Electro‐kinetic Separation of Rare Earth Elements Using a Redox‐Active Ligand

Abstract

Purification of rare earth elements is challenging due to their chemical similarities. All of the deployed separation methods rely on thermodynamic properties, such as distribution equilibria in solvent extraction. Rare-earth-metal separations based on kinetic differences have not been examined. Herein, we demonstrate a new approach for rare-earth-element separations by exploiting differences in the oxidation rates within a series of rare earth compounds containing the redox-active ligand [{2-(tBuN(O))C H CH } N] . Using this method, a single-step separation factor up to 261 was obtained for the separation of a 50:50 yttrium-lutetium mixture.

Magnetic Field Directed Rare‐Earth Separations

“…Since this strategy has the potential to be modular and applicable to a variety of established separations methods, we also incorporated a magnetic field into our previously reported electrokinetic separations (Table ,) which used the rate differences in a chemical oxidation process to partition two isostructural rare earth complexes . While almost no change was observed in the EF solid values when this modified electrokinetic method is performed in the presence of a magnetic field, the EF filtrate value nearly doubled, giving a larger SF Eu:Dy value when this separation was performed in the presence of a magnetic field (Table , entry 2).…”

Rare earth elements: Mendeleev’s bane, modern marvels

“…Subsequent vacuum distillation at 1000°C afforded the more volatile NdCl 3 with a separation factor estimated at 570, an impressive value for nearly adjacent REs (59). The above methods have focused on the RE redox chemistry; however, our group has demonstrated that the increasing Lewis acidity of the REs can affect the irreversible oxidative electron transfer rate of a coordinated redox-active ligand (60). In this case, the selectively oxidized complexes were separated by filtration.…”

Complexation and redox chemistry of neptunium, plutonium and americium with a hydroxylaminato ligand

“…This result is in agreement with our observations on related hydroxylamine ligands for the lanthanide series where a similar correlation was drawn and which allowed for the design of a separation system based on these small differences of oxidation potentials and rates caused by the increasing Lewis acidity of the central cations. 35 A second oxidation event can be observed and is attributed to the subsequent ligand-based oxidation of the hydroxylamine ligand to its oxoammonium form (NO • /N=O + ) at higher potential. 20,36 On the reductive side of the CV of 2, small ligand-based return reduction events were observed, in analogy with the processes observed for the Th complex.…”