Sorption of Radionuclides to Tuff in the Presence of Shewanella oneidensis (MR-1) Sherry Faye 1, Jen Fisher 2, Duane Moser 2, Ken Czerwinski 1 1 University of Nevada, Las Vegas Radiochemistry PhD Program 2 Desert Research Institute, Las Vegas, NV

Outline Objective, Background and Goals  Influence of bacteria on radioelement sorption Experimental  Tuff characterization  Bacteria preparation  Sorption Results Conclusions Future directions

Research Objectives Obtain data on sorption kinetics, equilibrium and fundamental surface interactions of radionuclides with tuff. Obtain a better understanding of interactions of the Shewanella oneidensis (MR-1) culture with tuff and radionuclides.

Background Studies from literature include:  Radionuclide sorption to various rock and minerals.  Interactions of radionuclides with bacteria.  Combined systems including rocks and minerals, radionuclides and bacteria. A combined system will be studied based on conditions at the Nevada Test Site.  Determine if bacteria can influence sorption.  Use results to evaluate against environmental conditions

Research Goals Characterize tuff.  Use scanning electron microscopy (SEM) to examine surface morphology.  Use energy dispersive spectroscopy (EDS) to determine elemental composition.  Use X-ray diffraction (XRD) for phase identification. Perform sorption studies with radionuclides in the absence and presence of bacteria.

Scanning Electron Microscopy Si, O, Al, K, Na Tuff, 50X

X-ray Diffraction Sanidine KAlSi 3 O 8 Cristobalite SiO 2 α-Quartz SiO 2

Bacteria Background MR-1 can be found in diverse environments. MR-1 can grow with or without oxygen and can use a variety of alternate electron acceptors. Well known for its metal reduction capabilities. Courtesy of Jen Fisher

Preparation of MR-1 Cultures Stock cultures stored at -80° C in glycerol are thawed on ice Plated on Luria Bertani agar Single colony picked and grown 24 h in liquid LB to density of ~10 9 cells/mL Cells pelleted 3500 rpm for 15 min) Cells resuspended with PO 4- and CO 3- free buffer 1 mL (~10 9 cells) added to FEP tubes Courtesy of Jen Fisher

Sample Composition Prepare solution phase  Radionuclide 50 – 100 Bq mL Am 50 – 200 Bq mL U  Buffer pH range 6 to 8  Dilutant – up to 20 mL DI Add tuff  Select particle size 500 – 600 μm  Select fraction of solid phase (Bq g -1 ) Solution to solid ratio

Batch Experiments Vortex for 2 minutes. Centrifuge samples for 2 minutes.  Time based on previous kinetic studies Liquid scintillation counting (100 μL into 10 mL liquid scintillation cocktail). Collect samples every minutes for the first two hours. * All samples were created in 50 mL FEP centrifuge tubes

RESULTS

Results – 241 Am Samples contain :  Solution phase: 100 or 200 Bq mL Am NaHCO 3 to obtain a pH of ~8 20 mL total volume, adjusted with DI  Solid phase: 1 gram tuff, ground to μm

Equilibrium Results – 241 Am

Kinetics Results – 241 Am

Results – 241 Am with MR-1 Nine samples, each had 20 mL of solution phase adjusted to pH 7 with NaOH. Bacteria were present in 5 samples ~ 1E+08 cells mL -1 : Concentration (Bq/mL)Mass Tuff (g)Am:tuff (Bq/g)

Results – 241 Am with MR-1

Results – 233 U To determine ideal conditions for sorption kinetic studies: Concentration (Bq/mL)Mass Tuff (g)BufferU:tuff (Bq/g) 1001 NaHCO NaOH NaHCO NaOH75

Kinetics Results – 233 U

Six samples were created to obtain kinetics and equilibrium data, all contained 20 mL solution phase and had a pH of ~7 using NaOH: Concentration (Bq/mL)Mass Tuff (g)U:tuff (Bq/g)

Results – 233 U

Results – 233 U with MR-1 Six samples, each had 20 mL of solution phase adjusted to pH 7 with NaOH: Concentration (Bq/mL)Mass Tuff (g)Bacteria (cells/mL)

Results – 233 U with MR-1

CONCLUSIONS AND FUTURE WORK

Conclusions Quick sorption kinetics were obtained for 241 Am and 233 U. Sorption of 233 U affected by carbonate formation when using NaHCO 3 as a buffer. Sorption of 241 Am and 233 U to MR-1/growth medium.

Future Work Repeat 241 Am and 233 U sorption in the presence of bacteria with replicates. Perform sorption experiments in the presence of bacterial growth medium and absence of MR-1 Repeat sorption experiments with other radionuclides of interest.  Tc, Np, Pu

Acknowledgements Richard Gostic Megan Bennett Dr. Ralf Sudowe Dr. Thomas Hartmann Tom O’Dou and Trevor Low Funding provided by DOE/EPSCoR Partnership Grant DE-FG02-06ER46295

UNLV Radiochemistry

Extra Slides

Results – 241 Am with MR-1

Equilibrium Results – 233 U