Effect of polyacrylamide polymers on floc size and rheological behaviour of kaolinite suspensions

The influence of cationic and anionic polyacrylamides (PAM) on the floe size, compressive yield stress, and rheological behaviour of kaolinite suspensions has been investigated at pH 7. At optimum polymer concentrations, the kaolinite floe sizes were larger in the presence of anionic PAM than cationic PAM. However, increasing the cationic and anionic surface charge from 10 to 35% reduces the floe size and increasing the anionic and catatonic molecular weight increases the floe size. The results show that the magnitude of the compressive yield stress, yield stress, critical stress, elastic and viscous modulus are strongly dependent upon the floe structure; with greater values being observed for the cationic PAM than for the anionic PAM. The difference in the compression or shear sensitivity of the flocculated slurries may be attributed to floe structure-related adsorption. It is found that the compressive yield stress, yield stress and viscoelastic behaviour are important factors that should be considered when selecting the type of polyelectrolyte for use in a particular solid-liquid separation. This work has been very successful in establishing the link between greater particle attraction and higher compressive yield stress yield stress, critical stress, and elastic and viscous modulus. (C) 2007 Elsevier B.V. All rights reserved.