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Metals
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Utilization of Industrial By-Products—Recovery of Rare Earth Elements
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Utilization of Industrial By-Products—Recovery of Rare Earth Elements

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

Deadline for manuscript submissions: closed (30 November 2021) | Viewed by 9698

Special Issue Editor

Prof. Dr. Maria Ochsenkuhn-Petropoulou

E-Mail Website
Guest Editor
School of Chemical Engineering, National Technical University Athens, Department of Chemical Sciences,Laboratory of Inorganic and Analytical Chemistry, Iroon Polytechneiou 9, Zographou Campus, 15780 Athens, Greece
Interests: utilization of industrial by-products in laboratory and pilot plant scale; recovery of rare earth elements and in particular of scandium from bauxite residue; speciation of metals and metalloids; preparation and characterization of superconducting powders and coatings; aerosol research in atmosphere; aerosol emissions from car catalysts exhaust and from burning of biomass; quality control of surface water and groundwater using modern analytical techniques
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

An industrial by-product is a production residue from an industrial process that is not a waste, with a minor net realizable value (NRV) when compared with the main products. However, a by- product can be useful and marketable. Rare Earth Elements (REEs), including Sc, Y, and the lanthanides, are elements of high techno-economical interest because of their use in high-tech materials and modern applications. The European Commission considers the REEs as the most critical raw materials group, due to their highest supply risk and their economic importance. As  economically exploitable minerals containing  REEs are very scarce, the available stockpiles have decreased and the recovery of REEs from  their deposits is difficult due to the coexistence of radioactive elements; therefore, it is necessary to investigate the potential to recover REEs from different  industrial by-products. These industrial streams contain relatively low concentrations of REEs in comparison to primary ores, but large volumes are available, and therefore they could become economically attractive secondary sources of REEs. This Special Issue aims to publish papers dealing with the recovery of REEs from different industrial-by products, such as slags produced by pyro-metallurgical metal recycling processes, bauxite residue (red mud), phosphogypsum, mine tailings, industrial wastewater, and others. The processes described have to be economically viable, environmentally friendly, and have the possibility to be scaled up.

Prof. Maria Ochsenkuhn-Petropoulou
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

  • rare earth elements recovery
  • industrial by-products utilization
  • slag valorization
  • bauxite residue
  • mine tailings
  • phosphogypsum

Published Papers (4 papers)

