Preparation of Fly Ash-Based Geopolymer Ecological Remediation Materials and Investigation of Their Adsorption and Stabilization Behavior Toward Cr(VI)-Contaminated Soil

Coal-fired fly ash poses both environmental challenges and resource utilization potential. In this study, a fly ash-based geopolymer ecological remediation material (MFA-MB) was synthesized from fly ash and bentonite through alkaline roasting activation, montmorillonite acidification, and alkali-activated polycondensation. The structural characteristics and Cr(VI) adsorption performance of MFA-MB were systematically investigated. Compared with raw fly ash, MFA-MB exhibited a more developed mesoporous structure, increased surface activity, and enhanced specific surface area from 19.473 m2/g to 30.813 m2/g. Adsorption experiments demonstrated that MFA-MB showed enhanced Cr(VI) adsorption affinity and rapid adsorption equilibrium behavior. The adsorption process was exothermic and likely involved combined physical adsorption and surface interaction effects. Field experiments further showed that MFA-MB effectively reduced Cr(VI) accumulation in Chinese cabbage while promoting plant growth. At the optimal dosage, Cr concentrations decreased from 0.145 mg/kg to 0.015 mg/kg in roots and from 0.081 mg/kg to 0.009 mg/kg in leaves. These results suggest that MFA-MB exhibits promising potential for fly ash resource utilization and Cr(VI)-contaminated soil remediation.