Adsorption and Oxidation of As(III) on Iron (Hydro)Oxides

Abstract

Iron (hydro)oxides, including poorly crystalline ferrihydrite and the more crystalline forms, hematite and magnetite, play an important role in the biogeochemical cycling of arsenic in aquatic environments. In this study, adsorption and oxidation experiments for As(III) were performed on ferrihydrite, hematite, and magnetite, respectively. The results showed that the three iron (hydro)oxides acted as a catalyst for the oxidation of As(III) in the presence of oxygen. The variation in the oxidation states of As(III) on iron (hydro)oxides were confirmed by X-ray Absorption Near-Edge Structure (XANES) spectra. Adsorption kinetics of As(III) followed a pseudo-second-order equation in the three iron (hydro)oxides systems. Oxidation of As(III) on the three iron (hydro)oxides was observed by the determination of total As(V) concentration. The pseudo-first-order equations satisfactorily described the oxidation kinetics data. The oxidation rate constants in the different iron (hydro)oxide systems followed the order: hematite > ferrihydrite > magnetite, that is, 0.0111, 0.0021, and 0.0009 h-1, respectively.