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Metals
Special Issues
Metal Removal and Recycling
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Metal Removal and Recycling

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

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 39517

Special Issue Editors

Prof. Dr. Francisco José Alguacil

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Guest Editor
National Center for Metallurgical Research (CENIM), Spanish National Research Council (CSIC), Avda. Gregorio del Amo 8, 28040 Madrid, Spain
Interests: metals recovery; metals removal; carbon nano adsorption technology; wastewater purification; hydrometallurgical operations
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Felix A. Lopez

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Guest Editor
Spanish National Research Council (CSIC) – National Center for Metallurgical Researcher (CENIM), Madrid, Spain
Interests: materials recycling; metals removal; carbon nano adsorption technology; wastewater purification; hydrometallurgical operations
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

It is impossible to conceive of daily life without the use of metals. For this reason, almost all people consider that metals exist somewhere and that they are easily obtained from any source. The situation is not as friendly as people imagine: some metals are scarce, others are critical, others are obtained from minerals whose deposits are in conflict zones, some of them are dangerous for the environment and health, etc. Therefore, and considering that metals come from exhaustible raw materials, it is necessary to develop efforts to encourage the recycling and reuse of post-consumer products and industrial waste, and also to eliminate those dangerous metals that may damage the environment, considering this in its broadest conception.

This Special Issue of Metals from the MDPI group explores the recovery of existing metals in waste and post-consumer products, with special emphasis on strategic metals (e.g., rare earths), toxic and precious metals, electronic scrap, batteries and scrap metal, among many other wastes and using techniques such as liquid–liquid extraction, electrochemical extraction, selective precipitation, ionic liquids, and many others. We invite you to send your contributions to this Special Issue.

Prof. Dr. Félix A. López
Prof. Dr. Francisco José Alguacil
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

  • Rare earths
  • Precious metals
  • Scrap metal
  • Toxic metals
  • Critical metals
  • Batteries
  • Ionic liquids and applications in smart technologies
  • Selective precipitation
  • Liquid-liquid extraction
  • Electrochemical extraction

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Published Papers (10 papers)

