Structure and kinetics of aggregating colloidal haematite
Photon correlation spectroscopy is used here to measure the hydrodynamic radius of haematite particles induced to aggregate by the addition of various concentrations of KCl. The kinetics of aggregation are followed over long time intervals (as long as the particles remain in suspension) and the results modelled using Smoluchowski's kinetic equation with rate constants modified to account for interaggregate repulsive and attractive forces and account taken of the nature of packing within the aggregate structure. The aggregating haematite particles are well described by a fractal geometry with a fractal dimension of 2.3 at salt concentrations greater than the critical coagulation concentration. A somewhat higher fractal dimension appears to be appropriate for aggregation under salinity conditions where a repulsion barrier exists.