Sulfite-assisted oxidation/adsorption coupled with a TiO2 supported CuO composite for rapid arsenic removal: Performance and mechanistic studies.

Owing to the lower toxicity and mobility of inorganic As(V), the oxidative removal of As(III) is deemed as the optimal approach for arsenic elimination from water. Herein, a synthetic TiO2-supported CuO material (Cu-TiO2) was coupled with sulfite (S(IV)) to remove As(III) at neutral pH. The combined process coupled oxidation with adsorption (i.e., As(III) removal by Cu-TiO2/S(IV)) was superior than a divided preoxidation-adsorption process (i.e., As(V) removal by Cu-TiO2) for arsenic removal. Attractively, low concentration of As(III) (50-300 μg L-1) could be completely removed by Cu-TiO2 (0.25 g L-1)/S(IV) (0.5 mM) within 60 min. Mechanism investigations revealed that the efficient As(III) removal was attributed to the continuous oxysulfur radicals (SOx•-) oxidation and Cu-TiO2 adsorption. The surface-adsorbed and free sulfate radicals (SO4•-) were further identified as the crucial oxidizing species. The Cu-TiO2 played the dual roles as a catalyst for S(IV) activation and an absorbent for arsenic immobility. The influence of operating parameters (i.e., As(III) concentration and sulfite dosage) and water chemistry (i.e., pH, inorganic anions, dissolved organic matters, and temperature) on As(III) removal were systematically investigated and optimized. Overall, the proposed process has potential application prospects in rehabilitating the As(III)-polluted water environment using industrial waste sulfite.