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Research

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12 pages, 2432 KiB  
Article
Design Optimization of Selective Lithium Leaching of Cathodic Active Materials from Spent Lithium-Ion Batteries Based on the Taguchi Method
by Yeon Jae Jung, Bong Young Yoo, Sung Cheol Park and Seong Ho Son
Metals 2021, 11(1), 108; https://doi.org/10.3390/met11010108 - 7 Jan 2021
Cited by 4 | Viewed by 2718
Abstract
The use of lithium-ion batteries (LIBs) has increased in recent years. Thus, efficient recycling is important. In this study, the Taguchi method was used to find the optimal selective lithium leaching parameters for spent LIB recycling. Orthogonal array, signal-to-noise ratio, and analysis of [...] Read more.
The use of lithium-ion batteries (LIBs) has increased in recent years. Thus, efficient recycling is important. In this study, the Taguchi method was used to find the optimal selective lithium leaching parameters for spent LIB recycling. Orthogonal array, signal-to-noise ratio, and analysis of variance were employed to investigate the optimization of selective lithium leaching. The experimental parameters were heat treatment and leaching conditions. The lithium leaching ratio was analyzed by inductively coupled plasma (ICP). The reaction temperature was analyzed by thermogravimetry differential scanning calorimetry (TG-DSC) using lithium cobalt oxide (LCO) and carbon powder, and X-ray diffraction (XRD) was performed after heat treatment at different temperatures. From the XRD analysis, a Li2CO3 peak was observed at 700 °C. After heat treatment at 850 °C, a peak of Li2O was confirmed as Li2CO3 decomposed into Li2O and CO2 over 723 °C. The Li2O reacts with Co3O4 at a high temperature to form LCO. The phase of lithium in the LIB changes according to the conditional heat treatment, affecting the lithium leaching rates. As heat treatment conditions, N2 atmosphere combined with 700 °C heat treatment is suitable, and the solid–liquid ratio is important as a leaching factor for selective lithium leaching. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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19 pages, 5207 KiB  
Article
Application of a Low-Cost Cellulose-Based Bioadsorbent for the Effective Recovery of Terbium Ions from Aqueous Solutions
by Lorena Alcaraz, Dayana Nathaly Saquinga, Floralba López, Lola De Lima, Francisco J. Alguacil, Esther Escudero and Félix A. López
Metals 2020, 10(12), 1641; https://doi.org/10.3390/met10121641 - 6 Dec 2020
Cited by 12 | Viewed by 3285
Abstract
The preparation of a low-cost cellulose-based bioadsorbent from cellulosic material extracted from rose stems (CRS) was carried out; rose stems are considered agricultural waste. After the required pretreatment of this waste and further treatment with an acidic mixture of acetic and nitric acids, [...] Read more.
The preparation of a low-cost cellulose-based bioadsorbent from cellulosic material extracted from rose stems (CRS) was carried out; rose stems are considered agricultural waste. After the required pretreatment of this waste and further treatment with an acidic mixture of acetic and nitric acids, the CRS product was produced. The resulting bioadsorbent was characterized by several techniques, such as X-ray diffraction, which revealed diffraction maxima related to the cellulose structure, whose calculated crystallinity index (CrI) was 75%. In addition, Fourier Transform Infrared spectroscopy (FTIR), 13C Nuclear Magnetic Resonance (NMR), and X-ray Photoelectron Spectroscopy (XPS) showed signs of acetylation of the sample. The thermal properties of the solid were also evaluated through Thermogravimetric Analysis (TGA). Scanning Electron Microscopy (SEM) showed cellulose fibers before and after the adsorption process, and some particles with irregular shapes were also observed. The CRS bioadsorbent was used for the effective adsorption of valuable Tb(III) from an aqueous solution. The adsorption data showed a good fit to the Freundlich isotherm and pseudo-second-order kinetic models; however, chemisorption was not ruled out. Finally, desorption experiments revealed the recovery of terbium ions with an efficiency of 97% from the terbium-loaded bioadsorbent. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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14 pages, 4294 KiB  
Article
Second Life Application of Automotive Catalysts: Hydrodynamic Cavitation Recovery and Photo Water Splitting
by Adrian Ciocanea, Eugeniu Vasile, Viorel Ionescu, Florentina Iuliana Maxim, Cornelia Diac, Cristina Miron and Serban N. Stamatin
Metals 2020, 10(10), 1307; https://doi.org/10.3390/met10101307 - 29 Sep 2020
Cited by 4 | Viewed by 2732
Abstract
