Modification of Molten Steelmaking Slag for Cement Application

The use of metallurgical slags in cement production depends on the phases present in such slags, which are affected by changes in slag composition as well as the cooling rates adopted during solidification. In this work, slags with distinct chemical compositions were melted and subjected to different cooling conditions. Slag samples were characterized by X-ray diffraction to identify and quantify mineralogical phases and by X-ray fluorescence to determine chemical composition. The microstructure of the samples was characterized by scanning electron microscopy coupled to energy dispersive spectroscopy for phase identification. The solidification of the slags was simulated using FactSage TM for solidification path evaluation, enabling a comparison of the phases determined by thermodynamic equilibrium with those analyzed in slag samples. Slags with low basicity (CaO/SiO2 < 1.25) and Al2O3 content of 11 wt% exhibited a high glassy phase content depending on the cooling conditions. The phases formed in slags with higher basicity (1.4 and 3.8) were less affected by cooling rate and were different silicates, such as larnite, merwinite, monticellite, akermanite, gehlenite and melilite, whereas slags with basicity < 1.37 exhibited RO phase (solid solution of FeO, MgO, CaO and MnO).