Americium pertraction across supported liquid membranes containing multiple diglycolamide ligands: Role of alkyl substitution and spacer length in carrier ligands

Liquid–liquid extraction and subsequent supported liquid membrane (SLM) transport studies involving Am³⁺ ion were carried out from nitric acid feed solutions using three N-pivot tripodal diglycolamide (DGA) ligands with varying substituent at the inner carboxamide N atom and spacer length. The ligand with an isopropyl substituent and with C2 spacer is termed as iPr₃-TREN-DGA, while the one without alkyl substituent is termed as TREN-DGA. The third ligand with no substituent but a C₃ spacer is termed as TRPN-DGA. The trend of metal ion extraction was iPr₃-TREN-DGA > TRPN-DGA > TREN-DGA when solutions of ca. 1.0 × 10⁻³ M ligand in 95% n-dodecane + 5% isodecanol were used. Stripping studies were carried out using 0.01 M HNO₃, 0.01 M EDTA (at pH 3.0) and 1 M α-HIBA (α-hydroxyisobutyric acid) The extraction and stripping kinetics studies suggested attainment of equilibrium in about 30 minutes. The SLM studies were carried out in a two-compartment cell with 20 mL feed as well as receiver phase volumes and PTFE (polytetrafluoroethylene) flat sheets as the solid support. The transport rates followed the same trend as that of the metal ion extraction study, suggesting comparable diffusion coefficients of the complexes (obtained by the lag-time method). Membrane stability studies indicated the best stability for the TRPN-DGA ligand.