Efficient Rare Earth Separation Technology

Reactive Innovations, LLC and the University of Nevada, Las Vegas (UNLV) have demonstrated an innovative improved process for extracting and separating light rare earth metals (La, Ce, Sm, Nd, Pr) from solution. Rare earth metals are valued for their unique magnetic, optical and catalytic properties. These materials are used in many clean energy technologies including wind turbines, electric vehicles, photovoltaic thin films and fluorescent lighting. Currently, China produces 95-97% of the world supply of rare earth metals and oxides, but is reducing exports and increasing prices to foreign consumers. The global impact of these restrictions is greatest in countries with large high-tech manufacturing sectors such as Japan, the USA and Germany.

Lanthanides are typically found in mineral deposits. While the mining of the mineral deposits is fairly straightforward, the separation and purification of the individual lanthanide elements is laborious and energy intensive. New technologies are sought to enable more rapid, flexible, efficient, environmentally-friendly extraction and separation of individual lanthanides from aqueous mixtures with the goal of increasing the domestic supply of rare earth elements and decrease the costs of processing high purity metals.

Our approach to extraction and separation of individual lanthanide metals involves selective electrodeposition from an ionic liquid media. Cyclic voltammograms taken for each of these systems clearly show multiple oxidation and reduction peaks which are characteristic of multi-valent electron transfer processes for these species as shown in Figure 1. Using this data, separate experiments were performed to electrodeposit individual rare earth metals using a constant potential method. Visually, we observed material deposited on grafoil substrates for each of the rare earth-IL systems. Further analysis by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) confirmed rare earth elements in the deposit. For illustrative purposes, Figure 2 is a representative SEM micrograph of a lanthanide deposited onto grafoil showing bulk deposition.

We also demonstrated selective electrodeposition from binary mixtures in limited studies. By overlaying the individual CVs of rare earth oxides we selected two rare earth systems and reduction potentials to use in a mixture for demonstration of selective deposition of one or the other rare earth metal. Based on the differences in these CVs we utilized different deposition potentials to preferentially deposit one of the rare earths from an equimolar mixture of lanthanum and praseodymium precursors. The SEM image for deposits obtained at one voltage are provided in Figure 3 along with the EDS spectra taken for that sample. The EDS analysis indicated that preferential deposition of La occurred at this potential with ~80% of the total deposits associated with this species (Figure 3). In separate experiments, we changed the potential to shift the composition to 68% La and 32% Pr.

The ability to concentrate, or selectively extract rare earth metals directly from a mixture of oxides in an environmentally benign solution (ionic liquid), could potentially replace the very laborious solvent extraction processes which produce oxide or carbonate species. We envision that our technology has potentially multiple insertion points into rare earth mining processes. Future work will focus on developing and optimizing these methods to result in a high efficiency process for rare earth metal recovery.

Acknowledgements

This work was accomplished with support from the Office of the Secretary of Defense (OSD) under contract no. N00014-13-P-1139.