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Highlights: [•] A three-liquid-phase extraction approach for removal of Al, Fe, Si from rare earths. [•] Al, Fe and Si enriched in PEG middle phase and rare earths in bottom phase of TLPS. [•] Rare earths concentrated in bottom aqueous phase can be group separation by TLPS. [•] A new strategy for group separation of multiple target metals by TLPS. [ABSTRACT FROM AUTHOR]

Abstract: The present work reports an interesting phenomena that the addition of hydrophobic ionic liquid, [C4mim]PF6, into the oil–water two phase system of diisopentyl sulfide (S201)–nonane organic solutions and hydrochloric acid aqueous solutions containing Pt (IV), Pd (II) and Rh (III) chloric-complexing anions could induce the formation of a stable liquid–liquid–liquid three layered liquids coexisting medium for extraction and one-step separation of platinum, palladium and rhodium. The influences of H+ and Cl− concentrations in equilibrating aqueous solutions, the initial Pt (IV) concentration, the volume ratio of added [C4mim][PF6] to hydrochloric acid aqueous solution and the different salt ions in equilibrating aqueous solutions on the three-liquid-phase partitioning behaviors of three platinum metal ions were evaluated. The transferring of into the [C4mim]PF6 bottom phase in TLPS was proposed to be according with an anion exchange between and in ionic liquid. Therefore, the separated ionic liquid phase is not the solvent of organic extractants, but provides an extended separation capacity than the literature reported ionic liquid based two-phase extraction systems. The present work indicated that this ionic liquid based three-liquid system can be used to separate multi-metal coexisting solutions. [Copyright &y& Elsevier]

• BSOLM extraction promotes extraction and separation of rare-earth ions. • An enhanced interfacial salt effect occurs during BSOLM extraction. • Extraction and separation of Er(III) enhanced at low concentrations of coexisting salts. • Specific interfacial salt effects of Mg(II), Fe(III), Al(III) cations are discussed. Understanding the essence of specific salt effect on mass transfer of metal ions acrossing liquid–liquid interface is of crucial importance to intensify extraction and separation of target metal ions. In present work, the effect from various typical coexisting electrolyte salt cations, Mg(II), Al(III), Fe(III) cations, in the in-situ leaching solutions of ion-adsorption type rare earth ores on extraction and separation of heavy rare earths (Er(III) ions as a representative) by our previously suggested new method, bubble-supported organic liquid membrane (BSOLM) extraction, was investigated. It is found that extraction and separation of low concentration Er(III) ions can be significantly enhanced, even when the concentrations of Mg(II), Al(III) and Fe(III) cations are low enough. It cannot be explained by the traditional salt effect theory. Experiments revealed that BSOLM extraction results in an enhanced interfacial salt effect due to its essence of mass transfer only occurring on the surface of thin-layer organic extractant liquid membrane. It is benefit for intensifying the interfacial competitive adsorption of coexisting salt cations. The competitive hydration of those salt cations at interface promotes the extraction of low concentration Er(III) ions, whereas their competitive adsorption is unfavorable of the separation of Er(III). The present work highlights the microscopic nature of specific interfacial effect of various coexisting electrolyte salt cations on extraction of target rare-earth ions. It is benefit for development of new methods to intensify extraction and selective separation of low concentration rare-earth ions from the electrolyte salt in-situ leaching solutions of ion-adsorption type rare earth ores. [ABSTRACT FROM AUTHOR]