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

Abstract

A new chemical model of supersaturation (S) was developed and applied to test for the precipitation of hydromagnesite [Mg5(CO3)4(OH)2·4H2O] in the MgCl2−Na2CO3 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 Mg5(CO3)4(OH)2·4H2O has been exactly constructed by calculating the activity coefficients of species in unstable solutions. Mg5(CO3)4(OH)2·4H2O 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 Mg5(CO3)4(OH)2·4H2O 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 Mg5(CO3)4(OH)2·4H2O 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.

Modeling solid–liquid equilibrium of NH4Cl‐MgCl2‐H2O system and its application to recovery of NH4Cl in MgO production

“…Thus, as indicated in Figure 8, for recovery of NH 4 Cl from an NH 4 Cl‐rich mixture obtained after separation in Refs 2. or3, the liquid phase composition can vary as follows: From NH 4 Cl unsaturation variety to the NH 4 Cl‐NH 4 MgCl 3 ·6H 2 O double saturation variety with swinging the temperature and increasing the concentration of MgCl 2 . During this period, only NH 4 Cl crystallizes. From the NH 4 Cl‐NH 4 MgCl 3 ·6H 2 O saturation variety to the MgCl 2 ·6H 2 O‐NH 4 MgCl 3 ·6H 2 O double saturation variety with further increasing the concentration of MgCl 2 .…”

“…This method badly encounters difficulty in the solid–liquid separation of Mg(OH) 2 suspension for its small particle size and gelatinous state. A novel process currently under development was proposed by authors2, 3 to extract magnesium by reaction (2) for precipitation of magnesium carbonate compounds, i.e., nesquehonite or hydromagnesite because of their good filtration properties. …”

Degradation rates and products of pure magnesium exposed to different aqueous media under physiological conditions

“…Nesquehonite, can be directly synthesized by the addition of a NaCO 3 solution to a MgCl 2 solution at room temperature [22]. At slightly elevated temperatures, the NaCO 3 -MgCl 2 system leads to the formation of hydromagnesite (Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O) [23]. Furthermore, the transformation of nesquehonite to hydromagnesite was reported in the context of dypingite (Mg 5 (CO 3 ) 4 (OH) 2 ·5H 2 O) [24,25], which was also found as a byproduct in the synthesis of magnesite (MgCO 3 ) [26].…”

Enhancing magnesite formation at low temperature and high CO2 pressure: The impact of seed crystals and minor components

“…After 14 days of reaction the XRD analysis indicates that magnesite has begun to grow (see Fig. 1b), but that brucite is still present along with the expected magnesium carbonate precipitates hydromagnesite and nesquehonite (Cheng and Li, 2010;Back et al, 2011;Case et al, 2011;Hopkinson et al, 2012;Wang and Li, 2012). For comparison, XRD analysis of samples without added magnesite (Fig.…”