How to select polyacrylamide?
What is polyvinylamine?
Polyacrylamide, referred to as PAM for short, is divided into cationic type, anionic type and non-ionic type, with a molecular weight of 4-20 million. The appearance of the product is white powder, easily soluble in water, and easy to decompose when the temperature exceeds 120 ℃. Polyacrylamide is a synthetic polymer flocculant, commonly known as siberan. It belongs to polyelectrolyte. It is widely used in the solid-liquid separation process of leaching pulp in Shuiye uranium plant (such as countercurrent decantation washing process), in order to improve the clarification, sedimentation and filtration performance of pulp.
Properties: colorless or yellow viscous colloid. It is a water-soluble resin, which can be dissolved in water in any proportion. It can only dissolve about 1% in a few solvents such as glacial acetic acid, acrylic acid, ethylene glycol, formamide, glycerol and lactic acid. And almost insoluble in organic solvents. It is easy to decompose when the temperature exceeds 120 ℃.
Acrylamide was synthesized from acrylonitrile in the presence of copper catalyst. Acrylamide was polymerized into polyacrylamide in the presence of K2S2O8. After alkali treatment and water washing, copper aluminum alloy is made into catalyst and put into hydration reactor. Acrylonitrile raw material is pumped into the storage tank and then put into the metering tank. The purified water after ion exchange treatment is sent to the metering tank, and then continuously injected into the hydration reactor by the pump through the raw material preheater in proportion. The hydration reaction was carried out at 85-125 ℃ to produce acrylamide aqueous solution. The remaining acrylonitrile is recycled to the condenser through the flash tower and flows into the water metering tank for recycling. Acrylamide solution flows into the storage tank from the flash tank, is pumped into the high-level tank, enters the resin exchange column, enters the storage tank to prepare monomer with concentration of 7-8%, and is sent to the polymerization kettle to make colloidal polyacrylamide package to obtain the finished product.
Polyacrylamide is mainly in two forms, one is powder and the other is colloid. Colloid is not easy to transport and use, so PAM powder is very popular with users. lately. Polymer dispersion, called PAM latex, has attracted much attention because of its easy solubility in water. Polyacrylamide index: relative molecular weight is one of the main performance indexes to distinguish polyacrylamide. High molecular weight PAM is mainly used as flocculant, medium molecular weight PAM is mainly used as dry strength agent of paper, and low molecular weight PAM is used as dispersant.
How to choose Cationic Flocculant？
Why is it the key to choose the ion type when cationic polyacrylamide is used to treat sewage? Because there are many enterprises that produce industrial sludge sewage, different types of cationic polyacrylamide are selected for different types of sewage, so what factors should be considered in selecting accurate cationic polyacrylamide?
1. First of all, we should understand the origin, nature, composition and solid content of sludge. According to the main components rich in sludge. Sludge can be divided into organic sludge and inorganic sludge. Generally speaking, cationic polyacrylamide is used to treat organic sludge and sludge dewatering, while anionic polyacrylamide is used to treat inorganic sludge. Cationic polyacrylamide is not easy to use when the alkalinity is very strong, but anionic polyacrylamide is not suitable when the acidity is very strong. Generally, the amount of polyacrylamide is large when the solid content of sludge is high.
2. Ionic degree selection of cationic polyacrylamide: for the sludge to be dewatered, polyacrylamide flocculants with different ionic degrees can be selected through small experiments to select the appropriate polyacrylamide, which can not only achieve good flocculation, but also reduce the dosage of polyacrylamide and save the use cost of water treatment agent. The key of ion selection depends on the size of floc and floc strength (moisture content)
a. Size of floc: too small floc will affect the settling speed of floc. Too large floc will bind more water and cause poor water permeability of sludge. The size of floc can be adjusted by adjusting the molecular weight of polyacrylamide.
b. Strength of flocs: flocs should remain stable without breaking under shear. Selecting polyacrylamide with appropriate ionic degree will help flocs obtain better strength.
Let's take several industries as examples.
Coal washing and sand washing are generally simpler, and cationic polyacrylamide is directly used;
Wastewater treatment in chemical industry;
The wastewater from bleaching and dyeing industry and papermaking industry are difficult to treat. The use quantity should be increased and set at a reasonable level;
Electroplating wastewater industry and ordinary industrial water generally do not exceed, in addition, the treatment of domestic sewage. Domestic sewage is treated according to different methods. The flocculant used is also different, if it is treated by biochemical method. Only cationic polyacrylamide is needed as sludge dehydrating agent. If physicochemical treatment is adopted, polyaluminium chloride can be added first and then anionic polyacrylamide. Cationic polyacrylamide is added for dehydration, and the dosage of different sewage shall also be determined according to the sewage quality.
If the coking plant wastewater can be properly treated, it can greatly solve the industrial problems such as the standard discharge of coal coking and coal gasification wastewater in the coal chemical industry. On the one hand, it can promote the technical steps of pollution control in the metallurgical and coking industries, directly promote the energy conservation and emission reduction of these industries and enterprises, promote the sustainable development of these industries, and have good environmental and social benefits; On the other hand, it is of great significance to improve the environmental quality of the basin.
For the sludge to be dewatered, a small test is carried out with flocculants with different ionic degrees to select a good and suitable polyacrylamide, which can not only obtain a good flocculant effect, but also reduce the dosage and save the cost.