Recycling steel plant by-products is a critical issue for achieving both environmental and economic
sustainability of integrated steel plants. A key steel plant by-product stream is dust from basic oxygen
steelmaking (BOS), which 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. This uncertainty affects the amount of dust recycled and how it interacts with the slag during
processing. BOS dust in stockpiles can undergo self-sintering reactions that oxidise 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.
To overcome difficulties associated with phase identification in the BOS dust (both fresh and selfsintered),
particularly the magnetite-zinc ferrite spinel solid solution using X-ray diffraction (XRD) /
scanning electron microscopy (SEM) / energy dispersive spectroscopy (EDS), high end
characterisation tools, transmission electron microscopy (TEM) and Mössbauer spectroscopy, were
also used. 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. While this spinel phase had been previously identified by XRD, it was not
clear that it contained zinc. The Mössbauer results provided definitive evidence of zinc within the
spinel phase.