Extraction of rare-earth metals by liquid surfactant membranes containing a novel cyclic carrier

Extraction behavior of three rare-earth metals (He, Er and Y), was systematically studied by liquid surfactant membranes (LSMs) containing a novel host compound, a calixarene carboxyl derivative, which is a cyclic compound connected to some phenol rings, as a mobile carrier in a stirred cell. Using the host compound, the extraction equilibrium of the metals in liquid-liquid extraction was also investigated in order to elucidate the complexation mechanism between the metal ions and the cyclic compound. The calixarene carboxyl derivative showed a high extractability for all rare-earth metal ions compared with the analog monomer compound. The extractability for the rare-earth metals was found to increase in the following order: monomer < tetramer < hexamer. However, the extraction rate of the tetramer was higher than that of the hexamer. The carboxyl derivative of calix[4]arene (tetramer) was an excellent carrier for the permeation of rare-earth metals by LSMs. The effects of several operation factors on the extraction of the metals by LSMs were systematically examined with the calix[4]arene. The permeation mechanism of the rare-earth metals by LSMs containing the mobile carrier was explained with an interfacial reaction model.