Question

discuss and describe the particle electrical charge theory with emphasis on electrical double layer theory and its significance during the design of water treatment coagulation unit?

Answer 1

Electrical Double Layer

Although individual hydrophobic colloids have an electrical charge, a colloidal dispersion does not have a net electrical charge. The diffuse layer in a colloidal dispersion contains a quantity of counter ions sufficient to balance the electrical charge on the particle. The charge distribution in the diffuse layer of a negatively charged colloid can be represented by the curve ABCD in the figure. The ions involved in this electroneutrality are arranged in such a way as to constitute what is called the electrical double layer.

Net repulsion force, which may be considered as energy barrier must be overcome before aggregation occurs. The magnitude of energy barrier depends on (1) charge on the particle, and (2) ionic composition of water.

Destabilization of Colloidal Dispersion

Particle destabilization can be achieved by four mechanisms:

• Change characteristics of medium-Compression of the double layer.

• Change characteristics of colloid particles-Adsorption and charge neutralization.

• Provide bridges-
  1. Enmeshment in a precipitate.
  2. Adsorption and interparticle bridging.