Chemical View of Single Uranium Atoms Attached to Mineral Surfaces


Uranium fission currently provides a significant portion of the world’s low-carbon energy. Mining of uranium ores, fuel processing, nuclear accidents, and spent fuel disposal all have resulted in the release of uranium to the environment. Furthermore, because of its chemistry, uranium is often enriched in fossil fuel ores (e.g., kerogens and black shales). Accurate modelling of uranium transport is paramount to understanding the risks from uranium release in the environment. Current models assume that reduction of U6+ to U4+ in bioreduced sediments results in the precipitation of the insoluble mineral uraninite (UO2). However, researchers at Argonne National Laboratory have shown that mineral surfaces have a significant role in stabilizing U4+ as isolated, adsorbed U4+ atoms at low U:surface ratios that are more typical of contaminated sites. Using two model minerals, rutile (TiO2) and magnetite (Fe3O4), the researchers found that the surface area threshold at which U4+ forms single-atom surface complexes and the stability of these complexes over time is dependent on the mineral chemistry. Adsorbed U4+ was produced by reactions representative of both biotic and abiotic U6+ reduction pathways, suggesting that non-uraninite U4+ associated with minerals may account for a significant portion of the U4+ balance in sediments. The results indicate the need to include such forms of U4+ in reactive transport models to better predict uranium mobility in the environment.


Latta, D. E., B. Mishra, R. E. Cook, K. M. Kemner, and M. I. Boyanov. 2014. “Stable U(IV) Complexes Form at High-Affinity Mineral Surface Sites,” Environmental Science and Technology 48(3), 1683-91. DOI: 10.1021/es4047389.