Dr. Dmitri Kopeliovich
Coagulation is the destabilization of Colloids by neutralizing the electric charge of the dispersed phase particles, which results in aggregation of the colloidal particles.
Aggregation is a formation of groups of particles (aggregates) bonded to each other by van der Waals or other intermolecular forces.
Aggregation usually refers to solid particles.
If a coagulation of a liquid or gaseous dispersed phase occurs the term coalescence instead of aggregation is used. Coalescence is characterized by disappearance of the boundary between the particles resulting in the reduction of the interfacial area.
In a stable colloid system the dispersed particles are electrically (commonly negatively) charged. Two charged particles repeal each other preventing collision and aggregation.
When the charges are neutralized the particles may collide and bond to each other.
A coagulation process may be subdivided in two stages: electric neutralization of the dispersed phase and aggregation of the destabilized particles.
The following methods are used for the destabilization of the colloidal particles by neutralization:
Aggregation of the dispersed particles of a destabilized colloidal system is determined by the frequency of particle-particle collisions and the collision energy, which is required for the bond formation.
There are two types of aggregation according to the force driving the process:
The term coagulation is often interchangeably used with the term flocculation. However the coagulation and flocculation processes are similar but not the same.
Flocculation is the aggregation of a colloid by polymer molecules (flocculant) bridging between the colloidal particles and forming large fragile network structures (flocs), which may be easily removed by sedimentation/flotation and filtering.