One-step extraction of zinc and separation of iron from hazardous electric arc furnace dust via sulphating roasting-water leaching

Abstract

The electric arc furnace dust (EAFD) is rich in zinc and iron, which is classified as a hazardous solid waste and generated during steelmaking in electric arc furnace. As an important secondary resource for zinc, the zinc extraction from EAFD has become crucial resource utilization direction. In this work, a novel process is proposed to extract zinc and separate iron for one-step through co-roasting EAFD with NH4HSO4, followed by water leaching. Through the co-roasting of EAFD and NH4HSO4, the zinc-containing phases in EAFD were transformed into ZnSO4, and the iron-containing phases were transformed into Fe2O3. The separation of Zn and Fe was then performed by water leaching. The determined optimal experimental conditions were the mass ratio of NH4HSO4/EAFD of 0.75, the roasting temperature of 600 ℃, the holding time of 3 h, and the leaching time of 1 h, in which 91.14% of Zn and 3.25% of Fe were dissolved in the leaching solution. Afterwards, the reaction mechanisms of the co-roasting process of EAFD and NH4HSO4 were revealed. When the temperature increased, the zinc-containing phase (NH4)2Zn(SO4)2 and iron-containing phase NH4Fe(SO4)2 were first generated. (NH4)2Zn(SO4)2 was then successively converted to ZnSO4, and NH4Fe(SO4)2 was decomposed into Fe2O3 and Fe2(SO4)3. SO3 produced by NH4HSO4 decomposition in the roasting process can continue to participate in the sulfation process. Subsequently, zinc was enriched in the leaching solution, which can be considered as the raw material for Zn electrodeposition. Iron entered the leaching residue as Fe2O3, which can be used as the raw material for ironmaking. The result of leaching toxicity test showed that most of the heavy metals (i.e., Pb and Cr) were fixed in the leaching residue, which met the national standards for leaching toxicity. This study provides a theoretical reference and technical support for zinc extraction from zinc-containing solid wastes.