EVALUATION OF THE CLAY FRACTION IN SOME DANISH SOILS, MAKING USE OF HIGH-GRADIENT MAGNETIC SEPARATION (HGMS)

After removal of the 'free Fe-oxyhydroxides', a high-gradient magnetic separation (HGMS) procedure was used to separate the minerals of the clay fraction in soil samples from different horizons of two Alfisols, a Mollisol, an Ultisol and a Spodosol into a magnetic and a non-magnetic fraction. The magnetic fraction constituted 12-19% of the total clay fraction in the Alfisols, 28-35% in the Mollisol, 9-10% in the Ultisol and 11-16% in the Spodosol. X-Ray diffraction (XRD), Mossbauer spectroscopy and total elemental analysis (TEA) were used for the characterization of the different fractions. The CBD-treated magnetic clay contained mainly paramagnetic 2:1 layer silicate clay minerals, including hydroxy-interlayered clay minerals (HICM) high in Fe. The nonmagnetic clay was composed of diamagnetic minerals such as quartz, feldspars, gibbsite, kaolinite and the diamagnetic 2:1 layer silicate clay minerals.