Interfacial charge in mixed-oxide aqueous suspensions

Abstract

Surface charge and point of zero charge (PZC) in an aqueous silica-hematite mixed system were determined as a function of pH and of mixture composition by “mass titration” and acid-base titration of the suspension. The experiments showed that charging was independent, i.e. the overall surface charge was approximately equal to the sum of the surface charges of each oxide. The PZC of metal oxide mixtures corresponds to the pH where the net (overall) surface charge is zero, while one oxide bears a positive and the other a negative charge. The PZC of mixed oxides was found to lie between the PZC of pure oxides, depending on specific surface area, mass fraction and the PZC of each oxide in the mixture. It is shown that “mass titration” could be used as a method for determination of the PZC and surface charge of pure oxides and that it also may be applied to their mixtures.