Extraction of Np(IV/VI) from nitric acid medium using three different tripodal diglycolamide ligands in ionic liquid: Batch extraction, spectroscopic and electrochemical investigations

Complexation of Np(IV) and Np(VI) ions was studied in a room temperature ionic liquid (C4mim.NTf2) using three tripodal ligands with an ‘N’ atom, a ‘C’ atom and a benzene ring at the center, which are termed as LI, LII and LIII, respectively. The studies include solvent extraction, visible-near infrared (vis-NIR) spectroscopy, and cyclic voltammetry. The trend of the extraction of Np4+ was LIII > LII > LI, which resembled that reported before in a mixture of molecular diluents but with about 10 times higher ligand concentration. Np(VI) was extracted to a much lower extent than Np(IV). Slope analysis of Np(IV) extraction suggested formation of Np(NO3)4.L species for LII and LIII, while a cationic species of the type [Np(NO3)2.L]2+ was seen for LI. On the other hand, for Np(VI), formation of NpO2(NO3)2.L species was proposed for LI and LIII and [NpO2(NO3).L]+ for LII. All the extracted species conform to a ‘solvation’ type extraction except for Np(IV) with LI and Np(VI) with LII which point to a ‘cation-exchange’ mechanism. The complexation of the metal ions with the tripodal ligands was supported by peak shifts in the vis-NIR as well as the cyclic voltammetric studies