Ln/An separation in different organic media by a selected calixarene based picolinamide ligand in presence of the synergistic agent Br-Cosan

The ligand considered in this work, hexakis(3-N-picolinamidepropyloxy)calix[6]arene, has been selected among a series of calixarene based picolinamide ligands as a potential compound to be used in a small scale An/Ln selective separation process. In fact, if - on one hand - it shows high extraction efficiency at [H+] < 10-1M, on the other hand it is able to easily release the previously complexed metal ions, if the acidic concentration is 1-2 orders of magnitude higher. In the liquid-liquid extraction experiments performed for this work 241Am was used as representative of the minor actinide family while 152Eu was employed to simulate lanthanides. Distribution coefficients and separation factors were obtained via γ-spectrometry. The synergism between the ligand and the lipophilic dicarbollide anion BrCosan was investigated. By increasing the synergizer concentration, a remarkable increase in the ligand efficiency was obtained at pH > 2. On the other hand, the synergistic effect of the anion seems to be negligible at higher acidity. From a process viewpoint, this behaviour is desirable, because it favours the extraction of actinides, without worsening the following stripping step. 2-nitrophenyl hexyl ether (NPHE) was mainly used as solvent. Other solvents or organic mixtures were considered, in order to evaluate the change of the extracting capabilities as a function of the polarity and of the dielectric constant of the medium. Moreover, viscosities of different organic phases have been measured in order to investigate their hydraulic behaviour. These studies play a significant role in the implementation of a future industrial process, in which a compromise between extracting performances of the ligand and hydraulic conditions must finally be struck. (author)