A Thermodynamic Analysis on the Roasting of Pyrite

A series of thermodynamic calculations are performed for the roasting of pyrite in changing temperatures and atmospheres. The relationship between (r)G and temperature in the range of T = 300-1200 K shows that, depending on the atmosphere it is in, reactions of pyrolysis, oxidation or reduction can occur. Both the pyrolysis of pyrite in an inert atmosphere and its oxidation by oxygen can form pyrrhotite (mainly Fe0.875S and FeS), but the temperature required for oxidation is much lower than that for pyrolysis. In an oxygen-containing atmosphere, the isothermal predominance areas for the Fe-S-O system indicate that a change in temperature and oxygen partial pressure can lead the pyrite to undergo desulphurization to pyrrhotite (FeS2 Fe0.875S/FeS) or iron oxides (FeS2 Fe3O4/Fe2O3), or sulphation to iron sulphates (FeS2 FeSO4/Fe-2(SO4)(3)). The presence of carbon is beneficial to the desulphurization of pyrite under an oxidizing atmosphere since iron sulphates can be converted to iron oxides at very low levels of P-CO/P-CO2. Results presented in this paper offer theoretical guidance for the optimization of roasting of pyrite for different purposes.