Synthesis and characterization of fly ash modified mine tailings-based geopolymers

Each year, the mining industry generates a significant amount of mine tailings. Storage of these tailings occupies large areas of land and leads to high monetary, environmental and ecological costs. In this research, a feasibility study is performed on geopolymerization of mine tailings so that they can be recycled and utilized as construction material. Considering the extremely high silicon to aluminum (Si/Al) ratio for the mine tailings, class F fly ash is used to adjust the Si/Al ratio. Sodium hydroxide (NaOH) solution is used as the alkaline reaction agent. The research consists of unconfined compression tests to evaluate the mechanical properties, scanning electron microscopy (SEM) imaging to investigate the microstructure, and the X-ray diffraction (XRD) analysis to study the phase compositions. The effects of fly ash content (which affects the Si/Al ratio), alkalinity (NaOH concentration), and curing time on the geopolymerization of mine tailings are studied in a systematic way. The results show that the Si/Al ratio and the alkalinity have profound effects on the mechanical and micro-structural properties of the mine tailings-based geopolymers. The curing time affects the mechanical and micro-structural properties of the mine tailings-based geopolymers mainly during the first 7 days. Based on the research, it can be concluded that mine tailings are a viable and promising construction material if the geopolymerization technology is utilized.