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Characterizing the Structure of Bacteriogenic Uranium Oxides

Characterizing the Structure of Bacteriogenic Uranium Oxides. Jonathan Stahlman, Carnegie Mellon University John Bargar, Stanford Linear Accelerator Center Eleanor Schofield, Stanford Linear Accelerator Center. Outline. Motivation Overall project This summer’s work Final results.

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Characterizing the Structure of Bacteriogenic Uranium Oxides

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  1. Characterizing the Structure of Bacteriogenic Uranium Oxides • Jonathan Stahlman, Carnegie Mellon University • John Bargar, Stanford Linear Accelerator Center • Eleanor Schofield, Stanford Linear Accelerator Center

  2. Outline • Motivation • Overall project • This summer’s work • Final results

  3. A BIG Problem • Our Cold War Legacy: • 1.7 trillion gallons of contaminated groundwater • 40 million m3 of contaminated soils • 3 million m3 of buried waste • Contaminants: radionuclides, metals, hydrocarbons How do we manage these threats?

  4. O2 2 e- One Possible Solution U(VI) Shewanella oneidensis MR-1 2 e- Nanoparticulate UO2 Uranium - green ; Oxygen - red

  5. Hypothesis • Incorporation of other cations present in groundwater into the UO2 structure will result in a more stable crystalline structure We will look at: Ca Mg Mn

  6. A Structured Approach • Ecole Polytechnique Fédérale de Lausanne (EPFL) • Sample preparation • Washington University in St. Louis • Dissolution studies • Stanford Synchrotron Radiation Laboratory • Structural studies (EXAFS, WAXS)

  7. This Summer’s Work • Wide angle x-ray scattering (WAXS) to examine lattice contraction • Experimental Setup • Compton Subtraction • Background Subtraction • Le Bail Fitting • Results a

  8. Wide Angle X-ray Scattering • Challenges: • Wet Samples • Radioactive Concerns • Anaerobic Conditions

  9. Raw Data

  10. 2Θ = 10° 2Θ = 120° Compton Subtraction • Compton - inelastically scattered x-rays • Can be easily separated at high angle due to difference in energy • Not true at lower angles

  11. Compton Fits 2Θ = 10° 2Θ = 120°

  12. Background Subtraction • XRD-BS: • Subtract the capillary reflections • Correct for absorption in the sample

  13. Le Bail Fitting • A derivative of the Rietveld Refinement • Used to extract the lattice constant • Parameters: Space Group, Particle Size, Background, Lattice Constant

  14. Magnesium Results Undoped Sample: 5.4307 ± .0016 Å 10 mM Mg Doped Sample: 5.4405 ± .0045 Å Sample pH: 8.0 Cleaning Method: NaOH

  15. Calcium Results Undoped Sample: 5.4437 ± .0029 Å 10 mM Ca Doped Sample: 5.4353 ± .0022 Å Sample pH: 6.0 Cleaning Method: NaOH

  16. Manganese Results Undoped Sample: 5.4331 ± .0016 Å Mn Doped Samples: .1 mM : 5.3956 ± .0061 Å 1 mM : 5.4387 ± .0016 Å 5 mM : 5.4018 ± .0022 Å Sample pH: 6.3 Cleaning Method: NaOH

  17. Cleaning Method Results No Dopants Added

  18. Conclusions • Possible lattice contraction in Mn samples • NaOH cleaning process is affecting the structure of bacteriogenic UO2 • Future Work: • Rietveld Refinement for more structural information • Possibly design new cleaning method

  19. Acknowledgments • Funding: • Department of Energy, SULI • Software: • Sam Webb: XRD-BS • A.C. Larson and R.B. Von Dreele: GSAS • B. H. Toby: EXPGUI • Nita Dragoe: Powder 4 • Other: • Apurva Mehta • John Bargar and Eleanor Schofield

  20. Summary • Long term sequestration of bacteriogenic UO2 depends on incorporation of cations • WAXS provides structural information about bacteriogenic UO2 samples • Le Bail fitting reveals: • Possible lattice contraction for Mn doped sample • NaOH cleaning method causing lattice contraction

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