Se fate during sulfidation of Se-bearing ferrihdyrite: Effects of S/Fe ratios, carbonate and silicate

Determining how Fe-mineral-associated selenium (Se) behaves under sulphidic conditions can help predict its behaviour in near-surface conditions and identify biosphere exposure pathways for its radioactive analogue. This work studies how Se that was previously adsorbed on ferrihydrite behaves when ferrihydrite reacts with sulphides. Targeted batch experiments will first investigate whether Se is released back into solution or is retained in the solid phase, and how S/Fe ratios and the presence of inorganic impurities affects the extent and magnitude of Se release/retention. Using X-ray absorption spectroscopy (XAS) at the Se K-edge, this study will then determine if Se underwent redox changes, whether it formed discrete selenide compounds or if it was incorporated in sulphidation reaction products. Depending on the form of Se, its migration behaviour and potential biological uptake pathways are likely to be affected.