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.