Introduction of Inorganic Polymer Flocculant
The advantage of Inorganic Polymer Flocculant is that it is more effective than traditional flocculants such as aluminum sulfate and ferric chloride, and cheaper than organic polymer flocculant.
Now PAC has been successfully applied in various treatment processes of water supply, Industrial Wastewater and Domestic Sewage Treatment, including pretreatment, intermediate treatment and advanced treatment, and has gradually become the mainstream flocculant.
However, in terms of morphology, polymerization degree and corresponding coagulation flocculation effect, inorganic polymer flocculants are still in the position between traditional metal salt flocculants and organic polymer flocculants.
The types of Inorganic Polymer Flocculants
Inorganic polymer flocculants of aluminum, iron and silicon are actually intermediate products of their hydrolysis, sol and precipitation processes, namely, hydroxy and oxy polymers of Al (Ⅲ), Fe (Ⅲ) and Si (Ⅳ).
Aluminum and iron are cationic positively charged, while silicon is anionic negatively charged. Their unit molecular weight in water-soluble state is about hundreds to thousands, which can be combined to form aggregates with fractal structure.
Their coagulation flocculation process is a comprehensive embodiment of the two functions of electric neutralization and adhesion bridging of particles in water. The particle size of suspended particles in water is from nanometer to micrometer, and most of them are negatively charged. Therefore, the positive and negative charges of flocculants and their morphology, the strength of electrical properties, the molecular weight, and the particle size of aggregates are the main factors that determine their flocculation effect. At present, there are dozens of types of inorganic polymer flocculants, with the output reaching 30%~60% of the total output of flocculants. The most commonly used and widely used is Polyaluminum Chloride, or PAC.
The Characteristics of Inorganic Polymer Flocculants
The hydroxy and oxy polymers of Al (Ⅲ) and Fe (Ⅲ) will further combine into aggregates, which will be kept in aqueous solution under certain conditions, with the particle size roughly in the nanometer range, so that the coagulation flocculation effect can be achieved with low dosage and high effect.
If their reaction polymerization speed is compared, the reaction of aluminum polymer is slower and the morphology is more stable, while the hydrolytic polymer of iron reacts quickly and tends to lose stability and precipitate.
The Characteristics of Polyaluminum Chloride(PAC)
Polyaluminum chloride, abbreviated as PAC, has the chemical formula ALn (OH) mCL3n-m. PAC is a multivalent electrolyte, which can significantly reduce the colloidal charge of clay impurities (mostly negatively charged) in water. Due to the large relative molecular weight and strong adsorption capacity, the flocs formed are larger, and the flocculating sedimentation performance is superior to other flocculants.
PAC has a high degree of polymerization, which can greatly shorten the formation time of flocs by quickly stirring after adding.
PAC is less affected by water temperature, and the effect is good when the water temperature is low. It can reduce the pH value of water less, and the applicable pH range is wide (it can be used in the range of pH=5~9), so alkali agent can not be added.
PAC has less dosage, less sludge production, convenient use, management and operation, and less corrosivity to equipment and pipelines. Therefore, PAC has a tendency to gradually replace aluminum sulfate in the field of water treatment. Its disadvantage is that its price is higher than that of traditional flocculants.
In addition, from the perspective of solution chemistry, PAC is the kinetic intermediate product of aluminum salt hydrolysis polymerization precipitation reaction process, which is thermodynamically unstable. Generally, liquid PAC products should be used in a short time (solid products with stable performance can be stored for a long time). The addition of some inorganic salts (such as CaCl2, MnCl2, etc.) or macromolecules (such as polyvinyl alcohol, polyacrylamide, etc.) can improve the stability of PAC, and increase the coagulation ability.
From the perspective of production process, one or several different anions (such as SO42 -, PO43 -, etc.) are introduced into the manufacturing process of PAC, and the structure and morphology distribution of polymer can be changed to a certain extent by using the polymerization, thus improving the stability and efficacy of PAC; If other cationic components, such as Fe3+, are introduced in the manufacturing process of PAC to make Al3+and Fe3+hydrolyze and polymerize alternately, composite flocculant polymeric aluminum iron can be prepared.
Industrial Wastewater and Domestic Sewage Treatment flocculant is a inorganic polymer flocculant, which can effectively coagulate suspended bcolloid and compound. The dosage concentration depends on the turbidity of raw water. The most appropriate dosage of flocculant shall be determined by the test of water sample. Too much or too little dosage will reduce the filtering effect.
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