1. Raw Material Classification
Aluminum Hydroxide Method: Produced from aluminum hydroxide and hydrochloric acid. Features high purity and low heavy metal content, suitable for drinking water treatment.
Bauxite Method: Produced from bauxite and hydrochloric acid. It has low cost with a small amount of impurities, and is applicable to industrial wastewater treatment.
Calcium Aluminate Powder Method: Produced from calcium aluminate powder and hydrochloric acid. It boasts high basicity and moderate cost, and is used for sewage and drinking water treatment.
2. Core Production Processes
One-step Method (Alkali Dissolution Method)
First, aluminum hydroxide powder undergoes high-temperature acid dissolution with hydrochloric acid in a reaction kettle. Then polymerization and curing reactions are carried out to generate liquid PAC. Finally, the finished solid product is obtained through drying (roller/spray drying), crushing and packaging processes.
Two-step Method (Acid Dissolution + Neutralization)
Firstly, bauxite or aluminum hydroxide reacts with hydrochloric acid via acid dissolution to prepare aluminum chloride solution. Secondly, calcium aluminate powder or lime is added to adjust the basicity and initiate polymerization reaction. Finally, solid PAC is produced through pressure filtration for impurity removal, concentration and drying.
3. Comparison of Drying Processes
Roller Drying: Low cost with high water-insoluble substance content, applied to industrial wastewater treatment.
Plate and Frame Filtration + Roller Drying: Medium purity, suitable for municipal sewage treatment.
Spray Drying: High purity (Al₂O₃ ≥ 30%) and fast dissolution rate, specially used for drinking water treatment.
III. Functions of PAC in Water Treatment
1. Core Mechanisms
Charge Neutralization: PAC hydrolyzes to produce high-valent cations, which neutralize the negative charges on the surface of water colloids (such as clay and organic matter), destabilizing and aggregating suspended impurities.
Adsorption and Bridging: The hydroxyl groups on the high-molecular chains of PAC can adsorb tiny flocs and bridge them into large and dense flocs (alum flowers).
Sweeping and Entrapping: The aluminum hydroxide precipitate formed by PAC hydrolysis can sweep and entrap fine particulate matters in water to accelerate sedimentation.
2. Main Functions
Turbidity and SS Removal: It can efficiently remove suspended solids and colloidal substances in water, with a turbidity removal rate of over 90%.
Phosphorus Removal: Aluminum ions react with phosphate radicals in water to form insoluble precipitates, achieving a total phosphorus removal rate of more than 80% and meeting the Class A discharge standard.
Decolorization and COD Reduction: It can adsorb dye molecules and organic pollutants in water, effectively reducing water chroma and chemical oxygen demand (COD).
Heavy Metal Removal: It has a good adsorption effect on heavy metal ions such as lead and cadmium in water, reducing the toxicity of effluent water.
Algae Removal and Sterilization: It can destroy algal cell structures, inhibit water bloom growth and improve black and odorous water bodies.
3. Application Advantages
Wide pH Adaptation Range: It is effective in the pH range of 5–9, superior to aluminum sulfate which is only applicable to pH 6–8.
High Efficiency at Low Temperature: It maintains stable treatment performance for low-temperature and low-turbidity water, suitable for use in northern regions in winter.
Low Dosage and Low Cost: The required dosage is only 1/3 to 1/2 of that of aluminum sulfate, with less sludge production and lower overall operating cost.
Low Aluminum Residue: Its special high-molecular structure reduces the dissolution of free aluminum ions, complying with the national drinking water standard GB 5749-2022.
4. Typical Application Scenarios
Drinking Water: Used for coagulation and sedimentation in water plants to remove water turbidity, algae and organic pollutants.
Municipal Sewage: Applied to advanced phosphorus removal and decolorization of secondary effluent to ensure up-to-standard discharge.
Industrial Wastewater: Suitable for treatment of high-turbidity and high-COD wastewater from printing and dyeing, papermaking, chemical industry, coal washing and other industries.
Landscape Water and River Water: Used for emergency algae removal and turbidity reduction to improve black and odorous water bodies.
IV. Summary
Polymeric Aluminum Chloride (PAC) is manufactured with raw materials such as bauxite and aluminum hydroxide through acid dissolution, polymerization and drying processes. Relying on the three core mechanisms of charge neutralization, adsorption bridging, and sweeping & entrapping, it can efficiently remove suspended solids, colloids, phosphorus, heavy metals and algae from water. It is currently the most widely used inorganic polymer coagulant in the water treatment industry.
