Characterizing the Structure of Bacteriogenic Uranium OxidesJonathan Stahlman, Carnegie Mellon UniversityJohn Bargar, Stanford Linear Accelerator CenterEleanor Schofield, Stanford Linear Accelerator Center

OutlineMotivationOverall project This summers workFinal results

A BIG ProblemOur Cold War Legacy:1.7 trillion gallons of contaminated groundwater40 million m3 of contaminated soils3 million m3 of buried wasteContaminants: radionuclides, metals, hydrocarbons How do we manage these threats?

One Possible SolutionU(VI)Uranium - green ; Oxygen - redShewanella oneidensis MR-12 e-Nanoparticulate UO2

HypothesisIncorporation of other cations present in groundwater into the UO2 structure will result in a more stable crystalline structureCaMgMnWe will look at:

A Structured ApproachEcole Polytechnique Fdrale de Lausanne (EPFL)Sample preparationWashington University in St. Louis Dissolution studiesStanford Synchrotron Radiation LaboratoryStructural studies (EXAFS, WAXS)

This Summers WorkWide angle x-ray scattering (WAXS) to examine lattice contractionExperimental SetupCompton SubtractionBackground SubtractionLe Bail FittingResultsa

Wide Angle X-ray ScatteringChallenges:Wet SamplesRadioactive ConcernsAnaerobic Conditions

Raw Data

Compton SubtractionCompton - inelastically scattered x-rays

Can be easily separated at high angle due to difference in energyNot true at lower angles

Compton Fits2 = 1202 = 10

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

Le Bail FittingA derivative of the Rietveld RefinementUsed to extract the lattice constant

Parameters: Space Group, Particle Size, Background, Lattice Constant

Magnesium ResultsUndoped Sample: 5.4307 .0016 10 mM Mg Doped Sample: 5.4405 .0045 Sample pH: 8.0 Cleaning Method: NaOH

Calcium ResultsSample pH: 6.0 Cleaning Method: NaOHUndoped Sample: 5.4437 .0029 10 mM Ca Doped Sample: 5.4353 .0022

Manganese ResultsSample pH: 6.3 Cleaning Method: NaOHUndoped Sample: 5.4331 .0016 Mn Doped Samples: .1 mM : 5.3956 .0061 1 mM : 5.4387 .0016 5 mM : 5.4018 .0022

Cleaning Method ResultsNo Dopants Added

Cleaning MethodNoneNaOHLyopH = 85.4753 .0025 5.4307 .0016 5.4702.0016 pH = 6.3-5.4331 .0016 5.4643.0017 pH = 6-5.4437 .0029 -

ConclusionsPossible lattice contraction in Mn samplesNaOH cleaning process is affecting the structure of bacteriogenic UO2Future Work:Rietveld Refinement for more structural informationPossibly design new cleaning method

AcknowledgmentsFunding: Department of Energy, SULISoftware:Sam Webb: XRD-BSA.C. Larson and R.B. Von Dreele: GSASB. H. Toby: EXPGUINita Dragoe: Powder 4Other:Apurva MehtaJohn Bargar and Eleanor Schofield

SummaryLong term sequestration of bacteriogenic UO2 depends on incorporation of cationsWAXS provides structural information about bacteriogenic UO2 samplesLe Bail fitting reveals:Possible lattice contraction for Mn doped sampleNaOH cleaning method causing lattice contraction