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Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for...
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Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes

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

Deadline for manuscript submissions: 10 August 2025 | Viewed by 15178

Special Issue Editors

Dr. Ilhwan Park

E-Mail Website
Guest Editor
Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University, Sapporo 060-0808, Japan
Interests: mineral processing; flotation; hydrometallurgy; leaching; electrochemistry; resource recycling; environmental remediation; acid mine drainage; sulfide passivation
Special Issues, Collections and Topics in MDPI journals
Dr. Sanghee Jeon

E-Mail Website
Guest Editor
Graduate School of Engineering and Resource Science, Akita University, Akita 010-0865, Japan
Interests: mineral processing; hydrometallurgy; resource recycling; leaching; cementation; electrochemistry

Special Issue Information

Dear Colleagues,

The global climate change crisis has become a major issue in recent years, and it has forced us to pursue carbon neutrality as our common, primary, and initiative goal. For this, more than 130 countries have set or considering setting a target of reducing the greenhouse gas (GHG) emissions to net-zero by 2050 by replacing fossil-fuel-based energy and transportation systems to low-carbon technologies (e.g., renewable energy, hydrogen energy, electric vehicles (EVs), etc.). However, these technologies require vast amounts of metals per unit generation compared to that of conventional fossil generation. Thus, the sustainable production of metals critical to a low carbon future (e.g., aluminum, cobalt, copper, lithium, nickel, platinum group metals (PGMs), rare earth metals (REMs), silver, vanadium, etc.) is of topical importance to combat CO2-induced climate change.

In this Special Issue, we invite articles that focus on recent advances in beneficiation (e.g., gravity separation, magnetic separation, flotation, etc.) and extractive metallurgy (e.g., atmospheric leaching, bioleaching, pressure leaching, solvometallurgy, etc.) for producing critical metals from primary, as well as secondary resources, such as tailings, metallurgical residues, slags, E-wastes, or wastewater. We welcome not only research papers but also review papers, short communications, and case reports.

Dr. Ilhwan Park
Dr. Sanghee Jeon
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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

  • carbon-neutrality
  • critical metals
  • beneficiation
  • gravity separation
  • magnetic separation
  • flotation
  • extractive metallurgy
  • leaching
  • solvent extraction
  • cementation
  • adsorption
  • precipitation
  • primary/secondary resources

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Related Special Issue

Published Papers (7 papers)

