Separation of the clay fraction from a calcareous soil usually involves chemical pretreatments which could affect the separated clays. A technique based on separating the flocculated particles (flocs) of a sonified soil-water suspension was used on highly calcareous samples and a highly gypseous one collected from a limestone ridge in Egypt. The relative abundance of the clay minerals in flocs (identified by XRD and electron microscopy) was found to be identical to that of < 1 μm clay separated by sedimentation. The suspensions were prepared by washing the soils repeatedly with distilled water (about 2 1/g) until spontaneous peptization.
Washing removed both 'amorphous' silica and alumina as detected in the flocs. The composition of poorly-ordered aluminosilicates (SiO2/Al2O3) of the 1μm clays was heterogeneous whereas in the flocs it was homogeneous.
Fluoride reactivity of both clay separates and prepared mixtures of CaCO3 with palygorskite (the dominant clay mineral present) was also studied.