Mining and Its Environmental Impactby R E Hester
This first Issue in the series contains nine articles written by leading British and American experts from the mining industry, regulatory authorities, and academia, and incorporates the latest research. Following an introductory overview of many of the issues of current concern to the field, the book deals with a wide variety of topics, ranging from the… See more details below
This first Issue in the series contains nine articles written by leading British and American experts from the mining industry, regulatory authorities, and academia, and incorporates the latest research. Following an introductory overview of many of the issues of current concern to the field, the book deals with a wide variety of topics, ranging from the environmental impact of gold mining in the Brazilian Amazon, through the issues relevant to coal mining, vegetative and other remediation strategies and procedures and water pollution, to a thorough analysis of environmental management and policy initiatives. The issues raised in Mining and its Environmental Impact may point the way to future solutions to the economic, technological and environmental problems associated with mining in all its aspects and make this volume key reading for practitioners and researchers in the field, as well as for environmentalists generally.
- Royal Society of Chemistry, The
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Mining and its Environmental Impact
By R. E. Hester, R. M. Harrison
The Royal Society of ChemistryCopyright © 1994 The Royal Society of Chemistry
All rights reserved.
Mining Non-ferrous Metals
A. K. BARBOUR
The products of the extractive industries, both metals and minerals, are of pivotal importance to modern life-styles. This situation will continue for the foreseeable future in spite of the inroads made into some non-ferrous applications by plastics, ceramics, and composites. Some of the many applications illustrating this point are indicated in Table 1.
In this introductory review, emphasis is placed primarily on the environmental impacts arising from the mining and concentration of non-ferrous metal ores. Brief reference is made to the efficient management of emissions from non-ferrous smelting processes, recycling, and the environmental issues arising from the significant power requirements of the industries involved.
Unlike organic chemicals and plastics, metals generally cannot be degraded chemically or bacteriologically into simpler constituents, such as carbon dioxide and water, which are relatively neutral environmentally. Metals occur naturally in a wide range of economic concentrations in the ground from approximately 0.05% for uranium, through 0.5–1% for copper, to approximately 60%–70% for iron, and invariably occur in admixture with a wide range of minor and trace metals. Many non-ferrous metals occur naturally as sulfidic compounds. Thus, metals use is essentially metals relocation and requires:
(1) Large energy inputs to extract the ore and to separate the desired metal from undesired mineral substrates and minor metal impurities, i.e. concentration effects.
(2) Consideration of the toxicity of metals and associated impurities, i.e. their chemical type in extraction, purification, and use (i.e. toxicological effects).
(3) Recycling after use or, where this is impracticable, permanent disposal in an environmentally acceptable manner, i.e. collection and process technology issues.
(4) Managing the effects of associated impurities, including associated minor metals and sulfur.
This overall set of processes is summarized in Figure 1.
The production, use, and recycling of non-ferrous metals thus requires a complex series of technologies carried out by organizations of widely varying size and sophistication in many areas of the world exhibiting extremes of climate, development, and political outlook.
2 Environmental Background
The desire to protect the environment from the perceived effects of both the extraction and processing industries is strong in the so-called 'developed world' (e.g. North America, Europe, Japan, Oceania) and growing rapidly in the 'developing' countries, largely through the efforts of various United Nations agencies. Politicians and regulators express these public wishes through increasingly stringent regulations whose true costs are usually impossible to estimate accurately. Slogans such as the 'Polluter Pays Principle' — whereas the consumer usually eventually pays — are sometimes used to suggest that eventually the costs of building new plants to meet modern environmental standards will become so high that such plants will either not be built or will be constructed in 'developing' countries where standards are thought to be lower.
In general, this view is illusory for new construction and largely so for the upgrading of older plants to modern environmental standards provided an adequate time-scale is allowed; say 5–7 years. It is likely that increasing importance will be attached to environmentally acceptable disposal routes for consumer durable and other end-products. This could result in some market restrictions which would find grudging acceptance from producers and consumers of all environmental standpoints.
The non-ferrous metals industry, in common with its product competitors, has also to manage the impact of quite rapidly rising power costs. Technically, these increases are attributed mainly to the cost of developing low-sulfur basic sources of energy and the cost of neutralizing acidic emissions at power stations burning coal of relatively high sulfur content, to minimize 'Acid Rain'. The cost of safely decommissioning time-expired nuclear power stations will also become an increasing factor.
Environmental issues are often presented confrontationally — development or environmental devastation; compliance with criteria versus costs; industry versus the regulators or the 'Greens' — and, indeed, there is never complete congruence between these different viewpoints.
However, the confrontational approach does scant justice to the desires of most people to improve their material standards, not at any cost, but inevitably through industrial activities which provide employment and income as well as products. It also fails to reflect the increasingly general management view that operations must be designed, run, and maintained to the best professional standards, rather than to those which appear to be the most economic in a short-term view.
