NEAREST (Neutral Ligand-Based REE Separation Technology): scaling neutral-ligand REE separations with mixer settlers

CMI researchers at Oak Ridge National Laboratory conducted the research for this highlight

Innovation 
Advancing scalable rare earth element (REE) separations through synergistic neutral ligand solvent extraction process.

Achievement
An REE mixture containing 89% LREEs and 11% HREEs was separated in just 4 extraction stages into two product streams: an LREE-rich phase and an HREE-rich phase, achieving group separation with Sm/Nd selectivity of >60.

Significance and Impact
The batch experiments are performed at the milliliter scale to probe and understand the separation processes and to model flowsheets. Practical applicability is demonstrated by running the separation flowsheet at the multi-liter scale in mixer settlers, a standard contactor platform for scaled solvent extraction operations.

Hub Target Addressed 
Developing highly selective separation from complex sources.

Schematic illustration of the initial separation stages: pre-equilibration of the DGA-6 solvent with HCl, extraction of heavy REEs (HREEs), and scrubbing of the HREE-loaded DGA-6 with concentrated NaCl to remove co-extracted HCl and light REEs (LREEs). Further optimization of flow rates and mixing rates is underway. Subsequent steps include (1) selective extraction of Nd-Pr with La-Ce remaining in the raffinate, and (2) selective scrubbing to recover individual REEs from the HREE-loaded DGA-6 solvent.
Schematic illustration of the initial separation stages: pre-equilibration of the DGA-6 solvent with HCl, extraction of heavy REEs (HREEs), and scrubbing of the HREE-loaded DGA-6 with concentrated NaCl to remove co-extracted HCl and light REEs (LREEs). Further optimization of flow rates and mixing rates is underway. Subsequent steps include (1) selective extraction of Nd-Pr with La-Ce remaining in the raffinate, and (2) selective scrubbing to recover individual REEs from the HREE-loaded DGA-6 solvent.