Abstract: MgCO₃·3H₂O crystal was prone to agglomeration and disorder during its preparation, resulting in uncontrollable morphology and size. This issue led to a significant decrease in its performance and could not meet the application requirements. In this paper, MgCl2·6H2O and Na2CO3 were used as reactants, and a confined swirling reactor was employed to prepare MgCO3·3H?O crystal to address this issue. The operating parameters were optimized by investigating the effects of reactor rotation speed and stator-rotor gap on the morphology and size of the prepared MgCO3·3H?O crystal. Firstly, parameters such as Reynolds number (Re), material mixing time (t?), nucleation induction period (tind), and Kolmogorov length scale (ηk) in the confined space flow field were simulated. The calculation results showed that when the reactor rotation speed was 3000~5000 rpm and the stator-rotor gap was 0.2~0.5 mm, the material flow state was mainly turbulent, and the reaction materials were fully mixed before the nucleation of MgCO3·3H?O. The mass transfer process of materials could be effectively enhanced in the confined swirling reactor. Subsequently, experiments on the preparation of MgCO3·3H?O were carried out under various reactor rotation speeds and stator-rotor gaps. The results showed that when the reactor rotation speed was 3000 rpm and the stator-rotor gap was 0.2 mm, the MgCO3·3H?O crystal was prepared with a narrow particle size distribution and a volume-average particle size of 8.919 μm. To further quantify the influence of operating parameters on the size of MgCO3·3H?O crystal, the partial elasticity of its volume-average particle size with respect to the reactor rotation speed and the stator-rotor gap was calculated respectively. It was found that the partial elasticity of the volume-average particle size with respect to the stator-rotor gap was larger than to the reactor rotation speed, which meant that the size of MgCO3·3H?O crystals was more sensitive to the change of stator-rotor gap.

Key words: Nesquehonite, Confined swirling reactor, Particle size distribution, Theoretical analysis