Cross-flow microfiltration of aggregated submicron particles

The charge effects on the particle aggregation and the performance of cross-flow microfiltration of submicron particles are studied. A cell model is proposed to model the packing of aggregates in a filter cake. The effective densities of aggregates are estimated by an empirical equation, and the porosity and the specific filtration resistance of the filter cake under various electrolyte concentrations are calculated based on a force analysis. The packing structure in a filter cake can be divided into two modes. The region near the filter membrane has a compact structure and a high filtration resistance, while the portion of cake near the cake surface has a high porosity and a low filtration resistance due to the separation of particles or aggregates. For acid suspension with low electrolyte concentrations (I < 0.01 M), the particles in suspension are stable and separate with each other. The porosity and the specific filtration resistance of cake, and the pseudo-steady filtration rate remain almost constants independent of electrolyte concentration due to the constant zeta potential of particles. However, in the conditions of high electrolyte concentrations (I > 0.01 M), the compression of electric double layer and the decrease of zeta potential result in a high cake porosity and low specific filtration resistance of cake due to the aggregation of particles. The pseudo-steady filtration rate therefore increases with increasing the electrolyte concentration due to the increase of aggregate sizes. The calculated results of average cake properties, such as the porosity and the specific filtration resistance of cake, under various operating conditions agree fairly well with the experimental data. (C) 2002 Elsevier Science B.V. All rights reserved.