Properties of a filter cake formed in dead-end microfiltration of binary particulate mixtures

In order to experimentally examine the influence of the electrostatic interactions of charged particles on the properties of a filter cake that accumulates on microfiltration membranes, microfiltration experiments are conducted using binary particulate mixtures of titanium dioxide and silicon dioxide having the different values of the isoelectric point for each material. Electrostatic forces affect the average porosity and the average specific filtration resistance of the filter cake formed during filtration. In the pH range where two particles have opposite electrical charges, the particles tend to aggregate, and the cake formed is loosely packed, resulting in a lower resistance to flow. In contrast, in the pH range where both particles are charged with the same sign, particles are well dispersed by repulsive electrostatic forces, and form compact cakes of higher resistance during filtration, leading to lower filtration rates. Moreover, it is found that such charge effects of particles are weakened in the presence of salts because the double-layer thickness is suppressed. An important result is that surface interactions (hence the suspension stability) are as Important as operating conditions for microfiltration processing of binary particulate mixtures.