Mining and Sustainable Development II - DTIE

More documents

Recommendations

Info

Mining Mining – facts, figures and environment Introduction The forward-looking articles in this millennium issue of Industry and Environment do not describe the mining industry or its environmental impacts in great detail. Since many readers are probably not well acquainted with this industry, however, the “Facts, Figures and Environment” section will provide some background. A number of technical terms used in the articles that follow are also explained. Part I: Mining – what, where and how? What is mining? A working definition of mining could simply be “the extraction of minerals from the earth”. The word “minerals” in this case would cover a wide variety of naturally occurring substances extracted for human use. Although this definition is adequate for our purposes, mining can also be seen as a process that begins with the exploration for and the discovery of mineral deposits and continues through ore extraction and processing to the closure and remediation of worked-out sites (Figure 1). Environmental impacts occur at all of these stages. Although the articles in this issue are mainly concerned with the extraction and processing stages, there are serious environmental issues surrounding mine closure, post closure monitoring and abandoned mine sites. Minerals are usually classified in four main groups: metals; industrial minerals (such as lime or soda ash, valued for certain special properties), construction materials and energy minerals (i.e. coal, natural gas, oil, etc.). Over 4.6 billion tonnes of coal were mined in 1998. Table 1 gives production figures for selected mineral commodities in 1998 –1999. The minerals extracted in the greatest quantities (but not shown in this table) are those used in construction. It is estimated that some 13 billion tonnes of stone, 10 billion tonnes of sand and gravel, and 500 million tonnes of clay are used annually. With the rapidly growing world population and increasing construction these figures are expected to increase. Where are minerals mined? While minerals are mined throughout the world, the London Mining Journal 1999 Annual Review detailed 158 countries for whom mining is a significant contributor to the national economy. Major metal production areas are shown in Figure 2. As has been the situation for many years, a high proportion of minerals are mined in poorer countries but consumed in richer ones. The world’s largest mining companies are listed in Table 2. How are minerals obtained? Once a commercially viable mineral deposit has been identified, the immediate problem is how to get it out of the ground. There are essentially two ways of doing this: by open pit mining and underground mining. An open pit is a surface excavation, usually conical in shape, dug for the purpose of extracting near-surface ore bodies. The rock overlying the ore body, called the overburden, is drilled and/ or blasted and loaded into trucks that carry it away from the pit. The ore body is then removed for initial processing. Most mines today are surface excavations. Underground mining, which takes place when minerals lie deep beneath the surface, is only economical for high grade ore bodies (see below). To get to the ore body, a vertical shaft, horizontal entrance or passage (adit), or inclined passageway (winze) must be drilled for ore and waste removal, Figure 1 Mining: from discovery of deposits to closure and remediation 1 Finding 2 Follow-up 3 Proving of reserves 4 Planning 5 Construction 6 Extraction 7 Processing 8 Closure Source: UNRFNRE environment protection guidelines Remote sensing Airborne surveys Regional mapping Geochemistry, geophysics Geological mapping Geochemistry, geophysics Limited drilling Grab sampling Close drilling Bulk sampling Limited metallurgical testing Drilling Pilot plant Choice of mining method Processing of ore Facility requirements Designing and engineering, evaluation Access Infrastructure Stripping Shaft sinking/tunnelling Underground/surface construction Ore production Waste dumping Water pumping Ventilation Crushing and grinding Separation Enrichment Tailings deposition Water treatment Clean-up Reclamation Sealing off works, dumps, etc. Revegetation 4 ◆ UNEP Industry and Environment – Special issue 2000
Mining Figure 2 Major metal production areas Canada Ag Au Co Cu Mo Ni Pb Pt Zn CIS (formerly USSR) Ag Al Au Co Cr Mn Mo Ni Pb Pt Ti V W Zn Ag = silver Al = aluminium Au = gold Co = cobalt Cr = chromium Cu = copper Fe = iron Mn = manganese Mo = molybdenum Ni = nickel Pb = lead Pt = platinum Sn = tin Ti = titanium V = vanadium W = tungsten Zn = zinc USA Ag Au Cu Mo Pb Ti Mexico Ag Mo South America Ag Al Co Cu Mn Mo Sn Zn Caribbean Al Cr West Africa Al Mn South Africa Au Cr Mn Pt V Turkey Cr Central Africa Co Cr Cu India Al Cr China Fe Mn Pb Sn V W Zn Australia Al Au Fe Ni Pb Zn SE Asia/Pacific Cu Ni Sn as well as to provide ventilation. Figure 3 illustrates these different types of underground mining, along with some technical terms. Placer mining is a widely used technique for extracting precious metals from sand or gravel deposits at or near the surface. The sand or gravel is