In the early days, only natural high molecular substances were used as flocculants. Such as sodium alginate, alkali starch, gelatin, tannic acid, etc. In recent years, various polymer flocculants have been synthesized, such as sodium polyacrylate and polyacrylamide. Compared with previous inorganic flocculants or natural water-soluble polymers. Synthetic polymer flocculant is characterized by high molecular weight. Due to the many functional groups in the molecular chain, the amount used in wastewater treatment is small; at the same time, it has superior performance in solid-liquid separation operations such as flocculation filtration and dehydration.
Among the synthetic polymer flocculants, the acrylamide type is used most. According to the charge, polymer flocculants can be divided into three categories: cationic, anionic and nonionic.
1. Cationic polymer
At present, cationic polymers commonly used as water treatment agents include polymers or copolymers containing cationic monomers such as dimethylaminoethyl methacrylate. Condensate of acrylamide and formaldehyde, etc. The flocculation performance of cationic polymers is not only manifested in the flocculation of suspended colloidal particles through charge neutralization. Moreover, it can react with negatively charged solutes to generate insoluble salts.
When the cationic polymer is used as a flocculant, it has the function of removing turbidity or decolorization. It is suitable for wastewater containing a lot of organic colloids, such as industrial wastewater such as dyeing, papermaking, pulp, food, aquatic product processing and fermentation.
Compared with inorganic flocculants with the same charge neutralization performance, cationic polymers have excellent performance of water treatment agents. But so far, its demand is not as large as that of anionic and nonionic polymers. In practice, anionic or nonionic polymer flocculants are used in combination with inorganic flocculants.
2. Anionic polymer
The main varieties are sodium polyacrylate, partial hydrolysis of polyacrylamide, sulfomethylated polyacrylamide, etc. Compared with cationic polymers, anionic polymers The particles are all of high molecular weight, and due to the mutual repulsion between the high sub-groups in the same molecule, the molecular extension in water is relatively large, so it has a good particle flocculation function.
The application range of polyacrylamide partially hydrolyzed flocculants is for suspensions with a pH value of neutral to alkaline and a lot of inorganic matter. Applicable. In addition to being used in wastewater treatment in production processes such as ironmaking blast furnaces, aluminum processing, papermaking, and river gravel washing, it can also be used in primary treatment of urban groundwater.
Sodium polyacrylate is not suitable for highly charged suspended particles, but it performs well for positively charged suspended particles such as metal hydroxides flocculation performance. It is suitable for recycling the sludge obtained in wastewater treatment and using it for the production of feed.
3. Non-ionic polymer
The main varieties of non-ionic polymers are polyacrylamide, polyethylene oxide, and condensed urea-formaldehyde resin. Compared with anionic polymer flocculants, nonionic polyacrylamide polymer flocculants have the following characteristics because they do not have ionic functional groups:
①Flocculation performance is less affected by wastewater pH and salt;
② Under neutral and alkaline conditions, the flocculation effect (sedimentation velocity) of wastewater is worse than that of anionic polymer flocculants, but it is lower than that of anionic polymer flocculants under acidic conditions. Anionic polymer flocculants are good;
③The floc strength is stronger than that of anionic polymer flocculants.
This type of flocculant is mainly used to treat comprehensive wastewater in aluminum processing, papermaking, pulp and other production processes.
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