Solid–Liquid Equilibria of the Quaternary System Li + , K + , Ca2+ // Cl––H2O at 323.2 and 348.2 K: Li/K Crystallization from Calcium-Rich Deep Brine

Abstract In view of the high calcium characteristics of deep brine and the temperature change during its mining, transportation, and storage process, the solid–liquid phase equilibria of the quaternary system Li+, K+, Ca2+ // Cl––H2O at 323.2 and 348.2 K were studied by the isothermal dissolution equilibrium method, and the multitemperature phase diagrams were compared with the literature data at 273.2 and 298.2 K. The results show that the crystal forms of lithium chloride and calcium chloride change as follows: LiCl·2H2O (273.2 K) → LiCl·H2O (≥298.2 K); CaCl2·6H2O (273.2 K) → CaCl2·6H2O + CaCl2·4H2O (298.2 K) → CaCl2·2H2O (≥323.2 K); LiCl·CaCl2·5H2O (≤298.2 K) was formed at low temperature, and KCl·CaCl2 (≥323.2 K) was formed at high temperature. With the increase of temperature, the crystalline phase region of KCl decreases, and the crystalline regions of LiCl·H2O and KCl·CaCl2 increase. The above phase diagram reveals the temperature step-by-step control separation route of “high temperature preferential precipitation of KCl·CaCl2, low temperature extraction of potassium, high temperature extraction of lithium”, which provides a theoretical basis for the classification and utilization of Li/K resources in high calcium deep brine.