Development of a fly ash derived Li4SiO4-based sorbent for CO2 capture at high temperatures

Li4SiO4-based sorbents from fly ash (FA) subjected to different pretreatments were developed for CO2 capture at high temperatures. Compared with original FA and precalcined FA, the sorbent derived from precalcined and acid leached FA (denoted as HCl/CFA-Li4SiO4) had smaller particle size and larger specific surface area. HCl/CFA-Li4SiO4 also presented an excellent CO2 capture capacity of 27.5 wt% within 25 min at 600 °C (approximately 2.7 times that of previously reported FA-derived Li4SiO4-based sorbents). Moreover, the transformation phenomena of the major elements Al, Fe, and Ca during cycling operations were investigated by X-ray analysis. Results show that Al and Fe species existed as LiAlO2 and LiFeO2, respectively, which cannot contribute to the CO2 sorption performance at 600 °C. This phenomenon for LiFeO2 was confirmed by thermodynamic analysis with FactSage 6.4 software. Interestingly, Ca species reversibly transformed from Ca2SiO4 and CaO to Li2CaSiO4 and CaCO3 in cyclic processes.