PH‐sensitive Flocculation: Settling Rates And Sediment Densities

The polyelectrolytes chitosan and polyacrylic acid have been used to flocculate alumina, silica, and zircon suspensions. The flocculant concentrations and pH were such as to cause attractive interaction forces between particles, resulting in rapid sedimentation. Initial settling rates were typically on the order of 0.1 to 5 m/hr. After the formation of a sediment bed, the pH was changed to establish repulsive forces between the particles; additional sediment consolidation was seen to occur. By creating repulsion between the particles in the sediment, the volume of sediments could be reduced by between 10 to 50% compared to attractive flocculation only. For each case, increasing the molecular weight of the flocculant increased the settling rate and improved the supernatant clarity, but decreased the density of sediments. © 2006 American Institute of Chemical Engineers AIChE J, 2006