Efficient solvent system containing malonamides in room temperature ionic liquids: actinide extraction, fluorescence and radiolytic degradation studies

Abstract

Solvent extraction studies of actinide metal ions such as Am(III), U(VI), Np(IV), Np(VI), Pu(IV) were carried out in a nitric acid medium using two diamides (L) viz. (DMDBTDMA (N,N′-dimethyl-N,N′-dibutyl-2-tetradecylmalonamide) and DMDOHEMA (N,N′-dimethyl-N,N′-dioctyl-2-(2′-(hexyloxy)ethyl)-malonamide) dissolved in different room temperature ionic liquids (RTILs). The use of RTILs as the diluent significantly enhanced metal ion extraction as compared to that observed in non polar diluent such as n-dodecane. The effects of parameters such as kinetics, aqueous phase acidity (0.01–3 M HNO₃), metal ion oxidation states, diamide concentration on the extraction of metal ions were studied. The stoichiometry of the extracted Am(III) species using these diamides varied with ligand concentration viz. (Am.3L)³⁺ ([L] = 0.005–0.02 M) and (Am.2–2.5L)³⁺ ([L] = 0.05–0.1 M). Time resolved laser induced fluorescence spectroscopy (TRLFS) studies showed that the extracted species of Eu(III) in an ionic liquid medium had no coordinated water molecules, in contrast to the presence of 1–2 water molecules in the extracted species in a n-dodecane medium. The radiolytic degradation behavior of the diamides/RTIL system has been studied using IR spectroscopy and gas chromatography-mass spectrometry (GC-MS). The data revealed that a significantly lower ligand concentration is required for actinide extraction in ionic liquids as the extraction media as compared to nonpolar diluents.