Abstract:

In order to obtain the crystallization law of each salt in the coexistence chloride system of lithium and rubidium，potassium and rubidium at 288.2 K，the solid-liquid equilibrium of two ternary systems of Li⁺，Rb⁺//Cl^--H₂O and K⁺，Rb⁺//Cl^--H₂O at 288.2 K were studied by isothermal dissolution equilibrium method.The solubilities and physical properties（density，refractive index） of the system at 288.2 K were experimentally determined.The composition of the equilibrium solid phase at the invariant point was determined by wet residue method，XRD，SEM-EDS，the corresponding phase diagrams were constructed based on the experimental data.The results showed that the ternary system of Li⁺，Rb⁺//Cl^--H₂O was a simple system without double salts or solid solution formed at 288.2 K.The crystallization region of RbCl was much larger than LiCl·2H₂O.The ternary system of K⁺，Rb⁺//Cl^--H₂O was a complex system at 288.2 K with the solid solution（K，Rb）Cl was formed，and the crystallization region was the largest.Comparing the phase diagrams of the system of K⁺，Rb⁺//Cl^--H₂O at 288.2，298.2 and 348.2 K，it was found that the solid solution（K，Rb）Cl was formed at all three temperatures，and the crystallization region of the solid solution（K，Rb）Cl was always the largest.With the increase of temperature，the crystallization region of KCl and RbCl became larger，and the crystallization region of（K，Rb）Cl became smaller.The density and refractive index of the equilibrium solution of these two systems were calculated by the empirical equation.The calculated results were in line with experimental values with the maximum relative error of less than 0.02.

Key words: phase equilibrium, lithium chloride, potassium chloride, rubidium chloride, solid solution