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<p>Red mud, a highly alkaline residue generated from the Bayer process, represents both an environmental burden and a potential secondary resource due to its high iron oxide content. This study investigates the recovery of zero-valent iron (ZVI) from red mud via direct electrochemical reduction in concentrated NaOH solution. Electrolysis experiments were conducted in a three-electrode configuration at current densities ranging from 189 to 755&#xa0;A/m² and temperatures from 30 to 110&#xa0;°C to elucidate the effects of operating conditions on iron deposition and competing reactions. The highest iron yield and current efficiency (41.2%) were achieved at a current density of 755&#xa0;A/m² and 110&#xa0;°C after 6&#xa0;h of electrolysis, yielding 1.718&#xa0;g of metallic iron. Cyclic voltammetry analysis confirmed that hematite reduction occurs at cathodic potentials below − 1.1&#xa0;V vs. Hg/HgO. At the same time, hydrogen evolution becomes significant at more negative potentials, acting as a parasitic reaction that limits faradaic efficiency during prolonged operation. SEM–EDS characterisation revealed dense dendritic iron deposits composed of micron-scale nodules, indicating diffusion-limited growth under strong cathodic polarisation. In addition to process performance evaluation, a preliminary techno-economic assessment at laboratory scale was performed. The results indicate that the proposed electrochemical route incurs lower capital and operational expenditures than laboratory-scale blast furnace/direct reduction analogues, primarily due to lower operating temperatures and the absence of high-temperature gas-handling systems. Overall, red mud electrolysis offers a low-temperature, modular pathway for iron recovery, supporting sustainable, circular metallurgical waste valorisation.</p>

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Direct electrochemical reduction of red mud to metallic iron in alkaline media with process performance and preliminary techno-economic assessment

  • 期刊论文

  • 发表日期：

    2026年4月3日

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  • Franky Michael Hamonangan Siagian,
  • Vincent Sutresno Hadi Sujoto,
  • Muhammad Stally Argha Pradipta,
  • Panut Mulyono,
  • Ferian Anggara,
  • Widi Astuti,
  • Gyan Prameswara,
  • Rosy Amalia Kurnia Putri,
  • Himawan Tri Bayu Murti Petrus

摘要

Red mud, a highly alkaline residue generated from the Bayer process, represents both an environmental burden and a potential secondary resource due to its high iron oxide content. This study investigates the recovery of zero-valent iron (ZVI) from red mud via direct electrochemical reduction in concentrated NaOH solution. Electrolysis experiments were conducted in a three-electrode configuration at current densities ranging from 189 to 755 A/m² and temperatures from 30 to 110 °C to elucidate the effects of operating conditions on iron deposition and competing reactions. The highest iron yield and current efficiency (41.2%) were achieved at a current density of 755 A/m² and 110 °C after 6 h of electrolysis, yielding 1.718 g of metallic iron. Cyclic voltammetry analysis confirmed that hematite reduction occurs at cathodic potentials below − 1.1 V vs. Hg/HgO. At the same time, hydrogen evolution becomes significant at more negative potentials, acting as a parasitic reaction that limits faradaic efficiency during prolonged operation. SEM–EDS characterisation revealed dense dendritic iron deposits composed of micron-scale nodules, indicating diffusion-limited growth under strong cathodic polarisation. In addition to process performance evaluation, a preliminary techno-economic assessment at laboratory scale was performed. The results indicate that the proposed electrochemical route incurs lower capital and operational expenditures than laboratory-scale blast furnace/direct reduction analogues, primarily due to lower operating temperatures and the absence of high-temperature gas-handling systems. Overall, red mud electrolysis offers a low-temperature, modular pathway for iron recovery, supporting sustainable, circular metallurgical waste valorisation.