and the environment

to ensure that the filter bed performs efficiently, it is necessary to backwash the filter. Auxiliary means, such as water jets and air jets, can be employed to “scour” the bed free of solids and oils. 3. Removal of oil: This is done through skimming, air flotation and ultraflotation. Pollutants, such as free oil, grease and soaps, float to the surface of the wastewater, and can be removed by skimming. Air flotation and clarification when used in conjunction with skimming, can improve the removal of both settling and floating materials. The removal efficiency of a skimmer depends upon the density of the material to be floated, and the retention time of the wastewater in the tank. Depending upon the wastewater characteristics, retention may take 1 to 15 mins. for phase separation and skimming to be effected. Since skimming is effective in removing naturally floating materials, it constitutes good pre-treatment and improves the performance of the treatments downstream. Some pollutants, such as dispersed or emulsified oil, do not float to the surface by themselves, and skimmimg alone cannot remove them. More sophisticated methods have to be used for the purpose. When directed to the filter, oils and greases, either floating or emulsified, are adsorbed on the filter media. If high concentrations of oils are allowed to reach the filter bed, it may get “blinded”, and should be promptly backwashed. The purpose of flotation is to cause particles such as metal hydroxides to float to the surface of the wastewater tank where they can be concentrated and removed. The methods of flotation differ from one another in regard to the ways of generating the minute gas bubbles, such as, froth, dispersed air, and dissolved air and vacuum flotation. Steel industry wastewaters may contain significant levels of toxic pollutants, such as chromium, copper, lead, nickel, zinc, etc. They can be precipitated by chemical means, and then removed by physical means, such as sedimentation, filtration and centrifugation. Lime or sodium hydroxide can precipitate several toxic metals as metal hydroxides, phosphate and fluoride as calcium phosphate and calcium fluoride respectively. Hydrogen sulphide and sodium sulphide can precipitate many metals as insoluble metal sulphides. The chemicals may be added to a flash mixer or pre-settling tank or they may directly be added to the clarifier. After the solid precipitates are removed, the pH adjustment is made. Chemical precipitation is a simple and effective means of removing many toxic pollutants from wastewater. Complications may, however, arise due to chelating agents, chemical interferences and the problems of storage of hazardous chemicals. When lime is used, it should be in the form of well-mixed slurry. 4. Removal of organic toxic pollutants: Activated carbon is made from coal, wood, coconut shells, petroleum base residues, etc. Its ability for adsorption arises from its low pore size (10–100 Å) and consequent high surface area (500–1500 m2/g). Activated carbon is very effective in removing dissolved organics in the wastewater. The activated carbon can be regenerated and reused through the application of heat and steam or solvent. The wastewater is pre-filtered to remove excess suspended solids, oils and greases before being subjected to carbon adsorption. Suspended

Control technologies for minimizing the mining environmental impact 207

solids in the influent should be less than 50 mg/l to minimize backwash requirements. Oil and grease should be less than 15 mg/l. If the influent contains large concentrations of dissolved inorganic material, it may cause scaling, and loss of activity. This can be taken care of by pH control or the use of acid wash on the carbon prior to reactivation. The advantages of the carbon treatment are its high removal efficiency, and applicability to a variety of organic pollutants. Where the carbon cannot be regenerated because of the high content of adsorbed compounds, it must be disposed off. Microbial treatment involving activated sludge can be used for the removal of pollutants such as ammonia-N, cyanide, phenols (4AAP) and toxic organics present in the wastewaters. The activated sludge system is sensitive to hydraulic and pollutant loadings, temperature and the presence of certain pollutants. Temperature not only affects the metabolic activities of the microorganisms, but also gas transfer rates. Some pollutants are extremely toxic to microbes, and could “kill” them. The activated sludge system significantly reduces the toxic organic pollutants more cheaply relative to the activated carbon. If wastewaters are properly pretreated before being subjected to activated sludge treatment, this process should work well. 5. Advanced technologies for treatment of wastewaters include ion exchange and reverse osmosis, but they may not be economical to treat large quantities of wastewaters. Figure 8.28 (source: UNEP, 1991, p. 53) depicts the method treatment of metalcontaining acid mine water. Metal hydroxide precipitation takes place in the tailings ponds. The capital cost of the system was approx. C $ 800,000 (1985) and the annual operating costs were C$ 550,000 (1985).

Figure 8.28

Treatment of acid mine water in Brunswick mine, Canada (UNEP, 1991, p. 53).

208 Mineral resources management and the environment

8.6

SUBSIDENCE

Mining involves the extraction of large quantities of rocks, liquids and gases from the depths of the earth, and therefore causes damage not only on the surface but also to depths of hundreds and thousands of metres. The extent of subsidence varies from a few mm (due to withdrawal of waters from underground aquifers) to more than 6 or 7 m (arising from the extraction of coal from thick seams or due to underground fires). Subsidence may cause direct air circulation due to goaved-out areas, and may cause spontaneous combustion and fires within the goaf areas. Fires starting in one seam in a coal mine may spread to seams above and below it, and to seams in the neighbouring mines (as has happened in the Jharia – Raniganj coalfields in India). The presence of faults and dykes/ sills and abandoned old workings may accentuate the problem of underground fires. The subsidence triggered by fires invariably spreads fast. As a consequence of subsidence movements in the underlying seams, the overlying coal seams may be rendered unworkable. The following impacts of subsidence are common: formation of depressions in the surface, abrupt changes in the road gradients, damage to underground pipelines and cables, damage to surface buildings, plants and pylons, disturbance in the aquifers leading to reduced and contaminated flows, retardation in the growth of vegetation due to reduced availability of water, waterlogging in the central part of subsided area, contamination of surface air due to emissions from the underground fires, flooding of underground mines due to the development of ruptures in the underground waterbodies, etc. (Sengupta, 1993, p. 28). In the case of surface mining, the extent of geomorphic change is related to the thickness of the overburden covering the deposit, the quantity of barren rock that needs to be excavated per unit of the extracted mineral and the area of the mine. Underground mining may lead to surface subsidence with consequent disturbance to surface runoff, formation of water-filled depressions, and flooding in the coastal areas or near lakes. Mining under water generally involves dredging of loose sediments under water. If the sediments involved are alluvial sediments, then river beds, flood plains and river terraces will be affected. Dredging may leave behind waste dumps and small valleys. The mining of estuaries and intertidal zones (usually for heavy minerals, and diamonds in the case of Namibia) disturbs the balance between land and sea, and may trigger beach erosion. When the material is removed by underground mining, it triggers ground movement and the consequential deformation of the surface. The nature and extent of deformation depends upon the following parameters: (1) geometry of the mineral deposit – the mining of a massive, flat-bedded deposit will cause more deformation than a vein deposit, (2) the method of mining – longwall mining is more likely to lead to subsidence than room-and-pillar mining, (3) the nature of the mineral deposit, and the nature of the overlying strata – there are less chances of deformation if the mineral deposit and overlying rock are competent, than when they are incompetent.

Control technologies for minimizing the mining environmental impact 209

Subsidence may lead to the following damages: 1. Fractures: The fractures may be continuous or discontinuous, and may range in size from millimeters to meters. They can cause severe damage to buildings and installations. 2. Surface trough: Continuous deformation may lead to the formation of a surface trough. Uniform displacement does not generally cause much damage. Differential displacement could adversely affect the groundwater flow, and could bring about changes in the gradients of roads, railways, water or gas pipelines, etc. Back filling of underground coal mines by hydraulic stowing of river sand is a common practice in India. Such a stowing reduces the surface subsidence below 10%, protects the aquifers, habitats, farms and fields. The township of Raniganj and the villages around it in the famous Jharia Coal Field in Bihar, India, did not suffer much damage for 75 years so long as the pillars in the underground mines were preserved. The unscientific depillaring of the thick coal seams (“slaughter mining”) triggered subsidence, mine fires and environmental pollution in the area. Due to underground mining in the Jharia Coal Field, surface subsidence took place over an area of 32 km2. The formation of goaf (void space) beneath the surface led to the formation of cracks on the surface, 5 to 10 m long, and about 0.5 m wide. There are also depressions caused by caves-in. At some places, smoke and gases emanate through the cracks. It has been estimated that about 34 Mt of coking coal has already been lost because of underground fires. About 70 fires (out of the initial 110) are still active and blocked out about 50 Mt of coking coal which hence cannot be worked. Singh, Mathur and Landge (1995) describe how subsidence is controlled in the case of Chapri-Sidheswar mine in the Singhbhum copper belt, Bihar, India: (1) No mining will be carried out at depths of less than 62.5 m – in other words, a 62.5 m cover will be left intact throughout the life of the mine, and (2) The Room and Pillar stopes will be supported by 1.5 m long bolts at 1.2 m spacing. The mined out stopes will be promptly backfilled with the sand fraction of the tailings from the concentrator plant. The slurry will have 70% solids by weight. There may be failure of the pit walls after an open-pit mine is abandoned. For instance, some of the open-pit copper mines in Zambia have steep walls of soft sedimentary rocks hundreds of metres in height, and driving in heavy vehicles near the tip of the mine could easily induce wall collapse. It is therefore necessary to designate a safety zone around the mine. The safety zones and other measures are designed taking into account the geological, structural, geotechnical and climatic conditions. Cavities are formed underground when geotechnical methods of mining (such as, leaching, dissolution, fusion) are used. This leads to increase in the porosity, and decrease in the strength of the rocks. The area becomes prone to collapse of roofs and surface subsidence. Instances are known of collapse of rock-salt mines when water entered an abandoned mine and dissolved the salt pillars left there for roof support. Underground gasification of coal in the former Soviet Union (involving a coal seam 5–15 m thick at a depth of 100–130 m, in an area of 1 km2) gave rise to

210 Mineral resources management and the environment

one of the biggest landslides in the world, with a volume of 0.8 km3 spread over an area of 8 km2 (Vartanyan, 1989, p. 42). Landslides and rock and mud flows are common in the mining areas, especially when the wastes are dumped on the hillsides. For instance, the volume of the mudflow arising from the Yimen copper mine in China, was of the order of 200,000 m3. Another mudflow of the volume of 100,000 m3 from a mine in Yunnan, China, destroyed 6.2 km2 of fertile land on the plains. Four types of remedial measures are available for mitigating the subsidence in an abandoned mine: point support, local backfilling, areal backfilling and strata consolidation (Sengupta, 1993, p. 439). In the point support method, a large number of grouting holes are drilled, and grouting materials are injected to form the grouting piles and support the roof. Depending upon the engineering method used, the point support method could take the form of gravel columns, grout columns, fly ash grout injection, and fabric formed concrete. The local backfilling does not involve drilling the grouting holes. In this method, small, shallow potholes or surface cracks are filled with gravel, refuse and dirt, by direct dumping. Areal backfilling is meant to protect large urban areas (of the order of hundreds of hectares) from subsidence. This is accomplished by injecting into the underground openings large quantities of grouting materials, such as sand, gravel, coal refuse, mine tailings, fly ash, etc. under pressure. In the strata consolidation method, the shallow strata beneath the damaged surface structure are grouted or bound into a single rigid unit. If the subsidence continues, the consolidated structure will move as a rigid body without being damaged. There are several ways of bringing about consolidation, such as the use of polyurethane binder, cement grout pad or rock anchor.

8.7

NOISE AND VIBRATION

Reference has earlier been made to noise (section 6.3.1) and vibration (section 6.3.3) from the standpoint of health hazards. In this chapter, they are considered from the stand point of damage to structures. The primary purpose of blasting operations in mining is the fragmentation of the rock. Fragmentation takes place when the potential energy contained in the explosive is suddenly released. An unintended and undesirable consequence of the blast is the displacement of the ground in the vicinity of the explosion. Air blasts refer to air vibrations caused by blasting operations. The severity of the air blast depends not only upon the type and quantity of the explosive used, the degree of confinement and the method of initiation, but also on the climatic conditions, local geology and topography and the distance and condition of the structure that may be affected by the air blast.

Control technologies for minimizing the mining environmental impact 211

Air blast waves may give rise to damage and nuisance. The effect of overpressure on structures is summarized in Table 8.5 (source: UNEP, 1991, p. 40) The ground vibrates as a consequence of blasting. The surface of the ground in the vicinity of the blast undergoes displacement. The amplitude of such displacement depends upon the distance of the point from the blast, the energy released in the explosives and the local geological conditions. The extent of damage caused is directly related to the peak particle velocity related to the ground vibration. The lower the frequency of vibration, the greater is the damage for a given peak velocity. The relationship between the peak particle velocity and the damage to structures is given in Table 8.6 (source: UNEP, 1991, p. 41): Blasting can generate both dust and gaseous contaminants. The adverse consequences of blasting can be controlled in the following ways: (1) wait for some time before entering the area affected by the blast, (2) wetting down with water before blasting, and (3) ventilation. It is necessary to mention that respirators for particles protect against dust particles only, but not against gaseous emissions, which require gas masks. Planting of dense tree belt has been suggested as a way to reduce noise. It has been reported in the literature (A. Bernetzky) that a tree barrier of 250 m depth can achieve a reduction of 40dB. In 1980, ILO has issued guidelines about protecting the workers from noise and vibration. In the case of the steel industry, there are three major categories of vibration, namely, mechanical vibration, vibration by combustion, and aerodynamic vibration.

Table 8.5

Effect of overpressure on structures.

Overpressure (g/cm2)

Structural effect

2–4
7
52 140
140

Loose window sash rattles Failure of stressed or badly installed window panes Failure of correctly installed window panes begins All window panes fall Plaster cracks begin, and, at higher pressure, masonry cracks may be evident

Table 8.6

Relationship between peak particle velocity and damage to structures.

Peak particle velocity (mm/s)

Damage

70 110 160 230

Nil Fine cracking and fall of plaster Cracking Serious cracking

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Technological solutions to mitigate the consequences of vibration depend upon how the vibration is caused (UNEP, 1986, p. 103–105): 1. Mechanical vibration: This kind of vibration arises from rotating and alternating machines, such as, heavy duty fans, blowers and compressors. In the case of rotating machines, the vibration is generally of low frequency. Vibration gets excited when there is a lack of dynamic and hydrodynamic balancing. In the case of reciprocating machines, high frequency vibrations are associated with the movements of various components, such as rods and pistons. The problem cannot be assessed from acoustic studies alone, as noise is caused not only by mechanical vibration as transmitted by structures, but also due to the turbulent flow of fluids. On the basis of theoretical and experimental studies about the dynamic and acoustic behaviour of machines, techniques of reducing vibration through balancing and elastic suspension have been developed. 2. Vibration due to combustion: This is particularly relevant to blast preheaters, where vibration may result in unstable combustion. Theoretical studies have shown that the combustion chamber behaves like a tube with one end closed, and another end open (cupola). Vibration gets initiated when the ratio between the length of the oscillation wave and the length of the air and gas ducts of the combustion chamber, reaches a particular critical figure. The instability in combustion gives rise to a pulsing phenomenon with an acoustic wave (  4–10 Hz) similar to that of the “singing” arc. In most cases, the vibration is not only unpleasant, but it may be dangerous for the operation of the plant and therefore for the plant staff. The vibration due to combustion could generally be mitigated by using appropriate lengths of the duct. In actuality, the phenomena are more complex. For instance, gas pressure, delay in combustion, holding temperature in the cupola, fuel injection in the blast furnace, atmospheric conditions, etc. have the effect of modifying the acoustic length, and thereby increasing the possible zones of instability. 3. Aerodynamic vibration: Aerodynamic vibration is caused by the transport and distribution of gas and fumes by numerous ducts equipped with regulation valves. There are three specific causes of vibration: “(1) flow turbulence created by decreases in the velocity of the fluids along the inner side wall of the pipes, with fluctuation of pressure at the outer limit, (2) periodic flow phenomena due to pressure modulation by the ventilator or by pulsating combustion of a burner, (3) phenomena of drag and aeroelastic coupling between the flow and the vibration of the obstacle (butterfly valve, for example)” (UNEP, 1986, p. 104). The third phenomenon may cause the structures to emit intense sound on one frequency, if the cavities in which the flow is contained, have similar acoustic modes. Apart from being an acoustic nuisance, resonance may endanger the safety of the staff and cause serious damage to plant. The principal remedies for suppressing resonance are: (1) avoidance of resonance by appropriate design of piping and valves, (2) mechanical decoupling of the source of vibration from the rest of the ducts, and (3) use of appropriate silencers (such as, diffusion silencers which reduce turbulence,

Control technologies for minimizing the mining environmental impact 213

absorption silencers, resonating silencers, which are based on the introduction of uneven, multiple dephasing of the quarter of the length of the wave).

8.8

PLANNING FOR MINE CLOSURE

Instances are known of the mine owners just abandoning the mines when the ore runs out. It is critically important that mine closure programme should be incorporated into any mining proposal right at the outset. Proper closure of the mine is absolutely essential, particularly if the mine wastes happen to be acid producing. The leachates from them can play havoc with the waters, soils and biota of the area for many decades, if not centuries. The issues of Acid Mine Drainage (AMD) and tailings disposal, have been dealt with earlier (under sections 8.1 and 8.2 of the Chapter). All access to underground mine workings should be closed properly. Shafts are recommended to be filled with inert material, and sealed with concrete. Adits should be plugged with concrete. If long-term subsidence that could cause damage to buildings is anticipated, appropriate subsidence control measures should be undertaken, if feasible. In the case of mines worked by room-and-pillar method, the vacant spaces inside the mine could be used for high-security storage, warehousing and even for mushroom cultivation. Open pits for coal and base metals can be very large, and backfilling them with waste overburden may be infeasible or uneconomical. Such pits can be used for purposes of water storage or recreation. An abandoned limestone pit in Vancouver, Canada, has been innovatively developed into a spectacularly beautiful flower garden with waterfalls and aviary. Now-a-days, governments are under pressure from the public to enforce the mine closure regulations more strictly. In most cases, it is not possible to trace the owners of the abandoned mines, and make them pay for rehabilitation. So the governments concerned have no option except to rehabilitate the mine in public interest with public money. In some areas, mines constitute the most important economic resource. The closure of mine may have a strong adverse socioeconomic impact. The social dislocation that the mine closure can cause can be mitigated in part through the retraining of the work force to newer employment opportunities, and newer enterprises. Sengupta (1993, p. 453–477) gave detailed case histories of decommissioning of gold heap-leaching operations. To plan for closure, it is necessary to model the following aspects: migration routes, through surface water flow through the underdrain, and the groundwater flow through the undersaturated zone, and environmental fate (mixing, dilution/attenuation/precipitation, etc.) of the solutes. The hydrologic event used for risk assessment is the maximum 24-hr rainfall over a 100-year interval. Metal-complexed (WAD) cyanide, copper, zinc, arsenic, etc. are usually present in the active heaps at levels which could adversely affect the environmental and

214 Mineral resources management and the environment

human receptors. Regulatory agencies invariably prescribe the permissible concentration of WAD (Weak Acid Dissociable) cyanide in the heap effluent. Cyanide gets strongly attenuated during unsaturated flow. Experience has shown that when the cyanide levels are brought down to compliant level, heavy metals such as arsenic, will invariably become attenuated and compliant. Solutes within the immobile or slow flow region would tend to mix with the solutes in the rapid flow or mobile region. The concentration outflow from the heap is determined from the following equation: Cout  Cmobile  (Cheap  Cmobile) Jt

(8.6)

Where Cout  concentration in outflow from the heap, Cheap  average cyanide concentration in the immobile region, Cmobile  average concentration in the mobile flow region, J  a diffusion term set by the user, t  elapsed time The following case history of the Borealis Mine, Hawthorene, Nevada, USA (quoted by Sengupta, 1993, p. 468–470) is instructive. The general criteria for leach pad closure in Nevada are: (1) WAD cyanide levels of effluent rinse water must be less than 0.2 mg/l, (2) the pH level of the effluent rinse water should be between 6.0 and 9.0, and (3) Contaminants in any effluent from the process water that result from meteoric events must not degrade state waters. The heap was rinsed with fresh water. It was found that the free cyanide levels got reduced from 1.2–3.7 mg/l to 0.2 mg/l in 2–10 days, and the entire pad was detoxified in 60 days. Among the various detoxification agents tried (such as, ferrous sulphate, alkaline chlorination, etc.), hydrogen peroxide has been found most suitable for the detoxification of heaps.

