Understanding the extraction behavior of Eu(III) from acidic medium and the feasibility of separation of simulated high level liquid waste compositions using a phosphonium ionic liquid containing diglycolamide extractant

Liquid-Liquid extraction behavior of trivalent lanthanides (by taking Eu(III) as a representative) in a strongly hydrophobic phosphonium based ionic liquid (IL) in conjunction with a diglycolamide (DGA) based extractant was perused in detail to emphasize the extraction pathway and coordination behavior. Trihexyl(tetradecyl) phosphonium nitrate (Cyphos nitrate: [P66614][NO3]) was chosen as IL solvent phase containing N,N,N',N'-tetra- (2-ethylhexyl)diglycolamide (T2EHDGA) (a well-known DGA ligand) as the extractant. The extraction behavior of Eu(III) was furnished at different experimental parameters such as the concentration of initial nitric acid, concentration of ligand, equilibration time and experimental temperature to explore the extractability of the proposed IL system. The extraction showed an increasing trend with an increase in the feed acidity followed by attaining a plateau region at higher acid concentration inferring the occurrence of a neutral solvation type coordination mechanism. The mixture of T2EHDGA/[P66614][NO3] was implemented on the extraction of Fast Reactor Simulated High Level Liquid Waste (FR-SHLLW) solution spiked with Am(III) and the results were promising with respect to efficacy of the proposed IL phase. All the trivalent Ln(III) and Am(III) were selectively separated from some of the co-extracting fission products using a suitable holding agent in the feed phase. IL composition chosen for the study was radiation stable exhibiting comparable extraction behavior for SHLLW metal ions. The present study uses only dilute nitric acid as the stripping agent without adding any aqueous phase complexing agent which is a major underscore as far as the economic and environmental benefits are concerned.