Methods to Effect Coagulation

Coagulation (or flocculation) is the precipitation of dispersed colloidal particles into a larger mass.

\[\text{Flocculation value }\propto\frac{1}{\text{Coagulating power}}\]

Hardy-Schulze Rule:

• Higher the valency of the active (oppositely charged) ion, greater its power to precipitate (coagulate) the sol
• Order of coagulating power: Al³⁺ > Ba²⁺ > Na⁺ or PO₄³⁻ > SO₄²⁻ > Cl⁻

Other Methods of Coagulation:

• Adding electrolyte — the oppositely charged ions of the electrolyte neutralise the charge on colloidal particles
• Electrophoresis — particles migrate to electrode and lose charge
• Boiling — increases collisions
• Mixing two oppositely charged sols — mutual coagulation

Protective colloids prevent coagulation — do not confuse them with lyophilic or lyophobic colloids.