Flocculation behaviour and mechanisms of cationic inorganic microparticle/polymer systems

Flocculation systems involving anionic microparticles/cationic polymers have become increasingly important in the past decade. However, very little work using inorganic cationic microparticles (CM) has been reported. In this work, fine clay flocculation was induced by a range of cationic colloidal alumina in conjunction with various linear polymers. Dynamic flocculation experiments, conducted with a photometric dispersion analyser (PDA 2000), showed that the effectiveness of CM as a single component flocculant was limited. However, in conjunction with an anionic polyacrylamide based copolymer, the flocculation efficiency improved significantly. Strong synergy between CM and anionic polymers also allow the system to be effective in a wide pH range and resistant to high shear. The sizes of clay flocs, formed by CM and various polymers under different levels of shear rates, have been characterised, and flocculation mechanisms have been revealed. The mechanisms suggest that bridging flocculation, contributed from the interaction between CM and anionic polymer, is the main function.