Removal of selenate from water by zerovalent iron

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 mu g L-1 in the presence of varying concentrations of Cl-, SO42-, NO3-, HCO3-, and PO43-. 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 SO42- 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 SO42- solutions, respectively. Analysis of Se species in ZV`I-Fe0H 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 SO42- 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 FeOH. The other is the adsorption of Se(VI) directly to FeOH, 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), NO3- (1, 5, and 10 mM), SO42- (5 mM), HCO3- (1 and 5 mM), or PO43- (1 mM) and only a slight effect in the presence of SO42- (50 and 100 mM), HCO3- (10 mM), and PO43- (5 mM) during a 2-d experiment, whereas 10 mM PO43- significantly inhibited Se(VI) removal. This work sug gests that ZVI may be an effective agent to remove Se from Se-containinated agricultural drainage water.