Analysis of Extraction Rate and Selectivity of Pr/Nd Separation by Solvent Extraction in the Presence of Diethylenetriaminepentaacetic Acid in Aqueous Phase.

Abstract

Non-equilibrium extraction separation of Pr and Nd was carried out in the presence of diethylenetriaminepentaacetic acid (DTPA) in the aqueous phase. The effects of experimental conditions such as hydrogen ion, DTPA and extractant concentrations on the extraction rates and selectivities were studied. The addition of DTPA was found to be useful to enhance the selectivity. In all cases, the extraction rates of Pr were higher than those of Nd. The extraction rates of Pr and Nd, which are light rare earth metals, were higher than those of the heavy rare earth metals reported previously. This result was attributable to the higher dissociation rates of the DTPA complexes in the aqueous phase for Pr and Nd. The dissociation rate constants of Pr-DTPA and Nd-DTPA complexes were estimated by using the constants available from the literature. The extraction rates and selectivities obtained were satisfactorily analyzed using not fitting parameters, but these estimated values as the dissociation rate constants of the DTPA complexes. This means that it is possible to analyze the extraction rates of the non-equilibrium separation in the presence of DTPA by using the constants available from the literature.