A calixarene-based phosphoric acid extractant for rare earth separation

A novel host compound, 37, 38, 39, 40, 41, 42 - Hexakis ( octyl hydrogen ph osphoryl )- 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 phosphor ic acid groups on the lower rim of the calixarene platform to create a chel ating effect, the extraction behavior of nine trivalent rare earth metal io ns in strong acidic media was systematically studied. The calix[6]arene pho sphoric acid derivative exhibited extremely high extractability for all the rare earth metals compared with the commercially available organophosphori c acid extractant D2EHPA and the monomer analog. The novel extractant prefe rred heavy rare earth metals in the series of lanthanides, and achieved a h igh separation efficiency compared with a calix[6]arene carboxylic acid der ivative. The calix[6]arene phosphoric acid appears to be one of the most po werful extractants currently available for rare earth extraction. Furthermo re, the stoichiometry for the metal complex was examined by Job's method. T he cyclic calixarene was found to form at ( 2 : 1 ) sandwich complex with r are earth metal ions in acidic media.