The influence of air and temperature on the reaction mechanism and molecular structure of Fe-silicate inorganic polymers

Abstract Fe-rich inorganic polymers are rising in importance because of their low CO2 emissions during production and their potential in upcycling metallurgical residues. Here, the oxidation of Fe during formation of the binder from 0.4CaO-1.2FeOx-SiO2 slag is investigated in more detail using 57Fe Mossbauer spectroscopy. It was shown that the oxidation at early stages is not influenced by (O2 in the) air. Later, the quadrupole split Fe2+ state in the binder transforms to Fe3+ when the samples are crushed and exposed to air as powder for 28 days at room temperature or 1 h at ≥200 °C. This transformation does not affect the connectivity of the silicate network according to infrared spectroscopy. During heating of the inorganic polymer powder, the Mossbauer spectra remain stable until 400–500 °C. At 400 °C the Fe2+ in the slag starts to be oxidized, showing the formation of new Fe3+ components.