A new strategy of three-liquid-phase partitioning for stripping of heavy rare earths from the loaded organic phase

Abstract The difficulties confronted during the extraction and separation of heavy rare earths (HREs) were low separation factors and high concentration of acid solution consumption. A new strategy for extraction separation and stripping of HREs by phase separation behaviors of the three liquid phases coexisting system consisting of Cyanex272/PEG 2000/(NH4)2SO4-H2O was investigated. It was found that the separation factors could be adjusted by phase-forming polymer PEG 2000 and electrolyte salt (NH4)2SO4 concentrations, aqueous pH, as well as water-soluble complexing agent DTPA. The stripping of HREs from organic phase and PEG-rich phase were easily achieved via regulation of phase-forming salt concentration instead of utilizing acid solution with high concentration. It was confirmed that the main driving force for transfer of HREs was a special hydrophobic interaction between RE(III)-DTPA complexes and PEG molecular chains occurring on oxygen atoms of C-O-C segments in PEG molecular chains by FTIR spectroscopy and molecular dynamics simulations on the molecular scale. The present work highlights a new understanding for microscopic molecular mechanism of rare earths partitioning into three liquid layers of three-liquid-phase system so as to be stripped from the loaded organic phase.