Abstract
Dissolved Se(VI) removal by three commercially available zero-valent irons (ZVIs) was examined in oxic batch experiments under circumneutral pH conditions in the presence and absence of NO(3) (-) and SO(4) (2-). Environmentally relevant Se(VI) (1 mg L(-1)), NO(3) (-) ([NO(3)-N] = 15 mg L(-1)), and SO(4) (2-) (1800 mg L(-1)) were employed to simulate mining-impacted waters. Ninety percent of Se(VI) removal was achieved within 4-8 h in the absence of SO(4) (2-) and NO(3) (-). A similar Se(VI) removal rate was observed after 10-32 h in the presence of NO(3) (-). Dissolved Se(VI) removal rates exhibited the highest decrease in the presence of SO(4) (2-); 90% of Se(VI) removal was measured after 50-191 h for SO(4) (2-) and after 150-194 h for SO(4) (2-) plus NO(3) (-) depending on the ZVI tested. Despite differences in removal rates among batches and ZVI materials, Se(VI) removal consistently followed first-order reaction kinetics. Scanning electron microscopy, Raman spectroscopy, and X-ray diffraction analyses of reacted solids showed that Fe(0) present in ZVI undergoes oxidation to magnetite [Fe(3)O(4)], wüstite [FeO], lepidocrocite [γ-FeOOH], and goethite [α-FeOOH] over time. X-ray absorption near-edge structure spectroscopy indicated that Se(VI) was reduced to Se(IV) and Se(0) during removal. These results demonstrate that ZVI can be effectively used to control Se(VI) concentrations in mining-impacted waters.