Liquid-liquid extraction and facilitated transport of f-elements using an N-pivot tripodal ligand

Diglycolamide (DGA)-functionalized tripodal ligands offer the required nine-coordinated complex for effective binding to a trivalent lanthanide/actinide ion. A N-pivot tripodal ligand (TREN-DGA) containing three DGA pendant arms was evaluated for the extraction and supported liquid membrane transport studies using PTFE flat sheets. Solvent extraction studies indicated preferential extraction of 1:1 (M:L) species, while the metal ion extraction increased with increasing HNO₃ concentration conforming to a solvated species extraction. Flat sheet-supported liquid membrane studies, carried out using 4.0 × 10⁻³ M TREN-DGA in 95% n-dodecane + 5% iso-decanol indicated faster mass transport for Eu³⁺ ion as compared to Am³⁺ ion. The determined transport parameters indicated slow diffusion of the M-TREN-DGA (M = Am or Eu) complex being the rate-determining step. The transport of lanthanides and actinides followed the trend: Eu³⁺ > Am^3+∼ Pu⁴⁺ >> UO₂²⁺ and Am can be selectively separated from a mixture of U and Pu by oxidizing the latter to its +6 oxidation state. The liquid membrane stability was not encouraging and was deteriorating the transport efficiency with time, which was attributed to carrier loss into the aqueous phases.