Covalently Bound Organic Silicate Aluminum Hybrid Coagulants: Preparation, Characterization, and Coagulation Behavior

Covalently bound organic silicate aluminum hybrid coagulants were synthesized by employing two silane coupling agents [diethoxydimethylsilane (DEDMS), gamma-aminopropylmethyldiethoxysilane (APDES)] as silicon sources. An additional coagulant was synthesized using another silane-tetraethylorthosilicate (TEOS) for comparison. Both the coagulant with DEDMS and that with APDES as the silicon source were shown to be covalently bound by infrared (IR) analysis. All three hybrid coagulants were characterized by pH, zeta potential, Al species distribution, and transmission electron microscopy (TEM) analysis. The results indicated that the silicon source played a significant role in aspects of the chemical and physical structure, Al species distribution, and electrochemistry characteristics. Specifically, the coagulant with APDES as the silicon source featured the highest zeta potential value, the highest content of Al(13), and reticulated aggregate. The coagulation behaviors of the three hybrid coagulants were also investigated by treating synthetic water containing humic acid (HA). The hybrid coagulant with APDES as the silicon source exhibited the best coagulation behavior in terms of HA removal and turbidity removal, due to the combination of the zeta potential, Al species distribution, and organic functional groups.