Abstract
The gelatinous precipitates from aqueous aluminium chloride solution on the addition of alkalies at various pH have been aged in the mother liquors for a given period of time. The resulting materials have been examined by Xβray diffraction studies. In addition, the changes in the pH value of the mother liquor and the amount of aluminium dissolved in the mother liquor during ageing have been checked under various conditions. As a result, it is found that the freshly precipitated gelatinous aluminium hydroxide exists in an amorphous type independently of the pH value and goes to pseudoboehmite by ageing, but the amount of aluminium dissolved in the mother liquor increases with rising pH value. By further ageing, however, hydrargillite is produced in contact with the aqueous medium at low pH, and bayerite at higher pH.
It is concluded that the crystallisation of gelatinous aluminium hydroxide precipitates aged with an aqueous medium occurs in the process magnified image and the presence of alkali plays an important role in promoting these transformations.