CHAPTER 9

Mitigation of mining impacts

9.1

MONITORING OF MINING IMPACTS

The purpose of the environmental monitoring in and around a mine is to identify changes in the environmental parameters as a consequence of mining, in relation to the baseline conditions that existed before the commencement of mining. The environmental conditions monitored include (1) physical characteristics, such as water flow and geotechnical stability, (2) chemical characteristics, such as water quality (pH, sulphate, alkalinity, acidity, iron, electrical conductance, major cations and anions, etc.), and (3) biological characteristics (fauna and flora and biodiversity). A monitoring programme involves two types of monitoring units: station(s) at the point of effluent discharge which are generally located on site, and station(s) in the receiving environment which are generally located outside the mine. There should be at least one station located at the point of direct discharge from the mine to the receiving environment, to monitor the surface water and/or groundwater discharge, and to serve as an “advance warning” station. This station should be monitored at least monthly, to detect any significant change in pH and sulphate content. For instance, a lowering of pH alerts to the onset of formation of acid mine drainage, allowing appropriate corrective action to be initiated. Stations are located along the gradient of the surface and groundwater flows in the receiving environment. By comparing the composition of the upgradient and downgradient waters, it would be possible to identify the degree and spatial extent of impacts due to each component. A simple visual inspection of iron stains in the seeps and stream courses in the receiving area could provide useful information about what is going on (Sengupta, 1993, p. 216). Now a days there is an increasing recognition of the usefulness of biological monitoring (in the form of, say, the Index of Biological Integrity) in understanding the environmental impact. Biocriteria integrate the effect of multiple stresses over time and space, thus minimizing the need for a large number of samples. The magnitude, frequency and duration of monitoring is critical to chemical criteria, but may not be necessarily so for biological criteria.

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9.1.1

Environmental monitoring of mine components

The ways of monitoring of the different mine components from the standpoint of water and generation of AMD, are summarized as follows (see, a good summary by Sengupta, 1993, p. 215–224). Environmental monitoring of open pits: The quantity of water would be the most important component to be monitored. Water entering an open pit consists of precipitation, surface water drainage and groundwater discharge. By its very construction, a pit is open to the atmosphere. Rainwater hence collects in the pit. In wet climates, precipitation may account for bulk of the pit water. Also, since a pit constitutes a depression in the local water table, groundwater will seep into the mine from the walls and from the bottom. Surface water drainage is usually diverted away from the mine, to avoid the need to pumping it. All water entering the pit is led into a sump, from where it is pumped out. The advance warning station is best located at the sump, and is monitored at least once monthly during the operation of the mine. The pit walls get weakened by the presence of water in them. The geotechnical stability of the pit walls is crucial for the safety and productivity of the mine. Where necessary, monitor wells may be installed around the perimeter of the pit, in order to control the quantity of groundwater entering the pit. The seeps from the pit walls are monitored once in every six months. An analysis of the water quality data of the seeps from the pit walls could indicate how much each wall is contributing to AMD. When the pit is closed, there will be no more pumping of the water from the sump or retaining pond. The pit will get flooded, and the water level in it will rise to the pre-operational level. The pit will then become a part of the local groundwater system. After the closure of the mine, a monitoring station for the groundwater for the receiving environment may be established, its location being dependent upon the hydraulic conductivity of the subsurface strata. If the aquifers have high permeability, the groundwater-monitoring network should be located downgradient. There should be at least one monitoring station for each aquifer, and the monitoring frequency should be at least once in six months (Sengupta, 1993, p. 219). Environmental monitoring of underground workings: Groundwater is the most important source of water in the underground mines. Some amount of surface water may enter an underground mine through a shaft, adit or decline. The movement of water in an underground mine is by infiltration, which is a slow process. Mine water is pumped out from the workings. The presence of water in the strata increases the pore pressure and adversely affects the geotechnical stability of the walls and roof, which is important for the safety and productivity of the mine. The advance warning station may be located near the underground sump, and the monitoring should be done at least monthly. The monitoring frequency for groundwater and surface water in the receiving environment should be at least once in six months. Environmental monitoring of waste rock dumps and ore stockpiles: Waste rock dumps, ore stockpiles, and heap-leach sites are sited on the surface, and are therefore exposed to atmosphere. Precipitation therefore is the principal source of water.

Mitigation of mining impacts 217

Rainwater infiltrates through the dumps. At the base of the pile, the leach water may completely enter the groundwater if the hydraulic conductivity is sufficiently high, or it may partly exit at the base of the pile, and partly enter the groundwater. Geotechnical monitoring is concerned with the physical integrity of the pile. Consolidation or settlement of the pile could induce changes in the hydraulic conditions within the structure of the pile, resulting in slumping or toe collapse. Advance warning stations for groundwater and surface water should be located at the point of discharge from the retention pond, and the monitoring should be done monthly. The monitoring frequency for groundwater and surface water in the receiving environment should be at least once in six months. Environmental monitoring of tailing impoundments: The tailing impoundments receive water from two sources: water in the mill tailings slurry, and precipitation. The supernatant water in the tailings ponds would flow to the low-lying parts of the impoundment and form ponds. Part of the water may percolate down through the unconsolidated tailings and enter the groundwater. The advance warning stations should be located at the direct discharge points from the impoundment, and should be monitored monthly. The monitoring frequency for groundwater and surface water in the receiving environment should be at least once in six months. 9.1.2

Comprehensive monitoring of mine impacts – a case study

In order to design measures for mitigating the adverse impacts of mining, geotechnical, hydrogeological, topographical and geochemical, etc. parameters need to be measured periodically. The procedure is illustrated with the case study of iron ore mining in Nizhni Tagil area of Russia. Iron ore mining in the Nizhni Tagil area (Middle Urals) in Russia, began in 1721 in the southern part in an area of 140 km2. In 1950, further iron ore mining commenced in the western part. Flux-grade limestone was mined from the eastern part since 1925. In the late 1980s, detailed geotechnical, hydrogeological, topographical and geochemical, etc. investigations have been made in the area, in order to assess the extent of damage to geoenvironment caused by mining, and to use the resulting information to mitigate the possible adverse impact in that mine and similar mines elsewhere. In the Nizhni Tagil area, surface mining takes place at depths of 120 to 220 m, and underground mining at depths of 350 to 700 m. The open pits had fairly stable slopes of 32–36°, but in some places, landslides and collapses have occurred. The underground mines suffered major subsidences, with collapses 100 m deep and slopes upto 70°. The rock shifts on the ground surface reached a width of 500 m. An area of about 23 km2 got degraded. The geotechnical consequences included man-induced weathering, karst, landslides, sinks, erosion, etc. There was reduction in run-off, and the river water got polluted. In the case of sulphate water, sulphate concentrations increased by 2 to 5 times, nitrogenous compounds increased by 1.5 to 3 times, and oil products and phenols made their appearance. In the case of the

218 Mineral resources management and the environment

groundwater, the aggregate mineralization increased by 1.5 to 3 times, the pH became acid (3.5), nitrogenous compounds increased by 1.5 times, and oil products and some metals made their appearance. Soils in 46% of the total area were contaminated with heavy metals to the extent of 2 to 10 times the background values. Part of the forest vegetation was destroyed. Figure 9.1 shows the observation network. Figure 9.2 shows the changes in the geotechnical conditions, and Figure 9.3 shows the changes in the hydrodynamic and hydrochemical conditions in the mining area (source: Vartanyan, 1989). The extent of damage to the geoenvironment may be looked at from the standpoint of the area affected. Groundwater regime was disturbed over an area 9.3 times the total area of mining; heavy metal contamination of the soils occurred over an area 7.1 times larger than the mining area; intensive man-induced change on the surface and rock mass covered an area 2.2 times larger than the mining area, and so on. On the basis of the study, it has been recommended that the topographicgeochemical observations (surveys) be made once or twice a year, geophysical surveys two to four times a year, and hydrological surveys about three times a month.

9.2

WAYS OF REDUCING THE MINING IMPACTS

Since mining itself cannot be avoided, a practical and sensible approach would be to plan the mining and extraction activities in such a manner that the impact on the environment will be minimal. A possible cost-effective and environmentally-sound strategy to reduce the adverse impact of mining on the environment, is described as follows (Vartanyan, 1989): 1. Mining of the minerals, with backfilling of the openings (rather than natural and forced caving of the roof): This prevents rock caving and formation of open jointing. Besides, when the waste rock is used for back filling, it serves to reduce the volume of the rock stored at the surface. This practice has a beneficial effect on the aquifers and the general environment – experience shows that the backfilling reduces the dewatering of mine by 18 to 25%. If pillars are left behind under the water bodies, surface subsidence is prevented and water resources are conserved. An innovative approach is to mine ore-rich rock selectively so that lesser volumes of wastes are generated. At present, the losses of coal in the underground mining are as high as 30%. 2. Improvements in the process technology: Development of no-waste or lowwaste process technology options, which produce a minimum quantity of waste water; use of improved technologies such as, high intensity magnetic fields, sealing of the wastewater disposal systems, etc. 3. Water management activities: When the mine effluents are discharged into streams, they have to be purified, so as to be below the level of the Maximum Allowable Concentration (MAC); reuse of the mine effluents after purification; prevention of pollution by siting the waste water lagoons on natural or

Mitigation of mining impacts 219

Figure 9.1 Diagram showing the observation network in regard to Nizhni Tagil mining area, Russia (source: Vartanyan, 1989, p. 172).

220 Mineral resources management and the environment

Figure 9.2 Changes in the geotechnical conditions in the Nizhni Tagil mining area, Russia (source: Vartanyan, 1989, p. 170). This figure appears on the cover page.

Mitigation of mining impacts 221

Figure 9.3 Changes in the hydrodynamic and hydrochemical conditions in the Nizhni Tagil mining area, Russia (source: Vartanyan, 1989, p. 171).

222 Mineral resources management and the environment

introduced impervious material. The groundwater that is abstracted in the course of the mining may be reinjected into the aquifers that are proposed to be used. Polluted groundwater may be contained by the use of impermeable grout curtains (called “hydrocurtains”). The height of the infiltration barriers ranges from 15 to 200 m. 4. Improvements in extraction technology: The more comprehensively the components of the ore are extracted, the less will be the volume of wastes that need to be disposed. In polymetallic sulphide ores, for instance, the usual practice is to extract two or three more abundant metals. There are cases whereby 15 elements are extracted from the ore from which only three elements were being previously extracted. In effect, the tailings arising from the extraction of one metal may constitute the feedstock for the extraction of another metal. Mining produces about 18 billion cubic metres of mine tailings per year. Mining affects the landscape and may cause landslides, subsidence, pollution of water and soil, lowering of groundwater, etc. Dumping of overburden, disposal of tailings, erosion brought about by rain and wind have an adverse impact on the biological productivity of the area.

9.3

REHABILITATION OF MINED LAND

Though the mining companies are required by law to submit plans and commit funds for the rehabilitation of the mined land when once the mine is closed, enforcement has not always been strict enough. It is particularly difficult in the case of artisanal miners (“here today, gone tomorrow”). Figure 9.4 (source: Chadwick et al., 1987, p. 203) shows the steps involved in the restoration of mined land. Though the climate, soil and hydrological characteristics and methods of mining vary greatly in different areas, there are some common elements in the techniques of rehabilitation: 1. Removal and retention of top soil, to be respread in the area that is being rehabilitated. 2. Reshaping the degraded areas and waste dumps in such a manner that they are stable, well drained, and suitably landscaped for the desired long-term use. 3. Minimizing the potentiality for wind and water erosion. 4. Deep ripping of the compacted surface. 5. Revegetating with appropriate plant species in order to control erosion, and facilitate the development of a stable ecosystem compatible with the projected long-term use. Amelioration methods can be custom-made for a given situation, as follows (Chadwick et al., 1987). Low pH (usually 5): Amelioration by liming. Acid-tolerant species may be planted;

Mitigation of mining impacts 223

Additional planting (trees, shrubs, etc)

Maintenance (fertilizing, mowing, grazing etc.)

Monitoring (plant growth and soil development)

Seeding (choice of method)

Site preparation (recontouring, drainage ameliorant application)

Development of amelioration programme (fertilizer, organic manures stabilizing agents, non-toxic wastes, sub-soil, soil, if available)

Development of seed misture (grasses, legumes, other herbs, tree and shrub seed, microbial inocula)

Formulation of ecological goal tor revegetation(inrelation toultimate land use)

Appraisal of site and substrate (climate, phisical properties, fertility, toxicity, etc)

Design of operation (orientation of dumps, deployment of overburden, shape of excavation, final landscaping, etc.)

Decision on ultimate land use (in relation to environment, social, needs financial return, possible reworking, planning requirements)

Figure 9.4

Steps involved in the restoration of mined land (source: Chadwick et al., 1987, p. 203).

High pH (usually
8): Salt content may be removed by leaching. Salt/alkalitolerant plants may be grown; Low nutrient status: Nitrogen deficiency may be ameliorated by nitrogenous fertilization or by growing legumes;

224 Mineral resources management and the environment

Low moisture levels: Ridging, furrowing and mulching, etc. and growing droughttolerant plants; Soil amendment: use of other wastes, such as fly ash, slag, etc.; Planting of artificial wetlands for the treatment of acid mine drainage and polluted runoff. Experience has shown that purely civil engineering techniques, such as terracing and cementing, do not work, as mining wastes may be inhospitable and often toxic. Rehabilitation through vegetation has a number of benefits, particularly with regard to the developing countries in the tropics: (1) it is environment friendly and cost effective; (2) it needs no costly or imported inputs or technology; (3) it can generate employment of unskilled people, particularly women; and (4) site beautification can also be accomplished in the process. Mining disfigures the landscape besides causing landslides, subsidence, pollution of water and soil, lowering of groundwater, damage caused by explosions, etc. Restoration of mined land involves landscaping and revegetating of spoil heaps, pits, disused industrial areas and other kinds of dereliction caused by the mining activities (Chadwick et al., 1987, p. 173). In general, restoration is aimed at restoring the productive features of the landuse, improving the aesthetic features of the landscape, and reducing the possibility of further environmental degradation. The mechanics of restoration would depend upon not only on the nature of the substrate, but also on the intended purpose of restoration, such as, building an industrial estate, arable use, pasture, woodland, etc. It may not be possible, and sometimes it may not be even desirable, to restore the landscape, vegetation and land use to the exact condition that obtained prior to mining. Often the restoration modality will be determined by the economics of the operations (expenditure on restoration as against the expected income from the new vegetation), social priorities, and the government regulations. It may turn out that the proposed restoration of the mined land may result in a better landuse than before. The following factors have to be taken into account in determining the restoration procedure: Climatic factors: Restoration in areas of dry or humid tropics is generally more difficult than in temperate climates. This is so because the evapotranspiration is high in tropical areas, and the rainfall is often unpredictable and uneven – for instance, half of the annual rainfall in an area may get precipitated in a matter of hours. This would lead to flash floods and severe erosion in unvegetated areas. Nature of the substrate: In the humid tropics, the soils tend to be leached, poor in nutrients and organic matter, and iron pans may develop in the soil structure. Sub-surface soil may sometimes be richer in nutrients, and this factor should be kept in mind in the process of restoration. Vegetation: Choice of plants to be used in revegetation needs a detailed knowledge of the needs for the establishment and maintenance requirements

Mitigation of mining impacts 225 Table 9.1

Characterisation of substrate for purposes of land restoration.

Parameter

Measurement and use

pH

Determine with pH meter after calibration with buffers of pH 4 and 7.

Pyrite content

If the spoils are pyritic, measure the pyrite content, and make an estimate of acid production.

Electrical Conductivity ECe

Measure with a conductivity meter on a 1 : 1 or 1 : 2 soil to water extract of saturation paste. ECe is reported in mS/cm. ECe (mS/cm) Total salt content (%) Crop reaction 0–2 0.15 Salinity effects negligible, except for the most sensitive plants 4–8 0.15–0.35 Yields of many crops restricted 8–15 0.35–0.65 Only tolerant crops yield satisfactorily
16
0.65 Only very tolerant crops possible.

Nitrogen

Plant available nitrogen should be determined. Substrates with less than 10 g/g of mineralizable nitrogen cannot support non-nitrogen fixing plants, without the addition of nitrogen fertilizer.

Phosphate

Phosphate content is determined by Olsen’s method of carbonate extraction. Phosphate addition would be needed if the substrate contains 5 g/g of P. There would be crop response if the phosphate addition is 5–15 g/g of P.

Cations

A minimum requirement should be to determine soluble concentrations of K, Ca, Mg and Na. In acid substrates, measure Al, Mn and Zn (all measurements by AAS).

Anions

Measure Cl, HCO3 and SO4 if the substrate is sodic or alkaline.

of the plants, but such knowledge is not available for non-crop tropical plants. Vegetation chosen should be able to survive in nutrient-poor, acid and toxic conditions. Social and economic factors: Social and economic factors are of crucial importance. If the society prefers to restore the mined land as a woodland, the kind of trees that need to be planted (fruit trees, timber trees, leguminous trees, etc.) and the economics (investment versus the returns) have to be carefully chosen. If the society favours the use of the restored land as a pasture, decision has to be chosen about the kinds of grasses that need to be planted, and the kind of animals that would be allowed to graze. In the Indian context, the mining companies simply plant lots of acacia trees in order to satisfy the government regulations about reclamation of mined land. If right from the outset, the mining company makes a projection of how much spoil, of what characteristics is likely to be produced, and maintains records where the spoils have been tipped, it would greatly aid in planning the restoration. 9.3.1

Characterization of the substrate

The characterization of substrate for purposes of land restoration is given in Table 9.1 (source: Chadwick et al., 1987, p. 178–179).

226 Mineral resources management and the environment Table 9.2 Available water capacity (in mm/m)* versus texture and stone content (source: Chadwick et al., 1987, p. 184). Texture

Stone-free

Many stones

Stones dominant

Coarse sand Sand Fine sand Sandy loam Loam Clay loam Sandy clay Clay Silty clay

70 80 100 130 160 130 100 140 140

40 40 50 70 80 70 50 60 70

10 10 10 10 20 10 10 10 10

*About two-thirds of the water capacity is readily available to plants.

9.3.2

Ground preparation prior to revegetation

In areas of both dry and humid tropics, there is the ever-present hazard of severe erosion caused by episodes of heavy rainfall. The following steps are useful to conserve moisture and prevent sheet erosion in the early stages of revegetation: Contour terracing, furrowing and trenching: When tips are deposited, they are quite often compacted, to reduce the chances of formation of acid drainage. Furrows are constructed by ripping and ploughing along the contours. By this method, moisture is retained in the substrate. The furrows would give protection to the plants planted in them. Erosion by wind is much reduced. Terraces with bank and ditch downslope not only retain both silt and water, but also can take care of excess water that may follow a heavy rain. The width of the terraces depends upon the slope as shown below: Slope 1–5% 5–10% 10–25%

Field width 5 to 6 m 4 to 5 m 2.5 m

Chemical stabilizers: These infiltrate into the substrate, bind the particles together, and prevent their being dislodged and carried away. Chemicals used should not be toxic to the plants. Chemicals using alginates are widely used because they are non-toxic. Moisture conservation: The higher the content of clays, the larger the content of organic matter, and the greater the bulk density, the greater will be the ability of the substrate to hold moisture. The estimated available water capacity (in mm/m) of subsoils in relation to their texture and stone content is summarized in Table 9.2. 9.3.3

Mulching

Mulching is a very effective method of improving the capacity of the substrate to retain moisture. Often, bulky waste products, which are available locally in large quantities, are used as mulches.

