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英文原文Environmental issues from coal mining and their solutionsBIAN Zhengfu1，INYANG Hilary I2 ，DANIELS John L3 ，OTTO Frank4， STRUTHERS Sue51. Institute of Land Resources, China University of Mining management of mining wastes; reuse of mine gas; mined land reclamation; clean coal mining1 IntroductionWhile coal makes an important contribution to worldwide energy generation, its environmental impact has been a challenge. In essence, the coal energy production system consists of coal mining, preparation or processing and energy generation. Fig. 1 shows the complete process of the coal energy system. Environmental issues arise at every stage of the process. This paper will discuss environmental issues due to coal mining. In fact, environmental problems from coal mining have been studied since coal mining became industrialized. Nevertheless, environmental issues from coal mining have become important concerns only since the 1970’s. The majority of the available literature related to mining and the environment date from the end of the 1970’s to the end of the 1980’s. However, coal production has changed significantly since the beginning of the 1990’s and as a result, the way and the extent that mining operation impact the environment are also different now. Fig. 2 shows the change in worldwide coal production over time, which illustrates that coal production increased strikingly after 2000. Six countries, the USA, Russia, India, China, Australia and South Africa, produced 81.9% of the total coal extracted throughout the world in 2006. These same countries have about 90% of the World’s coal reserves. Coal production in China accounted for 38.4% of the worldwide total and has increased about 66% over the past five years from 1.38 billion tons in 2001 to 2.3 billion tons in 2006. During the same time period the number of coal mines was reduced by 50%. The annual production of the Daliuta Coal Mine, one of the underground mines operated by the Shendong Coal Mining Company, reached 20 million tons from only two longwall work faces in 2007. In the U.S，the situation is similar to China. There were 2475 coal mines with a total production of 945424 thousand short tons in 1993 but 1438 coal mines producing 1162750 thousand short tons in 2006.north americchinasut iaeuropeast ifig.1 coal enrgy stermgeolic surveyingcoal resvm:surfmingoundergound migxvtdxtacipeaoechal s,sh,clnig,sr,omgenol productryti:pdcafeombuiyproductin102304501950202052102150 206:refncFig. 2 Worldwide coal productionChina consumes more coal than Europe, Japan and the United States combined; 40% of the world’s total. China’s coal use continues to grow every year and it is estimated that 90% of the rise in world coal consumption is from increased activity in China. As a result, mining intensity in some coalfields is ten times greater than it was in the past. Therefore, the impact of mining on the environment today is significantly different from that in the 1980’s. Thus, this paper focuses on environmental issues due to coal mining in the context of current mining operations. 2 Importance of coal mining to energy systems worldwide and challenges to the environmentThe main use of coal in the United States is to generate electricity. Coal generates half of the electricity used in the United States. Today, 91.9% of all the coal in the United States is used for electricity production. In contrast, less than 50% of all the coal mined in China was used for electricity generation in 2005 when 82% of the electricity used in China came from coal fired plants. Coal accounts for approximately 74% of China’s primary energy consumption. Coal is recognized as a dirty source of energy and has been rendered obsolete in many European countries. For example, France closed all coal mines in 2004 and, in early 2007, the German government announced that subsidies for coal production would be completely phased out by 2018. Whether this will mark the end of deep mining in Germany remains to be seen.Some experts and institutions forecast that coal will continue to underpin the economic and social development of the world’s biggest economies in both the developed and developing world. The World Bank Group estimated that coal is one of the World’s most plentiful energy resources and that its use is likely to quadruple by 2020. Global recover-able coal deposits exceed 1 trillion tons with enough deposits to last for the next 270 years at current consumption rates. Hence, it is reasonable to conclude that coal will continue to be an important energy source and that coal mining is not a sunset industry. This will be especially true in those countries with abundant coal reserves and increased energy demands for their development. Using coal as an energy source requires addressing environmental challenges from mining. This includes coal mine accidents, land subsidence, water pollution, air pollution, spoil heaps, acid mine drainage, disturbance