Solid–Liquid Equilibria in the Quinary System Na⁺, K⁺//Cl^–, Br^–, SO₄^2––H₂O at 323.15 and 348.15 K

Abstract

Aiming at the comprehensive utilization of bromine resources in bittern, the stable solid−liquid equilibria in the quinary system Na + , K + //Cl − , Br − , SO 4 2− −H 2 O at 323.15 and 348.15 K were studied using the isothermal dissolution equilibrium method. The corresponding phase equilibrium data were measured, and with which the simplified equilibrium dry-salt phase diagrams saturated with Na 2 SO 4 and K 2 SO 4 , respectively, Na + content diagrams and K + content diagrams were plotted. As a result, the quinary system saturated with Na 2 SO 4 at both two temperatures contains an invariant point, three univariant curves, and three crystallization regions including the single-salt KBr, the double-salt Na 2 SO 4 •3K 2 SO 4 , and the solid solution Na(Cl, Br). The crystallization areas of Na 2 SO 4 •3K 2 SO 4 , Na(Cl, Br), and KBr decrease in sequence. By comparison, the phase diagrams of the quinary system saturated with K 2 SO 4 at both 323.15 and 348.15 K are much simpler and have no invariant points, instead of one univariant curve and two crystallization regions (Na 2 SO 4 •3K 2 SO 4 and K(Cl, Br)). The crystallization area of Na 2 SO 4 •3K 2 SO 4 is essentially as large as that of K(Cl, Br).