Probe into carbonation mechanism of steel slag via FIB-TEM: The roles of various mineral phases

The nano-structures of carbonation products of various minerals in the steel slag were investigated by using FIB-TEM. In combination with XRD and NMR examinations, the roles of Ca, Mg, Si, Fe, Al played throughout the carbonation of steel slag were discussed. The results indicated that, for the carbonation of calcium silicate, Ca2+ leached from the calcium silicate as a result of H+ attack and then diffused to the outer layer to precipitate as CaCO3. SiO2 gel was formed locally after the Ca2+ leaching. M-S-H was found in the Si-rich area, which was probably attributed to the reaction between the newly formed SiO2 gel and Mg2+. Accordingly, a new insight into the carbonation mechanism of calcium silicates was proposed. Iron and alumina in the forms of iron manganese oxide and mayenite exhibited very low carbonation degree, showing very clear interfaces between them and the carbonation products in the TEM image.