Practical applications of the zeta potential

If the zeta potential is an indicator of the electrical state of the double layer then when the value of approaches zero the sols should become unstable, and this should lead to clarification. This has often been demonstrated where inorganic electrolytes have been used to lower the zeta potential of industrial 

Riddick has commented that the zeta potential is the most significant controlling factor in the achievement of coagulation, although it should not be regarded as the only parameter to be adjusted to produce the desired clarification. His remarks are pertinent to water clarification. 

La Mer has suggested that the term coagulation should be restricted to the chemical destabilization of sols whereby electrolytes are added to a sol so as to reduce the charge on the particles and allow close approach and aggregation. This is also adopted by the industry concerned with water treatment. A primary coagulant then becomes the salt which is added to achieve the effect. 

The useful practical effect consequent upon the addition of indifferent electrolytes is now discussed. 

It is now readily explained why primary coagulation is achieved when a sol is treated with either lime/alum (when net negatively charged sols coagulate) or with phosphates (when net positively charged sols coagulate). 

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