Controlled Supersaturation Precipitation of Hydromagnesite for the MgCl2−Na2CO3 System at Elevated Temperatures: Chemical Modeling and Experiment

A new chemical model of supersaturation ( S ) was developed and applied to test for the precipitation of hydromagnesite [Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O] in the MgCl 2 −Na 2 CO 3 system in supersaturated solutions over the temperature range of 50−90 °C. Based on the new model with the help of the OLI platform, the contour supersaturation of Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O has been exactly constructed by calculating the activity coefficients of species in unstable solutions. Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O crystals were identified using X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) images. It was found that the crystal properties, such as morphology, particle size distribution, filtration, and sedimentation characteristics, can be optimized by controlling the supersaturation during precipitation. With the control of supersaturation, well-developed spherical-like Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O crystals can grow to an average size of 30−40 μm, indicating a narrow particle size distribution, good filtration characteristics, and a high sedimentation rate. In addition, the Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O obtained was calcined to produce high-purity MgO at 800 °C. The size and morphology of MgO were similar to the same characteristics of the corresponding precursors.