Stability of Bacteriogenic Uranium(IV) Oxide Nanoparticles for Environmental Remediation

Biological reduction of uranium(VI) in contaminated groundwater can provide in situ immobilization of uranium contamination by producing less soluble and less mobile uranium(IV) precipitates. The reduction results in the precipitation of UO2 nanoparticles. The long-term stability of immobilized uranium depends on the size, composition, and structure of the UO2 nanoparticles and on groundwater geochemistry. A series of bacteriogenic UO2 nanoparticles and abiotically synthesized analogs have been studied with respect to their structures and dissolution rates. Structural information has been gained from wide-angle X-ray scattering, X-ray absorption near-edge spectroscopy, and extended X-ray absorption spectroscopy measurements. Dissolution rates of the nanoparticles have been examined in both batch and flow-through experiments as a function of pH, dissolved inorganic carbon, and dissolved oxygen. The relationships among synthesis conditions, structural properties, and dissolution rates provide insights into the most important factors for promoting long-term stability of immobilized uranium.