Company news about What is the difference of coagulant and flocculant

What is the difference of coagulant and flocculant

2026-01-26

What is the difference of coagulant and flocculant

The core difference between coagulants and flocculants lies in their working principles, molecular characteristics, and the stages of particle aggregation they target in water treatment. Here is a detailed comparison:

Aspect	Coagulants	Flocculants
Core Definition	Substances that neutralize the negative charge of colloidal particles in water, destabilizing them and making them collide and aggregate into small, dense flocs.	Substances that use long molecular chains to adsorb and bridge small destabilized flocs, forming large, loose, and settleable floccules.
Molecular Characteristic	Mostly inorganic salts with small molecular weights; no long molecular chains.	Mostly organic polymers with long, branched molecular chains; strong bridging ability.
Representative Examples	Inorganic salts: Aluminum sulfate, ferric chloride, polyaluminum chloride (PAC), ferric sulfate.	Organic polymers: Polyacrylamide (PAM), cationic polyacrylamide (CPAM), anionic polyacrylamide (APAM).
Working Mechanism	1. Charge neutralization: Eliminate the repulsive force between negatively charged colloids. 2. Compression of double electric layer: Reduce the thickness of the colloid's electric double layer to promote particle collision.	1. Bridging adsorption: Long molecular chains adsorb multiple small flocs at the same time. 2. Net catching: Form a polymer network to trap small particles and suspended matter.
Floc Characteristics	Produce small, dense, and compact flocs; fast initial aggregation speed.	Produce large, loose, and porous flocs; easy to settle or filter.
Usage Stage	Used in the primary stage of water treatment (coagulation stage) to break the stability of colloids.	Used in the secondary stage (flocculation stage), usually added after coagulants to enhance floc growth.
Dosage Requirement	Relatively high dosage is needed to achieve charge neutralization.	Very low dosage is sufficient due to the strong bridging effect of long chains.

Supplementary Key Points

Synergistic Application

In actual water treatment (e.g., wastewater decolorization, turbidity removal), coagulants and flocculants are often used together. For example, PAC (coagulant) is first added to destabilize colloidal particles, then a small amount of PAM (flocculant) is added to form large flocs, which improves sedimentation efficiency significantly.
Special Case: Inorganic Polymer Flocculants

Some inorganic polymers (e.g., polyferric sulfate) have both coagulation and weak flocculation properties, but their bridging ability is far weaker than organic polymer flocculants.

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