PNNL

Abstract

Rare earth elements (REE) are critical resources with significant economic value. However, our understanding of their absorptivity and solubility in minerals is limited. In this study, the adsorption and solubilization of scandium (Sc), yttrium (Y), and lanthanum (La) into aluminum hydroxide (gibbsite, Al(OH)3) were investigated. Based on spectroscopic investigations such as Inductively Coupled Plasma- Optical Emission Spectroscopy (ICP-OES) and Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS), only Sc exhibited favorable incorporation and adsorption, whereas Y and La demonstrated unsuccessful incorporation and adsorption. X-ray Diffraction (XRD) characterization and Density Functional Theory (DFT) calculations of the additional Sc to the gibbsite crystal structure led to slight changes in long-range and local structural changes. The octahedral coordination of Sc in the gibbsite was then determined with solid state 45Sc magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). The thermodynamic landscapes of REE-doped gibbsite were calculated by DFT+U, resulting in an energetic barrier of 0.63 eV for the La incorporation, and strong thermodynamic favorability (-3.25 eV) for Sc incorporation. Understanding the incorporation of REEs in gibbsite may provide insight into predicting their retention in natural systems and industrial waste streams.