Ligand-assisted elution chromatography for separation of lanthanides

In this study, a ligand-assisted elution chromatography process for the separation of Ln's was developed for the first time for titania, which is a robust and inexpensive inorganic sorbent. A selective ligand for Ln's, ethylenediaminetetraacetic acid (EDTA), was found to adsorb on the sorbent. The adsorbed EDTA became strong adsorption sites for the Ln's. Desorption of Ln's was driven by reversible reactions of Ln's with EDTA in the mobile phase. The overall sorbent selectivity for the reaction and adsorption process was approximately equal to the ratio of the sorbent selectivity to the ligand selectivity. The separation mechanisms were tested and verified using rate model simulations and experimental data for the separation of praseodymium (Pr), neodymium (Nd), and samarium (Sm). Simulations based on the model were used to design efficient linear gradient elution and stepwise elution processes. The purity and yield of all three Ln's were found to be above 95% in the designed processes. Stepwise elution can be implemented in a continuous process for increasing sorbent productivity and reducing costs for large-scale separation. Ligand assisted elution processes are much simpler and more environmentally friendly than the conventional solvent extraction processes.