Colloid Dispersion or Flocculation

Dispersion-flocculation processes are generally controlled by double layer swelling, adsorbed hydrolyzed Fe or Al, and chemical bridging (tactoid formation) (Stumm and O Melia, 1968). Once dispersed, clay colloids are kept dispersed by repulsive double layers (Van Olphen, 1971). The force of repulsion is related to the thickness of the double layer (see Chapter 4). This dimension is represented by the ions concentrated near the oppositely charged colloid surface. Any colloid that has a net negative or a net positive charge repulses a like-charged colloid. 

Note that the inverse of k in Equation 9.2 represents the thickness of a single double layer. 

The influence of counterion valence on the double layer thickness is described by the valency rule of Schulze and Hardy. It basically predicts that if a monovalent counterion is changed to a divalent counterion, the thickness of the double layer decreases by half and if the divalent counterion is changed to a trivalent ion, the thickness of the double layer decreases by three-quarters (Fig. 9.2). The relative amounts of counterions required to induce flocculation are 100 for a monovalent, 2 for a divalent, and 0.04 for a trivalent ion. 

At a constant ionic solution composition, the component )f0 is directly related to Rf, However, t0 of variable charge colloid surfaces is also related to pH. This is 

The influence of pH on Vo °f a colloid can be demonstrated indirectly by quantifying the increase in CEC as a function of pH (Marsi and Evangelou, 1991a). This relationship is demonstrated by the equation (Uehara and Gillman, 1980) 

---