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 m 3 of contaminated soils 3 million m 3 of buried waste Contaminants: radionuclides, metals, hydrocarbons How do we manage these threats?

4. One Possible Solution U(VI) Uranium - green ; Oxygen - red Shewanella oneidensis MR-1 2 e - O2O2 Nanoparticulate UO 2

5. Incorporation of other cations present in groundwater into the UO 2 structure will result in a more stable crystalline structure Hypothesis CaMgMn We will look at:

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

11. Compton Fits 2Θ = 120°2Θ = 10°

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

16. Manganese Results Sample pH: 6.3 Cleaning Method: NaOH 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

17. Cleaning Method Results Cleanin g Method NoneNaOHLyo 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

18. Conclusions Possible lattice contraction in Mn samples NaOH cleaning process is affecting the structure of bacteriogenic UO 2 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 UO 2 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