Study on the influence of different acid and alkali environments on the spontaneous combustion properties of coal

To examine the impacts of diverse acid and alkali environments on the autothermal oxidation characteristics of coal, the microporous structure, active functional groups and oxidative thermodynamic parameters were investigated using SEM, TG-DSC and FTIR experimental methods. The results show that the number of pores on the eroded coal increases and the pore size increases compared to the neutral environment of pH = 7. The content of major oxygenated functional groups decreases and is converted to more reactive oxygenated alkali metal structures, with an approximate reduction of 35 % for ketone carbonyl CO and 57 % for acid carboxylic acid CO at pH = 10. The acidic environment promotes the combination of hydroxyl-hydrogen bonding functional groups with oxygen. The reactive exothermic process of eroded coal was promoted in pH = 4, 6, 8, and 10, and the combustion-promoting effect on NMG was more obvious, in which the ignition point temperature T6 of HG was reduced by 7.6 °C, 5.9 °C, 8.2 °C, and 5.1 °C, respectively. During the fitting process using the model-free method, the best fit for the oxygen uptake and weight gain stage and the combustion pyrolysis stage was achieved by the KAS and Friedman methods, respectively, and efficient fire extinguishing could be achieved in the pre-combustion pyrolysis stage (0.1<α < 0.2).