Permeation behavior of rare earth metals with a calix[4]arene carboxyl derivative in a hollow-fiber membrane

Extraction of three rare earth metals (Er, Ho and Y) was performed by a microporous hydrophobic hollow-fiber membrane extractor using a novel calix[4]arene carboxyl derivative in toluene. It was found that the permeation rate through the membrane of metal ions with calix[4]arene carboxyl derivative was relatively slow, while the addition of a small amount of sodium ion into the aqueous solution drastically accelerated the permeation rate and also enhanced the selectivity between heavy rare earth metals (Er and Ho) and Y. The experimental results obtained under a variety of conditions were analyzed by a diffusion model which combined with the complexation reaction at the aqueous-organic interface, taking account of the velocity distribution of the aqueous and organic solutions through the inner and outer sides, respectively, of the hollow-fiber membrane extractor. The model well explained the permeation behavior of the rare earth metals through the membrane and the role of sodium ion on the acceleration effect of the permeation rate. Copyright (C) 2000 Elsevier Science B.V.