At what pH range does alum work best?

Alum, or aluminum sulfate, is an effective coagulant used in water treatment processes, particularly in the removal of suspended solids and turbidity. Its optimal performance in coagulation and flocculation occurs within a pH range of 5.8 to 8.5. This is due to the fact that at this range, the hydrolysis of aluminum ions, released from alum when it dissolves, occurs efficiently, leading to the formation of Floc, which helps in the aggregation of particles for easier removal.

At pH levels below 5.8, the conditions can become too acidic, preventing the formation of effective aluminum hydroxides which significantly decreases the coagulation efficiency. Conversely, pH levels above 8.5 can result in a reduced availability of aluminum in soluble forms, leading to less effective treatment outcomes. Therefore, maintaining pH within the specified range is critical for optimizing the performance of alum in water treatment applications.