Extraction of Ytterbium from Nitric Acid Solutions with Solutions of 2-Ethylhexyl Hydrogen 2-Ethylhexylphosphonate in Hexane

The extraction of ytterbium from nitric acid solutions with solutions of 2-ethylhexyl hydrogen 2-ethylhexylphosphonate (HEH[EHP]) in hexane was studied. The HEH[EHP] concentration was varied from 0.5 to 2.0 M; acidity, from 0.1 to 2.0 M; and lanthanide concentration, from 0.1 to 5 g/L. The dependences of the ytterbium distribution ratio on the solution acidity are described by equations of the type log D = a log[H⁺] + b, where the coefficient a depends on the extractant and lanthanide concentrations and varies from –1.26 to –3.0. Its variation is probably caused by the occurrence of the extraction by both cation-exchange and solvation mechanism. The model describing the dependence of the ytterbium distribution ratio on its concentration in the aqueous phase at different concentrations of the extractant and acid was suggested. The data predicted by the model reasonably agree with the experimental data.