The use of an on-line scanning laser microscope for measuring the size distribution of particle aggregates in concentrated suspensions is demonstrated. This method allows quantification of the aggregate size distribution under actual process hydrodynamic conditions. The kinetics of floc formation processes and the subsequent breakage of flocs (e.g. under the degradative influence of shear fields encountered during transportation) can be followed in real-time. This can be used to elucidate the optimal dosing protocol for flocculant addition (agitation rate, floc dosage, polymer type etc.). Here we report, for the first time, direct on-line measurement of silica floc breakage kinetics in a stirred vessel. The floc breakage functions can be deduced for a range of nominal velocity gradients and for flocs that have been formed in different ways. Hence it is possible to predict the manner in which a floc population will behave under different shear conditions in processing circuits (e.g. in pipelines, within separation equipment). Other applications for this measurement methodology for acheiving improved understanding and control of minerals processing plant are assessed.