Transformations of Na, Al, Si and Fe species in red mud during synthesis of one-part geopolymers

Reaction mechanism of one-part geopolymer formation using red mud (RM) was explored in this study. Leaching test, X-ray photoelectron spectroscopy (XPS), Mossbauer spectroscopy and nitrogen isothermal adsorption (NIA) were conducted to study transformations of Na, Al, Si, Fe species, binding energies of Al-O and Si-O, and pore structure, respectively. The alkali-thermal-activated RM could dissolve in water to release large amounts of soluble Na, Al and Si species for geopolymerization. But more dissolved Si is needed from added silica fume (SF) to form stable geopolymer gels. The binding energies of Al-O and Si-O bonds in the geopolymer increased with the polymerization of reactive SiO2 and Al2O3. The coordinated Fe3+ in RM played a role like Al3+ by replacing it in the aluminosilicates structure, and exerted no obvious impact on geopolymerization. The dissolved SF took part in the geopolymerization to form dense geopolymer matrices in long-term curing.