Real-time FTIR measurements of Fe-oxide transformation in presence of dissimilatory Fe-reducing bacteria
EMSL Project ID
19395
Abstract
The research will determine the nature, sequence and rates of formation of secondary Fe-oxides at a primary Fe-oxide surface colonized by dissimilatory Fe-reducing bacteria under a controlled hydrodynamic regime. The research will seek to elucidate which of the secondary Fe-precipitated formed on artificially-prepared primary Fe-oxides sequester U(VI) under highly controlled laboratory conditions in order to gain a better understanding of how iron precipitates formed in the presence of Fe-reducing groundwater microbial populations complex, transform and stabilize U present as soluble U(VI) in subsurface aquifers. The experimental approach will utilize a channel-flow bioreactor containing 2 CVD uv/vis/ir-transparent diamond windows, one of which is coated with a thin Fe-oxide film deposited at the Molecular Beam Epitaxy 1 facility and characterized using scanning probe STM/AFM and X-ray diffraction Four-Circle facilities at EMSL by Tim Droubay. Following bacterial inoculation of the Fe-oxide film in the bioreactor, artificial groundwater containing soluble U(VI) will be pumped through the bioreactor to promote bacterial reduction of the Fe-oxide film, formation of secondary Fe-containing precipitates and sorption and complexation of the U(VI) to the precipitates. Bacterial colonization of the surface of the Fe-oxide thin film will be monitored microscopically in real time in a nondestructive manner using reflected differential interference contrast optics and a long-working distance objective lens. The types of secondary Fe-oxide minerals formed at the primary Fe-oxide film surface during bacterial colonization and dissimilatory Fe-reduction and those with which U associates will be monitored by synchrotron Fourier transform infrared spectroscopy using a Fourier transform infrared microscope and beam line 1.4.3, at the ALS at LBNL by Peter Nico and Gill Geesey. Microbiologically mediated transformations will be distinguished from abiotically mediated reactions by comparing spectra collected from thin films in bioreactors inoculated with bacteria with those collected from films in uninoculated bioreactors. Three different primary Fe-oxide films will be evaluated: ferrihydrite, goethite, and hematite to assess the influence of the primary Fe-oxide on the nature, sequence and rates of formation of secondary Fe-containing precipitates. Identification of the products and their rates of formation are needed to improve the ability of linked equilibrium/kinetic biogeochemical transport models to predict the influence of microorganisms on the behavior of radionuclides in subsurface environments. This activity falls within the mission of the EMSL to provide integrated experimental and computational resources for discovery and technological innovation in the environmental sciences to support DOE?s need to develop safe, cost-effective management of environmental pollutants and the remediation of hazardous waste sites. This proposal relates to the goal of the Geochemistry/Biogeochemistry and Subsurface Science theme of EMSL to resolve reaction mechanisms at the microbe/mineral interface.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2006-07-21
End Date
2009-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members