Fe--FeS--H2S--SO2--Na2SO3--CaSO3

Iron $Fe$ + Iron sulfide $FeS$ + Hydrogen sulfide $H2S$ + Sulfur dioxide $SO2$ + Sodium sulfite $Na2SO3$ + Calcium sulfite $CaSO3$

Fe + FeS + H2S + 2O2 -> FeS2 + H2O
Iron + Iron sulfide + Hydrogen sulfide + Oxygen -> Iron disulfide $Pyrite$ + Water

FeS2 + 4O2 -> Fe2O3 + 2SO2
Iron disulfide + Oxygen -> Iron oxide + Sulfur dioxide

Fe2O3 + 3SO2 -> 2FeSO4 + SO3
Iron oxide + Sulfur dioxide -> Iron sulfate + Sulfur trioxide

2FeSO4 + Na2CO3 -> 2Na2SO4 + Fe2$CO3$3
Iron sulfate + Sodium carbonate -> Sodium sulfate + Iron carbonate

Fe2$CO3$3 + 3H2SO4 -> 3CO2 + 3H2O + Fe2$SO4$3
Iron carbonate + Sulfuric acid -> Carbon dioxide + Water + Iron sulfate

Fe2$SO4$3 + CaCO3 -> 3CaSO4 + Fe2$CO3$3
Iron sulfate + Calcium carbonate -> Calcium sulfate + Iron carbonate

Final conversion: 3Fe + CaCO3 + 3H2SO4 + 6O2 -> 3CaSO4 + 3CO2 + 3H2O + Fe2$SO4$3
Iron + Calcium carbonate + Sulfuric acid + Oxygen -> Calcium sulfate + Carbon dioxide + Water + Iron sulfate