CHARACTERIZATION OF THE ELECTROKINETIC PROPERTIES OF PLANE INORGANIC MEMBRANES USING STREAMING POTENTIAL MEASUREMENTS

We present and test a device designed to measure the streaming potenti al of plane inorganic membrane during filtration. Two kinds of micropo rous membranes (a membrane made of a mixture of alumina-titania and th is same type of membrane covered with an additional titania layer) are studied with different pH, ionic strength and electrolyte nature. The modification of the surface acid-basic equilibriums is analysed from the streaming potential measurements. The pores size of the studied me mbranes is large enough to avoid overlapping of the double layers. Str eaming potential measurements are used to determine the zeta potential of the membranes from the Helmholtz-Smoluchowski relationship, correc ted for the lowest ionic strengths studied. The shifting of the isoele ctric point of the membranes studied with CaCl2 and Na2SO4 solutions s hows specific adsorption of calcium and sulfate ions onto the surface. The additional titania layer on the alumina-titania support does not seem to modify the electrokinetic properties of the membrane. The inte ractions of the alumina-titania membrane with the H+ and OH- ions are analysed by studying the variations of pH between permeate and retenta te compartments. These variations allow determining the isoelectric po int of the membrane with a reasonable precision.