Solid–Liquid Phase Equilibria of the Aqueous Ternary System Containing Lithium Borate and Calcium Borate at T = (298.2, 323.2, and 348.2 K)

Abstract

Phase equilibria and diagrams can provide essential theoretical data for the enrichment and extraction of elements in the development and utilization of brines. For the composition of boron- and calcium-rich brines, the solid–liquid equilibria of the ternary system Li⁺, Ca²⁺// Borate–H₂O at 298.2, 323.2, and 348.2 K were studied. In this work, calcium borate CaB₆O₁₀·5H₂O was synthesized by a hydrothermal method for phase equilibria experiments, the structure and phase analyses of CaB₆O₁₀·5H₂O were performed by X-ray diffractometer (XRD), scanning electron microscope (SEM), and Fourier transform infrared (FTIR) spectrometer, and the purity of CaB₆O₁₀·5H₂O was determined by chemical analysis. Meanwhile, the solubility of CaB₆O₁₀·5H₂O at 273.2–348.2 K was determined, which showed that it increases first and then decreases with the rise in temperature. The solubility, density, refractive index, and pH of the system Li⁺, Ca²⁺// Borate–H₂O at 298.2, 323.2, and 348.2 K were measured, and the corresponding phase diagrams and physicochemical properties versus composition diagrams were constructed. The system Li⁺, Ca²⁺// Borate–H₂O is a simple system at 298.2, 323.2, and 348.2 K; two crystalline regions correspond to CaB₆O₁₀·5H₂O and Li₂B₄O₇·3H₂O (CaB₆O₁₀·5H₂O > Li₂B₄O₇·3H₂O) and with the increase in temperature, the crystallization region of CaB₆O₁₀·5H₂O increases.