China Nonferrous Metallurgy

Aluminium slag is a typical industrial solid waste generated in the production process of electrolytic aluminium and recycled aluminium. In this study, by regulating the phase composition of aluminium slag, magnesium aluminate spinel (MA) materials were prepared using the solid-state sintering method, and the effects of typical impurities in aluminium slag on the bulk density of the sintered body were systematically investigated. The results show that the four impurities SiO₂, CaO, Fe₂O₃ and TiO₂ can all increase the bulk density of aluminium slag-based MA sintered materials. Under the process conditions of sintering at 1 400 °C for 3 h, when 5%SiO₂, 5%CaO, 4.5%Fe₂O₃ and 6%TiO₂ were respectively added to the aluminium slag to sinter MA materials, the bulk density of the materials changed from 2.02 g·cm^-3 to 2.03, 2.05, 2.21 and 2.04 g·cm^-3, respectively. Among them, Fe₂O₃ promotes densification better than TiO₂ and CaO, while the densification effect of SiO₂ is relatively weak. The mechanisms by which different impurities enhance the bulk density of MA materials differ: SiO₂ and CaO can form low-melting-point liquid phases during sintering, strengthening the mass transfer process through liquid-phase sintering effects and thereby promoting material densification; Fe₂O₃ reacts with components in the system to form a (Mg, Fe)₂SiO₄ phase that is eutectic with the MA phase, causing the microstructure to develop multi-closed pore features, thus increasing bulk density; TiO₂ forms fine Mg_xAl_yTi_zO_(2x+3y+4z)/2 particles during sintering, which accumulate at the grain boundaries of MA coarse grains, providing grain boundary bonding to achieve material densification. In addition, the diffusion behaviour of impurity ions during sintering is also an important reason for the change in bulk density of MA materials.