Contribution of Ferrimagnetic Minerals to Oxalate- and Dithionite-Extractable Iron
- P. Fine and
- M. J. Singer
Magnetic removal of magnetite particles to minimize Fe contribution from a well crystallized iron oxide to the acid ammonium oxalate (AAO) extractable iron (Feo) has been recommended as a pretreatment in chronosequence studies. Samples from two soil chronosequences in California were examined to determine the efficacy of using a hand magnet to remove magnetic particles from soils, and sediments. Magnetic susceptibility (χ) was used as a measure of treatment effect. Samples from 74 horizons retained 74 ± 20% of their original (χ) after treatment with a small hand-held magnet. Clay and silt-sized ferrimagnetic particles, which were responsible for 4 to 91% of the soils' χ, were not removed from the samples. Also sand-sized ferrimagnetics could not be fully removed. Ferrimagnetics were more successfully removed from beach sand deposits. These retained only 14 ± 7% of their χ value. The AAO extraction of 31 magnetically depleted soil samples from typical soil horizons lost an additional 31 to 95% of their residual susceptibility, mostly as maghemite. The retention of a greater fraction of the ferrimagnetics within the soils, and their contribution to the Feo, proved the magnetic cleaning technique to be neither quantitative nor systematic. Magnetite was more resistant than maghemite to AAO. Magnetite was also fully resistant to the citrate-bicarbonate-dithionite (CBD) extractant whereas authigenic soil maghemite was completely dissolved in CBD. Magnetic monitoring of AAO- and CBD-treated soils offers some insight into the nature and distribution of the ferrimagnetics in the soil profile.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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