A composite inhibitor developed through mine-water resource utilization: synergistic mechanisms for suppressing coal spontaneous combustion

Coal spontaneous combustion remains a major safety hazard in coal mining, while large volumes of mine water generated during extraction create additional environmental pressure. This study developed a low-cost mine-water/MgCl 2 composite inhibitor and evaluated its suppression of coal low-temperature oxidation and combustion. Scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, programmed-temperature oxidation, and cone calorimetry were used to characterize its inhibitory performance and underlying mechanisms. Compared with raw coal and coal treated separately with mine water or MgCl 2 , the composite-treated sample exhibited the strongest inhibition. It reduced oxygen consumption and suppressed the formation of CO, CO 2 , and hydrocarbon gases. At 260 °C, its oxygen-consumption rate was approximately 23% lower than that of raw coal. The composite treatment also increased the apparent activation energy to 152.08 kJ·mol −1 during the high-temperature stage and reduced both the peak heat-release rate and total heat release, with the latter decreasing by approximately 25%. Microstructural analyses suggested that Mg 2+ may interact with reactive oxygen-containing structures, including hydroxyl, carboxyl, and carbonyl groups, potentially reducing the accessibility of oxidation-active sites. Inorganic ions in mine water also promoted the formation of a surface deposit layer that filled pores and restricted oxygen diffusion. The composite inhibitor therefore suppressed coal oxidation, gas evolution, and combustion through the synergistic effects of physical oxygen isolation and chemical passivation. This system integrates mine-water reuse with mine-fire prevention, offering both environmental and safety benefits. These findings provide a basis for developing sustainable technologies to control coal spontaneous combustion.