Abstract: Red mud, an alkaline solid waste generated in the aluminum industry, holds significant potential for efficient resource utilization to alleviate environmental pressure and promote sustainable development. This study aimed to optimize the performance of red mud-based ceramsite by systematically investigating the influence of aluminum-to-silicon molar ratio (A/S) variations on the foaming behavior, physical properties, crystalline phase composition, and pore structure under a nitrogen atmosphere. Results demonstrate that low oxygen partial pressure promotes the decomposition of hematite in red mud, generating FeO that preferentially reacts with Al₂O₃ to form granular hercynite (FeAl₂O₄). As the A/S increases, the content of spinel and plagioclase phases in the ceramsite rises significantly. This evolution in crystalline phases profoundly influences the properties of high-temperature melts and pore structure, thereby enhancing matrix strength. Based on these findings, lightweight high-strength ceramsite with compressive strength of 3.48 MPa, water absorption of 0.31%, apparent density of 0.72 g/cm³, and porosity of 76.6% is successfully prepared under conditions of 20% (mass fraction) red mud and 1 170 ℃ holding for 60 min in nitrogen atmosphere. This study provides valuable insights into the efficient utilization of red mud and the development of high-performance ceramsite.

Key words: red mud, ceramsite, spinel, plagioclase, crystalline phase composition, oxygen partial pressure