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

• Published in: Minerals (Basel) 2017-09, Vol.7 (9), p.172
• Main Authors: Zhu, Chen, Wang, Han, Li, Gen, An, Siyu, Ding, Xiaofeng, Teng, Hui, Zhao, Liang
• Format: Article
• Language: English
• Subjects: Absorption; absorption rate; Ammonia; Ammonium chloride; Carbon capture and storage; Carbon dioxide; Carbon dioxide fixation; Carbon sequestration; Carbonates; Carbonation; Chemical precipitation; Crystallization; Diffusion rate; Dye dispersion; GEOSCIENCES; Hot water; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Interactions; Kinetics; Magnesium; Magnesium carbonate; Magnesium chloride; Microprocessors; Phase transitions; Reaction kinetics; Removal; Solutions; Storage; Wetted wall columns
• ISSN: 2075-163X; 2075-163X
• DOI: 10.3390/min7090172

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 ( ≥2mol⋅L−1≥2mol•L−1 ) leads to the precipitation of roguinite [ (NH4)2Mg(CO3)2⋅4H2O(NH4)2Mg(CO3)2•4H2O ], 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.