When is use of a flocculant justified in terms of overall process economy?
- when it results in process improvement, such as producing a clear liquor for electrolysis, precipitation, ion exchange, or solvent extraction;
- when it results in satisfying requirements of pollution abatement ordinances;
- when it results In increased recovery of values that would otherwise be lost; or
- when it results in considerable savings in capital expenditure due to use of smaller equipment.
Flocculation is a process wherein individual particles are united into more or less tightly bound agglomerates or flocs, thereby increasing effective particle size of solids suspended in a liquid.
Degree of flocculation of a suspension of finely divided solids in a liquid is controlled by a combination of probability of collision between particles and probability of adhesion after the collision has occurred. Probability of collision can be increased commercially through use of a paddle-type flocculator, combination flocculator, and clarifier or flocculating-type feedwell. Probability of adhesion usually can be increased by addition of a reagent known as a flocculant.
Reagents act as flocculants through one or a combination of three possible mechanisms. The first is electrolytic neutralization of intermolecular repulsive force due to Zeta potential. This neutralization enables Van der Waal’s cohesive