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Metals
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Recovery and Utilization of Metallurgical Solid Wastes
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Recovery and Utilization of Metallurgical Solid Wastes

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Extractive Metallurgy".

Deadline for manuscript submissions: 31 July 2025 | Viewed by 8380

Special Issue Editor

Prof. Dr. Zhiwei Peng

E-Mail Website
Guest Editor
School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China
Interests: ferrous metallurgy; microwave processing; comprehensive utilization of resources; waste valorization; powder agglomeration; low-carbon technology; process simulation; dielectric characterization; electromagnetic shielding; synthesis of functional materials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The soaring demand for metals keeps boosting their production, simultaneously generating massive metallurgical solid wastes, e.g., slag, sludge, and dust. For the continuous growth of the metallurgical industry, it is vital to recover and utilize these wastes in view of the potential economic and environmental benefits. However, there are significant differences in the contents and occurrence forms of valuable elements in various types of the wastes. It is crucial to continuously innovate treatment processes for metallurgical solid wastes with the rapid development of the industry.

The past few years have witnessed enormous progress in treating metallurgical solid wastes, particularly the recovery of valuable components using novel physical, pyrometallurgical and hydrometallurgical methods or direct conversion of the wastes to a wide spectrum of value-added products by individual and combined technologies. Exciting findings have been stimulating the commercialization of many relevant processes to achieve cleaner metal production.

This Special Issue intends to bring together cutting-edge research in the field of the recovery and utilization of metallurgical solid wastes for realizing sustainable development of the metallurgical industry towards a greener, more resource-efficient, and climate-resilient economy. It particularly welcomes contributions detailing significant advances regarding innovative theories, methods, and technologies for the treatment of metallurgical solid wastes that possess the features of low-carbon footprint, little or no environmental hazards, and long-term economic viability.

Prof. Dr. Zhiwei Peng
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • waste characterization
  • waste valorization
  • metal recovery
  • physical separation
  • hydrometallurgy
  • pyrometallurgy
  • low-carbon recycling
  • environmental assessment
  • energy conservation

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Published Papers (5 papers)

