Enhanced ex-situ mineral carbonation at ambient conditions with industrial waste

Carbon dioxide sequestration by conversion to carbonates has become a promising option for CO ₂ storage. Experiments were conducted to determine the feasibility of CO ₂ sequestration at ambient conditions using a Ca-rich industrial waste in a carbonate solution. The Ca-rich industrial waste used in this study was lignite fly ash. Fly ash was chosen because it is cheap, available near large CO ₂ point sources, already in powder form, and reactive due to amorphous properties. In the experimental set-up, CO ₂ absorption was inferred by monitoring feed and exhaust gas CO ₂ concentrations. The addition of an alkali to a fly ash-distilled water solution provided a 50% increase in CO ₂ absorption of the solution. Absorption time also increased by 50% compared to a fly ash-distilled water solution. TGA analysis was used to determine the extent of CO ₂ sequestration in the carbonate form. At a liquid to solid ratio of 20:1, the conversion of "free" calcium to carbonates was 75%. A CO ₂ balance on the system concluded that at the current operating conditions 42% of the total CO ₂ fed to the system was sequestered in the carbonate form. SEM-EDS analysis of the fly ash particles before and after reaction with CO ₂ indicated that the carbonate compound being formed was calcium carbonate. The analysis identified rhomboidal structures on the surface of the fly ash particles after reaction with CO ₂,but not before. These rhomboids are characteristic of calcium carbonate formation and they had higher Ca, C, and O concentrations than the host spheres, suggesting calcium carbonate formation.