Simple and efficient sonochemical method for the oxidation of arsenic(III) to arsenic(V)

Abstract

A simple and efficient sonochemical method has been developed for the oxidation of acutely toxic As(III) to the less toxic As(V). The OH radicals produced during acoustic cavitation readily oxidize As(III) to As(V) in an aqueous environment The effects of various operational parameters of ultrasonication, such as power density and pulse mode, on the oxidation of As(III) were studied. Pulsed sonication showed a profound effect on the oxidation of As(III) to As(V) in comparison to the continuous mode of operation, that consequently reduced the reaction time and energy requirement for the process. Increasing acoustic amplitude led to an enhanced rate of oxidation of As(III). In the presence of As(III), the production of H2O2 was significantly reduced compared to that observed during the sonication of water alone, which suggests that OH radicals were involved in the oxidation process. The oxidation of As(III) was independent of the initial pH of the solution in the range 3 to 10.6. Continuous sparging of nitrogen through the reaction solution noticeably reduced the oxidation rate of As(III), indicating thatdissolved oxygen is involved in the oxidation process to a certain extent. It is concluded thatthe sonochemical treatment process is a simple and possibly cost-effective technique for the oxidation of As(III) to As(V) without assistance of any external chemicals or catalysts.