Recycling Of Metals Research Articles

Sustainable extraction and recycling of non-ferrous metals: a review from a European perspective.

This review article provides a comprehensive examination of sustainable extraction and recycling methods for non-ferrous metals, which are critical to a wide range of industries including electronics, construction and renewable energy. Focusing on metals such as aluminium, copper and silicon, the study highlights the importance of recycling in conserving resources and minimizing environmental impact. It discusses the challenges posed by material diversity in recycling processes and the advances in recycling technologies that have emerged in response. Special emphasis is placed on the importance of a circular economy in maintaining a sustainable balance between consumption and conservation of metal resources. Through detailed analysis, it advocates innovative recycling practices and improved design for recyclability and highlights the role of policy, industry and consumer behaviour in achieving sustainability goals. The findings contribute to the discourse on strategic self-sufficiency in Europe through recycling, providing insights into how to improve efficiency and manage the complexity of the global material cycle. This work calls for a collaborative effort towards sustainable metallurgy and underlines the critical need for advances in recycling infrastructure and technology to ensure the long-term availability and environmental stewardship of non-ferrous metals.This article is part of the discussion meeting issue 'Sustainable metals: science and systems'.

Removal of Cr (VI) by crosslinked chitosan adsorbent prepared using simulated copper-containing wastewater

A chitosan (CS) hydrogel bead cross-linked by Cu2+ with a macroscopic spheral shape (designated as CS-Cu-B) was synthesized using simulated copper-containing wastewater without additional crosslinking agents. The optimal conditions for CS-Cu-B formation were identified as 1500 mg/L of Cu2+ concentration, pH 5.4 and 50 °C under which CS-Cu-B was further utilized as an adsorbent for Cr(VI). The adjacent chitosan chains were crosslinked by coordination between positive-charged Cu2+ ions and the amino and hydroxyl groups of chitosan. This enhanced the surface charge and increased the specific surface area of CS-Cu-B, thereby augmenting its Cr(VI) adsorption capacity. The effect of adsorbent dosage, pH of Cr(VI) solution, and presence of coexisting ions on Cr(VI) adsorption was investigated. Detailed analyses of the adsorption kinetics, isotherms and thermodynamics of Cr(VI) on CS-Cu-B were also conducted. CS-Cu-B demonstrated a maximum Cr(VI) adsorption capacity of 90.76 mg/g at pH 4.0 and exhibited excellent reusability, retaining 87.90 % of its adsorption capacity after five adsorption-desorption cycles. Both experimental characterizations and DFT calculation elucidated that the electrostatic attraction adsorption is the main driving force for the adsorption of CS-Cu-B on Cr(VI). A consecutive preparation-adsorption strategy using simulated copper-electroplating wastewater was proposed to facilitate the recycling of heavy metals.

Surface display and application of cadmium-binding protein CADR on the cell wall of Chlamydomonas reinhardtii

Algae has been proven to have the potential to be efficient biosorbents in the detection and remediation of heavy metal pollution such as cadmium in the environment. This study aims to enhance the cadmium adsorption capacity of Chlamydomonas reinhardtii by expressing the cadmium-binding protein CADR on the cell wall by the surface display technology. Firstly, the golden gate technique was employed to construct the transformation vector PET-X-CADR, which anchored CADR to the cell wall with the cell wall protein GP1. The high-throughput screening with the fluorescence signal of the fusion tag YFP resulted in three engineered algal strains with high expression of CADR on the cell wall. Physiological experiments demonstrated that the CADR displayed on the cell wall did not affect the growth of the engineered algal strains exposed to cadmium with the concentration below 200 μmol/L. In the presence of 200 μmol/L cadmium, the growth rates of CADR-engineered algal strains were three times as that of the wild-type, indicating stronger tolerance of the CADR-engineered algae to cadmium. The protein lyase GLE released during the mating of Chlamydomonas was used to isolate the cell walls of wild-type and engineered strains, the cadmium content of which was compared. The results showed that the cell wall of the engineered strain exhibited an increase of 33% in cadmium adsorption capacity. This study gives insights into the application of algae in the management of cadmium pollution in the environment, especially in the recycling of heavy metals from the environment.

