The chemistry of colloidal clay suspensions is not completely understood, primarily because
fairly complex physical and chemical processes are involved. Clay particles are extremely small;
some are even smaller than bacteria. Therefore, they will not settle readily, even in still water. The small size of these particles means that they have an extremely high surface area relative to the volume of the particle. A clay particle can be envisioned as a flat plate cov-ered with a negative electrical charge that attracts the positive ions in water. Positive ions that are immediately adjacent to the clay particle are said to be “adsorbed,” while others that are farther away are less strongly attracted. In water, negatively charged clay particles are surrounded by clouds of positively charged ions. When these particles, surrounded by their ion
clouds, come close to each other they are repulsed, much the same way similar poles of two magnets will repel each other (Fig. 1). The cumulative effect of the repulsion of a huge number of small particles prevents their aggregation into larger, heavier particles that would settle more readily. Taken together then, the extremely small size of clay particles and the surface
electrical charge explain how particles remain in suspension.