Micro- to Molecular-Scale Investigation of Uranium and Radium Mobility from Rare Earth Mining Residues

Rare earth elements (REEs) are considered to be critical resources and play a key role in the development of advanced technologies. However, REE-bearing minerals often contain naturally occurring radioactive materials (NORMs), such as uranium and radium, which can pose radiological risks in mining operations if improperly treated. This study investigates the mobility and speciation of uranium and radium during weathering using a benchtop column model and three types of uranium sources: from the mine, from natural ore at secular equilibrium, and synthetically purified from decay products. Results indicate that radium exhibits a relatively high gradient of concentration in the leachate while uranium does not. Imaging techniques such as SEM-EDX revealed the colocalization of uranium within and on the surface of organic matter particles. Extended X-ray Absorption Fine Structure analysis suggests that uranyl species may be bound to the carboxylate complexes of the soil organic matter. These findings provide critical insights into the behavior of NORMs in REE mining environments, helping us to assess potential environmental risks.