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Characterizing the Structure of Bacteriogenic Uranium OxidesPowerPoint Presentation

Characterizing the Structure of Bacteriogenic Uranium Oxides

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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

Outline

- Motivation
- Overall project
- This summer’s work
- Final results

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?

O2

2 e-

One Possible SolutionU(VI)

Shewanella oneidensis MR-1

2 e-

Nanoparticulate UO2

Uranium - green ; Oxygen - red

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

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)

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

Wide Angle X-ray Scattering

- Challenges:
- Wet Samples
- Radioactive Concerns
- Anaerobic Conditions

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

Background Subtraction

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

Le Bail Fitting

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

Magnesium Results

Undoped Sample: 5.4307 ± .0016 Å

10 mM Mg Doped Sample: 5.4405 ± .0045 Å

Sample pH: 8.0 Cleaning Method: NaOH

Calcium Results

Undoped Sample: 5.4437 ± .0029 Å

10 mM Ca Doped Sample: 5.4353 ± .0022 Å

Sample pH: 6.0 Cleaning Method: NaOH

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

Cleaning Method Results

No Dopants Added

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

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

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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