Carbonation of high-calcium fly ashes and its potential for carbon dioxide removal in coal fired power plants

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 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 h, at temperatures ranging from 160 to 290 °C and CO2 pressures between 1 and 6 bar. A comprehensive characterization 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.