Intramolecular synergism for group separation extraction of trivalent rare earths by a cross type calix[4]arene with phosphonic and carboxylic acid bifunctionality

A well organized calix[4]arene derivative in the cone configuration with carboxylic and phosphonic acid groups positioned at distal pairs has been prepared in order to investigate the extraction behavior of trivalent rare earths together with selected divalent metals. This product exhibited high extraction ability for the rare earths over the divalent metals investigated due to the complementarity of these trivalent ions with the above two functional groups without chelation to the phenoxy oxygen atoms. The extraction of the rare earths takes place by one of ion-exchange, where three protons are replaced by one Ln(III) cation. The stoichiometry of rare earth complexation was also determined by slope analysis, loading test and the continuous variation procedures. The extraction ability of the above reagent towards the respective rare earth ions was constant and their group separation over other metal ions proved possible. It was concluded that the presence of the two different functional groups on the calixarene structure results in a favorable synergistic interaction with the lanthanides. The results of stripping experiments for the loaded metals are also reported.