Assessment of Ecotoxic Metal Leaching Behaviour of Coal Gangue using a Sequential Extraction Procedure

Abstract The environmental leaching characteristics of the ecotoxic metals Cr, Co, Ni, Cu, Zn, As, Se, Ag, Cd, Tl and Pb within six coal gangue samples from mines located in Poland are assessed herein using the BCR-2 sequential extraction procedure. The samples’ bulk mineralogical and chemical compositions are determined by petrographic examination, X-ray fluorescence spectroscopy, X-ray diffraction and inductively-coupled mass spectrometry (following acid digestion). In general, of the metals studied Cd (predominantly oxidizable but often exchangeable) and Pb (predominantly reducible) pose the greatest hazard to the environment. Ni (predominantly oxidizable) and Cr (predominantly reducible) are also highly abundant and potentially mobile. Zn and Cu are abundant and predominantly exchangeable in half of the samples examined. Leaching of all metals is likely to be accelerated by the samples’ acid-forming propensity, which arises from their considerable (though variable) inventories of framboidal pyrite. This is especially the case for the wastes from Bogdanka and Piast mines, since they possess an order of magnitude more sulfidic material than the other samples (up to 1.9 wt%). Management of repositories containing these wastes will require specific measures to prevent such acid generation and ecotoxic metal release into the environment. Specifically, encapsulation within acid-neutralizing (e.g. calcite-bearing) materials is essential for these wastes, but is also recommended for those from mines Jankowice, Marcel, Staszik and Chwalowice.