Extraction behavior of selected rare earth metals from acidic chloride media using tetrabutyl diglycolamide

Abstract

Rare earth elements (REEs) are vital to modern, high-tech devices. Recycling REEs from post-consumer electronics can potentially diminish supply chain risks. Toward that end, liquid-liquid solvent extraction of various REEs was investigated with tetrabutyl diglycolamide (TBDGA) in 1-octanol from hydrochloric acid media. Metal partitioning to the organic phase was shown to increase as [Cl-] increased. In contrast, increasing [H + ] did not improve extraction. The use of the polar diluent 1-octanol provided high extraction efficiency, especially for the partition of heavy lanthanides from solutions of high chloride concentration. Although the polar diluent also extracted molar amounts of water and acid, it was concluded that a neutral metal/TBDGA complex as mainly the di-solvate was extracted, and that complexation was observed to be exothermic. These results indicate that REE extraction from aqueous chloride solutions can be efficient without the use of high acid concentrations.

Extraction of Rare Earth Elements from Chloride Media with Tetrabutyl Diglycolamide in 1-Octanol Modified Carbon Dioxide

“…Cerium did not extract well at 8.27%, and the other REEs did extract >84% with Tb > Eu > Y. Cerium is low due to its larger ionic radius. These results are similar to what was observed in the 1-octanol/TBDGA extraction studied in Case et al [29]. The percent extraction for Eu was lower than the previous extractions when only a single-element with optimized conditions were conducted.…”

“…The percent extraction for the REEs is shown in Figure 11. The extraction efficiency is similar to what was observed in the liquid-liquid 1-octanol system (Figure 2 in Case et al [29]). Cerium did not extract well at 8.27%, and the other REEs did extract >84% with Tb > Eu > Y. Cerium is low due to its larger ionic radius.…”

“…1-octanol is a well-known diluent that has commonly been used for liquid-liquid solvent extraction. It has been specifically studied as a diluent for the extraction of lanthanides from HCl solutions with TBDGA [29]. In this study, improved extraction of Eu/TBDGA complexes was observed with 1-octanol as a co-solvent when compared against other modifiers previously studied [26].…”

“…When the extraction temperature was increased to >40 • C there is a significant drop in extraction; transitioning from 75% Eu extracted at 23 • C to approximately 13% Eu extracted at 40 • C. At temperatures higher than 50 • C there was little to no organic remaining in the aqueous phase, but due to thermodynamic instability of the Eu-TBDGA metal-ligand complex very little Eu was extracted out of the HCl. It was previously shown that the complexation between TBDGA and lanthanides is exothermic in chloride media [26,29]. Table 1.…”

“…Using acetone as a diluent modifier makes the diluent more polar, allowing for more polar metal-ligand complexes to have increased solubility in CO 2 . While this indicates the TBDGA-Ln-Cl species is polar, the complex is charge neutral [26,29]. The complex formation is shown in Equation 1:…”