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Uranium Adsorption onto Bacillus subtilis

The Significance:. Bacterial adsorption affects the circulation of uranium in water-rock systemsSurface complexation modeling can be used to analyze the issue of uranium in the environmentBacterial adsorption may be used as a method of cleaning up" uranium found at mine and radioactive settings.

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Uranium Adsorption onto Bacillus subtilis

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    1. Uranium Adsorption onto Bacillus subtilis Christina Arisio Drew Gorman-Lewis Dr. Jeremy Fein

    2. The Significance: Bacterial adsorption affects the circulation of uranium in water-rock systems Surface complexation modeling can be used to analyze the issue of uranium in the environment Bacterial adsorption may be used as a method of “cleaning up” uranium found at mine and radioactive settings

    3. B. Subtilis – An ideal candidate: Gram-positive Common soil bacterium Cell wall/ surface chemistry has been well identified High affinity for U binding

    4. Surface Chemistry:

    5. What’s been done before: Uranyl-bacteria adsorption has been modeled using a Gram-negative bacterium, in the pH range of 2-8 (Haas Group) Using B. Subtilis, the Fein group has modeled adsorption for a low to mid-pH range Both groups have successfully modeled adsorption for a deprotonated carboxyl group found on the cell surface of both types of bacteria

    6. The Fein Group Modeled uranyl adsorption for the pH range of 11/2- 5 Modeled adsorption for 2 sites on B subtilis: a protonated phosphoryl group and a deprotonated carboxyl group

    7. The Next Step: Tested the adsorption of UO22+ (uranyl) onto the cell wall of Bacillus subtilis Performed tests using a pH range of ~4-10 The data obtained will be used for surface complexation modeling

    8. Method Bacteria Grown in TSB Washed approx 7x with 0.1M NaClO4 (centrifuged to pellet bacteria, then resuspended in solution) Concentrations for experiments calculated from a “wet” weight of the bacteria taken after a long period of centrifugation

    9. Method Used 0.1M NaClO4 electrolyte solution to dilute a ~100ppm U stock solution to ~1.0ppm U parent for each experiment Made 1.5g/L, 1.0g/L, 0.75g/L, 0.50g/L, and 0.25g/L concentrations of bacteria in parent (Based on vol. of parent and wet weight of bacteria) Set aside enough parent (w/o bacteria) for later U conc. testing All U samples left for extended amounts of time were well acidified Each bacterial concentration was tested 3 times

    10. Method Placed 9ml of parent into 12 Teflon tubes Adjusted the pH of the samples with small volumes (µl) of NaOH and HNO3 to have ~4-10 pH range Placed samples on a slowly rotating wheel for 2-3 hours, allowing them to reach an equilibrium pH

    11. Method Samples were centrifuged at high speeds (12,500 and 13,500 rpm) for 15 mins Approx. 7 ml of each centrifuged sample was transferred to polypropylene tubes Samples were well-acidified with 16µl of 15.8M HNO3 and refrigerated Remaining amounts of uranium were analyzed using ICP-OES (Perkin Elmer)

    12. Preliminary Tests and Outcomes: A sticky metal Why use 1ppm U parent solutions? Why high speed centrifugation? Why use Teflon tubes?

    13. Hypothesis pH – As the pH increases, adsorption will increase, then decrease in a falling curve Bug Concentration – As the concentration of bacteria decreases, less uranium will be adsorbed Together – As the pH increases, the decreasing adsorption curve should fall off more dramatically with less bacteria

    18. What does it show? Max adsorption occurs from about pH 5-6 Adsorption hovers between 80% and 95% for 0.75g/L through 1.5g/L bug conc. (The curves stay relatively flat.) Adsorptions from 0.50 and 0.25 g/L agree more strongly with the predictions of the hypothesis Adsorptions after ~pH=8.5 begin to exhibit strange behavior

    19. What’s going on up there? The problem with higher pH’s The bacteria do not manage well in high pH Uranyl-carbonate speciation Competition between the bacteria and carbonate compounds

    20. U Speciation

    22. Future Experiments A lower bug conc., 0.125g/L A retest of 0.50g/L Run the tests after acid washing the bacteria Kinetics experiments Desorption experiments

    23. What’s left to be done

    24. Acknowledgements Dr. Jeremy Fein Jennifer Schaefer Jennifer Redding, Jennifer Forsythe, and the rest of the EMSI staff Rian Galloway, Dennis Birdsell, and the rest of the CEST staff Drew Gorman-Lewis

    25. References Haas, J.R., Dichristina, T.J., Wade Jr., R., 2001. Thermodynamics of U(VI) sorption onto Shewanella putrefaciens. Chem. Geol. 108, 33-54 Fein, J.B., 2000. Quantifying the effects of bacteria on adsorption reactions in water-rock systems. Chem. Geol. 169, 265-280 Fowle, D.A., Fein, J.B., Martin, A.M., 2000. Experimental study of uranyl adsorption onto Bacillus subtilis. Envi. Sci. Tech. 34, 3737-3741

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