Calcination of Aluminum Chloride Hexahydrate (ACH) for Alumina Production: Implications for Alumina Extraction from Aluminum Rich Fly Ash (ARFA)

Alumina rich fly ash (ARFA) has been regarded as the alternative to bauxite in China. Hydrochloric acid process could be favored for alumina extraction, necessitating calcination of aluminum chloride hexahydate (ACH). In this work, the TGA/DSC results of ACH were used to suggest calcination procedures. Two-step calcinations of 200-1000°C and 350-1000°C did not increase the surface area of alumina, by comparison with one step 1000°C calcination, and a slow heating rate could improve the surface area. Calcination temperature was increased from 950 to 1250°C in a step of 50°C, and XRD, XRF, BET and gas pycnometer were used to characterize the alumina from calcinated ACH. Consistent results were obtained by these different techniques, and two groups of impurities were identified and related to alumina purity and surface area. By comparison with clays, it was suggested to remove impurities such as MgO, Na₂ O, K₂ O, P₂ O₅ and SO₃ in hydrochloric acid leaching of ARFA.