Poster Presentation 21st International Conference on Biological Inorganic Chemistry 2025

Rare earth elements (REEs) are crucial for clean energy technologies, but the limited ore reserves and environmental impact caused by REEs extraction make efficient and eco-friendly separation strategies urgently needed. One solution is to recover these metals from their end-of-life waste materials. Their similar chemical properties, however, lead to extraction and separation challenges. Recent discoveries have also highlighted the important roles of these elements within bacterial enzymes, and proteins selective for these elements, called lanmodulins, have also been discovered. Inspired by these lanthanide-selective proteins, our group developed chelators based on diaza-18-crown-6 macrocycles, which show a strong binding preference for light REEs over heavy ones. The stability constant difference in REE complexes reached up to 7 log units, demonstrating high potential for selective separation. This approach offers a promising pathway for more sustainable and efficient REE recovery.

Herein, we present two organic-solvent-free REEs separation techniques using our macrocyclic chelator. First, a water-soluble chelator named G-macropa was designed and synthesized. This chelator can only form complex with light REEs, like neodymium, not heavy REEs, like dysprosium, in aqueous solution, allowing the free heavy REEs be precipitated by carbonate. Using this approach, analytically pure solid Dy₂(CO₃)₃ was obtained from aqueous solutions containing Nd³⁺ and Dy³⁺. Under optimized condition, the separation factor of Dy³⁺ to Nd³⁺ is 841 for preparation mixture and 421 for Nd₂Fe₁₄B magnet waste leachate, demonstrating a promising approach for isolating these critical minerals. Next, a chelator NH₂-BZmacropa was synthesized and appended to a solid resin for REE extraction and separation. The modified resin retained the binding preference for light REEs, obtaining highly pure light La³⁺ (>99%), middle Dy³⁺ (>90%), and heavy Lu³⁺ (>99%) fractions in a fixed-bed column from their binary mixture. The resin also exhibited selectivity for extracting REEs over non-REEs in a bacterial -derived bioleachate obtained from autoslag waste.