(493a) Multi-Zone Ligand Assisted Displacement (LAD) Chromatography Method for Producing High-Purity Nd, Pr, Ce and La from Mineral Concentrates

Rare Earth Elements (REEs), comprising lanthanides plus yttrium and scandium, are divided into light REE (La-Sm) and heavy REE (Y, Eu-Lu) based on atomic weight or chemical properties. These elements are indispensable, especially for Nd and Pr, which take over 65% of total REE market, for the production of permanent magnets, automobiles, aerospace electronics and various advanced technological devices due to their unique electronic and chemical characteristics. Despite their significant importance, they are used in small quantities, akin to "vitamins," across a myriad of applications. However, the global demand for REEs has been rising sharply, while production remains largely concentrated in China, which controls over 85% of the supply. This concentration of production introduces significant vulnerabilities, particularly for nations such as the U.S., which lacks domestic production of purified REEs and is heavily dependent on imports.

In this study, an advanced purification method, multi-zone ligand-assisted displacement (LAD) chromatography, was developed to purify four light REEs—Neodymium (Nd), Praseodymium (Pr), Cerium (Ce), and Lanthanum (La)—from concentrates of bastnäsite and monazite minerals. A model-based strategy for development, alongside a constant-pattern design approach, was applied for separation. This approach optimizes column utilization using intrinsic parameters, incorporates a zone splitting technique to improve productivity, and achieves over 99.5% purity for the targeted REEs with a total yield surpassing 99%. The productivity of the purified light REEs exceeds 200 kg of pure (>99.5%) REE ions per cubic meter of sorbent each day (kg REE/m³/day), including 33 kg for Nd and Pr, while maintaining a 99% yield with the multi-zone LAD technique. Following the LAD process, we established procedures for recycling the presaturants and ligands used in the LAD process, as well as techniques for converting the purified REE solution into rare earth oxides (REOs).