Reactions of plutonium(VI) with the iron oxide goethite

The adsorption of plutonium(VI) to the iron oxide goethite was studied as a function of pH, plutonium concentration, and carbonate concentration. X-ray absorption spectra including the x-ray absorption near edge spectra and the x-ray absorption fine structure spectra were collected in an attempt to identify the oxidation state and structure of the adsorbed plutonium complex. This work was motivated by the need for chemical understanding of the processes occurring in environmental systems, specifically those occurring in subsurface systems similar to those for proposed geologic repositories for nuclear waste.; The first chapter of this thesis describes fundamental reactions in aqueous systems including acid-base chemistry, complexation, hydrolysis, redox reactions, and reactions at mineral surfaces.; The second chapter presents the nuclear chemistry and aqueous chemistry of plutonium, and for comparison, its oxidation state analogues, U(VI), and Np(V). Data from the most recent and reliable literature were compiled to present the aqueous speciation of Pu(III), (IV), (V), (VI), Np(V), and U(VI). The redox stability of Pu and its complexes as a function of pH and E H are also presented.; Chapter three presents a survey of goethite chemistry and previous works relevant to this study with goethite and plutonium. The results of previous studies with actinides and goethite are discussed in their context to the experiments completed for this thesis.; The fourth chapter and the accompanying appendices detail the experimental procedures and special procedures developed for completing the experiments in this work. These procedures include detailed directions for the preparation and manipulation of pure oxidation states of plutonium, the safe packaging of plutonium for low temperature x-ray absorption measurements, and the design of a special cell for the x-ray absorption experiments.; Chapters five, six, and seven are presentations of the data from the sorption and x-ray spectroscopy experiments with plutonium and goethite, and neptunium and goethite. These chapters detail the findings related to the oxidation state distribution of plutonium in solution, sorption kinetics, and the sorption envelopes. The x-ray data are presented showing beam-induced redox reactions at room temperature that was remedied by cooling the samples to 20 K.; The first experiments of low temperature wet transuranium EXAFS are presented and provide interesting results relating to the oxidation state distribution of plutonium on the surface of the goethite as well as the structure of the adsorbed plutonium surface complex. Neptunium EXAFS are presented for comparison in chapter six and show similar structural features to the plutonium data in presented in chapter five.