Aggregation of concentrated colloidal silica dispersions in flow

Concentrated suspensions of nanoparticles subjected to transport or shear forces are commonly encountered in many processes such as precipitation, wet comminution or filtration. In these processes, particles are likely to undergo processes of aggregation and fragmentation under physicochemical interactions and hydrodynamic forces. This study is focused on the analysis of the behaviour of colloidal silica in dense suspensions subjected to hydrodynamic forces. The destabilization of a colloidal silica suspension is done adding sodium chloride salt to a stable dispersion, so modifying the ionic force of the system. Batch experiments, performed in an agitated vessel, were made in order to observe the behaviour of the suspended particles under fixed operational parameters. Various techniques of characterization of the particle size (photon correlation spectroscopy, acoustic spectroscopy) and of the physicochemical properties of the suspensions were used allowing defining the silica dispersions properties (particle size distribution, particle arrangement during the aggregation process, pH, zeta potential). This work presents a study of on-line particle sizing during the aggregation process of colloidal silica by ultrasonic attenuation spectroscopy. The evolution of the particle size distribution versus time showed the different stages of the silica aggregation whose kinetic rates depend either on physicochemical or hydrodynamics parameters.