Highly selective separation of 99TcO4−/ReO4− with rapid liquid-liquid two-phase disengagement by amine-diamide ligands

Efficient and selective extraction of pertechnetate (TcO 4 − ) from nitric acid medium has become a significant challenge, especially in the presence of a large excess of interfering anions. By employing a combined strategy involving H-bonding and electrostatic interaction, a highly selective extraction of TcO 4 − can be achieved. The present work reports three homologous amine-diamide ligands with different alkyl chain lengths on the amine N atom of 2,2′-(metylimino)bis( N , N -dioctylacetamide) (MIDOA), 2,2′-(butylimino)bis( N , N -dioctylacetamide) (BIDOA) and 2,2′-(octylimino)bis( N , N -dioctylacetamide) (OIDOA), and their extraction behaviors for TcO 4 − /ReO 4 − in HNO 3 solution are also investigated by using n -dodecane as a diluent. It has been shown that all of them exhibit excellent extractability and high selectivity to TcO 4 − /ReO 4 − . Their extractability and phase disengagement follow the order of OIDOA > BIDOA > MIDOA, revealing a greater extractability and rapider phase disengagement for the amine-diamide ligand with longer chain substituents on the amine N atom. Both slope analysis and loading capacity test indicate the formation of 1:1 metal/ligand extracted complex, which is also confirmed by the analyses of single-crystal X-ray diffraction (SC-XRD), electrospray ionization mass (ESI-MS), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS). The extraction of TcO 4 − /ReO 4 − by the amine-diamide ligand follows the anion exchange extraction model and is a spontaneous and endothermic process. Furthermore, a competing extraction test was also conducted and demonstrates excellent extractability and high selectivity to TcO 4 − /ReO 4 − .