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Research

Jump to: Review

15 pages, 8680 KiB  
Article
Cu(II) and Ni(II) Adsorption on Torrefied Wood Waste Biomass
by Marjana Simonič, Darko Goričanec, Aleksandra Petrovič, Ilda Silić and Danijela Urbancl
Metals 2025, 15(3), 304; https://doi.org/10.3390/met15030304 - 11 Mar 2025
Viewed by 347
Abstract
The aim of the research was to study the torrefaction processes of wood biomass, compare the product characteristics at different torrefaction temperatures, and assess both moisture adsorption on raw and torrefied samples, as well as metal (Cu(II) and Ni(II)) adsorption on torrefied biomass. [...] Read more.
The aim of the research was to study the torrefaction processes of wood biomass, compare the product characteristics at different torrefaction temperatures, and assess both moisture adsorption on raw and torrefied samples, as well as metal (Cu(II) and Ni(II)) adsorption on torrefied biomass. The novelty of the research was to investigate whether the presence of adsorbed metals in torrefied biomass significantly affects the energetic properties of the torrefied biomass, compared to torrefied biomass without metals. First, wood samples were torrefied at temperatures of 250 °C, 350 °C, and 400 °C. Following torrefaction, thermogravimetric analysis (TGA) was performed to evaluate mass loss and thermal stability. Next, changes in surface functional groups were examined, and higher heating values (HHV) were measured to assess the energy content. The results showed that torrefaction significantly increased the hydrophobicity of the biomass, leading to reduced moisture adsorption and enhanced material properties. Additionally, the adsorption of Cu(II) and Ni(II) ions on torrefied biomass was investigated. The results showed that the adsorption efficiency for Cu(II) was higher, reaching 62.4%, compared to Ni(II) at 21.2%. The adsorption process followed a pseudo-second-order kinetic model, which indicated that chemisorption was the dominant mechanism. Full article
(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)
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12 pages, 5231 KiB  
Article
Rare Earth Metal Ion-Associates in Ln3+—CO32−—H2O System
by Tatiana Litvinova, Stepan Gerasev, Vasiliy Sergeev and Egor Lidanovskiy
Metals 2025, 15(3), 239; https://doi.org/10.3390/met15030239 - 24 Feb 2025
Viewed by 410
Abstract
This study focused on the nature of rare earth metal complex compounds that can form during the carbonate–alkaline processing of industrial waste materials, such as phosphogypsum and red mud, at 70–100 °C and 1–10 atm. Experimental findings revealed that the dissolution of synthetic [...] Read more.
This study focused on the nature of rare earth metal complex compounds that can form during the carbonate–alkaline processing of industrial waste materials, such as phosphogypsum and red mud, at 70–100 °C and 1–10 atm. Experimental findings revealed that the dissolution of synthetic carbonates of rare earth elements (REEs) in a concentrated carbonate-ion medium (3 mol/L) leads to the formation of ion-associates of varying strengths. Light (lanthanum, praseodymium, and neodymium) and medium (samarium) REE groups exhibited a tendency to form loose ion-associates, whereas heavy REEs (terbium, dysprosium, holmium, erbium, thulium, lutetium, and yttrium) formed close ion-associates. To confirm the existence of these ion-associates, the specific conductivity of solutions was measured after dissolving thulium (III) and samarium (III) carbonates at phase ratios ranging from 1:2000 g/mL to 1:40 g/mL in a potassium carbonate medium. The decay of ion-associates, leading to the precipitation of rare earth metal (III) carbonates, was tested in an ammonium carbonate medium. Thermal decomposition of ammonium carbonate at 70–75 °C during 1–4 h was accompanied by full rare earth carbonates’ sedimentation and its in-the-way separation into groups because of the varied strength of ion-associates. The results of this study provide a basis for developing processes to separate rare earth metals into groups during their carbonate–alkaline extraction into solution. Full article
(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)
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17 pages, 15111 KiB  
Article
Microwave Treatment of Copper–Nickel Sulfide Ore for Promotion of Grinding and Flotation
by Xiaolei Fang, Zhiwei Peng, Tianle Yin, Mingjun Rao and Guanghui Li
Metals 2024, 14(5), 565; https://doi.org/10.3390/met14050565 - 11 May 2024
Cited by 4 | Viewed by 1603
Abstract
The effect of microwave treatment on the grinding and flotation performance of a typical copper–nickel sulfide ore was evaluated, based on the determination of its microwave absorption capability, grinding and flotation indexes such as crack percentage, mineral liberation degree, particle size distribution, relative [...] Read more.
