Mechanisms of Coagulation With Aluminum Salts

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Abstract
A model is developed that describes the charge neutralization aspects of coagulation, based on fundamental equations describing aluminum speciation and solubility, particle electrodouble‐layer characteristics, and the effect of aluminum‐hydroxide deposition on the surfaces of colloidal or suspended particles. Model predictions are compared with results from closely controlled jar‐test experiments employing the addition of aluminum salts to synthetic suspensions, with good agreement under most conditions. The model's success suggests that charge neutralization coagulation can be explained as the partial coverage of negatively charged particles by positively charged aluminum hydroxide. Predicted conditions of pH and coagulant dosage for optimal destabilization of typical raw waters correspond with those recommended in practice, both for aluminum‐ and iron‐salt coagulants.