Enhanced interfacial salt effect on extraction and separation of Er(III) from Mg(II), Al(III), Fe(III) sulfate aqueous solutions using bubble-supported organic liquid membrane

Abstract

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.