The effect of microwave treatment on the grinding and flotation performance of a typical copper–nickel sulfide ore was evaluated, based on the determination of its microwave absorption capability, grinding and flotation indexes such as crack percentage, mineral liberation degree, particle size distribution, relative work index (RWI), metal enrichment ratio and recovery. There were obvious differences between the microwave absorption capabilities of the main minerals in the ore, as demonstrated by their different microwave penetration depths. They also induced temperature differences between sulfide minerals and gangue minerals which could reach 418 °C after microwave treatment for 20 s. It was shown that microwave treatment could effectively improve the grindability of the ore, as proven by the increase in fine particles smaller than 0.074 mm and the decrease in RWI after grinding due to the higher crack percentage and mineral liberation degree. Moreover, microwave treatment affected the ore floatability because of the generation of cuprite, retgersite, and rozenite with poor floatability when the treatment time was extended. By microwave treatment for a proper time, 20 s, an optimal balance between the grindability and flotation performance could be achieved. Compared with the untreated ore, the RWI of the ore decreased by 11.5%. After flotation, the Cu and Ni enrichment ratios of the flotation concentrate increased by 0.3 and 0.2, respectively. Meanwhile, their corresponding recoveries increased by 4.2% and 3.1%. This study provides new insights for the treatment of copper–nickel sulfide ore to enhance the grinding and flotation process. Full article
(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)
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19 pages, 6671 KiB  
Article
A Pretreatment of Refractory Gold Ores Containing Sulfide Minerals to Improve Gold Leaching by Ammonium Thiosulfate: A Model Experiment Using Gold Powder and Arsenic-Bearing Sulfide Minerals
by Takunda Joseph Mhandu, Ilhwan Park, Sanghee Jeon, Sohta Hamatsu, Yogarajah Elakneswaran, Mayumi Ito and Naoki Hiroyoshi
Metals 2023, 13(8), 1357; https://doi.org/10.3390/met13081357 - 28 Jul 2023
Cited by 3 | Viewed by 4246
Abstract
The use of thiosulfate to extract gold from refractory ores is promising because of its non-toxicity and high selectivity. Sulfide minerals (i.e., pyrite, arsenopyrite, chalcopyrite), major gold carriers in refractory gold ores, however, hinder gold extraction due to the high consumption of a [...] Read more.
The use of thiosulfate to extract gold from refractory ores is promising because of its non-toxicity and high selectivity. Sulfide minerals (i.e., pyrite, arsenopyrite, chalcopyrite), major gold carriers in refractory gold ores, however, hinder gold extraction due to the high consumption of a lixiviant. In this study, a new method to improve gold extraction from sulfide bearing gold ores is proposed based on the model experiments using a mixture of gold powder and arsenopyrite-bearing sulfide (HAsBS) ore. The effects of HAsBS ore on gold leaching in ammonium thiosulfate solutions were investigated, and it was found that gold extraction in the presence of HAsBS ore was suppressed because of the unwanted decomposition of thiosulfate on the surface of sulfide minerals. To improve gold extraction in the presence of the sulfide minerals, this study investigated the effects of the pretreatment of HAsBS ore using ammonium solutions containing cupric ions and confirmed that HAsBS ore was oxidized in the pretreatment and its surface was covered by the oxidation products. As a result, thiosulfate consumption was minimized in the subsequent gold leaching step using ammonium thiosulfate, resulting in an improvement in gold extraction from 10% to 79%. Full article
(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)
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18 pages, 4113 KiB  
Article
Selective Cementation of Gold Using an Iron Oxide and Zero-Valent Aluminum Galvanic System from Gold–Copper Ammoniacal Thiosulfate Solutions
by Joshua Zoleta, Sanghee Jeon, Akuru Kuze, Nako Okada, Ilhwan Park, Mayumi Ito, Yogarajah Elakneswaran and Naoki Hiroyoshi
Metals 2023, 13(7), 1289; https://doi.org/10.3390/met13071289 - 18 Jul 2023
Cited by 5 | Viewed by 2521
Abstract
Ammonium thiosulfate leaching is a promising alternative to the conventional cyanide method for extracting gold from ores. However, strategies for recovering gold from the leachate are less commercially used due to its low affinity to gold. The present study investigated the recovery of [...] Read more.
Ammonium thiosulfate leaching is a promising alternative to the conventional cyanide method for extracting gold from ores. However, strategies for recovering gold from the leachate are less commercially used due to its low affinity to gold. The present study investigated the recovery of gold from the leachate using iron oxides (hematite, Fe2O3 or magnetite, Fe3O4). Cementation experiments were conducted by mixing 0.15 g of aluminum powder as an electron donor and 0.15 g of an electron mediator (activated carbon, hematite, or magnetite) in 10 mL of ammonium thiosulfate leachate containing 100 mg/L gold ions and 10 mM cupric ions for 24 h at 25 °C. The results of the solution analysis showed that when activated carbon (AC) was used, the gold was recovered together with copper (recoveries were 99.99% for gold and copper). However, selective gold recovery was observed when iron oxides were used, where the gold and copper recoveries were 89.7% and 21% for hematite and 85.9% and 15.4% for magnetite, respectively. An electrochemical experiment was also conducted to determine the galvanic interaction between the electron donor and electron mediator in a conventional electrochemical setup (hematite/magnetite–Al as the working electrode, Pt as the counter electrode, Ag/AgCl as the reference electrode) in a gold–thiosulfate medium. Cyclic voltammetry showed a gold reduction “shoulder-like” peak at −1.0 V using hematite/Al and magnetite/Al electrodes. Chronoamperometry was conducted and operated at a constant voltage (−1.0 V) determined during cyclic voltammetry and further analyzed using SEM-EDX. The results of the SEM-EDX analysis for the cementation products and electrochemical experiments confirmed that the gold was selectively deposited on the iron oxide surface as an electron mediator. Full article
(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)
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Review