Mitigation of mining impacts 227 Table 9.3 Properties of some mulch used in land restoration (source: Chadwick et al., 1987, p. 187). Material

Description

pH

Durability C : N

Application* Anchor

Wheat straw Yellow fibre

5.6–7.1

1 season

128 : 1

1.5–4 t/ha

Asphalt or crimping

Hay

Brown/green fibre

5.5

1 season

25 : 1

2–4 t/ha

Asphalt or crimping

Manure

Brown fibre, slurry liquid or Solid

6.6

6–12 m

25 : 1

15–40 t/ha

Disced into surface

Hardwood Bark

Variable colour milled or chipped

4–6 fresh, 6–8 composted

3–4 y


100 : 1
400 : 1

1–10 cm depth of mulch

No

Softwood bark

Variable colour milled or chipped

3.5–5.5 fresh, 6–8 composted

5–10 y 5–10 y


100 : 1
900 : 1

1–10 cm depth of mulch

No

Hardwood chips

White to yellow chips

4–6 (oak)

5–15 y

600 : 1

0.6–10 cm depth of mulch

No

Softwood chips

White to yellow chips

4–5

5–15 y

600 : 1

0.6–10 cm depth of mulch

No

Sawdust

Granular, green, 3.5–7.0 or composted

3–5 y

200 : 1 500 : !

1–10 cm depth of mulch

Asphalt

Leaves

Whole leaves, shredded and composted

6.5 composted

1 season

40 : 1

3–5 t/ha

May need crimping

Compost refuse

Fibre

7.5–8.5

1 season

45–55 : 1

20 t/ha

Discing

* The rate of application is least when the mulch is applied while seeding, medium when the mulch is applied for erosion control. Larger quantities of mulch are applied around already established plants. The same considerations hold good where the depth of the mulch is indicated.

The properties of mulches that could be used in the restoration of the mined land are given in Table 9.3 (source: Chadwick et al., 1987, p. 187). Form: Long fibred mulches are recommended to be used if the ground to be restored is sloping. Mulches, which are composed of large, coarse-textured solid particles, increase the pore space. On the other hand, fine-textured mulches fill the spaces between soil particles and impede movement of water. Colour: Cold soils restrict plant growth. Black mulches, which absorb the radiant heat, have a warming effect on the soils, and their application is therefore beneficial to cold soils. Light coloured mulches reflect heat. They could be applied to warm soils.

228 Mineral resources management and the environment

Durability: More durable mulches are to be preferred as their beneficial effect lasts longer. However, if a durable mulch dries out, it could become a fire risk. Chemical: A mulch soil will decompose by itself if the C : N ratio is 15 or less. If the C : N ratio is very large, the mulch will require extra nitrogen to decompose. If extra nitrogen is not applied, a high C : N mulch will deplete the soil nitrogen, and would impede plant growth. So mulches with C : N ratio of 20–25 : 1 are recommended to be used, to minimize the N depletion in the substrate. Composted mulch is desirable as it is invariably characterized by higher pH, and is therefore more effective in the restoration of acid substrate. Biological: Care should be taken not to introduce any pathogens or seeds of weeds with the mulches. Ideally, the mulch should inoculate the substrate with beneficial microorganisms, which decompose slowly. 9.3.4

Amendments and fertilizers

As the substrate tends to be acid, the most common amendment is lime. Calcitic limestone is most effective in facilitating the planting on acidic spoils. Most acidic soils require 30–50 t/ha of limestone, and some may require even 100–400 t/ha. Freshly exposed colliery spoil is invariably deficient in phosphorus and nitrogen. These nutrients need to be added to the substrate for some years to promote the growth of the vegetation. Regular supply of phosphorus is needed to maximize the fixation of nitrogen by leguminous plants. Most sites requite at least 1 t of triple superphosphate (45% P2O5). Then NPK 20 : 10 : 10 should be applied at the rate of 500–625 kg/ha if the mined land is to be developed as crop land, or 325–500 kg/ha if it is to be developed as amenity grassland (source: ‘Mine Environment and Management’, 1988, p. 143–144). Fly ash has emerged as an important amendment for soil conditioning of acidic soils, and by extension, acidic substrates in the mined land. Fly ash is the fine material (60–70% of which has a size below 0.076 mm). It is a waste, which is produced when pulverized coal is burnt in thermal power stations. Because of its fineness, it creates serious problem of dust pollution, besides needing considerable storage space. In India, about 80 thermal power stations produce 100 million tonnes of fly ash, about 15% of which is used in civil constructions, building material (brick making) and for the amelioration of wasteland. In the Industrialized countries, the percentage utilization of fly ash is 65%. Fly ash improves the soils in two ways: firstly, it improves the physico-chemical properties of soils, such as hydraulic conductivity, bulk density, porosity, water holding capacity, etc., and secondly, it contributes to the soil essential plant nutrients such as Ca, Mg, K, P, Cu, Zn, Mn, Fe, B, Mo, etc. Fly ash is applied at different doses, 25–500 t/ha, depending upon the properties of the soil to be amended. Amendment with fly ash has increased the crop yield from 25–50%.

Mitigation of mining impacts 229

9.3.5

Ecotypes and cultivars

There are not many plants, which can tolerate the high-acid, low-fertility substrates. Some grasses, such as Cynodon dactylon (Bermuda grass) and Agrostis capillaries (Common bent) have been found to be able to grow on different kinds of mine wastes. Chadwick et al. (1987, p. 194–199) gave a long list of plants that have been found useful in the reclamation of mined land for different kinds of tailings and under different climatic conditions, in Africa, Australia, Canada, USA, etc. (vide summary given below): South Africa Saline tailings: Atriplex lentiformis, Atriplex undulata, Atriplex rhagodiodes Nickel tailings: Atriplex nummularia, Kochia brevifolia Gold tailings: Tamarix pentandra, Tamarix aphylla Rapid growth on tailings: Acacia saligna (tree), Cynodon dactylon, Cynodon aethiopicus, Sporobolus virginicus, Panicum repens Flooded areas: Paspalum vaginatum Pyritic gold tailings Grasses: Agrostic tenuis (Common bent), Choloris gayana (Rhodes grass), Cynodon dactylon (Kweek, Couch or Bermuda grass), Dactylis glomerata (Cocksfoot or Orchard grass), Eragrostis curvula (weeping love grass), Festuca arundinacea (Tall fescue), Holcus lanatus (Yorkshire fog), Lolium perenne (perennial rye grass), paspalum dilatatum (Dallis grass). Legumes: Medicago sativa (Lucerne), Melilotus alba (American white clover), Trifolium repens var. latum (Italian clover), Trifolium repens (New Zealand wild white clover). Trees and shrubs: Atriplex semi-baccata (Creeping salt brush), Acacia baileyana (Bailey’s wattle), Acacia melanoxylon (Tasmanian blackwood). Rooted plant material: Cortaderia selloana (Pampas grass), Cynodon aethiopicus (Star grass), Hyparrhenia hirta (Thatch grass), Pennisetum macrourum (Hippograss). Australia Acacias (e.g. Acacia saligna, Acasia sophorae, etc.) and Eucalyptus sp. (e.g. Eucalyptus camaldulensis, Eucalyptus sargentii) are the dominant species used in reclamation. Grasses: Aristida sp. (wire grass), Axonopus affinis (carpet grass), Poa pratensis (Kentucky bluegrass), etc. Canada Grasses: Agropyron desertorum (crested wheatgrass), Bromus intermis (Bromegrass), Legumes: Coronilla varia (Crown vetch), Trifolium repens (white clover), Trees: Acer saccharinum (Silver maple), Picea mariana (Black spruce), etc.

230 Mineral resources management and the environment

USA Sub-humid, semi-arid and arid climates of western USA Grasses: Festuca arundinacea (Tall fescue), Poa pratensis (Kentucky bluegrass) Legumes: Coronilla varia (Crown vetch), Lotus corniculatus (Birdsfoot trefoil) Tress and shrubs: Cornus amonum (Silky dogwood), Fraximus pennsylvanica (Green ash) Northern Great Plains Grasses: Agropyron dasystachtyum (Thickspike wheatgrass), Panicum virgatum (Switchgrass) Legumes: Medicago sativa (Alfa alfa), melilotus alfa (Sweet clover), Trees and shrubs: Caragana arborescens (Siberian peashrub), Salix sp. (willow) Southern Great Plains Grasses: Buchloe dactyloides (Buffalo grass), Sorghastrum nutans (Indian grass) Legumes: Medicago sativa (Alfaalfa), melilotus alfa (Sweet clover), Trees and shrubs: Cetlis sp. (Hackberry), Juniperus (Junipers) Desert Southwest USA (saline and alkaline tailings) Atriplex canescens (Four-wing saltbrush), Panicum antidotale (Blue panic) 9.3.6

Bioremediation

Bioremediation through metal-accumulating plants and crops has emerged as an inexpensive and environmentally sound alternative. Stjerman and Ledin (2001, p. 802) made pot experiments to determine the possibility of phytoremediation of the tailings at Aitik copper mine in Sweden. The following are the physical and chemical characteristics of the tailings: Sand (0.05–2 mm): 87.5%, silt (2–50 m): 7%, clay (2 m): 5.5%; pH, 1 : 1 water, 6.4; Elements (mg/kg): Fe – 24,700; Al – 13,800, As – 11, Cu – 478, Cd – 1.3, Pb – 1.9, Zn – 96, Mn – 706, Mg-AL: 17, P-AL: 51, K-AL: 65, etc. Three plant species, barley (Hordeum vulgare), red fescue (Festuca rubra), and red clover (Trifolium pratense) were tested. Highest growth was achieved in reduced (not weathered) sand mixed with 16 and 33% by volume of sewage sludge, because pH was close to neutral and the content of nitrogen was high in these mixtures (Fig. 9.5; source: Stjerman & Ledin 2001, p. 802). Berti and Cunningham (1994) have presented a case history of utilization of this approach. “Hazardous” waste material is defined as having TCLP (Toxicity Characteristic Leaching Procedure – US EPA, 1990) Pb critical value of 5 mg/l. To bring down the soil Pb toxicity from 30 mg Pb/l in a dump to 5 mg/l level, two approaches were attempted: (1) use of lead accumulator plants, such as common ragweed (Ambrosia artemisiifolia), hemp dogbane (Apocynum cannabinum), musk or nodding thistle (Carduus nutans), and Asiatic dayflower (Commelina communis): these exhibited shoot concentrations of 400–1,250 mg Pb/kg; and (2) use of soil amendments, such as lime, fertilizers, biosolids, industrial byproducts, to promote plant

Mitigation of mining impacts 231

Figure 9.5 Above-ground biomass after two months of growing plant species in pots filled with reduced tailings treated with 0, 16 and 33% by volume of organic matter. The treatments are: a – moss peat, b – sewage sludge, and c – paper mill sludge. Bars represent confidence interval at 0.05 level (source: Stjerman & Ledin, 2001, p. 802).

232 Mineral resources management and the environment

growth, enhance the intake of metals by plants, prevent migration of metals, reduce soil erosion and downward flow of soil water. Efforts are being made to develop more efficient soil remediation methodologies by breeding or bioengineering plants, which have the ability to absorb, translocate, and tolerate Pb while producing sufficient biomass. There have been some spectacular developments in biotechnologically creating bacteria, which can remediate almost any kind of waste. The bacterium, Dienococus radiodurans, has extraordinary resistance to radioactivity – it can survive exposure to one million rads, whereas a human being exposed to 1000 rads of radiation dosage will die within a week or two. Though the radiation damages the bacterium’s genetic material, the bacterium can repair its DNA completely in 12 to 24 hours, as if nothing has happened. The bacterium, pseudomonas, can remediate chemical wastes, but it cannot survive exposure to highly radioactive environment. By introducing toxindegrading genes from Psuedomonas, into D. radiodurans, a new super bug has been created which can remediate the toxic chemicals in a highly radioactive environment. The new bacterium is capable of remediating special types of waste disposal sites, such as the one near Richland, Washington, D.C., USA, where the wastes contain both toxic chemical and radioactive wastes (Sciences, July/Aug. 1998, p. 16–19). The US EPA has been trying to develop cost-effective, “green” engineering solutions for the remediation of metal mining sites (Compton et al., 2001). Studies by the US Department of Agriculture have shown that the application of biosolids can render many heavy metals less bioavailable, besides improving the soil tilth, total organic carbon, and water holding capacity, fertility and cation exchange capacity. The contaminants in tailings to be remediated were Zn, Pb, Cd, Cu, and Mn, with Zn concentrations ranging from 50,000 to 100,000 ppm. Biosolids from the Denver Metro Waste Water Treatment Authority (at the rate of 224 t/ha) and equal amounts of lime were spread over 4.5 ha test plot. The consequences of the application of biosolids were checked after one year. Though the total metal concentrations did not show significant decrease, there was increase in pH and organic content and decrease in the bioavailability of metals. Consequently, soil toxicity to plants and invertebrates was generally eliminated. The possible risks to herbivorous mammals and omnivorous avian communities are being studied. 9.3.7

Miscellaneous revegetation methods

Where a opencast mine exists near a town or city, the municipal garbage can be dumped into the open pit, and covered with soil. The pit can be slowly filled up, and then revegetated. Van Wyk (1978) suggested a single treatment whereby soil stabilization, seeding and fertilizing can be accomplished, and maintenance minimized. Soil is mixed with sawmill dust, wood chips, hay and other plant material, and made into bricks

Mitigation of mining impacts 233

of the dimensions 30  10  10 cm. These bricks should be strewn around so as to cover about 30% of the area. Such bricks prevent surface erosion, and conserve the topsoil, and may be used for seeding the plant/grass material. Revegetation could be accomplished by the use of self-contained pellets. These are made by mixing the grass seeds with tank silt, farmyard manure, fertilizer, paper pulp waste, etc. and then spread around at the time of the onset of the rainy season. Instead of planting the seeds, a more practical approach would be to grow saplings of trees in polythene bags, and plant them when they are 9–12 months old, just before the onset of the rainy season. 9.3.8

Restoration of an iron ore mine site – a case history from Goa, India

Noronha (1995) gave a case study of afforestation for the ecological management of an iron ore mine in Goa, India. He recommended the following measures for preventing degradation and facilitating reclamation: (1) drawing up of plans right at the outset for rehabilitation of the areas after mining; (2) stocking of top soil for reuse; (3) construction of check dams and water filter beds at high contour levels to prevent suspended solids from reaching water bodies and agricultural fields; (4) impervious barriers at the toes of waste dumps to prevent fine particles and slime from being washed out during heavy rains; (5) construction of tailing ponds; and (6) continuous water sprinkling to prevent dust from being blown away from the waste dumps, etc. The economic value of a tree is estimated not only in terms of biomass yield (timber, fuelwood, forage, etc.) and its market price, but also in terms of its environmental benefits, such as soil maintenance, dust suppression, recycling of wastes, sheltering of birds and production of oxygen, etc. Acacia and Casuarina are useful as fuelwood and timber. They have no food value. A comparison in tree growth (8 years) between normal soil and dumpsite, shows that the tree growth on dumpsites is reasonably good. Tree crop (after 8 years) Acacia auriculiformis Casuarina equisetifolia

Normal soil Height: 14 m Girth: 87 cm Height: 16 m Girth: 71 cm

dumpsite 8m 58 cm 12 m 39 cm

A viable alternative is to grow cashew trees on waste dumps in coastal areas. Cashew yields excellent economic returns, while providing the same kind of environmental benefits as other trees. The cashew tree has a life span of 30 years. It is usually planted with spacing 8 m  8 m. It yields highly valuable nuts (150 kg/ha in the fifth year, going up to 750 kg/ha in the tenth year). The expense incurred for preparing the land for cashew cultivation (leveling, grading, drainage, digging pits, use of fertilizers and pesticides etc.) can be easily recovered. Technoeconomic evaluation shows that at discount rates of 5%, 10% and 12%, the current net value of cashew is 3 times more than that of Acacia.

234 Mineral resources management and the environment

In India, since the mined land reverts to the Government, the mining company has no further interest in it. As the mining companies are required to provide vegetal cover on the mined land, they tend to go in for fast-growing Acacia. The tree has good pH tolerance, good nitrogen-fixing ability, shallow root system, and can grow on the irregular, “holey” soil typically found on dumpsites. By allowing property/tenancy rights to the growers of the plant cover on the mined land, incentive could be created to grow economically valuable tree crops such as cashew and fruit trees. 9.3.9

Sudbury Nickel: A case history of successful reclamation

The Sudbury Nickel Irruptive is a well-known geological feature in the province of Ontario, Canada. A gigantic nickel coin installed by the mining companies atop a promontory in Sudbury, symbolizes what the area is famous for. Currently Inco Ltd., and Falconbridge Ltd. produce 51,000 t of nickel ore per day from 15 active underground mines in the Sudbury area. Another 50,000 t per day is produced in five other mines in the same belt. Nickel and copper are the principal metals extracted. By-products are: cobalt, platinum group metals, gold, silver, selenium, tellurium, sulphuric acid, etc. The slag produced is used for road construction. The nickel-copper ore was discovered in mid-nineteenth century by a blacksmith during the building of the Canadian Pacific Railroad. Production of ore started in 1886. Though the ore was rich in nickel, there was hardly any demand for the metal – the world demand for nickel in 1887 was less than 1000 tonnes! Nickel became a marketable commodity only in the twentieth century (incidentally, the case of nickel illustrates the validity of Zimmerman’s dictum, “Resources are not, they become”). The mining, stripping, sintering and smelting operations had a profound environmental impact. The forests all around got destroyed, and the area became barren. The emissions of sulphur dioxide arising from the smelting of the sulphide ores of nickel – copper were so intense that the soils were severely acidified. So much so when the restoration work began in 1969, germinating seeds died on contact with the acidified soils, and tree seedlings planted died within two years. The residents then tried a different approach. They applied lime to the soil, and planted grasses and clover. This worked. Slowly and steadily, the area got vegetated. Wildflowers, shrubs, poplars and birches started growing. The mining companies adopted a two-track approach: reduce the sulphur emissions, and plant trees. In 1972, Inco completed the construction of a giant smokestack, which drastically reduced the sulphur dioxide emissions, and planted the millionth tree. By 1994, further improvements in the process technology reduced the sulphur dioxide emissions to 10%. Falconbridge planted 600,000 trees on its properties in the Sudbury area. It recycles about half the water it uses, and treats wastewater to control acidity, heavy metal content and suspended solids. Using the treated water, Falconbridge could ameliorate an acidic wasteland into a wetland, which has now become a wildlife sanctuary.

