Role of reactive oxygen species in As(III) oxidation by carbonate structural Fe(II): A surface-mediated pathway

Abstract

Arsenite oxidation is commonly found during the removal of arsenite by iron minerals. The influencing factors and mechanisms of As(III) oxidation in reactive carbonate structural Fe(II) (CSF) suspensions were investigated in this study. Results showed that oxidation efficiency of As(III) was susceptible to CSF dosage, initial pH and dissolved oxygen (DO). It is interesting to note that the presence of iodide could conspicuously facilitate the oxidation efficiency of As(III) by accelerating Fe(III)/Fe(II) cycle. Scavenging experiments demonstrated that H2O2 and ·O2– were the crucial ROSs in the pH range of 5.0–9.0. Besides, the other predominant ROSs accounting for As(III) oxidation were Fe(IV) and surface-bound hydroxyl radical (·OH) in acid and neutral solutions while Fe(IV) became the main oxidant in alkaline solutions. Production of ROSs was attributed to the oxygenation of Fe2+ adsorbed on Fe(III) oxyhydroxides and complexed Fe(II) under neutral condition. No ROSs could be examined in the liquid phase, a surface-mediated mechanism was thus proposed: ROSs were generated on the surface of CSF while As(III) was adsorbed on the surface of CSF and then oxidized to As(V) by surface-bound ROSs. This study may shed light on molecular oxygen activation mechanism by carbonate structural Fe(II) during arsenite oxidation.