Solvent Extraction of Trivalent Rare Earth Metal Ions with Carboxylate Derivatives of Calixarenes

As novel calixarene or macrocyclic types of extradants, 37,38,39,40,41,42-hexakis(carboxymethoxy)-5,11,17,23,29,35-hexakis(l, 1,3,3-tetramethylbutyl)calix[6]arene and 25,26,27,28-tetrakis(carboxymethoxy)-5,11,17,23-tetrakis(l, 1,3,3-tetramethylbutyl)calix[4]arene as well asp-(1,1,3,3-tetramethylbutyl)phenoxy acetic acid, as their monoraeric analog, and 2,6-bis[2-carboxymethoxy-5-{ 1,1,3,3-tetramethylbuty l)benzyl]-4-(1,1,3,3-tetramethylbutyl)phenoxyacetic acid as a linear trimer analog, have been synthesized in order to investigate their extraction abilities of rare earth metal ions, RE³⁺ (RE=Y, La, Pr, Nd, Sm, Eu, Gd, Ho, Er), from an aqueous nitrate solution. It was found that the calixarene derivatives provide much higher extractability and greater separation efficiency than do the monomeric analog and the other acidic carboxylate extradants. The selectivity for rare earth elements in this system is not affected by the ring size. In extraction from an aqueous mixture of nitric acid-glycine, the stoichiometry of the extracted species was determined and the extraction equilibrium constants as well as the separation factors were evaluated for each extradant. A stripping test was also performed and the stripping of rare earths was found to be successfully achieved with diluted hydrochloric acid.