The removal of magnetic materials from surface soils. A solid state 13C CP-MAS n.m.r. study [soil organic matter determination]
1994
Skjemstad, J.O. | Taylor, J.A. (Commonwealth Scientific and Industrial Research Organisation, Glen Osmond (Australia). Div. of Soils) | Oades, J.M. (Cooperative Research Centre for Soil and Land Management, Glen Osmond (Australia)) | Clarke, P. (Waite Agricultural Research Inst., Glen Osmond (Australia). Dept. of Soil Science) | Newman, R.H. (Industrial Research Ltd, Lower Hutt (New Zealand))
Five surface soils of differing chemical and mineralogical compositions were subjected to either a sequence of dithionite-citrate extractions in which the soil: citrate ratio was varied or to a sequence of 1 percent or 2 percent HF extractions. The 2 percent HF treatment resulted in the removal of the highest Fe concentrations (79-95 percent) while the dithionite-citrate extractions were less effective in removing Fe from the same soils (18-75 percent). The Fe remaining after HF treatment appeared to be mostly associated with ilmenite crystals which were only slowly attacked by the dilute acid. During the 2 percent HF treatments, some organic carbon was lost (8-17 percent), but this loss had no significant effect on the organic chemistry of the samples as determined by CP-MAS 13C n.m.r. spectroscopy. The total 13C signal recovered after the various treatments was found to be correlated, in order of decreasing significance, with the mineral fraction present in the sample, the organic carbon-Fe ratio and the mass magnetic susceptibility. Prior to solid state CP-MAS 13C n.m.r. analysis, the recommended pretreatment for surface soils containing Fe involves a sequence of 2 percent HF extractions in the order 5x1 h, 2x16 h and 1x64 h.
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