Poly-silicic-cation coagulants (PSiCs) with different pH were prepared by synchronous-polymerization. The characteristics and coagulation performances of the coagulants were analyzed. The results show that the crystal, structure and morphology of PSiC are influenced by pH and the optimal preparation pH is 1.5. The crystal analysis shows that some new complex compounds are formed in PSiC. The polymerization form and complexation degree of PSiC with pH of 1.5 are better than at other pH values. The structure and morphology analyses imply that the contents of ionic polymerized bonds, high polymers and irregular PSiC units decrease, and cross-copolymerization of Fe (III) and Al (III) hydroxyl polymers is weakened when pH is too low or too high. Coagulation experiments also indicate that the PSiC with pH value of 1.5 exhibits better coagulation performance in removing turbidity, COD and chroma of paper mill wastewater. (C) 2014 Elsevier B.V. All rights reserved.