A hydrodynamic cavitation method was used to maximize the effect of destructuration of a honeycomb monolithic support of a spent Selective Catalyst Reduction (SCR) catalyst—V2O5-WO3/TiO2-type—for extracting crystalline titanium and tungsten oxides from the cordierite surface. [...] Read more.
A hydrodynamic cavitation method was used to maximize the effect of destructuration of a honeycomb monolithic support of a spent Selective Catalyst Reduction (SCR) catalyst—V2O5-WO3/TiO2-type—for extracting crystalline titanium and tungsten oxides from the cordierite surface. A high relative inlet pressure of 40 MPa was applied to a divergent nozzle for obtaining high shear stresses of the submerged cavitating jets and intensive micro- and nano-jets and shock waves acting on the particle surface of the milled catalyst. Scanning Electron Microscopy (SEM) analysis indicated the compact morphology of the thin metal oxide layer at the surface of the cordierite support and the high content of Ti and W elements in the sample. Energy dispersive spectroscopy (EDAX) performed along with TEM investigations on different nano-zones from the sample established the elemental composition of WO3-TiO2 agglomerates separated after hydrodynamic cavitation processing and identified as independent nanocrystalline structures through Bright Field Transmission Electron Microscopy (BF-TEM) and High Resolution Transmission Electron Microscopy (HR-TEM) measurements. The tetragonal anatase phase of TiO2 and cubic phase of WO3 were established by both interplanar d spacing measurements and X-ray diffraction analysis. The photoelectrochemical results showed the possible second life application of automotive catalysts. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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11 pages, 4472 KiB  
Article
A Sustainable Approach for Cadmium Recovery from Oxide Using Molten Salt Slag
by Ervins Blumbergs, Vera Serga, Ernests Platacis, Michail Maiorov, Arturs Brekis and Andrei Shishkin
Metals 2020, 10(7), 981; https://doi.org/10.3390/met10070981 - 21 Jul 2020
Cited by 2 | Viewed by 3969
Abstract
Alkaline nickel-cadmium batteries are among the most used industrial high-power sources. Despite stricter environmental requirements, nickel-cadmium batteries still remain as the main choice for highly reliable power sources for heavy-loaded equipment. Therefore, recovery of cadmium (Cd) from spent batteries is a challenge for [...] Read more.
Alkaline nickel-cadmium batteries are among the most used industrial high-power sources. Despite stricter environmental requirements, nickel-cadmium batteries still remain as the main choice for highly reliable power sources for heavy-loaded equipment. Therefore, recovery of cadmium (Cd) from spent batteries is a challenge for the modern recycling industry, particularly as it displays high bio-toxicity. The present study describes a new green approach for Cd recovery from cadmium oxide (CdO). The paper discusses using a ternary chloride composition consisting of calcium, potassium and sodium chloride, thereby avoiding the release of Cd vapour from the reaction volume during the reduction reaction from CdO. For the protective slag layer during the reduction process (which occurs at 650 °C), a 0.515:0.0796:0.405 molar ratio of CaCl2:KCl:NaCl was chosen, with the aim of achieving a melting point at 483 °C. To describe phase and elemental composition of obtained products X-ray diffraction analysis and energy dispersive X-ray spectroscopy, respectively, were applied. Electron and optical microscopy were used for morphological observations. The presence of the metallic Cd was noted. During the reduction reaction, it was noted that slag separated into two parts: a protective upper layer and bottom layer. It was also noted that metallic Cd accumulated with increasing reaction time in the bottom part of the slag. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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11 pages, 2963 KiB  
Article
Electrochemical Recycling of Platinum Group Metals from Spent Catalytic Converters
by Cornelia Diac, Florentina Iuliana Maxim, Radu Tirca, Adrian Ciocanea, Valeriu Filip, Eugeniu Vasile and Serban N. Stamatin
Metals 2020, 10(6), 822; https://doi.org/10.3390/met10060822 - 19 Jun 2020
Cited by 12 | Viewed by 6029
Abstract
Platinum group metals (PGMs: Pt, Pd, and Rh) are used extensively by the industry, while the natural resources are limited. The PGM concentration in spent catalytic converters is 100 times larger than in natural occurring ores. Traditional PGM methods use high temperature furnaces [...] Read more.