Mitigation of mining impacts 235

Thus, more than 3000 ha of land in the Sudbury area has been restored. An additional two million trees were planted under a job-creation programme funded by the Sudbury Regional Municipality, government and industry. The environmental transformation that has been accomplished in Sudbury attracted international attention – at the Rio Summit in 1992, Sudbury received the United Nations Local Government Honors Award (source: Metal Mining and the Environment – a brochure of the American Geological Institute, 1999). Two lessons could be learnt from the Sudbury case: (1) it is indeed possible to reverse and ameliorate even the most intensive and extensive environmental degradation, (2) biological methods, such as the vegetation, are not only cost-effective but are also environmentally and aesthetically appropriate. 9.3.10

Reclamation of Manganese spoil dumps, India

Manganese Ore India Limited (MOIL), a public sector company, has rehabilitated about 400 ha of manganese spoil dumps, through an innovative combination of restoration methods (Sahni, 1995): (1) a supportive and nutritive rhizosphere was built up through the use of sugar mill waste (pressmud), sewage sludge, etc. (2) use of cultures of Rhizobium, Azobacter, Mycorrizhae etc. which enables the plants to tolerate high manganese concentrations, and accumulate atmospheric nitrogen, (3) Inoculation of the plants with cultures of endomycorhizal fungi of Glomus spp. to promote root development and stress tolerance. The amendment of spoil with 100 t/ha of pressmud and the use of VAM-Rhizobium increased the water holding capacity of the spoils from 10.8% to 46.4%, reduced the bulk density from 1.84 g/cm3 to 1.42 g/cm3, improved the nutrient status in regard to N, P and K, and resulted in 13–15 fold increase in the rate of plant growth, in relation to growth in unamended spoil. Among the various amendment materials, pressmud proved to be the most effective – probably because it is not only rich in organic matter, but also contain sugars, which provide good substrate for microbial proliferation. Till 1994–95, about a million trees were grown on the amended spoils, prominent among them being: teak (Tectona grandis), shishum (Dalbergia sissoo), neem (Azadirachta Indica), cassia (Cassis fistula), karanji (Pongamia pinnata), bamboo (Dendrocalamus strictus), etc. In 1989, 40,000 mulberry trees were planted on the manganese spoils, which not only rehabilitated the degraded land, but also facilitated the development of employment-generating sericulture. 9.4

BENEFICIAL USE OF MINING WASTES

The volume of wastes generated in the process of mining increases with increased volume of mining activities, and increased mechanization. No-waste and low-waste mining technologies can in principle bring down the volume of wastes that need to be disposed of, but there is little doubt that wastes in mining cannot be avoided altogether. The use of waste rock for back-filling, recycling, and the large-scale use

236 Mineral resources management and the environment

of wastes for the construction of roads, buildings and other civil engineering structures are some of the ways by which the wastes can be used beneficially. Coal mining wastes: Taking the mining industry as a whole, there is little doubt that coal mining produces the largest volume of solid wastes. Mine gangue and coal-washing tailings are being increasingly used as filling materials, additives in concrete and for agricultural purposes. The gangue material in coal waste tips generally has a porosity of about 35%. The relatively high combustible content of the waste coupled with its high porosity, makes the waste liable for spontaneous combustion. It has been estimated that 40% of the 17,000 rock waste tips in the world, are burning. Smoke from the burning tips pollutes large areas around them. An ingenious way to reduce the porosity of the waste tips and thereby reduce their proneness for spontaneous combustion, is the addition of fly ash from the wastes of the thermal power plants. In this manner, one kind of waste is made use of to reduce the environmental harm from another kind of waste! After strengthening, the gangue material from the coal mining industry can be used in the construction of road embankments and railway lines, landscaping of building sites, and earth dams, etc. The porosity of the gangue is reduced and the strength increased by compaction with bulldozers, and addition of pore-filling materials, such as fly ash from power plants, sand, and flotation tailings. By this process, the porosity can be reduced to 20%, and the density increased to 2.1 t/m3. Clays with high content of organic matter can be used to make a material called karamzite. In Belgium and France, mine gangues and coal washing tailings are made use of to fabricate commercial building materials, trademarked AGRAL. The gangue material can also be made use of to make bricks, and as aggregates for light weight concrete. For instance, the brick-works of “Lvovstrojmaterialy” in Ukraine which produces 300 million bricks a year, found that the use of 10% coal wastes has reduced the consumption of fuel by 20–25%, besides improving the quality of bricks. The CSIR Laboratories in India (principally, the Central Building Research Institute, Roorkee, and the Regional Research Laboratory, Bhopal) have developed innovative approaches for the use of fly ash from the coal industry and red mud wastes from the aluminium industry (vide CSIR Rural Technologies, 1995, p. 83–88). Clay may be mixed with fly ash (to the extent of 10–40%) and made into bricks, which can then be fired in conventional Bull’s kiln, or intermittent type kilns at a temperature of 950 to 1050 °C. The use of fly ash permits the production of 40% more additional bricks from the same quantity of soil. The clay-fly ash bricks have lower bulk density, better thermal insulation and reduced dead load on the brick masonry structure. These bricks can be used for all types of construction, where normal clay bricks are used. In areas where good quality clay is not available, fly ash-sand-lime bricks can be made. Fly ash could be used to the extent of 70%. The bricks will have a wet compressive strength of 100–200 kg/cm and water absorption of 10 to 20%. Drying shrinkage (0.01–0.05%) and thermal conductivity are comparable to those of the clay bricks. Unlike the clay bricks, the fly ash – lime – sand bricks do not need drying.

Mitigation of mining impacts 237

The lime-fly ash blends can be used as stabilizers in road construction. For granular soils, 3–6% lime and 10–25% fly ash should be used. For clayey soils, 5–9% lime and 10–25% fly ash, need to be used. Bricks can be made with red mud wastes from the aluminium industry. Red mud improves the quality of bricks made from clay-deficient soils. When fired, bricks made with red mud develop a pleasing pale brown, orange or golden yellow colour, depending upon the composition of the raw material, and firing temperature. They therefore have a good architectural value as facing bricks. The presence of 4–5% alkalis in red mud makes for good fluxing action. Consequently, the red mud bricks have better plasticity and bonding than the normal bricks. They may be fired in the usual Bull’s trench kiln. Black coal flotation sludges can be dried to reduce their moisture content to 8 to 10%, and the resulting product can be burnt in the thermal power plants. Brown coal sludges are finding numerous uses in agriculture. When added to the soil, the humic acids contained in coal form organo-mineral humus and sorption complexes and becomes repositories of nutrient elements. This improves the structure, pH and fertility of the soil. In Russia, the combination of manure and high-ash coal (the so-called mineral manure) proved very successful. In Hungary, brown coal dust mixed with manure is used as a fertilizer. Coal waste can be used as bio-organic mineral fertilizer. Acid mine effluent often contains copper which can be recovered cheaply by treating the effluent with scrap iron. Methane generated in the underground mining can be collected and used to feed the boilers. Other kinds of mining wastes: Nepheline tailings in the production of apatite concentrates can be used in the production of glass, and as a binder for silica bricks. Wastes of chalcopyrite ore concentrates can be used for the manufacture of silicate wall and facing materials, glass, etc. Solid wastes from mining could be used as fillers in concrete and other cementbased materials (Moosberg, 2001). The following properties of the waste materials are tested in order to determine their suitability for the purpose: 1. Isothermal calorimetry measurements – they show the heat of hydration in fresh concrete and thus also the effect of the added byproducts, 2. Flowability – a rheology test that depends on material characteristics, 3. Strength measurements – how compressive and flexural strengths are affected by the addition of the filler, 4. Shrinkage and expansion – how the durability is affected. Three commercial quartz products from the mineral processing industry were chosen for the investigation. An examination of the relation between the water/ cement (w/c) ratio and compressive strength at 28 days showed that the more the filler replaced the aggregates, the higher the strength that was obtained (Fig. 9.6; source: Moosberg, 2001, p. 541). Harrison et al. (1999) report that mine soil fill material can be effectively used for the renovation of wastewater. Red mud waste is produced when bauxite is

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Figure 9.6 Water/cement ratio vs. compressive strength when quartz is used as a filler (source: Moosberg, 2001, p. 541).

processed to produce alumina, and is available in large quantities around the bauxite mines. It contains compounds of Al (22–37%), Fe (24–26%), Ca (2–4%), Na and Si. It has been found that red mud mixed with medium-sized sand is highly effective in removing P, BOD, suspended solids and faecal coliforms from domestic sewage (Brandes et al., 1975). Residential and municipal wastewaters contain numerous pathogens, such as enteric viruses (which can cause meningitis and hepatitis), bacteria (which can cause typhoid fever and gastroenteritis), protozoans (which can cause amoebic dysentery and giardiasis), and helminthes (which can cause a number of chronic diseases such as anaemia and gastroenteritis). Size-wise, the enteric viruses are the smallest, and the helminths the largest. Considerations of size enter the picture because the larger the organism, the more readily it is trapped and retained when wastewater containing the pathogen percolates through the soil. Consequently, the greater the percentage of fines (silt- and clay-sized particles) in the soil, the greater is its capacity to retain bacteria. Besides, the charged nature of bacteria and viruses facilitates their adsorption on soil constituents. As it is difficult to detect viruses in soils and waste disposal systems, the abundance of faecal streptococci, and faecal coliforms are used as indicators of pathogenicity. Excess amounts of NO 3 may be toxic to infants and young animals, and both NO and P promote eutrophication of surface waters. NH 3 4 concentrations have decreased to background levels after percolating through 76 cm of soil fill. The mine soil-fill has been found to be very efficient at removing PO 4 P from the wastewater. Wastewater could be applied at the rate of (say) 19.3 l/m/d on at least 0.76 m of mine soil-fill. Uniform distribution of effluent could be ensured by using lowpressure distribution or drip irrigation system (Harrison et al., 1999).

Mitigation of mining impacts 239

Tailings have been used in USA as bulk fill in highways, embankment material, as aggregate for sub-base and bituminous paving mixtures, in building bricks and blocks, and in the manufacture of low-grade glass (Collins & Miller, 1979). China’s largest gold producer, Shangdong Gold Group Co. Ltd, has recently commissioned a 4 million m3 tailings brick manufacturing plant – it is expected to generate annual profits of Yu 12 million and pay back the company’s investment in five years (Mining Journal, Aug. 18, 2000 issue). Zambia converted the abandoned open pits to fish ponds.

9.5

REUSE OF MINE WATER

Mine water is invariably highly acidic, besides containing undesirably high quantities of toxic metals (Table 9.4). There is severe scarcity of drinking water in the coalfield areas of eastern India. On one hand, the water-table has gone down to 200–250 m due to mining activities, thus making the tapping of groundwater prohibitively expensive. On the other hand, there is abundance of mine water, which, however, is not potable because of its high acidity, and the high content of metals, such as iron. The Central Mining Research Institute, (CMRI), Dhanbad, Bihar, 826 001, India, has developed a treatment process which is claimed to render the mine water potable (item 6.2.13, CSIR Rural Technologies, New Delhi, India, 1995). Filtration is done adjacent to the settling pond. Two filter beds are used to work alternatively at the time of changing the bed. A slow or rapid filtration may be employed depending upon the situation. A disinfectant is incorporated in the treatment process to destroy the pathogens. The presence of high iron content in groundwater is objectionable because of discoloration, turbidity, bad taste and tendency to form deposits in the distribution mains. The National Environmental Engineering Research Institute, Nagpur 440 020, India, developed a simple plant to remove iron from groundwater by precipitating the iron impurity as a ferric sludge (item 6.2.4, CSIR Rural Technologies, 1995). The plant is to be attached to a hand pump. It has a capacity of 2500 l/d (10-hr operation) and costs about USD 500. The plant has three chambers. “The water from the hand pump is sprayed over an oxidation chamber. The aerated water flows over baffle plates to a flocculation chamber and then to sedimentation chamber. The water then passes through plate settlers and to the filter from where the filtered water is drawn through a tap after chlorination”. The ferric sludge needs to be scoured out twice a month. 9.5.1

Treatment of mine water

Börjesson (2001) described a pilot-scale natural treatment system for the heavy metal drainage related to the alum shale tailings from Mount Billingen in southern

240 Mineral resources management and the environment Table 9.4 Range of chemical characteristics of raw mine water from lead and zinc mines (source: Hustrulid, 1982). Parameter

Mines with acidic characteristics (concentrations in mg/l)

Mines without acidic characteristics (concentrations in mg/l)

pH (units) TSS * COD ** Oil & grease P Ammonia Hg Zn Cu Cd Cr Mn Fe Sulphate Chloride Fluoride

3.0–8.0 2 to 5.8 15.9 to 95.3 0 to 3 0.002 to 0.075 0.05 to 4.0 0.0001 to 0.0013 1.38 to 38.0 0.02 to 0.04 0.016 to 0.055 0.17 to 0.42 0.02 to 57.2 0.12 to 2.5 48 to 775 0.01 to 220 0.06 to 0.80

7.4–8.1 2 to 138 10 to 631 3 to 29 0.03 to 0.15 0.05 to 1.0 0.0001 to 0.0001 0.03 to 0.69 0.02 0.002 to 0.015 0.02 0.02 to 0.06 0.02 to 0.90 37 to 63 3 to 57 0.3 to 1.2

* Total Suspended Solids; ** Chemical Oxygen Demand.

Figure 9.7

Natural treatment system for mine water (source: Börjesson, 2001, p. 53).

Sweden. The natural treatment system consists of the following components: aeration steps, sedimentation pond, sludge separator, pre-treatment filter, passive filter and an infiltration area (Fig. 9.7; source: Börjesson, 2001, p. 53). The sedimentation pond (8 m  12 m) was dug with slopes of 1 : 4. The bottom of the pond is covered with an impermeable mat to prevent infiltration. The pre-treatment filter consists of coarse gravel (25–32 mm). A geotextile mat was placed on the top of the drainage layer. As natural peat is an excellent scavenger of metals, it is used for the filter. The test run shows that there is complete removal of iron and arsenic. The reductions in zinc, cobalt and nickel were of the order of 50–65%, whereas the reduction of uranium was lower (36%). Improvements are being made in the natural treatment of mine water.

Mitigation of mining impacts 241

Figure 9.8

Water process scheme in Tara mines, Ireland (source: UNEP, 1991, p. 33).

Mine water, surface runoff, tailings from the beneficiation plant, etc. can be collected at one point, for possible treatment before release to the environment. Figure 9.8 (source: UNEP, 1991, p. 33) gives the water process scheme in Tara mines in Ireland. Figure 9.9 (source: UNEP, 1991, p. 54) gives the flow diagram of the treatment of acidic seepages at Noranda’s Waite Amulet mine. Sludge from the clarifier (about 4% by weight solids) is permanently disposed of in sludge drainage beds underlain by sands.

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Figure 9.9

9.5.2

Treatment of acidic water at Noranda’s Waite Amulet mine (source: UNEP, 1991, p. 54).

Lime neutralization and high-density sludge processes

Lime neutralization is the most effective process to remove metals such as Fe, Zn, Al, Cu, Mn, Cd, Co and Pb, and sulphate from the mining and metallurgical effluents.  2 Me2  SO2  3OH → Me(OH)2  CaSO4  H2O 4  H  Ca

(9.1)

The resulting precipitate, which consists of metal hydroxides and gypsum, is called the “sludge”. Lime may be used as quicklime (CaO) or hydrated lime (Ca(OH)2). Constituents such as arsenic, mercury and cyanide could be removed by a modified lime neutralization process. Depending on site factors, lime neutralization can vary greatly in sophistication, from basic to HDS (High Density Sludge) process. Figure 9.10 shows four types of lime neutralization, including Type-IV stage HDS

Mitigation of mining impacts 243

Figure 9.10 Lime neutralization method involving HDS (High Density Sludge) (source: Kuyucak et al., 2001, p. 356).

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Figure 9.11 The layout of the HDS treatment plant at Kristineberg mine, Sweden (source: Kuyucak et al., 2001, p. 360).

Figure 9.12 Two-stage treatment of Aznalcollar pit water, Spain (source: Kuyucak et al., 2001, p. 373).

neutralization method for neutralizing acid water using more than one reactor (source: Kuyucak, 2001, p. 356). The layout of the HDS treatment plant in the Kristineberg mine site is given in Figure 9.11 (source: Kuyucak et al., 2001, p. 360). All tanks, except the polymer preparation tanks, are made of mild steel covered with epoxy paint. Since the clarifier is the most expensive part of the plant, the size of the clarifier has been kept as small as possible. During the grinding and flotation of complex sulphide ores in alkaline media, oxidation of sulphide minerals produces a series of sulphur oxyanions, collectively called “thiosalts”. Figure 9.12 (source: Kuyucak et al., 2001, p. 373) shows the twostage process whereby the thiosalts in the Aznalcollar (Spain) pit water have been oxidized using H2O2, and the final treatment involving lime neutralization.

CHAPTER 10

Socio-economic dimensions of the mining impact

Collection, treatment and disposal of wastes (particularly industrial wastes), and remedial action in regard to land contaminated by such wastes, constitutes the most serious problem that the industrialized countries face (good part of the annual budget of USD 7–8 billion of US EPA is devoted to the rehabilitation of the waste sites). Most countries have laws to regulate the environmental impact of industries, including the mining industry. Mine operators should familiarize themselves with the environmental regulations as applicable to their facility. They should be able to recognize whether any non-compliance with the regulations is occurring in day-today operations, and if so how to remedy the situation. This is necessary to protect the company from being penalized by the regulating agency, and/or public interest litigation. Regulatory requirements continue to be made more and more stringent, as the public are increasingly concerned with the quality of environment as an integral part of the quality of life. The going is not expected to be easy for the mining industry, with its image as a gross despoiler of environment. The dilemma facing the society and the government is how to balance the need for resource development with the need for conservation and protection. Wisdom therefore lies in designing reasonable and sensible trade-offs among the interested parties. The International Standards Organization (ISO), Geneva, has issued a document (ISO 14001) setting up of standards to be followed by the mining industry. Appendix E gives the Environment Management System (EMS) that is consistent with ISO 14001.

10.1

ENVIRONMENTAL IMPACT ASSESSMENT

The main environmental consequences of the mining projects are shown in Figure 10.1 (source: UNEP Tech. Rept. No. 5, 1991, p. 84). Environmental Impact Analysis (EIA) may be described as a process for identifying the likely consequences for the biophysical environment and for man’s health and welfare while implementing particular activities, and to convey this information to the decision makers (Wathern, 1989, p. 6). EIA has been made the

246 Mineral resources management and environment

Figure 10.1 Main environmental consequences of mining projects (source: UNEP Tech. Rept. No. 5, 1991, p. 84).

requirement under the provisions of the US National environmental Policy Act (NEPA) of 1969. Many industrialized countries followed suit, and in July, 1985, the European Community formally made EIA mandatory for certain categories of projects, including Extractive Industry, Energy Industry, Production and preliminary processing of metals, Manufacturing of non-metallic mineral products, Chemical Industry, Metal Manufacture, etc. In almost all countries, EIA is obligatory for the whole range of industries covering mining, treatment, transportation, processing, etc. of ores. The procedure for Environmental Impact Assessment in the coal mining industry is shown in Figure 10.2 (source: Chadwick et al., 1987, p. 150). An Environmental impact may be defined as a change in the environmental parameters, over a specified period, and in a specified geographical area, resulting from a particular activity compared to the situation which would have existed had the activity not been activated. EIA may be considered as a data management process, with three components: (1) Identification and if possible, collection of appropriate information necessary for a particular decision to be taken, (2) projection of changes in environmental parameters arising from the implementation of the project, compared with the situation that could exist without the proposal, (3) recording and analysis of actual change (Wathern, 1989, p. 17). Nijkamp (1980) proposed a framework for integrating the environmental analysis with economic and social issues. The term “scoping” entered the EIA picture in 1979 as a result of the regulations under NEPA of USA. Lead agencies are required to undertake “an early and open process for determining the scope of the issues to be addressed and for identifying the significant issues related to the proposed action”. According to Beanland and Duinker, scoping may be defined as a “very early exercise in an EIA in which an

Socio-economic dimensions of the mining impact 247

Figure 10.2

Procedure for EIA in the coal mining industry (source: Chadwick et al., 1987, p. 150).

attempt is made to identify the attributes of the components of the environment for which there is public (including professional) concern upon which EIA should be focused”. There has been a great deal of litigation and public campaigns in USA and European Community countries, with regard to scoping.

