Removal of impurities for the synthesis of high-property alumina-spinel ceramic from secondary aluminum dross

Abstract

Alumina-based ceramics are characterized by reliable mechanical strength and chemical stability. However, the high cost and shortage of raw materials have discouraged the growing market. Secondary aluminum dross (SAD) is a hazardous waste that consists of a variety of tightly coupled aluminum phases such as metal Al, Al2O3, AlN, and MgAl2O4. In this study, a novel process to retain Al while removing impurities from SAD was developed to obtain high-purity alumina-spinel powder, which was successfully synthesized to high-property alumina-spinel ceramic by pressureless sintering. First, up to 97.6% metal Al, 99.6% AlN, 98.6% Al4C3, and 99.5% Al2S3 were oxidized and transformed to α-Al2O3. Meanwhile, 98.7% fluorine was removed from SAD by oxidizing roasting, verifying the results of thermodynamic analysis. About, 83.8% of Ca, 65.8% of Fe, 67.3% of Cu, and 44.5% of Zn were removed separately from SAD by grinding–acid leaching due to the poor stability of alumina solid solution, and 86.09% of Al was retained in SAD powder in the form of α-Al2O3. Finally, the alumina-spinel ceramics sintered at 1300 °C showed the optimum properties: the density of 3.73 g/cm3, the porosity of 1.6%, the hardness of 1703.1 Hv, and the flexural strength of 138.5 MPa, respectively, which met the standard of 95 Al2O3 ceramic. These results demonstrated that the process could realize thoroughly the normalization of complex components in SAD and the preparation of high-property ceramic, substantially promoting the consumption and high-value utilization of SAD.