Effect of high geothermal environments on microscopic properties and oxidation processes of waterlogged coal

In mines with deep levels and those exhibiting anomalous geothermal temperatures, high geothermal environments can affect the erosion process of waterlogged coal by immersion. To study the influence of a high geothermal environment regarding the self-ignition of waterlogged coal, immersion of the coals in aqueous solutions under various temperature conditions (room temperature 20 °C, 40 °C, 60 °C and 80°) for 30 days. Low-temperature nitrogen adsorption, infrared spectroscopy, and simultaneous thermal analysis were utilized to examine the alterations in the micro physicochemical structure and oxidation process of waterlogged coal samples at room temperature and high geothermal temperature. Compared with room temperature conditions, the high geothermal environment increased the number and volume of pores in the waterlogged coal, broke intermolecular hydrogen bonds, and increased the total number of reactive groups. These microstructural changes affected the oxidation process of the waterlogged coal, causing in the oxidation characteristic temperature points on the TG and DSC curves as well as the activation energies E of the second and third stages of TG being significantly lower than those of the waterlogged coal under room temperature conditions. This study suggests that the high geothermal environment enhances the spontaneous combustion tendency of waterlogged coal and accelerates its oxidation process.