Sequestration of tetravalent neptunium from acidic feeds using diglycolamide-functionalized dendrimers in a room temperature ionic liquid: extraction, spectroscopic and electrochemical studies

Quantitative extraction of Np(IV) was achieved using a room temperature ionic liquid containing sub-millimolar concentrations of two poly(propyleneimine) based dendrimer ligands with four (LI) and eight (LII) diglycolamide (DGA) moieties from nitric acid solutions. The extraction of the metal ion followed a cation exchange mechanism with decreasing extraction with increasing HNO3 concentration up to 4 M, the major exchanging species being Np(NO3)3L+. Beyond this acidity an increased metal ion extraction was seen, which was attributed to an anion exchange mechanism. UV-visible spectrophotometric studies showed a different nature of the extracted Np-L (LI or LII) complexes in the ionic liquid and molecular diluent. Quantitative back extraction of Np(IV) was achieved by using aqueous complexing agents. Cyclic voltametric studies of the extracted complexes exhibited differences in the electron-donating ability of the two ligands towards Np(IV). Both ligands showed a non-reversibility or a quasi-reversible nature of the Np reduction couple. The radiation stability of the present extraction system was not so high.