Hydrometallurgical Processes for the Recovery of Metals from Steel Industry By-Products: A Critical Review
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REVIEW ARTICLE
Hydrometallurgical Processes for the Recovery of Metals from Steel Industry By‑Products: A Critical Review Koen Binnemans1 · Peter Tom Jones2 · Álvaro Manjón Fernández3 · Victoria Masaguer Torres3 Received: 20 April 2020 / Accepted: 14 October 2020 © The Author(s) 2020
Abstract The state of the art for the recovery of metals from steel industry by-products using hydrometallurgical processes is reviewed. The steel by-products are different slags, dusts, and sludges from a blast furnace (BF), basic oxygen furnace (BOF), electric arc furnace (EAF), and sinter plant, as well as oily mill scale and pickling sludge. The review highlights that dusts and sludges are harder to valorize than slags, while the internal recycling of dusts and sludges in steelmaking is inhibited by their high zinc content. Although the objectives of treating BF sludges, BOF sludges, and EAF dust are similar, i.e., the removal of zinc and the generation of an Fe-rich residue to be returned to the steel plant, these three classes of by-products have specific mineralogical compositions and zinc contents. Because wide variations in the mineralogical composition and zinc content occur, it is impossible to develop a one-size-fits-all flow sheet with a fixed set of process conditions. The reason for the interest in EAF dust is its high zinc content, by far the highest of all steel by-products. However, EAF dust is usually studied from the perspective of the zinc industry. There are not only different concentrations of zinc, but also variations in the all-important ZnO/ZnFe2O4 (zincite-to-franklinite) ratio. In many chemical processes, only the ZnO dissolves, while the ZnFe2O4 is too refractory and reports to the residue. It only dissolves in concentrated acids, or if the dust is pre-treated, e.g., with a reductive roasting step. The dissolution of ZnFe2O4 in acidic solutions also brings significant amounts of iron in solution. Finally, due to its high potassium chloride content, sinter-plant dust could be a source of potassium for the fertilizer industry. Graphical Abstract
Keywords Hydrometallurgy · Iron · Industrial process residues · Steel · Recycling · Zinc The contributing editor for this article was Markus Reuter. Extended author information available on the last page of the article
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Introduction Producing one ton of steel in an integrated steel plant generates about half a ton of by-products, i.e., slags (90% by mass), dusts, and sludges. A blast furnace (BF) produces the most slag, with smaller amounts generated in a basic oxygen furnace (BOF) and an electric arc furnace (EAF). Dusts and sludges originate from the off-gas produced in BF, BOF, and EAF installations. Minor by-products include sinter-plant dust, oily mill scale, and pickling sludge. Although most steel slags have applications, dusts and sludges are often seen as waste. Research is turning to the valorization of those steel by-products that have no applications yet. The motivation can be the valorization of the metal content. Howe
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