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 (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 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. Crown