Deep learning approaches for classification of copper-containing metal scrap in recycling processes

Separating copper from iron scrap is a critical operation in metal recycling and achieving this with low cost sensoric equipment like RGB cameras instead of XRF/XRT is becoming increasingly attractive. In this article, the groundwork for creating an image classification model to separate copper from iron scrap has been performed. Twenty of the most common and most easily available CNN architectures were trained on 2200 metal scrap specimens and evaluated inline on a sensor-based sorting rig for their prediction accuracy and their inference latency to mimic real circumstances in an industrial setting. Out of these evaluated architectures, DenseNet-201 with 98% accuracy in inline tests is recommended if potent hardware is available. Otherwise AlexNet with 92% accuracy or MobileNet-V2 with 90% accuracy are recommended for further investigation and model creation if hardware restrictions apply. Based on the presented results in this article, the initial cumbersome surveyance of the most suitable network architecture can be substantially reduced and the creation of a sorting model can be streamlined. This article thus provides the basis for creating an inline applicable sorting method for scrap metal that uses low cost sensorics equipment and can provide reasonably high accuracy in its prediction.

Biotechnological Approaches for Metal Recovery from Electronic Wastes.

The disposal of electronic waste (EW) in open landfills has caused several toxic environmental effects. The harmful metallic components released in the environment due to deposition of EW act as hazards for living systems. EW management has been widely studied in recent days across the world. Though, several processes are implemented in extraction, recycling and recovery of heavy metals from the EW, most of them are not effective in recovering the precious metals. Various chemical processes are executed for efficient extraction of precious metals from e-wastes. Though the techniques are easy to process and rapid, however, the chemical leaching also has detrimental environmental consequences. Biological approaches, on the other hand, solves the purpose for efficient and environmentally friendly recovery of precious metals. Thus, both resource recovery as well as remediation can be targeted simultaneously. Biotechnological methods offer sustainable and efficient solutions for metal recovery from electronic wastes, presenting a viable alternative to traditional methods. Continued advancements in this field hold significant promise for addressing the growing e-waste challenge.

Performance evaluation on recycling metals from lithium cobaltate by supercritical water combining with leaching-precipitation methods

The recycling of metals from spent lithium-ion batteries is currently a hotspot of research. This paper introduces a novel recovery method that integrates supercritical water and leaching-precipitation techniques to efficiently extract metals from lithium cobaltate electrodes. This study investigates the dissolution behavior of lithium cobaltate in supercritical water, and the interaction between lithium cobaltate and organic impurity (Polyvinylidene Fluoride and N-methylpyrrolidone) during the supercritical water treatment process. Lithium cobaltate reacts with supercritical water to form cobaltous hydroxide and reacts with polyvinylidene fluoride to form cobalt oxide. During the reaction of supercritical water with polyvinylidene fluoride and N-methylpyrrolidone in supercritical water, lithium cobaltate is reduced to cobalt oxide. The addition of N-methylpyrrolidone promotes the reduction of cobalt ion and the decomposition of polyvinylidene fluoride. Subsequently, the cathode materials treated with supercritical water are leached by using hydrochloric acid and sulfuric acid respectively. Cobalt and lithium ions in the leaching solution are precipitated by adding sodium hydroxide and sodium carbonate. The maximum recovery efficiencies of lithium and cobalt are 73 % and 79.60 %, respectively.

Prediction of metal recovery potential of end-of-life NEV batteries in China based on GRA-BiLSTM

As Chinese new energy vehicle (NEV) sales continue to grow, end-of-life batteries have great potential for recycling in the future. In this study, a combined model based on Gray Relation Analysis and Bi-directional Long Short-Term Memory (GRA-BiLSTM) is proposed for predicting NEV sales, and the NEV battery life is modeled using the Weibull distribution. Then, the amount of end-of-life batteries, secondary utilization and metal recycling are calculated. The impact of end-of-life battery recycling on the supply and demand of key metals is studied. The results show that in 2040, the secondary utilization of end-of-life batteries in the Standard Growth Rate-Lithium Iron Phosphate Battery Dominated-High Secondary Utilization rate scenario (SGR-LFPH) is 391.76 GWh. The recycling volumes of lithium, nickel and cobalt are 45,900 tons, 92,900 tons and 22,100 tons, respectively. In the Standard Growth Rate-lithium nickel cobalt manganese oxide Battery Dominated-Low Secondary Utilization rate scenario (SGR-NCML), the recycling of lithium, nickel and cobalt is even greater, at 62,600 tons, 372,200 tons and 71,700 tons, respectively. End-of-life batteries recycling can reduce the demand for metals. However, as NEV sales continue to grow, the gap between metal supply and demand remains significant. The findings urge the Chinese government develop appropriate battery management strategies to increase the recycling rate of end-of-life batteries; and to encourage enterprises to research new types of batteries to resolve the conflict between supply and demand for metals.

Processing and Characterization of Spent Nickel-Metal Hydride Type AA Batteries to Recover Valuable Materials (Cobalt, Nickel and Rare Earth Elements).

