2000 Volume 11 Issue 2 Pages 125-136
Adsorption of orthosilicic acid on two low Si/Al (KyP and KiP) and one high Si/Al (KnP) nano-ball allophane samples was found to be controlled by the species type of the acid. There seemed to be a higher preference for the anion species to the neutral species. Adsorption increased with increasing solution pH with the highest adsorption occurring at initial pH 10. Further increase in pH, however, led to reduced levels in adsorption, particularly in the KnP sample due to repulsion between the negatively charged silanol groups and the anion species of the acid. Adsorption was higher in the low Si/Al samples due to their relatively higher number of aluminol groups per unit mass. The estimated Zero Point of Silicon Adsorption, which was pH dependent, was found to be higher in the KnP sample due to its higher inherent Si content. Adsorption data conformed only to the Freundlich model with the Freundlich parameters increasing with increasing solution pH to a maximum at initial pH 10. Release of Al occurred only at pH 10 and was highly correlated with Si adsorption in the low Si/Al samples suggesting a partial replacement of Al with Si at the pore region.