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Research

17 pages, 2561 KiB  
Article
Comparative Study of Steel Mill Dust Leaching with Phosphoric Acid and Sodium Hydroxide
by Fernando Sánchez, Ernesto de la Torre, Alicia Guevara, Katherine Moreno and Carlos F. Aragón-Tobar
Metals 2024, 14(9), 1087; https://doi.org/10.3390/met14091087 - 23 Sep 2024
Viewed by 1677
Abstract
Steel mill dust (SMD), produced by electric arc furnaces, is a highly polluting industrial waste due to its high content of metals (Zn, Fe, and Pb) and fine particle size (ca. 5.4 µm). This residue can be valorized to recover Zn using pyro [...] Read more.
Steel mill dust (SMD), produced by electric arc furnaces, is a highly polluting industrial waste due to its high content of metals (Zn, Fe, and Pb) and fine particle size (ca. 5.4 µm). This residue can be valorized to recover Zn using pyro and hydrometallurgical methods, with hydrometallurgy offering greater selectivity and lower energy costs. However, composition of SMD presents a challenge in identifying an optimal leaching agent. This study investigates the preferential extraction of Zn using two leaching agents, namely 150 g L−1 (1.5 M) phosphoric acid (H3PO4) and 240 g L−1 (6 M) sodium hydroxide (NaOH), in a two-stage leaching process (80 °C). Metallic Zn from the alkaline pregnant solution was recovered by electrodeposition (750 A/m2, graphite anode, stainless-steel cathode) and smelting (450 °C). The samples of SMD contained 26.3% Zn, 20.1% Fe, and 0.9% Pb, in compounds such as magnetite (Fe3O4), zincite (ZnO), and franklinite (ZnFe2O4). Each leaching agent successfully attained a 99% Zn recovery, demonstrating the proposed procedure’s high efficacy. However, H3PO4 leached also Fe and corroded the cathode during electrodeposition, thereby restricting the final recovery of metallic Zn. NaOH demonstrated greater selectivity for Zn over Fe and Pb, producing high-purity Zn deposits on the cathode by electrodeposition and 99% metallic zinc by smelting. Full article
(This article belongs to the Special Issue Recovery and Utilization of Metallurgical Solid Wastes)
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20 pages, 7779 KiB  
Article
A Metal Accelerator Approach for Discharging Cylindrical Lithium-Ion Batteries in a Salt Solution
by Erdenebold Urtnasan and Jei-Pil Wang
Metals 2024, 14(6), 657; https://doi.org/10.3390/met14060657 - 31 May 2024
Cited by 2 | Viewed by 1396
Abstract
Recycling lithium-ion batteries provides sustainable raw materials. Crushing and separation are necessary for extracting metals, like lithium, from batteries. Crushing a battery carries a risk of fire or explosion. Fully discharging the battery is crucial for safe production. Discharging batteries in a salt [...] Read more.
Recycling lithium-ion batteries provides sustainable raw materials. Crushing and separation are necessary for extracting metals, like lithium, from batteries. Crushing a battery carries a risk of fire or explosion. Fully discharging the battery is crucial for safe production. Discharging batteries in a salt solution is a simple and cost-effective large-scale process. However, it is important to note that there is a potential risk of corrosion and loss of battery elements when batteries are immersed in a salt solution. The purpose of this study is to investigate the effectiveness of two distinct methodologies at enhancing the voltage drop of a cylindrical battery when immersed in a salt solution while preventing corrosion. These techniques involve the application of iron and copper accelerators. A 20 wt.% salt water solution was chosen based on the research of several researchers. As the current flows through the metal parts, it encounters electrical resistance and forms an electric circuit with the electrolyte solution. This interaction converts electrical energy into various physical–electrical–electrochemical phenomena, leading to a decrease in battery voltage. Research revealed that the battery can be discharged up to 100% within 4 h without causing corrosion to its components. Another point to note is that if copper conductors are used, it is possible to decrease the battery voltage by around 90% within 8 h. The gap between the copper conductor and the battery had a direct impact on the battery’s discharge rate. Reducing the distance significantly increased the discharge rate, as confirmed by experimental evidence. This discharge mechanism was thoroughly described in a schematic, and, to further explain the electrochemical reaction, the Pourbaix diagram was utilized for both the Fe-Na-Cl and Cu-Na-Cl systems. Moreover, our theoretical predictions were validated through a chemical and mineralogical analysis of the precipitates that formed in the solution. Full article
(This article belongs to the Special Issue Recovery and Utilization of Metallurgical Solid Wastes)
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15 pages, 22665 KiB  
Article
CO–H2 Gas-Based Reduction Behavior of Cr-Rich Electroplating Sludge Mixed with Iron Ore Powder
by Jian Zhang, Zhiwei Peng, Lingyun Yi and Mingjun Rao
Metals 2024, 14(3), 325; https://doi.org/10.3390/met14030325 - 12 Mar 2024
Viewed by 1374
Abstract
Cr-rich electroplating sludge (CRES) is a complicated solid waste with high contents of chromium and iron. It can be used as a main feed of the FINEX ironmaking process, which requires gas-based reduction before smelting reduction to produce molten iron with the proper [...] Read more.
