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| | Acid Mine Drainage and Mining Below the Water Table
Author: BacTech Mining Corporation
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| | Quite often, sub-surface mining or mineral extraction takes place below the water table, meaning that, in order to prevent mines from flooding, it is necessary to consistently "pump" the water. After drilling ceases and a mine site is abandoned, water is no longer pumped and, as a result, flows back into the rock. This is the first step toward what is referred to as acid mine, or acid rock, drainage (AMD, ARD).
Subsequently exposed to air and water, either in an abandoned mine itself or in the left-behind tailings around a mine site, the metal sulfides in the materials oxidize and this overburden or "waste" generates high levels of acidity (especially with sulfide ores or pyrites, such as those found in zinc, copper, and nickel). Other elements, like colonies of bacteria and archaea, may exist that accelerate metal decomposition; microbes and other extremophiles - organisms that thrive in extreme conditions - then sustain or survive in these harsh conditions. The acidic substance runs off or "drains" into nearby bodies of water and into soils, potentially polluting an area for many miles, while also degrading surface-water sources.
AMD usually results from waters flooding into metal or coal sites, but it has also been known to occur in other areas where the earth has been disturbed, such as in construction sites, transportation corridors, and subdivision developments.
Organizations all over the world are in place to provide regulatory oversight and to reduce the effects of AMD. Many innovative solutions are being explored for existing drainage at abandoned mine sites, such as constructed wetlands (artificial marshes or swamps), and at existing sites, the acidic water is neutralized to pH levels approved for release into a stream.
BacTech can help to mitigate AMD via its proprietary bioleaching process, which remediates mine tailings and renders toxins benign before the oxidation process can occur. Where tailings have been sitting in water for years, bioleaching can be used to stave off additional drainage while other wastewater processes are employed to clean up the affected area. |
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