Special Issue "Solvent Extraction of Critical Metals"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 October 2018).

Special Issue Editors

Dr. Ana Paula Paiva
Website
Guest Editor
Centro de Química e Bioquímica / Centro de Química Estrutural, Faculdade de Ciências, Universidade de Lisboa Campo Grande, C8 1749-016 Lisboa, Portugal
Interests: liquid–liquid (solvent) extraction in hydrometallurgy; synthesis and characterization of organic extractants; extraction of platinum-group metals (platinum, palladium, rhodium and ruthenium), silver and iron from chloride media; hydrometallurgical recycling of end-of-life materials, e.g., spent catalysts
Prof. Gérard Cote
Website
Co-Guest Editor
PSL Research University, Chimie ParisTech - CNRS, Institut de Recherche de Chimie Paris (UMR 8247), 11, rue Pierre et Marie Curie 75231 Paris Cedex 05, France
Interests: urban mining, WEEE, nuclear fuel cycle, hydrometallurgy, solvent extraction, critical metals

Special Issue Information

Dear Colleagues,

Critical metals are those included in materials that are indispensable to modern life and for which an exponential increase in consumption is already a reality or will be in a short-term perspective. Current technologies involved in the manufacture of electrical and electronics equipment (EEE), photovoltaic cells, batteries, and catalysts intimately rely on the activity and function of some metals. For instance, tantalum, indium and ruthenium are key feedstocks for EEE; gallium, tellurium and germanium for photovoltaic cells; cobalt and lithium for batteries; and platinum-group and rare-earth metals for automotive and industrial catalysts.

To fulfil the requests of developed society, the scarcity of some of the above-mentioned metals in primary supply resources has to be conveniently balanced with recycling practices. In fact, the concentrations of some metals in those end-of-life materials are 100 times higher than in their natural ores. Accordingly, the reduction of the overall environmental impacts linked with the life cycles of the critical metals, together with their intrinsic value-adding benefits, favourably contribute to an important increase of resources efficiency. Although some industrial recycling circuit facilities are apparently well established, research and development of technical procedures involving novel recycling and refining concepts for these strategic metals are always welcome.

Nowadays, solvent extraction (SX) is a mature unit operation applied to separate, purify and concentrate metals from leaching solutions when a hydrometallurgical route is considered. This Special Issue aims to address the latest research devoted to exploring the potentialities of commercial or specifically synthesized extractants in the design of SX processes to efficiently and selectively recover critical metals from complex secondary materials leaching media. Advances in alternative separation techniques whose functioning relies on SX principles are also welcome. Research articles focusing on the development of integrated environmentally-friendly and cost-effective hydrometallurgical processes to recuperate critical metals are encouraged as well.

Assist. Prof. Ana Paula Paiva
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 papers will be 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 1600 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

  • Secondary materials
  • Spent catalysts and electronic scrap
  • Recycling practices
  • Critical and strategic metals
  • Hydrometallurgy
  • Complex leaching solutions
  • Solvent extraction
  • Commercial or synthesized extractants

Published Papers (7 papers)

