Speciation of Zinc in Electric Arc Furnace Dust by Particle Size

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Abstract

Electric arc furnace dust (EAFD) is a by-product in steelmaking from scrap and direct reduced iron in an electric arc furnace (EAF). The reported range of EAFD per ton of liquid steel is 10-30 kg [1]. EAFD consists mainly of Fe but other metals volatile at steelmaking conditions can also be found in EAFD. Zn is found in EAFD at higher concentrations because of its wide-spread use for galvanizing steel components for corrosion protection [2]. The Zn enters the EAF with the scrap. Because of the high temperature and the reducing conditions all Zn is volatized in the furnace and leaves it with the off-gas. During cooling of the off-gas Zn is mostly deposited on the dust particles. The Zn concentration values in EAFD are in the range of 2-43% [1]. EAFD is classified as hazardous due to containing heavy metals and other hazardous components [3]. Part of the EAFD is still sent to landfill, however, increasing shares of EAFD are utilized to recover Zn [4]. For Zn recovery several hydrometallurgical and pyrometallurgical process routes are available [4,5]. Independent of the recycling route a high Zn content makes recycling of EAFD more economical. Therefore, recycling of EAFD back into the EAF can be used to increase the Zn content of the discharged EAFD [6]. Since Zn is enriched in the finest size fractions of the EAFD air classification can be applied to optimize dust recycling [7]. In the EAFD Zn is mainly present as zinc oxide (ZnO, zincite) and zinc ferrite (ZnFe2O4, franklinite) [6]. Especially for hydrometallurgical processes it is essential in which compound Zn is present since zinc oxide is much more accessible [8].
EAFD from four different steel mills was air classified into five size fractions each. Details of such an air classification procedure and a description of the analytical methods can be found elsewhere [9]. The Zn concentration of EAFD A was 8.0%, for EAFD B it was 16.3%, for EAFD C it was 14.5% and for EAFD D it was 2.6%.
As to be expected the Zn concentration was significantly higher in the fine size fractions and lower in the coarser size fractions. Power functions can be used to approximate the Zn concentration as a function of the particle size. However, the exponents vary from -0.29 to -0.78. No correlation between the exponent and the Zn concentration of the EAFD. Further investigations including the off-gas conditions at the EAF are needed to identify the reason for the considerable variation of the exponent.
To distinguish between zinc oxide and zinc ferrite in the various size-fractionated EAFDs the samples were leached for 3h in 1 M sodium acetate in acetic acid at pH 5. After leaching, the samples were centrifuged and diluted prior analysis with ICP-OES. Leaching of pure zinc oxide (from Fluka) and zinc ferrite (from Alfa Aesar) under the same conditions showed that 72% of the zinc oxide were dissolved while zinc ferrite was not dissolved under these conditions. Thus, the fraction of Zn leached can be used as an indication for the fraction of Zn present as zinc oxide. A significant difference was found for the different EAFDs. Generally, the fraction of leached Zn was somewhat higher in the coarse size fractions compared to the fine size fractions.
To find the reason for the differences in the fractions of Zn in zinc oxide and zinc ferrite further investigations should include the operation conditions at the EAF.
Translated title of the contributionSpeciation of Zinc in Electric Arc Furnace Dust by Particle Size
Original languageEnglish
Pages46-47
Publication statusPublished - 2023
Event24th Polish Conference of Chemical and Process Engineering - Szczecin, Szczecin, Poland
Duration: 13 Jun 202316 Jun 2023
https://okichip24.zut.edu.pl/

Conference

Conference24th Polish Conference of Chemical and Process Engineering
Country/TerritoryPoland
CitySzczecin
Period13.06.202316.06.2023
Internet address

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