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Metal Recycling: From Waste to Valuable Resources

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Green Chemistry".

Deadline for manuscript submissions: closed (15 May 2026) | Viewed by 1599

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Guest Editor
Centro Nacional de Investigaciones Metalúrgicas (CENIM-CSIC), Madrid, Spain
Interests: recycling; extraction of critical metals; hydrometallurgy; metal; waste management; urban mining
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Special Issue Information

Dear Colleagues,

Metal recycling transforms discarded materials into valuable resources through collection, sorting, and processing, leading to significant environmental benefits like reduced energy use (up to 95% less for some metals compared to those produced from raw ores), lower greenhouse gas emissions, economic advantages such as cost savings and job creation, and improved resource conservation due to decreased demand for virgin metal. This practice is a vital part of a circular economy, turning waste into new products and sustainable solutions. The energy transition is built on electrification, relying on technologies that are metal-intensive, and recycling helps alleviate primary supply constraints. Steel and aluminium combined account for almost 10% of global emissions, but secondary aluminium production typically has a five- to twenty-five-times lower carbon footprint than primary aluminium production, and for steel, emissions are often halved by using scrap. Recycling also keeps reusable materials out of landfills. Geopolitical instability and the reliance on China for critical minerals have become major concerns in the United States and the European Union, among other places, and the use of domestically sourced recycled metal helps reduce reliance on imports or single sources of metals. This Special Issue aims to present advances in waste recycling, focusing on the separation and recovery of metals from batteries, mining waste, minerals, or post-consumer products (using pyrometallurgical and hydrometallurgical techniques, among others). We welcome articles and reviews on the development of any of the abovementioned recycling technologies, and innovative technologies that could be used for composites, as well as their applications. We hope to receive articles addressing the development of recycling technology (pyro- and hydrometallurgical processes with different novel extraction agents) for strategically separating metals from critical raw materials and their innovate applications; sustainability and circularity studies; and studies on other relevant topics.

Dr. María Isabel Martín Hernández
Guest Editor

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Keywords

  • metal recycling
  • waste recycling
  • batteries
  • mining waste
  • minerals
  • post-consumer products
  • pyrometallurgical and hydrometallurgical techniques
  • recycling technologies
  • critical raw materials
  • li-ion batteries

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Published Papers (2 papers)

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Research

21 pages, 5976 KB  
Article
Dissolution Processes of PFSA Polymers via Mixed Solvents and Their Effects on Structural, Morphological and Electrochemical Activity
by Mveliso Ester Hlwele, Opeoluwa O. Oyedeji, Edson L. Meyer, Nicholas Rono and Mojeed A. Agoro
Molecules 2026, 31(11), 1856; https://doi.org/10.3390/molecules31111856 - 28 May 2026
Viewed by 333
Abstract
Proton exchange membrane fuel cells (PEMFCs) exhibit high energy efficiency and rapid load response, but challenges are faced in membrane fabrication, including the need for renewable resources and cost-effective, non-toxic solvents. This study analyzes the morphological and structural properties of perfluorosulfonic acid (PFSA) [...] Read more.
Proton exchange membrane fuel cells (PEMFCs) exhibit high energy efficiency and rapid load response, but challenges are faced in membrane fabrication, including the need for renewable resources and cost-effective, non-toxic solvents. This study analyzes the morphological and structural properties of perfluorosulfonic acid (PFSA) ionomer membranes, FS-930 and F-14100, after the dissolution of membranes via ratios of 50:50, 80:20, and 20:80 by volume of dimethyl sulfoxide (DMSO) and water. Bode plot analysis indicates that membranes rich in DMSO show lower frequency phase angle peaks, suggesting better segmental motion and ionic conductivity. Additionally, higher DMSO content correlates with broader FTIR peaks, reflecting enhanced solute–solvent interactions. The untreated FS-930 membrane demonstrates significant intensity peaks linked to semi-crystalline domains, indicating strong baseline conductivity. SEM analysis revealed surface roughness variations in FS-930 linked to different water-to-DMSO volume ratios. DMSO-rich mixtures produced dense, hydrophobic PFSA membrane structures, whereas water-rich mixtures increased water uptake and ionic conductivity. Fumapem F-14100 showed superior hydration and proton conductivity compared to FS-930 because it contains more sulfonic acid groups. These findings are critical to understanding how membrane properties relate to solvent composition, aiding in the optimization of membrane fabrication for better performance and durability in fuel cells. Full article
(This article belongs to the Special Issue Metal Recycling: From Waste to Valuable Resources)
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26 pages, 3923 KB  
Article
Co-Bioleaching of Pyrite Flotation Tailings and Crushed Printed Circuit Boards
by Aleksandr Kolosoff, Vitaliy Melamud and Aleksandr Bulaev
Molecules 2026, 31(6), 985; https://doi.org/10.3390/molecules31060985 - 15 Mar 2026
Viewed by 608
Abstract
The aim of this study was to investigate the potential for co-bioleaching of ground printed circuit boards (PCBs) and flotation tailings using a single-stage biohydrometallurgical process. The ground PCB sample was a finely divided waste product from industrial shredding, which was collected using [...] Read more.
The aim of this study was to investigate the potential for co-bioleaching of ground printed circuit boards (PCBs) and flotation tailings using a single-stage biohydrometallurgical process. The ground PCB sample was a finely divided waste product from industrial shredding, which was collected using an air filtration system. The flotation tailings sample was mainly composed of pyrite (49%), quartz (29%), gypsum (8%), feldspar (8%), and chlorite (6%). The experiment was carried out in laboratory-scale reactors at 35 °C with constant aeration and a flotation tailings pulp density of 5% (solid-to-liquid ratio). In a control reactor, only flotation tailings were leached. In an experimental reactor, both flotation tailings and ground PCBs were leached simultaneously. The experiment was conducted in two stages. In the first stage, the experiment was carried out in a batch mode. The second stage involved two reactors operating continuously in cascade. During the experiment, we monitored the dynamics of several key parameters as a function of PCB concentration, including pH, redox potential, the concentrations of Fe3+ and Fe2+ ions, and the number of microbial cells. The 16S rRNA gene analysis revealed that the presence of PCBs had a significant effect on the composition of the microbial community. The concentration of PCB was gradually increased in order to examine the limits of the process and optimize potential economic benefits. The increase was done in 3 stages: 5 g/L in the first stage, from 5 to 12 g/L in the second stage, and up to 35.5 g/L in the third stage. However, this increase had a negative effect on the pyrite oxidation rate and the effectiveness of PCB bioleaching in continuous mode. The bioleaching efficiency of copper from printed circuit boards (PCBs) was above 70% in batch mode and above 80% in continuous mode at PCB concentrations up to 12 g per liter. Copper recovery decreased to around 53.1–61.6% as the PCB concentration continued to increase. The nickel leaching efficiency in batch mode was 46.3 ± 4.8%. In continuous mode, the nickel recovery decreased as the PCB concentration increased, reaching 48.53% in the first stage, then declining to 37.62% in the second stage and finally dropping to 27.06% in the third stage, depending on the higher concentration of PCB. Full article
(This article belongs to the Special Issue Metal Recycling: From Waste to Valuable Resources)
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