In this study, a combined process of acidic oxidation leaching and SO2 reduction was proposed to purify crude As2O3 recovered from antimony smelting arsenic-alkali residue. The effects of various process factors on crude As2O3 leaching were investigated based on the thermodynamic analysis. The results showed that the leaching efficiency of arsenic was 95.5% when crude As2O3 was leached with the mixed solution of H2SO4 and H2O2 under the conditions: the H2O2/As(III) molar ratio (n(H2O2): n(As(III))) of 0.93, leaching temperature of 75 degrees C, leaching time of 90 min and liquid -solid ratio of 4:1. The kinetic study of As(V) reduction with SO2 gas showed that the reduction process conformed to the first-order gas/liquid reaction kinetics, and was controlled by both diffusion and chemical reaction with an apparent activation energy of 16.69 kJ mol(-1). Arsenic could be directly recovered in the form of As2O3 from leaching solution by SO2 reduction, and the obtained product reached the standard of As2O3-1 (GB 26721-2011) after further purification. The direct recovery of arsenic was 85.8% after twice purifications for crude As2O3. In addition, no arsenic-containing wastes were produced in the purification process. Overall, this process is efficient and clean for the purification of crude As2O3. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.