Coal, as known as the food of industry, has an indispensable role in the development of the national economy. Affected by the development of new energy technology and economic development and policy, in recent years, the growth of consumption of coal as an energy source has slowed down, but production and consumption are still at a historical high, and production and sales are still very huge. Coal carbon whether in the production or use process, will produce a mixture of water and fine coal dust, such as coal industry coal washing wastewater, coal preparation plant slurry water, coal-fired power plant flushing wastewater, etc., and these coal washing wastewater mixtures are mainly characterized by the following: 1. high turbidity, fine particle size of solids, solid particles more negatively charged on the surface, due to the repulsive force of the same sex charge asked as well as by gravity and Brownian motion, so that these particles in the water to maintain the state of dispersion;. 2. Due to the interaction between the interface of solid particles in the coal slurry water (such as adsorption, dissolution, synthesis, etc.), so that the nature of the coal washing wastewater is quite complex, not only with the nature of the suspension, but also with the nature of the colloid. 3. The sludge resistance is large, the filtration water is poor, and the pressure filtration dewatering is difficult. Therefore, the coal wastewater is particularly stable, standing for several months will not naturally settle, it is difficult to naturally clarify, after precipitation supernatant still with a large number of coal slurry and other suspended black liquid, and contains a variety of additives in the production and processing and heavy metals and other hazardous substances, so it is very difficult to deal with. If these wastewater is discharged according to the standard, it will cause water pollution, siltation and loss of coal sludge, which not only cause environmental damage and waste of resources, but also cause huge economic losses. The good or bad of wastewater treatment seriously affects the development of the coal industry. Therefore, in the face of coal washing wastewater, the development of new products and new technologies is of great significance. 
Aiming at these characteristics of coal washing wastewater, we summarize the following coal washing wastewater treatment methods through a large number of experiments:
Firstly, add lime or calcium carbide slag into the wastewater (the composition is calcium oxide), neutralize the negative charge in the wastewater, destroy the stability of the water body, and achieve the purpose of mud-water separation. Secondly, add Flocculant (Polyacrylamide), after adding calcium oxide treatment of wastewater suspended matter settling speed is very slow, complete precipitation is difficult to realize, it takes a long time, because the polyacrylamide has a very long molecular chain, the molecular chain with different groups, the long molecular chain can absorb suspended particles collide with each other to form larger flocs adsorption settling, so add the polyacrylamide can increase the settling speed, so that the mud and water to achieve complete and rapid separation. Therefore, the addition of polyacrylamide can increase the settling speed, so that the mud and water can be separated completely and quickly. According to years of experience, coal washing wastewater treatment generally use anionic polyacrylamide or nonionic polyacrylamide, there are very few use of cationic polyacrylamide. It is recommended that when you use flocculants, you must first do the selection of flocculants to avoid unnecessary waste. Polyacrylamide flocculation product features 1.Can quickly form large flocs, sludge volume is small and fast flocculation and settlement; dissolve quickly and thoroughly, no insoluble matter (fish-eye); powder state products dissolve in 60 minutes or so; economical and practical, small dosage, good effect, high rate of dewatering 2.Low operating costs, low dosage can produce effective effect well and high performance of dehydration, very economical; excellent filtration and dewatering to improve the dewatering effect of sludge, can be automatically fed, easy to deal with. Product selection can be used exclusively for high viscosity of the water bath liquid state, is very good fluidity viscosity of the gel reduction system.
Need to pay special attention to:
Polyacrylamide aqueous solution additive amount is the key link in the coal slurry wastewater Water Treatment, take the right way to add, add the right amount, will help to improve the flocculation effect. Usually according to the selected coal sludge water treatment process and the nature of the coal sludge water through the test to determine. If the dosage of polyacrylamide is too small, it will lead to slow sedimentation of coal slurry, and the concentration overflow will exceed the standard very easily, which can't guarantee the required index of circulating water, and thus make it difficult to control the index of coal washing products stably. If the polyacrylamide dosage is too much, although it accelerates the precipitation speed of coal slurry, but it is easy to cause the concentration of concentrated underflow is too high, and the content of polyacrylamide in the underflow increases, resulting in difficulties in the transportation of the underflow and filtration, and it is not easy to dislodge the coal cake when unloading the coal cake in the filtration, which increases the operator's labor intensity, reduces the work efficiency, and results in the waste of pharmaceuticals, and makes the production cost increase. Therefore, the test to determine the appropriate amount of polyacrylamide, not only can improve the flocculation effect, effective treatment of coal slurry wastewater, but also has an important role in coal quality and production efficiency and reduce production costs.
