Solid–Liquid Equilibria of the Quinary System Li+, K+, Mg2+//Cl–, B4O72––H2O at 323.2 K

The solid–liquid equilibria of the quinary system Li+, K+, Mg2+//Cl–, B4O72––H2O at 323.2 K were investigated by the isothermal dissolution method. The solubility, refractive index, and density of the system were determined, and the corresponding space phase diagram, planar projection diagram, water content diagram, and density/refractive index vs composition diagrams saturated with MgB4O7 are constructed based on the experimental data. The result shows that there are double salts of lithium carnallite (LiCl·MgCl2·7H2O) and carnallite (KCl·MgCl2·6H2O) formed in the system. The space phase diagram consists of five invariant points, 16 isothermal solution curves, and eight crystalline regions (Li2B4O7·3H2O, K2B4O7·4H2O, KCl, MgB4O7·9H2O, KCl·MgCl2·6H2O, MgCl2·6H2O, LiCl·MgCl2·7H2O, LiCl·H2O). Under the saturation of salt MgB4O7, the crystalline region of Li2B4O7·3H2O is the largest in the planar projection diagram of this system, and the solubility of LiCl is the largest. A comparison of planar projection diagrams (under the saturation of salt MgB4O7) of the system at 273.2 and 323.2 K shows that the crystallization regions of Li2B4O7·3H2O, KCl·MgCl2·6H2O, LiCl·MgCl2·7H2O, and LiCl·H2O increase along with the temperature, while those of K2B4O7·4H2O and KCl decrease. The results show that low temperature is conducive to the extraction of potassium in the form of K2B4O7·4H2O and KCl and has less entrainment loss; high temperature is beneficial to the precipitation of Li2B4O7·3H2O.