Selenate reduction by sulfidized zero-valent iron (S-ZVI)

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One the one hand, selenium is an essential nutrient, on the other hand it is highly toxic at elevated concentrations. The most soluble species in water are selenite (Se(IV)) and selenate (Se(VI)). Because of their solubility, both species can rapidly attain toxic levels in the aquatic food chain. In this proposal we will explore the potential of sulfide modified zero-valent iron (S-ZVI) to reduce Se(VI) to Se(0) and/or Se(-II). Sulfidation of ZVI has received growing attention in the last 3 to 4 years as a method to enhance selectivity and specificity of contaminant degradation by using ZVI as an abiotic reductant. To date, no study has been performed the effect on selenate removal. In the proposed research we will study along three work packages the following hypothesis: i) The S/Fe ratio of S-ZVI determines its reactivity towards Se(VI), ii) the presence of oxygen and Fe(II) affects the effectiveness of S-ZVI to reduce Se(VI), iii) Se(VI) reduction by S-ZVI is affected by pH due to electrostatic effects, and iv) application of S-ZVI particles in filter-bed systems is an effective method for removal of selenate from solution. The kinetics and mechanisms of the interaction between S-ZVI and selenate will be studied in batch experiments in combination with synchrotron based methods in collaboration with the Canadian Light Source. In addition we will perform filter-bed experiments packed with S-ZVI.