Exploring Mobility of Nanoparticles from Uranium and Rare Earth Elements in Polymetallic Mine Waste
Waste from metal mining is a global and escalating issue. Risks are particularly severe for reactive minerals, which, upon exposure to oxygen, water and microbial activity, can cause widespread contamination (e.g., acid drainage from sulfide oxidation). This study investigates the nature of colloids within historic U-REE-Cu-rich mine wastes from Mount Painter in the Northern Flinders Ranges, South Australia. The primary mineralogical hosts of uranium (torbernite) and rare earth elements (monazite-(Ce)) are phosphate minerals, which are insoluble phases typically considered to limit U and REE mobility in groundwater. However, single particle ICP-MS analysis revealed substantial concentrations of polymetallic nanoparticles enriched in U-REE-(Fe) and concentrated within the surface layers (0-10 cm) of the waste. Microbial diversity is highest near the surface, which is interpreted to promote the dissolution of phosphate minerals and the transformation of liberated metals into nanoparticles. This correlation suggests the potential for microbial consortia to extract metals from stable minerals and transform them into environmentally mobile colloidal forms, with significant implications for the biogeochemical cycling and environmental management of metals such as U and REE released by mining of both base metals and critical minerals.