Effects of CO_2-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(CO_2).Considering the injection of CO_2 into abandoned coalmines,which are usually in the flooded condition,it is necessary to investigate the effect of CO_2-water-coal interaction on minerals and pore structures at different pressures,temperatures and times.It reveals that the CO_2-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 CO_2-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 co mplexities of the pore surface and pore volume,respectively.The re sults 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 D_(s2) had a negative correlation with the quartz and kaolinite contents.