Abstract
Alkali-activated Fe-rich non-ferrous metallurgical slag (AA-NFS), within the FeOx-SiO2-Al2O3-CaO-MgO system, were tested in 2 wt% sulfuric acid for 6 months. Corrosion depth and rate were measured non-destructively by micro X-ray computed tomography. Both intact and corroded areas were characterized by XRD, FTIR, SEM-EDX and NMR. AA-NFS with higher Ca/Si showed a higher resistance to sulfuric acid. The presence of Mg negatively affected the resistance, whereas higher Al concentrations slightly enhanced the resistance in the investigated chemical composition range. The corrosion degree is closely related to the NFS reaction extent in AA-NFS, and this corrosion process is diffusion-controlled. Leaching of the elements (Al, Ca, Mg, Fe and Na) leaves behind mostly silica-rich gels, causing the failure of the framework structure after long-term exposure. The leached Ca2+ reacted with SO42− in acid solution and formed expansive sulfate products, which possibly clog pores and offer an additional protective barrier for AA-NFS against sulfuric acid.
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