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PAM polyacrylamide and its application in water treatment
Environmental protection is the material foundation, and protection of water resources, water pollution control and governance is an important part of environmental protection. With the development of environmental protection, sewage and sludge produced in the process of water treatment disposal, people pay more and more attention. The polyacrylamide (PAM) has a very important role in the field of water treatment. In our country is very poor water resources area, average annual water resources total 2.8 trillion cubic meters, ranking sixth in the world, but the amount per capita only 271 cubic meters, equivalent to the world average amount per capita quarter, ranking No. 88 in the world. In China, the PAM application in water treatment is very important. PAM is a linear water soluble polymer, a water soluble polymer in one of the most widely used varieties. PAM and its derivatives can be used as effective flocculants, thickening agent, drag reduction agent, widely used in water processing, paper making, petroleum, coal, geology, construction and other industrial sectors. Due to the high molecular weight of PAM (103 ~ 107), water soluble, regulation of molecular weight and introduce a variety of ionic groups in order to obtain specific performance. Its molecular weight is an important flocculant, it is widely used in sewage treatment and drinking water. In groundwater, surface water and sewage containing impurities into many tiny particles exist, in order to remove these impurities, that is usually said the "removal of turbidity", by precipitation static or slow the flow of the impurities are removed by the gravity of the suspended particles. But to take advantage of natural substances are the removal of some organic compounds, and the sedimentation rate is very small, in more than 0.2 mm/s. With the development of modern industry and urban construction, natural sedimentation has been unable to meet the requirements, with the aid of chemicals accelerate the settlement of technology has been applied in production. The amide PAM (-CONH2) can be compatible with many substances, the formation of hydrogen bond adsorption. PAM with high molecular weight between the adsorbed particle formation of "bridging", make several or even dozens of particles connected together, the floc formation, accelerate the particles sink. This makes it the most ideal flocculant. Compared with the inorganic flocculant has the advantages of: many varieties, can adapt to a variety of conditions, measurement of small, high efficiency, less sludge generated, easy post treatment. It is about the dosage of inorganic coagulant 1/30 to 1/200. Because PAM is the highest performance of organic polymer flocculants, so it is the most widely used flocculants in china. PAM mainly exists in two forms: one is powder, is a kind of colloid. The colloids are easy to transport, and it is not easy to use, is commonly used in powder products. PAM and cationic, anionic and non-ionic, suitable for different applications and different flocculating object. In the application of PAM, the first to be dubbed in aqueous solution. Is generally powdery PAM slowly, small batch poured into the mixing of cold water, stirring speed should not be too fast, in order to avoid excessive shear induced fracture in polymer molecules. From the end group. Join the speed should be reduced with the increase of the viscosity of the solution and. A slightly higher temperature can slightly increase the dissolution rate, but the temperature should not exceed 60 DEG C. The highest PAM concentration of the polymer solution is 0.5%, the concentration of low molecular PAM can be configured into 1% or a little higher. The solution configuration for long time storage to prevent spoilage. For example: I plant sludge dewatering using dry powder polymer cationic PAM, dissolved concentration is 0.3%. Configuration while stirring while adding is agent of mist dispersed, in the medicine dissolving tank dissolved after the solution, continue stirring for 90 minutes, and on the day after use. Strict quality standard for drinking water, residual monomer content below 0.05%, dosage below 2 * 10-6; used in the treatment of, such as washing dishes to wash fruit food and industrial water water, or for food packaging paper, must also be strict quality standards, the special machine clearance approval and guarantee. Ionic PAM as the non ion type functional groups, therefore, and anionic PAM compared to have the following characteristics: flocculation performance is affected little by pH value of waste water and salts fluctuations; in neutral or alkaline conditions, the flocculating effect than anionic; floc strength is stronger than the anion.
Cationic PAM molecular weight is usually lower than the anionic or nonionic polymers and clarify its properties is mainly obtained by charge neutralization. The function of this kind of flocculant is mainly flocculation with negatively charged colloid, with except turbidity and decoloring function, suitable for high content of colloidal organic wastewater, such as dyeing, papermaking, food, aquatic products processing industrial wastewater and municipal water treatment process of sludge dewatering. Urban and industrial sewage commonly used activated sludge treatment method and sludge biochemical is often highly hydrophilic colloid, water is extremely difficult to remove. If the Cationic PAM flocculants can receive the good effect of dehydration. Anionic PAM flocculant used on the surface of particles with positive charge of the slurry, and the cationic compared, its high molecular weight, water molecules in the extension to a greater degree, so it has good particle floc properties. Can be effectively used for settling mineral suspension industry. Not only can be used for blast furnace ironmaking, aluminum processing, papermaking wastewater treatment, application in urban sewage treatment level. PAM flocculants can adapt to a variety of flocculating object, has special value in certain cases. The effect associated with the selection, dosage and flocculation process using application. For example: a steel mills that dust sewage flocculation clarification, the original use of anion of 20% ~ 30% PAM, the consumption of high reached 2.5 g / m3 of sewage, the use degree of anion PAM consumption only 0.2 g / m3. PAM the higher molecular weight Danhao generally lower. PAM can be used for treatment of water in thermal power plant. In the process, first of all to the raw water (such as water) for clarification. Chemistry is a commonly used method of PAM and inorganic coagulants (such as lime, aluminum sulfate) with the use of. Because such as single inorganic coagulant, need high concentration to be effective, combined with PAM, inorganic coagulating agent greatly decreased, which can avoid the inorganic coagulating agent dosage is large and easy to cooling tower heat transfer surface deposition and accelerate the equipment corrosion and fouling. For example: the lime, ferric chloride and PAM used together, will greatly enhance the ability of water clarification. In industrial water treatment, scale inhibitor of low molecular weight PAM can also be used as cooling water. Low molecular weight anionic PAM can prevent salt crystal precipitation and growth, the solid particle suspension and deposition, can play a role in inhibition of boiler, cooling tower and heat exchanger. Industrial water except for the need of flocculation of suspended matter, often ask for more, therefore, should take PAM polymer flocculant and inorganic flocculant and some other additives such as the use of scale inhibitor, bactericide and algicide and so on with. Since the founding of new China, especially after the reform and opening up to the outside world, our country although in the sewage treatment plant construction made certain achievements, but still failed to control water pollution. Due to China's serious water pollution, the 7 major river systems in nearly half reach due to different degrees of pollution. Lake and reservoir eutrophication serious, flows through the urban reaches more than three kinds of standards and does not apply to domestic water up to 78%, more than 50% of the urban groundwater have also been varying degrees of pollution. In sewage treatment, in the early 1990s, our country developed to 2000 urban sewage treatment rate reached 20% ~ 30% of the, industrial wastewater treatment rate of 34%, urban sewage facilities popularity rate is up to 70% of the water pollution control planning goals.