Carbon capture and storage using coal fly ash with flue gas

Rising CO₂ emissions call for actions to urgently address climate change and its impacts. To avoid the harmful consequences of climate change, limiting anthropogenic emissions of CO₂ are a sensible response recognized by the global scientific community. Carbon capture and storage technologies are an integral part of the climate change mitigation portfolio. Among the various technologies, mineral carbonation shows promising potential as it is safer and offers a permanent solution for carbon capture and storage in the form of solid carbonates. In this regard, direct mineral carbonation of alkaline solid residues is viewed with global interest as they offer permanent and leakage-free storage of CO₂. In this research work, CO₂ sequestration using Indian coal fly ash (class F type- CaO < 10%) has been studied through the direct mineral carbonation process using flue gas concentration of CO₂. Response surface methodology was used to design the carbonation experiments through gas–solid and aqueous routes. Aqueous carbonation of coal fly ash at optimum conditions (temperature-61.6 °C, pressure-48.7 bar, liquid/solid ratio-13.35, reaction time-50 min) resulted in a reduction of about 23% in the concentration of CO₂. The waste exhibited a maximum sequestration capacity of 50.72 g of CO₂/kg under aqueous carbonation and 20.03 g of CO₂/kg under gas–solid carbonation. Both temperature and pressure were found to be significant factors impacting the gas–solid carbonation process. In aqueous carbonation, temperature and liquid/solid ratio were the significant factors. The carbonation process was evidenced using Fourier-transform-infrared spectroscopy, X-ray diffraction, and scanning electron microscope studies. The results suggest that Indian coal fly ash could be considered a potential feedstock for sequestration of CO₂ with flue gas and requires further improvement for large-scale implementations.