Geochemical Interactions of Fe-Sulfide Minerals with Uranium and Microorganisms
in Sediments from the DOE UMTRA site at Rifle, Colorado
EMSL Project ID
35209
Abstract
Previous biostimulation field-experimental studies (by injecting acetate into the aquifer)conducted at the DOE UMTRA (Uranium Mill Tailings Remedial Action) site in Rifle, CO, havedemonstrated that the transition from Fe reduction to sulfate reduction significantly decreased the removal
of U(VI) from the groundwater [8-10]. After acetate amendment was terminated, U(VI) removal continued to increase before aqueous U(VI) concentration rebounded back to prior-experimental values. [8-10]. In another systematic mineralogical study conducted by scientists at Rifle (including Dr. Kukkadapu),
euhedral pyrites and framboidal pyrites were discovered [11-12]. A surprising finding of this work was that framboidal pyrites were of different sizes (~10 μm in diameter) and microcrystal morphologies and
internal porosities. Solid-phase U concentrations were higher in this naturally bioreduced zone, with
evidence for a significant amount of U(IV) present, based on U-XANES data. Uranium was detected in
high concentrations in pyrite samples [11-12]. The samples from this zone were depleted in bioavailable
Fe(III), indicating that microbial Fe(III) and sulfate reduction have occurred naturally in the sediment.
Increased concentrations of solid phase organic carbon in this region also suggests that natural bioreduction is stimulated by zones of high organic carbon content [11-12]. Microbial biomass and community composition varied along the bioreduction gradient [11-12]. Some framboidal samples recovered from the
Rifle site were covered with microbial biofilms of unknown origin. Their role in U attenuation is not
known. The objective of this research proposal is to understand the role of pyrites (FeS2) and that of other sulfide minerals such as mackinawite (FeS), in controlling the fate and transport of U, and the interactions in a system that includes U contaminant + Fe sulfides + microorganisms (i.e., sulfate reducing and iron
reducing microbes).
Project Details
Project type
Large-Scale EMSL Research
Start Date
2009-10-05
End Date
2010-09-30
Status
Closed
Released Data Link
Team
Principal Investigator