The experimental research was focused on the investigation of valuable material from spent Ni-MH type AA batteries, namely the metal grid anodes and the black mass material (anode and cathode powder). The materials of interest were analyzed by X-ray fluorescence spectroscopy (XRF), ICP-OES (inductively coupled plasma optical emission spectrometry), optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The analyzed grids have a high Fe content, but some of them correspond to the Invar alloy with approx. 40% Ni. In the black mass material, round particles and large aggregations were observed by SEM analysis, showing a high degree of degradation. The XRD analysis reveals the presence of only three compounds or phases that crystallize in the hexagonal system: La0.52Ce0.33Pr0.04Nd0.11Co0.6Ni4.4, Ni(OH)2, and La5Ni19. The obtained results provide useful and interesting information that can be used for further research in the recycling and economic assessment of metals from spent Ni-MH batteries.

Research on Magnetic Field of Permanent Magnet Rolls Arranged Periodically in Circumferential—Axial Direction

The separation of non-magnetic non-ferrous metals such as copper and aluminum from scrapped automobiles is a critical area of research due to the increasing number of end-of-life vehicles. Traditional eddy current separation methods have limitations, particularly in handling large-sized broken copper and aluminum parts. This paper proposes a novel magnetic roller model featuring a circumferential–axial periodic arrangement of permanent magnets. This study explores the external magnetic field distribution of this new roller design by constructing an equivalent current model, solving magnetic scalar potential equations, and employing simulation tools. The findings indicate that the new magnet array enhances both the magnetic field strength and the range of the external magnetic field, leading to improved separation efficiency of large-sized metal fragments. The results provide a theoretical basis for advancing the separation technology of large-sized broken copper and aluminum parts in scrapped automobiles, offering potential improvements in the recycling of non-ferrous metals from end-of-life vehicles.

Enhancing the recyclability of ELV plastic bumpers: Characterization of molecular, morphological, rheological, mechanical properties and ageing degradation

While the automotive industry has traditionally prioritized metal recycling, the increasing use of plastics in vehicles underlines the need for sustainable management of these materials. Recycling rates of plastics from end-of-life vehicles (ELVs) in Europe are low, but recent EU legislation requires 25 % of the plastics in new vehicles to be recycled, forcing innovative designs and strategies to enhance the recovery and quality of recycled resins. This study focuses on post-consumer bumpers, a significant recoverable component of ELVs, by assessing their molecular, morphological, rheological, and mechanical properties to investigate their homogeneity and quality from various sources to assess their suitability for recycling. Since the aging of these materials, caused by thermo-oxidative and thermo-mechanical degradation processes, can compromise the quality of recycled bumpers, we propose a blend of recycled PP from different bumper cars with virgin resin, representing a realistic scenario where the post-consumer ELV bumpers are collected. Interestingly, this blend, which can replace up to 50 % of the virgin resin without additional compatibilizers or additives, mitigates the degradation effects. Furthermore, the study evaluates the degradation resistance of these blends through multiple extrusion cycles and accelerated weathering tests in a temperature-controlled UV chamber to ascertain the number of cycles the material can tolerate without significant quality degradation, and to determine its suitability for long-term applications. Our results not only support the feasibility of using recycled PP for automotive components but also contribute to meeting the EU's recycling targets. This research highlights the potential for significant advances in the circularity of automotive plastics, providing a sustainable pathway for integrating recycled materials into new vehicle production.

Re-manufacturing of Pre-deformed Automotive Sheet Metal Stamping Scrap Without Melting

Abstract The recycling of aluminium sheet metal typically involves shredding and re-melting, processes which are both energy-intensive and challenged by the presence of metallic contaminants. To mitigate these issues, this study explores an alternative approach: the re-manufacturing of deep-drawn parts directly from scrap aluminium sheets, thus bypassing the melting step. We used 2 mm thick Al-Mg sheet metal in H111 temper to produce simulated stamping scrap (miniaturized bonnets). Blanks were cut from these bonnets and secondary parts in a cross-cup geometry were deep-drawn using two different forming processes: warm-forming at 200 °C and O-temper forming at room temperature. The resulting maximum draw depths were 20-22 mm for warm-forming and 25-30 mm for O-temper forming. While warm-forming resulted in lower draw depths, O-temper forming led to coarse recrystallized grain formation in some regions. Our approach could significantly reduce the energy consumption associated with aluminium recycling.

