(316b) Nanoparticle-Assisted Adsorption of Lbt Peptides for Selective Rare Earth Recovery By Ion Foam Flotation

Modern-day technologies depend heavily on rare earth elements (REEs) for their unique magnetic, catalytic, and luminescent properties. However, separating individual rare earth elements from feedstocks presents a major obstacle due to their similar sizes and chemical properties. Lanthanide (Ln) binding tag (LBTs) are peptides that bind selectively to Ln³⁺ cations and offer a promising solution for selectively separating rare earth elements. The molecular structures of LBTs can be engineered not only for ion selectivity but also to tune the amphiphilicity of the LBT:REE complexes, which can adsorb to the air-water interface and enable recovery by an energy-efficient foam fractionation process. Nevertheless, the separation efficiency greatly depends on foam stability and liquid fraction.

In this study, we investigate the adsorption of LBT:REE complexes onto nanoparticles to enhance foam stability, produce dry foam, and enable enhanced separation of REEs by ion foam flotation. We used the LBT1 peptide (YIDTNNDGWYEGDELLA), originating from the EF loop of calmodulin and engineered for high-affinity binding to terbium cations (Tb³⁺). Nanoparticles with a net positive surface charge were used to electrostatically adsorb the negatively charged LBT1:REE complexes. Additionally, the positive charge of the nanoparticles prevented nonselective adsorption of the trivalent cations onto the surface. Confirmation of complex adsorption onto the surface was validated by tracking the zeta potential of the nanoparticles. Dynamic light scattering (DLS) measurements were conducted to observe how peptide adsorption changed particle size and aggregation. The effectiveness of nanoparticles in enhancing foam stability was evaluated through surface tension measurements.

Subsequently, a lab-scale foam fractionation column was designed and employed for the separation of Tb³⁺ from non-REEs commonly found in ores. The foam stability was quantified in the presence and absence of nanoparticles Furthermore, the foam was collected from the top of the column and analyzed by elemental analysis and liquid-state nuclear magnetic resonance (NMR) spectroscopy. A higher Tb³⁺ content was observed over the non-REEs establishing selective complexation of REE³⁺ by LBTs. Overall, this study introduces an innovative strategy and process to enhance REE separation efficiency with LBTs by improving foam stability and decreasing foam liquid content.