Study on the Influence Mechanism of pH Regulation on the Oxidation Spontaneous Combustion Behavior of Coal Gangue

To address the issues of environmental pollution and resource waste caused by the spontaneous combustion of coal gangue piles, this study investigates the effects of aqueous solutions with varying pH levels on the oxidation spontaneous combustion characteristics of coal gangue. Taking medium-high sulfur coal gangue from the Qipanjing area of Ordos as the research subject, samples were subjected to soaking and re-drying treatments using aqueous solutions at pH = 4, 7, and 10. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TG-DTG) were employed to analyze the influence of pH on the oxidation characteristic parameters. The results indicate that pH significantly and variably influences the spontaneous combustion characteristics of coal gangue. Acidic treatment (pH = 4) led to a 16.3% increase in the ignition coefficient of coal gangue, a 32.6% increase in primary alcohol C–O content, and a 26.6% decrease in aliphatic C–O content. The apparent activation energy for the thermal decomposition and combustion stages decreased by 25.23% and 9.1%, respectively, indicating that acidic treatment promotes the spontaneous combustion process of coal gangue. Conversely, alkaline treatment (pH = 10) reduced the ignition coefficient by 16.6%, increased the Si–O and aliphatic C–O contents by 21.9% and 13.7%, respectively, and decreased the asymmetric stretching vibration contents of –CH2 and –CH3 by 4.4% and 2.8%. The apparent activation energy for these two stages increased significantly by 346.76% and 45.73%, respectively, effectively delaying spontaneous combustion development. Neutral treatment (pH = 7) exhibited a relatively weak influence. Correlation analysis reveals that the apparent activation energy for the two stages, Ea1 and Ea2, have a strong positive correlation with aliphatic C–O stretching vibrations (correlation coefficients of 0.81 and 0.84, respectively) and a strong negative correlation with the asymmetric stretching vibrations of aliphatic –CH3 and –CH3 (correlation coefficients of −0.89 and −0.95, respectively). This study provides a theoretical basis for preventing and controlling spontaneous combustion in coal gangue piles through pH regulation.