| Abstract
| - 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 physicochemicalproperties (density, viscosity, refractive index, conductivity, and pH value) of the equilibrium solutionswere determined. A phase diagram and physicochemical properties−composition diagrams were plottedon the basis of the solubility data. The isothermal solubility diagram of the quinary system (saturatedwith KCl) consists of 14 univariant curves, 7 invariant points, and 8 crystallization regions correspondingto NaCl, Na2B4O7·10H2O, K2B4O7·4H2O, Na2CO3·10H2O, Na2CO3·7H2O, Na2CO3·H2O, NaKCO3·6H2O,and K2CO3·1.5H2O, respectively. Pitzer's theory was adapted for theoretically describing relations of thehigh-concentration multicomponent systems in the study. Using Harvie's chemical equations, which arebased on Pitzer's theory, the solubility of the quinary system at T = 298.15 K was calculated. The calculatedvalues agree with the measured ones, with a deviation of less than 9.59%.
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