Exploring the chemistry of metakaolin-based geopolymers

This experimental study investigates the impact of different silicon-to-alumina (Si/Al) ratios on geopolymers synthesized from metakaolin. Various ratios of Si/Al (1:1, 1.5:1, 2:1, 3:1, 4:1, and 5:1) were employed, nano-silica was the source material to alter the Si ratio. Microstructure and strength were analysed using SEM, XRD, NMR, and compressive strength testing Geopolymerization, a sustainable material synthesis process, was investigated using FTIR spectroscopy and computational modeling. The dissolution rates of aluminum and silicon molecules, as well as the formation of N-A-S-H gel, were studied. Results revealed that a Si/Al ratio of 2:1 significantly enhanced the dissolution of silicon and aluminum, leading to the formation of Si-O-T bonds and superior compressive strength. Computational analysis confirmed that the mechanical performance was primarily attributed to the formation of N-A-S-H gel, rather than zeolitic nuclei or silicate derivatives. These findings provide valuable insights for the application of geopolymerization in valorizing mine tailings, which often exhibit high Si/Al ratios.