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You can't help but know the flocculation theory and difference of flocculant (mixed) flocculant!

来源:环保工程师 作者: 阅读:300 网友评论0 Updated: 2019-12-11 09:48 Source: engineer of environmental protection: Reading: 300 2010 0 comments

Nowadays, the application of flocculent (mixed) coagulant is very common in water treatment, but many colleagues generally don't know or understand the action mechanism of flocculent. Mechanism of coagulant——Coagulation is a general term for coagulation and flocculation. Here we introduce the two mechanisms of action separately!


Coagulation: mainly refers to the process of colloid destabilization and formation of tiny aggregates. The mechanism of condensation generally includes four explanations: compression double electron layer, adsorption-electrical neutralization, adsorption bridging, and net capture-scrolling.

1. Compression electric double layer

According to the DLVO theory, when an electrolyte containing positively charged ions with a high valence state is added, the high valence positive ions enter the surface of the colloidal particles through electrostatic attraction, replacing the original low-priced positive ions. In this way, the electric double layer remains electrically neutral, but the positive ions However, the number of particles decreases, that is, the thickness of the electric double layer becomes thinner, and the ξ potential on the sliding surface of the colloidal particles decreases.

When the ξ potential drops to 0, it is called an isoelectric state, at which time the repulsive barrier disappears completely.

The ξ potential drops to a certain value so that the potential barrier Emax = 0 on the total potential energy curve of the colloidal particles, and the colloidal particles aggregate, and the ξ potential at this time is called the critical potential ξk.

2. Adsorption-electrical neutralization

The colloidal particles are adsorbed on the surface with different ions, colloidal particles or polymers with different charges, thereby neutralizing the partial charge of the colloidal particles themselves, reducing the electrostatic attraction between the colloidal particles, and making the colloidal particles easier to settle. Driving forces include electrostatic attraction, hydrogen bonding, coordination bonds, and van der Waals forces. It can explain the re-stabilization of colloidal particles in water treatment.

3. Adsorption bridging

In the dispersion system, the German colloidal particles are bridged and connected by adsorption of organic matter or inorganic high-molecular matter, and aggregate into large aggregates to destabilize and settle. Divided into

Long chain polymer bridge; 2. Three types of short distance bridge:

①. The bridging between colloidal particles and uncharged high-molecular substances involves adsorption forces such as van der Waals forces, hydrogen bonds, and coordination bonds. ②. The bridging between the colloidal particles and the high-molecular substances with different charges, in addition to van der Waals' forces, hydrogen bonds, and coordination bonds, also has electrical neutralization. ③. The colloidal particles and the high-molecular-weight substances with the same number of bridges are formed, and the "electrostatic spot" acts

4. Net capture-sweeping effect

The coagulants such as aluminum salts and iron salts added to the water are hydrolyzed to form a large amount of three-dimensional three-dimensional structure of the hydrated metal oxides. When these hydrated metal oxides shrink and settle, the colloidal particles in the water are like a sieve. And the suspended particles were swept down to capture the volume. Net capture-scrolling is mainly a mechanical action.


Flocculation: Flocculation mainly refers to the process of destabilizing colloids or small suspended solids to aggregate into large flocs.

1. Perikinetic flocculation:

Collision of colloidal particles caused by Brownian motion. Brownian motion gradually weakens as the particle size increases. When the particle size increases to a certain size, Brownian motion no longer plays a role.

2. Orthokinetic flocculation:

Colloidal particles collide due to external force (stirring). Colloidal particles move in a certain direction under the action of external forces. Due to the speed difference between different colloidal particles, the collision aggregation of the particles is completed accordingly.


Coagulation: It has both agglomeration (colloid destabilization) and flocculation (destabilized colloid or tiny suspended matter aggregates). It is a general term for the two processes of coagulation and flocculation. It is the aggregation process of colloidal particles and tiny suspended matter in water.

In other words, "coagulation" includes the entire process from raw water administration to water mixing, drug reaction (destabilization, flocculation) to the formation of large particle floes. Flocculation refers to the stage of forming large floes from the formation of small floes after colloidal particles are destabilized.

4, the distinction between coagulation and flocculation

The definition of the name of flocculant in China is very clear, and it is distinguished by the role (colloid destabilization or SS aggregation) that is mainly played in practical applications. The colloidal destabilizer is called coagulant, the destabilized colloid or small suspended matter is called flocculant, and the colloidal destabilizer is also called coagulant.

For example, PAC, PFS and other inorganic polymer flocculants generally play a colloidal destabilizing role in coagulation and sedimentation. Therefore, in coagulation and sedimentation, PAC and PFS should be called coagulants; while sludge flocculation is not good, dosing PAC, PFS, etc. increase flocculation, and use its bridging function to flocculate disintegrated sludge together, and play a flocculation role, so in this case it is called flocculant by definition; PAM has both charge neutralization It has the effect of flocculation and flocculation, so it generally becomes a coagulant.

The name of the flocculant abroad is not as clear as the domestic one, and it is generally called a flocculant. The actual water treatment personnel in the country are generally called flocculants, and there is no special distinction, and it is not necessary to distinguish too clearly. The name is just a title, and there is nothing wrong with it being so conventional. For example, even if I call PAC XXX, it still plays its role! So don't care about these details!

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