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
Highlights
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)
The Modified Zincex Process involves the following steps to recover the zinc from zincite in EAF dust: (1) atmospheric leaching with 0.5 N H2SO4 at 40 °C, 1 h, pH 2 to dissolve ZnO; (2) purifying the leachate by precipitating the iron with lime; (3) extracting the zinc with bis(2-ethylhexyl) phosphoric acid (D2EHPA), (4) stripping the zinc from the loaded organic phase, and (5) electrowinning of the zinc metal [115]
Summary
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. Vanadium was recovered from Ca-rich slags by direct oxidative roasting, without added salt, followed by leaching with a sodium carbonate solution [26]. Zhang et al recovered the vanadium from slag using high-pressure oxidative acid leaching [21] where the fayalite and spinel phases are decomposed by H 2SO4, releasing vanadium and iron in solution, while the unreacted silicon and titanium are enriched in the residues.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
