Extraction behavior of lanthanides using a diglycolamide derivative TODGA in ionic liquids

Abstract

Liquid–liquid extraction of lanthanides from aqueous solutions into ionic liquids (ILs) has been investigated using N,N,N′,N′-tetra(n-octyl)diglycolamide (TODGA) as an extractant, and compared with that in the isooctane system. Application of ILs as the extracting phase provided unprecedented enhancement of the extraction performance of TODGA for lanthanides compared with that of the isooctane system. Slope analysis confirmed that TODGA in ILs formed a 1 : 3 complex with La³⁺, Eu³⁺, or Lu³⁺. On the other hand, the molar ratios of species extracted into isooctane were 1 : 3 for La³⁺ or 1 : 4 for Eu³⁺ and Lu³⁺, depending on the atomic number of the lanthanide. The transfer of lanthanides with TODGA into ILs proceeded via a cation-exchange mechanism, in contrast to ion pair extraction in the isooctane system. Furthermore, we clarified that TODGA provided selectivity for the middle lanthanides in the ILs systems, but heavier lanthanides in the isooctane system.