Study of the Phase Equilibrium and Solution Properties of the Quinary System Na⁺+ K⁺+ Cl^-+ CO₃^2-+ B₄O₇^2-+ H₂O atT= 298.15 K

The phase equilibria of the quinary system Na+ +K+ + Cl- + CO32- + B4O72- + H2O was studied at T = 298.15 K by the isothermal dissolution equilibrium method. The solubility and physicochemical properties (density, viscosity, refractive index, conductivity, and pH value) of the equilibrium solutions were determined. A phase diagram and physicochemical properties-composition diagrams were plotted on the basis of the solubility data. The isothermal solubility diagram of the quinary system (saturated with KCl) consists of 14 univariant curves, 7 invariant points, and 8 crystallization regions corresponding to NaCl, Na(2)B(4)O(7)(.)10H(2)O, K2B4O7-4H(2)O, Na(2)CO(3)(.)10H(2)O, Na(2)CO(3)(.)7H(2)O, Na2CO3-H2O, NaKCO3-6H(2)O, and K(2)CO(3)(.)1.5H(2)O, respectively. Pitzer's theory was adapted for theoretically describing relations of the high-concentration multicomponent systems in the study. Using Harvie's chemical equations, which are based on Pitzer's theory, the solubility of the quinary system at T = 298.15 K was calculated. The calculated values agree with the measured ones, with a deviation of less than 9.59%.