The third-phase formation behavior in ionic liquid (IL) extraction system using trioctylphosphine oxide (TOPO) was investigated. In the use of a relatively less-lipophilic IL, such as 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (CmimTfN), the third phase was formed between the aqueous phase and the IL phase. The third phase seems to have a relatively high lipophilicity compared to the IL phase. The main components of the third phase were suggested as being (HO)TOPO, IL anion (TfN), IL cation (Cmim) and free TOPO. In addition, the third phase showed an extraction concentration ability for the Fe(III)-thiocyanato complex.
The triphasic extraction system with two extract phases can be used to separate two materials simultaneously into each phase. In this article, a possible mutual separation of Fe(II) and Fe(III) was studied using the cyclohexane/water/ionic liquid (IL) triphasic extraction system for Fe speciation. For Fe(II) and Fe(III) extraction, 2,2′-bipyridine (bpy) and tri-noctylphosphine oxide (TOPO) were selected as extractants, respectively. It was suggested that [Fe II (bpy)3] 2+ and Fe III (TOPO)4 3+ •3Tf2Nwere extracted into the IL (1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, C4mimTf2N) phase and the cyclohexane phase, respectively, and both of the extractants also acted as masking agents. On simultaneous separation using the triphasic system, Fe(II) and Fe(III) were quantitatively extracted into the IL phase and the cyclohexane phase, respectively, and their mutual separation was achieved.
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