4 FeIIS2-I + 15 O20 + 2 H2O-II 2 Fe2III(SVIO4-II)3 + 2 H2SVIO4-II

This is an oxidation-reduction (redox) reaction:

8 S-I - 56 e- 8 SVI (oxidation)

4 FeII - 4 e- 4 FeIII (oxidation)

30 O0 + 60 e- 30 O-II (reduction)

FeS2 is a reducing agent, FeS2 is a reducing agent, O2 is an oxidizing agent.