Comprehensive Study on Spontaneous Combustion Risk of Pyrite and Pyrrhotite Based on Thermal Analysis Kinetics and Phase Evolution

The oxidation characteristics and spontaneous combustion propensity of pyrite and pyrrhotite are investigated using TG–DSC, FWO/KAS/Friedman kinetic analysis, XRD, and FactSage simulation. Both minerals exhibit intense exothermic events between 400°C and 650°C. Their peak temperatures shift to higher values and their exothermic enthalpies increase significantly with heating rate. The average apparent activation energies of pyrite, at 134.3 kJ/mol by FWO, 129.4 kJ/mol by KAS, and 136.7 kJ/mol by Friedman, are consistently lower than those of pyrrhotite, at 140.9 kJ/mol, 135.6 kJ/mol, and 142.2 kJ/mol, respectively, indicating a higher oxidation propensity for pyrite. Semi-quantitative XRD analysis using the RIR method reveals that Fe2O3 forms at 350°C for pyrite, with a content of 1.73 wt%. For pyrrhotite, the Fe2O3 content is 4.57 wt% at 350°C and 5.93 wt% at 400°C. A quantitative comparison between XRD-RIR measurements and FactSage simulations shows that the lower oxide‑formation temperature of pyrite is consistent with its lower activation energy. This suggests that oxide-formation temperature can serve as a supplementary indicator for evaluating spontaneous combustion susceptibility. These findings have practical implications for enhancing mine safety, predicting spontaneous combustion, improving ore storage management, and supporting industrial risk assessment.