4 FeIISVIO4-II 2 Fe2IIIO3-II + 4 SIVO2-II + O20

This is an oxidation-reduction (redox) reaction:

4 SVI + 8 e- 4 SIV (reduction)

4 FeII - 4 e- 4 FeIII (oxidation)

2 O-II - 4 e- 2 O0 (oxidation)

Change the oxidation states