Air-cooling of metallurgical slags containing multivalent oxides

During air-cooling, high temperature, reduced metallurgical slags are brought in contact with ambient air, resulting in a gradient in both temperature and oxygen partial pressure. In this article, the pO2 dependency of slags containing multivalent oxides is investigated. Computer simulations with an extended version of the Scheil solidification model indicate significant differences in both end mineralogy and solidification path depending on oxygen partial pressure and oxygen diffusion. It is shown that metallic particles can form inside the slag during cooling because of a lack of oxygen exchange with the surrounding atmosphere. This is confirmed by laboratory solidification experiments, which corroborate that the level of oxygen diffusion is indeed limited. The proposed solidification mechanisms are extrapolated to industrial practice, based on key features of a stainless-steel electric arc furnace slag. The possible implications for slag recycling are discussed.