Phase Equilibria of Aqueous Ternary Systems M // Cl–, Borate–H2O at 348.2 K (M = Li+, Na+, Mg2+)

Abstract

The phase equilibria of the ternary systems Li⁺ // Cl^–, Borate–H₂O, Na⁺ // Cl^–, Borate–H₂O, and Mg²⁺ // Cl^–, Borate–H₂O at 348.2 K were investigated using isothermal dissolution and Schreinemarkers’ wet reside methods. Solubility and density were measured, resulting in the corresponding phase and density diagrams. The results indicate that at 348.2 K, these systems belong to simple systems without double salt or solid solution formation, which are hydrate type I. The borate crystalline region is larger than the chloride phase region, which shows that borate is more likely to precipitate in crystalline form. When comparing multitemperature phase diagrams from 273.2 to 348.2 K, the crystalline region of lithium borate gradually expands, while that of lithium chloride initially increases and then decreases, transitioning from the crystalline form LiCl·2H₂O to LiCl·H₂O. From 298.2 to 363.2 K, the phase region of sodium borate also gradually increases, with a change in crystallization from Na₂B₄O₇·10H₂O to Na₂B₄O₇·5H₂O, while the phase region of sodium chloride similarly expands. Additionally, from 323.2 to 363.2 K, the phase region of magnesium borate increases, while that of magnesium chloride decreases.