Unusual transport behaviour of actinide ions with a novel calix[4]arene-tetra-diglycolamide (C4DGA) extractant as the carrier

A calix[4]arene appended with four diglycolamide moieties containing n-octyl groups (C4DGA) was evaluated for the transport of actinide ions such as UO22+, Pu4+, Pu3+, and Am3+ from acidic feed solutions across PTFE flat sheet supported liquid membranes. The supported liquid membrane (SLM) studies were carried out with C4DGA under varying feed acidities, carrier extractant concentrations, and membrane pore sizes. While low pH solutions resulted in no Am3+ transport, quantitative transport of the metal ion was observed when 0.01 M EDTA solution (pH 3.0) was used as the strippant in the receiver phase. The transport efficiency of the carrier solvent system was Pu4+ > Am3+ > Pu3+ ≫ UO22+, which is not in line with those observed for diglycolamide extractants, where Am3+ was extracted to a much higher extent than other actinide ions. The results were compared with those reported earlier for TODGA (N,N,N′,N′-tetra-n-octyldiglycolamide) and tripodal diglycolamide (T-DGA) under identical conditions. Eu3+ transport rates were found out to be significantly higher than those observed with Am3+. The selectivity factors of the C4DGA extractant were compared with those of other DGA-based extractants reported earlier. The diffusion coefficient for the Am(III)–C4DGA complex was obtained experimentally using the lag time method. The stability studies indicated significant deterioration of the liquid membrane with time even after only 3 days of operation.