Partitioning of rare earths in polymer-based three-liquid-phase system driven by transfer of hydrated PEGs: Understanding change of phase volume ratios

• Partitioning of rare earths in TLPS can be calculated based on phase volume ratios.
• Change in phase volume ratios comes from the transfer of hydrated PEG molecules.
• Partitioning of hydrated PEG is a main driving force for partitioning of rare earth.
• Partition of rare earths is related to hydrogen-bond interaction with hydrated PEG.

The relationship between the partitioning of rare-earth ions in polymer-based three-liquid-phase system (TLPS) of Cyanex 272/PEG 600/(NH4)2SO4-H2O and the change in volume ratios of PEG-rich middle phase to salt-rich bottom phase was investigated. It was found that the change in phase volume ratios might be attributed to the transfer of hydrated PEG molecules. Therefore, the partitioning of hydrated PEG is a main driving force for the partitioning of rare earths. The change in water content in PEG-rich phase should be taken into account for calculating partition coefficients of rare-earth ions. The traditional Diamond–Hsu model derived from Flory–Huggins theory considered only the partitioning of simple PEG molecules to calculate the partition coefficients of targets in polymer-based aqueous biphasic system, so that it could not reflect such influences from the change in phase volume ratios. The present work discusses the influences from the change of the concentrations of PEG and inorganic salt, Cyanex 272 concentration in top organic phase of TLPS, aqueous pH value and initial concentration of rare-earth ions, on the partitioning of rare-earth ions into PEG-rich middle phase of TLPS. Experimental results indicate that the partition coefficients of rare-earth ions have close relationship with the transfer of hydrated PEG molecules. The work implies that the partition behaviors of rare-earth ions in TLPS can be described more clearly based on the hydrogen-bond interaction of rare-earth ion with hydrated PEG molecules.

Figure optionsDownload as PowerPoint slideCorrelation of partition coefficients of rare earths with partitioning of hydrated PEG.