Preparation of vanadium tailings-fly ash alkali-activated materials via mechanical activation: Geopolymerization and heavy metal immobilization behavior

• Select the mechanical activation method to prepare alkali-activated geopolymer, aiming for industrial production. • The system studied the geopolymerization reaction and heavy metal immobilization behavior of vanadium tailings-fly ash geopolymers. • Effective immobilization of Cr, Cd, and Be was achieved through gel networks. • Increased V leaching occurred due to oxidation of V⁴⁺/V³⁺ to soluble V⁵⁺ species under alkaline conditions. The preparation of geopolymers from vanadium tailings represents a potential approach to address their accumulation issue and substitute for high-carbon building materials. To enable the industrial production of vanadium tailing-based geopolymers, this study employs mechanical activation, a method with low energy consumption and controllable parameters, supplemented by fly ash as an aluminum corrective material. Using characterization techniques including temperature monitoring and pH testing during alkali activation, compressive strength tests, heavy metal leaching tests, XRD, SEM-EDS, FTIR, and MIP, this study analyzes the geopolymerization kinetics, mechanical properties, heavy metal immobilization behavior, reaction products, microstructure, chemical structure, and pore characteristics of the vanadium tailings-fly ash geopolymer. The results indicate that the introduction of mechanical activation and fly ash effectively enhanced the reactivity of the vanadium tailings. The geopolymerization products were predominantly N-A-S-H gel, which formed a complementary network structure with a minor amount of C-A-S-H gel generated over the curing period. This combined effect increased the 28-day compressive strength of the material to 15 MPa and significantly strengthened its ability to chemically immobilize Cr, Cd, and Be, resulting in leachate concentrations that met safety standards. However, the study also found that the alkaline activation environment promoted the transformation of vanadium into highly soluble high-valence species such as VO₃⁻ and VO₄³⁻, leading to an increase in its leaching concentration beyond that observed in the raw tailings. This study developed an alkali-activated material applicable for solidification/stabilization at solid waste landfills and contaminated sites.