Kinetics of pyrite multi-step thermal decomposition in refractory gold sulphide concentrates

The behaviour and kinetics of pyrite thermal decomposition were studied in a nitrogen atmosphere using thermogravimetric analysis. Pyrite decomposition was confirmed in two successive steps via SEM–EDS analysis as follows: pyrite → pyrrhotite → troilite. The overlapping peaks of pyrite were accurately separated via Asym2Sig deconvolution. The kinetic parameters were evaluated using the Kissinger–Akahira–Sunose, Kissinger, Flynn–Wall–Ozawa, Friedman, and Coats–Redfern methods. The kinetics mechanism was established via a data comparison of model-free and model-fitting methods and was further verified by comparing microstructural changes between pyrite roasting, which was proven to be appropriate by comparing the fitted reconstruction and experimental curves. The decomposition of pyrite was random and formed a porous structure. Pyrite has a better thermal stability than pyrrhotite. The kinetics of the two steps were consistent with the random nucleation and growth of the Avrami–Erofeev model. The relationship in terms of temperature for the thermodynamic activation parameters was established, and the parameters were calculated at characteristic temperatures.