Hydrolysis-precipitation studies of aluminum (III) solutions. I. Titration of acidified aluminum nitrate solutions

Abstract

Acidified aluminum nitrate solutions were titrated with alkali (NaOH or KOH) over a temperature range of 24°C to 90°C. A homogeneous distribution of added base was achieved by: (i) in situ decomposition of urea (90°C); and (ii) a novel method involving injection through a capillary submerged in the agitated salt solution.

The experimental pH curves are characterized by two plateaus (or platforms) separated by a steep jump in pH. These characteristic features were not previously observed in continuous titration experiments. This is especially true of the second platform, which begins at an OH/Al ratio larger than 2.5. Stable colloidal solutions or gels are formed on traversing this plateau. The hydrolysis-precipitation behavior was also followed by light scattering and x-ray diffraction measurements.

A qualitative picture of the neutralization process is developed.