Calcined Alumina

Calcined alumina refers to the refined, anhydrous aluminum oxide (Al₂O₃) product produced by thermally treating aluminum hydroxide through the calcination process at temperatures between 950°C and 1,100°C. It is the primary feedstock for aluminum metal production via the Hall-Héroult electrolytic smelting process. Calcined alumina is a white, granular, free-flowing powder with a high melting point of approximately 2,072°C and exceptional hardness (Mohs scale: 9), second only to diamond. The product is characterized by its specific surface area, particle size distribution, phase composition, alpha-alumina content, soda (Na₂O) content, and bulk density — all of which must meet precise specifications demanded by aluminum smelters for efficient and stable cell operation. In smelting pots, calcined alumina is dissolved in molten cryolite electrolyte, where electrical current reduces it to aluminum metal. Beyond aluminum production, calcined alumina finds extensive applications as an abrasive, refractory material, ceramic raw material, catalyst support, and polishing compound. Its properties can be tailored by adjusting calcination temperature, residence time, and kiln atmosphere. Smelter-grade alumina (SGA) typically contains more than 99.4% Al₂O₃, with strictly controlled levels of silica, iron oxide, sodium oxide, and trace elements. Sandy alumina, produced at higher temperatures, and floury alumina, produced at lower temperatures, represent two major commercial variants with distinct performance characteristics in reduction cells.