Rare Earth Elements (REEs) are critical to modern technologies, from high-performance magnets in electric vehicles to catalysts and advanced electronics. As demand grows and primary resources remain limited, attention has shifted to secondary sources such as recycled end-of-life magnets, fluorescent lamp phosphors, and coal fly ash.
Solvent extraction remains the most practical and scalable method for separating and purifying REEs. Yet, the underlying chemistry is complex, and predictive modeling tools have not kept pace with the needs of researchers and engineers. Established extractants like D2EHPA, PC88A, and Cyanex 923 remain the industry standard, but they often require long, multi-stage circuits due to low selectivity between adjacent REEs.
Version 12.5 introduces a step forward in this space. By enabling simulation of neodymium (Nd) extraction with DGA-based extractants (TODGA/T2EHDGA), a neutral diglycolamide ligand known for its high selectivity and strong performance in acidic environments, this release lays the groundwork for a broader, more versatile modeling platform. The framework is designed for extrapolation, supporting expansion to additional REEs, extractants, and diluents in future updates.
Complexity and Limited Predictability
Recovering REEs from complex feed streams is challenging. Feedstocks range from end-of-life electronics to phosphogypsum, a by-product of phosphate fertilizer production, and to acid leachates from permanent magnets or phosphate ores. Target metals are often present at low concentrations alongside high dissolved solids, competing ions, and variable acidity.
Multiple extractants are under active evaluation for REE separation. Long-established organophosphorus acids like D2EHPA and PC88A, as well as neutral ligands such as Cyanex 923, are reliable but lack the selectivity needed to simplify operations. TODGA has gained significant attention in research and pilot studies for its ability to deliver higher selectivity, especially for light and middle REEs, while maintaining compatibility with highly acidic environments.
Although DGA-based extractants are not yet widely deployed at commercial scale, pilot demonstrations supported by the U.S. Department of Energy and industry partners have validated its potential. Manufacturing of TODGA-based extractants is already scaling to support pilot trials, signaling that broader adoption is possible.
For this release, Nd was selected as the starting point because of its commercial importance and its role as a practical surrogate for other lanthanides. Modeling the equilibria in Nd–TODGA systems establishes the thermodynamic foundation for expansion to other REEs and extractants, replacing empirical trial-and-error approaches with predictive, first-principles modeling.
A Thermodynamic Model for TODGA Systems
Version 12.5 introduces a rigorous equilibrium framework for simulating Nd extraction with DGA-based extractants (TODGA and T2EHDGA) in nitric acid systems. The model captures aqueous speciation and organic-phase complexation with the extractant, enabling accurate predictions of species distributions, phase loading, and extraction performance across a wide range of operating conditions.
This capability provides a foundation that will grow over time. By accurately representing the thermodynamics of Nd–TODGA/T2EHDGA systems, it creates a pathway for future modeling of other lanthanides, alternative extractants, and mixed-ligand systems. This shift allows process engineers to make data-driven decisions earlier in the design cycle, reducing reliance on extensive laboratory testing and improving confidence during scale-up.
Key Features
Support for Nd extraction: Captures Nd³⁺ speciation and the formation of 1:2 and 1:3 metal-ligand complexes in nitrate media.
Explicit phase chemistry: Models the formation of aqueous and organic species using activity-based thermodynamics for more reliable equilibrium predictions.
Acid extraction and loading limits: Accounts for nitric acid co-extraction as HNO₃·TODGA complexes, critical for understanding system performance at high acidity.
Third-phase prediction: Identifies limiting organic concentration behavior to highlight potential risks of phase separation under variable operating conditions enabling selection of optimized operating window.
Predictive Insights and Practical Impact
Simulations using the new framework align closely with published TODGA data, reinforcing its reliability for predictive applications.
- Increasing nitric acid concentration improves REE extraction up to a threshold, after which acid competes for the extractant and reduces capacity.
- Simulated performance in n-dodecane, the most studied diluent for TODGA systems, is consistent with reported experimental data.
- The model replicates the temperature breakpoint between 35 and 45 °C observed in the literature, driven by the exothermic nature of the extraction and changes in complex stoichiometry.
Figure 1. Modeled distribution of Nd³⁺ in organic phase as a function of nitric acid concentration
This capability extends beyond capturing equilibrium chemistry. It supports a more integrated approach to flowsheet design. Consider a scenario where a leach liquor contains significant iron and aluminum alongside neodymium and dysprosium. Engineers can use the model to optimize upstream purification, such as adjusting pH or precipitation conditions to maximize Fe and Al removal, then carry those optimized feed conditions into the TODGA simulation. This approach allows evaluation of how upstream process conditions affect solvent extraction circuit performance.
With this workflow, it becomes possible to evaluate how pre-treatment steps (T, P, and pH) may impact the efficiency of solvent extraction and whether additional units are required. This reduces uncertainty during design, shortens pilot testing cycles, and accelerates the path from concept to reliable industrial implementation.
As future updates expand coverage to other REEs and extractants, this framework will mature into a comprehensive platform for rare earth solvent extraction modeling that supports both pilot trials and commercial deployment.
Enabling Design and Scale-Up
This capability gives engineers a more robust starting point for designing TODGA-based solvent extraction circuits. By integrating predictive chemistry into the design process, it supports early feasibility studies, flowsheet optimization, and planning for scale-up without the need for repeated empirical adjustments.
Process teams can now evaluate the impact of acidity, organic concentration, and temperature on extraction efficiency and stability with greater precision. These insights help reduce the number of design iterations required, improving confidence in bench-to-pilot transitions and accelerating the move toward full-scale implementation.
Looking ahead, the framework will expand to cover additional rare earth elements and alternative extractants. These enhancements will make it possible to simulate complex, multi-component circuits across a wide range of feed compositions, from secondary recycling streams to primary ore processing.
Practitioners developing or refining REE separation flowsheets are encouraged to explore the new capability and provide feedback to help guide future development priorities.
Summary
Version 12.5 delivers more than a feature update. It introduces a thermodynamic modeling framework that addresses long-standing challenges in REE solvent extraction and establishes a platform for future innovation. By combining rigorous chemistry with practical, application-centered insights, this capability brings predictive modeling closer to the realities of industrial design and scale-up.