Which chemical is commonly used for aluminum coagulation in water treatment?

Aluminum sulfate, commonly known as alum, is widely used in water treatment processes for coagulation. Coagulation is the process of destabilizing and aggregating suspended particles in water, allowing them to clump together and form larger particles called flocs. When these flocs settle, they can be removed from the water, improving its clarity and quality.

Alum works effectively because it reacts with water to form aluminum ions, which have a positive charge. These aluminum ions neutralize the negative charges of suspended particles, causing them to aggregate and precipitate out of the water. This property makes alum particularly advantageous in water treatment applications, especially in removing turbidity and contaminants.

The other choices do not serve the same purpose in water treatment. Chlorine is primarily used for disinfection rather than coagulation. Sodium bicarbonate can adjust pH and control alkalinity but does not effectively assist in coagulation. Calcium chloride may be used for hardness adjustment or as a coagulant aid, but it does not serve as the primary coagulating agent in the same way that alum does.