Relationship between aggregate and sediment bed properties: Influence of inter-particle adhesion

The influence of the magnitude of inter-particle attraction and adhesion, aggregate size and aggregate structure on the shear and compressive rheological behaviour of flocculated suspensions has been studied. Ninety nanometer diameter silica particles have been flocculated with poly diallyldimethylammonium chloride based cationic polymers of molecular weight approximately 100–300 kDa and 10–100% cationic charge. The amount of charge on the polymer influences the adsorption conformation of the polymer which influences the dominant mechanism for inter-particle attraction. Low charge density results in primarily bridging flocculation while high charge density results in primarily charge patch attraction. Although the bridging adhesion is generally lower in magnitude than for the charge patch, the bridging flocculation typically produces large aggregates while the charge patch mechanism results in smaller aggregates due to the influence of shear during aggregation. The optimum dose for aggregation (supernatant clarity) of each type of polymer corresponds well with the polymer concentration which produces the maximum adhesive force measured with AFM. The influence of aggregate size on the compressive and shear yield stresses is weak, but the compressive and shear yield stresses increase linearly with increasing adhesion force.