Synergistic Extraction of Lanthanides (III) with Mixtures of TODGA and Hydrophobic Ionic Liquid into Molecular Diluent

ABSTRACT

The extraction of lanthanides(III) from aqueous nitric acid solutions with N,N,N’,N’-tetra(n-octyl)diglycolamide (TODGA) and with mixtures of TODGA and the hydrophobic ionic liquid (IL) [C₄mim][Tf₂N] into 1,2-dichloroethane (DCE) has been investigated. The extraction efficiency of Ln(III) ions was greatly enhanced by the addition of a small amount of IL to an organic phase containing TODGA. The synergistic effect comes from the higher hydrophobicity of Ln(III) extracted species formed by TODGA and the weakly coordinating Tf₂N⁻ anions compared with those formed by TODGA and NO₃⁻ ions as the counter-anions. The partition of Tf₂N⁻ anions between the organic and aqueous phases is the dominant factor governing the extractability of lanthanides(III) with mixtures of TODGA and [C₄mim][Tf₂N]. The extraction of Ln(III) from aqueous nitric acid solutions by TODGA alone and its mixtures with [C₄mim][Tf₂N] into DCE can be described on the basis of the solvation extraction mechanism. However, in the extraction system with added [C₄mim][Tf₂N], the partition of Tf₂N⁻ between two immiscible phases and the interaction between HTf₂N and TODGA in the organic phase should be taken into account. Possible reasons of the antagonistic effect in the TODGA–[C₄mim][Tf₂N] extraction system are discussed.

KEYWORDS:

• Ionic liquid
• lanthanides(III)
• solvent extraction
• synergistic effect
• TODGA

Funding

The present work was carried out with partial financial support from the Ministry of Education and Science of the Russian Federation in the framework of the Increase Competitiveness of NUST ≪MISiS≫ Program (N° K2-2016-070).

Additional information

Funding

The present work was carried out with partial financial support from the Ministry of Education and Science of the Russian Federation in the framework of the Increase Competitiveness of NUST ≪MISiS≫ Program (N° K2-2016-070).