Conditions for the Production of Active Aluminum Oxide Meeting the Requirements of Prospective Chloride Technology

Аннотация

The features of the dehydration and recrystallization processes were studied on samples of aluminum hydroxide obtained by carbonization of an aluminate solution at 40°C and isolated by Bayer’s decomposition. The main differences in the structural transformations of these samples consist in the individual sequence of the formation of polymorphic modifications of oxides in the dehydration of each aluminum hydroxide. The structural transformations of these types of hydroxide and the dynamics of the polymorphism of the decomposition products were studied in the temperature range of 100–1000°С. Data from crystallooptical, X-ray phase, and thermogravimetric methods of analysis showed that the recrystallization of the structure occurs more slowly when calcining the carbonized aluminum hydroxide than in the decomposition method. It is determined that, with the dehydration of the hydroxide, sodium aluminosilicate and carbon reduce the rate of formation of high-temperature modifications of alumina. The reactivity of aluminum oxide obtained by thermal decomposition of chemically pure sulfuric, hydrochloric, and nitric acid crystalline salts of aluminum salts is determined not only by the phase composition but also by the nature of the starting material. Despite the general morphology of the process of formation of aluminum oxide during the decomposition of the investigated crystalline hydrates, the formation of the phase composition of Al₂O₃ occurs at different temperatures and at different rates. Structural rearrangements during the decomposition of salts occur in the solid phase, which determines the total porosity and the specific surface area of each type of aluminum oxide. A study of the polymorphism of black alumina containing iron and silicon impurities was also carried out on samples obtained after leaching of the mineral part of the carbonaceous rocks with sulfuric, hydrochloric, and nitric acids in the temperature range of 100–1000°C. An inhibitory effect of impurities and a reducing agent on the formation of high-temperature structural modifications of aluminum oxide in the process of heat treatment of sulfuric, hydrochloric, and nitric acid crystalline hydrates of aluminum salts was revealed.