(538c) Surfactant-Modified Anionic Silica Nanoparticles (SANPs) for Rare Earth Element Separation Via Froth Flotation

Rare earth elements (REEs) are essential for clean energy technologies. Efficient methods for their recovery and separation are urgently needed to meet the growing demands of a rapidly evolving green economy worldwide. However, current separation technologies suffer from low selectivity, difficulty in recycling, and harmful environmental impacts due to the similar physiochemical properties of REEs and the use of organic solvents. To address these challenges, we are developing a froth flotation-based REE separation process that uses surfactant-modified anionic silica nanoparticles (SANPs) as vehicles to separate REEs in aqueous mixtures. We hypothesize that REEs can interact with SANPs via two different mechanisms: electrostatic interactions and pH-induced precipitation. As the solution pH is raised, REEs are known to form hydroxide precipitates at different pHs depending on their identity; SANPs could function as the nuclei for precipitation of hydrolyzed REEs. Under pH conditions that do not induce hydroxide formation, REEs can interact with SANPs via electrostatic interactions. The surfactant modification renders SiO₂ NPs hydrophobic, facilitating froth formation and its adsorption at air-aqueous interfaces. We explore the interactions of SANP with REEs at different pHs’ using inductively coupled plasma-optical emission spectroscopy (ICP-OES), zeta potential and surface tension measurements. We also show that the REE cations in the complex can be recovered by changing the pH, allowing for SANP recycling. Our results imply that the envisioned process is a promising alternative to the existing REE recovery and separation methods.