Characterizing%20the%20Structure%20of%20Bacteriogenic%20Uranium%20Oxides

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Characterizing the Structure of Bacteriogenic
Uranium Oxides

• Jonathan Stahlman, Carnegie Mellon University
• John Bargar, Stanford Linear Accelerator Center
• Eleanor Schofield, Stanford Linear Accelerator
  Center

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Outline

• Motivation
• Overall project
• This summers work
• Final results

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

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This Summers Work

• Wide angle x-ray scattering (WAXS) to examine
  lattice contraction
• Experimental Setup
• Compton Subtraction
• Background Subtraction
• Le Bail Fitting
• Results

a
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Wide Angle X-ray Scattering

• Challenges
• Wet Samples
• Radioactive Concerns
• Anaerobic Conditions

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Raw Data
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Compton Subtraction

• Compton - inelastically scattered x-rays
• Can be easily separated at high angle due to
  difference in energy
• Not true at lower angles

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Compton Fits
2T 120
2T 10
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Background Subtraction

• XRD-BS
• Subtract the capillary reflections
• Correct for absorption in the sample

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Le Bail Fitting

• A derivative of the Rietveld Refinement
• Used to extract the lattice constant
• Parameters Space Group, Particle Size,
  Background, Lattice Constant

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Magnesium Results
Undoped Sample 5.4307 .0016 Å
10 mM Mg Doped Sample 5.4405 .0045 Å
Sample pH 8.0 Cleaning Method NaOH
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Calcium Results
Undoped Sample 5.4437 .0029 Å
10 mM Ca Doped Sample 5.4353 .0022 Å
Sample pH 6.0 Cleaning Method NaOH
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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
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Cleaning Method Results
Cleaning Method None NaOH Lyo
pH 8 5.4753 .0025 Å 5.4307 .0016 Å 5.4702 .0016 Å
pH 6.3 - 5.4331 .0016 Å 5.4643 .0017 Å
pH 6 - 5.4437 .0029 Å -
No Dopants Added
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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

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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

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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