Effect of chelating agent on ionic liquid chelate extraction of trivalent metals using bidentate ligands

Eguchi, Ayano ; Morita, Kotaro*; Okamura, Hiroyuki   ; Hirayama, Naoki*

In chelate extraction of metal ions into organic solvents, formation of their uncharged complexes with ligands is required. Moreover, coordinatively saturated (unhydrated) complexes are more preferable as extracted species. On the other hand, in ionic liquid chelate extraction, ionic liquid can extract charged species and coordinatively unsaturated (hydrated) species. In this study, the effects of bidentate ligands on ionic liquid chelate extraction of trivalent metal ions, Fe(III), Al(III), Ga(III) and In(III), into 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imides ([Cmim][TfN], n=2,4,8) was studied using 8-quinolinol (HQ) and 2-mercaptopyridine -oxide (HSPyO) as extractants. The extraction selectivity order for trivalent metal ions was Fe Ga In Al for HQ and Fe In Ga Al for HSPyO. Namely, HSPyO was favorable for extraction of In(III). The extractability of Ga(III) was in the order of [Cmim][TfN] [Cmim][TfN] [Cmim][TfN] chloroform for HSPyO, whereas reversed order was obtained for HQ. These results were seemed to be based on difference in concentration of deprotonated bidentate ligands in water.