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).
Starting from the promising Minor Actinides (MA) affinity showed by the water-soluble ligands (PyTri-polyols) with the 2,6-bis[1H-1,2,3-triazol-4-yl]-pyridine chelating unit, different attempts were made to functionalize the same N 3-donor set with alkyl chains in the 1-position of triazole nuclei to obtain novel lipophilic extractants endowed with comparable MA selectivity. Solubility in organic diluents was found to be the main limitation to the development of efficient lipophilic ligands, thus resulting in less efficient extractants with respect to their hydrophilic analogues and sometimes impairing the selectivity evaluation. Interestingly, the ethyl hexyl derivative (PTEH) showed adequate extraction capability and a MA selectivity comparable to that of the hydrophilic PyTri family.
Within a spent nuclear
fuel recycling strategy, in the past few
years, the pyridine-bis-triazole unit was found to be rather effective
and selective in minor actinide (MA) separation from synthetic high
active raffinate (HAR). In this research work, the main features of
the recently studied PTEH ligand were investigated in
order to evaluate its potentialities in SANEX-like processes. Its
applicability in advanced separation processes was demonstrated, even
at process temperatures. It manifested satisfactory extraction properties
for a successful selective An separation from Ln, easy cation release,
and adequate extraction kinetics as well as outstanding hydrolytical
and radiolytical stability. All the results collected in this work
allowed the scientists on the committee of the H2020 GENIORS project
to promote PTEH as a concrete alternative to the reference
CyMe4-BTBP ligand.
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