Chemical composition of surface runoff from flotation wastes of Zn-Pb ore formation of the Mississippi Valley-type, Olkusz, Southern Poland

Mining wastes of Zn-Pb ores were studied at Olkusz, Southern Poland, using X-ray diffraction, SEM/EDS analyses. Additionally the chemistry of surface water runoff collected on the tailings slope was analyzed. The surface layer of tailing piles contains pyrite and marcasite, and dolomite as predominant carbonate mineral. The principal secondary sulfate mineral is gypsum, but the presence of trace epsomite was also inferred. Grains of dolomite are relatively fresh: the source of Ca necessary for crystallization of gypsum seems to be highly corroded minor calcite. In surface runoff, pH is close to neutral; Ca and sulfate are the dominant ions, followed by Mg. Concentrations of sulfate reaches 939 mg/l, whereas concentrations of Ca and Mg are 389 mg/l and 15.43 mg/l, respectively. The principal heavy metal in runoff is Zn, reaching 2.65 mg/l. Most species in runoff exhibited a negative correlation with the amount of precipitation in 5 days preceding the formation of surface runoff, due to their presence in efflorescent salts precipitated in dry period. Bicarbonate showed a positive correlation with the amount of precipitation, probably due to enhanced dissolution of calcite under high water saturation conditions. The results of this study indicate a dominant role of the surface layer of tailings and previous precipitation conditions in the formation of the surface runoff chemistry. In the future, surface runoff and fast releases of contaminants may become more important as a consequence of on-going climatic changes resulting in higher intensity of storm events. (C) 2013 Elsevier B.V. All rights reserved.