Experimental Study and Mechanism Analysis on the Inhibitory Effect of Inhibitors on Coal Spontaneous Combustion under Long-Term Freezing Conditions

Coal spontaneous combustion seriously threatens coal storage safety in high-latitude open-pit mines, where long-term freezing alters coal's properties and potentially undermines inhibitor effectiveness. This study systematically investigates the impact of prolonged freezing (-10 °C for 1, 2, and 4 months) on the efficacy of MgCl₂ and phytic acid (PA). Using temperature-programmed oxidation, thermogravimetric analysis, and Fourier transform infrared spectroscopy, we elucidated how the freezing duration governs macroscopic inhibition and microscopic pathways. Results show that PA offers optimal short-term inhibition, evidenced by a high activation energy increase (Δ<i>E</i> = 20.71 kJ mol^-1), a CO inhibition rate of 79.39%, and significant suppression of carbonyl groups. However, MgCl₂ surpasses PA after medium-term freezing, exhibiting higher apparent activation energy. Following long-term freezing, both inhibitors experience efficiency loss but PA demonstrates superior stability. The combustion index for PA increased by only 56.1% from its room-temperature value, markedly lower than the 92.7% increase for MgCl₂. Mechanistic analysis reveals that long-term freezing-induced pore expansion and enhanced connectivity are key to this divergence. PA functions via chemical bonding and chelation, processes whose effectiveness diminishes as excessive pore development reduces the active site density. In contrast, MgCl₂'s physical coverage is progressively weakened by pore-structure development. Consequently, PA's slower performance degradation underscores its greater suitability for long-term application in freezing environments, providing crucial guidance for strategic inhibitor selection in high-latitude mines.