Enhanced removal of aqueous arsenic(III) by sulfidated nanoscale zero-valent iron under oxic conditions: Performance and mechanism

Although sulfidated nanoscale zero-valent iron (S-nZVI) has shown significant promise in the removal of aqueous inorganic arsenic (As), there is a scarcity of studies comprehensively investigating their performance under oxic conditions, as well as the mechanism involving oxidation being elucidated. In this study, the synthesized S-nZVI exhibited a distinctive core-shell structure, characterized by an outer shell comprising iron oxides and FeS, while also demonstrating increased specific surface areas and decreased pHZPC value. Batch experiments revealed that sulfidation significantly enhanced the As(III) removal efficiency of nZVI under oxic conditions by increasing both the reaction rates and adsorption capacity (qm = 495.23 mg/g). Furthermore, several critical factors influencing the As(III) removal by S-nZVI were investigated, indicating that increased initial As(III) concentrations, initial pH values, and co-existing anions concentrations had negative impacts on the removal process; however, an increase in ionic strength showed certain positive effects. Based on the profiles of As and Fe, roles of reactive species, and characterization of reacted products, it could be concluded that As(III) removal by S-nZVI involves the synergistic effect of adsorption, co-precipitation, and oxidation. More importantly, sulfidation facilitated the corrosion of Fe0, accelerating the release of Fe2+ and promoting the activation of single-electron molecular oxygen reactions, thereby further enhancing the total As removal efficiency. This study highlights the excellent potential of S-nZVI for effectively removing As(III) under oxic conditions.