Direct construction of imidazoles via oxidative C(sp3)–H amination and annulation of aryethylamines by a Single-Atom cobalt catalyst

The development of reusable catalytic systems for achieving site-selective functionalization of C(sp3)-H bond remains a significant challenge. Herein, we designed a modified metal–organic framework (MOF)-derived N, P co-doped carbon supported single-atom cobalt catalyst, which was successfully applied in oxidative C(sp3)–H amination and cyclization of aryethylamines for construction of polysubstituted imidazoles. The advantages of the present method include: broad substrate scope, recyclable base metal catalyst, and naturally abundant O2 as green oxidant. The structural − activity relationship of the catalyst indicated that the atomically dispersed CoN3P1 is the active species responsible for the catalytic process. Furthermore, the synthesized imidazoles exhibited exceptional insecticidal activity against wheat pests, and may become lead molecules in the development of novel agricultural pesticide candidates, with significant application potential.

Utilisation of acid-tolerant bacteria for base metal recovery under strongly acidic conditions.

Hydrometallurgical bioprocesses for base metal recovery in environmentally friendly electronic device waste (e-waste) recycling are typically studied under neutral pH conditions to avoid competition between metals and hydrogen ions. However, metal leachate is generally strongly acidic, thus necessitating a neutralisation process in the application of these bioprocesses to e-waste recycling. To solve this pH disparity, we focused on acid-tolerant bacteria for metal recovery under strongly acidic conditions. Four acid-tolerant bacterial strains were isolated from neutral pH environments to recover base metals from simulated waste metal leachate (pH 1.5, containing 100 or 1000 mg L-1 of Co, Cu, Li, Mn, and Ni) without neutralisation. The laboratory setting for sequential metal recovery was established using these strains and a reported metal-adsorbing bacterium, Micrococcus luteus JCM1464. The metal species were successfully recovered from 100 mg L-1 metal mixtures at the following rates: Co (8.95%), Cu (21.23%), Li (5.49%), Mn (13.18%), and Ni (9.91%). From 1000 mg L-1 metal mixtures, Co (7.23%), Cu (6.82%), Li (5.85%), Mn (7.64%), and Ni (7.52%) were recovered. These results indicated the amenability of acid-tolerant bacteria to environmentally friendly base metal recycling, contributing to the development of novel industrial application of the beneficial but unutilised bioresource comprising acid-tolerant bacteria.

Engineered Biochar for Metal Recycling and Repurposed Applications

Engineered Biochar for Metal Recycling and Repurposed Applications

Mineralogical characterization of magnesium-based nanoparticles recovered from a swirl-stabilized magnesium flame by analytical and scanning/transmission electron microscopy

Abstract. The current climate emergency and the related energy transition require the development of technology producing zero-carbon energy. One viable option entails the utilization of recyclable metal fuels. The primary energy stored by the reduction in metal oxides can be transported and later released by metal combustion. Mg is among the most promising metal as a regenerable energetic vector, having an energy density of 25 MJ kg−1. The exploitation of the Mg oxidation and reduction loop has recently been demonstrated, and the loop combustion products are made of metal oxides. The mineralogical characterization of the MgO crystals generated by the Mg combustion is of utter importance for the optimization of the particle trapping capacity in the combustion system during the closed oxidation and reduction loop. In this paper we characterize MgO particles generated in a swirl-stabilized Mg flame by using powder X-ray diffraction, transmission electron microscopy and selected area electron diffraction, and atomic-resolution microscopy combined with energy-dispersive X-ray spectroscopy and dual-electron energy-loss spectroscopy. The MgO combustion products were chemically homogeneous at this level of investigation. Three representative morphologies (cubic, truncated octahedron, and spherical) and two isostructural phases were identified in the MgO combustion product. These findings may contribute to the optimization of system development, particularly in terms of the collection efficiency of the combustion end product.

Eco-friendly and Recyclable Liquid Metal Synthesis of Two-Dimensional Cr2O3 and CrN Nanosheets for Photoresponse and Field Effect Transistors

Eco-friendly and Recyclable Liquid Metal Synthesis of Two-Dimensional Cr₂O₃ and CrN Nanosheets for Photoresponse and Field Effect Transistors

A robust aerogel incorporated with phthalocyanine-based porous organic polymers for highly efficient gold extraction

