Lansfordite (MgCO3·5H2O) was synthesized via the reactive crystallization of MgCl2 with Na2CO3 under the regulation of NaHCO3. The effects of crystallization parameters on the crystallization process and products were experimentally investigated by means of SEM

XRD

TG techniques and taking into consideration the change of magnesium ion concentration during the crystallization process. MgCO3·3H2O was easy to generate as by-product in the synthesis process. Process conditions of pure MgCO3·5H2O preparation were as follows: NaHCO3 amount was ≥3.00 g·L-1

Na2CO3 feeding speed was 2—50 ml·min-1

reactive temperature was 0—5.0℃. The as-synthesized lansfordite crystals displayed prismatic morphology with smooth faces and a size of 20—160 μm. Analysis showed that crystallization kinetics was promoted with the addition of NaHCO3.?HCO3- group created the steric effect inhibiting nesquehonite growth but was beneficial for lansfordite crystallization. Therefore

pure lansfordite could be synthesized under the regulation of NaHCO3. Changes in process parameters could make the crystallization process shift between thermodynamic control and kinetic control

affecting crystal polymorph and morphology.