Novel Imaging Techniques, Integrated with Mineralogical, Geochemical and Microbiological Characterization to Determine the Biogeochemical Controls....
Tc(VII) will be reduced and precipitated in FRC sediments under anaerobic conditions in batch experiments (progressive microcosms). The complementary microcosm experiments using low pH/nigh nitrate sediments from 3 (near FW 009) are imminent, with the sediment cores already shipped to Manchester. HYPOTHESIS 2. Tc(VII) reduction and precipitation can be visualized in discrete biogeochemical zones in sediment columns using 99mTc and a gamma-camera. Preliminary experiments testing the use of 99mTc as a radiotracer to address hypotheses 2 and 3 have suggested that the 99mTc associates with Fe(II)-bearing sediments in microcosms and stratified columns containing FRC sediments. Initial proof of concept microcosms containing Fe(II)-bearing, microbially-reduced FRC sediments were spiked with 99mTc and imaged using a gamma-camera. In comparison with oxic controls, 99mTc was significantly partitioned in the solid phase in Fe(III)-reducing sediments in batch experiments. Column experiments using FRC background area soil with stratified biogeochemical zones after stimulation of anaerobic processes through nutrient supplementation, suggested that 99mTc transport was retarded through areas of Fe(III) reduction. HYPOTHESIS 3. Sediment-bound reduced 99mTc can be solubilized by perturbations including oxidation coupled to biological nitrate reduction, and mobilization visualized in real-time using a gamma-camera. Significant progress has been made focusing on the impact of nitrate on the biogeochemical behavior of technetium. Additions of 100 mM nitrate to FRC sediment microcosms, which could potentially compete for electrons during metal reduction, inhibited the reduction of both Fe(III) and Tc(VII) completely. Experiments have also addressed the impact of high nitrate concentrations on Fe(II) and Tc(IV) in pre-reduced sediments, showing no significant resolubilization of Tc with the addition of 25 mM nitrate. A parallel set of experiments addressing the impact of aerobic conditions on the stability/solubility of Fe(II) and Tc(IV), found 80 % resolubilization of the Tc. Column experiments exploring this behavior are being planned. HYPOTHESIS 4 The mobility of 99mTc in the sediment columns can be modeled using a coupled speciation and transport code. Microbiological and geochemical characterization of the column experiments is ongoing and transport and geochemical modeling experiments are being planned.
- Research Organization:
- University of Manchester, UK
- Sponsoring Organization:
- USDOE Office of Science (SC)
- OSTI ID:
- 893406
- Report Number(s):
- NABIR-1022748-2005; R&D Project: NABIR 1022748; TRN: US200625%%262
- Country of Publication:
- United States
- Language:
- English
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