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 57 Fe Mössbauer spectroscopy. It was shown that the oxidation at early stages is not influenced by (O2 in the) air. Later, the quadrupole split Fe 2+ state in the binder transforms to Fe 3+ when the samples are crushed and exposed to air as powder for 28 days at room temperature or 1 hour 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 Mössbauer spectra remain stable until 400-500 °C. At 400 °C the Fe 2+ in the slag starts to be oxidized, showing the formation of new Fe 3+ components.

Impact of the solidification path of FeOx–SiO2 slags on the resultant inorganic polymers

“…A significant increase in the intensity of the absorption peak of the Fe 3+ contribution is observed for all the samples, whereas the additional Fe 2+ IP component employed in the 28D samples is no longer needed to fit the spectra. This is in agreement with previous work …”

“…This is in agreement with previous work. 28,49 The 57 Fe Mössbauer hyperfine parameters of the Fe 3+ state are similar to the Fe 3+ component (IP1) formed at 28D samples although with slightly higher QS values, suggesting similar configuration of the ferric ions in the binder. It is worth noting that the sum of the AA of the slag components is decreased after 28 days and then increased after another 28 days.…”

Porous glass-ceramics made from microwave vitrified municipal solid waste incinerator bottom ash

“…Comparing the recorded spectra in the 825-1167 cm -1 region, a slight shift could be observed towards lower wavenumbers of the VBA absorption band at 929 cm -1 and an increased intensity of the absorption peak at 944 cm -1 , after alkali activation and pre-curing step. According to Peys et al [26], the dissolution of a synthetic ternary slag (CaO-FeOx-SiO2) entails a decrease in intensity of the Si-O-T band, which is associated with the starting material, and the emergence of a new band linked to the formation of an inorganic polymer network.…”

Valorization Potential of Polish Laterite Leaching Residues through Alkali Activation

“…The produced AAMs exhibit high compressive strength, strong acid resistance, good thermal stability, low shrinkage, and the tendency to immobilize hazardous elements [23][24][25]. However, their properties depend on several factors, namely the type and particle size of the raw materials and the type of activator, as well as the synthesis conditions, which mainly include the solids:liquids ratio, the H 2 O/Na 2 O and the SiO 2 /Na 2 O molar ratios in the alkali activating solution, and the curing temperature and the ageing period [26][27][28][29].…”