(60a) Modeling Aqueous Solutions of Rare Earth Elements (REE) Salts with Association Electrolyte Nonrandom Two-Liquid Activity Coefficient Model

This paper presents an extension of the association electrolyte nonrandom two-liquid (AeNRTL) activity coefficient model ^[1] to calculate the activity coefficients for aqueous salt solutions of rare-earth elements (REE). Given the extensive consumption and limited supply of REEs in electronics, clean energy, aerospace, automotive and defense, the separation and recovery of REEs are of national importance ^[2]. Rigorous thermodynamic modeling for aqueous salt solutions of REEs is a key enabling technology in the research, development, design, and simulation of chemical processes for the separation and recovery of REEs.

Development of comprehensive thermodynamic models for the aqueous salt solutions of REEs has been very limited in the literature due to the lack of experimental thermodynamic data and the lack of rigorous electrolyte thermodynamic models capable of modeling ions of exceedingly high surface charge density including the REE ions. The recent advent of the AeNRTL activity coefficient model offers a major breakthrough in electrolyte thermodynamics especially for aqueous electrolyte solutions with high surface charge density ions ^[1]. This work reports compilation of the appropriate experimental thermodynamic data and accurate representation of these thermodynamic data for aqueous salt solutions of REEs and their mixtures with AeNRTL. The resulting model should be a valuable tool in support of the development of efficient and robust separation and recovery processes for REEs.