Phase Equilibrium Study Of MgCl₂-NiCl₂/CoCl₂-H₂O Ternary System In The Hydrochloric Acid Leaching Solution Of Laterite Nickel Ore

In the hydrometallurgical process of laterite nickel ore,the atmospheric hydrochloric acid leaching process has been extensively studied due to its advantages of simple process,easy operation,and low energy consumption.The process mainly includes steps such as crushing,hydrochloric acid leaching,neutralization and impurity removal,nickel cobalt precipitation,and hydrochloric acid regeneration.The solution components after the neutralization and impurity removal steps are mainly MgCl₂,NiCl₂,and CoCl₂,It is necessary to continue adding alkaline substances to adjust the p H of the solution to precipitate nickel and cobalt ions in the form of nickel and cobalt hydroxide.However,the neutralization and nickel cobalt precipitation process takes a long time and is difficult to control,consuming more hydrochloric acid and introducing more impurities,increasing subsequent processing costs.However,according to the solubility differences of several substances,the separation effect can also be achieved by using the evaporation crystallization method to separate several substances in stages.Therefore,it is very necessary to study the phase equilibrium of nickel cobalt magnesium chloride system for the comprehensive recycling of laterite nickel resources.In this paper,the phase equilibrium experiments of MgCl₂-NiCl₂-H₂O ternary system at 303 K,313 K,323 K and MgCl₂-CoCl₂-H₂O ternary system at 303 K,313 K were carried out by using isothermal solution equilibrium method.The specific research work is as follows:（1）Firstly,the analytical methods for each ion in the equilibrium liquid phase were studied.Due to the physical and chemical properties of NiCl₂·6H₂O and CoCl₂·6H₂O in the system,such as being prone to weathering and water loss,the drying methods for the equilibrium solid phase in the two systems were studied,and the composition of the equilibrium solid phase in each system was determined by wet residue method combined with X-ray diffraction.（2）The experimental results show that the ternary system of MgCl₂-NiCl₂-H₂O and MgCl₂-CoCl₂-H₂O has a constant point,two isothermal dissolution curves,and three crystallization regions at the study temperature.The crystallization regions of NiCl₂ and CoCl₂ are both larger than those of MgCl₂,and there is neither double salt nor solid solution formation.Further crystallization separation experiments were conducted on the MgCl₂-NiCl₂-H₂O ternary system based on the experimental results of the phase diagram.The results showed that within a certain concentration range,NiCl₂ precipitated earlier than MgCl₂,and the crystallization product was NiCl₂·2H₂O.Moreover,with the increase of Ni content in the MgCl₂-NiCl₂-H₂O ternary system,the purity of the crystallized NiCl₂·2H₂O product was higher,which is consistent with the results of the phase diagram.（3）The Mixed Solvent Electrolyte Model（MSE）under OLI software was used to calculate the solubility of the MgCl₂-NiCl₂-H₂O ternary system at 303 K to 323 K.The comparison results indicate that the experimental data and calculated data have a good fit,and this model can be used to predict the solubility of the system.The model can be used to predict the solubility of the system.