A promising strategy for the large-scale preparation of spherical calcium carbonate by efficiently using carbon dioxide

Spherical calcium carbonate (CaCO3) is widely used in industries. However, its large-scale synthesis still remains a challenging issue. Herein, we report the preparation of spherical CaCO3 at a high calcium hydroxide (Ca(OH)2) concentration (1.08 M) using CO2 highly efficiently in methanol (CH3OH)-water mixed solvent with polyethyleneimine (PEI) as a crystal modifier by carbonation method. Experimental results revealed that the introduction of CH3OH in the reaction systems decreased the saturation Ca2+ concentration in the solvent, and then formed spherical CaCO3 under the controlled action of PEI. Besides, spherical CaCO3 with a particle size of about 1 µm can be obtained at concentration of Ca(OH)2 of 1.08 M, PEI of 5 g/L, and CH3OH volume content of 30%, stirring rate of 450 rpm, and CO2 flow rate of 1.4 m3/h. The formation mechanism of spherical CaCO3 indicated that the particles converted from an initial amorphous precursor, to needle-like, bundle-like, block-like and hemispherical shaped aggregates, and finally to a complete spherical CaCO3 morphology. This research provides an effective method for the preparation of high yield spherical CaCO3 by industrial carbonation method.