Kinetic enhanced separation of praseodymium and neodymium induced by specific ion effect

Abstract

The precise and controllable separation of Pr/Nd is the key to restricting the recovery of rare earths from neodymium magnets. However, it is difficult to realize the efficient separation by difference in thermodynamic properties of Pr3+ and Nd3+. In present work, the enhanced separation was achieved by a kinetic extraction strategy in systems with different salting-out agents. The comprehensive effect of multiple ions including salt anions and cations on enhanced separation of Pr3+/Nd3+ were investigated. Experimental results revealed that the separation coefficient can be higher than 8. The enhancing effect on separation of Pr3+/Nd3+ from different salting-out agents followed the order of NaCl < NaNO3 < NaSCN < LiNO3. It had a relationship with the salting-out effect, which could be influenced by the type and concentration of salting-out agents. In details, the salting-out effect was closely related with hydration of salt anions and cations. There are differences in the binding ability of rare earth ions to the above anions. The behaviors of rare earth ions arriving at the interface were different under specific ion effect of Li+ and Na+. By molecular dynamics simulations, it verified that the separation behaviors were related with diffusion mass transfer rate to the interface and the adsorption behaviors of rare earth ions at the interface. At the end, the recycling and recovery of lithium was suggested. This work provides a basis for developing a new method for efficient and green separation of adjacent rare earths.