Solvent extraction of europium(iii) to a fluorine-free ionic liquid phase with a diglycolamic acid extractant

Abstract

Europium(III) was extracted by bis(2-ethylhexyl)diglycolamic acid (DEHDGA) dissolved in the non-fluorinated ionic liquid tetraoctylammonium dodecyl sulphate, [N₈₈₈₈][DS]. The extraction behaviour of europium(III) was investigated as a function of various parameters: pH, extractant concentration, concentration of the europium(III) ion in the aqueous feed and concentration of the salting-out agent. A comparison was made with extraction of europium(III) by the acidic extractants bis(2-ethylhexyl)phosphoric acid (D2EHPA) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) in tetraoctylammonium dodecyl sulphate. DEHDGA was found to be the best extractant in these experimental conditions. The ionic liquid diluent has been compared with tetraoctylammonium dodecylbenzene sulphonate and trihexyl(tetradecyl)phosphonium dodecyl sulphate. The extraction efficiency increased with increasing pH of the aqueous feed solution up to a maximum at pH 5, followed by a decrease in efficiency at higher pH values. Europium(III) was found to be extracted by a proton exchange mechanism. Europium(III) could be stripped from the ionic liquid phase by 1 M nitric acid.