Extraction-separation of Eu(III)/Th(IV) Ions with a Phosphorylated Ligand in an Ionic Liquid

Extraction-separation of Eu(III) and Th(IV) ions from nitrate media into the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate by a phosphorylated salen extractant, bis(chlorophosphoryle)decahydro-2,4-di(2-hydroxyphenyl)benzo[d][1,3,6]oxadiazepine (DPO), is investigated. It is found that Eu(III) ions are extracted via a solvation mechanism, and the extraction of Th(IV) ions proceeds through an ion exchange mechanism. The analysis of the experimental data reveals that the extraction of Eu(III) and Th(IV) ions is taken place by formation of Eu(DPO)(NO3)3 and Th(DPO)2(PF6)4 complexes. A significant selectivity towards thorium ions with respect to trivalent lanthanides (lanthanum, europium, and erbium) was observed. Thorium(IV) can be efficiently extracted from nitric acid solutions into the studied ionic liquid in the presence of DPO.