Abstract:

 Red mud, a bulk solid waste generated by the alumina industry, is commonly stockpiled for long periods, which can induce environmental and geotechnical risks such as low pile strength and insufficient stability. Conventional cement stabilization, however, is constrained by high carbon emissions and limited immobilization efficiency. In this study, a low-carbon, all-solid-waste binder system for red mud stabilization was developed using steel slag, fly ash, and phosphogypsum as multi-source industrial solid wastes, and the mix proportions were optimized via the simplex centroid method. Results show that at a red mud/steel slag/fly ash/phosphogypsum mass ratio of 54:9:27:10, the system synergistically forms hydration products including calcium silicate hydrate (C-S-H), calcium aluminosilicate hydrate (C-A-S-H), and ettringite (AFt). The stabilized material achieved a 90-day compressive strength of approximately 14 MPa and a hydraulic conductivity of 7.4×10⁻⁷ cm/s. Consolidated undrained (CU) triaxial tests yielded a cohesion of approximately 13 kPa and an internal friction angle of approximately 30°, indicating pronounced improvements in the strength and stiffness of the stabilized material. The immobilization efficiency of Na⁺ was 63.5%, and those of heavy metals such as Pb, As, and Cr were all no less than 75.0%, with leachate concentrations below the corresponding leaching toxicity limits. After coupled freeze–thaw and salt-erosion exposure, both mass loss and strength degradation remained low, demonstrating favorable durability. These findings provide a low-carbon technical basis for in situ stabilization and resource-oriented utilization of red mud stockpiles.

Key words: red mud, all-solid-waste low-carbon binder, stockpile reinforcement, pollutant immobilization, durability