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

• Three tripodal diglycolamide extractants were evaluated for the extraction of Np(IV and Np(VI) • The studies using ionic liquids resulted in higher extraction as compared to those in molecular diluents. • The benzene based tripodal was the most efficient and extraction of Np(IV) was much higher than that of Np(VI) • The nature of the extracted species was determined by slope analysis and structural models are given. • The bonding in the extracted species was studied by Vis-NIR spectroscopy and cyclic voltammetry. Complexation of Np(IV) and Np(VI) ions was studied in a room temperature ionic liquid (C 4 mim.NTf 2) using three tripodal ligands with an 'N' atom, a 'C' atom and a benzene ring at the center, which are termed as L I , L II and L III , respectively. The studies include solvent extraction, visible-near infrared (vis-NIR) spectroscopy, and cyclic voltammetry. The trend of the extraction of Np4+ was L III > L II > L I , 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(NO 3) 4.L species for L II and L III , while a cationic species of the type [Np(NO 3) 2.L]2+ was seen for L I. On the other hand, for Np(VI), formation of NpO 2 (NO 3) 2. L species was proposed for L I and L III and [NpO 2 (NO 3). L ]+ for L II. All the extracted species conform to a 'solvation' type extraction except for Np(IV) with L I and Np(VI) with L II 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. [ABSTRACT FROM AUTHOR]