Acid Mine Drainage
Acid mine drainage (AMD ) in German known under the names of acidic mine drainage, acidic runoff, acid mine waters, acidic pile waste water, acid rock drainage and acidic Bergbauausflüsse, are acidic waters containing high levels of dissolved heavy metals (heavy metal ions) and sulfate ions, which from ore deposits, coal deposits, mines ( mines ) and mining dumps flow out, the heavy metal sulfide minerals, in particular, contain pyrite. Since there is no single German name, the English term acid mine drainage has naturalized in Germany.
Formation
Acid mine drainages caused by a complex coupling of abiotic and microbial oxidation of sulfide minerals. Both processes have to cooperate, a purely abiotic oxidation, ie without the specific microorganisms, is approximately 10,000 times slower. Sulfide is oxidized to sulfate in the oxidation of sulphide minerals, the heavy metals are dissolved as ions. Microbial moiety is in an oxidation of iron ( II) ions to iron ( III) ions and the oxidation of elemental sulfur and sulfur compounds to sulphate by sulfuric acid or specific bacteria and archaea. In the oxidation of sulphide minerals with an atomic ratio of sulfur to heavy metal in excess of 1, such as pyrite ( FeS2 ), sulfuric acid is formed, resulting in an acidification results. The oxidation of sulphide minerals is a form of decomposition represents the pyrite - oxidation is also known as pyrite decomposition.
Importance
Acid mine drainages represent a significant hazard due to the associated pollution; they harm the environment by contamination with heavy metals and acidification, buildings and equipment by corrosive action of the acid. As far as they occur in connection with mining, they therefore represent mining damage dar. main source of slag heaps that result from weathering and over again to a post-acidification. The water quality of lakes rest of opencast mines is significantly and sustainably determined by the sulfide content of the tipping material. Acidification can lead to pH values between 2 and 4 and residual lakes typically contain high concentrations of metals that may be toxic effects on living organisms. Use as a drinking water reservoir or for leisure activities is hardly possible. A particular danger is contamination of groundwater. The AMD residual lakes of the largest opencast mine in the world, Chuquicamata copper mine in Chile, have an area of 48 km ².
Treatment, prevention
The addition of lime ( CaCO3), the acid is neutralized ( pH raised) and the heavy metals are mostly precipitated as hydroxides and thus removed from the water. In the Rhenish lignite mining areas is prevented by the addition of limestone in the overburden containing pyrite pyrite weathering. The iron and sulfur oxidation -causing bacteria and archaea are in fact inhibited by higher pH values .