Enhanced removal of Se(VI) from water via pre-corrosion of zero-valent iron using H₂O₂/HCl: Effect of solution chemistry and mechanism investigation

Although the removal of Se(VI) from water by using zero-valent iron (ZVI) is a promising method, passivation of ZVI severely inhibits its performance. To overcome such issue, we proposed an efficient technique to enhance Se(VI) removal via pre-corrosion of ZVI with H₂O₂/HCl in a short time (15 min). The resultant pcZVI suspension was weakly acidic (pH 4.56) and contained abundant aqueous Fe²⁺. ⁵⁷Fe Mössbauer spectroscopy showed that pcZVI mainly consisted of Fe⁰ (66.2%), hydrated ferric oxide (26.3%), and Fe₃O₄ (7.5%). Efficient removal of Se(VI) from sulfate-rich solution was achieved by pcZVI compared with ZVI (in the absence and presence of H₂O₂) and acid-pretreated ZVI. Moreover, the efficient removal of Se(VI) by pcZVI sustained over a broad pH range (3–9) due to its strong buffering power. The presence of chloride, carbonate, nitrate, and common cations (Na⁺, K⁺, Ca²⁺, and Mg²⁺) posed negligible influence on the removal of Se(VI) by pcZVI, while the inhibitory effect induced by sulfate, silicate, and phosphate indicated the significance of Se(VI) adsorption as a prerequisite step for its removal. The consumption of aqueous Fe²⁺ was associated with Se(VI) removal, and X-ray absorption near edge structure revealed that the main pathway for Se(VI) removal by pcZVI was a stepwise reduction of Se(VI) to Se(IV) and then Se⁰ as the dominant final state (78.2%). Moreover, higher electron selectivity of pcZVI was attributed to the enhanced enrichment of Se oxyanions prior to their reduction.