Highly Efficient Pertraction of Tetravalent Neptunium Ions Across a Flat Sheet Supported Liquid Membrane Containing Two Different Aza-Crown Ether-Based Multiple Diglycolamide Ligands

Pertraction of Np(IV) across a PTFE membrane containing two different aza-crown ether-based multiple diglycolamide (DGA) ligands termed as L _I (3 DGA arms) or L _II (4 DGA arms) was investigated using nitric acid as feed solution. A few of the studies were also carried out with Pu(IV) for comparison purposes. The kinetics of the extraction of Np(IV) and Pu(IV) was fast at 3 M HNO₃ and within 10 min reaches the equilibrium distribution (D) ratio with both ligands. However, the stripping kinetics was slower especially with ligand L _II. The extraction and transport studies were carried out using 1.0 × 10⁻³ M ligand solution in 95% n-dodecane + 5% isodecanol. The transport rates were slower with ligand L _II than with L _I at higher nitric acid concentrations (>1 M HNO₃) and the transport rates decreased with nitric acid concentration with both ligands. The effective diffusion coefficients (D _eff) of Np(IV) were estimated using the lag-time method as 6.2 × 10⁻⁸ cm² s⁻¹ (L _I) and 4.6 × 10⁻⁸ cm² s⁻¹ (L _II). The stability data suggest that the L _I containing supported liquid membrane (SLM) is comparatively more stable than that of L _II and the transport flux remains the same up to nine days of operation in case of ligand L _I.