Thermodynamics of the decomposition of aluminum chloride hexahydrate to prepare alumina

High-alumina coal fly ash is a high-quality alternative to produce alumina as one of the raw materials for the production of aluminum. The extraction of alumina from coal fly ash with hydrochloric acid is a common treatment method. With this method, coal fly ash is leached with hydrochloric acid to obtain an aluminum chloride solution which is then separated, purified, and concentrated to form aluminum chloride hexahydrate. Alumina is then prepared by calcining aluminum chloride hexahydrate. The decomposition processes of aluminum chloride hexahydrate significantly affect the physical and chemical properties of the alumina product. In this paper, the effects of temperature and decomposition atmosphere on the thermal decomposition reaction were studied by thermodynamic analysis. The crystal phase transformation and microscopic morphology of the decomposition products were studied by combining chemical analysis, XRD, and SEM techniques. The results showed that the chlorine content of the decomposition products obtained in the water vapor atmosphere was significantly lower than that obtained in the argon atmosphere.