The Synergistic Mechanism of Coal Spontaneous Combustion Suppression and Air Leakage Sealing of Fly Ash Grouting Materials Based on CO2 Mineralization

This study aims to develop an efficient mineralized fly ash slurry with enhanced flame retardancy, investigate effective measures to prevent coal spontaneous combustion, minimize resource waste, and ensure personnel safety. Through the coal spontaneous combustion heating experiment, the optimal particle size of the fly ash in the mineralized fly ash was determined to be (200–400 mesh), the concentration of fly ash was (30%), and the increase in CaO content was (5%). Techniques such as Fourier-transform infrared spectroscopy (FTIR), electron spin resonance (ESR), and simultaneous thermal analysis (STA) have been employed to evaluate the resistive properties from both micro and macro perspectives. The experimental results show that the inhibitory effect of mineralized fly ash slurry on coal spontaneous combustion is reflected in the synergistic inhibition of macroscopic heat release and microscopic structural changes. At the macroscopic level, when the temperature exceeds 150°C, the maximum heat release power of coal samples treated with mineralization is significantly lower than that of raw coal, with the heat release rate reduced by 20%. At the microscopic level, the addition of the inhibitor significantly delays the generation of nascent radicals in raw coal, and the coal samples treated with mineralization exhibit better radical inhibition effects than other samples. Meanwhile, the growth rate of the g-value value of the treated coal samples in the high-temperature range decreases significantly. Particularly importantly, the mineralized fly ash slurry can effectively reduce the change rate of C = O and -OH groups during coal oxidation. In the critical temperature range of 130–180°C for coal spontaneous combustion, its inhibition efficiencies reach 79.5% and 85.2% respectively, significantly delaying the overall process of coal spontaneous combustion.