Seminar by Dr. Naresh Kumar 'Arsenic partitioning at redox interfaces'

The mobility and release of arsenic (As) in the environment is influenced by Fe and S redox cycling. Reducing environments promote As release through reductive dissolution of Fe(III)-(oxyhydr)oxides. However, in the presence of dissolved sulfide, As can form thiol species and/or be re-sequestered by sorption to Fe-S minerals, such as mackinawite and pyrite. The sorption behavior is different for thiolated vs. oxoanions of As and sorption of As to Fe(III)-(oxyhydr)oxides also differs mechanistically from that to Fe-sulfide minerals. The reductive dissolution of Fe(III)-(oxyhydr)oxides and subsequent Fe-S precipitation is controlled by S/Fe ratios, but the effect of sulfidation on the fate and speciation of As is poorly understood. Reductive dissolution and (re)-precipitation of newly formed minerals can successively release or trap metal contaminants, thus, controlling their mobility. Paradoxically, the reverse impact of metal(loid) contaminants on the kinetics and thermodynamics of mineral dissolution and nucleation have received minimal attention. We are interested in understanding the impact of metal(loid)s on these redox transformations and, hence, their own mobility.