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

Abstract

The reactivity of disordered, noncrystalline U(IV) species remains poorly characterized despite their prevalence in biostimulated sediments. Because of the lack of crystalline structure, noncrystalline U(IV) may be susceptible to oxidative mobilization under oxic conditions. The present study investigated the mechanism and rate of oxidation of biogenic noncrystalline U(IV) by dissolved oxygen (DO) in the presence of mackinawite (FeS). Previously recognized as an effective reductant and oxygen scavenger, nanoparticulate FeS was evaluated for its role in influencing U release in a flowthrough system as a function of pH and carbonate concentration. The results demonstrated that noncrystalline U(IV) was more susceptible to oxidation than uraninite (UO 2 ) in the presence of dissolved carbonate. A rapid release of U occurred immediately after FeS addition without exhibiting a temporary inhibition stage, as was observed during the oxidation of UO 2 , although FeS still kept DO levels low. X-ray photoelectron spectroscopy (XPS) characterized a transient surface Fe(III) species during the initial FeS oxidation, which was likely responsible for oxidizing noncrystalline U(IV) in addition to oxygen. In the absence of carbonate, however, the release of dissolved U was significantly hindered as a result of U adsorption by FeS oxidation products. This study illustrates the strong interactions between iron sulfide and U(IV) species during redox transformation and implies the lability of biogenic noncrystalline U(IV) species in the subsurface environment when subjected to redox cycling events.

Oxidative Degradation of Organic Contaminants by FeS in the Presence of O2

“…26−28 It was proposed that reactive oxygen species (ROS) and/or Fe(IV) were responsible for As(III) oxidation whereas a transient surface Fe(III) species was suggested as reactive species for U(IV) oxidation in oxic FeS systems. 26,28 Consistent with this earlier work, we identified the involvement of the showed moderate inhibition. 29 Additional sorption of these inorganic contaminants to FeS and its transformation products further complicates the assignment of the predominant reactive oxidant in oxic FeS systems.…”

Nanoparticulate Nickel-Hosting Phases in Sulfidic Environments: Effects of Ferrous Iron and Bacterial Presence on Mineral Formation Mechanism and Solid-Phase Nickel Distribution

“…Comparatively in the biogenic precipitates, SADP collected from spheroid-rich regions display diffraction rings with measured d-spacings of 3.38, 2.85, 2.42, 1.84, and 1.71 Å (Figure 5b, inset) that match the reflections from major planes of violarite/polydymite. Additional d-spacings obtained from imaging of lattice fringes are: (a) 5.4-5.7 Å from the nanosheets, most likely corresponding to reflections from the (001) plane of disordered mackinawite (Wolthers et al, 2003) while not ruling out overlapping reflections from pentlandite (111) and/or violarite (111) planes, and (b) ∼1.5 Å from the Ni-rich spheroids, corresponding to the (012) planes of millerite. Overall, the precipitates are likely mixtures of the aforementioned phases with varying degrees of crystallinity at various combination ratios.…”

Adsorption and reduction of roxarsone on magnetic greigite (Fe3S4): Indispensable role of structural sulfide

“…Iron sulfides, an abundant Earth mineral with high ferrous and sulfide contents, play an important role in the global cycles of carbon, oxygen, sulfur and other elements [24][25][26]. Recent studies have examined the efficacy of using iron sulfides as an adsorbent and/or reductant for remediation of chlorinated organic compounds, nitrate, and metal ions [27][28][29][30][31]. Among the various iron sulfides, greigite (Fe 3 S 4 ) has drawn particular attention as it contains both ferrous and ferric ions and has excellent magnetic properties [24].…”