Synergistic solidification and mechanism research of electrolytic manganese residue and coal fly ash based on C-A-S-H gel material

Electrolytic manganese residue (EMR) is known for high concentrations of Mn²⁺, NH₄⁺, and heavy metals. Failure to undergo benign treatment and landfill disposal would undeniably lead to negative impacts on the quality of the surrounding ecological environment. This study sought to mitigate the latent environmental risks associated with EMR using a cooperative solidification/stabilization (S/S) method involving coal fly ash (CFA). Leveraging leaching toxicity tests, the leaching behavior of pollutants in electrolytic manganese residue-based geopolymer materials (EMRGM) was determined. At the same time, mechanistic insights into S/S processes were explored utilizing characterization techniques such as XRF, XRD, FT-IR, SEM-EDS, and XPS. Those results confirmed significant reductions in the leaching toxicities of Mn²⁺ and NH₄⁺ to 4.64 μg/L and 0.99 mg/L, respectively, with all other heavy metal ions falling within the permissible limits set by relevant standards. Further analysis shows that most of NH₄⁺ volatilizes into the air as NH₃, and a small part is fixed in the EMRGM in the form of struvite; in addition to being oxidized to MnOOH and MnO₂, Mn²⁺ will also be adsorbed and wrapped by silicon-aluminum gel together with other heavy metal elements in the form of ions or precipitation. This research undeniably provides a solid theoretical foundation for the benign treatment and resourceful utilization of EMR and CFA, two prominent industrial solid wastes.