Study on improving the carbon sequestration properties of sintered red mud by regulating pressure

Red mud was a by-product discharged from the alumina refining process, which caused serious environmental problems. Since there are relatively few studies on sintered red mud (SRM) at this stage, SRM was selected in this paper to explore its carbon sequestration capacity under different pressures. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) were used to analyze the composition of SRM, and microstructure and elemental compositions were observed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Meanwhile, pore structures were characterized using Brunauer Emmett Teller (BET), and the production was quantitatively analyzed in combination with thermogravimetric analysis (TGA). The results showed that the carbon sequestration capacity of SRM was increased with pressure raised, but the growth rate gradually slowed down. During the carbonation process, the majority of Ca2SiO4 (C2S) reacted with water and CO2 to produce fine CaCO3, which could provide early strength. These CaCO3 were partly distributed on the surface of SRM, partly in the pores, and partly in the aqueous solution. The best carbon sequestration effect of SRM was achieved at a pressure of 2.2 MPa, and each kilogram of SRM could absorb 71.4 g CO2. The results also showed that the number of holes larger than 50 nm in carbonated sintered red mud (CSRM) decreased and the number of voids smaller than 50 nm increased. This was favorable to improve the mechanical properties of CSRM. The effects of wet carbonation had not been further revealed on the evolution, microstructure, and CO2 uptake capacity of the reaction products. This article was innovatively combined with the microscopic analysis to reveal the carbon sequestration mechanism of SRM in water, which was of great significance for the preparation of highly active mineral admixture. Meanwhile, it proved that SRM had a certain carbon sequestration capacity, which provided theoretical support for the utilization of SRM.