Iron Distribution in Geopolymer with Ferromagnetic Rich Precursor

Abstract

Geompolymers and their engineering applications have attracted significant attention of the scientific community. This is due to properties such as good thermal stability and high resistance to aggressive environments. Most studies on this subject are based on traditional precursor materials such as calcined kaolinite clay (metakaolinite) and fly ash. The iron content is significant, reaching around 10% in metakaolinite, for instance. The role of iron in geopolymers still lacks systematic investigation. This can be attributed to the limitations presenting nuclear magnetic resonance (NMR) spectroscopy, which is a widely used technique to study geopolymers structure. Ferromagnetic elements such as iron, which is often present in some precursors, affect the magnetic response of the material, compromising the proper analysis of its structure by NMR results. Iron content in some industrial residues may be several times higher as it is often found in metakaolinite. This work presents x-ray diffraction, infrared and Mössbauer spectroscopy studies on the distribution of iron species in iron oxide/hydroxide-rich precursor, which was used to synthesized geopolymers.

Recent progress in low-carbon binders

“…Detailed work is also ongoing to better understand the reactivity of fly ashes under alkali-activation conditions [36][37][38][39], and to valorize kaolinitic clay resources which are not of sufficient purity for use in other applications such as ceramic whitewares or coatings [40][41][42]. Common to many of these types of materials, the role of iron in alkali-activation precursors (and in the resulting binders) is beginning to be understood to some degree [19,43,44]. However, a detailed description of its reactivity and the structural implications of its inclusion in the binding gel still remain very much elusive.…”

Increasing the Dimensional Stability of Cao-Feox-Al2o3-Sio2 Alkali-Activated Materials: On the Swelling Potential of Calcium Oxide-Rich Admixtures

“…Van Deventer et al (2007) reported that reactive Fe species will most likely behave similarly to Ca 2+ , precipitating as hydroxide or oxy-hydroxide and decreasing the pH of the solution. Gomes et al (2010) used 57 Fe Mössbauer spectroscopy to determine the fate of iron during alkali activation and found that a small portion of Al 3+ could be replaced by Fe 3+ in octahedral sites. Nonetheless, Simon et al (2018) demonstrated that AAMs produced from Fe-rich slags are structurally different from "Fe-enriched" aluminosilicate geopolymers, in more than just Fe-Al substitution in tetrahedrally-coordinated sites.…”

Optimization of the Mix Formulation of Geopolymer using Nickel-laterite Mine Waste and Coal Fly Ash

“…Thus, when the amount of CFA is increased, more aluminosilicate can participate in the reaction [5]. Furthermore, the increase of SiO2 and Al2O3, with the additional presence of Fe 3+ in the mixture, may also influence the compressive strength of the product by replacing or substituting Al 3+ by Fe 3+ in the octahedral sites of an aluminosilicate structure [39,40] . This model indicates that the proper selection of precursors needs to be determined using characterization methods.…”