A comparative study of electrocoagulation and coagulation of aqueous suspensions of kaolinite powders.

Removal of kaolinite particles from their synthetically prepared suspensions was studied by electrocoagulation and coagulation to investigate the effect of such operating parameters as initial pH, coagulant dosage, applied voltage, current density, and time. Coagulation was more effective in a wider pH range (pH 5-8) than electrocoagulation which yielded optimum effectiveness in a relatively narrower pH range around 9, where, in both methods, these pH values corresponded to near-zero zeta potentials of kaolinite particles. The mechanism for both coagulation methods was aggregation through charge neutralization and/or enmeshment in aluminum hydroxide precipitates. The kinetics of electrocoagulation was very fast (<10 min) in approaching a residual turbidity, which could be modeled with a second-order rate equation.