Polyaluminum chloride and aluminum sulfate, as two common and efficient flocculants, play an important role in water treatment. However, there are some differences in composition, performance, application and effect. In this article, we will discuss the differences in detail to help you better understand and apply the two types of flocculants.
Composition and Property
Polyaluminum Chloride, also PAC, is a water-soluble inorganic polymer between AlCl3 and Al(OH)3. It usually exists in the form of white, milk, or yellow solid. PAC has stronger electric neutralization properties than aluminum sulfate.
Aluminum Sulfate is a white crystalline inorganic salt with the formula Al2(SO4)3·xH2O. It is acidic after dissolving in the water.
Flocculation Mechanism
Polyaluminum Chloride:
Through the electric neutralization, PAC can coagulate colloids and particles in water to form large and tight flocs, thus accelerating the precipitation process and improving purification efficiency. At the same time, the sinking flocs can sweep more colloids and effectively remove pollutants such as SS, COD, BOD and heavy metal ions in water.
Aluminum Sulfate:
Aluminum sulfate dissolved in water will slowly hydrolyze to form positively charged Al(OH)3 colloid, which can adsorb negatively charged suspended particles in the water and make fine particles and natural colloidal particles in the water condense into large flocs, and then the sediment can be filtered out.
Advantages of PAC Over Aluminum Sulfate
PAC can be considered as pre-hydrolyzed aluminum sulfate and has more excellent characteristics.
- Application Effect: Both can be used in drinking water, industrial water, sewage treatment and other fields. But PAC is more effective in the treatment of high turbidity water and wastewater containing heavy metal ions.
- Conditions and Restrictions: PAC is suitable for a wide range of pH (5-9), so it has a good water purification effect under various water quality conditions. PAC solution is less corrosive to pipeline equipment, while aluminum sulfate solution is more acidic (the pH value of 1% solution is slightly higher than 3), and the corrosion of the system is more obvious. So in some occasions with high water quality requirements (such as drinking water treatment), it should be prudent to use chemicals or take other anti-corrosion measures.
- Flocculation Effect:
PAC can achieve better flocculation effect than aluminum sulfate. PAC has a large sedimentation rate, which can quickly form tight flocs, and its processing capacity is 1.5-3.0 times of using aluminum sulfate.
Moreover, PAC can achieve better flocculation effect in a small dose, and the common dose is 30-60 mg/L. According to Al2O3, the amount of PAC in the water with low turbidity is 25-40% of aluminum sulfate, and the amount in high turbidity is 10-25% of aluminum sulfate.
In contrast, it requires a larger amount of aluminum sulfate in the water treatment to achieve the ideal purification effect, which will not only increase the cost of treatment, but also have a certain impact on the water quality. Yet PAC is prone to over-stabilization and requires more precise dosage control. The dosage can be easily determined by a jar test.
Conclusion
In summary, there are differences between PAC and aluminum sulfate in chemical composition, mechanism, application field and conditions. In practical applications, appropriate chemical substances should be selected according to specific needs and conditions. We are a leading Industrial Water Treatment Chemicals manufacturer in China, if you have any questions, please feel free to contact us.