Flocculation of clay suspensions separated from soils of different soil type

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Abstract
The critical coagulation concentration (c.c.c.) was measured for Na-saturated clay suspensions prepared from selected soils including Gray Lowland Soils, Yellow Soils, Red Soils, and Dark Red Soils by the addition of NaCl solution. A clear difference in c.c.c. was observed between the clays of Gray Lowland Soils and those of Red and Yellow Soils (Yellow Soils, Red Soils, and Dark Red Soils). The c.c.c. values for Gray Lowland Soils exceeded 2 me/dm3, whereas those for Red and Yellow Soils were for the most part less than 2 me/dm3. This difference was ascribed to differences in surface charge density. The value of 1 μe/m2 formed the boundary between the two groups. In each of the Gray Lowland Soils and Red and Yellow Soils, the clays containing smectite exhibited higher c.c.c. values than did the other clays.