The challenging issue of spent nuclear fuel (SNF) management is being tackled by developing advanced technologies that point to reduce environmental footprint, long-term radiotoxicity, volumes and residual heat of the final waste, and to increase the proliferation resistance. The advanced recycling strategy provides several promising processes for a safer reprocessing of SNF. Advanced hydrometallurgical processes can extract minor actinides directly from Plutonium and Uranium Reduction Extraction raffinate by using selective hydrophilic and lipophilic ligands. This research is focused on a recently developed N-heterocyclic selective lipophilic ligand for actinides separation to be exploited in advanced Selective ActiNide EXtraction (SANEX)-like processes: 2,6-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)pyridine (PyTri-Ethyl-Hexyl-PTEH). The formation and stability of metal–ligand complexes have been investigated by different techniques. Preliminary studies carried out by electrospray ionization mass spectrometry (ESI–MS) analysis enabled to qualitatively explore the PTEH complexes with La(III) and Eu(III) ions as representatives of lanthanides. Time-resolved laser fluorescence spectroscopy (TRLFS) experiments have been carried out to determine the ligand stability constants with Cm(III) and Eu(III) and to better investigate the ligand complexes involved in the extraction process. The contribution of a 1:3 M/L complex, barely identified by ESI–MS analyses, was confirmed as the dominant species by TRLFS experiments. To shed light on ligand selectivity toward actinides over lanthanides, NMR investigations have been performed on PTEH complexes with Lu(III) and Am(III) ions, thereby showing significant differences in chemical shifts of the coordinating nitrogen atoms providing proof of a different bond nature between actinides and lanthanides. These scientific achievements encourage consideration of this PyTri ligand for a potential large-scale implementation.
The “CHON” compatible water-soluble ligand 3,3′-(pyridine-2,6-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(propan-1-ol) (PTD) has shown promise for selectively stripping actinide ions from an organic phase containing both actinide and lanthanide ions, by preferential complexation of the former. Aiming at improving its complexation properties, PTD-OMe was synthesized, bearing a methoxy group on the central pyridine ring, thus increasing its basicity and hence complexation strength. Unfortunately, solvent extraction experiments in the range of 0.1–1 mol/L nitric acid proved PTD-OMe to be less efficient than PTD. This behavior is explained by its greater pKa value (pKa = 2.54) compared to PTD (pKa = 2.1). This counteracts its improved complexation properties for Cm(III) (log β3(PTD-OMe) = 10.8 ± 0.4 versus log β3(PTD) = 9.9 ± 0.5).
N,N'-Dimethyl,N,N'-dioctylhexylethoxymalonamide (DMDOHEMA) is used to separate An(iii) and Ln(iii) from fission products in several liquid-liquid extraction processes that aim at recycling actinides. The stoichiometry of the extracted complexes is important for a complete understanding of the processes. The presented work focuses on the complexation of Cm(iii) with DMDOHEMA studied by TRLFS in mono- and biphasic (solvent extraction) systems. The formation of [Cm(DMDOHEMA)n]3+ (n = 1-3) in 1-octanol containing 1.7 mol L-1 of water with log β'1 = 2.6 ± 0.3, log β'2 = 4.0 ± 0.5, log β'3 = 4.3 ± 0.5 was confirmed. In addition, fluorescence lifetime measurements indicated the formation of a 1 : 4 complex. Furthermore, solvent extraction experiments were performed, varying the proton and nitrate concentrations. TRLFS measurements of organic phases confirmed the existence of two species, [Cm(DMDOHEMA)3(NO3)(H2O)1-2]2+ (dominant at high proton and nitrate concentrations) and [Cm(DMDOHEMA)4(H2O)]3+ (dominant at low proton and nitrate concentrations). To support the proposed stoichiometries, vibronic side-band spectroscopy (VSBS) was employed, allowing the observation of vibrations of functional groups coordinated to the probed metal ion. Clear differences between the vibronic side bands of the 1 : 3 and 1 : 4 complex in the range of 900-1300 cm-1 were observed. Vibrational spectra calculated by DFT complimented the experimental data and confirmed the proposed stoichiometries. They revealed a monodentate coordination mode of the nitrate and two water molecules in the 1 : 3 complex.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.