Presentation on theme: "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."— Presentation transcript:
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
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 (centrifuged @ 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 -1 241 Am 50 – 200 Bq mL -1 233 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 10-15 minutes for the first two hours. * All samples were created in 50 mL FEP centrifuge tubes
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) 500--- 5010100 504250 502500 10021000
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) 501075 62.55250 1255500 1252.51000 187.52.51500 10012000
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