Mercury (Hg) is a contaminant of global concern, as bioaccumulation of methylmercury poses significant risk to aquatic ecosystems and human health. Although elemental mercury (Hg0) is far less reactive and toxic than the water-soluble ionic HgII species, the volatility of Hg0 results in long-range atmospheric transport of Hg0. The reduction of HgII to Hg0 can occur via both abiotic and microbially mediated processes; therefore, in addition to direct microbial reduction, abiotic reduction is a key component of global Hg biogeochemical cycling Reduction of Hg by FeII mineral phases like magnetite and green rust has gained significant attention in the past few years. However, iron in the form of FeII sorbed to minerals is far more common in the environment than FeII mineral phases like magnetite and green rust; hence, it is also important to evaluate the potential for sorbed FeII to reduce HgII. Here, we evaluated the potential of FeII sorbed to minerals (goethite and alumina) to reduce aqueous HgII by characterizing the solid-phase Hg and Fe species with  synchrotron X-ray Absorption Spectroscopy (XANES and EXAFS). We find that the redox reactivity, the reaction pathways, and the resulting Hg speciation strongly depend on the presence of complexing ligands. For example, the presence of chloride results in formation of a stable HgI complex (Hg2Cl2), which is reduced to Hg0 over a few months.

Reduction of Hg<sup>II</sup> by Fe<sup>II</sup> sorbed to minerals

245th National Meeting (2013)

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Reduction of HgII by FeII sorbed to minerals

Reduction of Hg^II by Fe^II sorbed to minerals