Acid mine drainage

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  1. Mineral processing and other anthropogenic activities leave by-products exposed to oxygen and moisture in the air. If the by-products are sulfide minerals they may start to bioleach out of control and cause the environmental problem known as acid mine drainage (AMD). AMD manifests itself as acidified groundwater contaminated by heavy metals.
  2. Drainage flowing from or caused by surface mining or coal refuse piles that are typically highly acidic with elevated levels of dissolved metals.

Sometimes AMD is mistaken for acid rock drainage (ARD) and acid rock generation (ARG) which have slightly different meanings.

Contents

Formation

Acid mine drainage is formed by uncontrolled bioleaching reactions - a series of complex geochemical and microbial reactions that occur when water and oxygen come into contact with pyrite (iron disulfide minerals) in for example coal, refuse or the overburden of a mine operation.

Kristineberg, Sweden. Acid mine drainage manifests itself as acidified groundwater contaminated by heavy metals - an environmental problem which can be prevented or treated. By courtesy of Roger Herbert and Magdalena Gleisner
Kristineberg, Sweden. Acid mine drainage manifests itself as acidified groundwater contaminated by heavy metals - an environmental problem which can be prevented or treated. By courtesy of Roger Herbert and Magdalena Gleisner
AMD in Rio Tinto river
AMD in Rio Tinto river

Risk factors for AMD

Very fine sulfide mineral particles are more prone to leaching since the reduced particle size will expose a greater surface area. As a consequence, leaching chemicals can more easily come into contact with the ore surface, leading to a faster leaching reaction.

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Strategies to prevent acid mine drainage

  • By covering waste with a sealing layer, as well as layers of water or soil, contact with oxygen is prevented. Another way to avoid oxygen contact is by backfilling the waste into exhausted underground mines. Since the microorganisms oxidise the sulfur and iron in the ore, they can't thrive without oxygen or water. Then leaching can't occur.
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Strategies to treat acid mine drainage

Active treatment of AMD by courtesy of Barrie Johnson
Active treatment of AMD by courtesy of Barrie Johnson

External links

Acid Rock Drainage at Enviromine

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