1. Introduction.
Rare-earth elements (REEs) have vital applications in 21^st century technology and medicine, and their low concentrations in mineral deposits demands the need for recycling. Separation of adjacent lanthanides has proven to be a challenge, but the use of ionic liquids as extractants is a promising solution. Lanthanides are particularly difficult to separate due to their preferential +3 oxidation state and similar ionic radii. This work aims to develop Cyphos IL 104 impregnated resins to study extraction of rare earth elements from an acid matrix.
2. Methods.
Ionic liquid impregnation began by mixing ionic liquid into one of four solvents: Acetone, 33.4% Ethanol, n-Hexane, and Kerosene at concentrations of 0.05, 0.2, and 0.5 mol_IL/L_solution. 10 mL of solution was mixed with 1 gram of dry resin for 24 hours. The liquid was separated from the resin and the impregnated resin was dried before being analyzed with IR spectroscopy. Extraction equilibrium experiments were conducted by adding 1 mL of 1ppm REE mix (pH=2.2) to 50 mg of resin. The samples were shaken for 5 min before the resin was separated from the solution using a PES membrane filter. 0.5 mL of solution was diluted in Nitric Acid and analyzed with ICP-MS to determine final REE concentrations. ICP-MS data was used to calculate equilibrium constants using the following equation: K_d = (C_initial-C_final)/C_final*V_sol/m_resin.
3. Results and Discussion.
K_d values were calculated from the ICP-MS data, and the log of those values was plotted. All solvents used in resin impregnation showed a similar extraction trend of rare-earth elements. At a 5 min equilibrium time, extraction using Cyphos IL 104 appeared to favor elements with lower ionic radii. This is consistent with other ionic liquids and extractants. The ionic radii dependent extraction may be exploited further by varying pH to improve near-lanthanide separation. This will manifest through column separations that will vary loading and separation environments to improve adjacent lanthanide selectivity.
4. Conclusion.
The development of more efficient methods to separate REEs is vital in ensuring continued use and improvements in advanced technology. Resin impregnated ionic liquids are an environmentally friendly alternative for separating REEs and show promise in separating near-lanthanides for various technology and medical applications.

Nicholas Dahlen

Appearances