Thermodynamic modeling of the LiCl-KCl-LaCl₃ system with Bayesian model selection and uncertainty quantification

Chloride molten salts are increasingly used in pyroprocessing techniques for the separation of lanthanides. Understanding their thermodynamic properties is essential for predicting their critical characteristics and optimizing the separation process. Various thermodynamic models, including the associate model, the two-sublattice ionic model, and the modified quasichemical model with quadruplet approximation (MQMQA), have been utilized to capture the complexity of molten salts. In the present work, the Bayes factor is used to guide the model selection process for the thermodynamic modeling of the KCl-LaCl₃ system and provide a statistical comparison of different models. The results indicate that the MQMQA model is the most favorable based on the available data. The LiCl-KCl-LaCl₃ system is further modeled with uncertainty quantification (UQ) using the MQMQA model. The thermodynamic properties of compounds in KCl-LaCl₃ are predicted by the quasiharmonic approach in terms of first-principles phonon calculations as a function of temperature. The calculated phase stability shows excellent agreement with experimental data, indicating that an appropriate thermodynamic model is important for accurately predicting the critical characteristics of complex molten salts.