GEOCHEMISTRY OF URANIUM AT MINERAL-WATER INTERFACES: RATES OF SORPTION-DESORPTION AND DISSOLUTION-PRECIPITATION REACTIONS Thesis by Daniel Giammar In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy California Institute of Technology Pasadena, California 2001 (Defended May 8, 2001) ii © 2001 Daniel Giammar All Rights Reserved iii Acknowledgments My advisor Janet Hering has supported and encouraged me throughout my graduate student career. From her I have learned a great deal about aquatic chemistry and, by her example, much about scientific curiosity and discipline. She is consistently my best and most thorough critic. Michael Hoffmann’s encouragement and suggestions have contributed in many ways to my work. George Rossman’s mineralogical insight led to some of the most interesting experiments in this work. Jim Morgan has been a mentor and role model throughout my study at Caltech, and I would particularly like to thank him for his emphasis on the fundamentals, both scientifically and on the basketball court. I would like to acknowledge the profound influence that Susan Leach, my middle school life and earth sciences teacher, had on my decision to pursue a career in environmental science and engineering. David Dzombak at Carnegie Mellon encouraged me to go to graduate school and remains a great role model for me. At Caltech, Gerald Wasserburg’s enthusiasm for geochemistry got me interested in uranium and his encouragement contributed to the initiation of this work. The summer undergraduate research projects of Helen Claudio and Yi-Ping Liu constitute portions of this work. When I would run into a problem with the X-ray diffractometer or scanning electron microscope, Chi Ma was always there to bail me out. Yulia Goreva gave generously of her time to get me started with SEM. Liz Arredondo helped me collect Raman spectra with remarkable efficiency. Andrea Belz sparked my interest in transmission electron microscopy, and Carol Garland’s expertise with the TEM made it possible to acquire meaningful images in the final weeks of this project. Peter iv Green and Yaniv Dubowski kept the ICP-MS running. Tatiana Piatina and Penny Kneebone lit my path at Caltech by getting me started in the lab. The smiles of Fran, Linda, Irene, Elena, and Belinda have all made Keck a great place to work. Outside of the lab, bicycling up Mount Wilson or over the Glendora Mountain Road with David Anderson and Piet Moeleker were real highlights. I will certainly miss Sunday soccer and all of my teammates. Wednesday noon basketball was the carrot-on- a-stick that got me through some long weeks, and I’d like to thank Rob, Jeff, Jason, Mike, Pat, Denis, Gordon, Jim, and all the others who made it so much fun. Delores Bing and Allen Gross offered great musical outlets in chamber music and the Caltech- Occidental Orchestra. I would particularly like to acknowledge Isaac See, David Fang, and Nick Knouf who have made string quartets such a joy over the last two years. My fellow 1996 first-years David Cocker, Tina Salmassi, Yael Dubowski, and Catherine Cornu have been great friends and colleagues. Life at Caltech would not have been the same without Rob Griffin, Ann McAdam, Peter Adams, Amy Rigsby, Matt Fraser and Brian King. I would particularly like to thank Jennie Stephens, Hugo Destaillats, and Tim Lesko for helping me through some difficult times. Far and away the biggest thanks go to my parents, Robert and Betty Giammar. By showing me the beauty in the natural world, valuing education so highly, acting as my financial safety net, and most importantly serving as my emotional support and inspiration, they have made everything possible for me. Lastly, I thank my wife and best friend Michelle Vollmar for her unwavering support through five long years. Her love has made it all worthwhile. Whenever my walls are collapsing, she is the truth standing in the center. v Abstract The extraction and processing of uranium for use in the nuclear weapons program and in commercial nuclear energy has led to extensive contamination of the environment. Migration of uranium is also a concern for the proposed long-term nuclear waste disposal in geologic repositories. Reactions occurring at mineral surfaces significantly affect the mobility of uranium in the environment. Both the equilibrium and kinetics of reactions at mineral surfaces must be understood in order to predict the extent of reactions on time scales pertinent to human exposure. Such information is needed to establish input parameters for reactive transport models and to design remediation technologies. Rates of uranium sorption on mineral surfaces and the dissolution of uranium- containing minerals have been investigated. Rates of sorption onto and desorption from goethite, an important