Extractive Metallurgy and Circular Economy: From Metallurgical Waste to New Products

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Environmental Sciences".

Deadline for manuscript submissions: closed (28 February 2021) | Viewed by 9759

Special Issue Editors

Politecnico di Milano, Dipartimento di Meccanica, Via La Masa 1, 20156 Milano, Italy
Interests: extractive metallurgy; circular economy; metallurgical residues valorization
Special Issues, Collections and Topics in MDPI journals
Politecnico di Milano, Dipartimento di Meccanica, Via La Masa 1, 20156 Milano, Italy
Interests: ironmaking and steelmaking; applied metallurgy; plastic deformation of metals
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The metallurgical industry is one of the most impacting human activities in terms of solid, liquid, and gaseous emissions. Metals production involves the extraction of metals ores processed by hydro-, pyro-, or hybrid metallurgical processes, and it is always associated with the generation of an important amount of wastes. Unfortunately, for certain metals, i.e., rare earths, and noble metals, a shortage of raw materials began a few decades ago due to an increase in their utilization for specific applications (solar panels, microelectronics, etc.). Generally, the solid and liquid residues from a specific metallurgy contain significant fractions of valuable elements suitable as raw materials for other metallurgies, such as EAF dusts for Zn production. Thus, this Special Issue of Applied Sciences focuses on the possibility to extract (or recover) metals, oxides, or other compounds from metallurgical wastes (slag, dusts, sludges, skims, and dross) produced by the most widespread metallurgies (iron-making, aluminum, copper, zinc, lead), noble metals (gold, silver, platinum, etc.), refractory metals (tungsten, molybdenum, cobalt, etc.), and rare earths. The purpose of this Issue is to collect novel and promising processes to recover valuable elements and compounds from waste products. Pyro-, hydro-, or hybrid metallurgical processes will be well accepted. Preference will be given to papers explaining a feasible process at laboratory scale; a pilot plant; or an existing process, with special regard to the economic aspects of compound extractions and the environmental impact of process residues.

Dr. Davide Mombelli
Prof. Carlo Mapelli
Guest Editors

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Keywords

  • circular economy
  • extractive metallurgy
  • metallurgical residues recovery
  • secondary raw materials
  • waste management
  • slag
  • dusts
  • sludges
  • skims
  • dross

Published Papers (4 papers)

