Speciation in Potential SANEX and GANEX Actinide/Lanthanide Separations
Using Tetra-N-Donor Extractants
Whittaker, Daniel M.
Griffiths, Tamara L.
Swinburne, Adam N.
Lewis, Frank W.
Harwood, Laurence M.
Sharrad, Clint A.
- Publisher: Figshare
Biochemistry | Medicine | Cell Biology | Ecology | 20199 Astronomical and Space Sciences not elsewhere classified | 39999 Chemical Sciences not elsewhere classified | luminescent lifetime studies | bidentate nitrate ion | coordination spheres | lanthanide speciation | ligand | structure data | ganex | pr | equimolar amounts | lanthanide species | potential sanex | eu | tbp | chemical models | electronic absorption spectroscopic titrations | solution spectroscopy | ln | tb | crystal structures | water molecule | complex | coordination environments | phase | lanthanide speciation | cyme
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 Pr<sup>3+</sup>, Eu<sup>3+</sup>, Tb<sup>3+</sup>, and Yb<sup>3+</sup> complexes
(CyMe<sub>4</sub>-BTPhen) and the Pr<sup>3+</sup>, Eu<sup>3+</sup>, and Tb<sup>3+</sup> complexes of 6,6′-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2′-bypyridine
(CyMe<sub>4</sub>-BTBP) were obtained. The majority of these structures
displayed coordination of two of the tetra-N-donor ligands to each
Ln<sup>3+</sup> 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 Ln<sup>3+</sup>/L<sub>N<sub>4</sub>‑donor</sub> species (Ln = Pr<sup>3+</sup>, Eu<sup>3+</sup>, Tb<sup>3+</sup>) in methanol when the N-donor
ligand was in excess. When the Ln<sup>3+</sup> ion was in excess,
evidence for formation of a 1:1 Ln<sup>3+</sup>/L<sub>N<sub>4</sub>‑donor</sub> complex species was observed. Luminescent lifetime
studies of mixtures of Eu<sup>3+</sup> with excess CyMe<sub>4</sub>-BTBP and CyMe<sub>4</sub>-BTPhen in methanol indicated that the
nitrate-coordinated species is dominant in solution. X-ray absorption
spectra of Eu<sup>3+</sup> and Tb<sup>3+</sup> 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-<i>n</i>-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 Ln<sup>3+</sup>/L<sub>N‑donor</sub> species.