This study proposes an advanced technology using post‐reaction filtrate as an ammonia carrier to synthesize magnesium hydroxide (MH) with small particles, which can benefit subsequent hydrothermal modification. In this work, the limitation of ammonia gas and ammonia water methods is avoided. The impact of operating parameters including MgCl2 concentration, temperature, ammonia‐to‐magnesium molar ratio, feed rate, volume of ammonia mother liquor and aging time on the magnesium yield, particle size, and morphology of MH is studied. The temperature and ammonia‐to‐magnesium molar ratio are identified as key factors affecting magnesium yield. MH with a half‐content diameter of 1.70 µm and a morphology resembling small irregular flakes is successfully synthesized at a magnesium yield of 90.06%. The predictions of idea crystal habits are also performed using Morphology and CASTEP modules with Materials Studio Software. The (0 0 1) face can be preserved with the largest facet area because of the slowest crystal growth rate and the smallest attachment energy, which exhibits that MH crystals tend to be flakes.
To overcome the drawbacks of strong polarity and easy agglomeration of ordinary magnesium hydroxide (MH), hydrothermal modification is customary applied to achieve its excellent dispersion as well as controllable morphology and particle size. In this paper, the influence mechanism of hydrothermal modification is elaborated from microstructure of MH. Structures and surface energy of crystal planes, affinity of water molecules for crystal planes, and crystal growth process are calculated by Materials Studio software. Furthermore, molecular dynamics simulations about solid-liquid interface model of MH and 1 mol L −1 NaOH solution at different temperatures are performed based on the theory of modified attachment energy model. The results indicate that (0 0 1) plane with the smallest surface energy has the strongest thermodynamic stability, equipping modified crystals with lamellar morphology and excellent dispersion. (0 0 1) plane cannot be dissolved easily because of the smallest affinity of water molecules. The magnesium atoms and hydroxyl groups on (1 0 1) plane dissolved are absorbed on (0 0 1) plane, resulting in the large value of I 001 /I 101 in the X-ray diffraction pattern. The relative growth rate of (1 0 1) plane R 101 decreases with the increasing temperature, explaining why crystals become thicker with raising temperature.
The flotation process to extract potassium salt from carnallite ores could produce the MgCl 2 mother liquor with flotation reagents�octadecyl amine hydrochloride (ODA) and dodecyl morpholine (DMP). The organic impurities would further affect MgCl 2 resource-integrated utilization for preparing magnesium hydroxide (MH). In this study, the effects of flotation reagents with different concentrations on the morphology of MH were investigated at a hydrothermal temperature of 200 °C for 6 h with the hydrothermal medium of a 4 mol/L NaOH solution. It was observed that the average thickness of MH crystal plates increased and the morphology of crystals changed from regular hexagonal plates to irregular polygonal plates with the increase of ODA and DMP concentrations. Molecular dynamics (MD) simulation was applied to further explain the effect mechanism. The results indicated that ODA and DMP molecules were more likely to be adsorbed on the (1 1 0) plane in contrast to the (0 0 1) plane due to the larger absolute values of adsorption energy on the (1 1 0) plane. The long carbon chains far away from the (1 1 0) plane would form steric hindrance to affect the growth rate of MH crystals in the [1 1 0] direction.
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