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Research

15 pages, 2978 KiB  
Article
Wastewater Treatment Using Alkali-Activated-Based Sorbents Produced from Blast Furnace Slag
by Saverio Latorrata, Riccardo Balzarotti, Maria Isabella Adami, Bianca Marino, Silvia Mostoni, Roberto Scotti, Maurizio Bellotto and Cinzia Cristiani
Appl. Sci. 2021, 11(7), 2985; https://doi.org/10.3390/app11072985 - 26 Mar 2021
Cited by 8 | Viewed by 2694
Abstract
Currently, slags from secondary steel production, foundries, and blast furnaces represent a major environmental problem since they end up mainly in landfills, and their valorization would bring undeniable advantages both to environment and economy. Moreover, the removal of heavy metal ions from mines [...] Read more.
Currently, slags from secondary steel production, foundries, and blast furnaces represent a major environmental problem since they end up mainly in landfills, and their valorization would bring undeniable advantages both to environment and economy. Moreover, the removal of heavy metal ions from mines wastewater is one of the challenges of the last decades, and adsorption has been proposed as one of the most promising techniques for this purpose. In this context, the use of alkali-activated slags as sorbent can be a good opportunity to develop low cost, environmentally friendly, and sustainable materials. Accordingly, wastewater decontamination by adsorption over a porous monolithic bed made of alkali-activated hydraulic binders is proposed. Alkali-activated materials were prepared using slags from the metallurgical industry and reacted with an alkaline component (high alumina calcium aluminate cement, CAC 80) at ambient conditions. The obtained monolithic foams were tested to evaluate the uptake efficiency towards metal capture. Solutions containing Cu(II), Fe(III), Ni(II), Mn(II), and simulating the metal concentrations of a real mine effluent were tested, both in single- and multi-ion solutions. Promising capture efficiency, values of 80–100% and of 98–100% in the case of the single ion and of the multi-ion solutions were obtained, respectively. Full article
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14 pages, 4429 KiB  
Article
Combination of Thermal, Hydrometallurgical and Electrochemical Tannery Waste Treatment for Cr(III) Recovery
by Evgenios Kokkinos, Aggeliki Banti, Ioanna Mintsouli, Aikaterini Touni, Sotiris Sotiropoulos and Anastasios Zouboulis
Appl. Sci. 2021, 11(2), 532; https://doi.org/10.3390/app11020532 - 07 Jan 2021
Cited by 5 | Viewed by 2015
Abstract
A combination of thermal (500–750 °C in air) and hydrometallurgical (acidic) treatments have been applied to dried tannery sludge, resulting in the initial conversion of Cr(III) to Cr(VI) and its subsequent leaching as wastewater with high Cr(VI) concentration content (3000–6000 mg/L), presenting an [...] Read more.
A combination of thermal (500–750 °C in air) and hydrometallurgical (acidic) treatments have been applied to dried tannery sludge, resulting in the initial conversion of Cr(III) to Cr(VI) and its subsequent leaching as wastewater with high Cr(VI) concentration content (3000–6000 mg/L), presenting an extraction efficiency over 90%. The optimal electrochemical conditions for the subsequent Cr(VI) reduction with respect to acid concentration and acid kind were established by applying appropriate rotating disc electrode (RDE) experiments, using a glassy carbon (GC) electrode, and found to be equal or higher than 0.5 M H2SO4 (for the respective Cr(III) concentration range studied). The result from leaching Cr(VI) wastewater was further treated in small electrochemical bench-scale reactor for its conversion back to Cr(III) form, potentially reusable in the tanning industry. Ti-based anodes and a reticulated vitreous carbon (RVC) cathode were used to treat small (350–800 mL) samples in batch, as well as in batch-recirculation prototype electrochemical reactors, under the application of constant current or appropriately applied potential to achieve Cr(VI) conversion/reduction efficiency over 95%. Full article
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14 pages, 4813 KiB  
Article
Investigation on the Chemical and Thermal Behavior of Recycling Agglomerates from EAF by-Products
by Thomas Willms, Thomas Echterhof, Stefan Steinlechner, Matti Aula, Ahmed Abdelrahim, Timo Fabritius, Davide Mombelli, Carlo Mapelli and Stefan Preiss
Appl. Sci. 2020, 10(22), 8309; https://doi.org/10.3390/app10228309 - 23 Nov 2020
Cited by 8 | Viewed by 2045
Abstract
In addition to the blast furnace converter route, electric steel production in the electric arc furnace (EAF) is one of the two main production routes for crude steel. In 2019, the global share of crude steel produced via the electric steel route was [...] Read more.
In addition to the blast furnace converter route, electric steel production in the electric arc furnace (EAF) is one of the two main production routes for crude steel. In 2019, the global share of crude steel produced via the electric steel route was 28%, which in numbers is 517 million metric tons of crude steel. The production and processing of steel leads to the output of a variety of by-products, such as dusts, fines, sludges and scales. At the moment, 10–67% of these by-products are landfilled and not recycled. These by-products contain metal oxides and minerals including iron oxide, zinc oxide, magnesia or alumina. Apart from the wasted valuable materials, the restriction of landfill space and stricter environmental laws are additional motivations to avoid landfill. The aim of the Fines2EAF project, funded by the European Research Fund for Coal and Steel, is to develop a low-cost and flexible solution for the recycling of fines, dusts, slags and scales from electric steel production. During this project, an easy, on-site solution for the agglomeration of fine by-products from steel production has to be developed from lab scale to pilot production for industrial tests in steel plants. The solution is based on the stamp press as the central element of the agglomeration process. The stamp press provides the benefit of being easily adapted to different raw materials and different pressing parameters, such as pressing-force and -speed, or mold geometry. Further benefits are that the stamp press process requires less binding material than the pelletizing process, and that no drying process is required as is the case with the pelletizing process. Before advancing the agglomeration of by-products via stamp press to an industrial scale, different material recipes are produced in lab-scale experiments and the finished agglomerates are tested for their use as secondary raw materials in the EAF. Therefore, the tests focus on the chemical and thermal behavior of the agglomerates. Chemical behavior, volatilization and reduction behavior of the agglomerates were investigated by differential thermogravimetric analysis combined with mass spectroscopy (TGA-MS). In addition, two melts with different agglomerates are carried out in a technical-scale electric arc furnace to increase the sample size. Full article
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10 pages, 1851 KiB  
Article
Micro-Raman Spectroscopy Investigation of Crystalline Phases in EAF Slag
by Alessandro Riboldi, Laura Borgese, Irene Vassalini, Giovanna Cornacchia, Marcello Gelfi, Marco Virginio Boniardi, Andrea Casaroli and Laura Eleonora Depero
Appl. Sci. 2020, 10(12), 4115; https://doi.org/10.3390/app10124115 - 15 Jun 2020
Cited by 6 | Viewed by 2167
Abstract
Electric arc furnace (EAF) slags were investigated by micro-Raman spectroscopy. A slag sample characterised by well-developed crystalline phases was obtained. The EDXS elemental composition made it possible to recognize the grains corresponding to the brownmillerite, larnite and magnesioferrite phases, as identified by XRD [...] Read more.
Electric arc furnace (EAF) slags were investigated by micro-Raman spectroscopy. A slag sample characterised by well-developed crystalline phases was obtained. The EDXS elemental composition made it possible to recognize the grains corresponding to the brownmillerite, larnite and magnesioferrite phases, as identified by XRD in the same powdered sample. The grains were collected and analysed by µ-Raman spectra, and the results showed good reproducibility in each grain and good agreement with spectra of the phases reported in the literature. A Raman database devoted to crystalline phases of EAF slag identification was created to be used by portable Raman instruments, allowing the phase characterisation of the slag directly during steel production. Full article
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