Keywords: 
• fly ash /
• carbide slag /
• CO2 /
• carbonation

Abstract: In order to utilize fly ash and carbide slag efficiently for building materials and to reduce CO2 emission, the carbonation characteristics of fly ash, carbide slag and their mixtures were studied in this paper. The pH of the reaction slurry which contained fly ash, carbide slag and fly ash-carbide mixture was tested online, respectively. The raw materials and products from the reaction system were characterized by X-ray diffraction，thermogravimetric analysis and SEM.The results indicated that the average carbonation reaction rate of a fly ash when pH decreased to 7.0 was 51 times that of carbide slag.Compared with the carbide slag carbonation, the average carbonation reaction rate of the fly ash and carbide slag mixture (4:1,g:g) increased by nearly 5.6 times when the pH decreased to 7.0, and the reaction time for the mixture was shortened by 31.6% than that of calcium carbonate-carbide slag mixtures, indicating that there is a synergistic effect between carbide slag and fly ash in the carbonation reaction. The result of TGA showed that the carbon sequestration rate for fly ash and carbide slag was about 2% and 61.3%，respectively.The carbon sequestration rate for the fly ash carbide slag mixture increased by 19.6% than the sum of fly ash and carbide slag. The CaCO3 produced by carbonation of fly ash and carbide slag mixture attached on the surface of fly ash particle in a state of dispersion,while the CaCO3 produced by the carbide slag carbonation attached on the surface of carbide slag particle in a state of agglomerate, which were verified by the SEM results. This is likely the main reason for the increase of carbon sequestration for the fly ash-carbide slag mixtures.