THE SEPARATION OF CLAY MINERAL FRACTIONS WITH L INEAR HEAVY L IQUID DENSITY GRADIENT COLUMNS

ABSTRACT: Because of increased interest in mineralogical nalysis of soils a rapid, generally applicable method to separate clay minerals is needed, and such a method is described here. The technique is a modification of the heavy liquid density gradient centrifugation method which is commonly applied in mineralogical practice. Modifica-tions are: (1) The use of suitable surface active agents to overcome the flocculation problem. (2) The use of the ultra centrifuge at about 33,000 g to hasten sedimentation. (3) The use of a linear density gradient which supplies in addition a quick identi-fication of the mineral composition. Preliminary experiments, evaluating different variables (e.g. cation form, ultra-sonic treatment, influence of surfactant), reveal the scope and limitations of the procedure presented. Clay minerals of different density can be separated. However, if the clay minerals of a mixture have overlapping densities, or if they contain a series of mixed-layer minerals, only a broad fractionation is possible. This is shown by X-ray diffraction and electron microscope studies of isolated zones (or parts of them) which develop in the centrifuged ensity gradient columns containing various pre-treated natural clays or clay mixtures