Structure of aluminum hydroxide gel II: aging mechanism.

The aging of aluminum hydroxide gel prepared by the reaction of aluminum chloride and ammonium hydroxide was studied by measurement of pH, acid-consuming capacity, hydroxide to aluminum ratio, chloride activity, and X-ray line broadening. The results were consistent with a polymer model involving particle growth by a deprotonation-dehydration mechanism. Anions inhibit this reaction by binding to the positively charged edges of the hydroxyaluminum polymers.