Preparation of Gelatinous Aluminium Hydroxide from Aqueous Solutions of Aluminium Salts by Reaction with Hexamine.

Abstract

The precipitation of gelatinous aluminium hydroxide from aqueous solutions of aluminium chloride or nitrate by reaction with hexamine (hexamethylenetetramine) has been investigatedunder various conditions. The resulting precipitates have been examined by X-ray diffraction study, infrared spectrophotometry and thermal analysis (TG and DTA). As a result, it isfound that the composition of the precipitates depends on the experimental conditions, especially the pH value of aqueous solutions: amorphous aluminium hydroxide is precipitatedatpH 4 at 50 and 75°C, but not at 25°C; pseudoboehmite is accompanied by amorphous aluminium hydroxide at pH 5 regardless of temperature. In addition, when the precipitate isformed at lower temperature or from the aqueous solutions of aluminium salt at higher concentrations and/or on addition of hexamine rapidly, bayerite or hydrargillite is accompanied by amorphous aluminium hydroxide and pseudoboehmite. The composition of the precipitatesis little affected by the kind of aqueous aluminium salt solutions.