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Metals
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Recovery of Critical Raw Materials from Industrial Wastes by Advanced...
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Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods

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

Deadline for manuscript submissions: closed (31 March 2025) | Viewed by 7478

Special Issue Editor

Dr. Stefano Ubaldini

E-Mail Website
Guest Editor
Consiglio Nazionale delle Ricerche (CNR)—Istituto di Geologia Ambientale e Geoingegneria (IGAG), Area della Ricerca di Roma RM 1, Montelibretti, Via Salaria Km 29,300—C.P. 10, 00015 Monterotondo Stazione, Roma, Italy
Interests: primary and secondary raw materials; low-grade georesources; metals recovery; precious metals; heavy metals; leaching; hydrometallurgy; bio-hydrometallurgy; bioprecipitation; electrowinning; remediation processes; environmental innovative technologies; industrial wastes; exhausted batteries; WEEE; minerals; wastewater; acid mine drainage
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Raw Materials (RMs) are crucial to the world economy. They form a strong industrial base, producing a broad range of goods and applications used in everyday life. Reliable and unhindered access to certain RMs is a growing concern within the EU and across the globe. To address this challenge, the European Commission has created a list of 30 critical raw materials (CRMs) for the EU, which is subject to a regular review and update. CRMs combine RMs of high importance to the EU economy and of high risk associated with their supply; moreover, they are closely linked to clean technologies.

The use as secondary RMs from marginal resources as industrial wastes, is of strategic importance for industrial production, due to their high concentration on valuable metals.

RMs (i.e. gold, silver, copper, zinc, manganese, nickel) and CRMs (i.e. platinum, indium, cobalt, vanadium, magnesium, antimony, niobium and  rare hearts), are essential for the application of emerging modern technologies and to preserve the environment from technological waste, avoiding the release of pollutants components.

The advancement of the innovative processes such as bio-hydrometallurgy, electrowinning, phytoremediation, bioprecipitation, compared with the conventional processes, are given by the lowest environmental impact and energy consumption, and by the greater degree of purity of the valuable metals obtained.

The economic value of the advanced methods for recovery of critical raw materials from industrial wastes, which is closely linked to the choice and optimization of the experimental parameters of the processes, is of great importance.

For publication in this Special Issue, those articles that contribute to the improvement of the of the above-mentioned methods considered.

I hope you accept this invitation, and help us to create a high-impact and high-quality Special Issue on "Recovery of Critical Raw Materials From Industrial Wastes by Advanced Methods".

Dr. Stefano Ubaldini
Guest Editor

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

  • critical raw materials
  • strategic raw materials
  • low-grade georesources
  • heavy metals
  • bio-hydrometallurgy
  • electrowinning
  • phytoremediation
  • bioprecipitation
  • industrial wastes
  • WEEE

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Published Papers (6 papers)

