Thermodynamic, kinetics, and physicochemical properties of carbon-containing pyrite under air roasting conditions

Spontaneous combustion in pyrite and coal coexistence systems has long been recognized as a potential hazard that threatens industrial development and the human living environment. To rationally utilize this negative effect, this study thoroughly investigates the effect of heat released during the roasting of carbon-containing pyrite on mineral transformation and physicochemical properties. In the temperature range of 400–600 °C, roasting results revealed that the mixed mineral phases of carbon-bearing pyrite were pyrite, hematite, and Fe2(SO4)3. These results were consistent with thermodynamic calculations. When the roasting temperature reached 600 °C, due to the C combustion, the released heat was transferred to the pyrite in the pyrolysis stage. When O replaced the vacant position of S, crystalline phase contraction and structural rearrangement occurred, leading to a rapid decrease in the average grain size of the pyrolysis product to about 30 nm. The presence of carbon reduced the activation energy of pyrite roasting (36.84 kJ/mol) and promoted thermal reactions. The magnetic properties of the pyrolysis product increased first and then decreased, and the saturation magnetization reached the maximum at 600 °C, about 2.80 emu/g. This study provides guidance for the separation of iron in practical applications.