A Study Of Theoretical Calculations Of Subsystem Phase Equilibria In The Quinary Na⁺, K⁺//Cl^-,Br^-, SO₄^2--H₂O System At323K

At present, most research about phase equilibria of salt-water system were focused on experimental studies under normal temperature conditions. The theoretical research about phase equilibria were reported less. In this paper, The solubilities of phase equilibria in salt-water systems with solid solution were calculated by using the chemical model of Pitzer’s electrolyte solution theory.The solubilities of phase equilibria in subsystems of quinary system Na+, K+//Cl-, Br-, SO42--H2O (two ternary systems and four quaternary systems) at323K were calculated using Pitzer’s equations. These sub-systems calculated are as following two solid solution ternary systems of Na+//Cl-, Br--H2O and K+//Cl-, Br--H2O, two simple quaternary systems Na+//Cl-, Br-, SO42--H2O and K+//Cl-, Br-, SO42--H2O, and two interaction quaternary systems Na+, K+//Cl-, SO42--H2O, and Na+, K+//Br-, SO42--H2O.Using the solubility data of ternary systems Na+//Br-, SO42--H2O and K+//Br-, SO42--H2O at323K, the corresponding ion-interaction mix parameters θBr,SO4, ψNa,Br,so4and ψK,Br,SO4for Pitzer’s equations were fitted by multiple linear regression method. These parameters obtained were used in the solubility calculations of the quaternary systems. Using the solubility data of ternary systems K+//Cl-, Br--H2O and Na+//Cl-, Br--H2O at323K, equilibrium constants of solid solution salts at323K were evaluated with Pitzer’s model by linear regression method. The relationship of dissolved equilibrium constant on solid solution K(Cl, Br) and Na(Cl, Br) between Ka and bromine salt mole fraction in the solid solution were given.The solubilities of ternary systems Na+//Cl-, Br--H2O, and K+//Cl-, Br--H2O were predicted by Pitzer’s equations with the solid solution equilibrium constants. The calculations data and experiments data were compared, the calculation diagrams of the phase equilibrium phase were plotted. The research results showed that the calculated values have a good agreement with the experimental data. There is only one solid solution crystalline in the phase diagram.The solubilities of quaternary systems Na+//Cl-, Br-, SO42--H2O and K+//Cl-, Br-, SO42--H2O at323K were calculated by Pitzer’s equations with corresponding ion-interaction mix parameters and the solid solution equilibrium constants. The calculations data and isothermal phase equilibrium experiment data were also compared, and the calculation diagrams of the phase equilibrium phase were plotted. The deviation and errors of the theoretical calculations and experimental data were analyzed. The results showed that the calculated values have part deviation with the measured data.There were two solid solution crystallization regions in the quaternary phase diagrams.The solubilities of interaction quaternary system Na+, K+//Cl-SO42--H2O and Na+, K+//Br-, SO42--H2O at323K were calculated by using Pitzer’s equations with corresponding ion-interaction mix parameters θBr.SO4, ψNa,Br,so4, ψK,Br,so4and the solid solution equilibrium constants. The comparison between the calculation data and the experiment data were made. The calculation diagrams were plotted. The calculated values are basically in agreement with experiment data. It also shows that reasonable parameters of the Pitzer model can be used in aqueous salt system Na+, K+//Br-, SO42--H2O and Na+, K+//Cl-, SO42--H2O.