Abstract:

The separation of rare earth elements (REEs) remains one of the most challenging and capital-intensive steps in hydrometallurgical processing, typically relying on multi-stage solvent extraction circuits with high chemical consumption and operational complexity. As demand for heavy REEs increases, there is growing interest in alternative separation technologies that reduce solvent use and enable more compact, modular processing.

This work explores electrodialysis (ED) employing in-house synthesized polymer membranes designed to enhance selectivity among trivalent REE ions. Unlike conventional ED applications focused on desalination or impurity removal, this study targets direct REE–REE separation in aqueous systems. The membranes are based on functionalized polymer backbones that incorporate functional groups known to interact differentially with light and heavy REEs. Membrane structure, functional group density, and crosslinking were tuned to modulate ion transport behavior under an applied electric field.

Bench-scale ED experiments were conducted using mixed REE chloride and sulfate solutions representative of light and high REEs. Key performance metrics included ion flux, separation factors between representative pairs, current efficiency, and energy consumption. The results indicate that selective transport of REEs can be achieved through a combination of size exclusion, hydration differences, and specific interactions between REE ions and membrane functional groups. Heavy REEs exhibited measurably different transport rates compared to light REEs under optimized conditions, enabling partial fractionation within a limited number of ED stages.

Compared to solvent extraction, the ED approach eliminates organic solvents and offers the potential for continuous operation with reduced footprint. While separation factors are currently lower than those achieved in optimized solvent extraction systems, the modularity and reduced chemical complexity of ED may enable hybrid flowsheets or niche applications where solvent-based processes are impractical.

Ongoing work focuses on improving membrane selectivity through polymer chemistry optimization, understanding transport mechanisms at the membrane interface, and scaling the process toward multi-stage configurations relevant to industrial REE separation.

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Prof. Yong Gao

Biography