Dynamic Modeling for the Separation of Rare Earth Elements Using Solvent Extraction: Predicting Separation Performance Using Laboratory Equilibrium Data

Abstract

Industrial rare earth element (REE) separation facilities utilize acidic cation exchange ligands such as 2ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) for solvent extraction processes. REE separations are costly and difficult due to their chemical similarities and subsequent low separation factors. Several empirical correlations are available in the literature to predict steady state extraction equilibria for various solvent systems. However, complete solvent extraction flow sheet design for REE separations requires complex scrubbing and stripping circuits to separate and produce individual pure species. Furthermore, dynamic modeling of extraction, scrubbing, and stripping in REE separations circuits will aid in process design, optimization, and management of process fluctuations. A dynamic MATLAB/SIMULINK REE equilibrium model has been coupled with dynamic acid balances to predict REE solvent extraction processes using laboratory equilibrium data. The model was used to predict a flow sheet that produced high purity neodymium from a 25 wt % praseodymium and 75 wt % neodymium feed. Laboratory mixer−settlers were used to verify and validate model performance.Results indicated that the model reasonably predicts the dynamic behavior of a countercurrent REE separation process, and accurately predicts the steady state REE concentration profiles across the cascade. Transient concentration predictions exhibit more deviation from experimental results due to the initial assumption of a homogeneous, well-mixed stage. The model was revised to account for variations in mixer−settler holdup volumes for future validation efforts. Current model limitations assume complete equilibrium is achieved in each stage. The model can be applied to any REE separation or solvent system provided adequate laboratory equilibrium data are available.

Environmentally friendly comprehensive hydrometallurgical method development for neodymium recovery from mixed rare earth aqueous solutions using organo-phosphorus derivatives

“…The + ΔH values of 17.04, 24.13, and 5.74 kJ/mol for Dy, Tb, and Nd while extracting with D2EHPA ensuring on the endothermic nature of extraction. The endothermic reaction of above metals have consistent numerical values and results are in well agreement with precious studies during extraction of REEs with acidic extractants while favoring the chemical reaction associated with the proposed solvent extraction process [26][27][28][29] . Furthermore, the change in free energy (ΔG) and entropy (ΔS) was evaluated based on the Eqs.…”

Gibbs Energy Minimization Model for Solvent Extraction with Application to Rare-Earths Recovery

“…We applied the GEM approach to the separation of REE mixtures relevant to recycling (NiMH) batteries (Neodymium, Nd; Praseodymium, Pr; Cerium, Ce; and Lanthanum, La). For this study, we collected a set of single-component and multicomponent REE extraction equilibrium isotherm data from the literature, ,− reported for M REE – HCl – PC88A systems, over a range of pH values, extractant fractions, and rare-earth concentrations (see Supporting Information S0-B for data sources). Having set up the problem, we first use visualization experiments to gain insight on the least-squares solution space, given the chemistry implicit in the experimental data sets.…”

“…Parameter estimation validation results comparing predicted and reported equilibrium molar compositions in both the aqueous and organic phases. (a) Compares predictions for single-component data from Li et al; (b) compares predictions for three-component data from Banda et al, and (c) compares steady-state predictions for aqueous and organic-phase rare-earth compositions with bench-scale laboratory data from Lyon et al …”

Separation of neodymium and dysprosium by solvent extraction using ionic liquids combined with neutral extractants: batch and mixer-settler experiments

“…Different models to study and understand the complexation and aggregation in both the aqueous and the organic phases have been proposed for the extraction of rare earths using different types of extractants and diluents. [60][61][62] Recycling of the organic phase…”