title: Fractionation of Selenium during Selenate Reduction by Granular Zerovalent Iron.
abstract: 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 δ(82/76)Se values from -0.94 ± 0.07‰ and -1.93 ± 0.20‰ to maximum values of 6.85 ± 0.52‰ and 5.68 ± 0.20‰ over 72 and 36 h, respectively. The effective fractionations associated with the reduction of Se(VI) were 4.3‰ within the CaCO3 saturated water and 3.0‰ in ultrapure water.
authors: Department of Earth and Environmental Sciences, University of Waterloo , 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
authors: Heather K
authors: HK
authors: Shrimpton
authors: Department of Earth and Environmental Sciences, University of Waterloo , 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
authors: David W
authors: DW
authors: Blowes
authors: Department of Earth and Environmental Sciences, University of Waterloo , 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
authors: Carol J
authors: CJ
authors: Ptacek
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry; D005591:Chemical Fractionation; D004784:Environmental Monitoring / Q000379:methods; D060587:Groundwater / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007554:Isotopes / Q000737:chemistry; D010084:Oxidation-Reduction; D064586:Selenic Acid / Q000737:chemistry; D012643:Selenium / Q000737:chemistry*; D014867:Water; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D018508:Water Purification / Q000379:methods; D056928:X-Ray Absorption Spectroscopy
chemical_list: D007554:Isotopes; D014874:Water Pollutants, Chemical; D014867:Water; D007501:Iron; D002119:Calcium Carbonate; D012643:Selenium; D064586:Selenic Acid