The removal of the most long-lived radiotoxic elements from used nuclear fuel, minor actinides, is foreseen as an essential step toward increasing the public acceptance of nuclear energy as a key ...component of a low-carbon energy future. Once removed from the remaining used fuel, these elements can be used as fuel in their own right in fast reactors or converted into shorter-lived or stable elements by transmutation prior to geological disposal. The SANEX process is proposed to carry out this selective separation by solvent extraction. Recent efforts to develop reagents capable of separating the radioactive minor actinides from lanthanides as part of a future strategy for the management and reprocessing of used nuclear fuel are reviewed. The current strategies for the reprocessing of PUREX raffinate are summarized, and some guiding principles for the design of actinide-selective reagents are defined. The development and testing of different classes of solvent extraction reagent are then summarized, covering some of the earliest ligand designs right through to the current reagents of choice, bis(1,2,4-triazine) ligands. Finally, we summarize research aimed at developing a fundamental understanding of the underlying reasons for the excellent extraction capabilities and high actinide/lanthanide selectivities shown by this class of ligands and our recent efforts to immobilize these reagents onto solid phases.
For the parallel-consecutive bimolecular reaction mechanism, a solution to the inverse kinetic problem can be approached directly using a characteristic equation specified in terms of the Lambert-W ...function, similar to the logarithmic and reciprocal plot-treatments for simple first and second order reaction kinetics, respectively.
Parallel-consecutive bimolecular reactions: a solution to the inverse kinetic problem and a characteristic equation involving the Lambert W function.
The synthesis, lanthanide complexation, and solvent extraction of actinide(III) and lanthanide(III) radiotracers from nitric acid solutions by a phenanthroline-derived quadridentate bis-triazine ...ligand are described. The ligand separates Am(III) and Cm(III) from the lanthanides with remarkably high efficiency, high selectivity, and fast extraction kinetics compared to its 2,2′-bipyridine counterpart. Structures of the 1:2 bis-complexes of the ligand with Eu(III) and Yb(III) were elucidated by X-ray crystallography and force field calculations, respectively. The Eu(III) bis-complex is the first 1:2 bis-complex of a quadridentate bis-triazine ligand to be characterized by crystallography. The faster rates of extraction were verified by kinetics measurements using the rotating membrane cell technique in several diluents. The improved kinetics of metal ion extraction are related to the higher surface activity of the ligand at the phase interface. The improvement in the ligand's properties on replacing the bipyridine unit with a phenanthroline unit far exceeds what was anticipated based on ligand design alone.
We report the first examples of hydrophilic 6,6'-bis(1,2,4-triazin-3-yl)-2,2'-bipyridine (BTBP) and 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen) ligands, and their applications as ...actinide(iii) selective aqueous complexing agents. The combination of a hydrophobic diamide ligand in the organic phase and a hydrophilic tetrasulfonated bis-triazine ligand in the aqueous phase is able to separate Am(iii) from Eu(iii) by selective Am(iii) complex formation across a range of nitric acid concentrations with very high selectivities, and without the use of buffers. In contrast, disulfonated bis-triazine ligands are unable to separate Am(iii) from Eu(iii) in this system. The greater ability of the tetrasulfonated ligands to retain Am(iii) selectively in the aqueous phase than the corresponding disulfonated ligands appears to be due to the higher aqueous solubilities of the complexes of the tetrasulfonated ligands with Am(iii). The selectivities for Am(iii) complexation observed with hydrophilic tetrasulfonated bis-triazine ligands are in many cases far higher than those found with the polyaminocarboxylate ligands previously used as actinide-selective complexing agents, and are comparable to those found with the parent hydrophobic bis-triazine ligands. Thus we demonstrate a feasible alternative method to separate actinides from lanthanides than the widely studied approach of selective actinide extraction with hydrophobic bis-1,2,4-triazine ligands such as CyMe
-BTBP and CyMe
-BTPhen.
Novel BTBP bis-(1,2,4-triazin-3-yl)-2,2'-bipyridine/BTPhen bis-(1,2,4-triazin-3-yl)-1,10-phenanthroline functionalized silica gels have been developed to extract minor actinides, lanthanides and ...other fission products. BTPhen functionalized silica gel is capable of near-quantitative removal of Am(iii) in the presence of Eu(iii) from aqueous HNO
, while BTBP functionalized silica gel is able to remove problematic corrosion and fission products that are found in PUREX raffinates.
