Effect of Silicon Dose and pH on Coagulation Performance and Floc Fractal Dimension of Poly-Silicic-Cation Coagulant

Abstract Poly-silicic-cation coagulants (PSiCs) were prepared from industrial wastes. Optimal conditions for synthesis of PSiCs were determined from orthogonal experiments. Coagulation performance was evaluated through jar tests in treatment of pulping and papermaking wastewater, and fractal dimensions of the flocs during coagulation were analyzed on basis of floc images on GRViewer. Results showed that coagulation performance and floc fractal dimension were significantly influenced by the Si/(Fe + Al) molar ratio and the pH of PSiCs. Optimal Si/(Fe + Al) ratio and pH were 0.8 and 1.5, respectively. Turbidity removal rate from pulping and papermaking wastewater decreased with the increasing Si/(Al + Fe) ratio, which increased with the rise of pH, but decreased at high pH. The floc fractal dimension was improved with the increase of silicon dose or pH, but decreased when the Si/(Fe + Al) ratio or pH was high. Adsorption bridging ability of PSiCs played a key role in the aggregation and breakup of flocs.