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Coal swelling because of methane and carbon dioxide was measured by the volumetric method in isothermal and non-isothermal conditions. These investigations are of key importance in the context of potential CO2 sequestration in deep unmined coalbeds. Changes of the temperature underground may disturb the adsorption balance, leading to volumetric processes in the coal strata (swelling or shrinking), which can give rise to leaks and gas desorption toward the ground surface. The isothermal results show that the strain exhibited by a coal sample during CO2 sorption is about twice that of CH4. The liner strain kinetics also show that the swelling of the sample when exposed to both gases is anisotropic and greater in the direction perpendicular to the bedding plane than parallel to it. In the case of the non-isothermal process, the pattern of dilatometric processes seems to be different. The temperature increase gives rise to the sample swelling when exposed to methane, yet the presence of CO2 leads to sample contraction, which can be attributed to the different mechanisms involved in CO2 deposition. CO2 accumulated in pores undergoes a rapid phase transition as a result of capillary condensation, leading to rapid desorption and, in consequence, shrinking of the coal sample.

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Carbonation of industrial wastes rich in earth-alkali oxides is found to have a significant potential for CO2 sequestration. This process opens new perspectives not only for carbon dioxide mitigation, but also for the valorization and new applications of industrial waste materials from coal-burning power 2 plants. In this study, mineral carbonation of high-calcium fly ash is investigated under dry and moist conditions in a continuous flow reactor during up to 2 hours, at temperatures ranging from 160 to 290 ºC and CO2 pressures between 1 and 6 bar. A comprehensive charaterization of treated and untreated samples was carried out before and after carbonation using X-ray diffraction, X-ray fluorescence spectroscopy, thermogravimetric analysis, infrared spectroscopy and scanning electron microscopy. The maximum sequestration capacity achieved was 117.7 g CO2/kg fly ash (48.14 % carbonation efficiency) under dry conditions. Results showed that increasing the pressure and temperature enhances the process of carbonation, as well as the presence of moderate amounts of water vapor in the CO2 gas flow. Newly formed carbonates were always present in the treated samples. This study shows that about 21% of all CO2 emissions of a coal-burning power plant could potentially be sequestered as carbonates.