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Physical Sciences

Geochemical and Biogeochemical Processes

hydration and protonation of the 021 and 110 surfaces of goethite
A scanning electron micrograph shows bacterial cells that accumulated on titanomagnetite iron oxide minerals upon exposure to groundwater at the Hanford Site. Titanomagnetite minerals are naturally occurring metal oxides comprising one type of iron source in the mineralogy of Hanford sediments. They are potentially important to microbiological activity and contaminant transport in the subsurface. Data from this controlled experiment is providing better understanding of energy and materials transfer in the subsurface. Enlarged View

We are focused on unraveling the fundamental biogeochemical interactions between minerals, solutions, and microorganisms in geologic environments. This capability emphasizes developing a molecular-level understanding of these interactions through the use of advanced surface spectroscopies and molecular and thermodynamic modeling simulations.

Understanding the fundamental nature of biogeochemical reactions (e.g., their identity, kinetics, and thermodynamics) is the key to determining the fate and transport of energy-derived contaminants in subsurface systems, developing remediation strategies for nuclear production facilities and other contaminated sites, and maintaining global water quality as populations increase. Determining the specific molecular-level mechanisms that determine these reactions as well as the location of contaminants in the environment is our key scientific challenge.

Some questions being addressed by our research include the following:

  • What are the structure, molecular architecture, and electrolyte/solvent properties of the mineral-microbe interface?
  • How can molecular mechanisms of oxidation/reduction at mineral-water interfaces be determined and how can they be used to predict macroscopic reactivity?
  • What factors control the spatial distribution of different functional organism groups in heterogeneous natural materials, and how do spatially distinct organism groups interact to control microscopic and macroscopic geochemical processes?
  • What biologic and abiotic molecular interactions/reactions occur at the mineral-microbe interface to regulate energy, chemical, and electron flux to and from microorganisms, and the environmental fate of contaminants?

Our research integrates three world-class research disciplines at PNNL: environmental microbiology, geochemistry and mineral surface science, and computational chemistry while drawing heavily on other capabilities in EMSL to develop a fundamental understanding of how contaminants interact with natural materials. The research includes

  • Investigations of molecular biogeochemical mechanisms utilizing the EMSL user facility
  • Experimental geochemistry and biogeochemistry investigations of the mineral-water and mineral-microbe interface supported by the Department of Energy's Office of Basic Energy Sciences (BES) and Office of Biological and Environmental Research
  • Computational geochemical studies of mineral surfaces and contaminant interactions supported by BES and Environmental Management Science Program
  • Field study of the macroscopic function of these processes in contaminated Hanford Site subsurface environments that are in dire need of scientific understanding and innovative cleanup techniques.

The impact of this research is an enhanced understanding of geochemical and biogeochemical controls on contaminant fate and transport; insights on the local workings of biogeochemical cycles that are driven by interfacial reactions; and applications for energy production technologies dependent upon oil and gas.

Contacts: Andy Felmy, Kevin Rosso

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