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Application Methods and Attentions of Polyacrylamide

        Before the formal use of a certain type of polyacrylamide product, small-scale tests should be carried out to determine the optimum dosage and use conditions. When used as flocculant, the general dosage is about 0.1-0.5 ppm.

       Polyacrylamide must be dissolved into a solution before use, so that the polymer chain can be fully stretched and reserved. Normally, non-ionic and cationic products are diluted to about 0.1%, and the dissolution is carried out in stirred tanks of plastics, ceramics or stainless steel. Since the PAM molecular chain is an irregular coil in solution, it is easy to intertwine and cross-link between the coils in preparation and dissolution, so that it has a certain viscosity from the appearance. A part of the macromolecule coil structure is deformed and separated from the middle when using a centrifugal pump with high speed of the impeller rotates. So that the cross-linking between the coils is destroyed and the viscosity decreases, which will reduce the use effect.

       The shear force acting on PAM molecular chains in solution will lead to the breakage and degradation of molecular chains, which will affect the performance. Therefore, when dissolving and diluting PAM, the stirring time should be reduced as much as possible, and the stirring speed should generally be controlled at 50-250 rpm, not too fast. When using PAM solution, the dosing point should avoid strong mechanical stirring as far as possible; when transporting PAM solution, the pipeline should be thick and the number of head changers and branch pipes should be less. It is better to choose Mono pump or diaphragm pump for transporting pump rather than centrifugal pump.

       Particular attention should be paid to the operation procedures of dry powder PAM products during dissolution to prevent the particles from adhering to each other and causing the dissolution operation to fail. Methanol can be used in small scale test. It can be wetted by ethanol and other organic reagents to improve the dispersibility of particles in water. In industrial application, it should be added to the container for 1-2 hours before using, which can be completely dissolved. Instant products can be dissolved in 0.5-1 hour. Proper heating can accelerate the dissolution of products, but should not exceed 60 C.

       When inorganic flocculant is mixed with PAM, inorganic flocculant and PAM should be dissolved in two mixing equipments respectively, otherwise the interaction between the two flocculants will result in agglomeration and affect the effect. When using, attention should be paid to the order of feeding. Generally speaking, when dealing with fine particles with particle size below 50um, inorganic flocculant should be added first. After that, PAM solution was added. And when the diameter of coarse particles was above 50um, PAM solution was added to bridge the adsorption process, then flocculant was added. Users should first carry out small-scale tests to determine the order of adding.

       As a general rule, the more conducive the solution is to the stretching of polymer molecular chains, the better the effect will be. Therefore, cationic PAM is suitable for acidic media, anionic PAM is suitable for alkaline media, and non-ionic PAM is suitable for acidic or weak alkaline media. Where conditions permit, PAM solution is diluted to 0.01%-0.05% before use, which is conducive to the further extension of molecular chains, thereby improving the use effect and saving the amount of use.

       PAM products should not be stored in iron containers. Dry powder PAM can generally keep stable performance for a long time. The performance of PAM dissolved in water will decrease with the increase of time, and the lower the concentration, the faster the performance decline. 0.05%-0.1% non-ionic or anionic PAM solution can only be stored for about half a month. 0.1% cationic PAM solution is extremely unstable. After 1-2 days, the performance begins to decline. Therefore, PAM products should be ready-to-use.

       Because of the uneven arrangement of lattice ions on the surface of mineral particles and the generation of excess charges, there is strong influence on PAM effectiveness. The bridging effect of PAM is very difficult to play. It can only interact with a single particle and suspend in the slurry. If the excess charges are eliminated by properly adjusting the PH value of the slurry, the flocculation effect can be increased.

       The consumption of PAM is proportional to the surface area of solid particles. If the diameter of minerals and invisible sediments is very small, there will be a large surface area and a large number of PAM will be needed.

       If the settling particles are viscous, loose and charged, it will be difficult to distribute PAM evenly, which reduces the settling and flocculation effect.

Toxicity of polyacrylamide:

       PAM is not toxic, only when the dosage is more than 5000 ppm, the absorption of nutrients into the intestinal and gastric mucosa of animals is obstructed and harmful.

       Residual monomers of acrylamide (Am) in PAM are toxic. For oilfield use and municipal sewage treatment products, residual monomers are generally allowed to be about 1%. For food use, such as clarifying sucrose juice for drinking, making paper that may contact food, etc., the content of residual monomers must be strictly controlled, generally less than 0.05%.

       In 1973, the Japanese Environmental Health Bureau stipulated that domestic water should not be treated with macromolecule flocculants. In 1975, the AM content in PAM of sewage treatment was 0.05%. China stipulates that the amount of residual monomers of polyacrylamide used in food is less than 0.5%.

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