| Abstract Scope |
Understanding the enrichment mechanisms of rare earth elements (REEs) during crystallization under hydrothermal conditions is critical for improving strategies for their separation and extraction. To address this, we have developed various advanced in situ techniques to investigate REE speciation, clustering, and mineralization under high-temperature and high-pressure conditions. Our approach employs hydrothermal diamond anvil cells and capillary capsules in combination with in situ confocal Raman spectroscopy, time-resolved laser fluorescence spectroscopy (TRLFS), synchrotron-based X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), and X-ray fluorescence (XRF). These tools enable real-time monitoring of molecular structures and phase evolution across a wide range of solution chemistries and pressure–temperature conditions. By collecting and analyzing extensive in situ data on REE speciation and crystallization, we have identified key aqueous precursor species and the conditions under which they transform into REE-bearing mineral phases. These experimental insights will significantly advance our understanding of REE mineralization processes in hydrothermal systems. |