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TECHNICAL REPORTS

Heavy Metals in the Environment

Removal of Selenate from Water by Zerovalent Iron

Department of Environmental Sciences, University of California, Riverside, CA 92521-0424

^* Corresponding author (william.frankenberger{at}ucr.edu)

Received for publication May 25, 2004. Zerovalent iron (ZVI) has been widely used in the removal of environmental contaminants from water. In this study, ZVI was used to remove selenate [Se(VI)] at a level of 1000 µg L^–1 in the presence of varying concentrations of Cl^–, SO^2–₄, NO^–₃, HCO^–₃, and PO^3–₄. Results showed that Se(VI) was rapidly removed during the corrosion of ZVI to iron oxyhydroxides (Fe_OH). During the 16 h of the experiments, 100 and 56% of the added Se(VI) was removed in 10 mM Cl^– and SO^2–₄ solutions under a closed contained system, respectively. Under an open condition, 100 and 93% of the added Se(VI) were removed in the Cl^– and SO^2–₄ solutions, respectively. Analysis of Se species in ZVI–Fe_OH revealed that selenite [Se(IV)] and nonextractable Se increased during the first 2 to 4 h of reaction, with a decrease of Se(VI) in the Cl^– experiment and no detection of Se(VI) in the SO^2–₄ experiment. Two mechanisms can be attributed to the rapid removal of Se(VI) from the solutions. One is the reduction of Se(VI) to Se(IV), followed by rapid adsorption of Se(IV) to Fe_OH. The other is the adsorption of Se(VI) directly to Fe_OH, followed by its reduction to Se(IV). The results also show that there was little effect on Se(VI) removal in the presence of Cl^– (5, 50, and 100 mM), NO^–₃ (1, 5, and 10 mM), SO^2–₄ (5 mM), HCO^–₃ (1 and 5 mM), or PO^3–₄ (1 mM) and only a slight effect in the presence of SO^2–₄ (50 and 100 mM), HCO^–₃ (10 mM), and PO^3–₄ (5 mM) during a 2-d experiment, whereas 10 mM PO^3–₄ significantly inhibited Se(VI) removal. This work suggests that ZVI may be an effective agent to remove Se from Se-contaminated agricultural drainage water.

Abbreviations: Fe_OH, iron oxyhydroxides • Se(0), elemental selenium • Se(IV), selenite • Se(VI), selenate • ZVI, zerovalent iron

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JEQ 2005 34: 403-407. [Full Text]  

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