Polyacrylamide (PAM) must be stirred in the container before use as a solid product. Due to its unique molecular structure, its dissolution method differs from that of inorganic flocculants. Generally, the following principles should be followed during the dissolution process.
Before using polyacrylamide products, a small-scale test should be conducted to determine the dosage and usage conditions. When used as a flocculant, the dosage is typically between 0.1 and 0.5 ppm.
2. Polyacrylamide products must be dissolved in solution prior to use to ensure that the polymer chains are fully extended and readily available. Typically, non-ionic and cationic products are diluted to approximately 0.1%, and the dissolution process is carried out in plastic, ceramic, or stainless steel mixing tanks. Since the PAM molecular chains are randomly coiled in solution, when they are prepared and dissolved, some water is encapsulated within the coils, resulting in large, full coils that are prone to entanglement and cross-linking, thereby creating a certain viscosity. If a centrifugal pump, with its impeller rotating at high speed, is used to rotate the high molecular weight coil structure, it separates from the middle, and the volume changes. The cross-linking between coils is reduced, and the viscosity decreases, thereby diminishing the effectiveness of use.
3. Shear forces from the PAM molecular chains in solution can cause chain breakage and degradation, affecting performance. Therefore, when diluting PAM, it is advisable to minimize stirring time to reduce the intensity of stirring; the stirring speed should be controlled at 50-250 rpm. The integration should not be too rapid.
4. When using polyacrylamide PAM solution, it is best to avoid vigorous mechanical stirring when adding. During the transportation of PAM solution, the pipeline should be thick, with fewer headers and branches, and a single pump or diaphragm pump should be used. Centrifugal pumps should not be used.
5. Pay special attention to the operation procedure when dissolving dry powder PAM products to prevent particles from sticking together, which may lead to failure in the dissolution process. Wet organic reagents such as ethanol can improve the dispersibility of particles in water. For industrial applications, the solution can generally dissolve completely within 1/2 hour after being added to the container, while quick-dissolving products can dissolve completely within 0.5 to 1 hour. Warmth from energy accelerates the dissolution of the product, but the temperature should not exceed 60°C.
6. When inorganic flocculants are mixed with polyacrylamide, the inorganic flocculant and PAM should be dissolved separately in two mixing devices to avoid interaction between the two flocculants, which can lead to aggregation and affect the effectiveness. The order of addition is typically to first add the inorganic flocculant, followed by the PAM solution, when dealing with particles smaller than 50μm. For processing coarse particles with a diameter of 50μm or larger, add the PAM solution first for adsorption bridging, then add the flocculant. Users should conduct small-scale experiments to determine the order of addition.
As a general rule, the better the solution conditions, the more effective the use of polymer molecular chains. Therefore, cationic PAM is suitable for acidic media, anionic PAM for alkaline media, and non-ionic PAM for acidic or slightly alkaline media; whenever possible, dilute the polyacrylamide PAM solution to 0.01%-0.05% before use, which will help further stretch the molecular chains, thereby enhancing performance and saving quantities.
8. PAM products should not be stored in iron containers. Dry powder PAM generally has stable long-term storage properties, while the performance of water-soluble PAM deteriorates over time, with lower concentrations experiencing faster performance decline. A 0.05% to 0.1% non-ionic or anionic PAM solution can only be stored for about half a month. A 0.1% cationic PAM solution is extremely unstable. Its performance starts to degrade within 1-2 days. Therefore, PAM products should be immediately procured and utilized.
9. Toxicity of Polyacrylamide: PAM itself is non-toxic. It becomes harmful and detrimental to animal gastrointestinal mucosa only when the concentration exceeds 5,000 ppm. The residual monomer acrylamide (Am) in PAM is toxic. For oil field use and urban wastewater treatment, residual monomers are typically allowed at about 1%. In the case of food, such as clarification of drinking sucrose syrup, it may be related to food production. The amount of residual monomer must be strictly controlled, such as in paper contact, generally less than 0.05%. China's regulations also stipulate that the residual monomer content of polyacrylamide in food should be less than 0.5%.
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