SHORT COMMUNICATION Air classification of blast furnace dust catcher dust for zinc load reduction at the sinter plant C. Lanzerstorfer 1 Received: 29 May 2015 / Revised: 27 September 2015 / Accepted: 7 October 2015 / Published online: 19 October 2015 Ó Islamic Azad University (IAU) 2015 Abstract The off-gas discharged from a blast furnace is de-dusted in a first stage by a dust catcher or a cyclone. The separated dust consists mainly of iron and coke. Therefore, most of this dust is recycled in the sinter plant. A higher Zn content of the dust is undesirable because the allowed Zn content in the sinter feed material is limited. The reduction of the Zn content of the dust by a simple process would be helpful in the case of higher Zn content in the blast furnace dust. In classification experiments, it has been demon- strated that the Zn content of the blast furnace dust increases with decreasing particle size. Thus, air classifi- cation of the dust can be applied to separate the Zn-en- riched fines. By separating a small fraction of fines (about 10–20 %) from the blast furnace dust, a reduction of the mass of Zn in the remaining coarse fraction for recycling in the range of 40–60 % is possible and only 5–10 % of the carbon is lost. Keywords Recycling Á Dust treatment Á Zinc separation Á Blast furnace residues Introduction The blast furnace (BF) process is the most important pro- cess in integrated steel mills for the production of hot metal (pig iron). There the iron ore is reduced to metallic iron. The off-gas discharged from the BF, the so-called top-gas, is de-dusted in a first stage by the dust catcher which separates the coarser dust form the top-gas (Lajtonyi 2006; Winfield et al. 2012). Alternatively, cyclones are used in some plants for the first off-gas cleaning step (Craig 2008; Suvorov 2009; Winfield et al. 2013). The final de-dusting is usually achieved in a subsequent scrubber (Streit 2007). In some BFs, especially in Japan and China, fabric filters are used for the second de-dusting stage (Murai et al. 1986; Zhang 2009; Lanzerstorfer and Xu 2014). For European BFs, the average amount of dust separated in the dust catcher is 18 kg dust per ton of hot metal pro- duced (Remus et al. 2013). The dust collected in the dust catcher consists mainly of iron oxides (15–40 % Fe) and coke particles (25–40 % C) which are fine enough to be carried by the discharged gas (Remus et al. 2013). Minor constituents are calcium oxide, aluminium oxide and silica (Das et al. 2007; Remus et al. 2013; Großpietsch et al. 2001). Therefore, the BF dust is usually recycled to the sinter plant (Hansmann et al. 2008; Skroch and Mayer- Schwinning 2012; Wie ˛cek and Mro ´z 2014) to recycle the valuable components. However, there is also some zinc in the dust catcher dust. The Zn content is typically in the range of 0.1–0.5 % (Remus et al. 2013). Zinc is an unwanted component in the sinter because it causes operational problems in the sub- sequent BF. It can form crusts in the upper part of the furnace and accumulates in the lining of the furnace which consequently deteriorates (Stepin et al. 2001; Koros 2003; Malemud et al. 2013; Doronin and Svyazhin 2011). Therefore, the total amount of zinc in the charge of a BF is usually restricted to 100–150 g/t of hot metal produced (Remus et al. 2013). The zinc in the charge of the BF is mainly contained in the sinter (Stepin et al. 2001). The sources of zinc in the sinter are usually recycling materials. In particular, dusts from the de-dusting of the BF & C. Lanzerstorfer christof.lanzerstorfer@fh-wels.at 1 School of Engineering/Environmental Sciences, University of Applied Sciences Upper Austria, Stelzhamerstraße 23, 4600 Wels, Austria 123 Int. J. Environ. Sci. Technol. (2016) 13:755–760 DOI 10.1007/s13762-015-0903-1