A highly efficient solvent system containing functionalized diglycolamides and an ionic liquid for americium recovery from radioactive wastes

Abstract

Three room temperature ionic liquids (RTILs), viz. C(4)mim(+)·PF(6)(-), C(6)mim(+)·PF(6)(-) and C(8)mim(+)·PF(6)(-), were evaluated as diluents for the extraction of Am(III) by N,N,N',N'-tetraoctyl diglycolamide (TODGA). At 3 M HNO(3), the D(Am)-values by 0.01 M TODGA were found to be 102, 34 and 74 for C(4)mim(+)·PF(6)(-), C(6)mim(+)·PF(6)(-) and C(8)mim(+)·PF(6)(-), respectively. The extraction of Am(III) decreased with increasing feed acidity for all three diluents, indicating an ion exchange mechanism for the extraction. The stoichiometry of the extracted species suggested that two TODGA molecules were associated with Am(III) during the extraction for all three RTILs and the conditional extraction constants have been determined. The D(M)-values for different metal ions followed the order: 75 (Am(III)) > 30.7 (Pu(IV)) > 3.9 (Np(IV)) > 1.19 (Pu(VI)) > 0.52 (U(VI)) > 0.12 (Cs(I)) > 0.024 (Sr(II)). The distribution behaviour of Am(III) was also studied with a recently synthesized calix[4]arene-4DGA (C4DGA) extractant dissolved in C(8)mim(+)·PF(6)(-). Using this extractant diluent combination, the D(Am)-value was 194 at 3 M HNO(3) using 5 × 10(-5) M C4DGA, suggesting a very high distribution coefficient at very low extractant concentrations. The stoichiometry of the extracted species containing Am was found to be 1:2 (M:L) in C(8)mim(+)·PF(6)(-). The thermodynamics of the extraction was also studied for both extractants in C(8)mim(+)·PF(6)(-). The use of RTILs gives rise to significantly improved extraction properties than the commonly used n-dodecane and an unusual increase in separation factor values was seen for the first time which can lead to selective separation of Am from wastes containing a mixture of U, Pu and Am.

Luminescence investigation on Eu–pillar[5]arene-based diglycolamide (DGA) complexes: Nature of the complex, Judd–Ofelt calculations and effect of ligand structure

“…Recently, pillararene platform tethered with functional groups were reported by us to be a novel class of extractants for Ln/An separation [8]. In particular, three structurally different pillar [5]arene-based diglycolamides (P5DGA) were found to be highly efficient in extraction of trivalent actinides and lanthanides from aqueous acidic solution [9]. Our attempts to grow single crystals were unsuccessful.…”

“…Herein we present the results of a corresponding study to understand the nature of the bonding and structure of the Eu 3+ -pillar [5]arene-based diglycolamide complexes ( Fig. 1) in ethanol/water mixture and a comparative study was also carried out with the molecular identity like TODGA.…”

“…Formation of reverse micelle aggregation by four TODGA molecules was reported to be responsible for unusually high extraction efficiency of trivalent actinides and lanthanides over other oxidation states [2][3]. In view of the above fact, several attempts were reported to study the actinide extraction using tripodal diglycolamide, where three diglycolamide moieties are attached in C pivotal position [4], diglycolamide functionalized calix [4] arenes and their different structural modifications, where diglycolamide moieties are anchored on a calix [4]arene molecular platform [5][6][7]. Recently, pillararene platform tethered with functional groups were reported by us to be a novel class of extractants for Ln/An separation [8].…”

Recent trends in metals extraction

“…However, the separation of these two elements is also possible by the use of tri-n-octylmethylammonium bis (2-ethylhexyl) phosphate and tri-n-octylmethylammonium bis (2-ethylhexyl) diglycolamate ionic liquids diluted in conventional diluents [110] . Moreover, the system selectively separates americium from uranium and plutonium [111] .…”

Alkylation and pre-organisation of diglycolamide ligands on flexible platforms for nuclear waste treatment

“…selectively from a mixture containing U(VI), Pu(IV) and Pu(VI). 205 The ionic liquid was also used to test the behaviour of the calix [4]arenes with SHLW, showing promising results. 206 Further study of the ionic liquid system revealed that better extractions were obtained at low HNO3 concentrations, reverting the usual trend observed in apolar solvents, 207 and the Am(III) extraction profile of both-side DGA-functionalised calixarene CalixDGA-5 was independent of the acidity of the aqueous phase.…”