Change of State of Lime Phase and Inhibition of Hydration Reaction by Coexisting Oxides in Steelmaking Slag

摘要

To promote the utilization of steelmaking slag, the hydration reactivity and electronic state of free lime (CaO) were observed in this study. It was confirmed by X-ray diffraction (XRD) and thermal analysis that the hydration reactivity decreases when CaO forms a lime-phase solid solution with FeO, and it was revealed by X-ray photoelectron spectroscopy (XPS) observations that the decrease in reactivity occurs due to deepening of the energy levels of the electron orbitals. The morphology and hydration reactivity of the free lime contained in a synthesized slag were observed by XRD and electron probe microanalysis. Fe-containing phases and double oxides were found to be adjacent to free lime; the former is considered to be related to the formation of a solid solution with FeO, and the latter closely surrounds the free lime and shields it from the outside; thus, both contribute to suppressing the hydration reaction. Furthermore, it was found that simply mixing lime with double oxides suppressed the hydration reaction. XPS and thermal analysis confirmed that a chemical change occurred on the surface of the free lime; that is, the energy levels of the electron orbitals are deepened and the hydration reaction is suppressed due to chemical interactions with the double oxides to stabilize the lime surface. It was clarified that in order to effectively promote the hydration of free lime, it must be exposed by breaking the structure of the slag that protects the free lime and suppresses hydration.