Crossflow microfiltration of mineral dispersions using ceramic membranes

Abstract

Crossflow microflltration experiments were performed on aqueous dispersions of titanium dioxide through a 0.1 Urn pore size ceramic membrane at various operating parameters. The initial transient flux decline follows dead-end filtration theory, with the membrane resistance determined from the initial flux and the cake resistance determined from the rate of flux decline due to cake build-up. For long times, the observed fluxes reached steady- or nearly steady-state values, presumably as a result of the cake growth being arrested by the shear exerted at its surface. The steady-state fluxes increased with increasing inlet crossflow velocity and decreasing feed concentration. Rheological work has shown that the titania dispersions exhibit shear-thinning behaviour. Extreme sensitivity with pH was observed, whereby the dispersion viscosity can be changed by as much as an order of magnitude with pH variation at constant volume fraction. The steady-state permeate flux values were determined from the steady-state model based on the Kozeny—Carman equation for cake resistance and Darcy's law applied over the filter area to relate filtration rate to average pressure difference between the feed and permeate sides of the filter. The model includes a cake resistance of the cake layer, which was determined for the titanium dioxide dispersions by fitting the experimental flux data to the model. The resulting fluxes obtained from the model using simple values for the membrane resistance, cake resistance, and rheological parameters for each data set are in good agreement with the measured fluxes.