There is still an evident need for selective and stable ligands able to separate actinide(III) from lanthanide(III) metal ions in view of the treatment of the accumulated radioactive waste and of the recycling of minor actinides. We have herein demonstrated that hydrophilic 2,6-bis-triazolyl-pyridines are able to strip all actinides in all the different oxidation states from a diglycolamide-containing kerosene solution into an acidic aqueous phase. The ascertained high actinide selectivity, efficiency, extraction kinetics, and chemical/radiolytic stability spotlight this hydrophilic class of ligands as exceptional candidates for advanced separation processes fundamental for closing the nuclear fuel cycle and solving the environmental issues related to the management of existing nuclear waste.

Four lipophilic 1,10-phenanthroline di(thio)amide, diester or diketone derivatives were studied as ligands for Am(III)/Eu(III) separation from acidic media. The synthesis of these compounds is reported together with the extraction tests in different solvents (kerosene, octanol and o-nitrophenyl hexyl ether), HNO3 concentrations and ratios between the ligand and the synergistic agent (Br-Cosan). The promising results obtained from the large number of solvent extraction tests carried out show that it might be possible to apply this class of ligands to advanced reprocessing of spent nuclear fuel. The experimental data indicate that, under the conditions that simulate the real radioactive waste, the extraction efficiency and Am/Eu separation factors are particularly high, thus suggesting that the combination of soft heterocyclic N-donor atoms and hard carbonyl groups of ester and amides affords a tetradentate donor set of atoms (ONNO) that gives rise to remarkable selectivities. ESI-MS studies and DFT calculations shed light on the possible structure of the Eu(3+) complexes indicating that the 1 : 1 : 2 (cation : ligand : anion) complex is slightly more stable than the 1 : 2 : 1 species.

The novel and fully combustible hydrophilic 1,10-phenantroline-2,9-dicarboxamide (1) was synthesized and investigated as Am(III) stripping agent in a simulated advanced hydrometallurgical process, in comparison with two other 1,10-phenanthroline-based ligands 2 and 3. The stripping efficiency and the Am(III)/lanthanides(III) selectivity of the TODGA (org) / phen-derivative (aq) extracting system were studied under several experimental conditions by liquid-liquid extraction tests. The results obtained clarify the main limitations of these ligands in the scope of the hydrometallurgical reprocessing but also enable to get indications to steer future investigations in the domain of the selective An(III) recovery for the advanced reprocessing of Spent Nuclear Fuel by hydrophilic ligands.