Platinum group metals (PGMs: Pt, Pd, and Rh) are used extensively by the industry, while the natural resources are limited. The PGM concentration in spent catalytic converters is 100 times larger than in natural occurring ores. Traditional PGM methods use high temperature furnaces and strong oxidants, thus polluting the environment. Electrochemical studies showed that platinum can be converted to their chloride form. The amount of dissolved PGM was monitored by inductively coupled plasma-optical emission spectroscopy and the structure was identified by ultraviolet-visible spectroscopy. An electrochemistry protocol was designed to maximize platinum dissolution, which was then used for a spent catalytic converter. A key finding is the use of potential step that enhances the dissolution rate by a factor of 4. Recycling rates as high as 50% were achieved in 24 h without any pretreatment of the catalyst. The method developed herein is part of a current need to make the PGM recycling process more sustainable. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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11 pages, 1557 KiB  
Article
Permeation of AuCl4− Across a Liquid Membrane Impregnated with A324H+Cl− Ionic Liquid
by Francisco José Alguacil and Félix A. López
Metals 2020, 10(3), 363; https://doi.org/10.3390/met10030363 - 11 Mar 2020
Cited by 8 | Viewed by 3100
Abstract
In the system Au(III)-HCl-A324H+Cl−, liquid-liquid extraction experiments were used to define the extraction equilibrium and the corresponding extraction constant; furthermore, the facilitated transport of this precious metal from HCl solutions across a flat-sheet supported liquid membrane was investigated using [...] Read more.
In the system Au(III)-HCl-A324H+Cl−, liquid-liquid extraction experiments were used to define the extraction equilibrium and the corresponding extraction constant; furthermore, the facilitated transport of this precious metal from HCl solutions across a flat-sheet supported liquid membrane was investigated using the same ionic liquid as a carrier, and as a function of different variables: hydrodynamic conditions, concentration of gold(III) (0.01–0.1 g/L), and HCl (0.5–6 M) in the feed phase, and carrier concentration (0.023–0.92 M) in the membrane. An uphill transport equation was derived considering aqueous feed boundary layer diffusion and membrane diffusion as controlling steps. The aqueous diffusional resistance (Δf) and the membrane diffusional resistance (Δm) were estimated from the proposed equation with values of 241 s/cm and 9730 s/cm, respectively. The performance of the present carrier was compared against results yielded by other ionic liquids, and the influence that other metals had on gold(III) transport from both binary or quaternary solutions was also investigated. Gold was finally recovered from receiving solutions as zero valent gold nanoparticles. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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17 pages, 8402 KiB  
Article
Roasting Pretreatment Combined with Ultrasonic Enhanced Leaching Lead from Electrolytic Manganese Anode Mud
by Huimin Xie, Shiwei Li, Libo Zhang, Yongmi Wang and Hailin Long
Metals 2019, 9(5), 601; https://doi.org/10.3390/met9050601 - 24 May 2019
Cited by 11 | Viewed by 3778
Abstract
A method of conventional roasting pretreatment combined with ultrasonic enhanced leaching with ammonium acetate was proposed to solve the difficult problem of lead in electrolytic manganese anode mud. The effects of concentration, liquid–solid ratio, temperature, leaching time and rotating speed on the leaching [...] Read more.
A method of conventional roasting pretreatment combined with ultrasonic enhanced leaching with ammonium acetate was proposed to solve the difficult problem of lead in electrolytic manganese anode mud. The effects of concentration, liquid–solid ratio, temperature, leaching time and rotating speed on the leaching process under conventional and ultrasonic conditions were studied, and the lead leaching rate can be as high as 93.09% under optimized process parameters. A leaching kinetic model under conventional and ultrasonic conditions was established to explore the restrictive links of the leaching process. The results show that the leaching process under both conventional and ultrasonic conditions is controlled by diffusion, and the activation energies are 29.40 kJ/mol and 26.95 kJ/mol for the conventional and ultrasound enhance leaching processes, respectively. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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12 pages, 4361 KiB  
Article
Modified Leach Residues from Processing Deep-Sea Nodules as Effective Heavy Metals Adsorbents
by Nguyen Hong Vu, Eva Kristianová, Petr Dvořák, Tomasz Abramowski, Ivo Dreiseitl and Aigerim Adrysheva
Metals 2019, 9(4), 472; https://doi.org/10.3390/met9040472 - 23 Apr 2019
Cited by 7 | Viewed by 3297
Abstract
The possible use of leaching residue from leaching deep-sea nodules in SO2/H2SO4/H2O medium as a low-cost adsorbent of heavy metals (Pb(II), Cd(II), Cu(II), Ni(II), Co(II), As(V)) was studied. The leaching residue was found to be [...] Read more.
