Characterization and microstructure observation of sintered red mud–fly ash mixtures at various elevated temperature

• Characterization of sintered red mud–fly ash mixtures.
• The phases evolution and dissociation as the function of sintered temperature.
• Correlation of the reaction mechanism with microstructural observation.

This study investigated the characterization and microstructure observation of sintered red mud–fly ash mixtures at various elevated temperature. The detailed analysis of the phase evolution during sintering process of red mud and fly ash as the function of sintering temperature were explored. Phase evolution and microstructure observation were carried out by X-ray diffraction method (XRD) and scanning electron microscope (SEM) method. Thermal analysis was carried out by thermogravimetric and differential thermal (TG-DTA) analysis. The mineralogical evolution revealed that quartz and goethite originates from the parent composition of red mud and fly ash. Microstructure observation revealed the transformation of globular grains towards elongated grains during the sintering process. Mass loss around 11% is observed in the thermal analysis patterns due to the dehydration, hydroxide-oxide phase transitions from iron (primary phase) and aluminum (secondary phase). The phase transition, evolution and dissolution as the function of sintering temperature were correlated as the function of temperature and the amount of fly ash content. The disappearance and appearance of the different phases confirms the decomposition and formation reaction suggested by thermal analysis.

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