Neptunium – Tri-n-butyl phosphate complexes in room temperature ionic liquids: Extraction and spectroelectrochemical studies

Abstract

The extraction of Np4+ and NpO22+ was investigated from nitric acid feeds using solutions of tri-n-butyl phosphate (TBP) in two room temperature ionic liquids viz. 1-butyl-3-methylimidazolium bis(trifluoromethane)sulfonamide (C4mim•NTf2) and 1-methyl-3-octylimidazolium bis(trifluoromethane)sulfonamide (C8mim•NTf2). For comparison purposes, the extraction of Pu4+ and UO22+ were also studied in select cases in view of their similarity with the tetra- and hexavalent neptunium ions. The nature of the extracted species was ascertained by slope analysis and two-phase extraction constants were determined. While the Np4+ ion bearing species of the type Np(NO3)3(TBP)2+ and Np(NO3)3(TBP)+ were extracted into C4mim•NTf2 and C8mim•NTf2, respectively, species of the type NpO2(NO3)2∙TBP were obtained for NpO22+ ion in both the ionic liquids. The extraction data were compared with those reported before in other solvent systems. Cyclic voltammetric studies were carried out using the Np(IV)-TBP extract in both the ionic liquid medium and the conversion to the penta-valent state (NpO2+) was confirmed by UV–visible spectrophotometric analysis of the extract.