Complexation and Extraction Studies of Trivalent Actinides and Lanthanides with Water-Soluble and CHON-Compatible Ligands for the Selective Extraction of Americium

Abstract

Novel hydrophilic ligands to selectively separate Am(III) are synthesized: 3,3′-([2,2′-bipyridine]-6,6′-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(propan-1-ol) (PrOH-BPTD) and 3,3′-([2,2′-bipyridine]-6,6′-diylbis(1H-1,2,3-triazole-4,1-diyl))bis-(ethan-1-ol) (EtOH-BPTD). The complexation of An(III) and Ln(III) with PrOH-and EtOH-BPTD is studied by time-resolved laser fluorescence spectroscopy. [ML 2 ] 3+ is found for both Cm(III) and Eu(III), while [ML] 3+ is only formed with Cm(III). Stability constants show a preferential coordination of Cm(III) over Eu(III) with PrOH-BPTD being the stronger ligand. The distribution of Am(III), Cm(III), and Ln(III) between an organic phase containing the extracting agent N,N,N′,N′-tetra-n-octyl-3-oxapentanediamide (TODGA) and aqueous phases containing PrOH-BPTD is studied as a function of time and temperature as well as the TODGA, BPTD, and HNO 3 concentrations. A system composed of 0.2 mol/L TODGA and 0.04 mol/L PrOH-BPTD in 0.33−0.39 mol/L HNO 3 allows for selective Am(III) back-extraction into the aqueous phase while keeping Cm(III) and Ln(III) in the organic phase, marking PrOH-BPTD as an excellent complexant for an optimized AmSel process (Am(III) selective extraction).

A Simple yet Efficient Hydrophilic Phenanthroline-Based Ligand for Selective Am(III) Separation under High Acidity

“…Curium isotopes were short-lived, intensively radioactive, and strong neutron emitters which were proposed to be separated as early in the separation process as possible in order to develop a compact separation process. , The equilibrium separation factor of Phen-2DIBA toward Cm­(III) and Am­(III) was determined to be around 4.4 (Figure d). To the best of our knowledge, this was among the best curium–americium separations in hydrophilic ligands. ,,,,− While the distribution ratios were quite low at about 0.055 for D Cm(III) and 0.015 for D Am(III) , adding NaNO 3 increased both D Cm(III) and D Am(III) by 1 order of magnitude to a similar extent (Figure S11). Considering the high selectivity of Phen-2DIBA in both Eu­(III)/Am­(III) and Cm­(III)/Am­(III) separation under high acidity, the fast extraction kinetics, the CHON-compatible nature, and the absence of buffer used in the separation process, Phen-2DIBA represented a leap forward toward a closed nuclear fuel cycle.…”

Novel hydrophilic bistriazolyl-phenanthroline ligands with improved solubility and performance in An/Ln separations

“…In the recent decade there has been signicant development in the area of novel hydrophilic ligands for the innovative SANEX process (i-SANEX), 1 currently the most attractive option for the industrial hydrometallurgical separations of minor actinides (An) from lanthanides (Ln) during the advanced reprocessing of nuclear high-level waste (HLW). [2][3][4] These include sulfonated versions of proven heterocyclic ligands such as SO 3 -Ph-BTP, 5 DS-BTBP, TS-BTBP, TS-BTPhen 6 and DS-Ph-DAPhen 7 as well as CHON compliant bistriazolyl-pyridines (PyTri ligands), 8 bistriazolyl-bipyridines (BPTD) 9 and bis-triazolylphenanthrolines (BTrzPhens). 10 Development of tetradentate BTrzPhen 10 ligands was inspired by the equivalent tridentate water-soluble PyTri ligands.…”

“…Another study is describing bis-hydroxylbistriazolyl-bipyridines. 9 In the light of these ndings it is valid to raise a question: are BTrzPhen ligands truly promising or are they inherently inferior to other more established ligands? [6][7][8][9] Theoretical studies by DFT modelling and calculations have determined thermodynamical parameters of BTrzPhen selectivity towards minor actinides, 16 however, some of DFT theoretical studies suggest inherent aws in the design of BTrzPhen ligands due to relatively smaller overall impact of triazolyl moieties.…”

Highly Promising Method for the Decontamination of Europium from Americium Using an Extraction Chromatography Resin Containing a Tripodal Diglycolamide and SO3Ph-BTP as Eluent

“…In order to separate the actinides from the lanthanides, for instance, mutual separation of Am 3+ and Eu 3+ in this case, a selective ligand is needed which can differentiate among the two. Fundamentally, we know that the extractants containing soft N -donor atoms show better selectivity for the “soft trivalent actinides” as compared to lanthanides. – In this context, N -donor complexants such as substituted bis-triazinylpyridine (BTP) have been shown to be quite efficient for the selective complexation of Am 3+ over Eu 3+ ions. – Two strategies are being explored for lanthanide/actinide separation with BTP-based ligands. The first one is to use these ligands as extractants for selective extraction of actinides, leaving all lanthanides in the aqueous stream. – The other one is to use water-soluble BTP ligands for selective complexation of actinides so that the poorly complexed lanthanide ions present in the aqueous stream can be extracted with a DGA ligand .…”