Fragmentation of polymer‐bridged silica flocs by high shear impact: experiment and population balance modelling

Abstract

Fragmentation of polymer-bridged flocs is commonly encountered in many areas of suspension processing such as solid-liquid separation, washing and clarification. The effect of high shear impact on the fragmentation of polyelectrolyte-bridged silica flocs was investigated. The monodisperse silica suspension was first flocculated and then subjected to prolonged breakage in a shear field until a constant size distribution was attained. These flocs were then subjected to high shear impact breakage. The evolution of particle size distribution vs shearing time was monitored. This temporal evolution of size density function was compared with that obtained via population balance modelling converted to logarithmic scale to counter the 6-12 decades in particle size in volume. The Method of Lines (MoL) was employed to solve the equation. At lower breakage speed of 1500 rpm, excellent agreement between experimental and model size density functions was obtained where excellent matching was observed with the first and second moments. However, at the higher speed of 2500 rpm, the agreement is less satisfactory particularly with the variance. Scanning electron microscope images showed physical breakage of particles at this high shear rate.