What are the main characteristics of polyaluminium chloride as a coagulant

Polyaluminum chloride, also known as basic aluminum chloride, also known as polyhydroxyaluminum chloride. It is a kind of inorganic polymer polyelectrolyte flocculant, which is divided into two types: polymeric hydroxyaluminum chloride and polymeric hydroxyaluminum sulfate. Polyhydroxyaluminum chloride is a kind of between aluminum chloride and aluminum chloride hydrolysis polymerization products, known as basic aluminum chloride, English name PAC.

The color of polyaluminium chloride varies with the size of the basicity. The basicity, also known as the degree of alkalinity, is equal to [OH]/3 [Al], that is, the molar (equivalent) ratio of hydroxyl and aluminum in polyaluminium chloride. When the basicity is in the range of 40%-60%, the polyaluminium chloride is light yellow and transparent, and gradually becomes colorless and transparent when it is above 60%, with sour taste. The shape of solid polyaluminium chloride also varies with basicity. When the basicity is below 30%, it is crystalline. 30%-60% is colloidal; Gradually become resinous when it is above 60%; When it is below 70%, it is easy to absorb moisture and liquefy, and when it is above 70%, it is not easy to deliquesce. Polyaluminum chloride and acid depolymerization reaction; reduce the degree of polymerization and basicity, the formation of positive aluminum salt, flocculation effect is also reduced. When reacted with alkali, it can increase its degree of polymerization and basicity, which will further generate aluminum hydroxide precipitation and aluminate. If mixed with aluminum sulfate or other polyvalent acid salt, it is easy to produce co precipitation, reduce or completely lose the flocculation performance. When the temperature is heated to above 110 ℃, decomposition will occur, hydrogen chloride gas will be released one after another, and finally decomposed into alumina. The content of alumina is a measure of the effective component of polyaluminium chloride.

In general, the greater the relative density, the higher the alumina content. The base degree is another important quality index of polyaluminum chloride, and it is the decisive factor of the structure, polymerization degree, flocculation ability, storage stability and pH value of the product. Under the same alumina content, the viscosity of polyaluminum chloride is lower than that of aluminum sulfate, so it is beneficial to transportation and use. Freezing temperature: the precipitation temperature of polyaluminum chloride is lower than that of aluminum sulfate, which is conducive to the use and storage of low temperature areas. pH value: Compared with other flocculants, the pH value of polyaluminum chloride is the highest at the same concentration. Therefore, its corrosion is minimal. Filtration performance: in water treatment, the precipitation effluent treated with polyaluminum chloride is smaller than the turbidity of aluminum sulfate, and the flocculation is large, so it is generally retained on the surface of the filter layer during filtration, which can shorten the flushing time and is easy to rinse. Polyaluminium chloride not only has good flocculation performance, but also when the turbidity of raw water increases, the increase of its dosage is less than that of ferric chloride, and the higher the turbidity, the more significant the difference. If compared with aluminum sulfate, the dosage of polyaluminum chloride is less than that of aluminum sulfate at any turbidity. Polyaluminium chloride can be applied to the treatment of high turbidity water in the Yellow River. In a certain range, the higher the turbidity of raw water, the greater the range of turbidity changes, and its superior performance is obvious.

After polyaluminium chloride is added to water, hydrolysis and polymerization occur to generate a series of aluminum salt hydrolysis polymers, which are then removed by flocculation precipitation and filtration. This effect is similar to that of aluminum sulfate and ferric chloride flocculant. According to the toxicity test, it is non-toxic, has no obvious accumulation effect in animals, has no teratogenicity and mutagenicity, and has no carcinogenic risk. The tap water purified with it meets the standard of drinking water. Polyaluminum chloride flocculant has the advantages of rapid floc formation, large floc particles, good mechanical strength and high settling speed. For high turbidity water, low temperature and low turbidity water, colored water and polluted water, can achieve good flocculation effect, and the pH value of raw water, temperature, turbidity, alkalinity, organic matter and other changes, have a strong adaptability. Such as combined with organic polymer treatment of high turbidity water, the effect is better.

Due to the high effective component of polyaluminum chloride (Al2O3), the dosage is small, and it is convenient for transportation, storage and use. Under the condition of achieving the same flocculation effect, the dosage of Al2O3 for low turbidity water is only 50%-75% of aluminum sulfate. For high turbidity water, about 30%-40% of aluminum sulfate. It has the advantages of low dosage and low cost of water purification, so polyaluminium chloride plays an important role in the development of water treatment industry.