Density separation of clay minerals

Graduation date: 1971Illite, chlorite, montmorillonite and kaolinite, as well as\ud natural marine sediments and mixtures of the standards were subjected\ud to density separation by centrifugation in a linear heavy-liquid\ud gradient.\ud The density layers yielded by centrifugation were recovered\ud and analyzed by X-ray diffraction. Separates were not monomineralic\ud but rather were polymineralic usually with minerals of invarient\ud density, such as quartz, in more than one layer. This incomplete\ud separation is attributed to insufficient centrifugation time. The\ud X-ray character of minerals of variable density changes in such a\ud way as to suggest increased crystallinity with depth in the density\ud gradient.\ud Although several samples were known to contain montmorillonite,\ud none of the density layers showed X-ray evidence of this material. The anomalous behavior of montmorillonite is attributed\ud to its imbibing of the polar organic chemicals used as surfactants\ud into its expandable crystal structure to produce an extremely large\ud basal spacing. This problem can be overcome in some cases by\ud heating the clay to 110°C for 8 hours, but in other cases this had\ud little or no effect in collapsing the expanded structure.\ud Even though the project was not a total success, the method\ud holds promise, providing the duration and intensity of the centrifugation\ud is increased and complete purging of polar organic molecules\ud from expandable layered clays can be accomplished