Mine Water

Abstract

Water is needed at mine sites for dust suppression, mineral processing, coal washing , and hydrometallurgical extraction. For these applications, water is mined from surface water bodies and ground water aquifers, or it is a by-product of the mine dewatering process. Open pits and underground mining operations commonly extend below the regional water table and require dewatering during mining. In particular , mines intersecting significant ground water aquifers, or those located in wet climates, may have to pump more than 100,000 liters per minute to prevent underground workings from flooding. At some stage of the mining operation, water is unwanted and has no value to the operation. In fact, unwanted or used water needs to be disposed of constantly during mining, mineral processing, and metallurgical extraction. At modern mine sites, water is collected and discharged to settling ponds and tail-ings dams. In contrast, at historic mine sites, uncontrolled discharge of mine water commonly occurs from adits and shafts into the environment. Generally, the volume of mine water produced, used and disposed of at mine sites is much larger than the volume of solid waste generated. At mine sites, water comes in contact with minerals and dissolves them. Hence, water at mine sites often carries dissolved and particulate matter. When such laden waters reach receiving water bodies, lakes, streams or aquifers, the waters can cause undesirable turbidity and sedimentation, they may alter temperatures, or their chemical composition may have toxic effects on plants and animals. For example, in the United States, it has been estimated that 19,300 km of streams and 72,000 ha of lakes and reservoirs have been seriously damaged by mine effluents from abandoned coal and metal mines (Kleinmann 1989). The worst example of poor mine water quality and associated environmental impacts is acid mine drainage (AMD) water, which originates from the oxidation of sulfide minerals (Sect. 2.3). Sulfide oxidation is an autocatalytic reaction and therefore, once AMD generation has started, it can be very difficult to halt. AMD is the most severe in the first few decades after sulfide oxidation begins, and the systems then produce lower levels of contaminants (Demchak et al.