The Geochemistry of Acid Mine Drainage

Mine wastes are the largest volume of materials handled in the world (ICOLD, 1996). The generation of acidic drainage and the release of water containing high concentrations of dissolved metals from these wastes is an environmental problem of international scale. Acidic drainage is caused by the oxidation of sulfide minerals exposed to atmospheric oxygen. Although acid drainage is commonly associated with the extraction and processing of sulfide-bearing metalliferous ore deposits and sulfide-rich coal, acidic drainage can occur wherever sulfide minerals are excavated and exposed to atmospheric oxygen. Engineering projects, including road construction, airport development, and foundation excavation are examples of civil projects that have resulted in the generation of acidic drainage. On United States Forest Service Lands there are (2-5)×104 mines releasing acidic drainage (USDA, 1993). Kleinmann et al. (1991) estimated that more than 6,400 km of rivers and streams in the eastern United States have been adversely affected by mine-drainage water. About (0.8-1.6)×104 km of streams have been affected by metal mining in the western United States. The annual worldwide production of mine wastes exceeded 4.5 Gt in 1982 (ICOLD, 1996). Estimated costs for remediating mine wastes internationally total in the tens of billions of dollars ( Feasby et al.,1991).