Stable Phase Equilibria of the Quaternary Water-Salt System Li+, Rb+, Mg2+//SO4 2--H2O at T = 273.2 K.

Abstract

The phase equilibria for the quaternary system Li+, Rb+, Mg2+//SO4 2- - H2O at 273.2 K were studied by the isothermal dissolution equilibrium method. Based on the measured data, the space diagram, stable phase diagram, water content diagram, and the diagram of density vs composition are plotted. The stable phase diagram in the system consists of four quaternary invariant points, nine univariate curves, and six crystallization zones. For the invariant points, E1 and E4 belong to the commensurate type, and E2 and E3 belong to the incommensurate type. The order of the crystallization area is Rb2SO4·MgSO4·6H2O > 3Li2SO4·Rb2SO4·2H2O > Li2SO4·Rb2SO4 > MgSO4·7H2O > Li2SO4·H2O > Rb2SO4. The density of the equilibrium liquid changed regularly with the content of Rb2SO4 in the solution. By comparing the stable phase diagram of the partial ternary subsystems at T = 273.2 K and T = 298.2 K, it is found that the crystallization regions of Rb2SO4 increases with the decrease in temperature, which indicates that cooling is conducive to the crystallization of Rb2SO4. By comparing the stable phase diagram of the system at T = 273.2 K and T = 308.2 K, it was found that the system was composed of four invariant points, nine univariate curves, and six crystal regions. The double salt 3Li2SO4·Rb2SO4·2H2O is converted to 3Li2SO4·Rb2SO4. The crystallization region of single salt MgSO4·7H2O, Rb2SO4 and double salt Li2SO4·Rb2SO4 decreased obviously.