Fractionation of Selenium during Selenate Reduction by Granular Zerovalent Iron

Batch experiments were conducted using granular zerovalent iron (G-ZVI) with either ultrapure water or CaCO3 saturated simulated groundwater to assess the extent of Se isotope fractionation in solution under the anaerobic conditions characteristic of many aquifers. G-ZVI is a common remediation material in permeable reactive barriers (PRB) to treat Se-contaminated groundwater, and stable isotopes are a potential tool for assessing removal mechanisms. The solution composition, speciation of Se, and Se isotope ratios were determined during both sets of experiments. Dissolved Se concentrations decreased from 10 to <2 mg L–1 after 3 d in the CaCO3 system and below 0.4 mg L–1 after 2 d in the ultrapure water system. XANES analysis of the solid phase showed spectra consistent with the formation of Se(IV), Fe2(SeO3)3, FeSe, FeSe2, and Se(0) on the G-ZVI. Selenium isotope ratio measurements in solution in the CaCO3 and ultrapure water experiments showed enrichment of δ82/76Se values from −0.94 ± 0.07‰ and −1.93 ±...