Relationship Between Aggregate and Sediment Bed Properties
The influence of the magnitude of inter-particle attraction, aggregate size and aggregate structure on the rheological behaviour of flocculated suspensions will be presented. Ninety nanometer diameter silica particles have been flocculated with poly acrylamide based cationic polymers of MW approx. 100kDa to 300kDa and 10% to 100% cationic charge. The amount of charge on the polymer influences the adsorption configuration 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. The bridging flocculation typically produced large, open aggregates while the charge patch mechanism results in smaller and denser aggregates. 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. Strong adhesion typically results in difficult to consolidate sediments and high shear yield stresses.