1. The Secondary Mineralization of Ferrihydrite Under Reducing Redox Conditions: An Electrochemical Study Aron Griffin Engineering Science and Mechanics Advisor: Dr. Christopher Gorski Civil and Environmental Engineering

2. Acknowledgments -Dr. Christopher Gorski -Rebecca Edwards -Prachi Joshi -Sarah Cronk -Patrick Duggan

3. Groundwater contamination is widespread domestically and internationally. “Recent (2004) estimates by the U.S. Environmental Protection Agency (EPA) indicate that expenditures for soil and groundwater cleanup at over 300,000 sites through 2033 may exceed $200 billion (not adjusted for inflation), and many of these sites have experienced groundwater impacts.” National Academy of Sciences 2014

4. Current treatment methods are costly and energy intensive.

5. Naturally occurring minerals can be used to fight contamination. Fe 3+ + e -  Fe 2+

6. Iron minerals are integral in the biogeochemical cycling of environmental contaminants. Uranium 6+ + 2e -  Uranium 4+

7. It is difficult to predict iron states for different site locations and conditions.

8. We aimed to determine what forms when ferrihydrite is present in reducing conditions. Ferrihydrite Fe 2+ aqueousFe 2+ oxideFe 3+ oxide

9. Applied mediated electrochemical techniques were used to model the microbial reduction of Fe.

10. A long series of trouble shooting perfected our electrochemical cell. Counter Electrode Reference Electrode Working Electrode Copper Tape

11. Chronoamperometry applies a set potential and measures the current response with time. ( F=96,495 c/mol )

12. Reduction products were analyzed using UV-vis spectrometry and Mossbauer spectrometry.

13. Mossbauer spectroscopy can determine the oxidation state and mineral phase of iron.

14. Control data at highly reducing conditions confirmed the accuracy of the experimental model. Total Fe 3+ added = Electrons Transferred = Fe 2+ in final solution

15. The effects of mediator and iron concentration on the system were investigated.

16. Higher mediator concentration resulted in further transformation from ferrihydrite.

17. Decreasing applied potential resulted in a greater extent of reduction.

18. Lower applied potential resulted in further transformation into magnetite.

19. We have gained insight into secondary mineralization processes in an effort to control contaminant fate.

20. Further work will be completed this summer to investigate Mossbauer uncertainties and reduction kinetics. T=4K Pt electrode