Extraction of Zinc and Iron from Steel Dust Waste

Tien, Chan Wai (2020) Extraction of Zinc and Iron from Steel Dust Waste. Final Year Project, UTAR.

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Abstract

Electric Arc Furnace Dust (EAFD) is a toxic by-product released from EAF steelmaking process. Conventional solution of landfilling EAFD is destroying environment and public health due to the presence of heavy metals such as zinc, iron, nickel and lead. Hence, it is necessary to develop cost effective and feasible remediation solutions to cope with increasing demand of treating EAFD waste. Zinc (Zn) and iron (Fe) which contribute to the largest composition of EAFD (approximately 10-50 wt% and 16-60wt% respectively) can be recycled through extraction and precipitation as easy filterable precipitates. This project focused on maximum extraction amount of zinc and iron through EAFD leaching in hydrochloric acid (HCl) using hydrometallurgical method followed by precipitation of leaching solution using sodium hydroxide (NaOH) to form iron oxide and zinc oxide eventually. For leaching, the acid concentration, temperature, experiment duration, dust-to-acid ratio, and stirring speed were fixed at 10M, 50 ℃, 15 minutes, 1:30, and 700 rpm, respectively. The results (almost 100% zinc and iron extraction) were obtained. After leaching, only traces of carbon exist in the residues, while zinc and iron were completely dissolved. For precipitation, the alkali concentration and stirring speed were fixed at 0.5M and 400 rpm at room temperature condition. NaCl and Fe (OH)3 were obtained when the pH of the solution was increased to 5 by NaOH solution. Subsequently, Zn5(OH)8Cl2·H2O and NaCl were achieved when the pH of the solution was increased to 6.34. TGA results suggested hematite was formed when pH 5 precipitate was heated at 240 ℃ in nitrogen atmosphere. Besides, TGA results also suggested zinc oxide was formed when pH 6.34 precipitate was heated up to 180 ℃ in nitrogen atmosphere. The results in this project indicated the feasibility of zinc and iron extraction from EAFD through leaching and precipitation which will be beneficial to solve the dust waste problems in steel industries.

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