FRESHLY FORMED ALUMINUM(III) HYDROXIDE COLLOIDS - INFLUENCE OF AGING,SURFACE COMPLEXATION AND SILICATE SUBSTITUTION

A new ''flash'' neutralization technique has been used to mix AlCl3/Na -2 tartrate solutions with different proportions of NaOH/Na2SiO3 solut ions at 25 degrees C. The colloids formed have been characterized with regard to their size, zeta potential and time stability. The results show that the initially formed aluminum hydroxide is characterized by a high-solubility product and is susceptible to dissolution with the f ormation of AlO4Al12(OH)(24)(H2O)(12)(7+) in slightly acidic solution and recrystallization in alkaline solution. The presence of tartrate i ons lowers the zeta potential via surface complexation and inhibits th e recrystallization process. The particles formed in the presence of s ilicate gradually turn increasingly anionic in character as the propor tion of silicate in the neutralizing solution increases. It is shown t hat, for each amount of silicate, the particle size passes a maximum w hich approximately coincides with the pH at which zero mobility is reg istered.