Solubilities, Densities, and Refractive Indices of the Quaternary System (LiBO2 + NaBO2 + KBO2 + H2O) and Subsystem (NaBO2 + KBO2 + H2O) at 288.15 K and 0.1 MPa

Solid-liquid phase equilibria of the quaternary system (LiBO2 + NaBO2 + KBO2 + H2O) and its subsystem are very important for the separation of lithium and boron salts from the salt lake brines. In this paper, the solubilities, densities and refractive indices of the quaternary system (LiBO2 + NaBO2 + KBO2 + H2O) and its subsystem (NaBO2 + KBO2 + H2O) at 288.15 K and 0.1 MPa were determined by the isothermal solution equilibrium method. The experimental results show that the (NaBO2 + KBO2 + H2O) system contains one invariant point and two single salt crystallization zones corresponding to NaBO2·4H2O and KBO2·1.33H2O. The crystallization zone of NaBO2·4H2O was much larger than that of KBO2·1.33H2O. The quaternary system (LiBO2 + NaBO2 + KBO2 + H2O) contains two invariant points, five univariate solubility curves, and four single salt crystallization regions corresponding to LiBO2·8H2O, LiBO2·2H2O, NaBO2·4H2O and KBO2·1.33H2O. LiBO2·8H2O is easily dehydrated and converted to LiBO2·2H2O in the high concentration of KBO2·1.33H2O.