Solid–Liquid Phase Equilibrium in Aqueous Quaternary System Li+,Rb+,Mg2+//Borate–H2O at T = 323 K

Abstract

The stable phase equilibria, densities, and refractive indices of the aqueous quaternary system Li+,Rb+,Mg2+//borate–H2O at 323 K were determined by the isothermal dissolution method. It was found that the phase diagram consists of one quaternary invariant point, two isothermal dissolution curves, and three fields of crystallization corresponding to three single salts Li2B4O7 · 3H2O, MgB4O7 · 9H2O, and RbB5O8 · 4H2O, respectively. The size of crystallization regions of salt decreased in the order MgB4O7 · 9H2O > RbB5O8 · 4H2O > Li2B4O7 · 3H2O. The comparison of phase diagrams of the system at 298–348 K shown that the crystalline form of salts lithium borate, magnesium borate, and rubidium borate did not change at 298–348 K. The crystalline area of MgB4O7 · 9H2O is the largest than that of 298 and 348 K. The crystalline area of RbB5O8 · 4H2O is the smallest than that of 298 and 348 K, while the crystalline are of Li2B4O7 · 3H2O is larger than that of 298 K, and smaller than that of 348 K.