Sustainable high strength geopolymer produced from mine tailings incorporating kaolin and slag: Mechanical performance and microstructural evaluation

Bahmanpour A.; Hedayat A.; Gorman B.P.; Tupa N.; Moreno Roque C.S.; Jara Gonzales J.M.; Bolaños Sosa H.G. · Construction and Building Materials (2026) · DOI: 10.1016/j.conbuildmat.2026.147471

Resumen

Mine tailings (MTs), as by-products of mining operations, pose significant environmental challenges due to their large volumes and long-term storage requirements. Owing to their aluminosilicate-rich composition, MTs have potential as precursors for the production of sustainable geopolymer; however, their inherently low reactivity limits direct geopolymerization and necessitates the incorporation of supplementary aluminosilicate materials. Although metakaolin is commonly used for this purpose, its high energy demand and cost undermine the environmental benefits of MTs-based geopolymers. Moreover, several conventional supplementary materials incorporated with MTs have been reported to experience strength degradation after prolonged exposure to water. This study systematically investigates the feasibility of using untreated kaolin, individually and in combination with slag, as low-energy supplementary precursors for MTs-based geopolymers, while maintaining a constant MTs content of 70 wt% in all mixtures. Sodium hydroxide (SH) solutions with concentrations of 5, 10, and 15 M were used as primary activators, and the influence of sodium silicate (SS) as a co-activator was evaluated at SS/SH weight ratios of 0, 0.5, 1.0, 1.5, and 2.0. The performance of the resulting geopolymer specimen was assessed through unconfined compressive strength (UCS), water-immersion strength retention, dry bulk density, and water absorption tests. Comprehensive microstructural and phase characterization was conducted using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) mapping, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) to elucidate reaction mechanisms and gel formation. The results demonstrate that MTs-based geopolymer produced using a combined kaolin-slag system activated with SH and an optimized SS dosage (SS/SH = 1.0) achieved compressive strengths exceeding 100 MPa while maintaining high strength retention (∼80%) after 7 days of water immersion. Comprehensive microstructural and phase analyses confirmed the dissolution of kaolin and slag precursors and the formation of a dense, well-connected calcium–alumino–silicate–hydrate (CASH) and sodium–alumino–silicate–hydrate (NASH) geopolymer gel network, which effectively encapsulated and bonded the MTs particles. These findings highlight the potential of kaolin and slag as cost-effective and low-carbon alternatives to metakaolin for producing high-performance, water-resistant geopolymer from MTs.

Instituciones: Universidad Nacional de San Agustín de Arequipa