The gold recovery from electronic waste liquid is of great significance to the recycling of precious metals and environmental restoration. Adsorption method is the preferred technique for gold recovery, but its expansion and application prospects were often limited by the workability and recyclability of common solid powder adsorbents. Herein, a solid absorbent powder (phthalocyanine-based POP, TD-POP) was integrated into chitosan/polyethyleneimine aerogel (TD-POP@CS/PEI-2) via a facile cross-linking and lyophilization strategy. As expected, TD-POP@CS/PEI-2 possessed outstanding mechanical toughness and stability, demonstrating efficient and specific adsorption for Au (III). The maximum adsorption capacity was 2169 mg g−1, higher than most of the absorbents. TD-POP@CS/PEI-2 aerogel also exhibited fast kinetics (recovery efficiency of 81.3 % within 3 h), good selectivity (recovery efficiency of 98.35 % at 10 times concentration of Al3+, Zn2+, Cu2+ Cd2+, Co2+, Ni2+, Mn2+, and Cr6+ than Au ions) and reusability (eight times). Multiple characterizations revealed the adsorption mechanism, which implied that the excellent adsorption properties of the aerogel were ascribed to the electrostatic attraction between cationic aerogel and AuCl4− anion, coordination interaction between nitrogen-containing active sites and Au (III), and reduction of Au (III) by TD-POP@CS/PEI-2 aerogel. This work provides a valuable and promising strategy to design scalable and sustainable adsorbents for capture precious metals, also promotes the development of integral adsorbent for environmental remediation.

Assessment of an eco-efficient process for the optimization of metal recovery in lithium cobalt oxide and lithium nickel manganese cobalt oxide batteries

The expansion of technology motivates the increase of global demands for critical minerals. In this context, the exploration of secondary sources of these components is expanding. End-of-life batteries can be seen as potential sources of lithium, cobalt, nickel and manganese for electric vehicles or diverse applications in electronic equipments. This paper provides a comprehensive evaluation of the recovery of metals from waste batteries with diverse chemistry composition. Lithium cobalt oxide (LCO) and lithium nickel cobalt manganese oxide (NMC) batteries were co-treated with polyvinyl chloride (PVC) channels under supercritical water, varying reaction temperature (400–600 °C) and PVC/Battery composition (0–3 m/m) in a tubular continuous reactor. Results show high recovery rates for all metals, with up to 90% percentage recovery of lithium and cobalt in all cases. Temperature and feed composition were identified as determining factors for the recovery of lithium from LCO batteries. In the case of cobalt, temperature was identified as the most important factor that affects its recovery. The selected optimal conditions for cobalt recovery in the solid products of reactions were identified for batteries LCO and NMC: temperature of 600 °C and PVC/Battery ratio of 3.0 and temperature of 500 °C and PVC/Battery ratio of 1.5, respectively. Environmental impacts, primarily Global Warming Potential (GWP), were minimal, with 4.71·10−5 kg CO2 eq., indicating the benefits of the process as an eco-efficient and promising route for the recycling of valuable metals.

Simultaneous utilization of copper and non-metals from waste integrated circuits for precious metal melting capture and organics thermal detoxification

Waste integrated circuits, with underlying resource attributes and environmental risks, are complex in composition. Current processes suffer from high resource inputs, excessive pollutant emissions and incomplete treatment of varied species. Therefore, a comprehensive resource recycling and safe disposal process integrated with precious metal enrichment, non-metal resource utilization, and organic detoxification was proposed. The copper and non-metals from waste ICs served as in-situ precious metal collector, slagging former and reducing agent for alternative to partial chemical inputs. Batch experiments indicated that optimized parameters enabled the recycling efficiencies of 94.3 %, 96.8 % and 98.4 % for copper, gold and silver, respectively. Meanwhile, oxide component, yielded as silicate slag, was synthesized into glass ceramics via high-temperature sintering. Furthermore, organic conversion process revealed that high-temperature smelting catalyzed bromine removal and contaminant detoxification, with decomposed reductive hydrocarbons facilitating metal capture in turn. And the capture mechanism was disclosed form thermodynamics and microdroplet motion perspectives. As process evaluation indicates, proposed recycling route allows remarkable reductions in negative environmental response and economic investment. In this work, metal recycling, waste minimization and pollutant detoxification were attained synergistically without residue, which contributes a novel insight into the disposal of comparable e-wastes.

Leaching of Neodymium From Hard Disk Drive Magnet Waste Using Citric Acid‐ Design of Experiments and Optimization

AbstractNeodymium magnet waste recycling and precious metal recovery have drawn a lot of researchers’ attention because of their vital role in contemporary technology. In this work, the potential of citric acid for the leaching of neodymium from hard disk drive waste magnets has been examined using statistical approaches like full factorial design(FFD) and central composite design (CCD).The variables have been screened and conditions are optimized to obtain higher leaching. The polynomial quadratic Model proves effective to predict optimized conditions for neodymium leaching. Leachant concentration and temperature were screened as the most effective factors. Optimization conditions for the leaching process were achieved through central composite design, revealing that 2 mol/L citric acid and a temperature of 333 K provide the ideal conditions for the complete dissolution of neodymium. This extensive study contributes to sustainable materials management and resource conservation by illuminating the effective recovery of important metals from neodymium magnets.