Environmental mobility of tin

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Environmental mobility of tin will be evaluated by the means of i) thermodynamic measurements and modeling, ii) chemical and structural investigation on weathering of primary tin sulfides in field settings, and iii) isotopic variations of Sn between primary sulfides and secondary oxidic materials. The thermodynamic measurements will consist of solution calorimetry (with resulting enthalpies of formation) and relaxation calorimetry (entropies) on a suite of tin hydroxides of the schoenfliesite group, □2(BSn)(OH)6, with B = Ca, Fe2+, Mg, Mn2+, Zn, Cu, and Fe3+. The data will be used to calculate solubility of these minerals under variable pH and to evaluate the saturation state of mine drainage waters with respect to these minerals. Weathered tin sulfides will be collected at selected field sites (historical mines) and investigated by polarized light microscopy, electron microprobe, micro-X-ray diffraction or transmission electron microscopy, in order to determine the nature of the secondary tin minerals. Limited preliminary work suggests that they may be close to the tin hydroxides of the schoenfliesite group. Weathering products of the associated primary minerals (e.g., pyrite, arsenopyrite) will be also analyzed for their Sn content, in order to evaluate tin mobility at the historical mining sites. Isotopic variations in Sn between the primary sulfides and secondary oxidic minerals have the potential to indicate geochemical processes in which tin is mobile and lost. Isotopic differences between the two reservoirs would indicate mobility of tin, even if not captured by the mineralogical investigation alone. The aim of this work is to predict mobility of tin at mining sites, in the presence of other metallic elements (Fe, Cu, Zn) which are able to form tin hydroxide minerals.