Biogeochemistry of Fe and Tc Reduction and Oxidation in FRC Sediment
The objectives are: (1) To rigorously characterize the distribution of Fe(II) and Fe(III) in FRC sediment. (2) To identify changes to Fe(II)/Fe(III) distribution and concentration resulting from DIRB activity. (3) To determine the dependence of Tc(VII) reduction rate on biogenic Fe(II) and it's forms. (4) To establish tendency of Tc(IV) and biogenic Fe(II) to oxidize and their effects on Tc immobilization. The mineralogic and chemical properties of the pristine, bioreduced, and chemically extracted FRC sediments were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), X-ray microscopy (XRM, at the PNC-CAT beamline at APS), Moessbauer spectroscopy, and scanning and transmission electron microscopy with lattice fringe imaging. Chemical extraction included dithionite-citrate-bicarbonate (DCB), acid ammonium oxalate (AAO), and hydroxylamine hydrochloride (HAH). The FRC sediment was incubated under anoxic conditions with the facultative dissimilatory metal-reducing bacterium Shewanella putrefaciens, strain CN32 in defined aqueous solutions/media with bicarbonate and PIPES buffers for time periods exceeding 75 d. Lactate was used as the electron donor. Aqueous and sorbed Fe(II) (ferrozine assay and 0.5 N HCl extraction) and Mn(II) (ICP-MS and 10 mM CuSO{sub 4} extraction), and pH were monitored to define the reduction progress and extent. The bioreduced materials were characterized using the abovementioned techniques. Bioreduced (pasteurized) sediment or chemically extracted/reduced sediment spiked with Fe(II) was washed with a PIPES buffer/electrolyte solution, and spiked with NaTc(VII)O{sub 4} to yield a concentration of 20 {micro}M. The Tc(VII)-spiked samples were agitated and equilibrated at 25 C and sampled over time to assess the Tc(VII) reduction rate. Selected sediment samples containing 20 {micro}M of reduced Tc [Tc(IV)] were subjected to oxidation by: (1) successive headspace replacements of air, and (2) open system equilibration with air. Removed aqueous samples were filtered (< 2 {micro}m) and counted to determine the Tc(VII) concentration. Thin sections of the bioreduced/chemically reduced Tc(VII) reacted/oxidized sediments were analyzed by backscattered electron microscopy and X-ray microspectroscopy.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- OSTI ID:
- 895565
- Report Number(s):
- CONF-NABIR2004-51; TRN: US0700499
- Resource Relation:
- Conference: Annual NABIR PI Meeting, March 15-17, 2004, Warrenton, VA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
54 ENVIRONMENTAL SCIENCES
59 BASIC BIOLOGICAL SCIENCES
ACID CARBONATES
BINDING ENERGY
BIOGEOCHEMISTRY
BUFFERS
CHEMICAL PROPERTIES
ELECTRON MICROSCOPY
FLUORESCENCE
HYDROXYLAMINE
LACTATES
MICROSCOPY
MOESSBAUER EFFECT
OXALATES
OXIDATION
SEDIMENTS
TRANSMISSION ELECTRON MICROSCOPY
VALENCE
X-RAY DIFFRACTION