Sorption of Radionuclides to Tuff in the Presence of Shewanella oneidensis (MR-1)

Sherry Faye1, Jen Fisher2, Duane Moser2, Ken Czerwinski1

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 KAlSi3O8

Cristobalite SiO2

α-Quartz SiO2

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 storedat -80° C in glycerolare thawed on ice

Plated on LuriaBertani agar

Single colony picked and grown 24 h in liquid LBto density of ~109 cells/mL

Cells pelleted(centrifuged @ 3500 rpm for 15 min)

Cells resuspendedwith PO4- and CO3- free buffer

1 mL (~109 cells) added to FEP tubes

Courtesy of Jen Fisher

Sample Composition

Prepare solution phase Radionuclide

50 – 100 Bq mL-1 241Am 50 – 200 Bq mL-1 233U

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

Results – 241Am

Samples contain: Solution phase:

100 or 200 Bq mL-1 241Am NaHCO3 to obtain a pH of ~8 20 mL total volume, adjusted with DI

Solid phase: 1 gram tuff, ground to 500-600 μm

Equilibrium Results – 241Am

0

20

40

60

80

100

120

0 50 100 150 200

100 Bq/mL 200 Bq/mL

% S

orb

ed

Time (h)

Kinetics Results – 241Am

0

20

40

60

80

100

120

0 0.5 1 1.5 2

100 Bq/mL 200 Bq/mL%

Sor

bed

Time (h)

Results – 241Am 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)

50 0 ---

50 10 100

50 4 250

50 2 500

100 2 1000

Results – 241Am with MR-1

0

20

40

60

80

100

0 0.5 1 1.5 2

100 Bq/g

No Bacteria 10^8 cells/mL

% S

orb

ed

Time (h)

Results – 241Am with MR-1

0

10

20

30

40

50

60

70

80

0 0.5 1 1.5 2

500 Bq/g

No Bacteria 10^8 cells/mL

% S

orb

ed

Time (h)

Results – 233U

To determine ideal conditions for sorption kinetic studies:

Concentration (Bq/mL)

Mass Tuff (g) Buffer

U:tuff (Bq/g)

100 1 NaHCO3 2000

100 1 NaOH 2000

50 10 NaHCO3 75

50 10 NaOH 75

Kinetics Results – 233U

0

20

40

60

80

100

0 0.5 1 1.5 2

75 Bq/g NaOH

75 Bq/g NaHCO3

2000 Bq/g NaOH

2000 Bq/g NaHCO3%

So

rbed

Time (hours)

Kinetics Results – 233U

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)

50 10 75

62.5 5 250

125 5 500

125 2.5 1000

187.5 2.5 1500

100 1 2000

Results – 233U

0

20

40

60

80

100

0 0.5 1 1.5 2

75 Bq/g

250 Bq/g

500 Bq/g

1000 Bq/g

1500 Bq/g

2000 Bq/g%

So

rbed

Time (h)

Results – 233U 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)

100 1 0

100 0 1010

100 1 104

100 1 106

100 1 108

100 1 1010

Results – 233U with MR-1

0

20

40

60

80

100

0 0.5 1 1.5 2

No Bacteria

No Tuff

10^4

10^6

10^8

10^10%

So

rbed

Time (hour)

CONCLUSIONSAND FUTURE WORK

Conclusions

Quick sorption kinetics were obtained for 241Am and 233U.

Sorption of 233U affected by carbonate formation when using NaHCO3 as a buffer.

Sorption of 241Am and 233U to MR-1/growth medium.

Future Work

Repeat 241Am and 233U 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 – 241Am with MR-1

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5

1000 Bq/g

No Bacteria 10^8 cells/mL%

So

rbed

Time (h)

Results – 241Am with MR-1

0

20

40

60

80

100

0 0.5 1 1.5 2 2.5 3 3.5

250 Bq/g

No Bacteria 10^8 cells/mL%

So

rbed

Time (h)

Equilibrium Results – 233U

0

20

40

60

80

100

0 50 100 150 200

75 Bq/g NaOH

75 Bq/g NaHCO3

2000 Bq/g NaOH

2000 Bq/g NaHCO3

% S

orb

ed

Time (hours)