Concentration of Iron Oxides from Soil Clays by Density Gradient Centrifugation
- W. F. Jaynes and
- J. M. Bigham
High speed centrifugation with a large-scale zonal rotor and a linear, tetrabromoethane-ethanol density gradient (1.0–2.8 Mg m−3) was utilized to fractionate the <0.2µm clay materials from three soils with differing Fe-oxide mineralogy. Hematite, goethite, and lepidocrocite were concentrated 4- to 10-fold in the high density range (>2.4 Mg m−3) while the low density fractions (<2.2 Mg m−3) were depleted in reductant-soluble Fe. Density gradient centrifugation also produced useful mineralogical separations of the soil phyllosilicates. In particular, smectite was concentrated in the 1.8 to 2.1 Mg m−3 density range whereas the 2.1 to 2.3 Mg m−3 density range was enriched with kaolinite, vermiculite, and clay mica. Electron microscopy and x-ray diffraction analyses indicated that Fe-oxides were present in the materials studied as discrete particles rather than as “coatings” on associated minerals.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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