Understanding Zinc-Containing Species in BOS Dust

Abstract Dust from basic oxygen steelmaking (BOS) can be recycled back to the BOS vessel as iron units and to aid slag formation. The major limitations for its recycling are zinc and the uncertainty in zinc speciation of the dust, which affects the amount recycled. BOS dust in stockpiles can undergo self-sintering reactions that oxidize the iron-bearing components. As this occurs, zinc (or oxide) may combine with iron oxides to form a zinc-iron spinel solid solution phase. Knowing which zinc-bearing species are present in the BOS dust is a key aspect in understanding and developing an efficient recycling process for the dust. High end characterization tools, TEM and Mössbauer spectroscopy, were used to overcome difficulties associated with phase identification in the BOS dust, particularly the magnetite-zinc ferrite spinel solid solution. Such an approach allowed improved phase identification of key zinc- and iron-bearing phases that were not previously resolvable. The zinc in fresh BOS dust was mostly present as extremely fine separate particles of zinc oxide, attached to the iron particles. These extremely fine particles were < 10 nm in size. Additionally, a small amount of zinc ferrite was also identified within the sample (most likely contained within a magnetite-zinc ferrite spinel solid solution). However, the zinc in the self-sintered BOS dust was found to be present entirely in a magnetite-zinc ferrite spinel solid solution using Mössbauer spectroscopy. While this spinel phase had been previously identified by XRD, it had not been clear if it contained zinc. Graphical Abstract