Thermal Decomposition of Aluminum Chloride Hexahydrate to Produce Aluminum Oxide

The paper highlights the issues of thermal decomposition of aluminum chloride hexahydrate which is applied to the integrated technology of ash processing from the combustion of Ekibastuz coal. To solve this problem the possibility of using thermal decomposition of AlCl3·6H2O crystals in a static state and in a fluidized bed is considered. This approach allowed conducting a comparative assessment and selection of the most rational method for the thermal decomposition of ACH from a technological and economic point of view. It was found that under the conditions of thermal decomposition of ACH in a static state, its maximum decomposition to Al2O3 is achieved at a temperature of 400°C. The residual chlorine content in alumina is 1.09%, and aluminum in the form of AlCl3 is 0.5% of the total aluminum content. At a temperature of 500°C, the residual chlorine content in alumina is 0.71%, and AlCl3 is practically not detected. It was found that crystals of AlCl3·6H2O almost completely decompose in a fluidized bed at a temperature of 500°C (residual chlorine content 0.75%). In this case, the degree of decomposition of AlCl3·6H2O crystals was 87% at 300°C and 95% at 400°C. After calcining the samples obtained at 900°C, the residual chlorine content in them decreased to 0.27%, and after calcining at temperatures above 1000°C, no chlorine was detected in the samples at all. The specific surface area of alumina obtained after thermal decomposition at 400°C was 169.6 m2/g. After additional roasting of the sample at a temperature of 1200°C, the specific surface area of alumina decreased to 7.8 m2/g.