Phase behaviour of the ternary systems Rb2SO4(1)-RbBr(2)-H2O(3)/Cs2SO4(1)-CsBr(2)-H2O(3) at T=288.15, 298.15, 308.15 K

The phase equilibrium and physic-chemical properties of Rb2SO4(1)-RbBr(2)-H2O(3)/Cs2SO4(1)-CsBr(2)H2O(3) systems at T = (288.15, 298.15 and 308.15) K were determined by the isothermal solution saturation method. At the three temperatures, the two systems both contain one invariant point, two univariant curves, and three crystallization regions. The Schreinemaker's wet residue method and X-ray powder diffraction method were used to verify the solid phase. The phase diagrams of Rb2SO4(1)-RbBr(2)-H2O(3) and Cs2SO4(1)-CsBr(2)-H2O(3) at the three temperatures show that higher temperature reduces the area of the crystallization region of the salts (RbBr and CsBr). The comparison of the two systems at 298.15 K suggests that the crystallization region area of the salts is strongly affected by the solubility and hydration ability of the salts. The refractive index of these systems reached the maximum at the invariant point. At different temperatures, the refractive index increases with increasing temperatures. The results in this paper may provide useful information for the separation of the salts from aqueous solution. (C) 2021 Elsevier Ltd.

Automated summary

The phase equilibrium and physic-chemical properties of Rb2SO4(1)-RbBr(2)-H2O(3) and Cs2SO4(1)-CsBr(2)-H2O(3) systems were determined at different temperatures, showing one invariant point, two univariant curves, and three crystallization regions. The area of the crystallization region for RbBr and CsBr salts decreases with higher temperatures. The crystallization region area is strongly influenced by the solubility and hydration ability of the salts.