An electrolytic treatment promoting aggregation compatible with the production of a dense aggregate was developed and studied in a batch test to thicken the retentate without coagulant dosage. A kaolin suspension with turbidity of about 200 NTU with a large fraction of fine particulates was used as the retentate. The aggregation of the electrochemically treated suspension increased with increasing mixing intensity in the range of 40-160 rpm for 5 min. The electrolytic treatment could also decrease the residual turbidity at the retention of about 150 h to one-fourth that of the untreated suspension, and moreover did not significantly change the sludge concentration, in contrast to the decreased sludge concentration of the acidified suspension maintained in the pH range of 4.5-5.0. A positive shift of the surface charge of particulates observed in the treated suspension suggests that the particle destabilization occurred in a pH range of 5.5-7.0, because of the hydrolysis of Al ions released electrochemically from kaolin clay. (c) 2007 Elsevier B.V. All rights reserved.