A calixarene-based phosphoric acid extractant for rare earth separation

A novel host compound, 37, 38, 39, 40, 41, 42 - Hexakis ( octyl hydrogen phosphoryl ) - 5, 11, 17, 23, 29, 35 - hexakis (1, 1, 3, 3 -tetramethylbutyl ) calix[6]arene has been designed and synthesized for the mutual separation of rare earth metals. With this novel extractant, which bears six phosphoric acid groups on the lower rim of the calixarene platform to create a chelating effect, the extraction behavior of nine trivalent rare earth metal ions in strong acidic media was systematically studied. The calix[6]arene phosphoric acid derivative exhibited extremely high extractability for all the rare earth metals compared with the commercially available organophosphoric acid extractant D2EHPA and the monomer analog. The novel extractant preferred heavy rare earth metals in the series of lanthanides, and achieved a high separation efficiency compared with a calix[6]arene carboxylic acid derivative. The calix[6]arene phosphoric acid appears to be one of the most powerful extractants currently available for rare earth extraction. Furthermore, the stoichiometry for the metal complex was examined by Job's method. The cyclic calixarene was found to form a ( 2 : 1 ) sandwich complex with rare earth metal ions in acidic media.