Compressive and shear properties of flocculated kaolinite–polyacrylamide suspensions

The influence of cationic and anionic polyacrylamides (PAM) on the compressive and shear properties of kaolinite suspensions has been investigated at pH 7. The compressive properties show cationic PAM based suspensions to be less compressible than the anionic PAM based suspensions. On the other hand, rheological measurements show that the kaolinite–PAM system is thixotropic with a measurable yield stress. A structural kinetic model (SKM) was used to characterize the thixotropic behaviour of the suspension, while the viscoelastic properties were measured using oscillatory and creep measurements. The shear properties show similar trends to compressive properties. It is found that the magnitudes of the yield stress, critical stress, elastic and viscous modulus are strongly dependent upon floc 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 floc structure-related adsorption. The strong electrostatic interactions between the kaolinite surface and cationic polymer chains produce stronger and less compressible flocs. This work has been very successful in establishing the link between compressive and shear properties for the flocculated kaolinite–PAM suspensions.