Thermal decomposition of precipitated low bulk density basic aluminium sulfate

Hydrated basic aluminium sulfates (BAS) are of great importance as precursor material for the preparation of activated and high pure calcined aluminas. Low bulk density category BAS powders have superior quality over higher bulk density varieties in terms of higher surface area, more active sites for adsorption, etc. A brief description on the processing route of low bulk density BAS powders utilizing aluminium sulfate and ammonia as hydrolyzing precipitant has been presented. Low Al3+ concentration and pH of around 7–7.2 were found to be crucial for formation of such material. Characterization of this low bulk density material and its different calcined products was also carried out. The characterization was performed through XRD, FTIR and DTA studies. The XRD analysis indicated precipitated powder to be an amorphous material. Interestingly, this amorphous structure is retained till 800 °C. At 900 °C, η-Al2O3 phase appears to be the only transitional phase during its transformation to α-Al2O3 at 1100–1200 °C. FTIR study showed characteristic vibration modes related to molecular water, co-ordinated sulfate and AlO bonds.