The solubility values and physicochemical properties (pH values, refractive indices, and densities) of electrolyte mixtures in quaternary system containing lithium, potassium, rubidium, and borate were investigated at 348 K by isothermal dissolution method. The space phase diagram, the planar projection diagram, the water content diagram, and the diagrams of physicochemical properties depending on the composition were obtained using the measured data. The phase diagram of this quaternary system contains one invariant point, three univariant curves, and three single salts corresponding to lithium tetraborate trihydrate (Li 2 B 4 O 7 •3H 2 O), potassium tetraborate tetrahydrate (K 2 B 4 O 5 (OH) 4 •2H 2 O), and rubidium pentaborate tetrahydrate (RbB 5 O 6 (OH) 4 •2H 2 O). This quaternary system is of a simple cosaturation type, no double salt or solid solution formed. The scope of areas of crystallization of salts is such that RbB 5 O 6can be more easily separated from the solution than the other coexisting salts at 348 K. The physicochemical properties of the solutions at equilibrium on the univariant curve CE increase obviously with increasing Janecke index, J(K 2 B 4 O 7 ); whereas on the univariant curve AE or BE, the physicochemical properties change slightly along with the changes of J(K 2 B 4 O 7 ).

Phase equilibria for the reciprocal quaternary system containing rubidium, magnesium, chloride, and borate in aqueous solution at 348 K was investigated by isothermal dissolution method. The compositions, densities, and refractive indices of the solution at equilibrium were measured experimentally. The space phase diagram, the planar projection diagram, the water content diagram, and the diagrams of the physicochemical properties (densities and refractive indices) vs composition were constructed using the measured data. Results indicate that the quaternary system is a complex type along with the double salt rubidium carnallite (RbCl•MgCl 2 •6H 2 O) formed at 348 K. The planar projection diagram consists of three invariant points, seven univariant curves and five crystallization zones corresponding to four single salts rubidium pentaborate tetrahydrate (RbB 5 O 6 (OHWith a view to the crystallization zones, the crystallization zone of salt RbB 5 O 6 (OH) 4 •2H 2 O occupies the largest part, meaning rubidium borate can be more easily separated from solution than the other coexisting salts in this system at 348 K. The water content and physicochemical properties of the equilibrium solution corresponding the univariant curve EH 3 change obviously with the increase of J(Mg 2+ ), whereas the water content and physicochemical properties change only slightly on the other univariant curves.

The metastable phase equilibrium of the quaternary system LiCl + KCl + RbCl + H2O at 348.15 K was done by using an isothermal evaporation method. The solubilities, densities, and refractive indices of the equilibrated solution were determined experimentally. On the basis of the measured data, the stereo phase diagram, the metastable phase diagram, the water content diagram, and the physicochemical properties versus composition diagrams were constructed. Results show that the quaternary system is of a complex type with the solid solution of potassium chloride and rubidium chloride [(K, Rb)Cl] formed at 348.15 K. The metastable phase diagram consists of two invariant points, five univariant curves, and four crystallization fields corresponding to single salts potassium chloride (KCl), rubidium chloride (RbCl), lithium chloride monohydrate (LiCl·H2O), and a solid solution of potassium and rubidium chloride [(K, Rb)Cl]. Salt RbCl has the largest solubility among the coexisting salts and presents the smallest crystallization field in the phase diagram. The crystallization region of [(K, Rb)Cl] almost occupies the entire phase region, which shows that it is difficult to separate potassium from rubidium in chloride solution by only using evaporation and crystallization methods. This is compared with the metastable phase diagram of the quaternary system at 298.15 K that shows that the crystallization forms have not changed, while the crystallization fields have slightly change. The refractive index of the solution has been calculated using an empirical equation. The maximum absolute deviation between the calculated and experimental data of the refractive index is less than 0.007.

The solubilities of electrolyte mixtures ternary systems KCl + RbCl + H2O and KCl + MgCl2 + H2O at 348.15 K were obtained by isothermal evaporation method. The corresponding physicochemical properties of the solution such as density and refractive index were also determined. The Scherinemakers’ wet residue method was used to determine the composition of the solid phase. The metastable phase diagram, density versus composition diagram, and refractive index versus composition diagram were constructed on the basis of the experimental data. Results showed that these two ternary systems were both complex type. The incommensurare double salt carnallite (KCl·MgCl2·6H2O) was found in the KCl + MgCl2+ H2O system at 348.15 K. Comparisons between the metastable phase diagrams of KCl + MgCl2+ H2O system at (298.15, 323.15, and 348.15) K show that the crystallization zone of carnallite decreases with the increase in temperature. The solid solution [(K,Rb)Cl] was formed in the KCl + RbCl + H2O system at 348.15 K. Comparisons between the metastable phase diagrams of KCl + RbCl + H2O system at (298.15, 323.15, and 348.15) K show that the crystallization zone of [(K,Rb)Cl] decreases with the increase in temperature. The empirical equation was used to calculate the refractive indices of the equilibrated solution. The calculated results keep in line with experimental values with the maximum relative error less than 0.005.

The mixed aqueous electrolyte system containing lithium, sodium, chloride, and carbonate has been investigated using the isothermal evaporation method at 273.15 K. The stereophase diagram and the planar projection diagram have been constructed based on the Jänecke method. The compositions of the equilibrated solid phases and liquid phase corresponding to equilibrium points were measured. The system contained only four single salts, sodium chloride (NaCl), lithium chloride monohydrate (LiCl·H2O), lithium carbonate (Li2CO3), and sodium carbonate decahydrate (Na2CO3·10H2O). Salt LiCl has a strong salting-out effect on the other salts. The density coefficients Ai which were used for the calculation of density at 273.15 K were obtained by fitting. The calculated values of density using an empirical equation have a maximum relative error less than 0.020.