Understanding of the Coagulation Mechanism

Understanding of the coagulation mechanism

With the deepening of people's understanding of nature, the understanding of coagulation mechanism has gradually changed. is generally believed that it is related to the type of coagulant, dosage, nature of colloidal particles and pH value of solution, etc. At present, there are the following situations:　　

1. Electrical neutralization:

The adsorption electric neutralization effect refers to the strong adsorption of particles on the surface of heterogeneous ions orloidal particles, which makes part of the charge neutralized and reduces the electrostatic repulsion, so it is easy to adsorb other particles and approach each other, mainly manifested as attraction. However, when Na   and dodecyl ammonium ion (C12H25NH3 ) remove the turbidity of negatively charged iodine silver solution it is found that the ability of the same valence organic amine ion to destabilize is much greater than that of Na , and excessive addition of Na ions will not cause the-stabilization of colloidal particles. When the dosage of aluminum salt and iron salt is high, it can cause re-stabilization phenomenon and bring about charge mutation This phenomenon is more suitable to be explained by the mechanism of electrical neutralization.　　

2. Adsorption bridging principle:

The adsorption bridging mechanism mainly to the adsorption and bridging of high molecular polymers and colloidal particles. Organic high molecular flocculant is linear structure, when high molecular polymer and colloidal particles, the group and colloidal particle surface produce special reactions and adsorb each other, and the rest part other than the group extends in the solution, and adsorbs with surface with empty position, which plays a role of bridge connection. When the colloidal particles are few, the above polymer is not easy to adhere to the second colloidal and can not play a bridge role, so that the colloidal particle is in a stable state. When the dosage of high molecular flocculant is too large, the colidal particles that have been bridged and flocculated may fall off from the surface of another colloidal particle and return to the original colloidal particle surface due to longterm violent stirring, resulting in a re-stable state. This mechanism can explain the phenomenon that the flocculation effect of anionic or nonionic high molecular flocculant is.

3. Rolling and sweeping principle

When metal salts (such as aluminum sulfate or ferric chloride) or metal oxides and hydroxides (such lime) are used as coagulants, when their dosage is large enough to quickly form hydroxide precipitates (such as Al(OH)3, Fe(OH3 or carbonate precipitates (such as CaCO3), colloidal particles in water can be captured by precipitates during the settling process. When the precipitate is charged, the settling rate can be accelerated due to the presence of negatively charged ions in the solution. Moreover, the colloidal particles themselves can be used as the core of theseitates, so the more colloidal particles, the less the amount of metal coagulant added.The above three mechanisms do not exist alone and isolated in water treatment, may exist simultaneously, but in some specific cases, one phenomenon is the main one.