What is the difference between coagulant, flocculant and coagulant aid?

Coagulant, flocculant and coagulant aid are widely used in water treatment technology, such as coagulation and flocculation, polyaluminium chloride and polyacrylamide. So for the three in the use of management process, what specific safety precautions need to pay attention to?

What is flocculant?

The “small alum ” formed in the process of coagulation can form a process of particles with larger flocs through adsorption, coiling and bridging.

Coagulant: It is the general term of coagulation and flocculation technology. It is the aggregation process of colloidal nanoparticles and micro suspended solids in water.

What is coagulant aid?

After adding coagulant, the colloids in water lose their working stability, and the colloidal particles develop and agglomerate with each other.

That is, “coagulation” includes the whole process from raw water to mixed water, drug reaction (de stabilization, flocculation) to the formation of large particle flocculant. Flocculation refers to the stage from the formation of small flocs to large flocs after colloidal particles are stabilized. Therefore, flocculation is only one step of coagulation!

Polyacrylamide flocculation

So, what are polyaluminum chloride and polyacrylamide?


Polyaluminum chloride (PAC) is also called basic aluminum chloride or hydroxyl aluminum chloride. Through it or its hydrolytic reaction products, the colloid in sewage or sludge can rapidly develop into a precipitate, which is convenient for separation.

The molecular formula of PAC is [Al2 (OH) nCl6-n] m, where n is any integer from 1 to 5, M is the degree of polymerization, that is, the number of chain links, and the value of M is not more than 10.

PAC condenses and in which the ratio of Oh to Al (n value size) is closely related, usually expressed by alkalinity B = [OH] / (3 [al]) X100%. 40-60% B, a suitable range of pH 5-9.


Polyacrylamide (PAM), commonly known as flocculant or coagulant, coagulant belongs to. PAM with average molecular weight from several thousands to tens of millions, which has several functional groups and ionizes in water, is the most suitable polymer electrolyte.

According to its properties in solution, it can be divided into anionic polyacrylamide, cationic polyacrylamide and nonionic group of polyacrylamide.

PAM appearance is white, as a powder, soluble in water, almost no need to be soluble in benzene, ether, esters, acetone and other organic solvents, polypropylene through amide aqueous solution form is almost transparent viscous liquid.

Solid PAM has hygroscopicity, hygroscopicity increases with the increase of ionic degree, PAM has good thermal stability; it has good stability when heated to 100 ℃, but it is easy to decompose above 150 ℃, and nitrogen is used in the production.

It is insoluble in water due to imidization. The density is 1.302 mg / L (23 ℃). The glass transition temperature is 153 ℃, and the effect of PAM on the stress is shown in the following table, which shows the influence of non Newtonian on the fluidity.


Cationic PAM and anionic PAM are suitable for sewage or sludge with negative charge and positive charge respectively. The activated sludge produced by biochemical method has negative charge, so Cationic PAM should be used for sewage or sludge with positive charge.

Such as iron and steel plant, electroplating plant, metallurgy, coal washing and dust removal. The non-ionic type has a good effect on cations and anions, but the unit price is expensive, which makes the treatment cost higher. In addition, the reaction conditions of the two drugs and the requirements of being administered.

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