Cr-rich electroplating sludge (CRES) is a complicated solid waste with high contents of chromium and iron. It can be used as a main feed of the FINEX ironmaking process, which requires gas-based reduction before smelting reduction to produce molten iron with the proper addition of iron ore powder. In this study, the CO–H2 gas-based reduction behavior of CRES mixed with iron ore powder was evaluated between 700 °C and 850 °C, with a focus on the variations of key components containing Fe, Cr, and S with reduction temperature and time. It was found that the iron oxides in CRES had stepwise conversions to metallic iron as the reduction reaction proceeded. The iron metallization degree of the mixture of CRES and iron ore powder increased obviously below 750 °C and then grew minorly with the further increase of temperature. Moreover, this index varied similarly with an extension of reduction time up to 80 min. After reduction at 750 °C for 60 min with the volume concentration of H2 of 30% and flow rate of 160 mL/min, the iron metallization degree reached 79.08%. The rate in the process was limited by a chemical reaction with an activation energy of 41.32 kJ/mol. Along with the stepwise reduction of iron oxides to metallic iron, the chromium hydroxide and sulfates in CRES were reduced to Cr2O3 and sulfites and sulfides, respectively. Full article
(This article belongs to the Special Issue Recovery and Utilization of Metallurgical Solid Wastes)
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15 pages, 19578 KiB  
Article
The Direct Alloying of Steel through Silicothermic Self-Reduction of Chromite Ore Utilizing Si-Containing Solid Waste
by Yiliang Chen, Zhengliang Xue and Shengqiang Song
Metals 2024, 14(2), 138; https://doi.org/10.3390/met14020138 - 23 Jan 2024
Viewed by 1619
Abstract
Organosilicon materials generate copious amounts of Si-containing solid waste during production, leading to severe environmental pollution and substantial resource squandering. In pursuit of the resource utilization of Si-containing solid waste, this study conducted experimental research on the direct alloying of molten steel through [...] Read more.
Organosilicon materials generate copious amounts of Si-containing solid waste during production, leading to severe environmental pollution and substantial resource squandering. In pursuit of the resource utilization of Si-containing solid waste, this study conducted experimental research on the direct alloying of molten steel through the silicothermic self-reduction of chromite ore using Si-containing solid waste as a reducing agent. Additionally, thermodynamic analysis was performed, employing the thermodynamic calculation software FactSage 8.2 (Thermfact Ltd., Montreal, QC, Canada and GTT-Technologies, Aachen, Germany), to examine the equilibrium reactions of the silicothermic reduction of chromite ore and the variations in the thermodynamic equilibrium compositions of slag and metal phases. The results indicate a reduction sequence for the reducible components in chromite ore as Fe2O3 → Cr2O3. The introduction of CaO and Al2O3 into the silicothermic self-reduction compacts altered the forms of Fe and Cr oxides in equilibrium, significantly reducing the standard Gibbs free energy (ΔG0) of the silicothermic reduction reaction. The initial slag melting point decreased from 1700 °C without the addition of CaO and Al2O3 to 1500 °C with the addition of CaO and Al2O3. Correspondingly, the slag viscosity at 1600 °C decreased from 134.1 Pa·s without CaO and Al2O3 addition to 1.81 Pa·s with CaO and Al2O3 addition. The addition of CaO and Al2O3 accelerated the reduction of Cr oxide in chromite ore and enhanced the recovery of Cr, consistent with the thermodynamic calculation results. In the process of steelmaking through the direct alloying of chromite ore silicothermic self-reduction compacts, the final recovery rate of Cr increased from 86.4% without CaO and Al2O3 addition to 95.4% with CaO and Al2O3 addition. Full article
(This article belongs to the Special Issue Recovery and Utilization of Metallurgical Solid Wastes)
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19 pages, 11898 KiB  
Article
Preparation of Spinel-Type Black Pigments Using Microwave-Assisted Calcination of Stainless Steel Dust: The Effect of Manganese Molar Content
by Xiang Zhang, Yanghui Xu, Zhiqiao Li, Mengke Liu, Tianyu Du, Ruixiang He and Guojun Ma
Metals 2023, 13(12), 1949; https://doi.org/10.3390/met13121949 - 28 Nov 2023
Cited by 1 | Viewed by 1541
Abstract
Stainless steel dust is rich in valuable metal elements including Fe, Cr, Ni and Mn, which can be utilized to prepare Fe–Cr–Ni–Mn series black pigments. Meanwhile, manganese can absorb the majority of the visible light wavelength range, which improves the color rendering performance [...] Read more.
Stainless steel dust is rich in valuable metal elements including Fe, Cr, Ni and Mn, which can be utilized to prepare Fe–Cr–Ni–Mn series black pigments. Meanwhile, manganese can absorb the majority of the visible light wavelength range, which improves the color rendering performance of Fe–Cr–Ni–Mn series black pigments. However, the coloring mechanism of manganese in the above black pigments is not clear. Therefore, the effect of manganese oxide content on the preparation of spinel-type black pigments from microwave-assisted calcination of stainless steel dust was studied in this work. The results show that with the increase in MnO content in the raw mixture, the crystal plane spacing of black pigments increases from 0.2525 nm to 0.2535 nm, the grain size grows from 61.4619 nm to 79.7171 nm, and the lattice constant grows from 0.8377 to 0.8406 nm. Moreover, the band gap is decreased from 1.483 eV to 1.244 eV, the absorbance increases significantly and has a consistent absorbance in the visible range, and the L*, a* and b* values reduce from 41.8, 0.6, 1.6 to 32.0, 1.0, 0.8, respectively. MnO can react with the spinel in stainless steel dust, forming Mn3O4, MnCr2O4 and Ni (Fe,Cr)O4 in the system, with a regular polyhedral structure. The prepared pigments have excellent thermal stability at 1100 °C and good compatibility with transparent glazes, which can be adhered to the surface of ceramic tiles after calcination to demonstrate better compatibility as the content of MnO increases. Full article
(This article belongs to the Special Issue Recovery and Utilization of Metallurgical Solid Wastes)
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