FeO2,heat−−−−→Fe3O4CO,600∘C−−−−−−→FeOCO,700∘C−−−−−−→Fe
FedilH2SO4−−−−−−→FeSO4H2SO4,O2−−−−−−→Fe2(SO4)3heat−−→Fe
FeCl2,heat−−−−−→FeCl3heat,air−−−−−→FeCl2Zn−→Fe
FeO2,heat−−−−→FeOdilH2SO4−−−−−−→FeSO4heat−−→Fe
In equation 1, FeCl3 cannot be reduced when heated in air. In equation 3, Fe2(SO4)3 cannot convert to Fe on heating; instead oxide(s) will be formed. In equation 4, FeSO4 cannot be converted to Fe on heating; instead oxide(s) will be formed.