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), Mössbauer 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 SiO{sub 2} and Al{sub 2}O{sub 3}. The coordinated Fe{sup 3+} in RM played a role like Al{sup 3+} 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. - Highlights: • Large amounts of Na, Al and Si dissolved from alkali-thermal-activated RM in water. • Low Si/Al geopolymers will dissolve and release soluble Al in long-term curing. • Dissolved Si from SF participates in the polymerization of soluble Na, Al and Si. • The binding energies of Al−O and Si−O will increase after geopolymerization. • The coordinated Fe{sup 3+} replaces Al{sup 3+} in aluminosilicate structure of geopolymer.