•Aqua and non-aqua mononuclear Ru oxidation catalysts are reviewed.•The role of ligands in the catalytic mechanisms is evaluated.•The influence of steric, electronic and other ligand properties is ...addressed.
Since first reported in 2005, mononuclear ruthenium water oxidation catalysts have attracted a great deal of attention due to their catalytic performance and synthetic flexibility. In particular, ligands coordinated to a Ru metal centre play an important role in the catalytic mechanisms, exhibiting significant impact on catalyst efficiency, stability and activity towards water oxidation. This review focuses on finding possible correlations between the ligand effects and activity of mononuclear Ru aqua and non-aqua complexes as water oxidation catalysts. The ligand effects highlighted in the text include the electronic nature of core ligands and their substituents, the trans–cis effect, steric hindrance and the strain effect, the net charge effect, the geometric arrangement of the aqua ligand and the supramolecular effects, e.g., hydrogen bonding and influence of a pendant base. The outcome is not always obvious at the present knowledge level. Deeper understanding of the ligand effects, based on new input data, is mandatory for further progress towards a rational development of novel catalysts featuring enhanced activity in water oxidation.
Lanthanide(III) complexes with N-donor extractants, which exhibit the potential for the separation of minor actinides from lanthanides in the management of spent nuclear fuel, have been directly ...synthesized and characterized in both solution and solid states. Crystal structures of the Pr3+, Eu3+, Tb3+, and Yb3+ complexes of 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline (CyMe4-BTPhen) and the Pr3+, Eu3+, and Tb3+ complexes of 6,6′-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2′-bypyridine (CyMe4-BTBP) were obtained. The majority of these structures displayed coordination of two of the tetra-N-donor ligands to each Ln3+ ion, even when in some cases the complexations were performed with equimolar amounts of lanthanide and N-donor ligand. The structures showed that generally the lighter lanthanides had their coordination spheres completed by a bidentate nitrate ion, giving a 2+ charged complex cation, whereas the structures of the heavier lanthanides displayed tricationic complex species with a single water molecule completing their coordination environments. Electronic absorption spectroscopic titrations showed formation of the 1:2 Ln3+/LN4‑donor species (Ln = Pr3+, Eu3+, Tb3+) in methanol when the N-donor ligand was in excess. When the Ln3+ ion was in excess, evidence for formation of a 1:1 Ln3+/LN4‑donor complex species was observed. Luminescent lifetime studies of mixtures of Eu3+ with excess CyMe4-BTBP and CyMe4-BTPhen in methanol indicated that the nitrate-coordinated species is dominant in solution. X-ray absorption spectra of Eu3+ and Tb3+ species, formed by extraction from an acidic aqueous phase into an organic solution consisting of excess N-donor extractant in pure cyclohexanone or 30% tri-n-butyl phosphate (TBP) in cyclohexanone, were obtained. The presence of TBP in the organic phase did not alter lanthanide speciation. Extended X-ray absorption fine structure data from these spectra were fitted using chemical models established by crystallography and solution spectroscopy and showed the dominant lanthanide species in the bulk organic phase was a 1:2 Ln3+/LN‑donor species.
We prepared Prussian blue (PB) nanoparticles immobilized on the surface of nanofibers to adsorb the Cs ions effectively. The nanofibers were fabricated by electrospinning of polyacrylonitrile (PAN), ...and polydopamine (PD) was polymerized to immobilize PB on the surfaces of the nanofibers. PD is known to adhere easily on any substrate, and it could coat the surface of the PAN nanofibers. The catechol groups in PD could also bind to Fe(III) and Fe(II) ions, and subsequently, the Fe ions reacted further to form PB nanoparticles, in which PB was located on the surface of PAN nanofibers. The colloidal PB nanoparticles were immobilized on the substrate, and thus they could be easily separated from the metal mixture after Cs ion adsorption. The adsorption isotherm and kinetics of the nanofibrous adsorbent were investigated, indicating monolayer chemisorption of the Langmuir type. The PB-modified nanofibers were stable and the removal efficiency for Cs ions was not varied after five times of regeneration.
It has been shown that modification of the phenanthroline backbone of CyMe4-BTPhen leads to subtle electronic modulation, permitting differential ligation of Am(III) and Cm(III) resulting in ...separation factors up to 7.
PDF
