Mechanism and performance of coal spontaneous combustion with a halide carrier inorganic salt inhibitor

Coal spontaneous combustion seriously restricts the safe production of coal mines, and adding an inhibitor is one of the effective methods to prevent coal spontaneous combustion. To improve the pertinence and high efficiency of the inhibitor, this paper considered the intrinsic properties and external conditions that affect the occurrence of coal spontaneous combustion, combined with the characteristics that the rare earth hydrotalcite can effectively improve the thermal stability, coupling, and flame retardancy of the coal and the halide inhibitor. The halide inhibitor can enhance the permeability, dispersion, and uniformity of the rare earth hydrotalcite as a carrier. The halide carrier inorganic salt inhibitor was prepared. To study the inhibition mechanism and performance of the halide carrier inorganic salt inhibitor on coal spontaneous combustion, differential scanning calorimetry (DSC) was used to test the variation law of parameters, such as stage characteristics, characteristic temperature, thermal effect, and apparent activation energy in the process of coal spontaneous combustion under the action of a rare earth hydrotalcite, MgCl₂ and a halide carrier inorganic salt inhibitor. Test results reveal that the OH of the rare earth hydrotalcite laminate can generate a weak hydrogen bond with acidic functional groups such as −COOH in coal molecules so that the activity of the acidic functional groups is weakened. Mg²⁺ complexes with −COO− in coal molecules to form −COOMg−, resulting in the weakening of the C=O activity in −COO−, which is the main mechanism of the halide carrier inorganic salts inhibiting coal spontaneous combustion. The endothermic peak of the DSC curve appears as a double peak or multi-peak after the addition of halide carrier inorganic salts to the coal sample. Compared with the raw coal, the peak temperature is shifted back by 50–60 ℃, the T₁ temperature is shifted back by 90–100 ℃, and the total heat release decreased by 19–27 kJ·g⁻¹. Furthermore, the apparent activation energy of each stage of the coal body is effectively improved. Results revealed that the halide carrier inorganic salt inhibitor could effectively inhibit the reaction process of coal spontaneous combustion.