Kinetics of flocculation of kaolin by chitosan-based flocculants and the floc structure

The development of green and efficient flocculants with multiple active sites is of great significance to construct an efficient solid-liquid separation process with low dosage of flocculants, and realize efficient treatment and recycling of mineral processing wastewater. In order to investigate the flocculation performance of natural cationic linear polymer chitosan grafted cationic polyacrylamide (Chi-g-CPAM), chitosan (CTS), acrylamide (AM) and dimethyl diallyl ammonium chloride (DMDAAC) were grafted and copolymerized by changing initiator concentration. Finally, Chi-g-CPAM with different molecular structure was synthesized. The adsorption behavior of different chain structure flocculants on the surface of silica chip and the kinetics of kaolin flocculation were studied by dissipative quartz crystal microbalance (QCM-D). Floc structure of kaolin was analyzed. The kinetic equations were fitted to reveal the flocculation mechanism. Finally, the settling performance of the flocculant was tested. Results indicated that when the dosage of initiator is 0.10%, the grafting ratio of Chi-g-CPAM is 580.0%, and its branch chains are relatively long and numerous. The maximum equilibrium adsorption capacity is -11.68±0.40 Hz on the surface of SiO2. The K values of the first two stages of adsorption were 0.1814 and 0.5054, respectively. The adsorption conformation tended to extend outwards. The amount of flocculated kaolin is small and the structure of the floc is loose. Under the combined action of electric neutralization, bridging and netting, the settlement rate was 12.18 m/h and the turbidity of supernatant was the lowest of 13 NTU. When the dosage of initiator is 0.15%, the grafting ratio of Chi-g-CPAM is 493.1%, and its branch chains are numerous and short. The equilibrium adsorption capacity of the flocculant on the surface of SiO2 is reduced to -6.44±0.10 Hz. The K values of the first two stages of adsorption were 0.1864 and 0.4050, respectively. The adsorption conformation was flat. The bridging ability was weak, but its electric neutralization capacity was excellent. The floc structure was dense. The settlement rate was 5.68 m/h. Its flocculation performance is inferior to Chi-g-CPAM with few and short branch chains. The processes of flocculation of kaolinite by Chi-g-CPAM with short branch chains were better described by the pseudo-first-order kinetic equation. However, the process of flocculation of kaolinite by Chi-g-CPAM with vast and long branch chains was more complicated, and the pseudo-first-order and pseudo-second-order and Elovich equations fitted it well. The molecular structure of multi-active functional flocculants affects their adsorption conformation on the mineral surface, which is the key factor to determine their flocculation performance. The study is of great significance for the design of the molecular structure of macromolecular agents in mineral processing.