Dissolved Selenium(VI) Removal by Zero-Valent Iron under Oxic Conditions: Influence of Sulfate and Nitrate

[Image: see text] 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.