Effects of CO2-water interaction with coal on mineral content and pore characteristics

There are a large number of abandoned coalmines in China, and most of them are located around major coal-fired power stations, which are the largest emission sources of carbon dioxide (CO2). Considering the injection of CO2 into abandoned coalmines, which are usually in the flooded condition, it is necessary to investigate the effect of CO2-water-coal interaction on minerals and pore structures at different pressures, temperatures and times. It reveals that the CO2-water-coal interaction can significantly improve the solubility of Ca, S, Mg, K, Si, Al, Fe and Na. By comparing the mineral content and pore structure before and after CO2-water-coal interaction, quartz and kaolinite were found to be the main secondary minerals, which increased in all samples. The structures of micropores and mesopores in the range of 1.5-8 nm were changed obviously. Specific surface areas and pore volumes first increased and then decreased with pressure and time, while both increased with temperature. By using the Frenkel-Halsey-Hill model, the fractal dimensions of all samples were analyzed based on D-s1 and D-s2, which reflected the complexities of the pore surface and pore volume, respectively. The results show that fractal dimensions had very weak positive correlations with the carbon content. D-s1 had a positive correlation with the quartz and kaolinite contents, while Ds2 had a negative correlation with the quartz and kaolinite contents. (C) 2020 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).