DUST RECYCLING IN INTEGRATED STEEL MILLS: REDUCING ZINC RECIRCULATION

Considerable amounts of Fe-containing fine dusts are generated in an integrated steel mill, mainly at the blast furnace (BF) and the basic oxygen furnace (BOF). Limitations in dust recycling via the sinter plant arise especially from the limit for Zn in the BF feed. Therefore, dust with an elevated Zn content is usually discharged to landfill, resulting in considerable losses of Zn. In this study the possibilities for increased internal dust recycling in integrated steel mills by implementing air classification of dusts are discussed. The aim of this concept is to avoid landfill of steel mill dust by recycling of the Fe in the steelmaking process while producing a Zn-enriched by-product that can be utilized in secondary Zn production. Since the distribution of Zn in the dusts is not even but depends on the size of the particles, air classification can be applied to separate dusts into a coarse Zn-depleted size fraction and a Zn-enriched fine fraction. Low-Zn content coarse fractions of the dusts can be recycled in ironmaking, medium-Zn content dust fractions could be recycled in steelmaking, where the Zn input is not as limited as in ironmaking and Zn-rich fine dust fractions with a Zn concentration high enough for use in secondary Zn production could be recycled there.