Application of Polyaluminum Chloride in Wastewater Treatment of Coal Washing plant

Polyaluminum chloride is generally used as a coagulant and filter aid in coal preparation plants. When the cementation of the coal slurry is serious, the effect of using only the flocculant is very poor, so it is necessary to add a coagulant to break the colloid before using the flocculant. Sometimes in the dehydration process, in order to improve the dehydration effect, polyaluminum chloride is also used as a filter aid.

Coal washing wastewater is wastewater discharged from wet coal washing. Coal washing methods are divided into wet coal washing and dry coal washing. The water consumption per ton of coal during wet coal washing is 2-8m3. The generated wastewater mainly contains suspended solids with a particle size of less than 50 μm. The main components of the wastewater are fine coal powder, sand, clay, shale, etc. Wastewater treatment methods generally use coagulation sedimentation or air flotation. The treated effluent can be reused for production.

The application of polyaluminum chloride in coal washing plants has been very extensive. The main features are its strong ability to treat water, fast speed, and the quality of effluent water can meet the discharge standards. At the same time, due to its low price (compared with large-scale water treatment In terms of equipment), it has gradually spread to many coal washing plants. From the perspective of our cooperating customers, most of the coal ash in coal washing water can be recovered after precipitation. At the same time, in some slightly polluted water, polyaluminum chloride The recycling and reuse of water can be realized, so the polyaluminum chloride used for coal washing water can greatly relieve the environmental pressure caused by the discharge of local industrial wastewater.

The dosage of polyaluminum chloride affects the treatment effect of coal washing wastewater. With the increase of the dosage of polyaluminum chloride, the effective density e of the coal slime group decreases. This is because the cohesion of the slime particles increases with the increase of the dosage of PAC, and it is easy to generate high-magnification particles. Such particles have a large void ratio, which leads to slime The granulation effective density e decreases; the effluent turbidity SSt decreases significantly with the increase of PAC dosage, and the effluent changes from turbid to clear. When PAC increases to 2.6mg/L, SSt changes little and basically tends to be stable. increase, the degree of destabilization of fine particles in coal washing wastewater is increased, the cohesion increases, and SSt drops sharply. When the amount of PAC reaches a certain value, most of the particles in the wastewater are almost completely destabilized and coagulated to achieve the best effect. The dosage of polyaluminum chloride does not make much sense; and in actual engineering, considering the cost of chemicals, it is necessary to control the dosage of polyaluminum chloride.

Adding an appropriate amount of water purifying agent products is the primary guarantee for coal washing water purification! However, regarding the treatment of coal washing wastewater, it is recommended to use polyaluminum chloride and polyacrylamide together. The principle is that the coal washing water discharged from the coal washing plant is firstly used in the coal slime sedimentation tank to settle the coal slime with a larger particle size, and then the coal washing water overflowing from the upper layer is adjusted to a pH value of 6.0- 7.5, and then the coal washing water with adjusted PH value is filtered through two-stage fly ash filter tanks successively, and the coal washing water can be purified.