Dissolution of zippeite via bacterial sulfate reduction.

Microbial reduction of U(VI) from solid uranyl phases, forming nanocrystalline uraninite (UO2) colloids, could promote dispersal and transportation of U in porous media. Under alternating redox conditions in the subsurface, bacterial reductive dissolution may promote U diffusion through recrystallization of U(VI) crystalline phases to finer-grained U(IV) particles, which would tend to solubilize upon encountering oxidizing conditions. Well-characterized synthetic uranyl U(VI) sulfate minerals were used as potential terminal electron acceptors in laboratory cultures o f Desulfovibrio desulfuricans. This research assessed the microbial respirative bioavailability of two zippeite group phases with different physicochemical properties and ion substitution. Solid phase characterization using X-ray absorption spectroscopy, field emission scanning electron microscopy and transmission electron microscopy o f mineral substrates before and after microbial exposure was performed to observe changes in oxidation and secondary mineralization products formed during microbial reduction. The greatest shift o f 1.5 eV to lower energies was observed in the Na-zippeite sulfur enriched conditions, with accompanying evidence of bacterial uraninite nucleation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CO-AUTHORSHIP STATEMENT The following thesis contains material from a manuscript that will be submitted in the near future. The manuscript entitled, “Dissolution of zippeite via bacterial sulfate reduction”, is co-authored by A.E. Forsyth, C. Weisener, P.C. Bums, V. Phoenix, and D.A. Fowle. The author performed laboratory work presented herein. The submitted version of this manuscript appears in Chapter 2. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENTS This creation is dedicated to my parents Barb Marwood, and Bill and Claire CresseyForsyth who have supported, encouraged, and believed in me throughout. My deepest gratitude goes out to my family and friends who have helped me forge on. I would also like to sincerely thank my supervisors, Dr. David Fowle and Dr. Christopher Weisener for all that I have learned from this challenge. For those who have lent a hand through the last three years, I thank my best friends, Paul Kenward and Keith Squires for their encouragement and laughter; Dr. Peter Bums for discovering my crystal-making mojo; Dr. Vemon Phoenix; Dr. Joel Gagnon; Matt Newville; J.C. Barrette; Sharon Home for all her patience; Dr. Iain Samson for being a friend; and lastly my GLIER and Earth Sciences friends and colleagues who always provided some sort of entertainment. A special thanks goes to my good friends and family, Sarah Frith and Romano Calvano, for getting me back on my feet. My sincerest appreciation goes to the guys, Mike Jones, Dave Ketcheson, and Paul Neals at Azimuth Environmental Consulting, Inc., without you I never would have finished. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. STATEMENT OF ORIGINALITY I certify that the thesis herein is a product of my own work, except as denoted in co­ authorship. All other work from other people is acknowledged.