CO₂ Absorption and Magnesium Carbonate Precipitation in MgCl₂–NH₃–NH₄Cl Solutions: Implications for Carbon Capture and Storage

CO₂ absorption and carbonate precipitation are the two core processes controlling the reaction rate and path of CO₂ mineral sequestration. Whereas previous studies have focused on testing reactive crystallization and precipitation kinetics, much less attention has been paid to absorption, the key process determining the removal efficiency of CO₂. In this study, adopting a novel wetted wall column reactor, we systematically explore the rates and mechanisms of carbon transformation from CO₂ gas to carbonates in MgCl₂–NH₃–NH₄Cl solutions. We find that reactive diffusion in liquid film of the wetted wall column is the rate-limiting step of CO₂ absorption when proceeding chiefly through interactions between CO₂(aq) and NH₃(aq). We further quantified the reaction kinetic constant of the CO₂–NH₃ reaction. Our results indicate that higher initial concentration of NH₄Cl ( $\ge 2\mathrm{mol}·{\mathrm{L}}^{-1}$ ) leads to the precipitation of roguinite [ ${\left({\mathrm{NH}}_4\right)}_2\mathrm{Mg}{\left({\mathrm{CO}}_3\right)}_2·4{\mathrm{H}}_2\mathrm{O}$ ], while nesquehonite appears to be the dominant Mg-carbonate without NH₄Cl addition. We also noticed dypingite formation via phase transformation in hot water. This study provides new insight into the reaction kinetics of CO₂ mineral carbonation that indicates the potential of this technique for future application to industrial-scale CO₂ sequestration. View Full-Text