Experimental investigation of the macroscopic characteristic parameters and microstructure of water-soaked coal during low-temperature oxidation

When a shallow-buried close-distance coal seam group is mined, the residual coal in the goaf of the upper coal seam is immersed in water for a prolonged period of time, increasing the risk of coal spontaneous combustion (CSC). In this study, the macroscopic characteristics of water-soaked coal (WSC) during low-temperature oxidation were analyzed using a temperature-programmed device. The microstructure changes at different oxidation temperatures (40, 80, 120, 160, and 200 degrees C) were investigated through liquid nitrogen adsorption and X-ray diffraction. The results revealed that, during low-temperature oxidation, macroscopic characteristic parameters such as the oxidation gas product concentration, temperature, and oxygen consumption rate of WSC changed, indicating higher oxidizability and lower apparent activation energy. The average pore size and macropore volume of the coal surface gradually increased during low-temperature oxidation. The mesopore volume increased at first and then tended to stabilize. The mineral content on the surface of the coal markedly diminished, but the mineral content did not participate in the oxidation process. Water leaching enhanced the interlayer spacing of the aromatic lamellae of the coal samples, curtailed the degree of coalification, and condensed the aromatic ring of the coal sample during the oxidation process. This analysis of the oxidation and macroscopic characteristics of WSC from micro- and macroperspectives is valuable for the prevention and containment of CSC.