The purifying agent polyaluminum chloride pac water purification principles and role

 

Compressing the electric double layer: the electrical double layer of the micelle structure and determines the maximum concentration in the micelle surface at the counter-ion, with the greater the distance outwardly of the micelle surface counter ion concentration lower, eventually equal to the concentration of ions in solution . When adding electrolyte to the solution, so that the concentration of ions in the solution is increased, the reduced thickness of the diffusion layer. When two micelle mutual proximity, since the reduced thickness of the diffusion layer, ξ potential decreased, therefore reduces the force that they are mutually exclusive, that is, a high concentration of ions in the solution gel repulsion between lower than the ion concentration to be smaller. The phase composition of the suction between the colloidal particles from water, but because of the diffusion layer thinning, when they collided with the distance is reduced, so that the suction between big. Dominated by the repulsive force becomes visible exclusion and attract synergies suction main (the exclusion potential disappeared), particles rapidly cohesion.

This mechanism can explain Harbour at the deposition phenomena, due to fresh water into the seawater, salts increase the ion concentration increased, freshwater entrainment micelle stability decreases, so easily deposited in the harbor at clays and other colloidal particles.
According to this mechanism, when the PAC solution plus electrolyte exceed occurred cohesion critical coagulation concentration, there will not be more over-the counter ions into the diffusion layer is not possible to re-stabilize the colloidal particles changes sign leaving colloidal situation. Such a mechanism is by simple electrostatic phenomena.

The electrolyte destabilization of colloidal particles, but it did not consider the role of other properties in the process of destabilization, such as adsorption, and therefore can not explain the complex destabilization phenomena, such as aluminum salts of trivalent iron salts as coagulants excessive dosage, cohesion effects worse, and even re-stabilize; polymer or organic polymer Another example is with the colloidal particles with the same power numbers may have good cohesion effect: isoelectric state should have the best effect of cohesion, but often ξ potential is greater than zero in the production practice coagulation effect was best ......

Actually coagulant dosing aqueous colloidal destabilization phenomena related to the three aspects of the interaction of colloidal particles and coagulants, particles with an aqueous solution, coagulant and aqueous solution, is a comprehensive phenomenon.