Introduction of Polyacrylamide
The products Polyacrylamide has the following three forms: powder, emulsion and colloidal. Powdered polyacrylamide is free from geographical restrictions. It is easy to transport and store, dissolve fast, used widely. Polyacrylamide emulsion is of more easily water-soluble, but it is subject to large transport volume, short storage time, high cost. Colloidal polyacrylamide is not easy to transport. It takes more time to dissolve, so it is rarely used.
Polyacrylamide is made up of by nonionic polyacrylamide and ionic polyacrylamide according to ions in its molecule. Ionic polyacrylamides also include anionic, cationic and amphoteric polyacrylamides.
Nonionic polyacrylamide is acrylamide homopolymer, mainly used as a reinforcing agent in papermaking , retention aid, drilling precipitation agent, tertiary oil extraction and so on. Compared to anionic PAM flocculants , Non-ionic PAM flocculants do not have ionic functional groups, so they are of the following characteristics. flocculation is less affected by water PH and salt fluctuations. Under neutral or alkaline conditions , the flocculation effect (sedimentation rate) is not as good as the anionic type, but it is better than the anionic type under the acidic condition. The flocculat effect is biger than that of the anionic polymer flocculant.
The amide group in the nonionic polyacrylamide can be translate into anionic polyacrylamide through partial hydrolysis. Anionic polyacrylamide is mainly used for sewage treatment,the neutral suspension of inorganic solid-based, suitable for water supply plant or sewage treatment plant sludge dewatering, coal washing process of filtration and other solid-liquid separation process. In the primary waste water cast 0.25mg / l anionic polyacrylamide, suspended solids and BOD (biological oxygen demand) removal rate of up to 66% and 23%, alone for the acidic environment is poor.
Cationic polyacrylamide can neutralize the negative charge and bridging flocs, with flocculating effect in biological sludge treatment, the effect will flocculate into large floc particles dispersed in water, accelerate the slurry separation and not adhesion of filter cloth. Cationic and amphoteric polyacrylamide flocculants are generally less molecular weight than anionic or nonionic polymers and their clarity is primarily achieved by charge neutralization. The main function of this kind of flocculant is the colloid with negative charge, which has the functions of removing turbidity and decoloring.
Amphoteric polymer has a cation and anion group in the molecule, its structure determines its use in a wide range of pH conditions, in particular, it makes the sludge dehydration, so that the sludge cake moisture content is reduced.
According to the survey, for the more serious pollution, pollutant variety, pH and alkalinity of raw water is low, nonionic polyacrylamide is relatively suitable for the flocculation of anionic polyacrylamide, slightly inferior, poor effect of cationic polyacrylamide. According to the theory of flocculation that may be polluted in dry season water turbidity is relatively low, less available for bridging particles in water, adding chlorine disinfection, after adding flocculant, structure of cationic flocculant may have destructive effect, has the addition of coagulant and disinfectant water, pH value is generally not more than 7, the water charge tendency is not obvious, the performance of anionic and cationic polyacrylamide is an advantage.
The pulp of filler and fine fiber with negative charge, so the use of retention aid for most cationic filter aid, the interaction between positive and negative electric charges, in order to improve the pulp fines and filler retention agent retention effect. Such as cationic polyacrylamide, cationic polyethyleneimine are often used as cationic retention agent. However, in the presence of mechanical pulp and waste paper pulp in the pulp, soluble anion containing a large amount of material, the material can soluble anionic and cationic charge on the retention effect, reduce the effect of the use of these cationic polymers, thus containing mechanical pulp and waste paper pulp system, using cationic polymer as retention agent retention effect is greatly reduced.