Soluble secondary minerals of antimony in Pezinok and Kremnica (Slovakia) and the question of mobility or immobility of antimony in mine waters

Abstract

Environmental contextAntimony enters the environment from tailings and mines but there are widely divergent statements about its mobility in the environment. This work addresses the question of mobility of Sb by a combination of mineralogical and geochemical studies. AbstractThis work characterises two occurrences with an abundance of the supergene Sb minerals brandholzite [Mg[Sb(OH)6]2·6H2O], klebelsbergite [Sb4O4(OH)2(SO4)] and peretaite [CaSb4O4(OH)2(SO4)2·2H2O]. Brandholzite forms from near-neutral waters, where stibnite (Sb2S3) decomposes in the presence of abundant carbonates. The SbIII sulfates form from acidic waters, where stibnite decomposes in the presence of marcasite or pyrite (FeS2). These initial supergene minerals form rapidly (brandholzite within weeks) and supply Sb into local waters. Calculation of saturation indices from underground water (present study) and many waters discharged from Sb mines (data from the literature) show that brandholzite (and related soluble Sb minerals) are undersaturated. Hence, if they do exist, they should dissolve. Insoluble Sb phases, such as tripuhyite (FeSbO4) are grossly supersaturated, but do not form (or form very slowly). Hence, we conclude that the mobility of antimony observed in geochemical studies is due to the solubility of the initial supergene minerals. The immobility of antimony stated in mineralogical studies is due to the slow but persistent formation of insoluble tripuhyite. When the kinetics of formation of these minerals are taken into account, the widely divergent statements about mobility or immobility of antimony in the environment can be reconciled.