Aqueous Actinide Speciation and Redox Behavior in the Presence of Organic Ligands, Calcium, and Elevated Temperature

The mobility of actinides is of primary concern when considering the safety of a deep geologic repository for permanently disposing of nuclear or transuranic waste. The first portion of this dissertation addresses the risk of plutonium mobility in the context of a repository environment by exploring Pu interactions with citrate—an organic ligand that could mobilize Pu through complex formation or redox transformation. The second focal point of this dissertation explores curium(III) behavior (a plutonium(III) and americium(III) analog) in the presence of citrate and calcium—a ubiquitous cation in cementitious systems and present in many host rocks in which a repository may be situated. Lastly, we discuss the speciation of neodymium(III) and praseodymium(III) (An(III) analogs) in the presence of the nuclear waste-relevant organic ligand ethylenediaminetetraacetic acid (edta). The impact of ligand concentration, pH, and elevated temperature are key focal points of this third project. The aqueous species described herein can influence the mobility of trivalent actinides and radioactive lanthanides in the context of nuclear waste disposal and spent nuclear fuel, and the behavior and thermodynamic and kinetics parameters determined in this work may be used in subsequent predictive models for repository performance assessments.