Solidification/stabilization of chromium slag in red mud-based geopolymer

Chromium slag is a hazardous solid waste, and its safe disposal and utilization are of great significance to the environment. In this study, the geopolymer containing more than 50 wt% red mud waste was used as the matrix to solidify/stabilize the heavy metal Cr in the chromium slag, and the durability of composite geopolymer in corrosive environments was evaluated. The mechanisms of the hydration and the solidification/stabilization were discussed, based on results of XRD, BET, and SEM-EDS. It revealed that in the geopolymer matrix with 60–70 wt% red mud, the safe dosage of chromium slag was less than 10 wt%; and the safe content of chromium slag reached up to 30 wt% in the geopolymer matrix with 50 wt% red mud. The addition of 10 wt% chromium slag had a promoting effect on the mechanical property of red mud-based geopolymer, but 20–30 wt% of chromium slag was the opposite. Under the erosion of sulfate, the acid rain, and the freeze-thaw cycle, the mechanical performance and the solidification/stabilization of geopolymer would be weakened. The solidification/stabilization of Cr by red mud-based geopolymer was attributed to the physical adsorption of hydration products such as C-(A)-S-H gel and natrolite. In addition, the hydration of geopolymer would refine the pore structure and block the transport channel of Cr ion, which was conducive to promote solidification/stabilization. This study is expected to provide a reference for resource utilization and harmless disposal of chromium slag and red mud.