Crystallization study of calcium sulfate dihydrate was studied under conditions of scales formation using pure chemicals and at low salinity. Calcium chloride and sodium sulfate were mixed in deionized water, and the conductivity of the reaction mixture was measured at different time periods to determine the induction time of gypsum crystal formation. Induction time was measured under different high supersaturation ratios (SR) ranging from 5.9 to 7.0. Using crystallization Downloaded by [University of Lethbridge] at 23:59 26 June 20162 equations that relate induction times with supersaturation ratios, the free energy barrier and critical nuclei radius were calculated with and without addition of scale inhibitor (Tri-Sodium Phosphate, TSP). The nucleation rates at supersaturation ratio of 5.9 are 7.6 × 10 26 nuclei/cm 3 .s and 2.3 × 10 26 nuclei/cm 3 .s with and without TSP addition, respectively. The surface energy increases with TSP compared to the baseline (without TSP). Numbers of molecules required for formation of stable nucleus are calculated to be from 15 to 22 molecules depending on supersaturation ratios and presence or absence of TSP.
Magnesium chloride hexahydrate crystal (MgCl2.6H2O) is an intermediate product used to obtain Mg metal from its ores. This work aims to produce purified MgCl2.6H2O crystals from natural Egyptian serpentine. Serpentine samples were collected from the Eastern Desert in Egypt and prepared for leaching with HCl solutions. Reaction temperature (°C), leaching time (h), solid/liquid ratio (g/mL), and acid concentration (M) were studied. The optimum leaching conditions achieved 97.6% MgO recovery optimized at particle size less than 75 µm (100%), 95 °C of the reaction temperature for three hours with solid-to-liquid ratio 1:5, and 5 M of HCl concentration. The serpentine dissolution kinetics were studied depending on the solid–liquid reaction and activation energy model. The resultant liquor was purified and crystallized. The kinetic studies indicated that product layer diffusion is the most likely rate-controlling step for serpentinite dissolution in the HCl solution.
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