Study On The Isothermal Phase Diagram Of The Quaternary System LiCl+MgCl₂+KCl+H₂O At323.15K

Abstract:In order to make the extraction of lithium resources from salt brine with high mass ratio of Mg:Li efficiently and economically, a method using potassium chloride as the magnesium precipitator for the extraction of lithium resources is considered to be an available one. For mastering the mechanium of the extraction of lithium resources, a research on the phase diagram of the quaternary system LiCl+MgCl2+KCl+H2O from low to high temperature is required. To date, the phase diagram of the quaternary system above room temperature has never been reported. So be dedicated to the research of this phase diagram at323.15K and carry out the following work:1. Research the phase diagram of this quaternary system by using the isothermal equilibrium method, the solid phase is determined by using the wet solid phase method as well as the X-ray diffraction. To ensure the accuracy of the experimental data, the methods of analyzing the ions present in the system have been improved and verified by experiments. The deviations of analyzing Cl-, Mg2+and K+are below±0.05%、±0.1%、±0.3%respectively. The results show that the phase diagram of quaternary system LiCl+MgCl2+KCl+H2O at323.15K is divided into five crystallization fields corresponding to LiCl·H2O, LiCl·MgCl2·7H2O, MgCl2·6H2O, KCl·MgCl2·6H2O and KC1. The crystallization field of KC1is the largest that it extends to75%of the area, while the field of MgCl2·6H2O is the smallest that it is only about1%of the area. Three cosaturated points corresponding to LiCl·H2O+LiCl·MgCl2·7H2O+KCl·MgCl2·6H2O, LiCl·H2O+KCl·MgCl2·6H2O+KC1, LiCl·MgCl2·7H2O+KCl·MgCl2·6H2O+MgCl2·6H2O can be found in this phase diagram and their accurate component has been gotten.2.<sed on the accurate experiment, A Pitzer-Simonson-Clegg (PSC) thermodynamic model which is suitable to describe electrolyte solutions at low to high concentration to simulate and predict the thermodynamic properties of this quaternary system LiCl+MgCl2+KC1 +H2O and its sub-systems. The parameters are fitted with the thermodynamic data of the sub-systems of the quaternary system LiCl+MgCl2+KCl+H2O by using PSC model. Then predict the phase diagram of the quaternary system LiCl+MgCl2+KCl+H2O at323.15K only using the binary parameters and ternary parameters to get the completed phase diagram of this system. It shows that the results predicted by PSC model and the experimental results are in good agreement. It indicates the reliability of the experimental data, as well as the good prediction to phase diagrams by using PSC model.