Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
The impact of dissolved trace metals on aquatic ecosystems and human health is controlled by sorption, i.e., binding to the surfaces of environmental particles. Since many environmental particles are coated with highly reactive substances, and since discrepancies in trace metal sorption behavior persist between oxides developed in the laboratory and environmental oxide phases, it was hypothesized that the physical form of oxide coatings may influence the chemical properties of the coated particle. Therefore, relationships between the physical forms of several different Fe(III) oxide coatings and the Cu(II) sorption behavior of the coated solids were investigated in comparison with the component phases and natural sedimentary materials. Goethite (alpha-FeOOH) was coated onto quartz and kaolinite grains. Coating method and thickness were varied. Physical properties of the coated solids were probed using multipoint N2 (g) adsorption and desorption analysis (BET), The morphology of the particles was studied by scanning electron microscopy (SEM), and the uniformity of oxide distribution on the grain surfaces was assessed by energy-dispersive X-ray (EDS) analysis. Chemical properties were investigated via batch Cu(II) adsorption/desorption experiments. Goethite physical form was found to vary with coating method and substrate mineralogy. Cu(II) sorption (uptake and release of dissolved Cu from goethite-coated particles) depended on the coating method, substrate, and thickness of the coating. Analysis of these variations indicated physical changes in the form of the coating, interactions between goethite and substrate, and changes in the surface chemical properties of one or both solid phases (goethite and substrate). The combined physical and chemical alterations in the properties of the solids produced distinct behavior in each of the laboratory-prepared solids studied. A parallel set of experiments was conducted on three geologically related sedimentary materials. Several physical and chemical differences were observed between crude kaolin and a cleaned reference kaolinite. One laboratory-prepared goethite coating matched a surface soil at precipitation-dominated Cu loadings, and another coated solid matched a subsurface material at all Cu loading ranges sampled. These results suggest that more complex laboratory-prepared sorbent phases may better reflect trace metal sorption properties of environmental particles.
© The Author
Duckenfield, Kea U., "Laboratory oxide coatings: Physical form and surface chemistry" (2003). Dissertations, Theses, and Masters Projects. Paper 1539616635.