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- The main applications of polyacrylamide(PAM,FLOCCULANT)
Before the formal adoption of some polyacrylamide product, it should take a small test, to determine the optimal dosage and the application conditions of this polyacrylamide.
The polyacrylamide granule must be dissolved into the aqueous solution before the usage, which makes the high polymer chain fully stretch for the practical usage and function. Usually, the nonionic type and the cationic type products should be diluted to about 0.1%, the dissolving operation should be carried out in the stainless steel stirred tank. Because the PAM molecular chain is an irregular coil in the aqueous solution, during the making up and the dissolving operation in the water, part of the water is get into the coils, the coils get larger and full, the coils are easily to interwind and crosslink, making them look form the exterior with a certain viscosity. If using the centrifugal pump with the impeller, the high speed rotating speed of the impeller will make the structure deformation of some high polymer coils, part of the coils are separated from the middle, the volume of the coils is decreased, and then the crosslink between the coils is destroyed and the viscosity is decreased, the PAM application effect is reduced.
In the aqueous solution properties, the shear force may influence and break the molecular chain of the PAM, and then lead to the degradation of the PAM, so it is required to reduce the dissolving time and the diluted time of the PAM as much as possible, in order to reduce the mixing time and the stirring intensity. The reduced stirring speed should be controlled at 50 ~ 250 rpm, not too fact. When using the PAM aqueous solution, the adding spot should be away as far as possible the severe mechanical stirring position. During the transmit of the PAM aqueous solution, the pipeline should be rough, using as less as possible the variable delivery pump head and the branch pipelines, the best delivery pump choice is the Monod pump or the diaphragm pump, do not use the centrifugal pump.
It requires special attentions to the operation procedures in dissolving the granule PAM products, to prevent the particles mutual adhesion which may result in the failure of the dissolving operation. In the minitype test, it could use the methanol or the ethanol etc organic reagents to get the PAM granules moist, and to improve the dispersion of the PAM in the water. In the industrial application, the PAM should be put into the container first, it will be basically dissolved completely after 1/2 hour, the instant type product can be completely dissolved in 0.5 ~ 1 hour, the appropriate heating can accelerate the dissolving of the product, but the temperature should not be over 60 degree.
When the inorganic flocculant is used with the PAM, the inorganic flocculant and the PAM should be dissolved in two separate stirring equipments, otherwise, it will result in the mutual reaction of these two type of flocculants and then generate the flocculating phenomena which will influence the application effect. In the usage, the adding sequence should be paid attention, generally speaking, when treating the fine particles with the diameter below 50 um, the inorganic flocculant is added first, and then add the PAM aqueous solution; while treating the particles with the diameter over 50 um, the PAM aqueous solution is added first to make the adsorption and the bridging, and then add the inorganic flocculant. Before the formal adoption, the minitype test should be done to determine the final adding sequence.
As a general rule, the more conducive to the high polymer molecular chain extend of the aqueous solution condition, the better effect in the practical use. Therefore, the cationic type PAM is suitable for the acidic medium, the anionic type PAM is suitable in the alkaline medium, and the nonionic type PAM is suitable in the acid or the alkaline medium. If possible, dilute the PAM aqueous solution to 0.01% ~ 0.05% before using, this will help to promote the molecular chain for the further extension, and then improve the effect of the use and save the dosage.
The PAM product should not be placed on the iron container. The PAM dry powder generally can be stored for a long term in the stable performance, the performance of the PAM dissolved in the water will decrease along with the time being, and the lower of the concentration, the faster of the performance dropping. The nonionic PAM or the anionic PAM aqueous solution of 0.05% ~ 0.1% concentration can only be stored for about half a month, the cationic PAM aqueous solution of 0.1% concentration is very unstable, after one or two days later, the performance of the aqueous solution begins to decline, so the PAM product should be used immediately after making up.
The inhomogeneous lattice arrangement on the surface of the mineral particles will generate the excess charges. The excess charges have a strong influence to the PAM molecular, therefore, it is hard to achieve the bridging effect of the PAM, the PAM can only have the effect with the single particles and suspend in the slurry. If eliminating part of the excess charges by appropriately adjusting the PH value of the slurry, it can increase the flocculating effect.
The consumption of the PAM is proportional to the surface area of the solid particles, if the diameter of the minerals and the intangible fallout is very small, with the larger surface area, the required consumption of the PAM will still be big.
If the settlement particles have big viscosity, with the loose surface and the charges, such as the iron oxide particles, the uniform distribution of the acrylamide will be very difficult, that will reduce the settlement effect and the flocculation effect.