Comparative evaluation of polymer inclusion membranes containing several substituted diglycolamides for actinide ion separations

Abstract

Diglycolamide (DGA) extractants are known to be highly selective for actinide ion extraction from moderate concentrations of nitric acid. Polymer inclusion membranes (PIMs) containing three different substituted DGA extractants were evaluated for the separation of actinide ions such as Am3+, Pu4+, UO22+ and Th4+ from dilute nitric acidic feed solutions. The DGAs studied were N,N,N′,N′-tetra-n-pentyl diglycolamide (TPDGA), N,N,N′,N′-tetra-n-hexyl diglycolamide (THDGA) and N,N,N′,N′-tetra-n-decyl diglycolamide (TDDGA).The PIMs were prepared using cellulose triacetate (CTA) as the polymer matrix, 2-nitrophenyloctyl ether (NPOE) as the plasticizer and the substituted DGAs as the carrier extractants. The membrane composition was optimized to 68.4% substituted DGA, 17.9% NPOE and 13.7% CTA. The uniform distribution of the components of the PIM was ascertained by Transmission Infrared Mapping Microscopy (TIMM). PIM containing TDDGA was found to be non-homogeneous as the extractant leached out during uptake studies. The uptake studies were carried out using feed solutions containing the target radiotracer at 1M nitric acid while the transport studies were carried out in a two-compartment cell containing 1M HNO3 as the feed and 1M alpha-hydroxy-iso-butyric acid (AHIBA) solution as the strip solution in the receiver compartment. The effect of alkyl chain length on the uptake of actinide ions was evaluated. Transport parameters such as effective diffusion coefficient (Deff) and permeability coefficient (P) values were experimentally determined.