Chemical Adsorption of Al and Rh lions on SiO2 in Aqueous Solutions
1997 Volume 18 Issue 8 Pages 506-509
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1997 Volume 18 Issue 8 Pages 506-509
Chemical adsorption of Al and Rh ions on SiO2 in aqueous solutions are examined. It is revealed that complex cations, such as [Al(H2O)6]3+, [Al(OH)(H2O)5]2+ and [Al(OH)2(H2O)4]+, are adsorbed on SiO2 in the pH range 4 to 9 and that the adsorption results in the shifts of values in zeta-potential up to ca. +60 mV. On the other hand, Rh ions, which are inert in the pH range, are not adsorbed on SiO2 and no substantial differences are observed between values of zeta-potentials in Rh solutions and those in metal-free solutions. In the pH range 10 to 12, however, it is observed that both Al and Rh ions are adsorptive on SiO2. In All Rh containing solutions, the values of zeta-potential are between -50 to -60 mV, which are about 10 mV smaller than those in metal-free solutions. Therefore, it is supposed that complex anions, such as [Al(OH)4(H2O)2]- and [Rh(OH)4(H2O)2]-, are adsorbed in the alkaline solutions. As for the mechanism, we propose that the adsorption proceeds through ligand-exchange reactions of hydrated Al/Rh ions.
