Spectroscopic study of soil particle surface redox reactions

UV-visible spectroscopy is described, which was applied to soil samples known to be active oxidizers of trivalent chromium to examine the fractionation of Cr oxidation and reduction activity with particle size. An aqueous fractionation scheme was used to select soil size fractions with enhanced Cr redox activity relative to the whole soil. Spectral examination of the soil material suspension showed broad featureless absorbance in the visible wavelength region. The reaction of soil material with Cr(III) could be followed by observing the change of absorbance intensity of the hexavalent Cr band, which is the oxidation reaction product. Manganese oxides were shown to be very important as reactive surfaces in the soils.