Dynamic Evolution of Functional Groups and Thermal Oxidation Effects in Acid/alkali-Eroded Coal During Heating Processes

To investigate the influence mechanism of acid/alkali erosion on coal spontaneous combustion (CSC), using C600 high-precision microcalorimeter and in-situ FTIR, we analyzed the oxidative thermal characteristics, critical temperature points, and dynamic evolution of functional groups during coal heating process under acid/alkali treatment. Correlation analysis was performed to quantitatively assess the correlation degrees among these parameters. The results demonstrate that under both ambient temperature and heating conditions, acid/alkali-treated coal exhibits increased functional group content, enhanced reactivity and greater heat release, with characteristic temperature t2 shifting forward. Acidic treatment demonstrates the most significant enhancement. Within the acidic regime, this promotion effect exhibits a strong negative correlation with solution pH (R = -0.97). Alkaline treatment is weaker than acidic but stronger than neutral treatment, which nevertheless maintains higher reactivity than raw coal. Furthermore, with prolonged erosion duration, acid/alkali treated coal exhibited significantly increased functional group quantity, reactivity, and heat release (pH4-90 sample showed 81% higher heat release than raw coal). In conclusion, acid/alkali erosion substantially enhances coal’s spontaneous combustion tendency, with acidic environments demonstrating the most prominent effect. These results establish the theoretical foundation for the prevention and control of spontaneous combustion in water-immersed coal within goaf areas.