Triethanolamine as a Sustainable Alternative to Lime in the Bayer Process: Significant Red Mud Reduction and Enhanced Iron Recovery

The alumina industry faces critical sustainability challenges from massive red mud (RM) discharge, which occupies vast land areas and poses severe environmental risks. Moreover, inefficient iron recovery from RM, due to poor mineral liberation, leads to the loss of valuable iron resources. This study introduces triethanolamine (TEOA) as a sustainable alternative to lime in the Bayer digestion to address these challenges. Optimal digestion conditions (265 °C, 10 wt % TEOA/bauxite, 100 min, 230 g/L Na 2 O), identified via full factorial design, achieved an iron recovery rate of 89.04% from RM via magnetic separation. The resulting iron concentrate (60.26% Fe) is an excellent secondary iron resource. Crucially, this integrated approach led to an 84.10% reduction in RM discharge as compared to the conventional lime-based method. The mechanism of TEOA-enhanced Bayer digestion was investigated through thermodynamic and kinetic studies, complemented by DFT calculations. TEOA decomposition was found to generate atomic hydrogen (H•), which reduces FeO 2 – on hematite surfaces to HFeO 2 –, promoting the transformation of hematite into magnetite. Concurrently, HFeO 2 – reacts with anatase to form ilmenite, which inhibits sodium titanate formation, thus ensuring high aluminum extraction efficiency with 95.97%. This work presents a novel and sustainable strategy for significantly reducing RM discharge and enhancing iron valorization in the alumina industry, offering a pathway toward a more circular economy.