Efficient extraction chromatography method for the separation of heavy rare earth elements from various sources

Abstract

Heavy rare earth elements (HREEs) are used in strategically important niche applications such as laser crystals, optical amplifiers, and high-tech alloys, thus regarded as essential resources that play an irreplaceable role in advanced technology and national defense. However, the huge demand and the lack of efficient separation technologies cause severe concerns about their supply. The environmental impact of their production is also a significant concern. Current industrial HREE separation is dominated by solvent extraction, which is technically inefficient and environmentally hostile. This work presents a continuous extraction chromatography method for separating HREEs as an efficient and greener alternative to solvent extraction. The proposed method uses ligand-coated C18-silica as a stationary phase and mineral acid as eluent, eliminating toxic and highly flammable organic solvents required for solvent extraction with significant environmental and safety advantages. Moreover, the method can be optimized easily to target the specific HREEs of value within the mix, namely Terbium, Dysprosium, Holmium, and Yttrium, which account for all the basket's value. This avoids the requirement to separate a full spectrum of REEs and simplifies the overall separation process. The technical feasibility of the method has been verified on a bench-scale pilot using mining-originated HREE concentrate and recycled neodymium magnet leachate with a purity of ≥ 99.9 % of individual REEs. The method showed high stability and consistent separation efficiency. In summary, the proposed extraction chromatography method has proven to be a promising green technology; hence, it might contribute to more efficient and sustainable HREE separation processes.