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High Gradient Magnetic Separation of Iron Oxides and other Magnetic Minerals from Soil Clays¹

ABSTRACT

A filter of ferromagnetic stainless steel wool, placed in a strong magnetic field, provides the magnetic field gradients necessary to trap weakly magnetic clay size particles from a flowing suspension.

Of the total dithionite-citrate-bicarbonate extractable Fe₂O₃ in the 2–0.2 µm size fraction of six soils, 70 to 94% was recovered in the magnetic fraction which consisted of 1.6 to 27.7% free Fe₂O₃ by weight. For the <0.2 µm size fraction, 11 to 40% of the total free Fe₂O₃ in the size fraction was recovered in the magnetic fraction which contained 2.8 to 53.1% free Fe₂O₃ by weight. Larger particles are captured more efficiently because of their greater overall magnetic attraction. Goethite, hematite, lepidocrocite, and anatase are concentrated in the magnetic fraction, while quartz is concentrated in the tailings. Chlorite is effectively concentrated in the magnetic fraction. Although mica, vermiculite, and smectite are often found in both the tailings and the magnetic fraction, vermiculite and mica appear to be more concentrated in the magnetic fraction. The concentration effect on kaolinite appears to be dependent on the particle size and rate of flow through the magnetic filter.

¹ Contribution from the Texas Agric. Exp. Stn., College Station, Texas. Invitational paper presented before Div. S-9 symposium "New Techniques in Soil Mineralogical Investigations." Soil Sci. Soc. Am., Los Angeles, Calif. 14 Nov. 1977.

² Formerly Graduate Assistant (Present Address: Institut fur Bodenkunde, der Technischen Universitat Munchen, 8050 Freising-Weihenstephan, West Germany) and Professor of Soil Mineralogy, Department of Soil and Crop Sciences, Texas A&M University, respectively.

Received for publication March 14, 1978. Accepted for publication March 19, 1979.