dc.description.abstract |
The study carried out a gas/solid/liquid three-phase carbonation reaction by using reductive slag as carbon dioxide sequestration material under gas flow rate of 1 LPM at ambient temperature and pressure conditions. The effects of various operation parameters, including solid-liquid ratio, initial calcium concentration in liquid phase, carbon dioxide concentration in gas phase, and intermittent/continuous aeration, on the carbonation efficiency and reaction mechanisms in a three-phase carbonation system were investigated.
The experimental results found that the carbonation efficiency did not increase with the increase of solid-liquid ratio under continuous aeration of carbon dioxide, and the optimum solid-liquid ratio was 20 g/L. When the initial concentration of cal-cium in liquid phase increased from 500 mg-Ca2+/L to 1500 mg-Ca2+/L, not only the calcium utilization efficiency in slag raised from 78.0% to 83.3%, but made calcium utilization efficiency in solution elevated from 78.8% to 97.3%. In addition, the cal-cium came from the different two phases resulted in the competitive phenomenon for carbonate ion in the reaction system. Under intermittent aeration of carbon dioxide, the carbonation reaction was interrupted temporarily during the period of stop-aeration. Consequently, the calcium in slag was further leached out and im-permanent increased the calcium concentration in slurry. Moreover, this study re-vealed that 92.2% carbonation efficiency was achieved under the operation conditions of continuous aeration, 12 vol% of CO2 gas, 0 mg-Ca2+/L of liquid and solid-liquid ratio of 30 g/L at 60 min reaction time in a three phase carbonation system.
The result of reaction kinetics analysis indicated that the reaction of carbona-tion under continuous aeration and 0 mg-Ca2+/L in initial solution conformed to the surface coverage model; also the rate limiting step was the leaching of calcium from slag. However, the fitting degree became lower with the increase of initial calcium in liquid phase. As for three-phase carbonation under intermittent aeration, it was not suitable to describe the reaction kinetics by surface coverage model, because the calcium carbonate layer would not be formed on the slag surface to obstruct the leaching out of calcium ion in slag. | en_US |