What is the optimal pH range for removing particulate matter using alum as a coagulant?

The optimal pH range for removing particulate matter using alum as a coagulant is typically between 6.5 to 7.2. At this pH level, alum (aluminum sulfate) is most effective in destabilizing colloidal particles due to the optimal formation of aluminum hydroxide, which facilitates the aggregation and settling of these particles.

Within this pH range, the hydrolysis of aluminum occurs efficiently, resulting in the formation of a charge neutralizing agent that helps bind fine particles together into larger aggregates, or flocs. This process enhances sedimentation and filtration. The conditions found between 6.5 and 7.2 strike a balance where particulate matter can be effectively removed from water, making this range ideal for the coagulation process with alum.

Outside of this pH range, coagulant performance may diminish. For example, at lower pH levels, the coagulant can lead to increased solubility and less effective aggregation of particles. Conversely, at higher pH levels, the precipitation of aluminum hydroxide may become controlled, again limiting the coaguation efficiency. Thus, the choice of pH for optimal particle removal using alum is crucial for achieving effective clarifying results in water treatment processes.