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Research

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Open AccessArticle
Solvent Extraction and Separation of Nd, Pr and Dy from Leach Liquor of Waste NdFeB Magnet Using the Nitrate Form of Mextral® 336At in the Presence of Aquo-Complexing Agent EDTA
Metals 2019, 9(2), 269; https://doi.org/10.3390/met9020269 - 25 Feb 2019
Cited by 3
Abstract
Solvent extraction and separation of Pr, Nd and Dy from a synthetic leach solution of spent NdFeB magnet from wind turbines in the presence of aquo-complexing agent Ethylenediaminetetraacetic acid (EDTA) was studied using the nitrate form of Mextral® 336At ([336At][NO3]) as [...] Read more.
Solvent extraction and separation of Pr, Nd and Dy from a synthetic leach solution of spent NdFeB magnet from wind turbines in the presence of aquo-complexing agent Ethylenediaminetetraacetic acid (EDTA) was studied using the nitrate form of Mextral® 336At ([336At][NO3]) as an extractant. The effect of different process parameters such as pH, extractant, nitrate, and EDTA concentrations on the extraction of Pr, Nd and Dy was studied. The extraction of these rare earths elements follows the order Pr > Nd > Dy, whereas EDTA forms stable complexes in the order Dy > Nd > Pr. The synergy of these two effects improved the selectivity among these elements as compared to when no aquo-complexing agent was used. The mechanism of extraction of rare earth elements was established by slope analysis method. The Fourier-Transform Infrared Spectroscopy (FTIR) spectra of [336At][NO3] and extracted Nd complex were recorded to understand the interaction of extractant with rare earth metal ions in the organic phase. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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Open AccessArticle
Nano ZrO2 Synthesis by Extraction of Zr(IV) from ZrO(NO3)2 by PC88A, and Determination of Extraction Impurities by ICP-MS
Metals 2018, 8(10), 851; https://doi.org/10.3390/met8100851 - 19 Oct 2018
Cited by 1
Abstract
High purity Zirconium (Zr) materials are essential in many components of nuclear reactors, especially fuel cladding tubes. Due to the matrix influence, determination of impurities in the Zr materials requires separation from the Zr matrix. Among extraction methods, solvent extraction is common and [...] Read more.
High purity Zirconium (Zr) materials are essential in many components of nuclear reactors, especially fuel cladding tubes. Due to the matrix influence, determination of impurities in the Zr materials requires separation from the Zr matrix. Among extraction methods, solvent extraction is common and suitable for large-scale production. In this study, extraction capability of Zr(IV) by 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (PC88A) was examined by FT-IR and UV of ZrO(NO3)2 salt, PC88A-toluene solvent, and Zr-PC88A-toluene complex. ZrO2 (obtained from Institute for Technology of Radioactive and Rare Elements—ITRRE), after being separated from the Zr matrix, was determined for impurities using internal standard (indium, In) by 50% of PC88A dissolved in toluene. Separation of impurities from the Zr matrix underwent two stages. First, one cycle of extraction of the Zr matrix and impurities in 3 M HNO3 using 50% PC88A/toluene was conducted. Second, impurities were scrubbed by 4 M HNO3 in two cycles. Results revealed that approximately 74% of Zr(IV) was separated to the organic phase and 26% remained in the aqueous phase. Determination of impurities after separation from the Zr matrix by ICP-MS using internal standard in revealed that the recovery of impurities achieved 95–100%. With the mentioned amount of Zr, the effect of the Zr matrix on the determination of elements by ICP-MS is negligible. Levels of impurities have relative standard deviations (RSD) of less than 6.9% and recovery of 88.6–98.8%. Therefore, the determination of impurities has high reliability and accuracy. The back-extraction of Zr(IV) in organic phase by 1 M H2SO4 has stripped about 99.5% of the Zr matrix back to the aqueous phase. Following this, NH3 was added to the solution containing Zr after back-extraction to form Zr(OH)4 which was then desiccated to produce ZrO2. X-ray Diffraction (XRD), Scanning and Transmission Electron Microscopy (SEM and TEM) images showed that the new ZrO2 product has spherical nanostructure with diameters of less than 25 nm, which is suitable for applications for the treatment of colorants, metal ions in wastewater sources and manufacture of anti-corrosion steel. In addition, the energy dispersive X-ray (EDX) of the new ZrO2 product showed that it has high purity. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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Open AccessFeature PaperArticle
Tantalum and Niobium Selective Extraction by Alkyl-Acetophenone
Metals 2018, 8(9), 654; https://doi.org/10.3390/met8090654 - 21 Aug 2018
Cited by 3
Abstract
A study has been carried out on Ta and Nb recovery by a liquid-liquid extraction process using 4-methylacetophenone (4-MAcPh) as the organic phase. The 4-MAcPh was compared to methyl isobutyl ketone (MIBK) with respect to extraction efficiencies (D values) at different concentrations [...] Read more.
A study has been carried out on Ta and Nb recovery by a liquid-liquid extraction process using 4-methylacetophenone (4-MAcPh) as the organic phase. The 4-MAcPh was compared to methyl isobutyl ketone (MIBK) with respect to extraction efficiencies (D values) at different concentrations of H2SO4 in the aqueous phase. The results showed a similar extraction of Nb for both solvents. However, for Ta, extraction efficiency is increased by a factor of 1.3 for 4-MAcPh. In addition, the MIBK solubilized completely after 6 mol∙L−1 of H2SO4 against only a loss of 0.14–4% for 4-MAcPh between 6 and 9 mol∙L−1 of H2SO4. The potential of 4-MAcPh has also been studied to selectively recover Ta from a model capacitor waste solution. The results showed a selectivity for Ta in the presence of impurities such as Ag, Fe, Ni and Mn. The 4-MAcPh also presents the advantage of having physicochemical properties adapted to its use in liquid-liquid extraction technologies such as mixer-settlers. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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Open AccessArticle
