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-ZVINa2S2O3) and Na2S2O4 (i.e., S-ZVINa2S2O4) were applied for the sequestration of Cr(VI) and corresponding FeSx involvements were explored. Results revealed that the largest effect for S-ZVINa2S2O3 and S-ZVINa2S2O4 observed at S/Fe molar ratio of 0.05 were 7.9- and 11.6- folds increase in removal rate (kobs) 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 ZVIH2O. 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.