Polyaluminium Chloride (PAC) is an indispensable chemical in the modern water treatment landscape, valued for its efficiency, versatility, and cost-effectiveness. As an inorganic polymer coagulant, PAC plays a critical role in purifying both drinking water and treating industrial and municipal wastewater. Understanding its fundamental properties, diverse applications, and proper handling procedures is crucial for optimizing its performance and ensuring safety.

Chemical Properties and Mechanism:

Polyaluminium Chloride is essentially a polymeric aluminum salt. Its chemical formula, often represented as [Al2(OH)nCl6-n]m, indicates its complex polymeric structure. This structure provides a high charge density, enabling PAC to effectively neutralize the colloidal charges present in water. The primary mechanism involves the destabilization of suspended particles, colloids, and organic matter. PAC facilitates this by compressing the electrical double layer surrounding these particles and forming stable, voluminous flocs through adsorption bridging. These larger flocs then settle rapidly, making them easily removable via sedimentation or filtration.

Key Applications:

The applications of PAC are broad and impactful:

  • Wastewater Treatment: PAC is extensively used in treating various types of industrial wastewater, including that from the leather, textile, paper, mining, and food processing industries. It is highly effective in removing suspended solids, reducing turbidity, COD, BOD, and color.
  • Drinking Water Purification: In municipal water treatment plants, PAC is employed to clarify raw water sources like rivers and reservoirs. It efficiently removes turbidity, algae, and other suspended impurities, ensuring the production of safe and clear drinking water.
  • Other Industrial Uses: PAC also finds applications in areas such as the paper industry as a retention agent, and in the cosmetic industry.

Advantages of Using PAC:

  • High Efficiency: Rapid floc formation, faster settling, and superior removal of contaminants compared to traditional coagulants.
  • Wide Applicability: Effective across a broad pH range (typically 5-9) and in varying water temperatures, including low temperatures.
  • Cost-Effectiveness: Lower dosage requirements lead to reduced chemical costs, and improved process efficiency can lower overall operational expenses.
  • Reduced Sludge: Generates less sludge than some conventional coagulants, simplifying sludge handling and disposal.

Handling and Storage:

Proper handling and storage are vital for maintaining the efficacy and safety of PAC. Solid PAC should be stored in a cool, dry, and well-ventilated area, away from moisture and direct sunlight. It is typically supplied in polypropylene woven bags with an inner liner. Liquid PAC should also be stored in appropriate containers, protected from freezing and extreme heat. When preparing solutions, it's advisable to dissolve solid PAC in water at a recommended concentration and allow it to stabilize before further dilution and application. Avoid mixing PAC with incompatible chemicals. Always refer to the manufacturer's safety data sheet (SDS) for detailed handling instructions and personal protective equipment (PPE) recommendations.

By understanding and correctly applying Polyaluminium Chloride, industries and municipalities can significantly enhance their water treatment processes, ensuring compliance with environmental standards and safeguarding public health.