Magnetizing Pre-treatment of Diaspore Bauxite with Bamboo Powder: Simultaneous Iron Recovery and Red Mud Reduction in Alumina Production

The red mud generated during the alumina production process is a highly alkaline solid waste, with a global stockpile exceeding 4 billion tons. Reducing red mud at the source and enhancing its comprehensive utilization are significant global challenges. Herein, we propose a pre-treatment method utilizing co-roasting of bamboo powder and diaspore bauxite. Characterization techniques, including XRD, SEM-EDS, and TESCAN Integrated Mineral Analyzer (TIMA), have demonstrated that roasting modifies the composition and structure of the bauxite. After roasting, diaspore undergoes dehydroxylation and transforms into alumina, while hematite is transformed into magnetite by reducing gases such as CO and CH4 produced from the pyrolysis of bamboo powder. Simultaneously, the roasting process created cracks in the alumina, resulting in an increased specific surface area and leaching rate of alumina. Under the optimal roasting conditions (diaspore bauxite to bamboo powder ratio of 30:1, 650 °C, 25 min), the roasted bauxite can be subjected to Bayer digestion at 260 °C with the addition of 4% calcium oxide, achieving a relative leaching rate of alumina of 98.8% and reducing red mud production by 17.3% at the source. Magnetic separation enabled the recovery of iron resources from red mud, with the iron concentrate obtained exhibiting a grade of 58.8% and an iron recovery rate of 85.6%, and the final red mud production was reduced by 63.6%, which is beneficial to the sustainable development of the alumina industry.