Highly efficient separation of actinides from lanthanides by a phenanthroline-derived bis-triazine ligand

The synthesis, lanthanide complexation, and solvent ex- traction 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, respec-tively. 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

Synthesis of novel BTPhen-functionalized silica-coated magnetic nanoparticles for separating trivalent actinides and lanthanides

BTPhen [bis-(1,2,4-triazin-3-yl)-1,10-phenanthroline] functionalized magnetic nanoparticles (MNPs), which selectively extracts Am(III) over Eu(III) from 0.1 M HNO3 with fast kinetics and a separation factor of 30 have been synthesized. These MNPs also show a small but significant selectivity for Am(III) over Cm(III) with a separation factor of around 3 in 0.1 M HNO3. We report also the synthesis of these BTPhen and related ligands via an improved synthetic route by-passing the problematic benzylic oxidation with stoichiometric SeO2

Separation of the minor actinides americium(III) and curium(III) by hydrophobic and hydrophilic BTPhen ligands: exploiting differences in their rates of extraction and effective separations at equilibrium

The complexation and extraction of the adjacent minor actinides Am(III) and Cm(III) by both hydrophobic and hydrophilic pre-organized 2,9-bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen) ligands has been studied in detail. It has been shown that Am(III) is extracted more rapidly than Cm(III) by the hydrophobic CyMe4-BTPhen ligand into different organic diluents under non-equilibrium extraction conditions, leading to separation factors for Am over Cm (SFAm/Cm) as high as 7.9. Furthermore, the separation of Am(III) from Cm(III) can be tuned through careful choice of the extraction conditions (organic diluent, contact time, mixing speed, ligand concentration). This ‘kinetic’ effect is attributed to the higher presumed kinetic lability of the Am(III) aqua complex towards ligand substitution. A dependence of the Am(III)/Cm(III) selectivity on the structure of the alkyl groups attached to the triazine rings is also observed, and BTPhens bearing linear alkyl groups are less able to separate Am(III) from Cm(III) than CyMe4-BTPhen. Under equilibrium extraction conditions, hydrophilic tetrasulfonated BTPhen ligands complex selectively Am(III) over Cm(III) and prevent the extraction of Am(III) from nitric acid by the hydrophobic O-donor ligand N,N,N’,N’-tetraoctyldiglycolamide (TODGA), giving separation factors for Cm(III) over Am(III) (SFCm/Am) of up to 4.6. These results further underline the utility of the BTPhen ligands for the extremely challenging separation of the chemically similar minor actinides Am(III) and Cm(III) in future processes to close the nuclear fuel cycle

Effective separation of Am(III) and Eu(III) from HNO3 solutions using CyMe4-BTPhen-functionalized silica-coated magnetic nanoparticles

It has been shown that CyMe4-BTPhen-functionalized silica-coated maghemite (c-Fe2O3) magnetic nanoparticles (MNPs) are capable of quantitative separation of Am(III) from Eu(III) from HNO3 solutions. These MNPs also show a small but significant selectivity for Am(III) over Cm(III) with a separation factor of around 2 in 4 M HNO3. The water molecule in the cavity of the BTPhen may also play an important part in the selectivity

Separation of minor actinides from lanthanides using immobilized ligand systems: the role of the counterion

A CyMe4-BTPhen functionalized silica gel that selectively extracts Am(III) over Eu(III) from 4 M HNO3 with a separation factor > 154 has been developed. Evidence is presented that the counterion surrounding the M(III) in the proposed 1:1 [BTPhen:M(III)] complex plays an important role in the complexation of Am(III) and Eu(III)

Extraction of minor actinides, lanthanides and other fission products by silica-immobilized BTBP/BTPhen ligands

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 HNO3, while BTBP functionalized silica gel is able to remove problematic corrosion and fission products that are found in PUREX raffinates

Hydrophilic sulfonated bis-1,2,4-triazine ligands are highly effective reagents for separating actinides(iii) from lanthanides(iii) via selective formation of aqueous actinide complexes

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 CyMe4-BTBP and CyMe4-BTPhen

Advancing solvent extraction technology for improved management of contaminated liquors

The separation of minor actinides (An) such as americium and curium (Am, Cm) from lanthanides (Ln) in spent nuclear fuel can reduce the radiotoxicity of the eventual waste product as well as the required size and environmental impact of any subsequent geological disposal. In addition, separation of these actinides from the lanthanides is essential for a strategy which aims to put the minor actinides back into the fuel cycle through transmutation by neutron bombardment, which would increase fuel efficiency. This work uses Density Functional Theory (DFT) and the Quantum Theory of Atoms in Molecules (QTAIM) to investigate the structure, stabilities and covalency of complexes of the lanthanides and minor actinides with several nitrogen donor ligands which have been developed for the difficult task of AnIII/LnIII separation. A systematic QTAIM study of Ln bond characterisation across the series is reported for one such ligand, bis-triazinyl-pyridine (BTP), confirming the general assumption that bonding in these complexes is ionic in character and largely similar. A small yet significant increase of the charge accumulation in the bonds of the An complexes of BTP was observed, and DFT studies of the An and Ln complexes found a slight energetic preference of the ligand for An complexation, together implying a small electronic contribution to the experimentally observed selectivity of the BTP ligand. A second nitrogen donor ligand, bis-triazinyl-phenanthroline (BTPhen) was studied, finding slightly higher measures of covalency in the metal-ligand bonds and a greatly improved energetic preference for An complexation. The effects of the addition of electron-directing groups to this ligand were investigated, finding little difference in the measures of covalency for these modified ligands. Several other nitrogen donor and mixed nitrogen/oxygen donor ligands were studied, including a novel sandwich complex, ultimately demonstrating a tentative correlation between enhanced covalency and stability

Plutonium coordination and redox chemistry with the CyMe4-BTPhen polydentate N-donor extractant ligand

Complexation of Pu(IV) with the actinide extractant CyMe4-BTPhen (2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline) was followed by vis-NIR spectroscopy in acetonitrile solution. The solid-state structure of the crystallized product suggests that Pu(IV) is reduced to Pu(III) upon complexation. Analysis by DFT modeling is consistent with metal-based rather than ligand-based reduction