(672c) Thermodynamics of Salt Lake System for Process Synthesis: Integration of Representation, Experiments and Visualization

Inorganic salts have wide applications in diverse fields. One of their major sources is salt lakes, and crystallization-based techniques have been utilized to extract the desired salts from the salt lake brine. For a feed with a given composition, the determination of which particular salt (or a mixture of salts) crystallizes under a specific set of operating conditions, and the development of the corresponding crystallization-based extraction process, requires knowledge of the solid-liquid equilibrium (SLE) phase behavior of the salt lake system and process design methods. Despite of the well establishment of phase-diagram based process synthesis procedures and process optimization methods, however, dealing with a salt lake system poses special challenges. The existence of a huge number of different species in a salt lake greatly complicates the representation, experimental determination and visualization of the thermodynamic data of such system, which thus causes difficulty in the process synthesis.

To tackle this problem, a coherent, systematic approach for the determination of solid-liquid phase behavior of a multi-component salt lake system for use in the synthesis of crystallization process is presented. It centers on the thermodynamics of such a salt lake system and integrates three interrelated activities - representation of the system phase behavior as a phase diagram/thermodynamic model, experimental determination of the necessary data and visualization of the relevant crystallization regions. To illustrate this approach, the thermodynamics of a simplified salt lake system Li⁺, Na⁺, K⁺, Mg²⁺//Cl^-, SO₄^2- - H₂O at 25^oC and 1 atm was determined. The identification of process alternatives using the resulting phase diagram for recovering Li₂SO₄*H₂O was also demonstrated.