Consequences of simple acid-pretreatments on geopolymerization and thermal stability of red mud-based geopolymers

Abstract

Red mud, a solid waste residue that forms as a by-product of the Bayer process in alumina production, is structurally modified by simple acid treatments (using 2 and 6 M HCl with digestion temperatures of 85 and 220 degrees C, respectively) followed by calcination at 800 degrees C prior to employing it as a raw material in geopolymer synthesis. The raw materials and their geopolymers are characterized by combining X-ray diffraction, Fourier transform infrared spectroscopy, X-ray fluorescence spectroscopy, thermogravimetric analysis, pore volume and surface area analysis, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Results reveal that acid modification of red mud followed by calcination plays an important role in activating red mud, significantly leading to enhanced geopolymerization and increased thermal stability of the corresponding geopolymers. The findings presented here can offer new opportunities for effective large-scale utilization of other waste material-based systems in geopolymerization.