Cationic Polyacrylamide as Dewatering Agent - CHINAFLOC
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Cationic Polyacrylamide as Dewatering Agent
2015-02-09 10:44:06

In the coal washing

The cationic polyacrylamide can be used as the slurry precipitation agent in the coal washing process. The coal washing waste water contains a certain amount of the hydrocarbon material; the unorganized emissions will pollute the soil and the groundwater. The coal washing slurry comes from the treatment of the sewage in the production, to deal with this sludge; the cationic polyacrylamide is strongly required in the treatment.

The influence of the sludge dehydration effect mainly depends on the roles of the flocculant.

The flocculant agent, on one hand, can make the sludge particle bridge and flocculate, which makes the sludge easy to be dehydrated, on the other hand, it also makes the sludge increase the viscosity which makes the mud cake more elastic, that will hinder the further dewatering effect to the sludge cake.

For the dosage of the polyacrylamide in the treatment of the coal slurry, it must be appropriate in order to effectively play its role in the flocculation effect. The appropriate dosage amount could be determined by the experiments based on the chosen process of the slime water treatment and the coal slurry property.

The less amount of the dosage will result in the slower speed of the coal slime sedimentation process, the concentrate overflow is easily exceed the standard, and can not ensure the required water circulation index, so that, the quality of the coal washing products is difficult to be stably controlled. 

The exceeded amount of the dosage, although this can accelerate the sedimentation rate of the coal slime, can easily cause the thickening underflow concentration to be too high. Generally, the concentration of the concentrated underflow is requirement at 500 gl, which can meet the pressing process requirement. The exceeded dosage of the polyacrylamide sometimes makes the concentration of the concentrated underflow at more than 700 gl, furthermore, the content of the polyacrylamide in the underflow is increased, that will make bad influence to the transportation of the underflow and the filtration production, the coal cake will not be easily fall off when unloading in the filter pressing process, which increases the labor intensity of the operators and reduces the working efficiency. At the same time, that also causes unnecessary waste of the polyacrylamide and increases the cost of the production.

Therefore, the appropriate use of the polyacrylamide can not only improve the flocculating effect and the treatment efficiency of the coal slurry, but also play an very important role in reducing the cost of the coal washing, in improving the working efficiency and in ensuring the production quality.

The cationic polyacrylamide can quickly form a larger floc particle in the slurry which will facilitate the separation of the sludge and the water. The shelf life of the cationic polyacrylamide is two years. Beyond this period, there is a risk of the failures. There are two aspects to determine the polyacrylamide failture, one is the decrease of the viscosity, the other is the variation of the flocculation effect.

In the treatment of the municipal sewage and industrial waste water.

The municipal sewage and the industrial waste water is usually treated by the activated sludge method processing, the biochemical sludge is often of a strong hydrophilic colloid with high organic content which is very difficult to be dehydrated.

According to the practical sludge properties, the corresponding cationic polyacrylamide can be chosen. The appropriate and suitable cationic polyacrylamide can effectively do help the process of the sludge gravity dehydration before the sludge getting into the filter press. During the dehydration, it can promote the formation of larger flocs, can prevent the flocs from being stuck onto the cloth, and can keep the flocs from loosing during the pressing process. With less dosage, the cationic polyacrylamie can achieve the high dewatering efficiency, and can meet the cake moisture content requirements below 80%.

The functional principle of the sludge dehydration by the polyacrylamide:

When the flocculant compounding aqueous solution is added into the waste water, it will produce the compression of the electric double layer, this electric double layer can make the suspending particles in the waste water loose the stability, the colloidal matter particles then become larger by the mutual cohesion and form the flocs and the alum. After getting to a certain volume, the flocs will deposit from the aqueous solution under the influence of the gravity, so as to remove a large amount of the suspending solids in the waste water, thereby, it greatly improves the dewatering effect. At the same time, it also reduce the water content after the dehydration process and then improve the working efficiency.

1. The flocculant used in the sludge dewatering process is mostly the polyacrylamide, which is divided into the anionic polyacrylamide and the cationic polyacrylamide.

2. In the sludge, the working principle of the polyacrymide in the dewatering is to neutralize the ions, to absorb the particles and to bridge the particles, flocculate the small granular sludge particles into the larger precipitation, and then separate the sludge and the water in the centrifuge or in the crawler machines.  

The cationic polyacrylamide as the flocculant is widely used in the purification of the drinking water and the treatment of the domestic sewage, in the purification of the industrial water and the industrial waste water, in the purification of the oil drilling fluid, in the treatment and the purification of the waste water of the paper making, the dyeing, the metallurgy, the coal washing and the leather industries. It can achieve the satisfied treatment result efficiently and at the same time reduce the production cost to the industries.