Oxidation Characterization of Water Immersion Coal on Pore Evolution and Oxygen Adsorption Behavior

The oxidation and spontaneous combustion of water immersion coal threatens the mine safety production after experiencing water evacuation in the underground goaf. The weathering effect creates disparate water content in coal that results in the distinct oxidation process. This paper investigates the immersion coal pore evolution and oxygen adsorption behavior at different water contents from the molecular dynamics perspective. Proximate analysis, ultimate analysis, 13 C NMR spectrum research, and XPS spectrum were used to construct the macromolecular coal model. There is a double-peak behavior for the water immersion coal porosity and specific surface area. The maximum porosity of water immersion coal was 25.7% and 28.9% arising at 5.9% and 10.2% water content, respectively. The adsorption loading and average oxygen adsorption density both exhibited the rise-decline-rise-decline trend with two remarkable peaks presented at the same site. The two peaks possessed the lowest oxygen adsorption total energy level of − 23.37 and − 21.73 kcal/mol. Temperature rise trial was conducted to evaluate and verify the double-peak characterization of the water immersion coal at the low-temperature oxidation stage. The temperature rising rate versus the heating time of higher water content slowed down at an elevated water bath temperature. There were two maximum immersion coal temperatures, 85.52 and 85.66 °C, with optimum water content of 6.0% and 12.0%, respectively, at the stabilization stage. The obtained achievement of the crucial optimum water content has important theoretical guiding significance for the scientific prevention of the water immersion coal oxidation spontaneous combustion disaster in an underground goaf.