Alkali-excited gel structure and compositions evolution in geopolymers synthesized from the spent FCC catalyst and steel slag

Abstract

The effect of the alkaline activation process, especially the SiO2/Na2O molar ratio (Ms) in the prepared alkaline activator, on the geopolymer materials prepared using the spent fluid catalytic cracking (FCC) catalyst and steel slag as raw materials is investigated in this study. The results indicate that the compressive strength of prepared geopolymers has been greatly affected by the alkaline environment. The compressive strength of obtained samples is improved obviously in the strong alkaline environment. Meanwhile, the number of amorphous gels in the prepared geopolymers increased with Ms decreasing. It is conducive for the silicon-oxo-aluminate species in the oligomers to polymerize into polymers with 3D polymeric structures, which would lead to the surface of as-prepared samples becoming smoother and the structure becoming denser. Moreover, the strong alkaline environment is beneficial for Ca2+ to involve in the geopolymerization reaction and form the N(C)ASH gel, which can further enhance the compressive strength of the prepared geopolymer.