Role of Fe species in geopolymer synthesized from alkali-thermal pretreated Fe-rich Bayer red mud

[Display omitted] •The coordinated Fe3+ replaced Al3+ in the aluminosilicate structure of geopolymer.•Binding energies of Al-O and Si-O increased in geopolymerization.•Alkali-thermal activated Fe-rich Bayer red mud was used to synthesize geopolymer.•Dissolution efficiencies of Al2O3 and SiO2 in the RM were improved by pretreatment.•Synergistic effect of pretreated RM and fly ash on geopolymer strength was proved. A geopolymer material was synthesized from alkali-thermal pretreated Fe-rich Bayer red mud (RM) and fly ash. Dissolution efficiencies of Al2O3 and SiO2 in the RM in alkaline solutions were improved by pretreatment. The transformation of mineral phases in the RM during synthesis of geopolymer was investigated by the alkaline leaching test, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The role of Fe species in geopolymerization was investigated by Mössbauer spectra. The results showed that binding energies of Al-O and Si-O increased in geopolymerization; the coordinated Fe3+ replaced Al3+ in the aluminosilicate structure of geopolymer.