of hydro-geology and so on. The impact of coal mining on the environment varies in severity depending on whether the mine is active or abandoned, the mining methods used and the geological conditions.2.1 Coal mine accidents Every year nearly 80% of the World’s total deaths due to coal mine accidents occur in China. The main causes of coal mine accidents are gas leaks, roof cave-ins, fires, blasts and floods/water bursting. Table 1 shows accident statistics for Chinese coal mines for the years 2006 and 2007. This data was compiled by the corresponding author from the State Administration for Coal Mine Safety safety bulletins. It is easy to see that coal dust and methane blasts are in the absolute majority. In addition, 117 of the 374 deaths in 2006, and 92 of the 399 deaths in 2007, occurred in coal mines with a production of less than 200 thousand tons. It was reported that coal mines with small scale production account for one third of total production, two third of the total coal mine accidents and 75% of the deaths. Table 1 Chinese coal mine accident statisticsAccidentsCoal dust andmethane blastWater burstingCO poisoningRoof cave-inFiresTimes 15 8 2 12006Death 322 31 14 7Times 21 3 2 1 12007Death 317 41 12 5 242.2 Land subsidence Approximately 60% of the world’s coal production comes from underground mines. Since 95% of the coal production in China is from underground mines and, in 2007, Chinese production was 2523 million tons, which accounts for more than one-third of the world’s production, China accounts for much of the underground operation, see Table 2. Table2 Percentage of coal production by mining method in the main coal producing countries (2006)Country Underground mining(%) Surface mining(%) Total(MT)China 95 5 2380.0USA 30.9 69.1 1053.6India 19 81 447.0Australia 22 78 405.1Russia 309.2South Africa 256.9Germany 197.2Indonesia 195.0Poland 156.1Total world 60 40 6195.1Land subsidence over underground mines is one important adverse impact of mining on the environment. About 1 million hectares of subsided land exists today. Mining ten thousand tons of raw coal will result in 0.2 hectares of subsiding land in China. Land subsidence not only reduces crop production but also causes other environmental problems, such as utility failures, plant death, surface fracture and soil loss, drainage system failure, building damage and so on. Subsidence falls into two forms of deformation: continuous and discontinuous. Continuous, or trough, subsidence involves the formation of a smooth surface profile free of steps. Discontinuous subsidence is characterized by large surface displacements over a limited surface area and by the formation of steps or discontinuities in the surface profile. Mining subsidence will affect land use or the environment differently depending upon the context of the terrain, groundwater level and the original type of land use. For example, in eastern China, which has plain land-form, shallow groundwater levels and was prime farmland before mining, mining subsidence has resulted in large area flooding. After this the land use was changed as buildings, roads and croplands were seriously damaged by major incidents of land subsidence. Mining subsidence in mountain areas will induce slope failure causing the loss of water and soil from the formation of surface cracks and overburden fracture from mining.2.3 Water environment Coal mining affects the water environment mainly by inducing a drop in the ground water table, causing water loss or water pollution and by altering water-courses. Mining drainage and mine subsidence have an immediate effect on the water environment due to the connection of underground water bodies to the mined space through fractured overburden. When water is redirected as a result of fracturing or cracking it interacts with the various subsurface strata with which it comes in contact. In these strata there are many compounds and sediments that may be dissolved by the flowing water to eventually leach into the drainage lines. Many of these newly exposed minerals can react with gaseous or liquid components in their new environment to yield contaminants. These have an impact on water chemistry and aesthetics and can increase the level of suspended solids in the water. This results in a significant reduction in the quality of the water and the aquatic habitat. Mine drainage can pollute surface water and the disposal of mining wastes will also affect water quality when contaminants leach into the surrounding surface or ground water. Acidic Mine Discharge (AMD) is formed when pyrite reacts with air and water to form sulfuric acid and dissolved iron. This acid run-off dissolves heavy metals such as copper, lead and mercury that may end up in ground and surface waters. In the United States AMD is still of great concern as it is estimated that there are over 1.1 million surface acres of abandoned coal mines, over 9000 miles of streams polluted by acid mine drainage and many miles of dangerous embankments, highwalls and surface impoundments. Surface watercourses have to be changed, obviously, to strip overburden and apply surface mining to coal resources. If coal resources are mined underground subsidence would change the slope of the relief, broaden the surface-water pathways and consequently change the surface water regime. 