Acid mine water
Acid mine water , often acid mine drainage ( AMD ), also known in German under the names acidic runoff , acid mine drainage , acidic pile waste water , acidic leachate and acidic Bergbauausflüsse , are acidic waters containing high levels of dissolved metal, semi-metal and sulphate - ions from ore deposits , carbon deposits , mines (mines) and mining Halden flow out and the sulfide - minerals , particularly the di-sulphide pyrite contained.
Emergence
Acid mine water is created through a complex coupling of abiotic and microbial oxidations of sulphidic minerals. Both processes have to work together, a purely abiotic oxidation, i.e. without the special microorganisms, runs around 10,000 times slower. Sulphide is oxidized to sulphate during the oxidation of the sulphide minerals , the metals and semimetals are dissolved as ions. The microbial part consists in the oxidation of iron (II) ions to iron (III) ions and in the oxidation of elemental sulfur and sulfur compounds to sulfuric acid or sulfate by special bacteria and archaea . During the oxidation of sulphide minerals with an atomic ratio of sulfur to metal or semi-metal of over 1, for example pyrite (FeS 2 ), sulfuric acid is formed, which results in acidification. The oxidation of sulphide minerals is a form of weathering . Pyrite oxidation is also known as pyrite weathering .
meaning
Acid mine water is environmentally hazardous. They damage the environment through contamination with metals and semi-metals on the one hand and through acidification, buildings and equipment through the corrosive effects of the acid on the other. As far as acidic pit water occurs in connection with mining, it therefore represents post-mining damage. The main source is spoil heaps, which repeatedly lead to acidification through weathering. The water quality of the remaining lakes from open-cast mines is largely and sustainably determined by the sulphide content of the dump material. Acidification can lead to pH values between 2 and 4, and residual lakes typically contain high metal concentrations that can be toxic to living organisms. Use as a drinking water reservoir or for leisure activities is only possible after extensive water treatment. Groundwater contamination is a particular risk . The remaining lakes of the largest opencast mine in the world, the Chuquicamata copper mine in Chile, cover an area of 48 km².
Treatment, prevention
By adding slaked lime or, more rarely, limestone (CaCO 3 ), the acid is neutralized and consequently the pH value is increased. This leads to the fact that the metals and semi-metals mostly precipitate as hydroxides and are thus removed from the water. In the Rhenish lignite mining areas , the addition of limestone to the pyrite-containing overburden prevents pyrite weathering. The bacteria and archaea that cause iron and sulfur oxidation are inhibited by higher pH values.
See also
literature
- DW Blowes, CJ Ptacek, JL Jambor, CG Weisener, D. Paktunc, WD Gould, DB Johnson: The Geochemistry of Acid Mine Drainage. In: HD Turekian, KK Holland (Ed.): Treatise on Geochemistry. 2nd Edition. Elsevier, Oxford 2014, ISBN 978-0-08-098300-4 , pp. 131-190.
- W. Geller, M. Schultze, R. Kleinmann, C. Wolkersdorfer: Acidic Pit Lakes - The Legacy of Coal and Metal Surface Mines: Environmental Science and Engineering. Springer, Heidelberg 2013, ISBN 978-3-642-29383-2 .
- Christine Röckmann: From pyrite to sulfuric acid. The acidification of residual lignite lakes. In: Forum Geoecology. Volume 12, No. 2, 2001. (geooekologie.de , PDF, 47 KB)
