Effect of pH value on spontaneous combustion oxidation behavior and microstructure of coal in high ground temperature environment

PAN Rongkun; YUAN Jiwei; WANG Zhiguo; HU Daimin; CHAO Jiangkun

doi:10.13347/j.cnki.mkaq.20250534

Abstract：In order to study the effect of pH value of mine water on spontaneous combustion oxidation behavior and microstructure of coal in high ground temperature mine,using the long-flame coal from Pingdingshan Mining Area,and the low-temperature oxida-tion test system and Vertex 70v infrared spectrometer were used to analyze the gas production rule of derived gas in low-temperature oxidation stage and the distribution characteristics of active groups in coal samples.By using the collected data,the oxidation charac-teristics and functional group structure parameters are calculated,and the microscopic mechanism of the effect of high temperature and pH on the spontaneous combustion characteristics of coal is revealed.The results show that both the rise of ground temperature and the increase of acidity of aqueous solution can promote the oxidation of coal samples,while the immersion of alkaline aqueous solution can inhibit the oxidation of coal samples,and the degree of inhibition becomes deeper and deeper with the increase of ground temperature.For coal samples immersed in water solutions with the same pH value,the increase of ground temperature can accelerate the appearance of the oxygen consumption different point.After the immersion of samples,the content of-CH decreased compared with that of raw coal,while the content of-CH3 and-CH2 showed an increasing trend.After the immersion in acidic and alkaline solutions,the content of oxygen-containing functional groups increased and decreased respectively,and the increase of-OH was the most significant.In the coal samples,the values of'C'and'I'in the coal samples decreased except for the 40℃&pH=8 coal sample,the rest samples have all increased compared to raw coal,and the increase of'C'value increased with the increase of acidity of the solution,and the change was not obvious with the ground temperature,and the ratio of-CH2 content to-CH3 content was positively correlated with the acidity and temperature of the solution.According to the experimental results,it is concluded that the aromatic ring reacts with water to form hydroxyl group in acidic environment,carbonyl group oxidizes to carboxyl group,oxygen-containing functional group increases,and oxidation activity increases.In the alkaline environment,the phenol hydroxyl group re-acts with the hydroxyl group to form water and oxygen anion,and the carboxylic group reacts with the hydroxyl group to form carboxylic acid group and water,which consumes the oxygen-containing functional group and reduces the oxidation activity.