Coagulation behavior of Al13 aggregates

The coagulation behavior of Al-13 aggregates formed in coagulation of kaolin was investigated by small angle static light scattering (SASLS), solid-state Al-27 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 Df. The in-situ AFM scanning in liquid system proved that the existence of linear A113 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. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.