The kinetics and mechanism of pyrite thermal decomposition

Abstract

AbstractPyrite (FeS2) decomposition in He, N2, CO2‐CO‐SO2, O2‐CO2 and H2S‐H2 gas mixtures was studied from 400–590°C using optical microscopy, X‐ray diffraction, electron microprobe analyses, and gas chromatography. The rate constants were determined from the weight loss and the thickness change of pyrite in reacted samples. The temperature dependent composition of the product, pyrrhotite (Fe1‐xS), was measured by electron microprobe analysis and X‐ray diffraction. Pyrite decomposition to pyrrhotite and sulfur vapor (dominantly S2) was observed in all gases and follows linear kinetics. The apparent activation energy of pyrite thermal decomposition is 297 + 34 kJ mol−1 in inert gases (e.g. He, N2), and 275 + 20 kJ mol−1 in purified CO2 and in low concentration CO‐SO2 gas mixtures with CO2. The rate constants are the same regardless of gas composition at a given temperature. In oxidizing (O2‐CO2) or reducing (H2S‐H2) gas mixtures, the rate constants are larger than that in inert gases because additional reactions between pyrite and oxidizing/reducing gases accelerate the overall process while reducing the apparent activation energies. A mechanism of pyrite decomposition, which explains our experimental results, as well as the discordant activation energy data in the literature, is proposed.