Coupling effect of steel slag in preparation of calcium-containing geopolymers with spent fluid catalytic cracking (FCC) catalyst

Abstract

Spent FCC catalyst coupling with steel slag has been used to synthesize a new calcium-containing geopolymer binding material with excellent performance. The effect of the composition of the raw materials on the performance of the obtained samples has been investigated systematically. The results indicate that the compressive strength of the prepared geopolymers was increased with the addition of steel slag. This is due to the calcium-containing components in the steel slag, which possess higher reactivity compared to the pure chemical reagent in the alkaline activation environment, which is beneficial for the generation of N(C)-A-S-H amorphous gel (where N = Na2O, A = Al2O3, C = CaO, S = SiO2, and H = H2O) in the obtained samples. Meanwhile, the other components of steel slag would embed in the cementitious material as skeleton materials, which are conducive for the improvement of the compressive strength performance. In addition, the role steel slag plays in the geopolymerization reaction has been studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectrometry (FT-IR). Results indicated that the catalyst-derived geopolymer gel (N-A-S-H) coexisted with slag activated gel (C-S-H/C-A-S-H) in the binding matrix, which are the main phases in the geopolymer, and the development of better compressive strength is attributed to the formation of Ca-rich gel phases. These results highlight the feasibility of using spent FCC catalyst and steel slag as raw materials for the production of geopolymer binding material with enhanced compressive strength.