Tuesday, November 14, 2006 - 9:00 AM
183-3
The Colloidal Structure of Soils--Characterized by X-ray Spectromicroscropy.
X-ray microscopy achieves a much higher resolution than conventional light microscopy due to the much shorter wavelength of X-rays. The smallest structures visible in an X-ray microscope at present are less than 20 nm in size. In addition, X-ray microscopy is capable of imaging specimens directly in aqueous media. By choosing the wavelength of the X-radiation appropriately, it is possible to perform spectromicroscopy studies. Thus, this tool is very well suited to study structures showing colloidal dimensions in the environment. Due to their surface activity these structures are principally involved in various chemical and physical processes. Substances can be bound and immobilized or transported, colloids can attach to micro-organisms building up microhabitats, and organic substances as humic substances can flocculate due the interaction with metals. A great variety of these structures have been studied with X-ray microscopy using its high spatial resolution as well as its high spectral resolution. Samples from soils and groundwater aquifers have been imaged to visualize the appearance of these structures. The effect of changing chemical conditions in an aqueous environment on the appearance of colloidal structures has been imaged and evaluated. Using spectromicroscopy, the distribution of organic and inorganic soil colloids has been studied; spectra have been analyzed for major chemical components. Spectra have been taken from humic substances with and without a coagulation agent. Different functional groups have been identified and changes have been mapped. Sulfur is an indispensable nutrient for plants and microorganisms, and soil is an important component of the biogeochemical sulfur cycle. X-ray spectromicroscopy has been used to assess different sulfur species in an entire soil profile. Clay dispersions and microhabitats as well as morphological effects of biologically induced redox changes of humic substances have been imaged tomographically, which conveys a detailed three-dimensional presentation of the specimen structure.
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