Stabilization and solidification of iron ore tailings using alkali-activated geopolymer

Iron ore tailings (IOT) exhibit weak mechanical properties and pose environmental concerns, limiting their direct application in geotechnical engineering. This study demonstrates that alkali activation with ground granulated blast furnace slag (GGBFS) enables simultaneous enhancement of mechanical performance, significant reduction in heavy metal mobility, and lower environmental impacts. Specifically, up to 95% decrease in heavy metal leaching and approximately 35% reduction in environmental impacts were achieved. IOT was activated using sodium hydroxide (NaOH) solutions ranging from 0 to 5 M in combination with GGBFS at replacement levels of 0-9 wt%. Specimens were prepared at optimum moisture content obtained from standard compaction tests and cured for 7, 14, and 28 days. The mechanical, environmental, and microstructural characteristics were evaluated through UU triaxial compression test, one-dimensional consolidation test, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), toxicity characteristic leaching procedure (TCLP), and life cycle assessment (LCA). The results indicate that alkali activation considerably improves the undrained shear strength of IOT, while GGBFS addition further enhances this improvement. Under a confining pressure of 200 kPa and 5 M NaOH, increasing slag content from 0% to 9% increased shear strength from 1,265 to 5,824 kPa. This behavior was associated with intensified geopolymerization reactions and the formation of a denser microstructure, resulting in nearly doubled cohesion and an approximately 20% increase in internal friction angle compared with untreated tailings. A LCA revealed that using geopolymer-based tailings could lower the global warming potential and energy demand by approximately 35% compared to Portland cement. Beyond the reductions in energy use and CO₂ emissions, the stabilization method also dramatically suppressed heavy metal mobility, up to a 95% reduction in certain specimens. Overall, the findings confirm the potential of alkali-activated IOT as a sustainable and high-performance material for geotechnical applications.