Effect of in-situ nano-alumina on the properties of alumina ceramics from secondary aluminum dross

Secondary aluminum dross (SAD), a hazardous solid waste derived from the metal aluminum (Al) smelting process, contains 65-90 % aluminide and over 30 different impurity elements, thus being an alternative material for alumina ceramic production to replace traditional sources such as bauxite or industrial alumina powder. The presence of inherent impurities would seriously deteriorate the mechanical properties of ceramics prepared from SAD. This study proposed an innovative process involving grinding-alkali leaching-CO2-assisted in-situ precipitation of nano-alumina to effectively eliminate the influence of impurities on the ceramic mechanical properties. Grinding greatly reduced the median particle size from 67.4 to 3.17 mu m, improving the particle structure and specific surface area. The active aluminum components were transferred from the interior of SAD particles to the surface to form nano-alumina by alkaline leaching and in-situ precipitation. The nano-alumina layer could completely coat the ground SAD particles. As a result, these impurities in SAD would not form the connected liquid phase but instead form isolated liquid phase points inside the particles during the high-temperature firing process. The sintering mechanism of ceramics changes from liquid phase sintering to solid phase sintering. The fracture mechanism of ceramics changes from intergranular fracture to transcrystalline fracture, and the mechanical properties of ceramics are greatly improved. Alumina ceramics sintered at 1500 degrees C showed the density, porosity, hardness and flexural strength of 3.42 g/cm3, 3.7 %, 1457 Hv, and 235 MPa, respectively. This process eliminates the negative effects of 21.54 % impurities in SAD and produces alumina ceramics that meet the 90 Al2O3 ceramic standard.