Coagulation behavior of Al13 aggregates

The coagulation behavior of Al13 aggregates formed in coagulation of kaolin was investigated by small angle static light scattering (SASLS), solid-state 27Al NMR and tapping mode atomic force microscope (TM-AFM). A kaolin suspension was coagulated by PACl containing high content of Al13 polycation (PACl-Al13). The results indicated that Al13 was predominant in destabilizing kaolin particles for PACl-Al13 coagulation even though at alkaline pH (pH 10). At such high pH, Al13 aggregates were observed when the dosage of PACl-Al13 was increased. In addition, the mechanism of coagulation by PACl-Al13 at alkaline pH was affected by dosage. When the dosage was insufficient, coagulation was caused by electrostatic patch, which led to compact flocs with high fractal dimension (Df). Interparticle bridging dominated the coagulation when the coagulant dosage approached the plateau of adsorption, which caused the looser flocs with low Df. The in-situ AFM scanning in liquid system proved that the existence of linear Al13 aggregates composed of a chain of coiled Al13 in coagulation by PACl-Al13 at a high dosage and alkaline pH. Meanwhile, several coiled Al13 aggregates with various dimensions were observed at such condition.