The efficiency differences and mechanisms of inhibitors in inhibition of coal spontaneous combustion under alkaline water erosion conditions

To reveal the differences in the efficacy of inhibitors in inhibiting the spontaneous combustion characteristics of coal under the condition of alkaline water erosion and their inhibition mechanisms, the inhibition effects of the physical inhibitor CaCl 2 and the chemical inhibitor TPPI on the raw coal, neutral water, and alkaline-water-eroded coal (pH=8/10) were compared using temperature-programmed experiment, TG-DSC, and FTIR analysis. The results demonstrated that the alkaline-water-eroded coal significantly weakened inhibitor effectiveness, with CaCl 2 being less affected than TPPI. The CO and -COOH inhibition rates of the eroded coal (pH=8) inhibited by CaCl 2 were 0.91 and 0.25 times those of the raw coal-inhibited samples. For the eroded coal (pH=10) inhibited with TPPI, the CO and C=O inhibition rates were 0.8 and 0.47 times those of the raw coal-inhibited samples, and 0.62 and 0.42 times those of the CaCl 2 -inhibited samples. Further analysis showed that alkaline water erosion modifies coal surface chemistry, reducing inhibitor adsorption capacity. CaCl 2 forms thermally stable Ca(OH) 2 through reaction with residual OH - on coal surfaces, resulting in relatively mild inhibition efficacy reduction. In contrast, TPPI not only experiences severe adsorption hindrance on modified coal surfaces but also undergoes hydrolysis in alkaline environments, leading to significant efficacy deterioration.