Effect of experimental parameters on the carbonate mineralization with CaSO4⋅2H2O using CO2 microbubbles

• Carbonate mineralization fixes CO2 as CaCO3 with CaSO4 without pH swing.
• Ratio of [OH−]/[Ca2+] affects the CO2 fixation efficiency.
• CO2 microbubble enhances the CO2 fixation efficiency.

Carbonate mineralization fixes CO2 as carbonate minerals such as CaCO3 mitigating anthropogenic CO2 related problems. However, studies on the carbonate mineralization using CaSO4⋅2H2O have not been made widely, even though it is a good source of Ca2+. In this study, the CO2 fixation using CaSO4⋅2H2O was investigated without swinging pH. In addition, the effect of using microbubbles was evaluated and compared with the conventional CO2 bubbles. We injected CO2 microbubbles into the CaSO4⋅2H2O suspension in which the NaOH solution added to maintain alkaline pH. The development of the carbonation reaction was considered by quantitative analysis of the solid phases using an X-ray diffraction technique. The phase composition study revealed that the efficiency of the carbonate mineralization changes with the concentration ratio (OH−/Ca2+). The condition for 100% CaCO3 was achieved when the concentration ratio was chosen to be between 2 and 3. We also suggested the transformation pathways of CaSO4⋅2H2O to CaCO3 in terms of the concentration ratio. We believe that the result in this study would be helpful to find the optimal reaction conditions for the CO2 fixing carbonate mineralization when calcium source was chosen from various materials.