Abstract
AbstractAcid mine drainage (AMD) occurs after mining exposes metal sulfides to oxidizing conditions. Leaching of reaction products into surface waters pollute over 20 000 km of streams in the USA alone. The coal mining permitting process requires prediction of AMD potential, most commonly via overburden analysis. Where a potential exists, AMD control measures including spoil handling plans, alkaline amendment and dry covers may be required to stop or hinder AMD generation. Other AMD control technologies include injection of alkaline materials (coal ashes and limestone products) into abandoned underground mines and into buried acid material in mine backfills, remining of abandoned areas, and installation of alkaline recharge trenches. In the event AMD is formed, effluent treatment is required. Treatment chemicals include Ca(OH)2, CaO, NaOH, Na2CO3, and NH3, but chemical treatment is costly, requires expensive equipment and facilities, and often extends for decades. Passive treatment systems may also be employed to treat problem drainages and are effective under certain flow and acidity conditions. Such systems include aerobic and anaerobic wetlands, anoxic limestone drains, vertical flow wetlands, open limestone channels, and alkaline leach beds. This chapter discusses the process of AMD formation, preventative measures, and treatment methods for existing AMD discharges.
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