Investigation on Thermal Decomposition of Pyrite Part I

Thermochemical decomposition of pyrite in air-gas medium has been studied by means of MOM-Q 1500D Derivatograph. The derivatograms have been obtained at a heating rate of 5 K min^-1 and air flowrate of 25 1 h^-1 to final temperatures of 833, 933 and 1273 K, chosen on the basis of the stepwise oxidation of pyrite. The solid product is analyzed using X-ray powder diffraction and Mössbauer spectrometer techniques. The formation of nonstoichiometric sulfides (pyrrhotines) as intermediates has been confirmed. The second stage of decomposition is the oxidation of these pyrrhotines to hematite. The recorded weight losses are lower than the theoretically possible because of the formed nonstoichiometric iron sulfides. The complicated structure of the intermediate products has been confirmed by means of other techniques.