Interaction between sequestered supercritical CO2 and minerals in deep coal seams

Abstract

This study investigates the interaction between supercritical CO2 (scCO2) and minerals in coal that may occur during CO2 sequestration into deep coal seams. Two low-rank coals with low-ash content, one low-rank coal with high-ash content and one high-rank coal with low-ash content were used to study the interactions. A coal-CO2 geochemical interaction experiment with a typical high-ash coal was conducted to investigate change of the water-soluble elements after scCO2 interaction. X-ray powder diffraction (XRD) was used to determine the effects of scCO2–H2O on the minerals in the four coals. In addition, the influence of scCO2 on pore structure of four coals was studied based on liquid nitrogen adsorption experiment. The results suggest that scCO2 can effectively enhance the solubility of all elements from coal in water because of scCO2 interaction. ScCO2 can significantly improve the solubility of trace elements than that of major elements. Because of the relatively low mineral content in coals and the short experimental period, secondary minerals formed by scCO2-mineral-water interaction were not determined with XRD. However, the content of primary minerals changed; the apparent content of quartz increased and the content of kaolinite, carbonate minerals and pyrite decreased. For the experimental coals in this study, scCO2 can enlarge the pore size of the micropores for low-ash coal and mesopores for low-rank coal, but shrinks that of micropores for high-ash coal and mesopores for high-rank coal.