In the process of concentration, dehydration and clarification of slime water, flocculant is used to make the fine particles in suspension form flocs and accelerate the sedimentation. There is an electric double layer on the surface of particles suspended in slime water, which forms a stable suspension system and hinders the settlement of slime. After adding flocculant, the suspension stability is destroyed by coagulation and flocculation. Flocculants include inorganic coagulant and organic polymer flocculant. Adding coagulant can compress the thickness of the electric double layer on the surface of the particles to produce condensation, which is called condensation. Adding organic polymer flocculant, with the help of its linear macromolecular polar groups, especially the role of hydrogen bonds, firmly adsorbed on the surface of the particles, forming a bridge between the particles, prompting the particles to aggregate into clusters, called flocculation. Common inorganic coagulants include ferric chloride, aluminum chloride, lime, sodium hydroxide and alum. Polyacrylamide is widely used as flocculant. The factors that affect the effect of flocculant are as follows

1. Hardness of slime water. When the content of calcium and magnesium ions in slime water is low, the flocculation effect is not good.

2. Coal slurry concentration and particle size composition. The dosage of flocculant is directly proportional to the total specific surface area of dispersed particles, so the effect of slime particle size decreasing and concentration increasing is the same. Not only the amount of flocculant increased, but also the structure of flocs was not as dense as that of coarse flocs.

3. Temperature of slime water. With the increase of temperature of slime water, the settling speed of flocs is accelerated.

4. Composition of slime. The adsorption capacity of flocculant molecules on the surface of coal and various minerals is different, and more flocculants are usually adsorbed on the surface of coal. Washing water containing a large amount of fine mud is difficult to clarify and settle, so coagulant and flocculant are often needed.

Coal slime water treatment mainly adopts classification, desliming, concentration, clarification, flotation, filtration, pressure filtration and other operations. Different combinations of operations constitute different slime water systems.