Biostimulated Uranium Immobilization Within Aquifers-From Bench Scale To Field Experiments

In situ bioremediation of uranium-contaminated aquifers through microbially catalyzed reduction of mobile U(VI) species can only be successful if the U(IV) products are immobilized over long time-scales. Although uraninite is known for its low solubility and has been produced in nano-particulate form by several species of metal-and sulfate-reducing bacteria in laboratory studies, little is known about the stability of biogenic U(IV) in the subsurface. Using an up-scaling approach, we investigated the chemical and environmental stability of biogenic UO2 nano-solids. Our results show that diffusive limitations due to aquifer porosity and microstructure may retard uraninite corrosion. Corrosion was also retarded by adsorption or incorporation of manganese. On the other hand, U(VI) bioreduction in field sediments generated U(IV) that was more labile than biogenic UO2.