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Research

13 pages, 5748 KiB  
Article
Recovery of Palladium and Silver from Copper Sludge and Spent Petrochemical Catalysts via Effective Pyrometallurgical Processing
by Hyunju Kim, Hyunsik Park and Joohyun Park
Metals 2025, 15(4), 466; https://doi.org/10.3390/met15040466 - 21 Apr 2025
Viewed by 119
Abstract
Copper-containing sludge and spent petrochemical catalyst (SPC) were investigated for recovering palladium (Pd) and silver (Ag). Increasing the mixing ratio of alumina-based SPC leads to reduced recovery rates at 1500 °C. Specifically, as the SPC mixing ratio increases from 10% to 30%, the [...] Read more.
Copper-containing sludge and spent petrochemical catalyst (SPC) were investigated for recovering palladium (Pd) and silver (Ag). Increasing the mixing ratio of alumina-based SPC leads to reduced recovery rates at 1500 °C. Specifically, as the SPC mixing ratio increases from 10% to 30%, the recovery rate of Pd and Ag sharply decreases to 62.1% and 91.0%, respectively. This is attributed to an increase in the slag viscosity as well as to the higher sulfur content in the metal phase by decreasing the CaO/Al2O3 ratio of the slag. An increase in the slag viscosity causes a decrease in the metal recovery, as it lowers the settling velocity of metal droplets, resulting in imperfect metal separation, i.e., an increase in physical loss. Additionally, the presence of sulfur at the slag–metal interface was found to reduce interfacial tension, facilitating the entrapment of copper droplets within the slag. This further hindered phase separation and contributed to an increase in physical loss. This study highlights that physical loss is more serious in metal recovery rather than chemical loss, which is dependent on the thermochemical solubility of the target metals in the slag. The results emphasize the need for the precise control of slag properties to maximize the metal recovery processes in conjunction with a mitigation of CO2 emissions. Full article
(This article belongs to the Special Issue Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods)
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17 pages, 12063 KiB  
Article
The CaO Enhanced Defluorination and Air-Jet Separation of Cathode-Active Material Coating for Direct Recycling Li-Ion Battery Electrodes
by Piotr Siwak, Volf Leshchynsky, Emil Strumban, Mircea Pantea, Dariusz Garbiec and Roman Maev
Metals 2024, 14(12), 1466; https://doi.org/10.3390/met14121466 - 23 Dec 2024
Viewed by 748
Abstract
With the rapid growth of the lithium-ion battery (LIBs) market, recycling and re-using end-of-life LIBs to reclaim the critical Li, Co, Ni, and Mn has become an urgent task. Presently, high temperature, strong acid, and alkali conditions are required to extract blended critical [...] Read more.
With the rapid growth of the lithium-ion battery (LIBs) market, recycling and re-using end-of-life LIBs to reclaim the critical Li, Co, Ni, and Mn has become an urgent task. Presently, high temperature, strong acid, and alkali conditions are required to extract blended critical metals (CM) from the typical battery cathode. Hence, there is a need for more effective recycling processes for recycling blended Li, Co, Ni, and their direct regeneration for re-use in LIBs. The goal of the offered paper is the development of recycling technology for degraded battery cathode-active materials based on the thermal decomposition of polyvinylidene fluoride (PVDF) using calcination and air-jet stripping of active materials. The proposed air-jet erosion method of calcined cathode material stripping from Al foil allows for the flexible industry-applicable separation process, which is damage-free for both particles and substrate. The CaO calcination air-jet separation process and equipment can significantly improve the PVDF decomposition and the separation efficiency of the cathode materials. It is demonstrated that low-temperature CaO calcination at 350–450 °C associated with air-jet separation of active material is characterized by low environmental impact, high purity of the recycled material, and low cost as compared to pyro- and hydrometallurgical methods. Full article
(This article belongs to the Special Issue Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods)
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15 pages, 4165 KiB  
Article
Recycling Li-Ion Batteries via the Re-Synthesis Route: Improving the Process Sustainability by Using Lithium Iron Phosphate (LFP) Scraps as Reducing Agents in the Leaching Operation
by Francesca Pagnanelli, Pietro Altimari, Marco Colasanti, Jacopo Coletta, Ludovica D’Annibale, Alyssa Mancini, Olga Russina and Pier Giorgio Schiavi
Metals 2024, 14(11), 1275; https://doi.org/10.3390/met14111275 - 9 Nov 2024
Viewed by 1963
Abstract
The development of hydrometallurgical recycling processes for lithium-ion batteries is challenged by the heterogeneity of the electrode powders recovered from end-of-life batteries via physical methods. These electrode materials, known as black mass, vary in composition, containing differing amounts of nickel, manganese, and cobalt [...] Read more.
The development of hydrometallurgical recycling processes for lithium-ion batteries is challenged by the heterogeneity of the electrode powders recovered from end-of-life batteries via physical methods. These electrode materials, known as black mass, vary in composition, containing differing amounts of nickel, manganese, and cobalt (NMC), as well as other chemicals, such as lithium iron phosphate (LFP). This study presents the results of the hydrometallurgical treatment of mixed NMC and LFP black masses aimed at creating flexible recycling processes. This approach leverages the reducing power of LFP to optimize the leach liquor composition for re-synthesizing NMC precursors. In particular, the leaching conditions were optimized based on the LFP content in the solid feed to maximize the extraction of key metals (Ni, Mn, Co, and Li). The leaching solid residue, graphite, was treated and characterized as a secondary raw material for new anode preparation. Iron phosphate was recovered by increasing the pH of the leach liquor, and the NMC precursors were obtained via coprecipitation. This process achieved a recycling rate of 51%, based on the black mass input and the mass of recovered elements in the output products. Additionally, substituting LFP scraps as the reducing agent in place of H2O2 reduced the recycling process’s environmental impact by avoiding 1.7 tons of CO2-equivalent emissions per ton of NMC black mass. Full article
(This article belongs to the Special Issue Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods)
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18 pages, 2540 KiB  