environmental sorbent, were determined by measuring the responses of goethite suspensions (pre-equilibrated with or without uranium) to perturbations of the solution chemistry. Dissolution rates were measured for a set of laboratory-synthesized minerals: the uranyl oxide hydrate schoepite, the uranyl silicate soddyite, and a uranyl phosphate phase. These minerals have been observed in contaminated environments and are produced during the corrosion of spent nuclear fuel. Mineral dissolution and transformation were monitored in batch reactors, while dissolution rates were quantified in flow-through reactors. In both sorption and dissolution-precipitation studies, measurements of bulk solution chemistry were integrated with solid phase characterization. vi While sorption processes were rapid, dissolution and surface-precipitation reactions occurred more slowly. Adsorption and desorption reactions of uranium onto or from goethite reached greater than 50% completion within minutes and completion on a time-scale of hours. In some uranium-goethite suspensions, a meta-stable sorption state persisted for as long as three weeks before a schoepite-like phase precipitated. Dissolution reactions proceeded at time-scales of hours for schoepite and days to weeks for soddyite and the uranyl phosphate. Common groundwater cations affected dissolution rates and, in several cases, resulted in the precipitation of uranium in secondary phases. In several schoepite and soddyite batch dissolution experiments, uranium ultimately reprecipitated in sodium or cesium uranyl oxide hydrate phases which subsequently controlled the dissolved uranium concentration. vii Contents Acknowledgments .. .. .. .. .. .. .. .. iii Abstract .. .. .. .. .. .. .. .. .. v 1 Introduction .. .. .. .. .. .. .. .. 1-1 1.1 Motivation .. .. .. .. .. .. .. 1-1 1.2 Research Scope and Objectives .. .. .. .. 1-7 1.3 Research Approach .. .. .. .. .. .. 1-10 2 Environmental Geochemistry of Uranium in Soil, Sediment, and Groundwater Systems .. .. .. .. .. .. 2-1 2.1 Aqueous Uranium Geochemistry .. .. .. .. 2-1 2.2 Uranium in Sediments and Soils .. .. .. .. 2-5 2.2.1 Overview .. .. .. .. .. .. 2-5 2.2.2 Contamination at Department of Energy of Facilities 2-5 2.2.3 San Joaquin Valley .. .. .. .. .. 2-8 2.2.4 Uncontaminated Soils .. .. .. .. 2-9 2.2.5 Ore Bodies .. .. .. .. .. .. 2-10 2.2.6 Transport Modeling in Natural Systems .. .. 2-11 2.3 Uranium Sorption on Mineral Surfaces .. .. .. 2-12 2.3.1 Overview of Sorption Equilibrium and Kinetics .. 2-12 2.3.2 Uranyl Sorption on Iron Oxyhydroxide Minerals .. 2-13 viii 2.3.3 Uranyl Sorption on Aluminosilicate Minerals .. 2-16 2.3.4 Uranyl Association with Natural Organic Materials .. 2-18 2.4 Mineralogy of Uranium-Containing Minerals .. .. 2-19 2.4.1 Uranyl Mineral Structures .. .. .. .. 2-19 2.4.2 Environmental Uranyl Mineral Transformations .. 2-19 2.4.3 Uranyl Oxide Hydrates .. .. .. .. 2-21 2.4.4 Uranyl Silicates .. .. .. .. .. 2-24 2.4.5 Uranyl Phosphates .. .. .. .. .. 2-25 3 Kinetics of Uranyl Sorption on Goethite .. .. .. .. 3-1 3.1 Introduction .. .. .. .. .. .. .. 3-1 3.2 Materials and Methods .. .. .. .. .. 3-4 3.2.1 Materials .. .. .. .. .. .. 3-4 3.2.2 Experimental Methods .. .. .. .. 3-4 3.3 Results and Discussion .. .. .. .. .. 3-7 3.3.1 Adsorption and Surface Precipitation .. .. 3-7 3.3.2 Sorption Kinetics .. .. .. .. .. 3-10 3.3.3 Environmental Implications .. .. .. .. 3-17 Acknowledgments .. .. .. .. .. .. .. 3-18 4 Investigation of Uranium-Loaded Goethite By Electron Microscopy 4-1 4.1 Introduction and Background .. .. .. .. 4-1 4.2 Experimental Materials and Methods .. .. .. 4-4 ix 4.3 Results .. .. .. .. .. .. .. 4-7 4.3.1 Scanning Electron Microscopy .. .. .. 4-7 4.3.2 Transmission Electron Microscopy .. .. .. 4-9 4.4 Discussion .. .. .. .. .. .. .. 4-15 4.4.1 Nature of Solid-associated Uranium .. .. .. 4-15 4.4.2 Utility of Electron Microscopy .. .. .. 4-17 4.4.3 Need for Additional Characterization .. .. .. 4-18 4.4.4 Conclusions .. .. .. .. .. .. 4-19 5 Dissolution and Transformation of Uranyl Oxide Hydrates .. 5-1 5.1 Introduction and Background .. .. .. .. 5-1 5.2 Experimental Materials and Methods .. .. .. 5-4 5.2.1 Materials .. .. .. .. .. .. 5-4 5.2.2 Batch Dissolution and Transformation Experiments .. 5-6 5.2.3 Flow-through Dissolution .. .. .. .. 5-7 5.2.4 Analytical Methods .. .. .. .. .. 5-7 5.2.5 Equilibrium Calculations .. .. .. .. 5-9 5.3 Results .. .. .. .. .. .. .. 5-9 5.3.1 Characterization of Synthesized Solids .. .. 5-9 5.3.2 Batch Dissolution Experiments .. .. .. 5-12 5.3.2.1 Determining the Influence of Sodium .. 5-12 5.3.2.2 Experiments with Cesium, Ripened Schoepite, Dilute Solution, and Fluoride .. .. .. 5-19 x 5.3.2.3 Post-equilibration Electrolyte Addition Experiments