Controllable enhancement of mass transfer kinetics related with the thickness of organic thin-layer liquid membrane on surface of gas bubble

•Extraction rate is closely related with thin-layer thickness of organic liquid membrane covered on the surface of gas bubble.•A theoretical kinetic equation of gas bubble supported organic liquid membrane extraction is established.•The validity of the suggested kinetic equation is demonstrated. Gas bubble supported organic thin-layer liquid membrane extraction is a unique mode of gas-liquid-liquid three phase extraction for enrichment and enhanced separation of low-concentration target metal ions from various complex aqueous solutions. We found that the extraction rate of metal ions has a close relationship with the thickness of organic liquid membrane on the surface of gas bubble. Further, the thickness of organic liquid membrane could be easily controlled by changing the ratios of the volume flowrate of gas versus organic phase pumped into the extraction column. Therefore, the reaction behavior of target metal ions can be controlled purposefully by adjusting the thickness of organic membrane for enhanced kinetic separation of different co-existing metal ions. In present work, extraction of low-concentration rare-earth ions from the in-situ leaching solutions of ion-adsorbing type rare-earth ores was suggested as an example to detect such a surprising phenomenon. A quantitative relationship of the extraction rate of rare-earth ions with the thickness of organic liquid membrane was obtained. Accordingly, a theoretical prediction of the extraction efficiency of the gas bubble supported organic thin-layer liquid membrane was possible. Experiments were performed to demonstrate the validity of the suggested kinetic equations. [Display omitted]