Numerical Thermodynamic Modeling of the H2O–LiCl–MgCl2 Fluid System in the Temperature Range from −78 to +130°C Using the Pitzer–Simonson–Clegg (PSC) Equations

The numerical thermodynamic model of the H2O–LiCl–MgCl2 fluid system has been verified and refined for the temperature range from –78 to +130°C using ion-interaction parameters and refined solubility product constants of solid phases. The Pitzer–Simonson–Clegg (PSC) equations are applied to the calculation of solubility isotherms and the mass balance of solid and liquid phases. As a result, a phase diagram is constructed, showing the eutectic point E'' and the peritectic points P'' , P₁^'' , P₂^'' , P₃^'' , P₄^'' , P₅^'' , P₆^'' , P₇^'' , and P₈^'' calculated for the H2O–LiCl–MgCl2 ternary system, as well as various phase boundaries. The diagram also presents the calculated eutectic point E and peritectic points P, P1, and P2 for the H2O–MgCl2 binary system, and the eutectic point E' together with the peritectic points P' , P₁' , P₂' , and P₃' for the H2O–LiCl binary system. Comparison of the calculated eutectic and peritectic characteristics in the binary subsystems and the solubilities of solid phases shows good agreement with the experimental data. An example of the practical application of the model for predicting crystallization during cooling of a natural lithium-bearing brine is also presented.