Coal Mining and Production

Pollution Prevention and Abatement Handbook WORLD BANK GROUP Effective July 1998 Coal Mining and Production Industry Description and Practices waste streams: fine materials that are discharged as a slurry to a tailings impoundment, and coarse Coal is one of the world’s most plentiful energy material (typically greater than 0.5 millimeters) resources, and its use is likely to quadruple by that is hauled away as a solid waste. 2020. Coal occurs in a wide range of forms and qualities; but there are two broad categories: (a) Waste Characteristics hard coal, which includes coking coal, used to produce steel, and other bituminous and anthra- The main impacts of surface mining are, in gen- cite coals used for steam and power generation, eral, massive disturbances of large areas of land and (b) brown coal (subbituminous and lignite), and possible disruption of surface and ground- which is used mostly as onsite fuel. Coal has a water patterns. In some surface mines, the gen- wide range of moisture content (2–40%), sulfur eration of acid mine drainage (AMD) is a major content (0.2–8%), and ash content (5–40%). These problem. Other significant impacts include fugi- can affect the value of the coal as a fuel and cause tive dust and disposal of overburden and waste environmental problems in its use. rock. The depth, thickness, and configuration of the In underground mines, the surface disturbance coal seams determine the mode of extraction. is less obvious, but the extent of subsidence can Shallow, flat coal deposits are mined by surface be very large. Methane generation and release can processes, which are generally less costly per ton also be a problem under certain geological con- of coal mined than underground mines of simi- ditions. If groundwater systems are disturbed, lar capacity. Strip mining is one of the most eco- the possibility of serious pollution from highly nomical surface processes. Here removal of saline or highly acidic water exists. Impacts may overburden and coal extraction proceed in par- continue long after mining ceases. allel strips along the face of the coal deposit, with Table 1 presents the levels of liquid effluents, the spoil being deposited behind the operation solid waste, and dust generated by the major in the previously mined areas. In open pit min- mining techniques. ing, thick seams (tens of meters) are mined by Beneficiation plants produce large volumes of traditional quarrying techniques. Underground tailings and solid wastes. Storage and handling mining is used for deep seams. Underground of coal generates dust at rates of as much as 3 mining methods vary according to the site con- kilograms per metric ton (kg/t) of coal mined, ditions, but all involve the removal of seams fol- with the ambient dust concentration ranging lowed by more or less controlled subsidence of from 10 to 300 micrograms per cubic meter (µg/ the overlying strata. m3) above the background level at the mine site. Raw coal may be sold as mined or may be pro- cessed in a beneficiation/washing plant to re- Pollution Prevention and Control move noncombustible materials (up to 45% reduction in ash content) and inorganic sulfur (up Early planning and careful design of operations to 25% reduction). Coal beneficiation is based on are the key to minimizing pollution associated wet physical processes such as gravity separa- with mining activities. Specific responsibilities tion and flotation. Beneficiation produces two should be assigned for the implementation and 282 Coal Mining and Production 283 Table 1. Loads Per Unit of Coal Production, by Mining Technique (tons per 1,000 tons coal produced) Surface mining Underground mining Waste characteristic Contour Area Conventional Longwall Liquid effluents 0.24 1.2 1 1.6 Solid waste 10 10 3 5 Dust 0.1 0.06 0.006 0.01 Note: Local conditions will form the basis for choosing the appropriate mining method. Source: Based on Edgar 1983. monitoring of environmental measures. Before • Reduction of dust by early revegetation and mining begins, a mining plan and a mine closure by good maintenance of roads and work ar- and restoration plan must be prepared and ap- eas. Specific dust suppression measures, such proved. These plans define the sequence and as minimizing drop distances, covering equip- nature of extraction operations and detail the ment, and wetting storage piles, may be re- methods to be used in closure and restoration. quired for coal handling and loading facilities. The plans should be updated regularly (every 3 Release of dust from crushing and other coal to 5 years) as mining progresses. processing and beneficiation operations should be controlled. Development Plan • Control of the release of chemicals (includ- ing floatation chemicals) used in beneficiation The development plan defines the sequence and processes. nature of extraction operations and describes in • Minimization of the effects of subsidence by detail the methods to be used in closure and res- careful extraction methods in relation to sur- toration. At a minimum, the plan must address face uses. the following: • Control of methane, a greenhouse gas, to less than 1% by volume, to minimize the risk of • Removal and proper storage of topsoil. explosion in closed mines; recovery of meth- • Early restoration of worked-out areas and of ane where feasible. (When methane content is spoil heaps to minimize the extent of open above 25% by volume, it normally should be areas. recovered.) • Diversion and management of surface and • Development of restoration and revegeta- groundwater to minimize water pollution tion methods appropriate to the specific site problems. Simple treatment to reduce the dis- conditions. charge of suspended solids may also be nec- • Proper storage and handling of fuel and chemi- essary. (Treatment of saline groundwater may cals used on site, to avoid spills. be difficult.) • Identification and management of areas with Mine Closure and Restoration Plan high potential for AMD generation. • Minimization of AMD generation by reducing The plan should include reclamation of open pits, disturbed areas and isolating drainage streams waste piles, beneficiation tailings, sedimentation from contact with sulfur-bearing materials. basins, and abandoned mine, mill, and camp • Preparation of a water management plan for sites. Mine reclamation plans should incorporate operations and postclosure that includes the following measures: minimization of liquid wastes by methods such as recycling water from the tailings wash • Return of the land to conditions capable of plant. supporting prior land use, equivalent uses, or • Minimization of spillage losses by proper de- other environmentally acceptable uses sign and operation of coal transport and trans- • Use of overburden for backfill and of topsoil (or fer facilities. other plant growth medium) for reclamation 284 PROJECT GUIDELINES: INDUSTRY SECTOR GUIDELINES • Contouring of slopes to minimize erosion and from these levels must be described in the World runoff Bank Group project documentation. The emis- • Planting of native vegetation to prevent sions levels given here can be consistently erosion and encourage self-sustaining devel- achieved by well-designed, well-operated, and opment of a productive ecosystem on the re- well-maintained pollution control systems. claimed land The guidelines are expressed as concentrations • Management of postclosure AMD and benefi- to facilitate monitoring. Dilution of air emissions ciation tailings or effluents to achieve these guidelines is un- • Budgeting and scheduling of pre- and post- acceptable. abandonment reclamation activities. All of the maximum levels should be achieved for at least 95% of the time that the plant or unit Upon mine closure, all shaft openings and is operating, to be calculated as a proportion of mine adits should be sealed or secured. annual operating hours. There is a need to reserve money over the life of the mine to cover the costs associated with Air Emissions mine closure. The amount of money and the type of financing required will depend on a number Controls may be required on individual sources, of factors, such as the projected life of the mine, such as ventilation exhausts, if they have a sig- the nature of the operations, the complexity of nificant effect on ambient particulate levels. If environmental issues, the financial and environ- coal crushers or dryers are used, fabric filters or mental management capacity of the borrower or other systems should be used to recover coal and project sponsor, and the jurisdiction in which the reduce particulate emissions to levels below 50 mine is located. The mine reclamation and clo- milligrams per normal cubic meter (mg/Nm3). sure plan, the timing of its submission, and its financing should be discussed and agreed on Liquid Effluents with the borrower or sponsor as early as possible. Target Pollution Loads Settling ponds to catch stormwater and to reduce suspended solids should be provided for all effluent before discharge from the site. Implementation of cleaner production processes Where treatment of AMD or other effluents is and pollution prevention measures can provide required, the effluent levels presented in Table 2 both economic and environmental benefits. The should be achieved during operation and after loads presented in Table 1 can be used as a guide mine closure. for pollution prevention purposes. The figures relate to each of the production processes before Ambient Noise the addition of pollution control measures. Emissions Guidelines Noise abatement measures should achieve either the levels given below or a maximum increase in Emissions levels for the design and operation of each project must be established through the en- Table 2. Acid Mine Drainage and Liquid vironmental assessment (EA) process, on the ba- Effluents from Coal Mining sis of country legislation and the Pollution Prevention (milligrams per liter, except for pH) and Abatement Handbook as applied to local con- Parameter Maximum value ditions. The emissions levels selected must be justified in the EA and acceptable to the World pH 6–9 a Bank Group.

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