4 CaI2-I + 5 H2SVIO4 4 CaSVIO4 + H2S-II + 4 I20 + 4 H2O

This is an oxidation-reduction (redox) reaction:

SVI + 8 e- S-II (reduction)

8 I-I - 8 e- 8 I0 (oxidation)

H2SO4 is an oxidizing agent, CaI2 is a reducing agent.