Extraction and separation of rare earth metals using microcapsules containing bis(2-ethylhexyl)phosphinic acid

The separation of rare earth metals using microcapsules (MC) consisting styrene (St)–divinylbenzene (DVB) copolymer and containing bis(2-ethylhexyl)phosphinic acid (PIA-226) has been investigated. Microcapsules containing PIA-226 can be prepared by adding PIA-226 to the dispersed phase during the preparation process. The extraction of rare earth metals with the microcapsules progresses via the same scheme, as proposed in the conventional liquid–liquid extraction system up to a loading ratio of 0.4 and the extraction behavior can be expressed using the same equilibrium formulations, as determined in the liquid–liquid extraction system. A high loading of rare earth metals up to a loading ratio of about 0.8 is achieved in the microcapsule system, while that in the liquid–liquid extraction system is limited to about 0.4 due to emulsion difficulties. Separation studies for Pr/Sm using a column packed with microcapsules show that Pr with high purity is obtained initially from the aqueous effluent solution, and that Sm with high purity is finally obtained in the microcapsules.