Mechanical, microstructural, and toxicological properties of alkali-activated iron ore tailing with GGBS and fly ash

The large-scale generation and improper disposal of Iron Ore Tailings (IOT) pose significant environmental and geotechnical challenges, necessitating sustainable reuse strategies. This study investigates the geopolymer-based stabilization of IOT using alkali-activated binders composed of Ground Granulated Blast Furnace Slag (GGBS) and Fly Ash (FA). The IOT content was fixed at 90%, while FA and GGBS (10% total) were varied in three proportions: 90:2.5:7.5, 90:5:5, and 90:7.5:2.5 (IOT: FA: GGBS). Sodium hydroxide (NaOH) solutions of 2.5 M and 5 M were combined with sodium silicate (Na₂SiO₃) at NaOH: Na₂SiO₃ ratios of 1:1 and 2:1. Mechanical testing revealed that the 90:2.5:7.5 mix activated with 5 M NaOH at a 1:1 ratio achieved the highest 28-day strengths of 11.14 MPa (UCS) and 0.93 MPa (STS). Statistical analysis (ANOVA) confirmed curing duration and NaOH molarity as the dominant parameters governing strength development. Microstructural investigations (XRD, SEM, EDS) demonstrated that enhanced performance is associated with the formation of hybrid C-A-S-H and N-A-S-H gel networks, resulting in matrix densification and improved interparticle bonding. Toxicity Characteristic Leaching Procedure (TCLP) results verified reduced heavy metal leachability within regulatory limits. The findings establish that geopolymerization enables effective transformation of IOT into a high-performance, cement-free geomaterial, offering a sustainable pathway for large-scale tailings valorization and construction applications.