Coagulation behavior of Al(13) aggregates

The coagulation behavior of Al(13) aggregates formed in coagulation of kaolin was investigated by small angle static light scattering (SASLS), solid-state (27)Al NMR and tapping mode atomic force microscope (TM-AFM). A kaolin suspension was coagulated by PACl containing high content of Al(13) polycation (PACl-Al(13)). The results indicated that Al(13) was predominant in destabilizing kaolin particles for PACl-Al(13) coagulation even though at alkaline pH (pH 10). At such high pH, Al(13) aggregates were observed when the dosage of PACl-Al(13) was increased. In addition, the mechanism of coagulation by PACl-Al(13) 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 (D(f)). Interparticle bridging dominated the coagulation when the coagulant dosage approached the plateau of adsorption, which caused the looser flocs with low D(f). The in-situ AFM scanning in liquid system proved that the existence of linear Al(13) aggregates composed of a chain of coiled Al(13) in coagulation by PACl-Al(13) at a high dosage and alkaline pH. Meanwhile, several coiled Al(13) aggregates with various dimensions were observed at such condition.