Real-time investigation of the CO2 mineral carbonation reaction rate through direct aqueous route using semi-dry desulfurization slag

•Real-time CO2 concentration revealed the carbonation process.•Carbonation caused the sample particle size to be more uniform.•The wastewater that remained after the carbonation reaction could be reused.•The controlling mechanism of film diffusion, chemical reactions, and product layer diffusion has been revealed. Mineral carbonation via alkaline solid wastes is considered an effective approach to capture and store flue gas CO2 from industries and power plants. In this study, direct mineral carbonation of semi-dry desulfurization slag (SDe-S) through an aqueous route was investigated with an online carbonation setup to measure the amount of CO2 consumed by Ca(OH)2 at atmospheric pressure in a slurry reactor. The carbonated solid and liquid products were characterized by X-ray fluorescence, X-ray diffraction and field emission scanning electron microscopy with energy dispersive X-ray spectrometry. The results show that carbonation caused the sample particle size to become more uniform. A large amount of Ca2+ was dissolved in the waste solution which could be recycled, thus increasing the utilization rate of Ca2+. The CO2 carbonation efficiency and absorption rate of SDe-S could be improved by controlling the reaction operation parameters. The optimal reaction conditions of this reactor were 100 g/L, 60 °C, 400 rpm and 300 mL/min, and the optimal reaction termination time was limited to 249 min to ensure a CO2 absorption efficiency of higher than 90 %. The carbonation process was controlled first by the film diffusion of liquid CO2, then by the chemical reaction, then by the film diffusion of liquid Ca(OH)2, and finally by the diffusion of the product layer. Experimental simulation suggests that the semi-dry desulfurization ash could achieve high CO2 absorption efficiency at atmospheric pressure and low temperature without producing any waste liquid. That is, it pretty economical and environmentally friendly.