From a mining and processing standpoint, aspects of implementation of this policy are outlined in the following review. Though mineral extraction, processing, smelting, and refining can never be environmentally neutral, the overall areas of impact are generally quite small. A fully professional approach can achieve a high degree of amelioration provided it is applied consistently and continuously, on a long-term basis, from project initiation to final 'close-out' of the restored and remediated mine and/or refinery.
From the economic standpoint, the cost of meeting inevitably stricter environmental regulations — and the non-regulatory aspects of such disparate issues as accident prevention, including planning for disaster prevention and mitigation, occupational health, product safety, and 'environmental friendliness' in the ultimate end-product — should be judged on a comparative basis, relating one product's total cycle costs to those of its market-place competitors. Whilst the future situation vis-à-vis competition from plastic and composite materials is much more difficult to estimate with any accuracy, it seems likely that non-ferrous metals will retain many, though not all, applications dependent upon electrical conductivity, ease of repetitive manufacture, and the long-term maintenance of essential physical properties such as strength and relative absence of 'creep' and brittleness. The aesthetic properties of fabricated and well-finished metals will ensure that they are specified for a high proportion of prestige architectural and decorative applications.
Ease and practicability of recycling is already of increasing importance. Unlike metals, most current plastics cannot be recycled without some loss of their original physical properties and so find re-use in less demanding applications. Furthermore, most current plastics are not bio-degradable, e.g. in landfills, so that such materials as have to be disposed to landfill can present long-term environmental problems.
Bio-degradable plastics are being developed and, whilst relatively costly at present, plastics may in future be able to add 'environmental friendliness' to their current virtues of relatively easy availability and low finished-item production cost. However, it is virtually impossible to combine bio-degradability with long-term performance in an engineering plastic and, here, metals are likely always to have the advantage, particularly if their relatively easy reprocessing can be exploited in practice to provide higher levels of economic recycling.
General consideration will now be given to the environmental aspects of the separate stages in non-ferrous metals extraction and use.
3 Extraction and Concentration (Mining and Milling)
The production of non-ferrous concentrates can be depicted schematically as in Figure 2.
As noted earlier, natural concentrations of some non-ferrous metals are very low and invariably contain unwanted impurities. Hence, the tonnages of waste products in the form of tailings and overburden can be very large, amounting to many million tonnes per annum from an individual copper or uranium mine. Due to the in-ground concentration effect, tonnages moved and processed are often of the same order for large copper and iron mines. In relation to all foreseen needs, there are ample resources of all metals to be found in the top mile of the earth's crust. The limitations to winning these metals are the availability of cheap power and, to a lesser degree, practicable technology to isolate and extract deeply occurring metals.
Non-ferrous ores are extracted from both open-pit and underground mines, and occasionally from the two in combination. Where a choice is possible from technico/economic considerations, the balance has to be struck between ensuring the health and safety of the miners, usually easier in open-pit than underground mines, and the disposal of waste products, which is usually less intrusive in underground than open-pit mines which have the added problem of 'hiding the hole' at closure. Successful restoration of a worked-out underground mine is usually a simpler task than for an open-pit operation.
Environmental Impact Assessment
Codification and evaluation of all environmental impacts likely to arise from mining and minerals developed is now required in the form of detailed, independent Environmental Impact Assessments by almost all 'developed' and increasing numbers of 'developing' countries before the authorities will grant a licence to proceed. Some of the issues requiring detailed analysis and at least outline ameliorative or mitigation procedures are set out in the following sections.
Location and access. The location of the mine and its ancillaries is usually fixed by the nature of the deposit, though sometimes the mining plan can be modified to take account of particular features, a relatively common one being a feature of great historical or ethnic significance. The locations of the processing plants, intermediate and final product storages, and waste-rock dumps have to be studied with great care, taking account of the historical factors noted above, the restoration/revegetation plan which should be established in outline in the early planning stages, and the minimization of dust-blow from storage piles and conveyors. The areas selected for the deposition of waste rock must not encourage contamination of local streams by run-off nor hinder the restoration plan. The type and location of tailing areas will also justify a major study for all of the above reasons and additional ones, such as dump stability (particularly in seismic areas), rainfall run-off during storms, and dust-blows if high winds occur during arid seasons. The development of suitable and safe access routes to service the mine during both the construction and operational phases is always of vital importance from both the operational and aesthetic standpoints. All of the above factors become of enhanced importance if the operation is located near to significant residential areas or to areas of unusual scientific or ecological value.
Dust-blow. Total elimination of dust arising from blasting, transportation, handling, and storage is impracticable, particularly if the mine is located in an arid area subject to windy conditions. Neither is it practicable to eliminate completely all human activity from the areas generating and emitting dust. Thus many types of amelioration have to be applied, and these include: (1) dampening all areas of dust generation to the maximum practicable extent; (2) paving haul roads at the earliest practicable time, prior to which some chemical treatment or dressing with waste oil are useful temporarily; (3) providing respiratory protection for all exposed workers and ensuring its use; (4) providing mobile equipment operators with a supply of adequately filtered air; (5) ensuring that residential, office, school, and hospital areas are located as far away as possible in areas of minimum dust exposure; (6) covering permanently dumps, conveyors, etc. wherever practicable.
