Effect of Weakly Acidic and Weakly Alkaline Water Immersion on the Crystal Structure and Oxidative Thermodynamic Properties of Long-Flame Coal

Goaf water is mainly composed of weakly acidic and weakly alkaline water, but research on the oxidative thermodynamic properties of coal soaked in weakly acidic and weakly alkaline water is lacking. In this study, long-flame coal samples soaked in pure, weakly acidic, and weakly alkaline water (pH 7, 6.5, and 7.5) for 30 days were prepared. X-ray diffraction and thermogravimetry – differential scanning calorimetry were performed to analyze the microcrystalline structure and oxidative thermodynamic properties of the coal samples. Results showed that the aromatic lamellae of the soaked coal were loosely arranged, and the coal body had a strong water-locking capacity. Water could not easily dissipate, which reduced the heat absorption at the low-temperature stage and the heat release at the high-temperature stage. Soaking under different pH conditions exerted different effects on the crystal structure and oxidative thermodynamic properties of coal. Weakly alkaline water (pH = 7.5) had the most remarkable effect, weakly acidic water (pH = 6.5) had a moderate effect, and pure water (pH = 7) had the least effect.