Controlled precipitation of nesquehonite (MgCO3·3H2O) by the reaction of MgCl2 with (NH4)2CO3

In this study, homogeneous (unseeded) precipitation of nesquehonite (MgCO3·3H2O) by the reaction of MgCl2 with (NH4)2CO3 in supersaturated solutions was investigated. Factors that influence the precipitation of MgCO3·3H2O, such as reaction temperature, initial concentration, stirring speed, titration speed, equilibration time, have been studied. SEM images and particle size distribution show that the temperature, initial concentration and titration speed have significant effect on nesquehonite's crystal morphology and particle size. In addition, stirring speed and equilibration time also have some influence on its properties. X-ray powder diffraction (XRD) results show that the obtained crystals compositions are greatly affected by the reaction temperature. With the morphological transformation, their corresponding composition also change from MgCO3·xH2O to Mg5(CO3)4(OH)2·4H2O in the interval of 288–333 K. With the optimization of operating conditions, the crystals can grow up to a length of about 40 μm and a width of 5 μm, indicating good filtration properties. High-purity nesquehonite obtained in this study was calcined to produce highly pure MgO at 1073 K as shown by XRD results.