Abstract
Rare earth elements (REE) have a wide range of applications due to their unique chemical, electrical, magnetic, optical and catalytic properties. The continuous growing of technological applications of these elements has increased the interest for the development of an efficient technology for their recovery by extraction from wastes and aqueous effluents. Ionic Liquids (ILs) are considered as good alternative for organic solvents in extraction processes. However, the higher or lower extraction efficiency in ILs remains difficult to predict because of a lack of understanding of the extraction mechanisms in this class of diluents, which render their application difficult to generalize. We have studied and compared the extraction behavior of N,N'-dimethyl-N,N'dioctylhexylethoxymalonamide (DMDOHEMA) diluted in n-dodecane and ionic liquids (ILs), 1ethyl-1-butylpiperidinium bis (trifluoromethylsulfonyl)imide [EBPip$^+$] [NTf2$^-$] and 1-ethyl-1octylpiperidinium bis (trifluoromethylsulfonyl)imide [EOPip$^+$] [NTf2$^-$], toward La(III) and Eu(III) dissolved in aqueous solution, at room temperature. Fe(III) was introduced to the aqueous phase in order to study the selectivity with regard to La(III) and Eu(III) and the effect of pH on extraction was investigated by using of several HNO3 concentrations. We found that the ionic liquid with shorter alkyl chain [EBPip$^+$] [NTf2$^-$] shows a higher extraction ability than [EOPip$^+$] [NTf2$^-$] and that the use of ILs as organic solvent instead of n-dodecane, greatly enhances the extraction efficiency in all cases. Cation ([EBPip$^+$] or [EOPip$^+$]) and anion ([NTf2$^-$]) concentration in the aqueous phase, has been determined in order to elucidate the extraction mechanisms.