Rapid removal of selenate in a zero-valent iron/Fe3O4/Fe2+ synergetic system

Abstract

Batch experiments were conducted to investigate selenate reduction in a hybridized zero-valent iron (ZVI or Fe0) system that was easily created by mixing magnetite and Fe2+ with ZVI particle (20mesh) and preconditioning for 24h prior to selenate addition. The performance of the hybrid ZVI/Fe3O4/Fe2+ system (hZVI) were compared with those of non-hybrid (ZVI, Fe2+ and Fe3O4 alone) or partial-hybrid systems (ZVI/Fe2+, Fe3O4/Fe2+ and ZVI/Fe3O4). The results showed that precondition of 24h significantly increased the reactivity of hZVI towards selenate reduction possible due to the formation of reactive interface between ZVI and magnetite. hZVI achieved the most effective selenate removal than any of other systems. ZVI/Fe3O4/Fe2+ was a synergetic system, in which any constituent was indispensable for rapid removal of selenate. ZVI was the primary electron donor for selenate reduction. Fe2+ instead of acidic pH (H+) participated in selenate reduction together with ZVI. Moreover, Fe2+ rejuvenated the passivaed surface of ZVI and magnetite, and thus sustained the reactivity of hZVI for rapid removal of selenate. Magnetite served as the primary reaction sites for selenate removal. Se speciation extraction and X-ray photoelectron spectroscopy evidences indicated stepwise reduction of SeVI to SeIV and then to Se0 or Se−II in the hZVI system. Findings of this study could help develop an hZVI technology suitable for treating various selenium-contaminated wastewaters.