The Direct Carbonation Behavior of Steel Slag with CO2-Containing Water Vapor

Steel slag, which is the industrial waste produced by the steel-making process, contains more than 4% unstable free calcium oxide, which limits its applications. The problem of CO2 emission also needs to be solved; steel slag carbonation can not only achieve CO2 emission reduction, but also improve the stability of the steel slag. In this paper, the carbonation of steel slag at different temperatures and reaction times was investigated by combining mass balance analysis, XRD, and SEM observation. The results showed that, based on the thermodynamic analysis, a temperature of less than 1100 K is more appropriate for carbonation reactions. The carbonation of steel slag increases as the temperature increases within a certain range. Under the condition of the mixture of carbon dioxide and water vapor as the carbonation atmosphere for 30 min, the carbonation efficiency at 973 K was shown to be better than that of 873 K; additionally, the carbonation ratio was higher, and the efficiency of further heating to 1073 K decreased. At 973 K, the effect of carbonate formation for 30 min was better than that of 15 min, and when the carbonation time was increased to 45 min, the carbonation efficiency decreased. Moreover, the carbonation process can make the microstructure of steel slag more compact and reduce the particle size.