Characteristics of aggregates formed by electroflocculation of a colloidal suspension

Electroflocculation (EF) is becoming recognized as an alternative process to conventional coagulation/flocculation, although both are somewhat different. The electrical current applied in EF to generate the active coagulant species creates a unique chemical/physical environment which affects coagulation mechanisms and subsequent aggregate formation. The chemical and physical characteristics of an electroflocculated kaolin suspension and the morphology/fractal dimension of the resulting aggregates were examined. An EF cell was operated in batch mode and comprised of two concentric electrodes-a stainless steel cathode (outer electrode) and an aluminum anode (inner electrode). The cell was run at constant current between 0.05 and 0.3 A, velocity gradients were 0-30 s^-1. The results show that the simultaneous hydrolysis occurring has a profound effect on the final pH and consequently on the coagulation mechanisms as indicated by differences in ζ potential measured. Moreover, the electrical field induced by passage of a current has an apparent effect on particle transport. A linear correlation between floc size and current was observed and lower fractal dimensions were obtained for larger floc sizes. The fractal dimensions of the flocs obtained in EF are on average lower than those reported for conventional coagulation.