NEAREST (neutral ligand-based REE separation technology): recycling of chemicals

General illustration of the two-ligand REE separation process. DOODA is a neutral tetradentate ligand soluble in aqueous media and DGA is a neutral tridentate ligand soluble in oil phase.
General illustration of the two-ligand REE separation process. DOODA is a neutral tetradentate ligand soluble in aqueous media and DGA is a neutral tridentate ligand soluble in oil phase. DOODA is a neutral tetradentate ligand soluble in aqueous media and DGA is a neutral tridentate ligand soluble in oil phase.

CMI researchers from Oak Ridge National Laboratory conducted the activity for this highlight

Innovation 
The use of water-soluble ligands in REE separation has been avoided due to their limited stability in acidic aqueous solutions. The new process uses aqueous alkali chloride media instead of hydrochloric acid, preserving ligand stability and allowing continuous recycling.

Achievement
DOODA ligand maintains excellent chemical stability in 3-4 M alkali chloride media, with up to 0.3 M hydrochloric acid present. In contrast, 3 M HCl causes 60% ligand hydrolysis in just 40 days at 24 °C.

Significance and Impact

  • At 0.1 M concentration in 2–4 M alkali chloride media, DOODA selectively recovers specific REEs from the oil-soluble DGA-6 phase. 
  • Two oil-soluble ligands then quantitatively re-extract these REEs, enabling continuous DOODA reuse.

Hub Target Addressed 
Minimizing hazardous chemical use and waste generation.
 

DOODA is a neutral tetradentate ligand soluble in aqueous media and DGA is a neutral tridentate ligand soluble in oil phase. The overlay of 1H NMR spectra of 0.1 M DOODA in aqueous media demonstrates its fast hydrolysis in 3 M HCl. DOODA shows excellent stability in 3 M HCl when complexed with Sm3+. In alkali chloride media DOODA is stable in the absence and presence of Sm3+ (not shown).
The overlay of 1H NMR spectra of 0.1 M DOODA in aqueous media demonstrates its fast hydrolysis in 3 M HCl. DOODA shows excellent stability in 3 M HCl when complexed with Sm3+. In alkali chloride media DOODA is stable in the absence and presence of Sm3+ (not shown).