Enhancing rare-earth element separation

Hans-LanM (Download Image)

A Hans-LanM dimer as determined by Penn State researchers using x-ray crystallography.

The irreplaceable roles of rare-earth (RE) elements in ubiquitous modern technologies ranging from permanent magnets to light-emitting diodes (LED) and phosphors have renewed interest in one of the grand challenges of separation science—efficient separation of lanthanides. However, the separation of these 15 elements is complicated due to their similar physicochemical properties. Conventional extraction methods for RE production require dozens or even hundreds of stages and have large environmental impacts. Thus, research efforts are looking for alternative separation methods.

LLNL researchers and collaborators at Penn State are studying the natural lanthanide-binding protein lanmodulin (LanM) as a sustainable alternative to conventional solvent-extraction-based RE separation methods. LanM is a small protein found in methylotrophic bacteria that binds REs tightly and selectively. In a paper published in Nature, the research team characterized a new LanM from Hansschlegelia quercus (Hans-LanM), a bacterium isolated from English oak buds. Leveraging the unique RE selectivity of Hans-LanM, LLNL researchers developed a column chromatography process that achieved high-purity separation of the chemical element dysprosium from neodymium, which has important implications for RE recycling from end-of-life consumer products.

Comparison of Hans-LanM to the prototypal LanM from Methylorubrum extorquens (bacterium) reveals distinct metal coordination strategies, rationalizing Hans-LanM’s greater selectivity within the rare-earth elements. Their results illustrate how intermolecular interactions—common in proteins but rare in small molecules—may be exploited to improve RE separations. Furthermore, this work showcases the natural diversity of selective lanthanide recognition motifs, which the team is currently exploring with the goal of developing an all-aqueous, protein-based RE separation process.

[J.A. Mattocks, J.J. Jung, C.-Y. Lin, Z. Dong, N.H. Yennawar, E.R. Featherston, C.S. Kang-Yun, T.A. Hamilton, D.M. Park, A.K. Boal, J.A. Cotruvo Jr, Enhanced rare-earth separation with a metal-sensitive lanmodulin dimer, Nature (2023), DOI: 10.1038/s41586-023-05945-5.]

Physical and Life Sciences Communications Team