MODELING ION ADSORPTION ON ALUMINUM HYDROXIDE MODIFIED SILICA

The effect of component hydroxide and oxide interaction on Cd2+ and SO42- adsorption in suspensions of Al(OH)3/SiO2 was modeled using two kinds of surface site distributions incorporated in the triple-layer surface complexation model. The mixed site distribution assumes that Al(OH)3 surface sites are uniformly distributed on the SiO2 surface with the overall surface potential contributed by both Al(OH)3 and SiO2 surface sites. The patch site distribution assumes that two kinds of surfaces are present on the particle and that the double layer associated with one surface does not affect surface reactions on the other. Enhanced Cd2+ adsorption and reduced SO42- adsorption at low Al to SiO2 ratios were modeled using the mixed site distribution. The modeling results suggest that the change in surface potential caused by the formation of AI(OH)3 on SiO2 surface has significant effects on Cd2+ and SO42-adsorption.