Oxyanion Adsorption by Iron and Ruthenium Oxides: A Macroscopic, Spectroscopic, and Kinetic Investigation
Luxton, Todd Peter
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The adsorption and desorption behavior of trace element contaminants was evaluated solids-goethite and ruthenium oxide. The importance of anion displacement as a mechanism responsible for arsenic release from iron oxides was investigated on goethite. The adsorption and polymerization of silicate on goethite was examined as a function of surface concentration determine the influence of adsorbed silicate monomers and polymers on arsenite adsorption desorption. A kinetic model was employed to describe arsenite adsorption and desorption absence and presence of silicate. The potential environmental impacts of the research discussed. Hydrous and crystalline ruthenium oxides were extensively characterized traditional colloidal surface characterization techniques, dissolution experiments, and macro- spectroscopic experiments. The two ruthenium oxide phases exhibited large specific areas, a high density of reactive surface functional groups and the presence of multiple oxidation states in both solids. Enhanced dissolution of hydrous ruthenium oxide occurred presence of oxalate and ascorbate. While enhanced dissolution of the crystalline phase only in the presence of oxalate at pH 3. Results from the dissolution experiments were develop possible mechanisms for the oxalate and ascorbate promoted dissolution of ruthenium oxides. Macroscopic adsorption studies of arsenate adsorption on both ruthenium oxides examined over a broad pH (3-10) and initial solution concentration range (0.01 to Results from the adsorption studies indicate arsenate forms a stable surface complex with ruthenium oxide phases. Extended x-ray absorption fine structure spectroscopy and Pressurejump relaxation studies indicates arsenate is specifically adsorbed the ruthenium oxide Chromate adsorption on ruthenium oxides was investigated as a function of pH and chromate solution concentration. Macroscopic adsorption studies and zeta measurements suggest chromate forms an inner-sphere surface complex with both oxide X-ray absorption near edge spectroscopy data indicates chromate (Cr(VI)) is reduced chromium (Cr(III)) on the ruthenium oxide surface. Modeling of the first Cr shell indicated two oxygen backscattering distances similar to the Cr-O atomic distances reported for coordinated to Cr(VI) and Cr(III) providing additional evidence for Cr(VI) reduction.
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