2.4 Mining wastes disposal Waste products from underground coal mining comprise coarse discard (mine stone or coal reject) and fines that are produced by the washing process. The former comes to the surface, mostly with ‘run of mine’ coal, as a result of the cutting of roadways and drives or other underground development work and the high degree of automation applied to variable geology. Surface coal mining involves material that must be removed to gain access to the coal resource including topsoil, overburden and waste rock. While the coalfield operator does not seek to produce waste unnecessarily geology and mining methods combine to increase the waste quantities involved. Theoretically, mining methods could be made more sustainable by minimizing waste production. The need to accommodate both dry mine stone and ‘wet’ fines imposes the main engineering constraints on tip design and that controls the pace of progressive restoration. Although waste reduction and reuse have recently become the most preferable methods of waste management (for example, mine stone has been accepted in many places as alternative aggregate for use in embankment, road, pavement, foundation or building construction) most of the coal mining waste still must be transported to dumps or used to fill gullies or tipped as a hill. Mining wastes have significant impacts on the environment in the following ways: slope failure and erosion; occupation of lands; potential leaching of contaminants into groundwater; dust pollution driven by wind; air pollution and explosion by spontaneous combustion; visual and landscape impact; and land use constraints. Oxidation of pyrite within spoil-heap waste will pollute the air as well as ground water. This oxidation is governed by access to oxygen, which in turn depends upon the particle size distribution, the amount of water saturation and the degree of compaction 。The impact of mining waste can have lasting environmental and socio-economic consequences and be extremely difficult and costly to address through remedial measures. Coal mining wastes have, therefore, to be properly managed to ensure the long-term stability of disposal facilities and to prevent or minimize any water and soil pollution arising from acid or alkaline drainage and leaching of heavy metals.2.5 Air pollution Air pollution from coal mines is mainly due to the fugitive emission of particulate matter and gases including methane, sulfur dioxide and oxides of nitrogen. Surface mining operations like drilling, blasting, movement of heavy earth moving machinery on haul roads, collection, transportation and handling of coal and the screening, sizing and segregation units are the major sources of such emissions. Underground mining also emits dust from uncovered coal piles and wastes dumps. The emission of CO, CO2, NOx, SOx happens because of spontaneous coal combustion and methane leaking from the coal strata and coal seams. Methane is a “greenhouse gas” that is 21 times more potent in its greenhouse effect than carbon dioxide. Methane emission from coal mining depends on the mining method, the depth of coal mining, the coal quality and the entrapped gas content within the coal seam. As mining proceeds methane is released into the mine air to be eventually discharged into the atmosphere. Methane emissions from coal mining are listed in Table 3 by country in terms of the rank as of 2000. Methane is highly explosive and has to be drained during mining operations to keep working conditions safe. At active underground mines in China, large-scale ventilation systems move massive quantities of air thereby releasing methane into the atmosphere at very low concentrations.Table 3 Methane emissions from coal mining (million tons CO2 equivalent)Most recent year availableRank as of 2000Country Methane emissionYear Methane emissions1 China 117.6 2004 1932 Us 56.2 2003 54.03 Russia 29.0 2002 20.64 Ukraine 28.3 2001 27.05 Australia 19.6 2005 21.86 India 15.8 2005 19.57 Poland 11.9 2003 6.78 Germany 10.2 2005 5.42.6 Landscape change Coal mining changes the local landscape dramatically by introducing things such as mining waste dumps, high shaft towers, large scale surface scarring from surface mining or land subsidence from underground mining. All of these are typical within the mine landscape. In addition, land use can change, native residents may migrate away from the coal mining or the course of rivers may change. All these things will affect the structure and function of the ecosystem. For example, in the Yulin coal mining area, which is located in western China, fallow land decreased by 125148 hm2 between 1985 and 2000 while