The effect of chemical composition, microstructure and geometrical features on leaching behaviour of Electric Arc Furnace (EAF) carbon steel slag

The Electric Arc Furnace (EAF) slag could be exploited in several fields of application, such as land filling, road constructions and concrete production. However, their use is limited by the presence of polluting chemical elements (Cr, Ba, V, etc.) that can be dangerous to humans and the environment. Thus, chemical and structural stability is a fundamental requirement, especially when the slag may come in contact with water. The leachate is produced under conditions that can vary as a function of different physical parameters like chemical composition, microstructure, particle size and liquid-on-volume ratio. Therefore, the interaction between slag and water is key, in order to classify the slag as a safe raw material. In this work, the investigation on the main factors ruling chemical leaching on about seventy EAF carbon steel slag from different productions steel grades was performed. Elution test on slag bulks and powders were performed at different liquid-on-solid ratio and the water was analysed by ICP-OES to quantify the dangerous elements concentration. Morphological and microstructural characterizations were performed by means of SEM and XRD analysis in order to identify the main phases constituting the slag. The survey makes possible the identification of safe chemical composition areas on the main ternary diagrams, able to transfer stability to the slag. The analyses also allowed for the identification of the phases responsible for heavy metal leaching (larnite and brownmillerite), as well as those that were not involved in dissolution phenomena (gehlenite and kirschsteinite).