Ways of Controlling Acid by Ecotechnology

Abstract

Geogenic acidification results from the oxidation of sulfidic minerals that had been stable for millennia because of anaerobic conditions in the underground. The geochemical process is microbially intensified and therefore a natural process. However, it is also man-made, because the sulfidic minerals are oxidized as a consequence of aeration due to mining activities. Open-cast lignite mining starts with the dewatering of the overburden, of the lignite and of the uppermost layers below the coal. Pyrite and marcasite are then in contact with atmospheric oxygen instead of anaerobic groundwater. The acidity results from the oxidation of sulfur and iron and from the hydrolysis of iron (see also Evangelou, this Vol.). Bodies of water become acidified when the sulfuric acid and iron (II)-sulfate are leached and transported into the lake by the groundwater. In the case of refilling with groundwater, the resulting mining lakes are acidic, with pH between 2 and 3. Their water is brown because of the high content of dissolved iron hydroxide. The low pH is strongly buffered by iron. Other heavy metals formerly present in the overburden are dissolved and contaminate the lake water. Living conditions differ widely from those in natural lakes in Germany.