2 FeIIS2-I + 15 Na2O2-I Fe2IIIO3-II + 4 Na2SVIO4-II + 11 Na2O-II

This is an oxidation-reduction (redox) reaction:

4 S-I - 28 e- 4 SVI (oxidation)

2 FeII - 2 e- 2 FeIII (oxidation)

30 O-I + 30 e- 30 O-II (reduction)

Change the oxidation states