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<p>Red mud is a solid waste generated during the production of alumina from bauxite. Its high alkalinity and complex composition limit its large-scale utilization, leading to the stockpiling of most red mud for disposal, which poses a significant threat to the ecological environment. This study proposes a novel method focused on high-value end-use, achieving efficient recovery of sodium oxide and alumina from red mud through high-temperature calcification transformation and leaching, while producing a new type of red mud characterized by an almost alkali-free structure. The research thoroughly investigates the thermodynamic characteristics of red mud during the calcification transformation process and the mechanisms governing key process parameters. By employing analytical techniques such as XRF, XRD, and SEM, a systematic characterization was conducted on the chemical composition, crystal structure, and microscopic morphology of red mud and its products at various stages of the calcification transformation. Experimental data revealed that reaction temperature and the calcium-to-silicon molar ratio significantly influence the calcification transformation. Under high-temperature conditions, optimizing the amount of calcium addition can effectively enhance the extraction efficiency of sodium oxide and aluminum oxide from red mud. Furthermore, high-pressure differential scanning calorimetry (HP DSC) was utilized to conduct an in-depth study of the non-isothermal phase transition behavior and its kinetic characteristics during the calcification transformation process. At a calcination temperature of 260&#xa0;°C, with a calcium-to-silicon ratio (C/S) of 2, a liquid-to-solid ratio (L/S) of 4:1, a mother liquor caustic concentration of 210&#xa0;g/L, and a reaction time of 60&#xa0;min, the recovery rates of alumina and sodium oxide from high-iron red mud were found to be 68.34% and 74.8%, respectively. This process reduced sodium oxide loss in the Bayer process digestion stage by over 70%. The new red mud, enriched in iron oxide and low in sodium oxide content, can be transformed into ironmaking pellets by adding an appropriate amount of iron concentrate and binder, thus achieving full utilization of the new red mud and facilitating the clean production of alumina.</p> Graphical Abstract <p></p>

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Unlocking the Potential of Red Mud: High-Temperature Calcification for Sodium Oxide and Alumina Extraction and Alkaline-Free Red Mud Transformation

  • 期刊论文

  • 发表日期：

    2025年10月7日

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  • Xin He,
  • Guo-zhi Lv,
  • Zhuang-zhuang Yun,
  • Zhi-hui Gu,
  • Bai-qiang Zhao,
  • Qing-dong Li,
  • Xiao-lei Zhang,
  • Ting-an Zhang

摘要

Red mud is a solid waste generated during the production of alumina from bauxite. Its high alkalinity and complex composition limit its large-scale utilization, leading to the stockpiling of most red mud for disposal, which poses a significant threat to the ecological environment. This study proposes a novel method focused on high-value end-use, achieving efficient recovery of sodium oxide and alumina from red mud through high-temperature calcification transformation and leaching, while producing a new type of red mud characterized by an almost alkali-free structure. The research thoroughly investigates the thermodynamic characteristics of red mud during the calcification transformation process and the mechanisms governing key process parameters. By employing analytical techniques such as XRF, XRD, and SEM, a systematic characterization was conducted on the chemical composition, crystal structure, and microscopic morphology of red mud and its products at various stages of the calcification transformation. Experimental data revealed that reaction temperature and the calcium-to-silicon molar ratio significantly influence the calcification transformation. Under high-temperature conditions, optimizing the amount of calcium addition can effectively enhance the extraction efficiency of sodium oxide and aluminum oxide from red mud. Furthermore, high-pressure differential scanning calorimetry (HP DSC) was utilized to conduct an in-depth study of the non-isothermal phase transition behavior and its kinetic characteristics during the calcification transformation process. At a calcination temperature of 260 °C, with a calcium-to-silicon ratio (C/S) of 2, a liquid-to-solid ratio (L/S) of 4:1, a mother liquor caustic concentration of 210 g/L, and a reaction time of 60 min, the recovery rates of alumina and sodium oxide from high-iron red mud were found to be 68.34% and 74.8%, respectively. This process reduced sodium oxide loss in the Bayer process digestion stage by over 70%. The new red mud, enriched in iron oxide and low in sodium oxide content, can be transformed into ironmaking pellets by adding an appropriate amount of iron concentrate and binder, thus achieving full utilization of the new red mud and facilitating the clean production of alumina.

Graphical Abstract