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10.1.1

Matrix diagrams

The EIA process starts with the “screening” of the projects for their likely consequences. This is followed by “scoping” which is concerned with the identification of the main issues that should be examined. The matrix diagram is one of the most useful aids available for the EIA process. The purpose of the matrix diagram is to identify which environmental parameters will be affected by the activities of the project and to what extent. All human activities that the project would involve are listed along one axis, and all natural factors that are likely to be affected as a consequence of such activities are listed on another axis. Thus, if there are x number of human activities, and y number of environmental factors, there will be xy number of matrix slots. All slots corresponding to the recognized impacts are first slashed. Evidently, all impacts would not be of the same magnitude. So the magnitude of impact in the scale of 1 (least impact) to 10 (greatest impact) is indicated in each slashed slot. Figure 10.3 (source: UNEP Tech. Rept. No. 5, 1991, p. 83) is a matrix diagram which enables the visualization and estimation of how various mining activities, such as, exploration, opencast mining, underground mining, ore processing, tailings,

Figure 10.3 Matrix diagram for the visualization of mining impacts (source: UNEP Tech. Rept. No. 5, 1991, p. 83).

Socio-economic dimensions of the mining impact 249

rehabilitation of the mined land, etc. in regard to a given mining project have impacts in terms of social environment, physical environment and biological environment. Matrix diagrams are undoubtedly useful, but they suffer from the shortcoming that they cannot bring out the linkages and interactions between various environmental parameters. The environmental effects of mining, such as the release of the pollutants, degradation of the landscape, disturbance in the habitat, etc. are inter-related. Consequently, change in one particular environmental component (e.g. process technology) will often cause direct and indirect changes in other components (e.g. tailings disposal). So it is necessary to adopt a holistic approach in the EIA process. “EIA is a dynamic process of examination, review and reformulation of project options until a consistent view emerges as the likely impact of the various options” (UNEP Tech. Rept. No. 5, 1991, p. 78). Four key steps are involved in this cyclic process: (1) Identification of the kind of consequences that the project could lead to, (2) Prediction of the extent of changes in the environmental parameters that could arise from the project, (3) Evaluation of the significance of the changes, and (4) Mitigation of the environmental impact. EIA documents are usually prepared by multi-disciplinary teams. The personnel involved should have both environmental expertises, as well as technical knowledge of the project itself. They should evaluate various techno-socio-economic options, and come up with their recommendation for the most practicable option. The EIA for a mining project should include a detailed description of the project, projected development of the area and sites for waste disposal. Particular attention should be paid to the location and design of the tailings ponds to take care of potential overflows and runoff of rainwater. Remedial measures, such as control of AMD, rehabilitation of the mined land, and mine closure, should be planned for, and integrated into the mine plan. 10.1.2

Environmental monitoring

Environmental monitoring serves several useful purposes. It is necessary to have baseline information about the environment before the operations begin. By periodical monitoring, it would be possible to measure the impact of the operations on the quality of air and water (surface and underground), chemical contamination of soils, impact on fauna and flora and biodiversity, impact on human and animal health, etc. This kind of monitoring would enable the mine management to pinpoint the source(s) of environmental degradation – such as, poor performance of the treatment plant, inadequacy of facilities for the collection of dust and gases, unsafe waste disposal, poor maintenance of the safety equipment, etc.. Monitoring has also an economic angle. For instance, an examination of the chemical composition of the wastewater could indicate whether any valuable raw material or refined material (e.g. gold) is being lost due to inefficient process technology. This would permit appropriate changes to be made in the process chemicals and flowsheet.

250 Mineral resources management and environment

A mining company should have an environmental policy and a management plan, to ensure that the key impacts are effectively minimized. A management structure needs to be created whereby the environmental and production personnel work harmoniously together. The company should maintain transparency in liaising with the media, public and governmental agencies. Accidents do happen in mining, but they involve the mineworkers. They do not normally endanger the general population. But there are instances, such as, the failure of the tailings dams, which affect the whole community. When such failure occurs, the public should be immediately informed about the ways to cope with the emergency. For this purpose, UNEP Industry and Environment Programme in Paris has developed systems for APELL (Awareness and Preparedness for Emergencies at the Local Level). 10.1.3

Issues to be addressed by EIA

The issues that need to be addressed in EIA are summarized as follows (source: The World Bank, as quoted by UNEP Tech. Rept. No. 5, 1991, p. 81). The list is reasonably comprehensive, but not exhaustive. 1. Natural hazards: Whether the area is affected by natural hazards, such as floods, volcanism, earthquakes, tidal waves? If so, what is the extent of risk, and what specific measures need to be taken to be prepared for them, and minimize the damage from them? 2. Biological diversity: Will the project threaten the endangered plant and animal species, critical habitats and protected areas? 3. Tropical forests: Will the project degrade the tropical forests? What steps need to be taken to protect and manage the flora and fauna, and provide compensation to those affected by it? 4. Wetlands: If there are wetlands (including estuaries, lakes, mangroves and other swamps or marshes) in the area, what steps will be taken to avoid damage to them? 5. Coastal and marine resources management: How will the project be designed to protect coastal resources, including coral reefs, mangroves, and wetlands? 6. Watersheds: If there are dams, reservoirs, or irrigation systems in a watershed where the mining will be undertaken, how will the project assist in protecting and managing them? 7. Land settlements: How will the mining project involve changes in the patterns of land use? What steps are envisaged to harmonies the physical, biological, socio-economic and cultural issues involved in land settlement? 8. Mining hazards: Does the project design include the prevention and management of hazards (such as rock bursts, roof collapse, methane emissions, etc.)? 9. Hazardous and toxic materials: If the project involves the use or production of hazardous and toxic materials, how will it be ensured that they are used, transported, stored and disposed in a safe manner?

Socio-economic dimensions of the mining impact 251

10. Cultural properties: How will the project protect archeological sites, historical monuments or religious shrines in the area? 11. Tribal people: How would the project affect the traditional rights (such as, hunting, forest and water rights) and way of life of the tribal people? Will the project result in induced development (secondary growth of settlements and demand for infrastructure)? 12. Transboundary effects: Will the project have any transboundary impacts in regard to water and air, movement of wildlife, etc.? 13. International treaties and agreements: Will the project have any impact on the existing or pending international agreements on environment, natural resources, quality and quantity of water flows, navigation on international waterways, etc.? 10.1.4

Outline of EIA

A sample outline of the Environmental Assessment Report is as follows (source: The World Bank, as quoted by UNEP Tech. Rept. No. 5, 1991, p. 82). Environmental Assessment Reports should be concise, and limited to the environmental issues of direct concern to the project. The level of detail provided in regard to a given item, should be commensurate with the importance of the item. The Reports are aimed at project designers, project decision-makers and project financing agencies. 1. Executive summary: A summary of significant findings and recommended actions. 2. Environmental regulations: The policy, legal and administrative framework in which the project will be implemented. This is particularly necessary in the case of projects, which are co-financed by institutions from different countries with different legal requirements. 3. Project description: This constitutes the core of the document. It should cover the technical, geological, geographic, ecological, economic, social, cultural, etc. dimensions of the project. It could include particulars regarding roads, pipelines, power plants, water supply, and housing, storage facilities that are relevant to the project. 4. Baseline data: Description of the relevant biophysical (quality of water, soil, air, land use, etc.) and socioeconomic (cost of living, quality of life, etc.) situations at the time of the commencement of the project. 5. Analysis of alternatives: Alternatives to the proposed project, including the option of “No action”. Potential environmental impact, capital and recurring costs, institutional capacity building, personnel and monitoring requirements for all the options of design, site, technology and operational alternatives. 6. Environmental impacts: The negative and positive impacts likely to result from the proposed project, and comparison with alternatives. An assessment should be given of the quality of the available data, additional key data that are needed, estimates of uncertainties and confidence limits for predictions, etc.

252 Mineral resources management and environment

7. Mitigation plan: Scenarios for possible techno-socio-economically viable measures of mitigation, so that the environmental impact could be brought down to acceptable levels. If compensation is recommended to be granted where mitigation cannot be implemented effectively, an estimate of such a compensation should be indicated. 8. Monitoring plan: Description of the technical, managerial and administrative structure for the monitoring activities to ensure compliance with environmental regulations. The monitoring may be carried out by an individual or an agency. The cost estimates and other requirements, such as training, should be provided. 9. The following Appendices should be provided: (1) Personnel and organizations involved in the environmental assessment, (2) Persons and organizations contacted, including their addresses, telephone and fax nos., e-mail etc., (3) References to written material used in preparation (published papers, unpublished/openfile documents, etc.), (4) Record of interagency/forum meetings: This includes the list of invitees as well as persons who actually attended. Summary of the discussions.

10.2

ENVIRONMENTAL REGULATIONS

Almost all the countries have environmental regulations. In the case of some developing countries, the regulations just remain on paper, for the simple reason that the state does not have either the equipment or skilled personnel to monitor the environment, and enforce the regulation by penalizing the polluter. This is particularly so in the case of some organic pollutants, which are toxic even in extremely small concentrations, but which are very expensive to measure. The US Congress passed a number of Acts to regulate the environment. The following is the summary of environmental regulations, which are relevant to the mining industry (see Sengupta, 1993, p. 29–31). In 1980, the US Congress passed the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA), better known as Superfund, to address the issue of the collection, treatment and disposal of wastes (particularly industrial wastes), and remedial action in regard to land contaminated by such wastes. This regulation is based on “Polluter Pays” principle. A related regulation is the Resource Conservation and Recovery Act (RCRA). Under the provisions of CERCLA – RCRA regulations, liability for cleanup costs and damages accrue not only to the current owners but also to former owners and lenders. Under the provisions of these Acts, US EPA could call for a Remedial Investigation – Feasibility Study (RI-FS) or Resource Conservation Investigation (RCI). CERCLA has prescribed procedures for the immediate cleanup of hazardous waste contamination, accidental spills or chronic contamination (from abandoned mines or hazardous waste disposal sites). Under the provisions of CERCLA, US EPA

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has promulgated regulations making it mandatory to report concentrations of hazardous substances in the environment (water, soil, air, etc.) beyond the allowable limits. The Superfund Amendments and Reauthorization Act (SARA) have two main components. Subtitle A is concerned with the setting up of a state emergency response commission to handle emergencies. Subtitle B requires certain facilities to provide information to the prescribed official authorities, the type, amount, location, use, disposal and release of specified chemicals. Section 311 applies to facilities covered by the Occupational Safety and Health Act. Section 312 establishes the list of toxic chemicals whose emissions must be reported by the facilities meeting certain criteria. The RCRA Hazardous Waste programme deals with all aspects of management of hazardous wastes. The companies, which treat, transport, store, and dispose such wastes, have to get permits for the purpose, and comply with the standards. The Clean Air Act (1971) provides the framework for air quality control. Under the provisions of the Act, EPA prescribed two sets of air quality standards: primary standards which are meant for the protection of human health, and secondary standards which refer to the ambient levels considered safe for the environment (plants, materials, etc.). The Clean Water Act (1972) envisages the maintenance of freshwaters in “fishable and swimmable” condition. The Act covers both point sources (such as industrial discharges) and non-point sources (such as mining) that cause runoff into streams. EPA regulates the point sources through NPDES (National Pollutant Discharge Elimination System) permits, which requires the dischargers to comply with effluentbased standards for criteria pollutants. States are responsible for the control of nonpoint sources, through appropriate land use regulations. The attainment of the water quality standards of both point and non-point sources was sought to be monitored through the TMDL (Total Maximum Daily Load) approach which is based on various chemical, physical and biological criteria (incidentally, the author had the privilege of reviewing in the journal, Eos of AGU, Dec. 25, 2001, a document prepared by NRC at the request of US Congress, entitled, “Assessing the TMDL Approach to Water Quality Management”, National Academy Press, Washington, D.C., 2001). The Safe Drinking Water Act (SDWA) is meant to protect public health through the conservation and regulation of supplies of drinking water. Under this Act, EPA established a series of drinking water standards to protect public health. These standards are revised as new data become available (for instance, the Maximum Contaminant Level prescribed by EPA of arsenic in drinking water, 50 g/l, is in the process of being reduced to 10 g/l). As defined, the EPA regulations are applicable to industrial establishments, which have more than 25 employees. SDWA empowers EPA to protect usable aquifers from contamination by leachates from hazardous wastes, toxic effluents, and underground injection of brines, etc. which arise from the mining industry. The Toxic Substances Control Act (TSCA) gives authority to EPA to regulate the chemical substances that are entering or have entered the environment. It strengthens

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the existing toxic substance regulations (such as sections 112 and 307 of the Clean Water Act and Section 6 of the Occupational Safety and Health Act). Section 6(a) of TSCA empowers EPA to take steps to phase out PCBs.

10.3

ENVIRONMENTAL AUDITS

Environmental auditing involves not only the biophysical monitoring of the environment, but also the monitoring of the administrative and managerial factors. An assessment is made as to whether the environmental control personnel are performing their jobs (e.g. chemical analytical services) efficiently, whether the company policies and directives are being implemented competently, etc. Thus the environmental audit enables the company to determine whether the environmental control is cost-effective, and whether the emissions and effluents are in compliance with the regulations. All industries, including the mining industry, are required to provide a detailed account of how they propose to address the projected environmental impact of their operations, to ensure compliance with the environmental regulations regarding the emissions. The regulatory agencies (such as, the US Environmental Protection Agency) make use of the environmental audits to ensure that the companies comply with the environmental regulations (regarding, say, the waste emissions and effluents). Philbrook (1991) gave an account of the different kinds of environmental audits, which could be tailored to suit the requirements of a mining company. The following summary is reproduced from Sengupta (1993, p. 32): Site assessment audits: This consists of a thorough examination of previous and current environmental hazards and physical conditions on or surrounding facility-site. Its purpose is to assess potential on-site problems or sources of external encroachment, contamination, or threat. This audit includes measures to remediate or reduce such problems before they affect the operations. A site assessment audit is particularly useful as a planning and predevelopment decision-making tool for suspected problem sites. It is necessary before property transfer or asset sale/acquisition. Permit performance audits (compliance and monitoring): This is a review of the environmental quality assurance plans, environmental permits, and agency-required operating instructions–procedures. It assesses possible or actual nonconformance (especially regarding air and water emissions and hazardous materials management). This type of audit also interprets regulatory agency permit conditions and suggests measures for ongoing permit conformance. It may also involve long-term monitoring of environmental activities. Regulatory requirement audit: This provides a detailed evaluation of facility operations that are or may be governed by local, state and federal environmental regulations. It identifies applicable regulations to pinpoint potential noncompliance or conflict with such regulations. Procedures are also recommended for coming into compliance.

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Environmental management practice audits: This type of audit examines the existing management structure, procedures and policies used by the client to implement environmental compliance and to communicate environment-regulatory awareness (including health and safety) to work-force personnel. Recommendations are also provided for remediation of deficient practices. Technical processes-practices audits: Production practices and facility conditions are reviewed to determine whether design or practice modifications should be made to accomplish specific environmental goals (such as, minimizing hazardous waste, waste stream treatment, or technology transfer). Risk management audits: Practices, procedures and policies are surveyed to identify sources of risk. It suggests how risks of environmental (health and safety) incidents, accidents, and liability exposure can be reduced or eliminated. A risk management audit may also include a formal risk assessment study or contingency planning component. Special purpose audit: This is a one-time audit conducted in response to unusual circumstances or requirements, such as an EPA consent decree, determination of insurance-liability impairment, or emergency response plan. Phase-one site assessment audit will help the regulatory agency to determine whether any contamination problems could be expected from the proposed mining activity. Site audit would be useful to the present and future property owners and the lender to reduce their financial exposure, under the terms of CERCLA – RCRA investigations. Phase-two and phase-three assessments are more detailed and deal with the alternatives for remedial action. Phase-three audits are performed as a consequence of regulatory requirements.

10.4

ENVIRONMENTAL CODE – THE SWEDISH MODEL

Very few countries in the world care for the quality of the environment as Sweden does. The Swedish Environmental Code, which came into force on January 1, 1999, is almost unique in the world in its perception of sustainable development and ways and means of achieving it. It is explained here in some detail as it sets a good example for other countries to follow. The Code is based on the premise that the right of humans to alter and utilize nature is linked to the responsibility to protect nature (Carlsberg, 2001). It seeks to achieve the following fifteen environmental quality objectives: (1) Clean air, (2) High-quality groundwater, (3) Sustainable lakes and watercourses, (4) Flourishing wetlands, (5) Balanced marine environment and sustainable coasts and archipelagos, (6) No eutrophication, (7) Natural acidification only, (8) Sustainable forests, (9) A varied agricultural landscape, (10) A magnificent mountain landscape, (11) A good built environment, (12) A non-toxic environment, (13) A safe radiation environment, (14) A protective ozone layer, and (15) Limitation of climate change.

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A precautionary approach which is linked to the burden of proof, underlies all the provisions of the Code. This is designed to ensure that whatever activity is to be carried on by an operator, will not result in any environmental harm. Before the operation starts, the operator has to prove that he has the required knowledge to determine the environmental effects that may arise from his activity. He will also have to spell out the preventive measures that he will take in order to avoid damage to human health and environment. If an activity can be carried out at different locations, the location that allows the activity to have minimal environmental impact must be chosen. The Code also stipulates that all operations must conserve raw materials and energy and utilize all opportunities for reuse and recycling. The use of hazardous chemicals must be avoided. Every effort should be made to replace hazardous chemicals by harmless chemicals. The liability for remedying polluted sites rests with the operator (“polluter pays” principle). Environmental Impact Assessment has to be done statutorily to help in decision-making. A novel feature of the Environmental Code is the provision for environmental courts. There are regional environmental courts located in five cities in Sweden, and a court of appeal. The Supreme Court is the final arbiter. The provisions of the Minerals Act are implemented in conjunction with the Environmental Code. The Code introduces a new charge, called Environmental Sanction Charge, which has to be paid by the operator who has violated the regulations of the Code. It makes no difference whether the violation is intentional or accidental, or whether the operator got any benefit from the violation.

10.5

INTERNATIONAL INITIATIVES

All mining companies are signatories to the UNEP’s International Declaration of Cleaner Production. In June 2000, UNEP set up the Global Reporting Initiative (GRI) Sustainability Reporting Guidelines, to which all the mining companies agreed to adhere. The vision of UNEP (Hoskin, 2001) to achieve environmentallysustainable mining industry in the early part of the twenty-first century, has the following components: 1. Recycling of metals should approach 100% – recycling of metals reduces disposal pressures, and results in great energy savings. The limited amount of virgin metal that may be needed should be obtained from highest-grade reserves. 2. Technological improvements: (1) Application of remote sensing and hydrospectral analysis in exploration, and monitoring of tailing impoundments, closed mines, and compliance with environmental regulations, (2) minimization of mine wastes, reducing air and water pollution to essentially zero level, and fabrication of lighter, stronger and more durable materials, and secondary recovery of useful materials from mine wastes, (3) Remediation of abandoned mine sites to increase arable land for agricultural production.

