Acid mine drainage (AMD) resulting from the disposal of mining waste containing sulphide minerals is considered one of the most significant environmental problems facing the mining industry today. AMD is formed as a result of the oxidation of sulphide minerals that ultimately results in the release of metal-rich acidic waters.
The oxidation of iron sulphides is catalyzed by bacteria and proceeds according to the following reaction:
2FeS2(pyrite) + 7.5O2 + 7H2O 2Fe(OH)3 + 4H2SO4
Most mining wastes contain >10% iron sulphides (by weight) and some may contain more than 50%. These waste materials may be in the form of finely divided particles called “tailings” or in the form of coarse “waste rock” of various sizes including boulders.
Environmental Impact
The environmental impacts of acid mine drainage can be long-term. Even after a mine property has been abandoned, acid mine drainage flows continue for decades and, even for more than a century. Acid mine drainage can cause a serious pH depression in receiving waters and an increase in dissolved metals toxic to flora and fauna. In general, acid mine drainage can destroy almost all local aquatic life in a receiving stream. Stream bottoms become covered with chemical precipitates that are deleterious to algae, invertebrates and fish.
Current Approach
The traditional approach to the AMD problem has been to treat the leachate with lime creating a disposal problem with metal laden sludge. Another alternative has been to use a physical barrier, ie., soil covers, water or geotextile liners to prevent oxygen infiltration into the tailings.
The AmdEL solution – stopping the formation of AMD at the source.
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