Speciation of Ruthenium(III) Chloro Complexes in Hydrochloric Acid Solutions and Their Extraction Characteristics with an Amide-Containing Amine Compound
Metals 2018, 8(7), 558; https://doi.org/10.3390/met8070558 - 20 Jul 2018
Cited by 3
Abstract
The refining of platinum group metals is based mainly on solvent extraction methods, whereas Ru is selectively recovered by distillation as RuO4. Replacement of distillation by extraction is expected to simplify the purification process. To develop an effective extraction system for [...] Read more.
The refining of platinum group metals is based mainly on solvent extraction methods, whereas Ru is selectively recovered by distillation as RuO4. Replacement of distillation by extraction is expected to simplify the purification process. To develop an effective extraction system for Ru, we analyzed the Ru species in HCl with ultraviolet-visible (UV-Vis) and Ru K-edge extended X-ray absorption fine structure (EXAFS) spectroscopies, and we examined the properties of Ru extracted with N-2-ethylhexyl-bis(N-di-2-ethylhexyl-ethylamide) amine (EHBAA) and trioctylamine (TOA). EXAFS and UV-Vis spectra of Ru in HCl solutions revealed that the predominant Ru species in 0.5–10 M HCl solutions changed from [RuCl4(H2O)2] to [RuCl6]3− with the HCl concentration. The extraction percentages (E%) of Ru in the EHBAA system increased with increasing HCl concentration, reached 80% at [HCl] = 5 M, and decreased at higher HCl concentrations; the corresponding E% for TOA were low. EXAFS analysis of the extracted complex indicated that the Ru3+ had 5 Cl and 1 H2O in its inner coordination sphere. The similarity of the dependence on HCl concentrations of the E% in the EHBAA system and the distribution profile of [RuCl5(H2O)]2− on [RuCln(H2O)6n]3−n suggested that the EHBAA extracted the pentachlorido species. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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Open AccessFeature PaperArticle
Calix[4]arene-Based Amino Extractants Containing n-Alkyl Moieties for Separation of Pd(II) and Pt(IV) from Leach Liquors of Automotive Catalysts
Metals 2018, 8(7), 517; https://doi.org/10.3390/met8070517 - 05 Jul 2018
Cited by 2
Abstract
Pt, Pd, and Rh platinum group metals (PGMs) are utilized in automotive catalytic converters to reduce the level of harmful gas emissions. To evaluate the separation efficiencies of PGMs from the leach liquors of automotive catalysts, their extractabilities from both single-component solutions and [...] Read more.
Pt, Pd, and Rh platinum group metals (PGMs) are utilized in automotive catalytic converters to reduce the level of harmful gas emissions. To evaluate the separation efficiencies of PGMs from the leach liquors of automotive catalysts, their extractabilities from both single-component solutions and leach liquors were determined using three p-dialkylaminomethylcalix[4]arenes (alkyl: n-hexyl~n-octyl; 35) as extractants, and the obtained results were compared with the data of acyclic p-di-n-octylaminomethyldimethylphenol (6) and those previously reported for macrocyclic calix[4]arene- and thiacalix[n]arene-based amine and amide extractants. Various extraction parameters, including the contact time, HCl concentration, and concentrations of Pd(II) and Pt(IV) ions, were examined, and the distributions and stoichiometry ratios of the recovered Pd(II) and Pt(IV) species were calculated. All macrocyclic extractants 35 exhibited high and selective extractabilities of Pd(II) and Pt(IV) ions contained in the leach liquors of automotive catalysts. The E% values of 35 from the leach liquors were 94.2, 93.0, and 97.7 for Pd(II) and 91.7, 94.0, and 92.5 for Pt(IV), respectively. Acyclic compound 6 did not perform well even though higher ratios of extractant used. Furthermore, the results of reusability testing demonstrated relatively large extractability values obtained for these two metals even after five extraction/stripping cycles. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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Open AccessFeature PaperArticle
Understanding the Recovery of Rare-Earth Elements by Ammonium Salts
Metals 2018, 8(6), 465; https://doi.org/10.3390/met8060465 - 19 Jun 2018
Cited by 4
Abstract
While the recovery of rare earth elements (REEs) from aqueous solution by ionic liquids (ILs) has been well documented, the metal compounds that are formed in the organic phase remain poorly characterized. Using spectroscopic, analytical, and computational techniques, we provide detailed chemical analysis [...] Read more.
While the recovery of rare earth elements (REEs) from aqueous solution by ionic liquids (ILs) has been well documented, the metal compounds that are formed in the organic phase remain poorly characterized. Using spectroscopic, analytical, and computational techniques, we provide detailed chemical analysis of the compounds formed in the organic phase during the solvent extraction of REEs by [(n-octyl)3NMe][NO3] (IL). These experiments show that REE recovery using IL is a rapid process and that IL is highly durable. Karl-Fischer measurements signify that the mode of action is unlikely to be micellar, while ions of the general formula REE(NO3)4(IL)2 are seen by negative ion electrospray ionization mass spectrometry. Additionally, variable temperature 139La nuclear magnetic resonance spectroscopy suggests the presence of multiple, low symmetry nitrato species. Classical molecular dynamics simulations show aggregation of multiple ILs around a microhydrated La3+ cation with four nitrates completing the inner coordination sphere. This increased understanding is now being exploited to develop stronger and more selective, functionalized ILs for REE recovery. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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Review