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3. One of the major sources of accidents in the mining industry is the failure of tailings’ dams (vide Appendix D). This problem can be mitigated by (1) new technologies to dewater waste slurries – production of paste-consistency material from mill tailings, (2) A thorough analysis of all the design components including site selection, drainage systems, impoundments, measurements and inspections needed with respect to water balance, taking into consideration unusual conditions arising from rain, ice and snow and seismic activity. 4. Training and assistance to small-scale miners, particularly in Africa, Asia and Latin America, to improve the commodity recovery, reduce environmental damage, and improve local health and safety conditions. Phasing out of the use of mercury in artisanal gold mining. 10.5.1

Mining industry in the context of globalization

The process of globalisation involves movement of investment, technologies and expertise where they can get the best returns. Globalisation has created new stresses, which can only be solved by international cooperation (for instance, trade in endangered species cannot be controlled effectively by a country, if open markets existing in other countries provide attractive incentives for their exploitation). Globalisation has created both challenges and opportunities for the mining sector. Opinion Polls show that mining companies have about the same kind of negative image as (say) the tobacco companies. This has profound economic implications, such as, whether the best graduates would choose the mineral industries as a career, whether investors would choose to hold mining stocks, whether markets are open or closed for mineral industries, how hard it is to get concessions or permits, and so on. The Mining Minerals and Sustainable Development (MMSD) project is sponsored by about thirty leading mining companies, and a variety of labour, environmental, governmental and international organizations, with the objective of bringing about sustainable development in the minerals sector. Danielson & Leyton (2001) suggest an international framework for cooperation for sustainable development in the mining sector, based on voluntary initiative. This initiative will define (1) “norms” (such as, guidelines, standards, code of conduct, etc.) that can define the level of practice which we seek to achieve, (2) “Facility” – an organizational structure to serve as forum, develop norms, determine compliance with norms, etc., and (3) Incentives and Consequences – which constitutes an expression of corporate social responsibility. The European Union and associated countries have set up Ore Mining and Environmental Technology Information Network (OMENTIN) project to raise the public awareness and understanding of ore mining. 10.6

TOTAL PROJECT DEVELOPMENT – A VISIONARY APPROACH

The Total Project Development (TPD) is a new holistic approach to mining (Struthers, 2001, p. 814–823). Under this approach, a mining project is developed

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as a part of much wider, multi-activity regional development. All the material extracted by a mining company is put to productive use. Waste rock, mine tailings, excess mine water, etc. are used as raw material for a variety of downstream ancillary industries. Tailings are used for underground backfill, embankments and sealants for reactive waste rock, and production of construction materials for mine use. All excess tailings are used for “soil” development. Excess process water (after use in recycling) is treated for being used in fish farm ponds and crop irrigation. The TPD approach benefits the various entities in the following ways: 1. Mining company benefits from (1) increased metal recoveries and additional revenue through the retrieval and sale of non-target minerals, (2) reduced operational expenses through the maximum utilization of tailings in backfill, preparation of tailings/concrete blocks for underground and surface constructions, and replacement of topsoil, (3) reduced mining costs by saving on the construction of tailing ponds and waste rock dumps, (4) reduced rehabilitation costs, and (5) income from productive use of post-mine land use. The mining company would also have some intangible benefits such as good public image, making it easier to get the required environmental permits. 2. The local community benefits from increased employment and income levels, long-term food security and livelihood after the closure of the mine. The improved infrastructure helps in communications, and access to wider markets. TDP benefits the environment through the elimination of waste rock dumps, drastic reduction in AMD and contamination from dust, heavy metal contamination of soil and water, etc. As Struthers (2001) pointed out, most companies have been practicing some element or other of the TDP. What is needed is to plan and implement all the components of TDP for every mine, through the cooperation of the government, mining companies, local communities, and technical experts (such as, engineers, mineral economists, etc.).

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Appendix A

Prefix names of units of multiples and submultiples. Prefix

Symbol

Factor by which unit is multiplied

Exa Peta Tera Giga Mega Kilo Hecto Deka Deci Centi Milli Micro Nano Pico Femto Atto

E P T G M k h dk d c m  n p f a

1018 1015 1012 109 106 103 102 101 101 102 103 106 109 1012 1015 1018

Base units in Systéme International (SI). Property

SI unit

Symbol

Length Mass Time Electric current Temperature Amount of substance

Meter Kilogram Second Ampere Kelvin Mole

m kg s A K mol

In this book, t means tonne (106 g  103 kg). When m is used as a prefix (as in mg  milligram, or mmol  millimole), it means milli (103). When m is used as a suffix (as in 97.8 m), it means meter. M means million.

266 Appendix A

Physical quantity Name of SI unit

Symbol for SI unit Definition of unit

Force Pressure Energy Power Frequency

N Pa J W Hz

Newton Pascal Joule Watt Hertz

kg m s2 kg m1 s2 (Nm2) kg m2 s2 kg m2 s3 (Js1) s1 (cycles per second)

Conversion of older units into SI units. Quantity

SI unit

Old unit

Value of old unit in SI unit

Force Pressure Energy

Newton (N) Pascal (Pa) Joule (J)

Dyne Atmosphere Calorie

105 N 101.325 kPa 4.184 J

1 bar  105 Pa  106 dynes/cm2  750 Torr  0.98692 atm  14.504 lb/in2 (psi: pounds per square inch). 1 MN/m2  1 N/mm2  1 MPa  approx. 145 psi; 1 Mg m3  62.4 pcf (pounds per cubic foot). Some commonly used units (in relation to SI base units). Property

Unit

Symbol

Charge concentration

Moles of charge per cubic meter Moles per cubic meter Farad Couloumb Volt

molc m3 mol m3 F C V

m2 kg1 s4 A2 As m2 kg s3 A1

Siemens per meter

S m1

m3 kg1 s3 A2

Joule Newton Kilogram per cubic meter Moles per kilogram of solvent Pascal Moles of charge per kilogram of adsorbent Hectare per kilogram Newton-second per square meter

J N kg m3 mol kg1

m2 kg s2 m kg s2

Pa mol c kg1

m1 kg s2

ha kg1 N s m2

104 m2 kg1

Concentration Electric capacitance Electric charge Electric potential difference Electrolytic conductivity Energy Force Mass density Molality Pressure Specific adsorbed charge Specific surface area Viscosity

SI relation

Appendix A 267

Values of some important physical constants. Constant

Symbol

Value

Atomic mass unit Avogadro constant Boltzmann constant Diffuse double-layer parameter(at 298.15 K) Faraday constant Molar gas constant

u NA kB b

1.6606  1027 kg 6.022  1023 mol1 1.3807  1023 J K1 1.084  1016 m mol1

F R

9.6485  104 C mol1 8.3144 J K1 mol1

Useful conversion coefficients: 1 BTU (British Thermal Unit)  1.055  103 Joules (J) 1 erg  1 dyne/cm  2.39  108 calorie  1  107 Joule  9.4805  1011 BTU Fuel value of 1 m3 of fuelwood  9.4 gigajoules (GJ); 1 t of coal  28.9 GJ 1 ton of oil  41.7 GJ  1.44 t of bituminous coal 1 million tonnes coal equivalent  1 million tonnes of coal at 28.0 MJ/kg, or  6692 kcal/kg gross calorific value. 1 t of coal at 25.1 MJ/kg or 6000 kcal/kg can produce 7.5–9.0 t of cement, 1 t of coal at 25.1 MJ/kg or 6000 kcal/kg can produce 2400 kwh of electricity. A 1000 MW power station would require annually 3 Mt of coal, at 25.1 MJ/kg. 1 t of coal with 28.0% volatile matter, after coking, will reduce approximately 1.5 t of iron. 1 micron (m)  106 m  104 cm  103 mm  104 Å 1 Ångstrom (Å)  104 m  108 cm  1010 m; 1 nm  109 m  10 Å 1 metre  100 cm  1000 mm  3.2808 ft  1.0936 yd 1 sq. metre (m2)  10.764 sq. ft  1.196 sq. yd. 1 cubic metre  1 m3  106 cm3  35.31 cu. ft  1.308 cu.yd 1 hectare (ha)  100 m  100 m  104 m2  2.47 acres 1 sq. km (km2)  100 ha  247 acres; 1 acre  4840 sq. yd  4046.8 m2 1 cu. km (km3)  105 ha. m; 1M ha m  10 km3; 1 ha.m  8.1 acre-ft 1 acre-ft  0.1235 ha.m  1235 m3; 1 Maf (million acre-ft)  1.235 km3 1 L  1 dm3  103 m3; 1 m3  103 L  106 mL 1 US gallon  3.875 L; 1 Imperial gallon  4.546 L 1 barrel (crude oil)  42 U.S. gallons  35.80 Imp. Gallons  162.75 L 1 acre-ft  326,000 gallons 1 m3 s1  0.03156 km3 y1; 1 km3 y1 31.68 m3 s1 1 Ld 1  0.365 m3 y1; 1 m3 y1  2.74 L d1 1 L s1  15.48 gpm (gallons per minute); 1 gpm  0.0646 L s1

268 Appendix A

1 tonne (t)  103 kg  106 g; 1 kg  2.2046 lb  32.150 oz 1 troy.oz  31.10348 g  20 pennyweights (dwt)  480 grains  1.0971 av.oz 1 pennyweight (dwt)  1.5517 g  24 grains 1 part per million (ppm)  106 g g1  1 g t1  0.032 oz t1  0.644 dwt t1 1 part per billion (ppb)  109 g g1  1 mg t1 K  T °C  273.15 1 year  365.25 days  8,766 hours  5.26  105 min  3.156  107 sec 1 day  24 hours  8.64  105 sec.

Appendix B

Particulars of metal mines in the world with production of
1.0 Mt/y (source: Mining Magazine, Jan. 2000). Capacity A:
7.0 Mt/y; B: 3.0–7.0 Mt/y; C: 1.5–3.0 Mt/y; D: 1.0–1.5 Mt/y; Methods OP: open pit; UG: underground. Name

Province

Methods Capacity Products

Canada Bouchard-Hebert Brewery Creek Brunswick Carol Lake Copper Cliff North Copper Cliff South Creighton Dome Doyon Golden Giant Huckleberry Kidd Creek Lac de Iles Levack Louvicourt McGreedy East Mount Polley Mount Wright Musselwhite Myra Falls

Quebec Yukon New Brunswick Newfoundland Ontario Ontario Ontario Ontario Quebec Ontario British Columbia Ontario Ontario Ontario Quebec Ontario British Columbia Quebec Ontario British Columbia

UG OP UG OP UG UG UG OP, UG UG UG OP UG OP UG UG UG OP OP UG UG

D B B A D D D B D D B C D D C D B A D D

Pamour Polaris Ruttan Selbaie Stobie

Ontario NW Territories Manitoba Quebec Ontario

OP, UG UG UG OP UG

D D C B B

Zn, Cu, Au, Ag Au Zn, Pb, Cu, Ag Fe Ni, Cu, Co, PGM Ni, Cu, Co, PGM Ni, Cu, Co, PGM Au, Ag Au Au, Ag Cu, Mo, Ag, Au Ag, Cu, Pb, Zn PGM, Cu, Au Ni, Cu, Co, PGM Cu, Au, Ag, Zn Ni, Cu, Co, PGM Au, Cu Fe Au Zn, Ag, Cu. Au, Pb Au, Ag, Cu Zn, Pb Zn, Au, Ag, Cu Ag, Au, Cu, Zn Ni, Co, Cu, PGM

270 Appendix B

Name

Province

Methods Capacity Products

Sudbury Operations Sullivan (Cominco) Thompson Troilus Wabush Williams

Ontario Ontario Manitoba Quebec Newfoundland Ontario

UG UG UG OP OP UG

C C C B B C

Ni, Cu, Co Zn, Pb, Ag Ni, Cu, Co Au, Cu Fe Au

USA Bagdad Bald Mountain Balmat Barneys Canyon Battle Mountain Beartrack Betze-Post Mine Bingham Canyon Briggs Carlin Castle Mountain Chino Cortez Doe Run Empire (Inland Steel) Eveleth Florida Canyon Fort Knox Golden Sunlight Gordonsville Griffon Henderson Hibbing Homestake Hoyt Lakes Iron Mountain Jerritt Canyon Johnson Camp Kinsley Mountain Lone Tree Complex Marigold McCoy/Cove McLaughlin

Arizona Nevada New York Utah Nevada Idahop Nevada Utah California Nevada Nevada New Mexico Nevada Missouri Michigan Minnesota Nevada Alaska Montana Tennessee Nevada Colorado Minnesota South Dakota Minnesota Wyoming Nevada Arizona Nevada Nevada Nevada Nevada California

OP OP UG OP OP OP OP OP OP OP, UG OP OP OP UG OP OP OP OP OP UG OP UG OP UG OP OP OP, UG OP OP OP OP OP OP

A C C C B B B A B A B A B A A B A A C C C B A C A D D B C B D B C

Cu Au Zn, Pb Au Au, Ag Au Au Cu, Au, Ag, Mo Au, Ag Au Au Cu Au Pb, Zn Fe Fe Au, Ag Au Au, Ag Zn, Cu Au Mo Fe Au Fe Fe Au Au Au Au Au Au Au, Ag

Appendix B 271

Name

Province

Methods Capacity Products

Meikle Mesquite Miami Mineral Ridge Minntac Mission Complex Montana Tunels Morenci National Steel Pellet North Shore Paradise Peak Pikes Peak Rand Randburg Raw Hide – Denton Red Dog (Cominco) Ridgeway Rochester Round Mountain Ruby Hill Sierrita Silver Bell Smith Ranch Sweetwater Tennessee Tilden Twin Creeks Tyrone Victor (Anglo) West Fork Wharf Yankee Yerington/MacArthur Yuba

Nevada California Arizona Nevada Minnesota Arizona Montana Arizona Minnesota Minnesota Nevada Colorado California California Nevada Alaska South Carolina Nevada Nevada Nevada Arizona Arizona Wyoming Missouri Tennessee Michigan Nevada New Mexico Colorado Missouri South Dakota Nevada Nevada California

UG OP OP OP OP OP, UG OP OP OP OP OP OP OP OP OP OP OP OP OP OP OP OP OP UG UG OP OP OP OP UG OP OP OP OP

D A A D A A B A A B D A B B B C B A C D A B D D C A A A A D B B B B

Au Au Cu Au Fe Cu, Ag Au, Ag, Pb, Zn Cu, Ag, Au, Mo Fe Fe Au, Cu Au, Ag Au Au Au, Ag Zn, Pb, Ag Au, Ag Au, Ag Au Au Cu, Mo Cu U Co, Cu, Pb, Zn Zn Fe Au Cu, Ag, Au Au, Ag Zn, Pb Au Au Au Au

Mexico Cananea Fresnillo

Sonora Zatecas

OP UG

A B

Eldorado La Caridad

Sonora Sonora

OP OP

C A

Cu, Au, Ag, Mo Ag, Au, Cu, Pb, Zn Au, Ag Cu, Au, Ag, Mo

272 Appendix B

Name

Province

Methods Capacity Products

La Herradura Moris San Francisco Santa Barbara

Sonora Chihuahua Sonora Chihuahua

OP OP OP UG

C D B C

Taxco

Guerrero

UG

D

Argentina Aguilar Bajo de Alumberra

Jujuy Catamarca

UG OP

C A

Zn, Pb, Au Cu, Au

Bolivia Kori Kollo

Western Bolivia

OP

A

Au, Ag

Brazil Aguas Claras Brucutu Capitao do Mato Caraiba Corrego de Feijao Corumba Fabrica Fazenda Brasilero Germano Igarape Bahia Itabira Morro do Ouro Mutuca Northern System Papagaio plato Pico Rio de Norte Sao Bento Southern System Tamandua

Minas Gerais Espito Santo Rio de Janeiro Bahia Minas Gerais Mato Grosso(Sul) Minas Gerais Minas Gerais Minas Gerais Minas Gerais Minas Gerais Minas Geris Rio de Janeiro Para Rio de Janeiro RJ Para Minas Geris Espirito Santo Rio de Janeiro

OP OP OP OP, UG OP OP OP UG OP OP OP OP OP OP OP OP OP UG OP OP

B C D B A D A D A C A A A A A A A D A C

Fe Fe Fe Cu Fe Fe Fe Au Fe Au, Ag Fe Au Fe Fe Baux. Fe Baux. Au Fe Fe

Chile Andacollo (Aur) Andacollo (Dayton) Andina Candelaria

IV Region IV Region Region V Region III

OP OP, UG OP, UG OP

C B C A

Cu Au Cu, Mo Cu, Au, Ag

Au Au, Ag Au Zn, Pb, Au, Ag, Cu Ag, Au, Cu, Pb, Zn

Appendix B 273

Name

Province

Methods Capacity Products

Cauquenes Cerro Colorado (Rio Algoma) Chuquicamata Collahusi East Boulder El Abra El Algarrobo El Romeral El Soldado El Teniente Escondida La Cascada La Coipa La Aguirre Lomas Bayas Los Bronces Los Colorados Los Pelambres Mantos Blancos Mantoverde Michilla Punta del Cobre Quebrada Blanca Redomiro Tomic Refugio Salvador Zaldivar

Metropolitan Reg. OP Region I OP

A A

Cu, Mo Cu

Region II Region I Montana Region II Region III Regional IV Region V Region VI Region II Region I Region III Metropolitan Reg. Region II Metropolitan Reg. Region III Region IV Region II Region III Region II Region III Region I Region II Region III Region III Region II

OP OP, UG UG OP OP OP OP, UG UG OP OP, UG OP OP OP OP OP OP OP, UG OP OP, UG UG OP OP OP OP, UG OP

A A C A B B A A A D B D A A B A A B B C B A A A A

Cu, Au, Mo, Ag Cu, Ag, Mo PGM Cu Fe Fe Cu Cu, Mo Cu, Mo, Au, Ag Cu Au, Ag Cu Cu Cu, Mo Fe Cu, Au, Ag, Mo Cu, Ag Cu Cu Cu, Ag, Au Cu Cu Au Cu, Mo Cu

Guyana Aroaima Omai

Georgetown Georgetown

OP OP

B A

Baux. Au

Peru Andaychagua Carahuacra Casapalca Cerro de Pasco Cerro Verde Marcona Pierina San Cristobal (Peru)

Junin Junin Lima Pasco Arequipa Ica Ancash Junin

UG OP, UG UG OP, UG OP OP OP UG

C C D C A C A C

Zn, Pb, Ag Zn, Pb, Ag Zn, Pb, Cu, Ag Zn, Pb, Ag, Cu Cu Fe Au, Ag Cu, Pb, Zn, Ag

274 Appendix B

Name

Province

Methods Capacity Products

Tintaya Uchucchacua Yanacocha

Cusco Lima Cajamarca

OP UG OP

B C A

Cu, Au Ag, Pb, Zn Au

Suriname Coermotibo Lelydorp

Paramaribo Para

OP OP

C C

Baux. Baux.

Venezuela Cedeno Cerro Bolivar Cerro LasPailas Cerro Los Barrancos El Pao San Isidro

Bolivar Estado Bolivar Estado Bolivar Estado Bolivar Estado Bolivar Estado Bolivar

OP OP OP OP OP OP

B C B C C A

Baux. Fe Fe Fe Fe Fe

Dominican Republic Falcondo Santa Domingo Pueblo Viejo Cotui

OP OP

B D

Ni Au, Ag

Honduras San Andres

Copan

OP

B

Au

Jamaica Clarendon Discovery Bay St. Elizabeth

Clarendon St. Ann St. Elizabeth

OP OP OP

D B D

Baux. Baux. Baux.

