Adsorption and Charge Neutralization

Some chemical species are capable of being adsorbed at the surface of colloidal particles. If the adsorbed species carry a charge opposite to that of the colloids, such adsorption causes a reduction of surface potential and a resulting destabilization of the colloidal particle. Reduction of surface charge by adsorption is a much different mechanism than reduction by double layer compression.

1. The sorbable species are capable of destabilizing colloids at much lower dosage than nonsorbable "double layer compressing" ions.
2. Destabilization by adsorption is stoichiometric. Thus, the required dosage of coagulant increases as the concentration of colloids increases.
3. It is possible to overdose a system with an adsorbable species and cause restabilization as a result of a reversal of charge on the colloidal particle.