| Abstract Scope |
Rare earth elements (REEs) are critical for clean energy, manufacturing, and national security, yet their extraction and separation remain challenging because REEs exhibit similar chemistry and occur in complex mineral systems. Hydrothermal fluids provide tunable environments for REE transport, enrichment, and mineralization, but the dynamic pathways controlling coordination, partitioning, and selective concentration remain poorly understood. We use real-time multimodal characterization, including Raman spectroscopy, time-resolved laser-induced fluorescence spectroscopy (TRLFS), X-ray absorption spectroscopy (XAS), synchrotron X-ray fluorescence microscopy (XRF), and X-ray micro-computed tomography (micro-CT), to track REE speciation and enrichment under hydrothermal conditions. These techniques resolve ligand coordination, hydration environment, oxidation state, spatial redistribution, dense-phase formation, and crystallization pathways. Our results show that REE enrichment is governed by transient, spatially heterogeneous intermediate states rather than only final crystalline products, providing mechanistic insight into critical mineral formation, recovery, and separation. These findings support improved strategies for predictive critical mineral processing and resource utilization. |