Effect of Inhibitors on Hydrogen Bond Reduction and Kaolinite Dissolution for Enhanced CO₂ Adsorption in Coal

Abstract

The application of an inhibitor to the remaining coal in the goaf not only prevents spontaneous combustion of the coal seam in the mining area but also greatly enhances the capacity of coal to adsorb CO2. To investigate the mechanism by which inhibitors improve the CO2 adsorption capacity of the coal seam in the goaf, we conducted swelling experiments, infrared spectroscopy, scanning electron microscopy, and X-ray diffraction analyses to examine the microstructural changes in the adsorption of CO2 before and after inhibition. The results indicate that after inhibition, the number of hydrogen bonds between coal macromolecules decreased, and the samples exhibited approximately 5% swelling. This swelling of the coal macromolecular structure and the increased distance between coal particles create additional space for CO2 sequestration, which is a critical factor contributing to the enhanced CO2 adsorption capacity of coal. The mineral composition of coal consists of 75.6% kaolinite, and inhibition leads to a reduction in kaolinite content by 0.8–7.9%. After inhibition, the swelling and disintegration of kaolinite cause uneven stress, resulting in changes to the pore structure. Closed pores filled with kaolinite transform into open pores, and the original pores crack, forming new pores and pore channels. The dissolution of kaolinite particles increases the porosity of the coal, further facilitating gas adsorption. Among the three inhibitors tested, the most effective in enhancing CO2 sequestration by bituminous coal in the mining area was the urea solution. This study holds significant importance in improving the CO2 sequestration capacity of residual coal in goaves.