Properties and quality indicators of polyacrylamide (cationic, anionic, non-ionic)
Polyacrylamide referred to as PAM, is divided into cationic type, anionic type, non-ionic type, the relative molecular weight between 400~2000, the product appearance is white powder, soluble in water, easy to decompose when the temperature exceeds 120 degrees.
Anionic polyacrylamide is characteristic of polymer electrolyte in neutral and alkaline medium, sensitive to salt electrolyte, and high metal ions can be crosslinked into insoluble gel, it is mainly used for living and production water, industrial and urban sewage treatment, can also be used for the dehydration of inorganic sludge.
Cationic polyacrylamide aqueous solution is a polymer electrolyte, with a positive charge, the suspension of organic colloids and organic matter can effectively coagulate, and can strengthen the process of solid-liquid separation, so mainly used in water suspension and suspension of turbidity flocculation precipitation, or organic sludge dehydration.
Non-ionic polyacrylamide does not contain ionic groups on the large molecular chain, but the amide group and many substances, such as clay, cellulose, can produce hydrogen bonds, due to adsorption bridge and condensation.
In water treatment, polyacrylamide is usually used as white powder particles, with 0.1%~0.3% aqueous solution, aqueous solution is uniform, transparent, viscous solution. When dissolved, negative and cationic polymers need to be stirred for 1 to 1.5h, and non-ionic polymers need to be stirred for 2 to 3h.
Mechanism of action of polyacrylamide
The mechanism of action of polyacrylamide is generally considered to be adsorption - electrical neutralization - bridging, but electrical neutralization is not the main mechanism. In the process of flocculation, when the polymer concentration is low, the long polymer chain adsorbed on the surface of the particle may adsorb on the surface of another particle at the same time, and two or more particles are linked together by bridging, which leads to flocculation. This is the bridging mechanism of the polymer flocculation. The necessary condition of bridging is that there is a blank surface on the particles. If the polymer concentration in the solution is very large and the surface of the particles has been completely covered by the adsorbed polymer, the particles will not flocculate through bridging, and the polymer plays a protective role. Therefore, there is an optimal range of the amount of polymer flocculant, beyond which the flocculation effect will be poor.