Mechanisms of Alumina Formation from Metallic Raw Materials under Electrolysis Conditions

Resumo

The mechanisms of alumina formation from metallic aluminum in aqueous solutions and in molten salts are considered. The author technology of processing of dump slags from secondary metallurgy with the preparation of an aluminum deoxidizer alloy and the technology of the electrochemical oxidation of metallic aluminum with the formation of high-purity alumina (raw materials for manufacturing synthetic sapphires) are examined. The behavior of aluminum and alumina in the key technological process (electrolysis), in particular, in an oxyfluoride melt and in an aqueous salt solution, is considered when analyzing the technologies. The influence of the electrolyte composition on the electrolysis and side processes of dissolution of various metals (iron, copper, zinc, and others) is analyzed. The thermodynamic evaluation of possible reactions in the working medium (electrolyte) affecting the quality of the final product is performed. The possibilities of the retention of the proper quality of the final product are considered on the basis of thermodynamic calculations. Measures for decreasing the probability of unfavorable reactions are proposed. The technological preparation of an aluminum deoxidizer alloy and high-purity alumina using the electrochemical method is found to be possible only due to the high affinity of aluminum to oxygen. The main requirements imposed on the final products of the considered technologies are presented, and the priority areas of their application are designated.