Three-dimensional simulation was performed to predict the flux during the microfiltration of multi-dispersed iron oxide particles. The rate of particle deposition on the membrane surface was considered with the focus on particle transport mechanisms as a function of particle size. It was estimated that for the conditions of this study charge repulsion is the most important mechanism reducing cake formation. The voidage of the cake layer was estimated to be 0.39 for mono-dispersed particles and was decreased to 0.33 with moderate multi-dispersity. Taking pore blocking and cake layer formation in a random manner into consideration, flux vs. time curves could be simulated for any concentration of slurry. The simulated flux declines compare well with the experimental results.