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

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) [C(4)mim][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 [C(4)mim][Tf2N]. The extraction of Ln(III) from aqueous nitric acid solutions by TODGA alone and its mixtures with [C(4)mim][Tf2N] into DCE can be described on the basis of the solvation extraction mechanism. However, in the extraction system with added [C(4)mim][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-[C(4)mim][Tf2N] extraction system are discussed.