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14 pages, 880 KiB  
Review
Mechanochemical Treatment for the Extraction of Lithium from Hard Rock Minerals: A Comprehensive Review
by Yuik Eom, Laurence Dyer, Aleksandar N. Nikoloski and Richard Diaz Alorro
Metals 2024, 14(11), 1260; https://doi.org/10.3390/met14111260 - 7 Nov 2024
Viewed by 1697
Abstract
Lithium (Li) extraction from Li hard rock minerals involves thermal activation at elevated temperatures and the use of corrosive reagents. The reagents can damage the environment if they are not adequately contained as part of the process, and the high temperatures require large [...] Read more.
Lithium (Li) extraction from Li hard rock minerals involves thermal activation at elevated temperatures and the use of corrosive reagents. The reagents can damage the environment if they are not adequately contained as part of the process, and the high temperatures require large amounts of energy, which can contribute to greenhouse gas emissions unless renewable energy sources are used. These concerns have motivated research into many alternative methods to partially or completely replace the conventional process while maintaining or enhancing the Li extraction rate. Mechanochemistry is one of these alternative methods, as it has the potential to increase the reactivity of Li resources with reagents while reducing the need for corrosive reagents. Mechanochemistry has been applied to mineral processing, particularly introduced as the pre-treatment method before pyro- or hydrometallurgical processes, for several decades. In recent years, a few studies about direct Li extraction from mechanochemically activated hard rock minerals utilizing various co-grinding additives have been reported. This review deals with the application of mechanochemistry to process the Li-bearing hard rock minerals, spodumene and lepidolite, and the mechanisms of the mechanochemical treatment. Full article
(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)
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29 pages, 1160 KiB  
Review
Technospheric Mining of Critical and Strategic Metals from Non-Ferrous Slags
by Bona Lim, Mark Aylmore and Richard Diaz Alorro
Metals 2024, 14(7), 804; https://doi.org/10.3390/met14070804 - 10 Jul 2024
Cited by 1 | Viewed by 3082
Abstract
The technosphere consists of material stocks accumulated by human activities, which can include processing residue, such as slag. Various smelting processes generate slag, and some valuable elements are concentrated in this by-product. In this review, the extraction of critical and strategic metals from [...] Read more.
The technosphere consists of material stocks accumulated by human activities, which can include processing residue, such as slag. Various smelting processes generate slag, and some valuable elements are concentrated in this by-product. In this review, the extraction of critical and strategic metals from non-ferrous slags is discussed. Critical and strategic metals are materials that are vital for the nation’s economy and defence, as well as its industries, and have common features, such as expected shortfalls, increasing demand, and few substitutions. There are several definitions, methods, and classifications of critical and strategic elements by different organisations. In this study, reports from seven institutions around the world are summarised, and a list of recommended critical and strategic metals is presented. Non-ferrous slags contain a considerable amount of critical and strategic elements, and research on technology and process development using both pyro- and hydrometallurgical methods is very attractive. When it comes to the extraction of values from slag and the development of technology, it is not only important to consider the economic aspect but also to ensure the processes are low in emissions and energy consumption but high in efficiency and recycling. Full article
(This article belongs to the Special Issue Toward Achieving a Carbon-Neutral Society: Beneficiation and Extractive Metallurgy for Producing Critical Metals from Ores/Wastes)
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