FLOCCULATION is used to describe the action of polymeric materials which form bridges between individual particles. Bridging occurs when segments of a polymer chain adsorb on different particles and help particles aggregate. Flocculants carry active groups with a charge which will counterbalance the charge of the particles. Flocculants adsorb on particles and cause destabilization either by bridging or charge neutralization.
An anionic flocculant will usually react against a positively charged suspension (positive zeta potential). That is the case of salts and metallic hydroxides.
A cationic flocculant will react against a negatively charged suspension (negative zeta potential) like silica or organic substances.
However the rule is not general. For example, anionic flocculants agglomerate clays which are electronegative.
Three groups of flocculants are currently used