Use of direct gas-solid carbonation process for fixation of CO2 as mineral carbonates in Turkish fly ashes

Fly ash containing high alkaline metal oxides has been an attractive material for CO2 sequestration in a form of stable mineral carbonate. This study revealed the potential of Turkish fly ashes in terms of CO2 using a gas-solid carbonation process that was performed under different CO2 pressures at ambient temperature. Five fly ashes were collected from thermal power stations (Elbistan [EFA], Yatagan [YFA], Seyitomer [SEFA], Orhaneli [OFA], and Soma [SFA]). The ratio of FA:H2O was kept as 1:1, which promoted the carbonation reaction. The properties of fresh and carbonated fly ashes were determined using XRD, SEM, and TG analyses. TG analyses show that the CO2 storage capacity of fly ashes using the gas-solid carbonation under CO2 pressure of 3 bar for 2 h was found to be 1.14 g CO2/100 g-EFA, 2.63 g CO2/100 g-YFA, 0.17 g CO2/100 g-SEFA, 0.12 g CO2/100 g-OFA, and 7.28 g CO2/100 g- SFA, respectively. The amount of CO2 sequestrated in carbonated SFA increased within increasing CO2 pressure and carbonation time. Experimental findings reveal that 14.25 g CO2 was captured per 100 g-SFA in the form of cubic calcite crystals with a maximum carbonation efficiency of 43.41% under CO2 pressure of 5 bar for 15 h. However, there was no significant change determined in terms of the carbonation efficiency comparing with that of 6.5 h. This study shows a good alternative for the use of Turkish fly ash to capture CO2 as solid mineral carbonates under low CO2 pressure at ambient temperature.