China Nonferrous Metallurgy

Aluminium slag belongs to hazardous waste generated by the aluminium industry， containing a large amount of Al， while impurity elements such as Ca， Si， and Mg limit its high-value utilisation. Based on the mechanism that Fe， Ca， Si， Mg and other elements can form pyroxene-type magnetic substances which can then be removed by magnetic separation， this study adopts a roasting-magnetic separation process to investigate impurity removal from aluminium slag. Thermodynamic software was used for analysis to obtain the appropriate elemental ratio for forming pyroxene-type magnetic substances， and aluminium slag was then prepared according to this ratio； the effect of temperature on the roasted products of the prepared aluminium slag was studied， and thermogravimetric-differential thermal analysis and characterisation analysis were used to explore the phase reconstruction characteristics； finally， magnetic analysis was conducted to verify the formation of pyroxene-type magnetic substances. the main temperature range for the formation of iron-bearing pyroxene-type magnetic substances is concentrated between 1 100-1 300℃. Under the roasting temperatures of 1 250℃ and 1 350℃， the roasted products of the prepared aluminium slag were Ca（Fe， Mg）Si₂O₆ and Ca（Mg， Fe， Al）（Si， Al）₂O₆， respectively； magnetic analysis of the generated pyroxene substances showed that they have soft magnetic material characteristics， with remanent magnetisation of 0. 12 T and 0. 07 T at temperatures of 1 250℃ and 1 350℃ respectively， meeting the requirements for magnetic separation processes. The aluminum ash slag was used for roasting verification， and the test results were consistent with the prepared aluminum ash slag. That is， the Ca， Si， and Mg impurities in the aluminum slag can generate magnetic material pyroxene products， which are separated from the roasted sample by magnetic separation process. After magnetic separation at 1 250℃ and 1 350℃， the content of SiO₂， CaO and Fe₂O₃ in aluminum slag decreased （the proportion of magnetic substances at 1 250℃ was 6. 5%， and the proportion at 1 350℃was 5. 3%）. The aluminum ash after magnetic separation can be used as high aluminum material in the field of advanced ceramics. The results show that the roasting process of aluminum slag can generate magnetic substances， and the impurity removal and quality improvement can be further realized， which provides a new idea for the high-value utilization of aluminum slag.