Effect of Ultrasound Irradiation on Arsenic Adsorption from Aqueous Solution into Iron Compound

We confirmed the influence of ultrasound irradiation at 200 kHz on the removal of As(III) from an aqueous solution through coprecipitation with a trivalent iron compound. We compared the removal ratio obtained with ultrasound to that obtained with stirring alone. We also considered the impact of various atmospheres on the removal process, conducting the experiments in air, Ar, O2, and N2 atmospheres. The treatment of As(III) solution with ultrasound irradiation in combination with the application of trivalent iron caused a decrease in residual As concentration in the solution that was lower than that treated only by the trivalent iron in Ar or O2 atmospheres. Ultrasound irradiation oxidizes As(III) to As(V), which is then easily adsorbed from the aqueous solution into the trivalent iron compound. However, the removal ratio of As(III) in the solution using ultrasound irradiation was reduced by increasing irradiation time in an air atmosphere; this decrease can be attributed to the redissolution of the iron compound, which is caused by a decrease in pH value by generated nitric acid. Our results suggest that the treatment of As(III) solutions with sonication in combination with the application of trivalent iron is most effective in Ar or O2 atmospheres.