Calixarene-based picolinamide extractants for selective An/Ln separation from radioactive waste

Eleven novel ligands having picolinamide or thiopicolinamide binding groups at the upper or lower rim of calix[4]-, calix[6]- and calix[8]arenes have been synthesised. The conformational properties of some of these ligands were studied in solution by means of NMR spectroscopy and in the solid state by X-ray diffraction. Their ability to extract Am-III or Eu-III from water to NPHE (o-nitrophenyl hexyl ether) was tested at different concentrations of LiNO3, HNO3 and of a lipophilic dicarbollide anion (BrCosan). The data show a high cooperation between binding sites of the calixarene ligands in comparison to data obtained with the model ligand N-butyl picolinamide (19). Some of these ligands show very high distribution coefficients for Am3+ (D-Am > 300) and good Am/Eu selectivity at pH 3, which open up interesting perspectives for their application in the treatment of low acidity radioactive waste.