Sulfidation of zerovalent iron for improving the selectivity toward Cr(VI) in oxic water: Involvements of FeSx

Recognition of the general roles of FeSx in selectivity of zerovalent iron (ZVI) toward target contaminants is of great significance but challenging, especially in oxic water system. Herein, the ZVI amended with Na2S2O3 (i.e., S-ZVI(Na2S2O3)) and Na2S2O4 (i.e., S-ZVI(Na2S2O4)) were applied for the sequestration of Cr(VI) and corresponding FeS x involvements were explored. Results revealed that the largest effect for S-ZVI(Na2S2O3) and S-ZVI(Na2S2O4) observed at S/Fe molar ratio of 0.05 were 7.9- and 11.6- folds increase in removal rate (k(obs)) of Cr(VI), respectively. respectively. Correspondingly, the electron efficiency (EE) of S-ZVI for reducing Cr(VI) were mainly from 2.1- to 2.4- folds greater than that that of the ZVI(H2O). Further, this work suggested that the improved selectivity of ZVI toward Cr(VI) by sulfidation should be mainly ascribed to the involvements of FeSx, which could tune the reactive sites and corrosion products of ZVI for synergistically improving the mass transfer of Cr (VI) and subsequent electron transfer from iron core to Cr(VI). Overall, this work offers a new platform for improving ZVI selectivity for water decontamination.

Automated summary

This study investigated the impact of sulfidation on the selectivity of ZVI towards Cr(VI), finding that sulfidation significantly increased the removal rate of Cr(VI) and was mainly attributed to the involvement of FeSx. Sulfidation can tune the reactive sites and corrosion products of ZVI to improve the mass transfer and electron transfer of Cr(VI), providing a new approach to enhance the selectivity of ZVI for water decontamination.