Principle and Classification of Flocculants

Effect

The effect of adding flocculant is mainly used to reduce or eliminate the sedimentation stability and polymerization stability of the dispersed particles in water, make the dispersed particles agglomerate, flocculate and remove the suspended solids, and strengthen the solid-liquid separation.

Principle

When the size of suspended particles in water is small enough, the energy of Brownian motion is enough to prevent gravity from settling. Moreover, the surface of micro particles usually carries the same negative charge, and the repulsive particles between the same charges are not easy to merge and become larger, which increases the stability of the suspension. The flocculant is an organic polymer with a specific charge. The flocculation process is to add positive charge to make the particles “Unstability”. Through collision, the particles attract each other, and the combination becomes larger, so as to strengthen the precipitation effect of particles.

Classification 

1. The most commonly used inorganic polymer flocculants are PAC (polyaluminum chloride) and PFS (polyferric sulfate); they are easy to tolerate in water and have certain corrosivity. It can be added in the form of solution or granule.
2. PAM (polyacrylamide) is the most commonly used organic polymer flocculant; it is soluble in water, but the dissolution rate is very slow. Generally, it is prepared into solution before adding. It can be divided into anion type and cation type. Anionic flocculant is generally used for sewage flocculant, and cationic type is generally used for sludge dewatering. PAM is easy to absorb water and deliquesce into blocks, and the storage place must be dry.