Magnesium chloride hexahydrate crystal (MgCl_2.6H_2O) is an intermediate product used to obtain Mg metal from its ores. This work aims to produce purified MgCl_2.6H_2O 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. Similar content being viewed by others Hydrometallurgical Leaching of Manganese Using Hydrochloric Acid in The Presence of Thiourea from Um Bogma Area, Sinai, Egypt Article 14 November 2024 Preparation of Magnesium Chloride from Magnesite Dust Using Hydrochloric Acid Leaching and Spray Drying Article 06 July 2022 Removal of Magnesium from Liquor Produced by Nickel Mining by Crystallization Chapter © 2017 Explore related subjects Discover the latest articles, books and news in related subjects, suggested using machine learning. After leaching, the soluble magnesium chloride salt is separated from the insoluble residue and purified [ 2 ]. Commonly used lixiviants are hydrochloric acid [ 12 , 13 , 14 ], sulfuric acid [ 3 , 8 ], and other inorganic and organic acids. Several investigations into serpentinite rock have been done to understand its dissolution characteristics better. Singh et al. investigated the effect of solvent concentration, sample size, reaction temperature, and reaction time on Mg extraction that was explored using three acids: HCl, H 2 SO 4 , and HNO 3 . The activation energy was calculated for the dissolution kinetics of Mg, which follows the product layer diffusion process with 17.45 kJ·mol −1 (0–30 min) and 14.12 kJ·mol −1 (60–120 min) [ 15 ]. Abou El-Leef et al. investigated the best conditions for leaching Mg 2+ ions from serpentine ore using sulfuric acid. They found that the rate of magnesia dissolution in H 2 SO 4 acid solutions was regulated by a chemical reaction on the surface of the serpentine ore The following conditions were used to study the effect of the temperature on MgO recovery by leaching with aqueous HCl solution: Reaction time is 1 h, solid-to-liquid ratio is 1:5 g/ml, and acid concentration is 5 M. The results are shown in Fig. 2 a, which reveal that MgO recovery increases as temperature increases. The optimum temperature is 95 °C, which results in a MgO recovery of 86.5%. Fig. 2 Full size image Effect of leaching parameters on MgO recovery: Reaction temperature ( a ), Reaction time ( b ), Solid/liquid ratio ( c ), and Hydrochloric acid concentration ( d ) 3.2.2 Effect of Reaction Time The reaction time effect was studied at different time periods (1-4 h), where temperature, solid/liquid ratio, and acid concentration were set at 95 °C, 1:5 g/mL, and 5 M to optimize the recovery of MgO at the optimum reaction time. Figure  2 b shows that the interaction of serpentine with hydrochloric acid is a high-rate spontaneous reaction. The mole ratio of MgO to HCL was kept at a constant value while changing the ratios of solid (ore) and liquid (solution) by adopting the HCl concentration. Figure  2 c indicates that a higher solid-to-liquid ratio (1:20) results in a lower magnesium chloride concentration (83.4%) because of the decreased corresponding acid concentration. The low concentration of magnesium salts resulting from the increasing solid-to-liquid ratio leads to intensive energy consumption during the evaporation and crystallization step in the magnesium salt production process. It is worth mentioning that the reaction time required to achieve a certain degree of conversion of the magnesium is not an independent quantity, but it mainly depends on the size of the serpentinite particles and on the concentration and temperature of the acid. 3.3 Kinetic Analysis Experimental studies reveal that the Mg recovery from serpentine ores depends on the varied parameters of the applied process synchronized with its dissolving behavior. Material dissolving behavior is determined by the interaction between the acid reactant and the solid. This reaction is determined by the solid–liquid reaction model and the energy of activation. There are mainly three methods, product layer developed on the surface of the particle, film diffusion, or chemical reaction caused by unreacted ore, controlling the solid–liquid reactions. The slowest step of these methods controls the reaction rate. The dissolution characteristics of serpentinite rocks have been studied by many researchers, as shown in Table 2 . This research work conducted experiments with particle size 100%-200 mesh of the sample, 5 M acid concentration of 5 M, and at various applied temperatures in the reaction. The results of the experiments are presented in Fig. 3 for various times and temperatures. 6 Full size image Block flow diagram for preparation of magnesium chloride hexahydrate from serpentine ore 4 Conclusions This study concluded the optimum leaching conditions of Egyptian serpentine ores to achieve 97.6% MgO recovery at particle size less than 75 µm (100%), 95 °C of the reaction temperature for 3 h with solid-to-liquid ratio 1:5, and 5 M of HCl solution concentration. This study found that serpentine ore dissolution kinetics depended on the solid/liquid reaction model and activation energy. The kinetic studies proved that product layer diffusion could be the most appropriate rate-controlling step for the serpentine dissolution by HCl.