The possible use of leaching residue from leaching deep-sea nodules in SO2/H2SO4/H2O medium as a low-cost adsorbent of heavy metals (Pb(II), Cd(II), Cu(II), Ni(II), Co(II), As(V)) was studied. The leaching residue was found to be an effective adsorbent for all of the tested elements; however, it was inactive in the solution containing As(V). The chemical activation of adsorbent in 10 vol. % HCl resulted in the greatest improvement of adsorption properties, while the activation in 10 vol. % HNO3 and heat treatment at 250 °C did not significantly affect the sorption characteristics of treated adsorbents compared with the original leaching residue. After HCl activation, the maximal adsorption capacities for lead (12.0 mg/g at pH 5.0 after 1 h), nickel (3.1 mg/g at pH 5.5 after 4 h) and cobalt (2.0 mg/g at pH 5.0 after 2 h) were achieved. Additional mechanical treatment connected with HCl activation provided the highest adsorption capacities for cadmium (11.5 mg/g at pH 4.0) and copper (5.7 mg/g at pH 4.5). Coprecipitation of Fe/Al-based particles on the surface of the leaching residue increased As(V) removal of the adsorbent. Surface coating based on AlIII was extremely effective, causing the increase of the adsorption capacity from 0 with the original leaching residue, to 28.1 mg/g (pH 7.0, 24 min). Kinetics studies showed the rapid progress of adsorption for Pb(II), Cd(II), and As(V) in tens of minutes, while the adsorption of Cu(II), Ni(II) and Co(II) approached a steady state after 2 h. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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10 pages, 2150 KiB  
Article
Characterization of Double Leached Waelz Oxide for Identification of Fluoride Mineral
by Suchandra Sar, Lena Sundqvist Öqvist, Tobias Sparrman, Fredrik Engström and Caisa Samuelsson
Metals 2019, 9(3), 361; https://doi.org/10.3390/met9030361 - 20 Mar 2019
Cited by 8 | Viewed by 4904
Abstract
Double leached Waelz oxide (DLWO), with 76% zinc, is a secondary zinc containing raw materials obtained by the treatment of electric arc furnace dust. The content of fluoride in DLWO is still too high for direct leaching, as fluoride has a detrimental effect [...] Read more.
Double leached Waelz oxide (DLWO), with 76% zinc, is a secondary zinc containing raw materials obtained by the treatment of electric arc furnace dust. The content of fluoride in DLWO is still too high for direct leaching, as fluoride has a detrimental effect on electrowinning for zinc production. Knowledge of the characteristics of DLWO, and especially on how a fluoride mineral might exist, can contribute to further improvement of the selective leaching for the removal of fluoride. In this study, DLWO was characterized using analytical techniques, such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), 19F liquid-state nuclear magnetic resonance (19F LS NMR), X-ray powder diffraction analysis (XRD), scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) and 19F solid-state nuclear magnetic resonance (19F SS NMR). This study showed that DLWO mainly consisted of zincite (ZnO), cerussite (PbCO3) and a spinel containing zinc, iron and manganese. The fluoride mineral identified was calcium fluoride (CaF2). In SEM analysis, fluorine was found in larger grains together with calcium and oxygen, which was possibly calcium carbonate. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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Review

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33 pages, 2295 KiB  
Review
Adsorption Processing for the Removal of Toxic Hg(II) from Liquid Effluents: Advances in the 2019 Year
by Francisco J. Alguacil and Félix A. López
Metals 2020, 10(3), 412; https://doi.org/10.3390/met10030412 - 23 Mar 2020
Cited by 19 | Viewed by 4528
Abstract
Mercury is a toxic metal, thus, it is an element which has more and more restrictions in its uses, but despite the above, the removal of this metal, from whatever the form in which it is encountered (zero valent metal, inorganic, or organic [...] Read more.
Mercury is a toxic metal, thus, it is an element which has more and more restrictions in its uses, but despite the above, the removal of this metal, from whatever the form in which it is encountered (zero valent metal, inorganic, or organic compounds), and from different sources, is of a widespread interest. In the case of Hg(II), or Hg2+, the investigations about the treatment of Hg(II)-bearing liquid effluents (real or in most cases synthetic solutions) appear not to end, and from the various separation technologies, adsorption is the most popular among researchers. In this topic, and in the 2019 year, more than 100 publications had been devoted to this field: Hg(II)-removal-adsorption. This work examined all of them. Full article
(This article belongs to the Special Issue Metal Removal and Recycling)
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