Solid–Liquid Equilibria in the Quinary System KCl–KBr–NaCl–NaBr–H2O at 298.15 K and Its Application

Solid–liquid equilibrium is a vital foundation for extracting bromine from bittern, which contains a high concentration of bromine resources. The phase equilibrium data of the quaternary system KCl–KBr–NaCl–NaBr–H2O at 298.15 K were measured by the approach of isothermal dissolution, and the phase diagram was plotted. The results showed that the quaternary system has an invariant point, three univariant curves, and three crystallization zones corresponding to three solid solutions: Na(Cl, Br), K(Cl, Br), and Na(Cl, Br)·2H2O. An improved model was used to calculate the solubilities of the quaternary system, and the computed values agree well with the experimental data. On the basis of the quaternary system KCl–KBr–NaCl–NaBr–H2O at 298.15 and 348.15 K and the ternary system NaBr–NaCl–CH3OH at 298.15 K, a new process was developed to extract NaBr products of which the purity was 98.23%. Above all, this method realized the full circulation of the mother solution.