Influence of Water Immersion Type and Duration on Coal Spontaneous Combustion and High-Temperature Combustion Behavior

Mine water is an inevitable byproduct of underground coal mining and is increasingly reused through goaf reservoirs. However, the residual coal in these reservoirs is exposed to long-term water immersion, which alters its oxidation characteristics. This work investigates the oxidation kinetics of coal under different water immersion conditions using samples from Xuzhuang Coal Mine. The simultaneous thermal analyzer, temperature-programmed furnace and pore structure analyzer are employed to systematically compare the properties of different treated coal samples. Water immersion enhances the spontaneous combustion initiation sensitivity of coal samples. The spontaneous combustion tendency index of raw coal is 900.10, while those of mine water‑treated coal and deionized water‑treated coal are lower at 882.88 and 853.23, respectively. As the water immersion time increases from 0 to 14 days, the reaction rate of mine water‑treated coal decreases exponentially from 0.27 min−1 to 0.13 min−1, and that of deionized water‑treated coal decreases logarithmically to 0.17 min−1. Water immersion reduces the specific surface area in coal samples, while increases its pore wall roughness, and total pore volume. This work can offer scientific support for assessing the spontaneous combustion risk in water‑stored goafs and optimizing mine water resource utilization strategies, and contribute to the safe operation and sustainable management of coal mine.