Anthropogenetic and geogenetic influence on the regional hydrogeochemistry by lignite mining Mineralogical signature of the mixed sediments of the overburden at Cospuden and Zwenkau / Anthropogener und geogener Einfluss auf die regionale Hydrogeochemie durch Oeffnung der Braunkohlenlagerstaetten Mineralogische Signaturen des Abraums in Cospuden und Zwenkau

Determination of the mineralogical signatures of excavation residues as a task of this work has demonstrated that the mineral phase inventory has changed characteristically since the mixing and deposition of dead sediments. These changes are caused by the oxidation of pyrite due to aeration. In the mixed sediments deposited, a mean pyrite concentration of 3.6% was measured. This corresponds to 35 kg pyrite per cubic meter of excavation residues. In the presence of air, an oxidation zone is formed rapidly. It was discovered first by a depth-depending mineral phase analysis of samples obtained by SGM drilling in the covered dump of Cospuden. There, this zone is preserved together with water-soluble inventories and reaches a thickness of several hundred meters in the area of the former dump surface, which is now at a depth of about 20 m. Oxidation of the pyrites that predominantly originate from dead sediments and partly from lignite leads to the formation of water-soluble FeSO_4 and sulfuric acid (29 kg m"-"3). It drives the dissolution of a number of minerals in the excavation residues and the formation of secondary phases. A scenario of the flooding of dumps with their oxidation zones will be presented. Unfortunately, it cannot be modeled due to lacking structure parameters. There is no doubt, however, that flooding will cause a dispersion of the acid, water-soluble, and ecotoxic inventories over the entire dump, with the pH value afterwards remaining below 2.5. A large-area contamination of the groundwater may only be prevented by so far unknown measures to be taken prior to dump flooding. However, these measures still remain to be studied extensively. (orig.) / SIGLE / Available from TIB Hannover: ZA 5141(6398) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische Informationsbibliothek / DE / Germany