Solvent extraction of Eu(III) from hydrochloric acid solutions using PC88A and Cyanex 572 in kerosene

Solvent extractions of europium (Eu(III)) from hydrochloric acid solutions using 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) and Cyanex 572 (chemical structure not reported) diluted in kerosene are compared and discussed. Pourbaix and speciation diagrams for Eu(III) in chloride solutions are presented to clarify the chemistry of solution at different acidities and chloride concentrations. Preliminary structures, energies and free energies of Eu(III) species in both aqueous and organic phases (the latter consisting of phosphonic acid in heptane) were calculated and compared using molecular modeling. The effects of pH (1-5), extractant concentration (1-100 mM) and ionic strength (0,05-1 M) are studied to systematically characterize the extraction behavior of Eu(III) and, based on these results, an extraction mechanism is suggested. It is found that under similar experimental conditions a higher extent of extraction is obtained with PC88A compared with Cyanex 572. The infrared spectra of the loaded organic solutions support the hypothesis that the Eu(III) extraction reaction is driven by a cation exchange mechanism. Separation studies of Eu(III) from other rare earth elements (REEs) were also carried out and revealed that PC88A provides higher separation of Eu(III) from light REEs while Cyanex 572 achieves higher separation from heavy REEs.