Chemical, mineralogical and morphological characterisation of basic oxygen furnace dust Ja ´n Veres ˇ *1,2 , Vladimı ´r S ˇ epela ´k 1,3 and Slavomı ´r Hredza ´k 1 The occurrence and recovery of metallurgical wastes from steelmaking and ironmaking processes is nowadays a great problem, mainly because of their large amount and environmental pollution caused by heavy metals. Elements, such as Fe and Zn, which are important to the industries, are the main ones in basic oxygen furnace (BOF) dust. Because of their presence, it becomes very important to know how these elements are combined before studying new technologies for their processing. The aim of this work was to carry out chemical, physical, structural and morphological characterisation of the BOF dust. The investigation was carried out by using granulometric analysis, chemical analysis, SEM, EDAX, XRD and Mo ¨ ssbauer spectro- scopy. These findings deepened our understanding of zinc speciation present in zinc-containing steelmaking wastes. Keywords: BOF dust, Zinc, Iron, XRD, Mo ¨ ssbauer spectroscopy, SEM analysis Introduction The primary source of iron as a feed to iron and steel facilities comes from the oxide ores containing minerals such as haematite (Fe 2 O 3 ) and magnetite (Fe 3 O 4 ), which usually carry a negligible amount of non-ferrous metal as an impurity. However, some scrap is always used as a secondary source of iron and it usually carries significant amount of zinc. These scrap originates from a variety of sources such as old cars, cans, bridges, rails and demolished buildings, and in most cases, it is in galvanised form, which accounts for the presence of zinc (Kelebek et al., 2004). Dust and sludge collected from the gas-cleaning systems during the steelmaking processes in the steel- making industry is an important type of byproduct (Wang et al., 2012). Every year, a large amount of such kind of metallurgical residues is generated. It is estimated that each year, 5–7m t of basic oxygen furnace (BOF) sludge is generated worldwide (Veres ˇ et al., 2011; Das et al., 2007; Veres ˇ et al., 2012). They often have complex composition and contain several components that have negative effects not only on environment but also on steelmaking processes (Kretzschmar et al., 2012). Demands from society and enterprise itself have exerted the pressure to minimise the amount of metallurgical residues and to find an appropriate way to treat these wastes and to recycle their valuable components (Wang et al., 2012). Zinc is one of those elements which should be paid attention to in particular. This element is easy to volatilise during the metallurgical process because the boiling point of zinc is below the melting temperature in furnace, and it subsequently condenses and accumulates to form particles in the form of dust or sludge when passing through the gas-cleaning system (Wang et al., 2013). Usually, these dust and sludge cause risks in two ways. One is the negative influence on the environment. This kind of metallurgical residue is often composed of fine particles, and it can be easily discharged into the atmosphere and gets accumulated in the soil during transportation and landfill. Although zinc is an essential element for human beings and plants, it can cause poisoning and environmental risks at high concentra- tions (Machado et al., 2006; Mansfeldt and Dohrmann, 2004; Steer et al., 2014; Veres ˇ et al., 2010; Wang et al., 2012). The second is about the negative effect on steelmaking process. Generally, dust and sludge must be disposed off at a hazardous waste disposal site, which incurs high transport and disposal costs. These costs could be reduced if metals, such as iron, zinc, and so on, could be recovered or sold. The most common way to utilise this dust and sludge is by reusing them as a secondary source of raw material because of its high iron content. However, if reused, undesirable consequences will occur. In particular, the presence of zinc will damage the production equipment, blast furnace for example. When the dust and sludge are recycled in a blast furnace, zinc will accumulate on the walls, penetrate the lining, take part in the deformation and disintegration of the lining, and subsequently damage the blast furnace (Asadi Zeydabadi et al., 1997; Wang et al., 2013). Since the mobility of inorganic elements largely depends on their chemical forms, it is necessary for us to obtain a thorough knowledge of zinc spe- ciation. Chemical and structural characterisation of 1 Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, SK-043 53 Kos ˇice, Slovakia 2 VS ˇ B – Technical University of Ostrava, Energy Research Center, 17. Listopadu 15/2172, 708 33 Ostrava – Poruba, Czech Republic 3 Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann- von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany *Corresponding author, email veres@saske.sk ß 2015 Institute of Materials, Minerals and Mining and The AusIMM Published by Maney on behalf of the Institute and The AusIMM Received 17 October 2013; accepted 1 August 2014 DOI 10.1179/1743285514Y.0000000069 Mineral Processing and Extractive Metallurgy (Trans. Inst. Min Metall. C) 2015 VOL 124 NO 1 1