Article
Biotechnological Tool for Metal(loid)s as Cd, Cu, Ni, and P Management with Multiple Approaches: Bioremediation, Recovery of Raw Materials, and Food Safety
by Adalgisa Scotti, Ana Rosa Castaño Gañan, Vanesa Analía Silvani, Andrea Juarez, Gabriela Coria, Sofía Utge Perri, Roxana Paola Colombo, Inmaculada García-Romera, María Luisa Izaguirre-Mayoral, Alicia Godeas and Stefano Ubaldini
Metals 2024, 14(11), 1259; https://doi.org/10.3390/met14111259 - 6 Nov 2024
Viewed by 1041
Abstract
Contaminated soils are a challenge for implementing biotechnology in bioremediation, the recovery of Critical and Strategic Raw Materials (CRMs and SRMs), and food security. European Union (EU) Governments have established strict limits on As, Pb, Cd, and Hg in foods (Document 32023R0915) and [...] Read more.
Contaminated soils are a challenge for implementing biotechnology in bioremediation, the recovery of Critical and Strategic Raw Materials (CRMs and SRMs), and food security. European Union (EU) Governments have established strict limits on As, Pb, Cd, and Hg in foods (Document 32023R0915) and requested the recovery of 34 CRMs within a circular economy (CE) (5th CRMs list). This study proposed a biotechnological tool for the decontamination of soil with heavy metal(loid)s by arbuscular mycorrhizal (AM)-assisted phytoextraction and the subsequent recovery of CRMs or by phytostabilization to prevent their entry into the food chain. It consisted of placing Baccharis salicifolia plants, inoculated or non-inoculated with AM fungi, into bioreactors (BRs) containing mining soil with Cd, Ni, and Cu, according to the Argentinian Patent (AR090183B1). The bioextractive potential (BP) was also estimated at the highest Technological Readiness Level (TRL) using a vegetable depuration module (VDM, TRL 6). Inoculated plants showed significantly higher aerial bioaccumulation coefficients (Cd: 68.62; P: 2.99; Ni: 2.51; Cu: 0.18) in BRs, and the BP values reached 1.16 g, 9.75 g, 2.40 g, and 213.1 g for Ni, Cd, Cu, and P, respectively. Finally, these CRMs and SRMs could be recovered from biomass through hydrometallurgy within a CE framework. Full article
(This article belongs to the Special Issue Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods)
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20 pages, 11391 KiB  
Article
Leaching of Rare Earths from End-of-Life NdFeB Magnets with Citric Acid Using Full Factorial Design, Response Surface Methodology, and Artificial Neural Network Analysis
by Pietro Romano, Adriana Zuffranieri, Soroush Rahmati, Roshanak Adavodi, Francesco Ferella and Francesco Vegliò
Metals 2024, 14(8), 932; https://doi.org/10.3390/met14080932 - 16 Aug 2024
Cited by 4 | Viewed by 1208
Abstract
In recent years, the increasing demand and rising prices of rare earth elements (REEs), along with their attendant supply risk (about 95% of these elements are supplied by China), have led the European Commission to consider REEs as critical raw materials. Developing and [...] Read more.
In recent years, the increasing demand and rising prices of rare earth elements (REEs), along with their attendant supply risk (about 95% of these elements are supplied by China), have led the European Commission to consider REEs as critical raw materials. Developing and optimizing processes for recovering REEs from secondary sources such as NdFeB magnets is fundamental in this context. A novel method to recover REEs by leaching with citric acid and subsequently separating these elements using the solvent extraction method has been introduced. Therefore, this research investigates the leaching efficiency of REEs, Fe, and B from NdFeB magnets. A full factorial design, with 18 experimental setups, was conducted to optimize the citric acid concentration (1–3 mol/L), leaching time (1–3 h), and solid–liquid ratio (5–10%wt./vol.). All tests were carried out at room temperature and 150 rpm. Different optimizations (response surface methodology (RSM) and artificial neural network (ANN) analysis) are used to maximize the REEs’ leaching efficiency. RSM resulted in a maximum extraction yield of total rare earth elements (TREEs) of about 89% in the investigated experimental plan. This result is similar to that for ANN analysis (about 86%), but more accurate than that for RSM. In fact, for the ANN, an overall R-value higher than 0.99 was obtained. This result indicates that the developed ANN can be used as an accurate model for estimating the leaching efficiencies of REEs from NdFeB magnets. Full article
(This article belongs to the Special Issue Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods)
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17 pages, 6038 KiB  
Article
Correlation between Thermodynamic Studies and Experimental Process for Roasting Cobalt-Bearing Pyrite
by Erdenebold Urtnasan, Avneesh Kumar and Jei-Pil Wang
Metals 2024, 14(7), 777; https://doi.org/10.3390/met14070777 - 30 Jun 2024
Viewed by 1367
Abstract
Cobalt is a critical metal widely distributed in nature, but cobalt ore has hardly been found as an independent mineral. Cobalt-bearing pyrite tailings separated from iron ore is one of the resources for recovering cobalt. In the following study, roasting is carried out [...] Read more.
Cobalt is a critical metal widely distributed in nature, but cobalt ore has hardly been found as an independent mineral. Cobalt-bearing pyrite tailings separated from iron ore is one of the resources for recovering cobalt. In the following study, roasting is carried out to oxidize cobalt-bearing pyrite tailings for preparing and recovering the cobalt by acid leaching. The further aim of the research is to determine and control the optimal technological regime for roasting by using thermodynamic modeling. The phase transition in Fe–S–O and Co–S–O systems and its mechanism are analyzed under the partial pressure of oxygen and sulfur dioxide at constant temperatures. Thermodynamic modeling proves that iron and cobalt sulfides can be intensively oxidized at a relatively high temperature (>900 °C) under an atmosphere of logp(O2) > −5, leading to the formation of SO2 (logp(SO2) < 0). The results of the roasting experiment indicate 98% desulfurization degree upon holding for about 4–5 h and at > 1000 °C. Based on these thermodynamic modeling and experimental results, the roasting of cobalt containing pyrite can be optimized with substantial productivity with regard to the metal oxide and cobalt thereof. Oxidative roasting also allows the elimination of environmentally hazardous gases such as sulfur during the process. Full article
(This article belongs to the Special Issue Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods)
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