Application and advantage of polyaluminum chloride in water treatment

Application and advantage of polyaluminum chloride in water treatment

Overview of polyaluminum chloride

Polyaluminium Chloride (PAC) is an efficient inorganic polymer coagulant. Its general chemical formula was ₆ [Al₂(OH)ₙCl₆]ₘ, where n≤5 and m < 10. In ₃, between AlCl and Al(OH)₃, it is formed through hydroxyl bridging polymerization and has a better coagulability than traditional aluminum salts.

Second, the production process of polyaluminum chloride

At present, the industrial production of PAC mainly has the following methods:

Aluminum ash acid dissolution method: the use of aluminum ash and hydrochloric acid reaction preparation, the process is simple but the product impurities more

Aluminum hydroxide acid dissolution method: industrial aluminum hydroxide as raw material, reaction with hydrochloric acid to prepare

Bauxite process: polymerization of bauxite by reaction with hydrochloric acid

Pyrolysis of crystalline aluminum chloride: high purity PAC is prepared by pyrolysis of crystalline aluminum chloride

Third, the action mechanism of polyaluminum chloride in water treatment

Electric neutralization: PAC hydrolysis produces a large amount of high positive charge, which can effectively neutralize the negative charge on the surface of colloidal particles, reduce the ζ potential, and destroy the stability of colloidal particles

Adsorption bridging action: The active group on the PAC molecular chain can adsorb multiple colloidal particles to form a "colloid-Pac-colloidal" flocculate

Net sweeping action: the formed alumina hydroxide precipitate can net and sweep the tiny particles in the water during the settling process

Fourth, the specific application of polyaluminum chloride in water treatment

1.Drinking water treatment

Effectively remove suspended matter, colloidal matter and some dissolved organic matter in water

The treatment effect of low temperature and turbidity water is better than that of traditional aluminum salt

The residual aluminum content is low, which meets the drinking water sanitation standard

2.Industrial wastewater treatment

Printing and dyeing wastewater: It has good decolorization effect on dye molecules

Paper wastewater: Effective removal of lignin and fine fibers

Food processing wastewater: High removal rate of oil and protein contaminants

Electroplating wastewater: can remove heavy metal ions

3.Urban sewage treatment

The sludge yield is 20-30% less than that of conventional coagulants

The formed floc is dense and the settling speed is fast

The removal rate of phosphorus can reach more than 90%

4.Comparative advantages of polyaluminum chloride and traditional coagulants

Polyaluminum chloride (PAC) Conventional aluminum salts (e.g., aluminum sulfate)

Flocculation effect Flocs large, dense, fast settling flocs loose, slow settling

pH adaptation range 5-9(wider) 6.5-7.5(narrower)

The dosage is lower and higher

The residual aluminum is less and more

The corrosion is weak and strong

Low temperature adaptability is poor

The sludge production is much less

Six, use precautions

Optimal dosage determination: need to be determined by beaker test, excessive dosage may lead to colloid re-stability

Dissolution and dilution: Solid products should be dissolved and diluted into 10-15% solution before adding

pH control: The best pH range is 5-9, beyond this range need to be adjusted

Mixing conditions: Rapid mixing (30-60s) is conducive to drug dispersion

Storage conditions: Liquid products to avoid long-term exposure, solid products moisture-proof

Vii. Future Development Trend

Composite PAC: Development of composite products containing elements such as iron and silicon to enhance specific properties

Nanotechnology application: Study on nano-scale PAC to improve coagulation efficiency

Green production process: Develop clean production process with low energy consumption and low pollution

Intelligent dosing system: combined with online monitoring to achieve accurate automatic dosing

Specialty PAC: Development of specially formulated products for specific water quality

As an efficient and economical water treatment agent, with the continuous progress of process technology, polyaluminum chloride will play a more important role in the field of water purification, and make greater contributions to ensuring water resources safety and environmental protection.