mixed with water which is then agitated so that the metals sink. The lighter unwanted material is then washed away. Panning for gold is a simple, small-scale example of placer mining. Processing For some minerals, such as those used in construction, processing is usually limited to washing and separation. For others, especially metallic ores, processing may involve a number of chemical and physical separation steps that can have serious implications for the environment. The most widely used of these processes are described below. The sought-after ores (known as the values) must be separated from the less valuable or valueless material in which they are found, known as the gangue. The amount of mineral contained in the removed material, expressed either as a percentage or by weight, is known as the grade of an ore. A productive economic ore body can range from a few pounds per million (gold) to a few percentage points (lead, zinc) or higher (e.g. 17 per cent for potash; 30 per cent for manganese; 40 per cent for iron). The remainder is waste. To clarify what this means: 1000 tonnes of ore at an average grade of 0.91 per cent will result in 9 tonnes of metal and 990 tonnes of waste. The first step in processing most often consists of crushing or grinding. The combined wastes generated by extraction and milling are known as tailings. The entire process of crushing, grinding, sizing, and separation of ore into waste and value Hanging wall Vein Stope Overburden Drift Underground mining Outcrop Crosscut Level Footwall Surface mining Winze Sump is often called beneficiation. After the mineral grains have been liberated in this way, they can be physically separated using one of several methods: magnetic separation, gravity methods or chemical methods. The magnetic and gravimetric methods do not generally present environmental hazards, but the chemical methods do. The most common chemical methods are flotation, cyanidation, amalgamation and heap leaching. These methods use large amounts of organic compounds, cyanide, mercury and acids (frequently Figure 3 Mining methods Shaft Adit Tailings Quarrying The mining method chosen depends on the type and grade of mineral and rock being excavated and the distance of the ore body from the surface sulphuric), all of which need to be properly handled and are frequently found in the tailings. Part II: Environmental impacts of mining Given the scale of mining activities, it is not surprising that they have a wide range of environmental impacts at every stage of operations. Potential environmental problems associated with mining projects are listed in Table 3. Some can be UNEP Industry and Environment – Special issue 2000 ◆ 5
Page 1 and 2: UNEP ISSN 0378-9993 Industry and En
Page 3: E d i t o r i a l Editorial Mining
Page 7 and 8: Mining Table 2 The world’s 50 lar
Page 9 and 10: Mining Activities Programme in the
Page 11 and 12: Mining Mined Output (% of total val
Page 13 and 14: Mining the Western economies (prima
Page 15 and 16: Mining centration levels between me
Page 17 and 18: Mining resources), human-made capit
Page 19 and 20: Mining does not easily incorporate
Page 21 and 22: Mining address these issues where g
Page 23 and 24: Mining 2. Profile of Reporting Orga
Page 25 and 26: Mining Mining Industry Report Compa
Page 27 and 28: Mining • assist members in meetin
Page 29 and 30: Mining time-scales required to judg
Page 31 and 32: Mining 2. Evaluate the hazards and
Page 33 and 34: Mining States 1 ; the World Conserv
Page 35 and 36: Mining (AMEEF) Environmental Manage
Page 37 and 38: Mining mercury levels from the cont
Page 39 and 40: Mining Rehabilitation measures: wat
Page 41 and 42: Mining liques inorganiques en phase
Page 43 and 44: Mining in the context of mining as
Page 45 and 46: Mining most countries, but often on
Page 47 and 48: Mining Environmental impacts of tra
Page 49 and 50: Mining competing interests and need
Page 51 and 52: Mining ronment? Third, what lessons
Page 53 and 54: Mining miners are already at work.
Page 55 and 56:
Mining funding life cycle of a mini
Page 57 and 58:
Mining Social issues Mining and the
Page 59 and 60:
Mining indigenous traditions and cu
Page 61 and 62:
Mining ticipants in that workshop r
Page 63 and 64:
Mining Mining and indigenous people
Page 65 and 66:
Mining Key Recommendations from the
Page 67 and 68:
Mining despite great improvements,
Page 69 and 70:
Mining between NGOs and the public
Page 71 and 72:
Mining The case for auditing and ce
Page 73 and 74:
Mining of local relevant mining leg
Page 75 and 76:
Mining Tailings dams In order to re
Page 77 and 78:
Mining structures that are specific
Page 79 and 80:
Mining Il est difficile de ne pas f
Page 81 and 82:
Mining Cas où le coût de l’extr
Page 83 and 84:
Mining Voluntary non-regulatory and
Page 85 and 86:
Mining stances by the year 2000. Re
Page 87 and 88:
Mining Viewpoints on future challen
Page 89 and 90:
Mining Selection of World Heritage
Page 91 and 92:
Mining area agencies and managers h
Page 93 and 94:
Mining ◆ Aprovechar racionalmente
Page 95 and 96:
THE UNEP DIVISION OF TECHNOLOGY, IN
show all

Mining and Sustainable Development II - DTIE

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?