Thermal decomposition of pyrite. Kinetic analysis of thermogravimetric data by predictor-corrector numerical methods

The thermal decomposition of pyrite has been studied by combining thermogravimetric (t.g.) and microscopic techniques. Predictor-corrector methods, coupled with screen graphics, were used to solve the differential equations representing kinetic models of t.g. data. Kinetic conclusions from t.g. data are in good agreement with microscopic observations. Decomposition occurs in two stages. The first and major stage of mass loss proceeds by formation of a porous layer of pyrrhotite around each particle with the reaction interface advancing inwards in three dimensions. A contracting-volume kinetic model with chemical rate control gives an excellent fit to experimental t.g. data for first-stage decomposition. The second stage is further decomposition to lower members of the pyrrhotite series, and this is described well by a kinetic model based on solid-state diffusion of species from the reaction interface.