Processing operations, particularly crushing and conveying, require specific attention to the design of dust capture and arrestment systems to reduce in-plant dust levels to the relevant standard.
Mine safety. Physical safety standards are always a prime consideration in the design and construction of both open-pit and underground mines and, in most countries, are supervised by a specialist Safety Inspectorate. As in other areas, occupational health standards are correctly being tightened in the light of new information on the effects on health of exposure to contaminants encountered in non-ferrous mining generally; such exposures also include noise and vibration. In general terms, compliance represents a rather small additional cost and, somewhat paradoxically, infractions seem to receive less attention from groups external to the industry, than do environmental issues.
Erosion of Waste-rock Dumps. Unlike the chemical and metallurgical processing industries, mines have to be located where economic mineralization naturally occurs. Since large tonnages of extracted low-value materials have to be transported for upgrading, concentration plant associated with the mine also has to be located nearby. Extraction operations naturally break up the terrain and hence increase greatly the surface area of material exposed to rainfall which, in many parts of the world, falls as intense storms of relatively short duration, giving a high risk of flash flooding.
In these circumstances, 'wash-out' from waste-rock piles is inevitable. Fortunately, by definition, waste-rock contains low concentrations only of the desired elements, which are often relatively toxic, but the clays and silts eroded can cause local streams to become opalescent due to the high burden of suspended solids. Ameliorative measures of general applicability do not exist, though occasionally it is possible to channel run-off streams via the tailings impoundment. Fortunately, a corollary of 'spatey' rainfall is that there are often periods of several months of relatively dry weather when erosion is small and stream discoloration is much less marked. Practical problems arise only where streams subject to serious erosion are used for cattle watering. In these circumstances, provision of alternative supplies of water suitable for the purpose should be provided by the mine operators. This is usually not a particularly onerous requirement since the area of influence of even large, open-pit mining operations is usually quite small and clean supplies can be obtained by the provision of relatively small local impoundments either collecting rainfall or storing the water required for the operations of the milling and processing areas.
Run-off problems can be more serious where sulfidic (pyritic) deposits are being worked or where high-sulfur coal is being extracted. Acid is generated by oxidation reactions:
2FeS2 + 2H2O + 7O2 [right arrow] 2FeSO4 + 2H2SO4 4FeSO4 + 2H2SO4 + O2 [right arrow] 2Fe2(SO4)3 + 2H2O Fe2(SO4)3 + 6H2O [right arrow] 2Fe(OH)3 + 3H2SO4
Many methods have been proposed for dealing with acidic run-off, including deep injection, neutralization with lime, and dilution. None are of general applicability; such treatments can only be applied where run-off follows well-defined channels, and, in any case, neutralization is both expensive and difficult to operate effectively. Reliance usually has to be placed on the natural absorptive powers of local streams and the ameliorative measures outlined in the preceding paragraph.
In assessing the impact of, and ameliorative measures for, acid generation the following factors would usually require analysis in the Environmental Impact Assessment: (1) location of waste-rock and tailings disposal areas; (2) contribution of each source to the total generated, e.g. waste-rock, tailings, mine, processing, etc.; (3) practicability of collection by interceptor drains followed by sedimentation, neutralization, etc. together with a disposal policy for the solids produced; (4) environmental effects and significance of a no-treatment policy.
Liquid Effluents from Milling. Milling is the comminution of the extracted ore into particles which can be subjected to a recovery process which separates the valuable materials (concentrate) from the valueless (gangue). The term is now usually used to cover the flotation process (or a chemical treatment process in the cases of alumina production from bauxite; gold; and uranium) which is now an essential part of all non-ferrous mining operations.
Excerpted from Mining and its Environmental Impact by R. E. Hester, R. M. Harrison. Copyright © 1994 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Meet the Author
The series has been edited by Professors Hester and Harrison since it began in 1994.
Professor Roy Harrison OBE is listed by ISI Thomson Scientific (on ISI Web of Knowledge) as a Highly Cited Researcher in the Environmental Science/Ecology category. He has an h-index of 54 (i.e. 54 of his papers have received 54 or more citations in the literature). In 2004 he was appointed OBE for services to environmental science in the New Year Honours List. He was profiled by the Journal of Environmental Monitoring (Vol 5, pp 39N-41N, 2003). Professor Harrison’s research interests lie in the field of environment and human health. His main specialism is in air pollution, from emissions through atmospheric chemical and physical transformations to exposure and effects on human health. Much of this work is designed to inform the development of policy.
Now an emeritus professor, Professor Ron Hester's current activities in chemistry are mainly as an editor and as an external examiner and assessor. He also retains appointments as external examiner and assessor / adviser on courses, individual promotions, and departmental / subject area evaluations both in the UK and abroad.
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