Solvent extraction and molecular modeling studies of Dy(III) from chloride solutions using acidic extractants

Abstract In the present work, solvent extraction of Dy(III) from chloride solutions using 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) and Cyanex 572 (mixture of phosphonic and phosphinic acid extractants) diluted in kerosene has been reported. Pourbaix and speciation diagrams were plotted to understand the chemistry and formation of different species of Dy(III) in chloride solutions. Effect of different extraction parameters such as pH (1–5), extractant concentration (1–60 mM) and chloride concentration (0.05–1 M) were investigated. PC88A was found to extract Dy(III) ions better than Cyanex 572 under similar conditions. Experimental results showed that Dy(III) extraction reaction occurred via cation exchange mechanism, which was further supported by Fourier-transform infrared spectroscopy (FTIR) studies of organic solutions loaded with Dy(III). Separation studies of Dy(III) from a mixed solution of 16 rare earth elements (REEs) indicate that PC88A works better for light REEs/Dy separation while selectivity of middle and heavy REEs over Dy(III) are superior with Cyanex 572. Molecular modeling was employed to calculate the free energies of Dy ions in aqueous and organic phases (consisting of phosphonic acid in heptane), which supported the experimental results.