Nicaragua La Libertad

Managua

OP

C

Au

Botswana Phoenix

Francistown

OP

C

Ni, Cu

Demo. Repub. Congo Kambove Shaba Kamoto-Diva Shaba Kolwezi Shaba

OP OP/UG OP

C B B

Cu, Co Cu, Co Cu, Co

Ghana Ayanfuri Bibiani Damang Idupriem

OP OP OP OP

D C B B

Au Au Au Au

Dunkwa-on-Offin Bibiani Tarkwa Tarkwa

Appendix B 275

Name

Province

Methods Capacity Products

Obotan Obuasi Tarkwa Teberebie

Accra Obuasi Accra Accra

OP OP, UG OP, UG OP

C B B A

Au Au, Ag Au Au

Guinea Boke Fria Lero Siguiri

Conkry Conkry Conkry Koron

OP OP OP OP

A C D B

Baux. Baux. Au Au

Mali Sadiola Hill Syama

Bamako Bamako

OP OP

B C

Au Au

Namibia Navachab

Karibib

OP

B

Au

Northwest Prov. Chromite Orkney Orkney Orkney Atok Rustenburg

OP UG UG UG UG UG UG

D B D D D D A

Orange Free State Postmasburg Northern Cape Transvaal Transvaal Brakpan

UG OP UG UG OP, UG OP

C B C C B A

Au PGM, Rh, Ni, Cu Au Au Au PGM PGM, Au, Ag, Ni, Cu Au, Ag Fe Ag, Cu, Pb, Zn Au Au, Ag Au, Ag

Transvaal Transvaal Roodeport Mooinooi Transvaal Brakpan Boksburg Evander Orange Free State

UG UG OP, UG UG UG OP UG UG OP, UG

D B B B C A D C A

Au Cu, Au, Ag Au, Ag PGM Au, Ag Au, Ag Au, Ag Au Au

South Africa Afrikander Lease Amandelbult Section ARM1 ARM2 ARM4 Atok Bafokeng/ Wildebeestfontein Beatrix Beeshoek Black Mountain Blyvooruitzicht Buffelsfontein Daggafontein Division Deelkraal Dreifontein Durban Roodepoort Eastern Platinum Elandsrand ERGO Division ERPM Evander Freegold (Ops)

276 Appendix B

Name

Province

Methods Capacity Products

Gold Stockpile1 Goldridge Great Noligwa Grootylie Harmony Gold Hartebeestfontein HJ Joel Kloof Kopanang Kroondal Libanon Loraine Mponeng Northham Oryx Palabora Pering Potgietersrust Randfontein Rustenburg Savuka Sishen Tau Lekoa Tautona Thabazimbi Venterpost Western Platinum

– Mareetsane Vaal Reefs Springs Orange Free State Stilfontein Virginia Transvaal Vaal Reefs Rustenburg Transvaal Orange Free State Transvaal Thabazimbi Eerstemyn Phalaborwa North Cape Prov. Potgietersrus Randfontein Rustenburg Transvaal Northwest Vaal Reefs Transvaal Northern Prov. Gauteng Marikana

OP OP UG UG OP, UG UG UG UG UG OP, UG UG OP, UG UG UG UG OP, UG OP OP OP, UG OP, UG UG OP UG UG OP UG UG

C C C C B B D C C D C C C C D A D B D A D A C C C D B

Au Au Au Au, Ag Au, Ag Au Au Au Au PGM Au Au, Ag Au Au, Os, Ir, PGM Au Cu, Ni, U3O8 Zn, Pb PGM, Ni, Cu Au, Ag PGM, Ni, Cu Au Fe Au Au Fe Au PGM

Zambia Baluba Bwana Mkubwa Konkola Mufulira Nchanga Nkana Nkana Slag Dump

Luanshya Ndola – – Chingola – –

UG OP UG UG OP, UG OP, UG OP

D C C C A D D

Cu, Co Cu, H2SO4 Cu Cu Cu, Co Co, Cu Co, Cu

Zimbabwe Blanket Cam & Motor Dalny Freda-Rebecca

– Harare Bulawayo Bindura

OP, UG OP OP, UG UG

D D D D

Au Au Au Au

Appendix B 277

Name

Province

Methods Capacity Products

Shangani Trojan (Bindura)

Shangani Bindura

OP, UG UG

D D

Ni Ni

Armenia Ararat

Yerevan

OP

C

Au

China Dexing Gongchangling Xiaotiashan Yongping

Jiangxi Liaoning Lanzhou Jiangxi

OP OP, UG UG OP

A A D B

Cu Fe Cu, Zn, Pb Cu

Georgia Madneuli

Bolnisi region

OP

D

Cu, Au, Ag

India Bailadilla no.14/11 Bailadilla no. 5 Donimalai Gua Khetri Copper Malanjkhand Panchpatmali Zawar

Madhya Pradesh Madhya Pradesh Karnataka Bihar Rajasthan Madhya Pradesh Orissa Rajasthan

OP OP OP OP OP, UG OP OP UG

A B B A D C C D

Fe Fe Fe Fe Cu Cu Baux. Zn, Pb

OP OP OP, UG OP OP OP

A C A A D D

Cu, Au, Ag Ni Cu, Au, Ag Au, Ag Au Au, Ag

Soroako

Sumbawa Maluku Irian Jaya Kalimantan Sulawesi Utara Central Kalimantan South Sulawesi

OP

A

Ni

Iran Sarcheshmeh Tohoghart

Kernan province –

OP OP

A B

Cu, Au, Ag Fe

– –

OP OP

C B

Cu, Zn Cu

– OP Ust-Kamenogorsk OP

A C

Fe Zn, Pb

Indonesia Batuhijau Gebe Island Grasberg/Ertsberg Kelian Minahasa Mount Muro

Kazakhstan Nikolayevski Sayaksky SokolovskoSarbaiskoye Zyryanovski

278 Appendix B

Name

Province

Methods Capacity Products

Kyrgyzstan Kumtor

Bishkek

OP

B

Au

Mongolia Erdenet Copper

Orkhon

OP

A

Cu, Mo

Myanmar Monywa

Yangon

OP

B

Cu

Philippines Antamok Bulawan Padcal Santo Tomas II

Baguio City Sipalay Bonguet Tuba

OP OP, UG UG UG

C D B B

Au Au, Ag Cu, Au Cu, Au, Ag

Saudi Arabia Sukhaybarat

–

OP

C

Au, Ag

Tajikistan Zeravshan

Sogdiana

OP

C

Au, Ag

Uzbekistan Kalmakyr Zarafshan

Tashkent Kyzylkum

OP OP

A A

Cu, Au, Mo Au

Australia Agnew Ballarat-Last Chance Bardoc-Davyhurst Big Bell Consolidated Blue Bird Boddington Bounty Brocks Creek Broken Hill Bronzewing Bullfinch Cadia Cannington Channar Dalgaranga Elura Ernest Henry Fortnum

Western Australia Western Australia Western Australia Western Australia Western Australia Western Australia Western Australia Northern Territor. New South Wales Western Australia Western Australia New South Wales Queensland Western Australia Western Australia New South Wales Queensland Western Australia

UG OP UG OP, UG OP OP, UG OP, UG OP OP, UG UG OP, UG OP UG OP OP UG OP OP

D D C C B A D D C C D A C A D D A D

Au Au Au Au, Ag Au Au Au Au, Ag Zn, Pb, Ag Au Au Au, Cu Zn, Pb, Ag Fe Au Zn, Ag, Pb Cu, Au, Co Au

Appendix B 279

Name

Province

Methods Capacity Products

Fosterville Golden Feather Goldsworthy Gove Granny Smith Greenfields Hedges Hellyer Huntly Jumblebar Jubilee Jundee Kambalda Nickel Kanowana Belle Kidston Kookynie Koolyanobbing Lawlers Leinster Nickel Ops. Marvel Loch McArthur River Middleback Ranges Mount Charlotte Mount Isa Mount Keith Mount Leyshon Mount Lyell Mount Magnet (ex Metana) Mount McClure Mount Pleasant Mount Tom Price Mount Whaleback Murrin Murrin New Celebration Nifty Nimary Northparkes Olympic Dam Ora Banda Osborne

Victoria Western Australia Western Australia Northern Territor. Western Australia Western Australia Western Australia Tasmania Western Australia Western Australia Western Australia Western Australia Western Australia Western Australia Queensland Western Australia Western Australia Western Australia Western Australia Western Australia Northern Territor. Southern Austral. Western Australia Queensland Western Australia Queensland Tasmania Western Australia

OP OP OP OP OP OP, UG OP UG OP OP OP OP UG UG OP OP OP OP, UG OP, UG OP, UG UG OP UG UG OP OP UG OP

D C A A B D B D A B D B D C A D B D C C D C C B A B C C

Au Au Fe Baux. Au Au Au Zn, Cu, Pb, Ag Baux. Fe Au Au Ni Au Au Au Fe Au Ni Au Zn, Ag, Pb Fe Au Cu, Pb, Zn, Ag Ni Au, Cu Cu, Au Au

Western Australia Western Australia Western Australia Western Australia Western Australia Western Australia Western Australia Western Australia New South Wales South Australia Western Australia Queensland

OP, UG OP OP OP OP OP, UG OP OP OP, UG UG OP UG

C C A A B C D B B A D C

Au Au Fe Fe Ni, Co Au Cu Au Au, Cu, Ag Ag, Au, Cu, U Au Cu, Au, Ag

280 Appendix B

Name

Province

Methods Capacity Products

Paddington Pannawonica Pillara Plutonic Ranger Ravenswood Sons of Gwalia St.Ives Sunrise Dam Super Pit Tanami (Normandy) Tanami (Otter/Acacia) Tarmoola Telfer Union Reefs (Acacia) Weipa Willowdale Worsely Yandi Yimuyn Manjerr

Western Australia Western Australia Western Australia Western Australia Northern Territor. Queensland Western Australia Western Australia Western Australia Western Australia Northern Territor. Northern Territor. Western Australia Western Australia Northern Territor. Queensland Western Australia Western Australia Western Australia Northern Territor.

OP OP UG OP, UG OP OP OP, UG OP, UG OP OP OP, UG OP OP OP, UG OP OP OP OP OP OP

B A C B C C D B D A D D B A C A C A A A

Au Fe Zn, Pb Au U Au Au Au Au Au Au Au Au Au Au, Ag Baux. Baux. Baux. Fe Au

New Caledonia Kouaoua/Thio

–

OP

B

Ni, Co

New Zealand Macraes

South Island

OP

B

Au, Ag

Papua New Guinea Lihir Misima OK Tedi Porgera

– Milne Bay Provi. Western Province Mount Hagen

OP OP OP OP

B B A B

Au Au, Ag Au, Cu Au

Austria Erzberg

–

OP

D

Fe

Finland Pyhasalmi

Pyhasalmi

UG

C

Cu, Zn

Greece Kassandra

Chalkidiki

OP, UG

B

Au, Ag, Zn, Pb

Ireland Lisheen Tara

County Tipperary UG County Meath UG

D A

Zn, Pb Zn, Pb

Appendix B 281

Name

Province

Methods Capacity Products

Poland Lubin Polkowi. Sieroszowice Rudna Portugal Neves Corvo

Lubin Ul. Kopalniana 1

UG UG

A A

Cu Cu

Rudna – –

UG – UG

A – D

Cu – Sn, Cu

Spain Los Frailes

Sevilla

OP

B

Zn, Cu, Ag, Pb

Sweden Altik Bjorkdal Boliden Kiruna Laisvall

Gallivare Bjorkdalsgruven Boliden Kiruna Norbotten District

OP OP OP, UG UG UG

A C C A C

Cu, Au, Ag Au Zn, Cu, Pb, Au, Ag Fe Ag, Pb, Zn

Appendix C

World Production of minerals/metals in 1998 (source: Minerals Yearbook, 1998, v.1, US Geological Survey, 2000) (t  tonnes; Mt  millions of tonnes; kg  kilogram). Metals, mine basis Antimony (t) Arsenic trioxide (t) Bauxite (Mt) Beryl (t) Chromite (Mt) Cobalt (t) Columbium & tantalum concentrate (gross weight) (t) Copper (Mt) Gold (kg) Iron ore (gross weight) (Mt) Lead (Mt) Manganese ore (gross weight) (Mt) Mercury (t) Molybdenum (t) Nickel (Mt) Platinum Group Metals (kg) Silver (t) Tin (t) Titanium concentrates (ilmenite, including leucoxene) (Mt) Rutile (t) Tungsten (t) Vanadium (t) Zinc (Mt) Metals, refinery basis Aluminium (Mt) Bismuth (t) Cadmium (t) Cobalt (t) Copper, primary & secondary (Mt) Iron & steel Direct-reduced iron (Mt)

140,000 40,800 122 7,220 12.7 26,300 44,800 12.2 2,480,000 1,020 3.1 18.7 2,320 135,000 1.14 287,000 16,400 206,000 4.65 426,000 32,200 42,000 7.54 22.1 3,780 19,600 30,900 14.1 37.5

284 Appendix C

Iron, pig (Mt) Steel, raw (Mt) Lead, primary & secondary (Mt) Magnesium, primary & secondary (t) Nickel (Mt) Selenium (kg) Tellurium (kg) Tin, smelter (t) Zinc, smelter, primary & secondary (Mt) Industrial minerals Asbestos (Mt) Barite (Mt) Boron minerals (Mt) Bromine (t) Celestite (t) Cement, hydraulic (Mt) Clays Bentonite (Mt) Fuller’s earth (Mt) Kaolin (Mt) Diamond, natural (1,000 carats) Diatomite (Mt) Feldspar (Mt) Fluorspar (Mt) Graphite, natural (t) Gypsum (Mt) Iodine (crude) (t) Lime (Mt) Magnesite, crude (Mt) Mica, including scrap & flake (t) Nitrogen, N content of ammonia (Mt) Peat (Mt) Perlite (Mt) Phosphate rock, gross weight (Mt) Potash, K2O equivalent(Mt) Pumice (Mt) Salt (Mt) Sand and gravel, industrial, silica (Mt) Soda ash (Mt) Sulphur, all forms (Mt) Talc & pyrophyllite (Mt) Vermiculite (t)

541 781 5.88 468,000 1.05 1,450,000 115,000 225,000 8.23 1.84 5.89 4.44 514,000 276,000 1,520 9.33 3.32 39.8 115,000 2.15 8.08 4.7 578,000 107 21,300 115 10.7 288,000 106 25.5 1.84 145 25.1 11.5 192 110 31.7 57.8 8.14 292,000

Appendix D

Chronology of Reported major mining-related environmental incidents since 1975 (source: Hoskin, 2001) M  million. Year

Country

Cause of release

1975 1976 1977 1978 1978 1980 1982 1985 1985 1985 1985

USA Yugosla. USA Japan Zimbab. USA Philippi. USA Chile Chile USA

Dam overtopping Dam failure Pipe failure Dam failure Dam overtopping Dam failure Dam failure Dam failure Dam failure Dam failure Dam overtopping

1985 1986 1988 1988 1991 1992 1994

Pipe failure Dam failure Pipe failure Dam overtopping Dam overtopping Dam failure Dam failure

1995 1995 1995 1995 1996 1996 1997 1998

Italy Brazil USA China USA Philippi. South Africa Guyana Australia Australia Philippi. Philippi. Bolivia USA Kyrgystan

1998

USA

Dam failure Dam failure Dam overtopping Dam failure Pipe failure Dam failure Dam failure Transportation Accident Pipe failure

Type of operation

Quantity

Deaths

Cyanide No No No No data No data No No No data No No No

Lead/zinc Lead/zinc Uranium Gold Gold Copper Copper Gold Copper Copper Sand & gravel Fluorite Iron Coal Molybden. Gold Copper Gold

150,000 m3 300,000 m3 30,000 m3 80,000 m3 30,000 t 2 M m3 27 M m3 25,000 m3 500,000 m3 280,000 m3 11,000 m3

0 0 0 1 1 0 0 0 0 0 0

200,000 m3 100,000 t 250,000 m3 700,000 m3 39,000 m3 80 Mt 600,000 m3

268 7 0 20 0 0 0

No No No No Yes No Yes

Gold Gold Gold Gold Copper Pb/Zn/Ag Copper Gold

4 M m3 40,000 m3 5,000 m3 50,000 m3 1.5 Mt 400,000 t 230,000 m3 1,800 kg NaCn

0 0 0 12 0 0 0 0

Yes Yes Yes No No No No Yes

Gold

Several tonnes

0

Yes

286 Appendix D

Year

Country

Cause of release

1998

Spain

Dam failure

1998 Philippi. 2000 Romania 2000 Romania 2000 PNG 2000 Romania 2000 Romania 2000 PNG 2000

Peru

2000 Romania 2000 Sweden 2000 PNG 2000 2000

China China

2000

USA

2000 2000 2000 2000 2000 2000 2000 2000 2001 2001

China China China China China India China Ukraine India Philippi.

2001 2001

Pipe failure Dam failure Dam failure Transportation Accident Dam failure Dam failure Transportation Accident Transportation Accident Pipe failure Dam failure Transportation Accident Gas explosion Transportation Accident Dam failure

Type of operation

Quantity

Deaths

Cyanide

5 M m3

0

No

0 0 0 0

Yes Yes No Yes

Cyanide Pb/Zn/Cu Cyanide

700,000 t 100,000 m3 22,000 m3 150 kg NaCn 100,000 m3 20,000 t 2 t NaCn

0 0 0

No No Yes

Mercury

150 kg

1?

No

Zinc/lead Copper Diesel

N/a 6.8 M m3 4,000 L

0 0 0

No No No

Coal Cyanide

N/a 5,200 t NaCn

160 0

No Yes

Coal

0

No

20 25 4 29 13 12 21 9 30 8

No No No No No No No No No No

29  3 missi. 93 missi. 2 4

No

Pb/Zn/ Cu/Ag Gold Gold Base metals Gold

Phosphate Coal Kaolin Copper Coal Coal Gold Coal Coal Gold

China

Rock slide Explosion Tunnel failure Dam failure Fire Collapse Tunnel failure Explosion Flooding Landslide triggered by storm Explosion

250,000,000 gallons of liquefied coal waste N/a N/a N/a N/a N/a N/a N/a N/a N/a N/a

Coal

N/a

China

Explosion

Coal

N/a

Explosion Explosion

Nickel Coal

N/a N/a

2001 Russia 2001 Ukraine

No No No

Appendix E

International Organization for Standardization (ISO) ISO 14001 Guidance Manual (1998) (prepared by Dr. Raymond Martin, National Centre for Environmental Decisionmaking Research, Oak Ridge National Laboratory, Tennesse, USA, 1998, 97 pp.). The Manual deals with the following components: 1. Policy: Internal review or gap analysis, management commitment, define programme intent, 2. Planning: Aspects, Impacts, regulatory issues, Internal Performance Criteria, Environmental Management programme, 3. Implementation: Responsibility/Accountability, staff – physical and scientific capabilities, EMS integration, 4. Measure and Evaluate: Operational control, Communication/Reporting/ documentation, Performance Indices, 5. Review and Improve: Problem reports, management issues, problem resolution, 6. Environmental Opportunity: Process improvements, cost savings, enhanced image. ISO 14001-4.5.1 Monitoring and Measurement “The organization shall establish and maintain documented procedures to monitor and measure, on a regular basis, the key characteristics of its operations and activities that can have a significant impact on the environment. This shall include the recording of information to track performance, relevant operational controls and conformance with the organization’s environmental objectives and targets. Monitoring equipment shall be calibrated and maintained and records of this process shall be retained according to the organization’s procedures. The organization shall establish and maintain a documented procedure for periodically evaluating compliance with relevant environmental legislation and regulations”. ISO 14001-4.5.4 Environmental Management System Audit “The organization shall establish and maintain programmes and procedures for periodical environmental management systems audits to be carried out, in order to: (a) determine whether or not the environmental management system 1. conforms to planned arrangements for environmental management including the requirements of this International Standard, 2. has been properly implemented and maintained; and (b) to provide information on the results of audits to management.

288 Appendix E

The organization’s audit programme, including any schedule, shall be based on the environmental importance of the activity concerned and the results of previous audits. In order to be comprehensive, the audit procedures shall cover the audit scope, frequency and methodologies, as well as the responsibilities and requirements for conducting audits and reporting results. ISO 14001 EMS Registration In USA, the terms certification and registration are used interchangeably. “Certification is a procedure by which a third party gives written assurance that a product, process or service conforms to specified requirements. Certification to ISO 14001 stipulates that a company is in compliance with an environmental management system (EMS) that meets all requirements of ISO 14001. The evaluation by an Accredited body will include an examination the company’s environmental policy, environmental management system and its documentation, EMS auditing programme and procedures, and environmental records. It will include a thorough on-site audit to determine conformance to the ISO 14001 Standard. When the company’s environmental management system is verified to conform to the requirements of ISO 14001, the Certifier will issue a certificate describing the scope of the environmental management system that has been certified. The certification is then listed in a register or directory that is available to the public. The Registrar allows the company to display the Registrar’s mark on advertising, stationery, etc. as evidence that it has achieved certification”.

