Schwertmannite precipitated from acid mine drainage in the Western Sudetes (SW Poland) and its arsenate sorption capacity

Abstract

This paper contains XRD, Mössbauer and IR spectroscopy, chemical composition and thermal analysis results for the mineral schwertmannite present in the weathering zone developed in two abandoned sulphide mines in the Sudetes (SW Poland). In Wieściszowice a pyrite deposit was exploited, and in Radzimowice the deposit consisted of polymetallic mineralization with predominant arsenopyrite. In both localizations schwertmannite is developed as dripstones in underground workings and loose sediments precipitating from the acid mine drainage (AMD) waters. Schwertmannite forms tiny, needle-like crystals 2-3 mm in size, usually grouped in botryoidal aggregations. The chemical composition of schwertmannite from Wieściszowice is typical for this mineral, and in Radzimowice the mineral contains up to 5.20 wt. % of As2O5. Due to highly developed specific surface and structural features, schwertmannite has the strongest sorption capabilities among the components of ochres, and takes up the largest amounts of arsenate oxyanion from AMD, as well as considerable amounts of phosphates and heavy metals. About 71-87% of arsenate is sorbed on to the surface of the schwertmannite crystals and may readily be released into solution, 12-30% is bound into the structure of the mineral, and about 1% is an admixture of insoluble ferric arsenates.