Cationic starch as the effective flocculant of silica in the presence of different surfactants

The efficiency of cationic starch (CS) as the flocculating agent of silica particles in the presence of different surfactants was studied. Using such techniques as UV-Vis spectroscopy, surface tensiometry and electrophoretic mobility, it was established that cationic starch is an effective flocculant of the silica particles. Furthermore, bridging flocculation was proposed as the main mechanism of flocculation when the concentration of cationic starch is in the range from 1 to 100 ppm. It was also observed that at high polymer concentrations (800 ppm) depletion stabilization of the system occurs. However, the presence of surfactants influences the flocculation process. The conducted measurements show that the interactions between the cationic starch and some anionic surfactants (hydrocarbon as well as fluorinated and silicone ones) lead to the formation of polymer-surfactant complexes. In such case, the efficiency of CS as the flocculating agent is greatly reduced. The paper emphasizes the importance of cationic starch as an effective flocculant but it also points out that in the presence of surfactants, the flocculation conditions have to be adjusted. These results could find many industrial applications for example in the wastewater treatment.