Coagulation-flocculation of colloidal suspensions of kaolinite, bentonite, and alumina by chitosan sulfate

This article reports on the removal of colloidal suspensions of kaolinite, bentonite, and alumina using chitosan sulfate (ChS). ChS was synthesized by partial introduction of sulfate groups in the chitosan (Ch) structure. The polyampholyte (chitosan sulfate) shows variable charge depending on the pH of the solution. ChS was characterized by FTIR, 13C-NMR, elemental analysis, and potentiometric titrations. The ChS coagulation-flocculation capacity for kaolinite, bentonite, and alumina aqueous suspensions was systematically studied. The coagulation-flocculation process was carried out at various pH values and ChS concentrations. The pH range in which the largest ChS removal capacity was observed depended on particle type (4.5-5.5 for kaolinite, 4.5-7.0 for bentonite, and 7.0-8.0 for alumina). The removal of colloidal particles is explained by charge neutralization due to electrostatic interactions between ChS and particles and particle entrapping when the polyelectrolyte precipitates. © 2011 Wiley Periodicals, Inc