Hydrometallurgical Processes for the Recovery of Metals from Steel Industry By-Products: A Critical Review

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

Residue Valorization in the Iron and Steel Industries: Sustainable Solutions for a Cleaner and More Competitive Future Europe

“…New branches of extractive metallurgy treatment via leaching are an environmentally friendly and CO 2 -free alternative to pyrometallurgical treatment for metal recovery from steelmaking residues [24,25]. Within the scope of the EIT Raw Materials project SAMEX (project number 19205, https://eit-samex.eu/, accessed on 16 May 2021), an ammoniacal process is being developed to treat fine BOF sludge (see Figure 8 [26]).…”

Research Progress on Heavy Metals Pollution in the Soil of Smelting Sites in China

“…Hydrometallurgical processes are more selective and thus more efficient while also reducing pollutants. During the last five years, China’s research on recovering vanadium from vanadium slags has increased dramatically [ 142 ]. Waste can be segregated and treated to make new products, and waste is not a waste until it is wasted.…”

Steel Manufacturing EAF Dust as a Potential Adsorbent for Hydrogen Sulfide Removal

“… 30 , 6 Recently, low-end applications for EAF dust have been developed, such as an additive material in asphalt or concrete. 31 , 4 The current best option for recycling EAF dust in the zinc raw material loop is by the Waelz process, in which approximately half of the world’s EAF dust is processed. 32 , 33 By introducing new applications for the zinc-containing side streams, recycling would become more profitable.…”

“…The EAF route generates Zn-rich dust as a side stream, especially during the recycling of galvanized steel. Basic oxygen furnace or blast furnace dust also contains zinc but in significantly lower concentrations . Production of 1 steel ton generates 10–20 kg of fine electric arc furnace dust (EAFD), which is collected by bag filters or electrostatic precipitators. , The global generation of EAFD is estimated at about 8 million tons annually .…”

“…Primary zinc adsorbent cost is heavily dependent on the ZnO market price, and therefore its use in large-scale gas purification applications may not be economically viable, especially since its regeneration can be challenging. , Concurrently, large amounts of zinc-containing side streams are generated in the steel industry. EAFD recycling mainly aims at recovering the zinc portion of the material. , Recently, low-end applications for EAF dust have been developed, such as an additive material in asphalt or concrete. , The current best option for recycling EAF dust in the zinc raw material loop is by the Waelz process, in which approximately half of the world’s EAF dust is processed. , By introducing new applications for the zinc-containing side streams, recycling would become more profitable. One of these applications could be the use of EAF dust for H 2 S removal.…”