Studies on Temperature Dependent Ionic Liquid Solid-Liquid Extraction Behavior of Rare Earth

Abstract

Temperature dependent solid-liquid extraction behavior of eight rare earth elements (REs) was investigated using N-butyl pyridinium hexafluorophosphate ([BPPF6) as an ionic liquid solvent and 8-hydroxyquinoline (HQ) as an extractant at 80 °C. Parameters including the amount of [BPPF6, HQ concentration, extraction time, extraction temperature and pH were investigated and optimized. The extracted species was neutral REQ3 in the RE3+-[BPPF6-HQ solid-liquid extraction system. The extraction percentage of RE3+ could be higher than 99%. The recovery of RE3+ extracted into [BPPF6 can be achieved using the mixture of hydrazine hydrate and ethylenediamine tetraacetic acid as stripping agents. The extraction equilibrium constants and the pH1/2 values of eight REs and their separation factors between adjacent rare earths were estimated and comparatively studied. REs were extracted into solid ionic liquid phase with smaller volume and concentrated to some extent. Furthermore the temperature dependent solid-liquid extraction allows to recover [BPPF6 after the extraction procedures. These results indicate that the proposed procedure can be used for the preconcentration and separation of REs using [BPPF6 with high melting point.