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Open AccessFeature PaperReview
Recycling of Palladium from Spent Catalysts Using Solvent Extraction—Some Critical Points
Metals 2017, 7(11), 505; https://doi.org/10.3390/met7110505 - 16 Nov 2017
Cited by 11
Abstract
Electrical and electronics equipment and automotive and industrial catalysts are some examples of top technological devices whose functioning rely on the use of platinum-group metals (PGMs). The PGMs’ high economic value and difficult to replace technological properties, together with their scarcity in the [...] Read more.
Electrical and electronics equipment and automotive and industrial catalysts are some examples of top technological devices whose functioning rely on the use of platinum-group metals (PGMs). The PGMs’ high economic value and difficult to replace technological properties, together with their scarcity in the Earth’s crust, justify concerns about their critical condition and reinforce the importance of developing recycling practices for PGM end-of-life materials. This article presents and discusses recent advances regarding the use of hydrometallurgical solvent extraction to recover one PGM, palladium, from spent catalysts. Two different tendencies are implicit in the literature concerning Pd(II) extraction: a few groups focus on the adjustment and optimization of current commercial extractants, while others prefer to design new extracting compounds. Actually, the leach solutions obtained from the treatment of anthropogenic materials generally exhibit different compositions when compared to those coming from the primary resources. The pros and cons of both approaches are critically discussed, and the assumptions backing some of the reported achievements are also appraised. Full article
(This article belongs to the Special Issue Solvent Extraction of Critical Metals)
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