Relative Reactivity of Biogenic and Chemogenic Uraninite and Biogenic Noncrystalline U(IV)

Abstract

Aqueous chemical extractions and X-ray absorption spectroscopy (XAS) analyses were conducted to investigate the reactivity of chemogenic uraninite, nanoparticulate biogenic uraninite, and biogenic monomeric U(IV) species. The analyses were conducted in systems containing a total U concentration that ranged from 1.48 to 2.10 mM. Less than 0.02% of the total U was released to solution in extractions that targeted water soluble and ion exchangeable fractions. Less than 5% of the total U was solubilized via complexation with a 0.1 M solution of NaF. Greater than 90% of the total U was extracted from biogenic uraninite and monomeric U(IV) after 6 hours of reaction in an oxidizing solution of 50 mM K2S2O8. Additional oxidation experiments with lower concentrations (2 mM and 10 mM) of K2S2O8 and 8.2 mg L−1 dissolved oxygen suggested that monomeric U(IV) species are more labile than biogenic uraninite; chemogenic uraninite was much less susceptible to oxidation than either form of biogenic U(IV). These results suggest that non-crystalline forms of U(IV) may be more labile than uraninite in subsurface environments. This work helps fill critical gaps in our understanding of the behavior of solid-associated U(IV) species in bioremediated sites and natural uranium ore deposits.

Geochemical Control on Uranium(IV) Mobility in a Mining-Impacted Wetland

“…A recent study further showed that monomeric U(IV) species are more susceptible to oxidation than uraninite. 17 In our recent field study at a mining-impacted wetland in France, we demonstrated that a labile monomeric U(IV)-like species (noncrystalline U(IV) bound to Al−P−Fe−Si amorphous aggregates) was predominant in a U-bearing clay-rich layer within the top 30 cm of the soil. 18 The lability of this U(IV) species resulted in the association of U(IV) with Fe(II) and organic matter colloids in the porewater, which significantly increased U(IV) mobility in the wetland, even though more than 99% of U in the wetland is associated with soil.…”

Mononuclear U(IV) complexes and ningyoite as major uranium species in lake sediments

“…Such U(IV) mononuclear species could either be sorbed to the surface of phosphate as well as silicate minerals, or be bound to organic phosphoryl groups (Alessi et al, 2014b). The major occurrence of such species in lacustrine sediments has important environmental implications since mononuclear U(IV) species are potentially more labile than uraninite (Cerrato et al, 2013;Alessi et al, 2014a) and polymerised non-crystalline U(IV) phosphate phases (Alessi et al, 2014b). Such lability raises issues concerning the long term fate of the mononuclear U(IV) species, especially when subjected to sharp redox changes, for example in sediment remediation strategies as dredging operations.…”

Rapid Mobilization of Noncrystalline U(IV) Coupled with FeS Oxidation

“…Only a few studies, however, have examined the reactivity of biogenic noncrystalline U(IV) in laboratory systems. 16,17 Alessi et al 16 showed that the noncrystalline U(IV) fraction can be selectively extracted from a U(IV)−U(VI) mixture by an anoxic 1 M bicarbonate solution. Cerrato et al 17 further demonstrated that the U(IV) species can be readily oxidized by dissolved oxygen (DO) and persulfate.…”