Stable Phase Equilibria of Ternary Systems Li(+),Rb(+)//SO(4)(2–)–H(2)O and Li(+),Cs(+)//SO(4)(2–)–H(2)O at 273.2 K

[Image: see text] The stable phase equilibria of ternary systems Li(+),Rb(+)//SO(4)(2–)–H(2)O and Li(+),Cs(+)//SO(4)(2–)–H(2)O at 273.2 K are studied herein by the isothermal dissolution equilibrium method. The solubility and density of the systems are measured experimentally, and the related phase diagrams, density versus composition diagrams, are plotted. Results show that the ternary systems Li(+),Rb(+)//SO(4)(2–)–H(2)O and Li(+),Cs(+)//SO(4)(2–)–H(2)O are both complex systems with two kinds of double salts formed at 273.2 K. The stable phase diagrams of these two ternary systems all consist of one unsaturated solution region, three co-crystallization regions, three invariant points, four invariant curves, and four crystallization regions. By comparing the phase diagrams of the ternary system Li(+),Rb(+)//SO(4)(2–)–H(2)O at 273.2 and 298.2 K, it is found that the crystallization regions of the two double salts (3Li(2)SO(4)·Rb(2)SO(4)·2H(2)O and Li(2)SO(4)·Rb(2)SO(4)) and the single salt Li(2)SO(4)·H(2)O all decrease, while that of Rb(2)SO(4) increases when the temperature drops. Also, it can be seen from the phase diagram of the ternary system Li(+),Cs(+)//SO(4)(2–)–H(2)O at 273.2 and 298.2 K that the crystallization regions of the double salt 3Li(2)SO(4)·Cs(2)SO(4)·2H(2)O and the single salt Cs(2)SO(4) increase, while those of the double salt Li(2)SO(4)·Cs(2)SO(4) and the single salt Li(2)SO(4)·H(2)O decrease as the temperature drops.