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Coal Washing Wastewater Treatment Process


Coal washing wastewater contains a lot of suspended solids, slime and silt, so it is also called slime water. The concentration of suspended solids in untreated slime water can reach more than 5000mg / L.

Due to the hydrophobicity of coal itself, some micro pulverized coal in the coal washing wastewater is particularly stable in the water. Some ultra-fine pulverized coal is suspended in the water and will not settle naturally for several months.

Characteristics of coal washing wastewater

Coal washing wastewater is a weakly alkaline colloidal system, which is characterized by a strong negative charge on the particle surface.

High concentration and CODcr; high content of fine particles; high viscosity; large specific resistance of sludge, poor filtration performance.

Treatment process

The coal washing water is first collected into the regulating tank. 

The sewage from the regulating pool is lifted by the pump, and a coagulant mixer is set on the pipeline behind the pump. Before and after the coagulant mixer, coagulant aids and coagulants are added respectively, and then it enters the purifier.

First, the clean coal is sorted out by the clean coal separation device, discharged by the equipment, and then separated by the Johnson dewatering screen to recover the clean coal

After the recovery of clean coal, the waste water is discharged from the top of the purifier through the processes of centrifugal separation, gravity separation, dynamic check filtration and sludge concentration, and the treated clear water is sent to the clean water tank for reuse or discharge. The concentrated coal sludge discharged from the bottom of the purifier is discharged to the coal sludge percolation drying tank or used after being dried by the drying equipment.

Lime coagulation

The method of lime polyacrylamide coagulation and sedimentation has a good effect on the treatment of coal washing wastewater, but the way of adding lime, the property of polyacrylamide and the order of adding agent have a certain effect on the treatment effect, especially the order of adding agent is different from the traditional order of adding agent.

When lime is wet added, the concentration of lime solution has an effect on the treatment effect.

When the lime dosage is fixed, the lower the concentration is, the faster the settling speed is, and the higher the separation rate of clean water is. However, the amount of clean water actually separated from the coal washing wastewater decreases slightly with the decrease of the lime concentration.

The settling speed increases with the decrease of the lime solution concentration, mainly because the decrease of the lime solution concentration leads to the increase of the volume of the mixed solution after dosing, so that the concentration of 33 in the mixed solution is reduced, at the same time, it plays a role in the hydraulic washing of the slime and the viscosity is reduced, so the settling speed is increased.

The effect of adding polyacrylamide first and then lime is good, not only the settling speed is fast, but also the separation rate of clean water is high.

In addition, from the appearance of the flocculent, the particle size generated by adding polyacrylamide first is large, and the strength is also high, which is conducive to further dehydration.

The change of pH value has great influence on the flocculation of polyacrylamide.

Generally speaking, polyacrylamide has high efficiency in a wide range of pH value, but with the change of 56 value, the function of polyacrylamide also changes greatly.

Calcium carbide slag and PAM coal washing wastewater are a colloidal dispersion system, and the surface of the colloidal particles has strong negative charge. Therefore, in the treatment of this kind of coal washing wastewater, coagulant must be added to the wastewater to reduce the potential and destroy the stability of the colloid, so as to achieve the goal of mud water separation.

The treatment effect of lime and carbide slag is the best, but the particle size is small, the settling speed is slow, and the filtering performance of the agglomerate is poor, so it is difficult to further dehydrate, so flocculant should be added.

As the chemical composition of lime and carbide slag is basically the same, and carbide slag is industrial waste, carbide slag can destroy the stability of coal washing wastewater and make the slime particles coagulate and settle, but the settling speed is relatively slow. Flocculant should be added to improve the settling speed and settling performance.

Through the experiment and considering the economic factors, the non-ionic PAM was selected as the flocculant, and the amount of calcium carbide slag and PAM and the mixing time after dosing were considered to have an effect on the settling speed.

The main factor affecting the settlement effect is the amount of PAM, followed by the amount of carbide slag.

In the coal washing wastewater treatment process, the wedge wire mesh product is essential, we can provide customized services.
Solid-liquid separation equipment for coal washing plants: Parabolic Screen.