Nanoparticulate FeS as an Effective Redox Buffer to Prevent Uraninite (UO2)

Uranium (U) is one of the most prevalent radionuclide contaminants in soils and groundwater across the world as a result of nuclear fuel production, weapons manufactur-ing, and research activities. The environmental risks posed by U are determined largely by the degree of its mobility, which strongly depends on redox conditions. Under oxic condi-tions, U(VI) is soluble and forms stable complexes with carbonate and calcium in ground-water. In contrast, reduced U(IV) species are often immobilized as sparingly soluble U(IV) solid phases such as uraninite (UO2) by biotic or abiotic redox processes. Naturally-occurring nanoscale iron sulfide (FeS) has been shown to supply electrons for abiotic uranium reduction in biostimulated aquifers. Reduced U(IV) forms uraninite (UO2) precipitates, which are relatively insoluble and less mobile than dissolved U(VI) in ground-water. The close association of UO2 with FeS suggests that FeS may serve as an effective redox buffer for long-term U stabilization in subsurface environments. Upon oxidant intrusion, FeS may therefore be expected to inhibit reoxidation of reduced-U solid phases formed during a reductive bioremediation phase. Understanding the role of FeS in protecting UO2 against reoxidation is therefore important for assessing the long-term stability of U-bioremediated contaminated aquifers. A recently published study in Geochimica et Cosmochimica Acta by researchers from th