ANALYSIS OF EXTRACTION RATE AND SELECTIVITY OF PR ND SEPARATION BY SOLVENT-EXTRACTION IN THE PRESENCE OF DIETHYLENETRIAMINEPENTAACETIC ACIDIN AQUEOUS-PHASE/

Non-equilibrium extraction separation of Pr and Nd was carried out in the presence of diethylenetriaminepentaacetic acid (DTPA) in the aqueo us phase. The effects of experimental conditions such as hydrogen ion, DTPA and extractant concentrations on the extraction rates and select ivities were studied. The addition of DTPA was found to be useful to e nhance 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 eart h metals reported previously. This result was attributable to the high er dissociation rates of the DTPA complexes in the aqueous phase for P r and Nd. The dissociation rate constants of Pr-DTPA and Nd-DTPA compl exes were estimated by using the constants available from the literatu re. The extraction rates and selectivities obtained were satisfactoril y analyzed using not fitting parameters, but these estimated values as the dissociation rate constants of the DTPA complexes. This means tha t it is possible to analyze the extraction rates of the non-equilibriu m separation in the presence of DTPA by using the constants available from the literature.