Coagulants and flocculants

Reagents

We are accustomed to classified in three categories the water compounds: suspended solids, colloidal particles (less than 1 micron) and dissolved substances (less than several nanometers). 

The coagulation-flocculation processes facilitate the removal of SS and colloidal particles. It’s used in the final stage of solids-liquids separation: settling, flotation or filtration.

Coagulation is the destabilization of colloidal particles brought about by the addition of a chemical reagent called as coagulant.

Flocculation is the agglomeration of destabilized particles into microfloc and after into bulky floccules which can be settled called floc. The addition of another reagent called flocculant or a flocculant aid may promote the formation of the floc.

The factors, which can promote the coagulation-flocculation, are the velocity gradient, the time, and the pH. The time and the velocity gradient are important to increase the probability of the particles to come together. Moreover the pH is a prominent factor in the removal of colloids.