Characterization and coagulation performance of covalently bound organic silicate aluminum hybrid coagulants: effects of Si/Al, B value and pH

Covalently bound inorganic-organic hybrid coagulants are believed to be the goal of coagulant development for water treatment. In this study, covalently bound organic silicate aluminum hybrid coagulants were synthesized by employing gamma-aminopropylmethyldiethoxysilane (APDES) as silicon source with different Si/Al molar ratios (Si/Al = 0.1, 0.2, 0.3, and 0.4) and basicity values (B = 0.5, 1.0, 1.5, and 2.0). The APDES-Al hybrid coagulants (HC-As) were characterized by the measurement and analysis of pH, zeta potential, Al species distribution, and morphology. The results indicated that Si/Al and B played important roles in aspects of the physical structure, the Al species distribution, and the electrochemistry characteristics. Specifically, the HC-A with Si/Al = 0.4 and B = 2.0 featured the highest content of Al-13, the reticulated aggregate and the largest pH range for high zeta potential. The coagulation performances of HC-As were also investigated by treating synthetic water. At a low dosage, the HC-A with Si/Al = 0.4 and B = 2.0 exhibited the best coagulation behavior in terms of humic acid removal and turbidity removal. Besides Si/Al and B, the effect of pH on the coagulation performance of HC-A was also studied using an additional hybrid coagulant with tetraethoxysilane as the Si source for comparison. The results showed that HC-A has a larger pH range for simultaneous humic acid and turbidity removal.