Kinetics of the oxidation reactions and decomposition of pyrite

Abstract

Abstract Despite the great abundance of pyrite in nature and its role as one of the main sources of SO2 emissions in industrial processes, there is little definitive information about the kinetics and mechanisms of pyrite oxidation and decomposition reactions. This work aimed to determine the viability of applying the Friedman method for kinetic parameter determination to the oxidation and decomposition reactions of pyrite from the coal mining industry in order to obtain pyrite-based magnetic materials. Such method is based on the use of experimental weight loss data obtained using thermogravimetric analysis (TG) for the determination of the reaction activation energies. Thus, the activation energy, the pre-exponential factor and the reaction order were obtained using TG curves with different heating rates (2.5, 5.0, 7.5 and 10.0 K.min-1). For inert atmosphere, the calculated activation energies of approximately 280 kJ.mol-1 agree with the literature values. The reaction in oxidant atmosphere showed two predominant weight loss regions, suggesting the existence of two different reactions. The 482 kJ.mol-1 value obtained for the activation energy of the second weight loss that occurred at approximately 770 K was similar to the results reported by other authors. For the observed weight loss at approximately 650 K, similar values were not found in the literature to compare to the results of the Friedman method. The theoretical activation energy was therefore determined with empirical equations. A theoretical value of approximately 1000 kJ.mol-1 was obtained for the decomposition of pyrrhotite. The values found for the other kinetic parameters showed inconsistencies.