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The Function of Poly Aluminum Chloride in Water Treatment

Poly Aluminum Chloride in Water Treatment

There are different types of suspended and colloidal materials in surface waters that in order to remove these in water treatment plants, must Coagulant should be used. One of the newest coagulants is poly aluminum chloride, also known as PAC.

In recent years, poly aluminum chloride has become very popular in the water treatment industry, beating out its longtime competitors, aluminum sulfate and ferric chloride. This popularity is due to the fact that PAC has high coagulation efficiency and has the highest range of pH and temperature application compared to other chemicals used in the treatment system. Today, this polymer has become one of the most common coagulants used in water and wastewater treatment in most countries, including the United Kingdom, the United States, France, Canada, China, and Italy.

Why is Poly Aluminium Chloride used in Water Treatment?

One of the prominent features of this polymer in its performance is the stable neutralization of colloidal particles, which creates suitable conditions for chemical coagulation of particles and ultimately the instability of colloidal particles. Once the mixture is in good condition to stabilize the suspended particles, while the solution is slowly stirring, the time required for the particles to coagulate and eventually flocculation is provided.

Finally, as water passes through the sedimentation pond, the solid particles clot and are separated by sedimentation. The performance range of poly aluminum chloride in water treatment at pH is between 5 to 9 and the most suitable performance range, neutral pH, is between 6.5 to 7.6. By forming hydroxyl ions and polyvalent anionic polymers, this substance causes the formation of electrically inorganic molecules and macromolecules in water, resulting in the coagulation and flocculation of suspended particles.

Poly Aluminum Chloride in Water Treatment

What is the coagulation and Flocculation process? 

In the coagulation and flocculation process, chemical coagulants are added to water, effluent, or wastewater to remove Excess water material, such as suspended solids, colloidal particles, and various solutions. Colloidal particles are the most important substances that must be removed in the flocculation process. These particles do not dissolve or settle in water but are mixed with water and dispersed in it. These particles are between 1 and 100 nanometers in size and often have a surface charge. The presence of this surface charge makes it difficult to remove these materials. This is where coagulants come into play. One of the materials used for this purpose is poly aluminum chloride.

Coagulation Process by Poly Aluminum Chloride:

To remove colloidal materials and water impurities, two mechanisms must be used: engaging with sediment clots and stabilizing the electrical charges of the material. Colloidal particles in water are mainly negatively charged; aluminum salts, which form several cations, bind to these negative substances. The important point here is the amount of coagulant used. It must be used in the required amount and otherwise it will give the opposite result. Eventually, these particles are bonded together by poly aluminum chloride and possibly other auxiliaries and settled.

Some Advantages of PAC When Used in Water and Wastewater Treatment:

Poly aluminum chloride has long been used as an effective and efficient material for the treatment of municipal water, wastewater, and industrial effluents. The structure of this product is composed of aluminum ions in the form of aluminum sulfate. One of the effective reasons for using poly aluminum chloride in water treatment is its availability and cost-effectiveness. Other notable benefits include:

  • Increase power in removing water turbidity
  • Wide pH range of action
  • More cost-effective than aluminum sulfate
  • No change in the chemical texture of water
  • Lowering the pH for water that has a lower alkalinity


poly aluminum chloride is an inorganic compound found in the form of yellow solid powder and is one of the most important compounds in the water and wastewater treatment industries. As you know, the use of methods and materials that can improve the efficiency of water and wastewater treatment has recently been considered by researchers, because hygiene is very important in this area.

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6 thoughts on “The Function of Poly Aluminum Chloride in Water Treatment

  1. 李娜 says:

    If PAC is needed, at what stage of the water treatment process is this compound added?

    1. china chemicals says:

      Polyaluminum chloride can be added before coagulation, during chemical addition, or during the settling step, before sand filtration. In the first stage, it is removed from the water during the coagulation process, and in the second stage, through filtration.

  2. anna says:

    What is the suitable pH for coagulation of poly aluminum chloride in water treatment?

    1. china chemicals says:

      Due to the fact that in the coagulation process, any coagulant, including poly aluminum chloride, is within a certain range of pH, pH control is of particular importance. Studies on pH have shown that the proper pH significantly removes contaminants and the appropriate range for improving the performance of poly aluminum chloride is between 5 and 7.

  3. nili says:

    What is the difference between coagulant and flocculant?

    1. china chemicals says:

      Coagulation and flocculation are two separate processes, used in succession, to overcome the forces stabilizing the suspended particles. While coagulation neutralizes the charges on the particles, flocculation enables them to bind together, making them bigger, so that they can be more easily separated from the liquid.

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