Investigation of three-liquid-phase extraction systems for the separation of Ti(IV), Fe(III) and Mg(II)

Three-liquid-phase extraction system (TES) composed of an organic solvent-rich top phase, a polymer-rich middle phase and a salt-rich bottom phase has been considered to be a promising method of isolation and separation of multi-component. In this paper, we tried to use TES to treat multi-metal solutions including Ti(IV), Fe(III) and Mg(II) for the first time. Different combinations of organic extractant–polymer–inorganic salt were evaluated. And the effects of solution acidity, complexing agents and additives on the metal ions partitioning were investigated. The results indicated that Mg(II) was concentrated in the salt-rich bottom phase, whereas Ti(IV) and Fe(III) were quantitatively extracted into the trialkylphosphine oxide (TRPO) (or di-2-ethyl-hexyl phosphoric acid (D2EHPA))-rich top phase. And the addition of ethylenediaminetetraacetic acid (EDTA) enabled Fe(III) to distribute into the polyethylene glycol with molecular mass 2000 (PEG 2000)-rich middle phase. The transfer of Fe(III) greatly improved the selectivity of the top phase for Ti(IV) and made a significant impact on the separation of Ti(IV), Fe(III) and Mg(II).

Research highlights▶ Separation of Ti(IV), Fe(III) and Mg(II) in three-liquid-phase systems. ▶ TRPO (or D2EHPA)-PEG-(NH4)SO4 TLPS is suitable for the metal separation. ▶ EDTA reduced co-extraction of Fe(III) by the top phase. ▶ EDTA enabled Fe(III) to distribute into the PEG-rich middle phase.