In this paper the influence of dispersion pH, ionic strength, and coagulant type on ceramic membrane microfiltration of TiO₂ dispersions were studied. A series of cross-flow microfiltration experiments were carried out at various pH values, ionic strengths and with various multivalent inorganic salts. Filtration behaviors were analyzed based on measurements of zeta potential of alumina membrane and TiO₂ particle and particle size distribution of the TiO₂ suspension. The results showed that inorganic anions affect the microfiltration of TiO₂ dispersion by changing the surface properties of both the alumina membrane and TiO₂ particle. The solution environment affects the dispersion of TiO₂ particles and plays a major role in the filtration flux.

Cross-flow microfiltration is a pressure-driven membrane process for separating dispersed matters in the range of sizes from 0.05 to 10 mm from liquids. The principle of solid/liquid separation can be described as a pressing of pure liquid through the membrane pores and through the deposit of solid particles on the membrane wall. In the absence of membrane fouling, the increasing thickness of the deposit of particles (cake formation) causes the initial rapid decrease of flux and limits the wider application of microfiltration. In spite of this, the separation process finds increasing use in water purification, wastewater treatment, brewing and biotechnology industries, amongst others.

The main factor limiting the application of cross-flow microfiltration and other pressure-driven membrane processes is flux decline due to membrane fouling and concentration polarization (Schafer et al., 2000). The steady-state value of permeate flux depends, besides hydrodynamic conditions (cross-flow velocity, the Reynolds number, shear stress and shear rate at the membrane surface) in the membrane system (Broussous et al., 2000) on physicochemical particle-particle and particle-membrane interactions (Huisman et al., 1999). One way of characterizing these particle-particle and particle-membrane interactions is the knowledge of the z-potential of both particle and membrane. This electrostatic characterization of membranes is a useful way to predict and interpret the performance of microfiltration process. The magnitude of the z-potential gives the information of the stability of the system. Near the isoelectric point—IEP (the value of pH where the charge and therefore z-potential of particles is equal to zero) the system is unstable and the particles tend to flocculate. Therefore, the stability of the particles and the particle-membrane system could affect the separation process. Many studies showed that permeate flux, J, can be easily changed by pH (kind of added salt), and salt concentration of the microfiltration dispersion (Nazzal and Wiesner, 1994; Mullet et al., 1997; Moritz et al., 2001; and Martín et al., 2003).

Chemical Engineering Journal, Microfiltration, Ionic Strength, Coagulation, Membrane Fouling, Zeta Potential, Alumina Membrane, Filtration Flux, Hydrodynamic Conditions, Cross Flow Velocity, Particl Membrane System, Cross Flow Microfiltration, Microfiltration Experiments.