Slide 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 Slide 2 Outline Motivation Overall project This summers work Final results Slide 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? Slide 4 One Possible Solution U(VI) Uranium - green ; Oxygen - red Shewanella oneidensis MR-1 2 e - O2O2 Nanoparticulate UO 2 Slide 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: Slide 6 A Structured Approach Ecole Polytechnique Fdrale de Lausanne (EPFL) Sample preparation Washington University in St. Louis Dissolution studies Stanford Synchrotron Radiation Laboratory Structural studies (EXAFS, WAXS) Slide 7 This Summers Work Wide angle x-ray scattering (WAXS) to examine lattice contraction Experimental Setup Compton Subtraction Background Subtraction Le Bail Fitting Results a Slide 8 Wide Angle X-ray Scattering Challenges: Wet Samples Radioactive Concerns Anaerobic Conditions Slide 9 Raw Data Slide 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 2 = 120 2 = 10 Slide 11 Compton Fits 2 = 1202 = 10 Slide 12 Background Subtraction XRD-BS: Subtract the capillary reflections Correct for absorption in the sample Slide 13 Le Bail Fitting A derivative of the Rietveld Refinement Used to extract the lattice constant Parameters: Space Group, Particle Size, Background, Lattice Constant Slide 14 Magnesium Results Undoped Sample: 5.4307 .0016 10 mM Mg Doped Sample: 5.4405 .0045 Sample pH: 8.0 Cleaning Method: NaOH Slide 15 Calcium Results Sample pH: 6.0 Cleaning Method: NaOH Undoped Sample: 5.4437 .0029 10 mM Ca Doped Sample: 5.4353 .0022 Slide 16 Manganese Results Sample pH: 6.3 Cleaning Method: NaOH Undoped Sample: 5.4331 .0016 Mn Doped Samples:.1 mM : 5.3956 .0061 1 mM : 5.4387 .0016 5 mM : 5.4018 .0022 Slide 17 Cleaning Method Results Cleanin g Method NoneNaOHLyo pH = 8 5.4753 .0025 5.4307 .0016 5.4702 .0016 pH = 6.3 - 5.4331 .0016 5.4643 .0017 pH = 6 - 5.4437 .0029 - No Dopants Added Slide 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 Slide 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 Slide 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