CO2 sorption by dry sorbent prepared from CaO–SiO2 resources

High-temperature CO2 sorbents were prepared by leaching and recrystallizing of calcium resources such as steel slag, tail-wollastonite, waste cement and fly ash. Alumina and small amount of silica in the sorbents were useful to maintain the CO2 sorption for more than 30 cycles. However, the silica, if included more than 10 mol% with respect to CaO, had negative effect on the sorption by more than its mole fraction. Thus, it was necessary to control Si dissolution for the resources composed of calcium silicate such as steel slag. The highest sorption of the sorbents from steel slag was 49% with 66% calcium utilization. On the other hand, if silica is in ‘free’ state, such as in waste cement, it hardly dissolves in the acid. Therefore, the sorbent could be prepared in core(SiO2)–shell(CaO) type by restructuring waste cement to show 100% utilization of the calcium in the shell.

► Calcium resources were restructured for high-temperature CO2 sorbents.
► Alumina in the sorbents enabled the repeated CO2 sorption kept high.
► The silica in them reduced their sorption by more than its mole fraction.
► Using the ‘free’ silica, the core(SiO2)–shell(CaO) type sorbents were prepared.
► The sorbent showed 100% utilization of the calcium.