Effect of steelmaking dust characteristics on suitable recycling process determining: Ferrochrome converter (CRC) and electric arc furnace (EAF) dusts

- Properties of steelmaking dust and its implication on determine recycling method were studied.
- EAF dust is rich in zinc, while CRC is relatively low in zinc, but richer in chromium.
- In CRC, zinc is found as zinc oxide, while in EAFSS & EAFCS zinc is found as zinc ferrite.
- Pyrometallurgical methods are more suitable for processing EAFSS and EAFCS dusts.
- Hydrometallurgical methods will be more efficient than pyrometallurgical methods for processing CRC.

Utilization of dusts generated from steelmaking industries will avoid disposal of wastes, enhance the use of secondary raw material fines and save costs. Understanding the properties of dust is necessary before determining the suitable recycling method. The present paper describes the chemical, morphological and mineralogical characterization of steelmaking dusts produced in steel plants in Finland. In this paper three different steelmaking dusts: ferrochrome converter (CRC) and electric arc furnace stainless steel (EAFSS) dusts from Outokumpu (Tornio, Finland), and electric arc furnace carbon steel (EAFCS) dust from Ovako (Imatra, Finland) were characterized.The characterization study showed that, the dusts from carbon steelmaking (EAFCS) are rich in zinc, while the dusts from stainless steelmaking (CRC) and (EAFSS) are relatively low in zinc, but richer in chromium. The zinc contents in CRC, EAFSS and EAFCS dusts are 10.83, 19.84 and 35.76 wt%, respectively, while the chromium contents are 20.88, 3.19 and 0.47 wt%, respectively. In the dust from CRC, zinc is found as zinc oxide (zincite, ZnO), while in the dusts from EAFSS & EAFCS zinc is found mostly as zinc ferrite (franklinite, ZnFe2O4). Scanning electron microscopy (SEM) investigations indicated that CRC dust is dominated by non-spherical form and composed mainly of aggregates of irregular particles of chromite, in addition to zincite sphere. EAFSS dust particles are characterized by encapsulation phenomenon, franklinite particles enclosed inside calcium-iron-silicate glass sphere. Manganese (Mn) concentrations show positive correlation with Zn, which suggests the occurrence of Mn mainly with franklinite phase. EAFCS dust is dominated by spherical form, and zinc found as franklinite and zincite. In the large particles > 3 μm of EAFCS dust, franklinite enclosed inside glass sphere, while in finer particles < 1 μm, both zincite and franklinite existed as spheres.The investigations indicate that steelmaking dusts from CRC, EAFSS, and EAFCS show significant difference in concentration and mode of occurrence of zinc in the dusts, which will influence the determination of suitable processing methods.

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