The interfacial “push and pull” competitive complexation and enhanced separation of praseodymium and neodymium

Abstract

The separation of praseodymium (Pr) and neodymium (Nd) is particularly challenging within the lanthanide series. A new strategy was developed for enhanced separation of Pr and Nd, using interfacial “push and pull” complexation induced by a kinetic effect. We found that the specific addition order of diethylenetriaminepentaacetic acid (DTPA) had an obvious influence on the separation behaviors of Pr/Nd. Notably, the separation coefficient was up to 3.25 with the addition of DTPA when the extraction process just started. This suggested that different complexation rates decided differences of extraction kinetics between Pr and Nd. It revealed differences in complexation rates of adjacent RE(III) with DTPA and dissociation rates of RE-DTPA complexes by stopped-flow spectrophotometry. The results indicated that the complexation rate constant of Nd3+ was higher than Pr3+. On contrary, the dissociation rate constant of Nd-DTPA was smaller than Pr-DTPA. Molecular dynamics (MD) simulations showed that the interfacial “push and pull” complexation effect led to differences in interfacial molecule arrangements and diffusion mass transfer rates near the interface. And thus, the separation of Pr/Nd can be enhanced. This research provides an efficient strategy for the purification of metals that are difficult to separate.