Effects of Alkali-Treated Coal Fly Ash on Carbonation Efficiency and Its Implication for Carbon Mineralization

The CO2 storage capacity in coal fly ash (CFA) for carbon mineralization is often limited due to the dominance of the alumina-silicate phase on its particle surface. This study aims to enhance the carbonation efficiency by using the alkaline activator. H2O and NaOH solutions (1 and 3 M) were mixed with CFA with an L/S ratio of 0.15, respectively, and were carbonated using a direct gas–solid reaction. The highest carbonation efficiency was 43.57% for CFA-NaOH 3 M, while CFA-Raw had the lowest. With the NaOH addition, the binding energy shifted to a lower value for Si 2p and Al 2p in X-ray photoelectron spectroscopy (XPS) analysis and Si–O–Al bond was also shifted to a lower wavenumber in attenuated total reflectance Fourier-transform infrared (ATR FT-IR) analysis. Both analyses show how OH– ions affect the alumino-silicate bonds and disrupt their arrangement. X-ray diffraction (XRD) analysis revealed the appearance of Na–Ca–Si-hydrate, which turned into gaylussite (another carbonate form), which increased the amount of CO2 stored in CFA.