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Research

19 pages, 34137 KiB  
Article
Direct Phosphoric Acid Leaching of Bauxite Residue for Selective Scandium Extraction
by Lamprini-Areti Tsakanika, George Panagiotatos, Theopisti Lymperopoulou, Elias Chatzitheodoridis, Klaus Ochsenkühn and Maria Ochsenkühn-Petropoulou
Metals 2022, 12(2), 228; https://doi.org/10.3390/met12020228 - 26 Jan 2022
Cited by 6 | Viewed by 2612
Abstract
Bauxite residue, the high alkaline and fine-grained byproduct of Bayer process for alumina’s production, is a material rich in numerous minerals and elements of high value and techno-economical interest in high tech applications such as rare earths, including scandium. Lately, the European Committee [...] Read more.
Bauxite residue, the high alkaline and fine-grained byproduct of Bayer process for alumina’s production, is a material rich in numerous minerals and elements of high value and techno-economical interest in high tech applications such as rare earths, including scandium. Lately, the European Committee has characterized scandium as a critical element because of its risk supply chain. Scandium's high concentration in Greek bauxite residue classifies the waste as a candidate for low cost and high availability of the element, additionally improving its environmental fingerprint. For scandium recovery, hydrometallurgical treatment with inorganic acids is the most common, effective and simple method. In this study, the efficiency of phosphoric acid is investigated for scandium recovery by a direct leaching of bauxite residue without pretreatment. Multi leaching variables, such as acid molarity, solid/liquid ratio, process temperature and leaching time, were examined and optimized individually as well as in a comparative way aiming to scandium selective extraction (mainly with regard to iron) and process viability. A Sc selective recovery of 40% was obtained for phosphoric acid molarity 5 M, solid/liquid ratio 10%, leaching time, 60 min under ambient conditions with low iron leachability, no gel formation and no energy consumption. Full article
(This article belongs to the Special Issue Utilization of Industrial By-Products—Recovery of Rare Earth Elements)
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15 pages, 34850 KiB  
Article
Electrochemistry, Electrodeposition, and Photoluminescence of Eu (III)/Lanthanides (III) on Terpyridine-Functionalized Ti Nanospikes
by Min Hee Joo, So Jeong Park, Hye Ji Jang, Sung-Min Hong, Choong Kyun Rhee and Youngku Sohn
Metals 2021, 11(6), 977; https://doi.org/10.3390/met11060977 - 18 Jun 2021
Cited by 2 | Viewed by 1745
Abstract
Terpyridine-functionalized Ti nanospike electrodes (TiNS-SiTpy) were developed and applied to cyclic voltammetry and amperometry of Ln (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) ions and mixed Eu (III) + Ln (III) ions in a 0.1 M [...] Read more.
Terpyridine-functionalized Ti nanospike electrodes (TiNS-SiTpy) were developed and applied to cyclic voltammetry and amperometry of Ln (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) ions and mixed Eu (III) + Ln (III) ions in a 0.1 M NaClO4 electrolyte. Electrodeposition was successfully performed over TiNS-SiTpy electrodes, which were fully examined by scanning electron microscopy, X-ray diffraction crystallography, Fourier-transform infrared spectroscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, photoluminescence (PL), and PL decay kinetics. The Gd and Tb ions were found to increase PL intensities with 10× longer lifetimes of 1.32 μs and 1.03 μs, respectively, compared with that of the electrodeposited Eu sample. The crystal phase and the oxidation states were fully examined for the mixed Ln (Eu + Gd and Eu + Tb) complex structures. Full article
(This article belongs to the Special Issue Utilization of Industrial By-Products—Recovery of Rare Earth Elements)
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11 pages, 1599 KiB  
Article
Study of Microbial Cultures for the Bioleaching of Scandium from Alumina Industry By-Products
by Kyriaki Kiskira, Theopisti Lymperopoulou, Lamprini-Areti Tsakanika, Charalampos Pavlopoulos, Konstantina Papadopoulou, Klaus-Michael Ochsenkühn, Gerasimos Lyberatos and Maria Ochsenkühn-Petropoulou
Metals 2021, 11(6), 951; https://doi.org/10.3390/met11060951 - 11 Jun 2021
Cited by 14 | Viewed by 2696
Abstract
The disposal of voluminous, highly alkaline, bauxite residue (BR), the industrial by-product of alumina production by the Bayer process, constitutes an intricate global environmental problem. BR, containing valuable metals such as rare-earth elements (REEs)—in particular, scandium (Sc)—can be used as a secondary source [...] Read more.
The disposal of voluminous, highly alkaline, bauxite residue (BR), the industrial by-product of alumina production by the Bayer process, constitutes an intricate global environmental problem. BR, containing valuable metals such as rare-earth elements (REEs)—in particular, scandium (Sc)—can be used as a secondary source for REE extraction. The scope of this study was the investigation of bioleaching as an innovative and environmentally friendly approach for the extraction of Sc from BR. The bioleaching parameters were studied on Greek BR and experiments were performed using different microbial cultures and solid to liquid ratios (S/L). The maximum extraction of Sc was 42% using Acetobacter tropicalis in a one-step bioleaching process at 1% S/L. The main organic acids produced were acetic, oxalic, and citric. The bioleaching data indicated a probable synergistic effect of the different organic acids produced by microorganisms along with a more targeted leaching mechanism. Full article
(This article belongs to the Special Issue Utilization of Industrial By-Products—Recovery of Rare Earth Elements)
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10 pages, 2219 KiB  
Article
Dissolution and Online Monitoring of Nd and Pr Oxides in NdF3–PrF3–LiF Electrolytes
by Samuel Senanu, Arne Petter Ratvik, Henrik Gudbrandsen, Ana Maria Martinez, Anne Støre and Wojciech Gebarowski
Metals 2021, 11(2), 326; https://doi.org/10.3390/met11020326 - 13 Feb 2021
Cited by 6 | Viewed by 1846
Abstract
Concentrations of dissolved rare earth metal oxides, Nd2O3, and Pr2O3 or their mixtures in different fluoride electrolytes composed of NdF3, PrF3, and LiF at ca. 1040 °C were monitored using a graphite [...] Read more.
Concentrations of dissolved rare earth metal oxides, Nd2O3, and Pr2O3 or their mixtures in different fluoride electrolytes composed of NdF3, PrF3, and LiF at ca. 1040 °C were monitored using a graphite probe inserted into the electrolyte during the dissolution process. Fast voltage sweeps of 100 V/s were applied to the graphite probe, and the current response was measured. As the oxide concentration in the diffusion layer towards the electrode depletes, a passive layer is, at a certain point, formed on the probe, resulting in a current drop. The magnitude of the peak current attained before the formation of the passive layer reflects the concentration of the dissolved oxide and, thus, is applied to determine the oxide concentration. The oxide concentration in the electrolyte samples determined using the inert gas fusion technique showed a good correlation to the peak current determined by the probe. Full article
(This article belongs to the Special Issue Utilization of Industrial By-Products—Recovery of Rare Earth Elements)
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