This is due to water and a fraction of the carbon dioxide come from the atmosphere. The other fraction of CO2 is released by the pyrolysis of the residual coal. It is also observed that the relative intensity of CO2 increase as temperature goes up. The formation of SO2 is evidenced by the strong bands at 1450–1300 cm−1 and 1150 cm−1. It is found that the relative intensity of SO2 increases with the increasing of temperature, and reaches a maximum at 444 ◦C and then decreases. When the thermal decomposition of the coal-derived pyrite into the primary stage, more gaseous products are released out. After analysis, a conclusion can be drawn that the mass loss in this stage is mainly caused by the release of SO2, with the unique existence of characteristic bands at 1450–1300 cm−1 and 1150 cm−1. Therefore, it can be concluded that the SO2 released in the temperature range of 410–470 ◦C is caused by the oxidation of the surface of the coal-derived pyrite particle, in accordance with Eq. (1). When the temperature increased up to 444 ◦C, the total amount of the evolved gas SO2 begin to drop off.