Liquid–Liquid Extraction and Supported Liquid Membrane Transport of Neptunium(IV) Across a Flat-Sheet Supported Liquid Membrane Containing a TREN-DGA Derivative

Liquid–liquid extraction and liquid membrane transport behavior of tetravalent actinide ions viz. Th(IV), Np(IV), and Pu(IV) were investigated for the first time using a diglycolamide (DGA) based dendrimer with a tris(2-aminoethyl)amine (TREN) scaffold as the organic extractant. The generation of 1 dendrimer with six DGA pendent moieties (termed as TREN-G1-DenDGA) extracted Np(IV) more effectively than the other two ions, the trend being Np(IV) > Pu(IV) > Th(IV). The extraction studies of Np(IV) from 3 M HNO₃ indicated a 1:1 (metal:ligand) species and the extraction efficiency increased with increasing nitric acid concentration (1–6 M). The transport efficiency of Np(IV) increased with the nitric acid concentration (1–6 M) as well as with the ligand concentration. A very low concentration of 5.75 × 10⁻⁴ M ligand, when used as the carrier, resulted in the transport of ca. 25% metal ion transport in 5 h, which increased to >85% with 4.4 × 10⁻³ M ligand. The transport efficiency of the metal ion across the SLM followed the trend Np(IV) > Th(IV) > Pu(IV). The membrane stability was not satisfactory as seen over a period of 5 days suggesting long-term use may require regular replenishment of the carrier solvent. The effective diffusion coefficient (D _eff) of Np(IV)-TREN-G1-DenDGA were determined by the lag-time method and was found to be 5.1 × 10⁻⁸ cm²/s.