Adsorption of hydrolyzable metal ions at the oxide—water interface. II. Charge reversal of SiO 2 and TiO 2 colloids by adsorbed Co(II), La(III), and Th(IV) as model systems

Abstract

The detailed electrophoretic mobility behavior, supplemented by streaming potential data, for Si02 in aqueous solutions of Co(II), La(III), and Th(IV) has been determined as a function of metal ion concentration, pH, ionic strength, and percentage solids. The several charge reversals (CR) observed are, in order of increasing pH, shown to represent the point-of-zero charge (PZC) on the Si02 substrate (CR 1), the pH of surface nucleation of metal hydroxide (CR 2), and at high pH, the PZC of the metal hydroxide coating (CR 3).