Author index

Abbruzzese, C. 263 Abernathy, C.O. 260, 263 Akagi, H. 63, 259 Aleva, G.J.J. 61, 259 Alexieva, T. 196, 259 Alsong, D. 110, 262 Angelos, M. 172, 174, 175, 176, 178, 259 Archer, A.A. 5, 124, 259 Aswathanarayana, U. 64, 79, 112, 259 Attewell, P., 78, 259 Axelrod, R.S. 262 Ayres, B.K., 174, 259 Azcue, J.M. 260, 261, 262, 263 Banerjee, N.N. 263 Bartlett, P.J. 57, 259 Bateman, A.M. 60, 66, 77, 79, 164, 261 Berti, W.R. 230, 259 Beveridge, T.J. 259 Bhattacharya, G. 260, 262, 263, 264 Boger, D.V. 190, 191, 192, 193, 263 Börjesson, E. 239, 240, 259 Brandes, M. 238, 259 Brierley, C.L. 177, 178, 259 Brierley, J.A. 177, 178, 259 Calderon, R.L. 260, 263 Carlsberg, T. 255, 260 CCORE 195, 260 Chadwick, J. 12, 260 Chadwick, M.J. 25–30, 32–34, 36–49, 51, 123, 140, 141, 143, 186, 222–227, 229, 246, 247, 260

Chappell, W.R. 260, 263 Chatterjee, P.C. 102, 104, 263 Chatterjee, S.K. 99, 260 Chen, C.J. 129, 260 Cheng, W.W. 259 Chowdhry, N.A. 259 Christensen, D. 259 Clayton, C.R.I. 184, 187, 188, 189, 263 Collins, R.J. 239, 260 Compton, H. 232, 260 Cooke, R. 147, 262 Cox, D.P. 158, 260 Croll, A. 57, 259 Cummins, A.B. 48, 260 Cunningham, S.D. 230, 259 Danielson, L. 257, 260 Das, A. 99, 260 Davé, N.K. 178, 179, 180, 181, 260 Davidson, M.S. 259 Davison, J. 178, 260 Day, M.G. 112, 260 Dhar, B.B. 121, 263 Diaz, G. 57, 260 Dold, B 168, 260 Dowon, C.G. 133, 134, 135, 260 Doyle, R.J. 259 Duffield, S. 56, 260 Eger, P. 178, 260 Elander, P. 262 El–Hinnawi, Essam E. 119, 120, 260 Ellis, D.V. 181, 196, 260 Enjing, Z. 264 Eriksson, N. 173, 174, 260, 261

Farmer, J.W. 112, 260 Fergusson, J.E. 64, 120, 125, 261 Ferrow, E.A. 159, 261 Fontbote, L. 168, 260 Förstner, U. 1, 113, 120, 121, 261, 263 Forssberg, E. 147, 264 Gadd, G.M. 177, 264 Given, I.A. 48, 260 Govindarajalu, S. 11, 12, 262 Grayson, R.L. 142, 261 Gupta, J.P. 263 Gusek, J.A. 176, 261 Hagedorn, C. 261 Haimes, Y.Y. 113, 114, 116, 261 Håkansson, K. 262 Hammer, O.A. 38, 134, 260, 261 Harrison, A–L. 237, 238, 261 Haycocks, C. 119, 262 Hellier, W.W. 170, 171, 261 Heslop, T.G. 56, 261 Highton, N.H. 260 Höglund, L.O. 172, 261 Hoskin, Wanda M.A. 256, 261 Houseman, L. 155, 261 Hultqvist, J. 261 Hummer, J.W. 261 Hustrulid, W. 44, 45, 54, 97, 240, 261 Hutchinson, R.W. 158, 261 Isaksson, K.E. 262 Iwasaki, I. 151, 261

290 Author index Jensen, M.L. 77, 79, 261 Jones, M.J. 259, 260 Joshi, S.C. 260, 262. 263, 264

Nordström, K. 262 Noronha, L. 233, 262 O’Kane, M. 259

Kay, D. 56, 261 Khanna, T. 8, 14, 15, 261 Klapper, H. 181, 182, 261 Kolbash, R.L. 177, 261 Kuyucak, N. 243, 244, 261 Lacki, M.J. 176, 261 Laconte, P. 113, 114, 116, 261 Låg, J. 259 Landge, P.R. 209, 263 Lanteigne, L. 259 Lapakko, K. 178, 260 Ledin, S. 230, 231, 263 Leyton, P. 257, 260 Lindström, P. 262 Lindvall, M. 260, 261, 262 Ljungberg, J. 262 Luttig, G.W. 259 Martens, P.N. 194, 195, 262 Mathur, G.B. 209, 263 Matsui, K. 43, 44, 262 Maxwell, P. 11, 12, 262 McDougall, S. 147, 262 McNulty, T. 16, 17, 160, 262 McQuiston, P.W. 150, 262 MEND 1, 173, 175, 195, 261, 262 Mengxiong, C. 110, 262 Michalski, P. 183, 186, 187, 263 Miller, R.O. 262 Miller, R.H. 239, 260 MiMi 1, 167, 172, 174, 262 Moellerherm, S. 194, 195, 262 Moosberg, H. 237, 238, 262 Moshiri, G.A. 260 Mpendazoe, F.M.T. 65, 262 Naganuma, A. 63, 259 Nijkamp, P. 246, 262 Niskanen, P. 172, 174–176, 178, 259

Pai, B.H.G. 123, 127, 136, 262 Paktunc, A.D. 178, 179, 180, 181, 260 Palmer, J.P. 260 Philbrook, J.N. 254, 262 Puhakka, T. 54, 262 Pukkila, J. 54, 262 Redford, M.S. 58, 262 Reed, W.R. 119, 262 Reneau, Jr., R.B. 261 Richard Cothern, C. 259 Rirk, K.J. 260 Robbins, G. 64, 165, 263 Robertson, J.D. 181, 196, 260 Romanovski, T.L. 177, 261 Rust, F. 184, 187, 188, 189, 263 Sahni, D.K. 235, 263 Salomons, W. 120, 121, 263 Sandberg, M. 260 Saraswat, S.P. 263 Sa˘rkka¯, P. 262 Saxena, S.K. 102, 104, 263 Schultze, M. 181, 182, 261 Sengupta, M. 7, 40, 41, 208, 210, 213, 214, 215, 216, 252, 254, 263 Serrano, J.R.A. 261 Shenoi, B.V. 123, 127, 136, 262 Shimada, H. 262 Shoemaker, R.S. 150, 262 Sikka, B.K. 263 Singer, D.A. 260 Singh, B. 121, 263 Singh, R.S. 209, 263 Skarzynska, K.M. 183, 186, 187, 263 Smirnov, V.I. 69, 263 Snezhko, I.I. 259 Sofra, F. 190–193, 263

Stjerman, L. 230, 231, 263 Stocks, H. 133–135, 260 Stottmeister, U. 181, 182, 263 Struthers, S. 257, 263 Sturk, H. 261 Sun, G.F. 129, 263 Sundquist, T. 261 Swarup, R. 263 Szabo, M.F. 100, 263 Terbrugge, P.J. 58, 262 Tewary, B.K. 121, 263 Thomas, L. 80, 263 Tiwary, R.K. 118, 263 Tobar, P. 57, 260 Trifoni, F.M. 263 Ubaldini, S. 153, 263 UNEP, 8, 25, 26, 49, 50, 53, 84–87, 89, 91, 92, 95, 96, 98, 100, 101, 128, 132–134, 137, 138, 149, 151, 160–162, 184, 185, 198, 200, 202–204, 207, 211, 212, 241, 242, 245, 246, 248, 249–251, 256, 263 Van Stratten, P. 64, 263 Vartanyan, G.S. 8, 105–108, 112, 210, 218–221, 263 Veglio, F. 263 Vermuelen, N.J. 184, 187–189, 263 Vig, N.J. 262 Wadhwan, S.K. 60, 264 Wang, Y. 147, 264 Wathern, P. 246, 264 Webster, H.J. 261 Wei, C. 264 Weiss, N.J. 150, 162, 264 Welborn, L.E. 260 Westman, E.C. 119, 262 White, C. 177, 264 Wood, P.A. 112, 264 Wyk, Van J.P. 232, 264 Zhenru, Z. 159, 160, 264

Subject index

Acid Mine Drainage 1, 25, 69, 81, 96, 98, 111, 113, 141, 167, 169, 172, 176, 213, 215, 224 acid formation 15 acid lakes 180 acid potential 15 anoxic limestone drains (ALD) 171, 176 biologically-supported water cover 172, 173 causes 167 covers and seals 174, 175 decision-making 170 Elliot Lake uranium tailings 178 leaching tests 169 passive treatment 176, 178 sulphidic mine tailings 68 wetlands 176, 177 Aerosols 125, 126, 129 Aluminium industry 78, 83, 92–94, 199, 236, 237 environmental impacts 93 pollutants from Al-smelters 94, 95 red mud 83, 93, 94, 114, 157, 190, 236–238 Artisanal mining 3, 54, 62, 64–66 innovative technologies 64 mercury pollution 62, 64 Backfill 14, 52, 190, 181, 194, 195, 209, 210, 213, 218, 235 Base metals 5, 69, 95–98, 147, 155, 156, 158, 194, 213

Beneficial uses of mine wastes 235–239 agriculture 237 brick-making 236, 237 construction industry 236, 237 embankments 236 glass 237 Biodiversity 102, 121 biomass 102–104 plant species 102–104 Bioremediation 230, 231 Bioleaching 14, 155–157 environmental benefits 157 Block caving 53–57, 194 Coal 2, 5, 6, 7, 15, 25–29, 32–36, 38–44, 47–53, 58, 79–81, 83, 85, 86, 89, 90, 93–95, 99, 100, 102, 106–111, 113, 115, 117, 118, 120, 121, 123, 124, 127–131, 136–138, 140–143, 145, 146, 152, 167. 176, 183, 186, 187, 197, 198, 200, 202, 206, 208–210, 213, 218, 228, 236, 237, 246, 247 mode of formation 79 post-depositional changes 81 rank of coal 79–81 sedimentary sequences 9 syn-depositional changes 80 Coal industry in the world 2, 5 energy contribution 5, 7 production in different countries 6

reserves in different countries 6 status 5 Coal mining 5, 25, 26, 29, 40, 43, 44, 108–110, 117, 123, 142, 186, 236, 246, 247 environmental impacts 100 methods 25–32 washing 145, 146 wastes 113–118 Coal preparation flowsheet 33 Coke-making 100 flow-sheet 101 pollution 100 Cut-and-fill process 50 Cyanidation 3, 16, 98, 149, 150, 153, 160, 162–164 alternative lixiviants 16 environmental mitigation 164–166 Diamond drilling 25, 26 Dragline excavators 43 Drift mine 45, 46 Dust control technologies 91 dust control chemicals 199 electrostatic precipitators 91, 92, 95, 198 high-energy scrubbers 91, 199 mechanical dust catchers 198 Dusts 110, 124, 128, 130, 197, 200 analytical methods 130 carcinogenic effects 129, 130 characterization 131 fibrogenetic effects 129 pathological effects 128

292 Subject index e-Business 17–24 definition 17 economics 19 future 23 how to start new e-business 19 Internet 20 linkages 18 mining industry 17, 21 present status 21 Quadrem 21, 22, 24 value/volume relationships 20 Electrostatic precipitators 90, 91, 92, 95, 198 Emissions due to mineral industries 118–121 Environmental audits 254 Environmental Code 255, 256 Environmental Impact Assessment 245–249 matrix diagrams 248, 249 outline 251 procedures 252, 254, 255 scoping 246–248 Environmental monitoring 215, 217, 249 geotechnical monitoring 2, 17 hydrochemical monitoring 217 observation network 218, 219 open pits 216, 217, 239 tailings dams 250, 257 underground mines 216, 217, 234 waste rock dumps & stockpiles 216 Environmental Protection Agency of USA 252 Environmental regulations of USA CERCLA 252, 255 Clean Air Act 253 Clean Water Act 253, 254 NPDES permits 253 RCRA 252, 253, 255 Safe Drinking Water Act 253 SARA 253 Superfund 252, 253

Toxic Substances Control Act 253 Explosions in mines 8 Falls in mines 137 Ferrous metals 69, 71, 72 Flotation 36, 60, 66, 69, 96, 98, 99, 134, 146–152, 155, 156, 160, 162, 163, 206, 236, 237, 244 chemicals 50 environmental impacts 149 principles 148 procedures 152 Flowsheets Cawse flowsheet 154 gold concentrator flowsheet 160, 161 gold recovery flowsheet 62 Pb-Zn concentrator 151 Globalization and Mining industry 257 Gold 3, 10, 11, 14–17, 21, 55, 56, 59, 62–66, 69, 70, 79, 96, 99, 109, 111, 123, 127, 136, 147, 152, 153, 156–165, 184, 187–189, 194, 196, 213, 229, 234, 239, 249, 257 cyanidation 3, 16, 98, 149, 150, 153, 160, 162, 163, 164 how to extract gold 160 how to look for gold 159 mineral deposit models 158, 159 mineralogical association 159, 160 mode of occurrence 70 where to look for gold 157 Health hazards due to mining 123–140 biological hazards 140 chemical hazards 137 dust hazards 124 mental hazards 140 other physical hazards 124 Heat problems in mining 135 Kolar gold fields, India 136

Highwall mining 44 Hydrometallurgy 153 Impact of mining 12, 102, 105–107, 110, 111, 218 atmosphere 110, 111 biosphere 111 hydrosphere 107–110 lithosphere 106–107 Industrial minerals 2, 5, 62, 70, 76, 77, 102 ISO 14001 10, 245 Liquid effluents from mining 115 LKAB Iron ore mine – case study 66 Longwall method of mining 48 Low-waste technologies in steel industry 200–202 continuous processing 201 direct reduction of iron ore 200 low-pollution pickling 201 remelting of wastes 202 scrap preparation 200 Mass mining 53–56, case histories 56, 57 equipment automation 54 Matrix diagrams 248, 249 Mercury pollution 62, 64 Metal mining industry in the world 1 important metal mines 269–281 mineral production 283, 284 Metallic minerals 2, 5, 53, 62, 69, 76 Microorganisms 155, 156, 177, 178, 207, 228 Dienococus radiodurans 232 sulphate-reducing bacterria 177, 178 Thiobacillus ferrooxidans 155, 167, 168 typha 177 wetlands 170 Mine closure, 8, 213, 249

Subject index 293 Mine design process 26–40 geographical factors 28 geological & structural setting 29 geotechnical considerations 36 meteorological factors 29 stripping ratio 38 technoeconomic viability 32, 36 Mining and the Environmental agenda 7 economics of environmental protection 11, 12 environmental challenges 7, 8 ISO 14001 certification 10 public image of the mining industry 8 technology trends 12 Mining industry in the developing countries 8 dilemmas 10 implementation of regulations 11 Mining-related environmental incidents 8, 285 Mitigation of mining impacts 218–222 Monitoring of mining impacts 215–218 Noise 9, 11, 37, 67, 92, 110, 123, 131–136, 141, 143, 199, 200, 201, 210–212 risk of loss of hearing 132, 134 sound frequencies 132 threshold of audibility and pain 132, 133 Non-ferrous metals 69, 73, 74 Offshore mining 58, 59 environmental impact 58 floating plants 59 land-based plants 59 marine placers 72 Opencast mining 3, 14, 15, 29, 36, 40, 42, 43, 45, 49, 93, 110, 123, 137, 180, 248

advantages 40 mine layout 41 projected advances 44, 45 Ores 5, 13, 15, 17, 69, 72–76, 79, 86, 87, 95, 96, 98, 99, 115, 145–147, 149, 151–153, 155–157, 160, 162–164, 200, 222, 234, 244, 246 Paste technologies 15, 190, 194 mine backfill 194, 195 rheological characteristics 184, 191, 193 shear rate vs. shear stress 190 slope of tailings pile 197 thickened tailings 184, 190, 191, 194 underwater placement of pastes 195, 196 Planning for mine closure 213 Pollution 8, 9, 11, 14, 62, 64, 65, 67, 79, 87–92, 94, 97, 98, 100, 111–114, 131, 136, 139, 141, 155, 178, 197, 199, 205, 209, 218, 222, 224, 228, 256 Precious metals, 69, 70, 71 Preparation of coal 145 Preparation of metallic ores 46

ground preparation prior to revegetation 226 miscellaneous vegetation methods 232 mulching 224, 226 Rehabilitation case histories 233–235 iron ore mine, Goa, India 233 manganese ore spoils, India 235 Sudbury nickel, Canada 234 Room-and-pillar method of mining 48, 49 Scrubbers 69, 90, 91, 92, 199 Slope mine 45, 46 Solid wastes from mining 113, 114, 237 Steel industry 78, 83, 85, 87–89, 91, 92, 94, 117, 128, 132–134, 136, 137, 139, 188–200, 202, 204–206, 211 Strip mining 41, 42, 59 Subsidence 8, 9, 28, 36, 40, 52, 80, 106–109, 111, 112, 141, 208–210, 213, 218, 222, 224 back-filling 209 impacts 208 remedial measures 210 Sustainable mining 8, 10 Indonesia case study 10

Quadrem 21, 22 Radioactive elements 69, 76 Recycling 16, 87, 100, 139, 154, 160, 163, 168, 200–202, 204, 205, 233, 235, 256 Recycling of wastes in steel industry 87, 204 Rehabilitation of mined land 11, 222–235 amendments and fertilizers 228 bioremediation 178, 230 characteristics of substrate 225 ecotypes and cultivars 229

Tailings dams 17, 181, 185, 190, 196, 250 centre-line methods 186 downstream methods 186 upstream methods 185 Tailings disposal 124, 181, 184, 186, 190, 191, 193, 195, 213, 249 characteristics of tailings 183, 184 coal mine tailings 186 environmental risks 181 gold mine tailings 187 methods of disposal 184, 185 paste technologies 190, 194

294 Subject index risk assessment 196, 197 underwater placement 195, 196 Total Project Development 258 Treatment of mine water 239, 240 microbial treatment 207 recycle systems 204 removal of oil 206 removal of suspended solids 205

methodologies, special problems 52 UNEP 8, 25, 26, 49, 50, 53, 84–87, 89, 91, 92, 95, 96, 98, 100, 101, 128, 132–134, 137, 138, 149, 151, 160–162, 184, 185, 198, 200, 202–204, 207, 211, 212, 241, 242, 245, 246, 248–251, 256 international initiatives 256

Underground mining 13, 14, 25, 28, 36, 38–40, 43, 45, 48, 52, 54, 56, 104, 106, 108, 110, 123, 127, 137, 142, 194, 208, 209, 218, 237, 248 advantages 40, 45 automation 13–14, 54, 136

Vertical shaft mine 45–48 Vibration 9, 136, 141, 143, 200, 210–212, aerodynamic vibration 136, 211, 212 mechanical vibration 136, 211, 212 vibration due to combustion 212

Washing 35, 59, 94, 95, 99, 100, 114, 131, 141, 163, 216 Wastes 5, 8, 15, 25, 69, 78, 87, 94, 107, 111, 113–117, 124, 139. 140, 148, 149, 172, 174, 178, 186, 210, 213, 218, 222, 224, 229, 232, 233, 235, 237, 245, 252, 253, 256 Wetlands 69, 170, 176–178, 224, 250, 255 World mining industry 1 list of important metal mines 269–281 production of coal 6 production of industrial minerals 5, 284 production of metallic minerals 283, 284 production of metals 1, 4, 283, 284