2 HOH + 2 FeIIICl3 + SIVO2 2 FeIICl2 + H2SVIO4 + 2 HCl

This is an oxidation-reduction (redox) reaction:

SIV - 2 e- SVI (oxidation)

2 FeIII + 2 e- 2 FeII (reduction)

SO2 is a reducing agent, FeCl3 is an oxidizing agent.