Precipitation of boehmite from aluminum chloride solution: effect of pH and temperature

Aluminum hydroxide occurs in several polymorphs. The formation conditions of these polymorphs from a mother liquor still remain obscure. This study investigates the effects of pH values and precipitation temperature on the crystalline structure of the precipitated aluminum hydroxides. The aluminum hydroxides were precipitated from 0.5 M anhydrous aluminum chloride solution as precursor. Three pH values of 5.5, 7.0, and 9.0 and two aging temperatures of 20 and 85 °C were considered as precipitation conditions. All precipitates were aged for 24 h. The formed aluminum hydroxides were characterized using X-ray diffractometry. The experimental results revealed that the precipitation at 20 °C under neutral and acidic pH values lead to an amorphous structure. While, the precipitation at 20 °C under a basic pH resulted in a poorly crystalline nature, corresponding to the formation of pseudoboehmite. The precipitation at 85 °C under neutral and basic conditions evidently facilitated the formation of boehmite.

Keywords:

Aluminum hydroxide , Boehmite , X-ray diffractometry , Aluminum monohydroxide