Polyaluminum chloride as a coagulant What is its main characteristic? Poly aluminum chloride, also known as basic aluminum chloride, also known as polymeric aluminum hydroxychloride. It is an inorganic polymer multivalent polyelectrolyte flocculant, divided into polymeric aluminum hydroxychloride and polymeric aluminum hydroxy sulfate two categories. The polymeric aluminum hydroxychloride is a hydrolysis between aluminum chloride and aluminum hydroxide polymerization products, commonly known as basic aluminum chloride, the English name PAC. Polyaluminium chloride color with the size of the base change. The basal degree of alkalinity, also called alkalinity, is equal to [OH] / 3 [Al], ie the molar equivalent ratio of hydroxyl to aluminum in polyaluminum chloride. Polyaluminum chloride is light yellow and transparent when the basicity of the salt is in the range of 40% -60%. When it is more than 60%, it gradually becomes colorless and transparent with a sour and astringent taste. The shape of solid polyaluminum chloride also varies with the degree of salt. When the basicity of the salt is below 30%, it is crystalline; 30% -60% is colloidal; when it is more than 60%, it gradually becomes resinous; when it is below 70%, it is easy to absorb moisture and liquefy, while not more than 70% deliquescent. Polyaluminium chloride and the role of acid depolymerization reaction; so that the degree of polymerization and reduce the base to form a positive aluminum salt, flocculation effect will also be reduced. When reacted with a base, it increases its degree of polymerization and the degree of basicity of the salt, which further generates aluminum hydroxide precipitates and aluminates. If mixed with aluminum sulfate or other polyvalent salts, easy to produce co-precipitation, reduce or completely lose the flocculation performance. When the temperature is heated to above 110 ℃, decomposition occurs, gradually released hydrogen chloride gas, and finally decomposed into alumina. The alumina content is a measure of the effective composition of polyaluminum chloride. In general, the greater the relative density, the higher the alumina content. The basicity of the salt is another important quality index of the PAC, which is the determinant of the structural morphology, degree of polymerization, flocculation capacity, storage stability and pH value of the product. Under the same alumina content, the polyaluminum chloride has a lower viscosity than aluminum sulphate, and is therefore beneficial to transport and use. Freezing temperature: Poly aluminum chloride precipitation temperature is lower than aluminum sulfate, is conducive to low temperature use and storage. pH: Polyaluminium chloride has the highest pH at the same concentration as other flocculants. Therefore, it is the least corrosive. Filtration performance: In water treatment, polyaluminum chloride treated precipitation than the use of aluminum sulfate turbidity is small, floc large body, so the filter is generally retained in the filter surface, can shorten the flushing time and easy to clean . Polyaluminum chloride not only has good flocculation performance, but also increase the turbidity of raw water, the dosage of less increase than the rate of ferric chloride, the higher the turbidity, the more significant difference. As compared with aluminum sulfate, at any turbidity, polyaluminium chloride dosage are less than aluminum sulfate dosage. Polyaluminum 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, its superior performance is obvious. After the polyaluminum chloride is added into the water, hydrolysis and polymerization occur, a series of aluminum salt hydrolyzed polymers are generated, which are then removed by flocculation and filtration. The effect is similar to that of aluminum sulfate and ferric chloride. According to toxicity test showed that it is non-toxic, no significant accumulation in animals, teratogenicity and mutagenicity, no carcinogenic risk, use it to clean tap water meet drinking water standards. Polyaluminum chloride flocculant has the advantages of rapid formation of flocs, floc particles, good mechanical strength and high settling velocity. For high turbidity water, low temperature and low turbidity water, colored water and contaminated water, can achieve good flocculation effect, and the raw water pH value, temperature, turbidity, alkalinity, organic matter, etc., are more Strong adaptability. Such as organic polymers with high turbidity water treatment, the better. Due to the high content of Al2O3, the dosage is small, and it is easy to transport, store and use. When it reaches the same flocculation effect, it can be calculated as Al2O3 for low turbidity water and the dosage is only sulfuric acid Aluminum 50% -75%; for high turbidity water, equivalent to about 30% -40% aluminum sulfate. It has the advantages of less dosage and lower cost of pure water, so that PAC plays an important role in the development of water treatment.