Which coagulant is described as more alkaline and suitable when alkalinity is favorable for coagulation?

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Coagulation works best when the water’s chemistry supports the formation of metal hydroxide flocs, and alkalinity plays a big role because it buffers pH and supplies the ions needed for hydrolysis. Sodium aluminate is a basic coagulant; when added it hydrolyzes and releases hydroxide ions, raising the water’s alkalinity while providing aluminum for floc formation. This makes it a good choice when alkalinity is favorable for coagulation and you want a coagulant that contributes alkalinity rather than depleting it. In contrast, aluminum sulfate and ferric chloride are acidic coagulants that tend to consume alkalinity and lower pH, and polymers act as flocculants rather than true coagulants.