at the same time grassland and woodland increased by 107975 and 17157 hm2 , respectively [9]. The major factors responsible for these changes are a change in the government policy on preserving the environment, continued growth in mining and urbanization. Efforts to restore the deteriorated ecosystem have reaped certain benefits in reducing the spatial extent of sandy land through replacement by non-irrigated farmland, woodland and grassland. On the other hand, continued expansion of the mining industry and of urbanization has exerted adverse impacts on the landscape. Coal mining has caused the destruction of land resources and the fragmentation of the landscape accompanied by land desertification; the situation is even serious in some localities. In the Xuzhou coal mining area, which is located in eastern China, farm land decreased by 13.04% from 1987 to 2001, construction areas increased by 37.62% and flooded land resulting from mining subsidence increased by 137.62%. This subsidence accounts for 30% of the total subsided land. 3 A conceptual framework and potential solutions to the mine environment 3.1 A conceptual framework for solving mine environmental issues The key words green mining, ecological mines, recycling economy, industrial ecology, site characterization for remediation of abandoned mine lands and life cycle assessment were proposed by environmentalists, economists and scholars working in the field of mining science. The core ways to solve mine environmental problems may fall into two types. One is the taking of measures to lessen the impact of mining on the environment during mining. The other is the taking of measures to clean or remediate or restore or reclaim the environment post mining as illustrated in Fig. 4. Fig. 4 A conceptual framework for solving mine environmental issuesGreen mining as posed by Professor Qian, a Chinese Engineering Academician, is one of many ideas proposed to solve the environmental issues. The foundation of these ideas is the distribution behavior of joints, Envirometalisufrocalmingeitl plinldspe hwatr polutinair polutinming wastesoil cnaitoland subieclan usechgmigraton ftivesifrstucrdicl orditrstai rlatiuring mi optingfractures and bed separations and the see-page flow of methane and water through broken rock strata caused by mining [11]. Green mining techniques under development include water-preserved-mining, coal mining under infrastructures, grouting into the space between separated rock layers to reduce surface subsidence, partial extraction and backfill mining, simultaneous extraction of coal and coal-bed methane, underground roadway support, underground discharge of partial mining wastes and underground coal gasification. The principles of industrial ecology and mining science also should promote the rational utilization of natural resources by reducing waste, reusing waste and recycling waste. A reduction in the mining waste produced by excavating roadways along coal seams and other innovative mining methods are one approach to this. Using coal mining waste as fuel for thermal electric plants is a good example of reusing mining wastes. Recycling of mining waste is a more environmental friendly technique. For example, after mining waste is burned in an electric plant the fly ash can be used as raw material for cement production. Or rather than just converting fly ash into cement some useful elements of the fly ash , such as refractories, can first be extracted. 3.2 Use of mine gas Venting mine gas imposes a considerable burden on the environment and also wastes valuable energy. Because mine gas is explosive in certain concentrations it is traditionally removed by intricate ventilation systems during active operations of the mine. Recent statistics show that the number of Chinese coal mines with high methane concentrations is 49.8% of all the mines and coal production from these mines accounts for 42% of the total production. Furthermore, coal mine accidents from mine gas explosion account for 94.97% of the total accidents and deaths in these accidents account for 96.25% of all deaths. Reducing mine accidents and making full use of methane as a new energy source is an important goal. The Ministry of Environmental Protection and the General Administration of Quality Supervision, Inspection and Quarantine of China have jointly issued the Emission Standard of Coal bed Methane Coal Mine Gas (on trial). The Standard requires that measures to drain and utilize the mine gas must be taken before mining. Coal mining operations may only be implemented after the methane content in the coal seam is reduced to less than eight cubic meters per ton of coal. If the concentration of methane is higher than 30% atmospheric release is prohibited. There are currently two ways to drain mine gas in China. One is by drilling wells through the coal seam at the coalfield before mining operations begin. The concentration of methane obtained this way is higher than 90% the other method i