Rapid catalytic oxidation of arsenite to arsenate in an iron(III)/sulfite system under visible light

Removal of arsenic in industrial wastewaters proceeds often through oxidation of As(III) to As(V) following by precipitation and/or adsorption. In this work, the catalytic oxidation of As(III) to As(V) in an iron(III)/sulfite system and the removal of As(V) under visible light using sunlight or a light-emitting diode lamp were investigated. Our results show a significant enhancement of efficiency of As(III) oxidation at near-neutral pH, whereas 93% of As(III) was removed from solution by centrifugal treatment after 30min of irradiation. Mechanism investigations revealed that the pathways of As(III) oxidation at circumneutral pH involved free radicals (mainly HO center dot, SO4-center dot and SO5-center dot) and ligand-to-metal charge transfer between As(III) and colloidal ferric hydroxide particles. Sequential addition of sulfite could improve the oxidation efficiency for water having high concentrations of As(III) (i.e., 66.7 mu M). These results clearly show that the visible light/iron(III)/sulfite system significantly enhances As(III) oxidation. This finding may have promising implications in developing a new cost-effective technology for the treatment of arsenic-containing water using sunlight. (C) 2015 Elsevier B.V. All rights reserved.