4 As2IIIS3-II + 5 HClVIIO4 + 12 H2O 12 S0 + 8 H3AsVO4 + 5 HCl-I

This is an oxidation-reduction (redox) reaction:

8 AsIII - 16 e- 8 AsV (oxidation)

12 S-II - 24 e- 12 S0 (oxidation)

5 ClVII + 40 e- 5 Cl-I (reduction)

As2S3 is a reducing agent, As2S3 is a reducing agent, HClO4 is an oxidizing agent.