CHARGE EFFECTS ON INORGANIC MEMBRANE PERFORMANCE IN A CROSS-FLOW MICROFILTRATION PROCESS

Cross-flow microfiltration experiments were performed with 0.5 mu m si lica particles using an inorganic membrane of 0.2 mu m pore size. We a nalysed how several physico-chemical factors, such as solution pH, sal t concentration, and valency of the salt influenced permeate flux and fouling tendencies. The electrostatic properties of silica particles ( feed suspension) and alpha-alumina particles (active layer of the memb rane) were characterised by performing zeta potential measurements. It was found that the permeate flux is dependent on the surface charge o f the suspended particles and possibly dependent on the surface charge of the membrane. High permeate fluxes are obtained at high pH and low salt concentration. Under these circumstances the repulsion between t he silica particles is strong. In contrast, low filtration fluxes are measured at high salt concentration, low pH, and with a CaCl2 electrol yte, i.e. when the surface charges are weak and in the presence of spe cific cations. The net energy of interaction between the charged surfa ces involved in the microfiltration process was calculated using the D LVO theory. This gave qualitative arguments for the explanation of the observed changes in the permeate flux. (C) 1998 Elsevier Science B.V.