Thermodynamic Study Of System LiCl-CaCl₂-H₂O

Metallic lithium and its compounds have bright prospects in many fields. In the new century , it will be a new approach to recover lithium from salt lake brines for the industry of lithium salts. The research of phase equilibrium of lithium water-salt system has the very vital significance, not only to electrolyte peroxide solution theory, but also to the development of the saline lake lithium resources. The existence of CaCl2 is very general in natural brine. Even in some natural chloride type brine contain many calcium and small magnesium. Thermodynamic properties of the ternary system LiCl-CaCl2-H2O, including its solid-liquid phase diagram, are of essential importance in the extraction of lithium from natural salt brine containing magnesium and lithium chloride mainly or containing calcium and lithium chloride mainly. Up to now, although some solubility isotherms of this system has been measured, large disagreement still exist among them, complete solubility phase diagram on this system including the crystallization field of the double salt LiCl·CaCl2·5H2O at temperatures other than 298.15 K is unavailable yet. In this paper, we use oxalate gravimetric analysis determine calcium content in lithium salt.The solubility isotherms of the system LiCl-CaCl2-H2O have been elaborately measured at 283.15 K and 323.15 K. Several thermodynamic models were applied to represent the thermodynamic properties of this system. By comparing the predicted and experimental water activities in the ternary system, an empirical modified BET model was selected to represent the thermodynamic properties of this system. The solubility data determined in this work at 283.15 K and 323.15 K, as well as those from literature at other temperatures, were used for the model parameterization. In this way, a complete solubility phase diagram of this system between T = (273 and 323K), as well as the Gibbs-energy of formation of the hydrates CaCl2·4H2O(s), CaCl2·2H2O(s), LiCl·2H2O(s) and LiCl·CaCl2·5H2O (s), was obtained and compared with literature data. The BET model parameters can consistently describe the activities and solubility isotherms of the ternary system, The Gibbs energy of formation of the hydrates CaCl2·4H2O(s), CaCl2·2H2O(s), LiCl·2H2O(s) and LiCl·CaCl2·5H2O(s) obtaining in this work should be reliable.