Dynamic Simulation of the Thermal Decomposition of Pyrite Under Vacuum

The ultrasoft pseudopotential plane wave method is applied to dynamic simulation of the thermal decomposition mechanism of FeS₂ under vacuum. The FeS₂ (100), (111), and (210) surface relaxation and the geometric and electronic structure of the reactants and products are calculated. The results indicate that FeS₂ (100) is the most preferred surface to dissociate and also the most common cleavage surface. The thermal decomposition mechanism of FeS₂ is explained by dynamic simulation on a micro stratum: in general, the S-Fe bond gradually elongated until it fractured, the S-S bond strengthened gradually, the S-Fe bond was cleaved to form S, the force is relatively weaker between different layers, and thermal decomposition occurred easily between the layers. Simultaneously, the intermediate products, such as Fe _x S _y , were formed. Evidence of Fe pyrolysis into Fe metal was not found, and the intermediate products decomposed further. The contributions of the p and d orbitals of Fe increased, whereas that of the s orbital decreased. The contributions of the s and p orbitals of S decreased. The results obtained from FeS₂ thermal decomposition experiments under vacuum and differential thermal analysis—thermogravimetry are consistent with the results of calculation and simulation.