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Metals
Special Issues
Recovery and Recycling of Valuable Metals
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Recovery and Recycling of Valuable Metals

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

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 56532

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editor

Dr. Dariush Azizi

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Guest Editor
Solutions Manager – Metallurgy & Mineral Processing, IGS Impact Global Solutions, Greater Montréal Metropolitan Area, Delson, QC, Canada
Interests: mineral processing; extractive metallurgy; molecular modeling; green mining; urban mining
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Metals have always played a significant role in human life, and the current global growth and prosperity are directly dependent on these materials. With the rapidly growing global demand for metals, their extraction from natural minerals (as their primary sources) has been enhanced, causing a significant reduction in the grade and quality of the ores in ore deposits and leading to the production of huge amounts of waste which needs management. In light of this, new ideas to develop more advanced metal recovery technologies from minerals are required. Besides, the huge quantity of waste generated through all steps of metal production is known to be a source of environmental pollution, while its valorization can create value via recycling metals or even though use in the production of other valuable materials. Such waste valorization is also in line with the United Nations’ Sustainable Development Goals (SDGs) as well as implementation of the Paris Agreement. On this matter, the recycling of end-user products in order to reproduce valuable metals can also create significant values and reduce mining activities, and thus their harmful consequences all around the world. Therefore, research and development in the state-of-the-art technologies for the recovery and recycling of metals are absolutely necessary.   

In this Special Issue, the endeavor is to collect a range of articles on different aspects of valuable metal recovery and recycling from primary and secondary sources. The objective is to decipher all new methods, processes, and knowledge in valuable metals production. We hope this open-access Special Issue will provide a great opportunity to demonstrate the work of researchers working in this area all around the world. Articles on all areas of hydrometallurgy, mineral processing, and waste recycling and valorization are highly desired.

Dr. Dariush Azizi
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

  • metal production
  • mineral processing
  • hydrometallurgy
  • extraction technologies
  • pyrometallurgy
  • waste valorization
  • primary metal sources
  • secondary metal sources
  • waste and end-user product recycling
  • process development

Published Papers (18 papers)

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Editorial

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2 pages, 174 KiB  
Editorial
Recovery and Recycling of Valuable Metals
by Dariush Azizi
Metals 2022, 12(1), 91; https://doi.org/10.3390/met12010091 - 4 Jan 2022
Cited by 1 | Viewed by 1197
Abstract
Metals have always played a significant role in human life; contemporary global growth and prosperity are directly dependent on these materials [...] Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)

Research

Jump to: Editorial, Review

10 pages, 4037 KiB  
Article
Influence of Dysprosium Compounds on the Extraction Behavior of Dy from Nd-Dy-Fe-B Magnet Using Liquid Magnesium
by Sun-Woo Nam, Sang-Min Park, Mohammad Zarar Rasheed, Myung-Suk Song, Do-Hyang Kim and Taek-Soo Kim
Metals 2021, 11(9), 1345; https://doi.org/10.3390/met11091345 - 26 Aug 2021
Cited by 4 | Viewed by 1689
Abstract
During the liquid metal extraction reaction between a Nd-Dy-Fe-B magnet and liquid Mg, Nd rapidly diffuses out of the magnet, whereas Dy is not extracted due to the reaction with the matrix and the formation of Dy2Fe17 phase. In addition, [...] Read more.
During the liquid metal extraction reaction between a Nd-Dy-Fe-B magnet and liquid Mg, Nd rapidly diffuses out of the magnet, whereas Dy is not extracted due to the reaction with the matrix and the formation of Dy2Fe17 phase. In addition, theDy2O3 phase exists at the grain boundaries. Until now, only the effect of the Dy2O3 phase on the extraction of Dy has been reported. In this study, the effect of the Dy2Fe17 phase on the extraction of Dy from the Nd-Dy-Fe-B magnet was investigated in liquid Mg. The formation of the Dy2Fe17 phase during the reaction between Mg and matrix (RE2Fe14B) was first examined using a thermodynamical approach and confirmed by microstructural analysis. It was observed that Dy extraction was dominated by Dy2Fe17 phase decomposition from 3 h to 24 h, followed by Dy2O3 phase dominant reaction with Mg. Comparing the activities of the Dy2Fe17 phase and the Dy2O3 phase, the reaction of Dy2Fe17 is dominant, as compared to the Dy2O3 phase. Finally, at 48 h, the high Dy extraction percentage of 93% was achieved. As a result, in was concluded that the Dy2Fe17 phase acts as an obstacle in the extraction of Dy. In the future, if research to control the Dy2Fe17 phase proceeds, it will be of great importance to advance the recycling of Dy. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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14 pages, 1362 KiB  
Article
Chelation-Assisted Ion-Exchange Leaching of Rare Earths from Clay Minerals
by Georgiana Moldoveanu and Vladimiros Papangelakis
Metals 2021, 11(8), 1265; https://doi.org/10.3390/met11081265 - 11 Aug 2021
Cited by 15 | Viewed by 2796
Abstract
The effect of biodegradable chelating agents on the recovery of rare earth elements (REE) from clay minerals via ion-exchange leaching was investigated, with the aim of proposing a cost-effective, enhanced procedure that is environmentally benign and allows high REE recovery while reducing/eliminating ammonium [...] Read more.
The effect of biodegradable chelating agents on the recovery of rare earth elements (REE) from clay minerals via ion-exchange leaching was investigated, with the aim of proposing a cost-effective, enhanced procedure that is environmentally benign and allows high REE recovery while reducing/eliminating ammonium sulfate usage. A processing route employing a lixiviant system consisting of simulated sea water (equivalent to about 0.5 mol/L NaCl) in conjunction with chelating agents was also explored, in order to offer a process alternative for situations with restricted access to fresh water (either due to remote location or to lower the operating costs). Screening criteria for the selection of chelating agents were established and experiments were conducted to assess the efficiency of selected reagents in terms of REE recovery. The results were compared to extraction levels obtained during conventional ion-exchange leaching procedures with ammonium sulfate and simulated sea water only. It was found that stoichiometric addition of N,N′-ethylenediaminedisuccinic acid (EDDS) and nitrilotriacetic acid-trisodium form (NTA-Na3) resulted in 10–20% increased REE extraction when compared to lixiviant only, while achieving moderate Al co-desorption and maintaining neutral pH values in the final solution. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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11 pages, 2712 KiB  
Article
Viscosity and Structural Investigation of High-Concentration Al2O3 and MgO Slag System for FeO Reduction in Electric Arc Furnace Processing
by Youngjae Kim and Dong-Joon Min
Metals 2021, 11(8), 1169; https://doi.org/10.3390/met11081169 - 23 Jul 2021
Cited by 9 | Viewed by 2154
Abstract
In the present study, the viscosity of the CaO–SiO2–FeO–Al2O3–MgO slag system was measured for the recovery of FeO in the electric arc furnace (EAF) process using Al dross. Considering the MgO-saturated operational condition of the EAF, the [...] Read more.
In the present study, the viscosity of the CaO–SiO2–FeO–Al2O3–MgO slag system was measured for the recovery of FeO in the electric arc furnace (EAF) process using Al dross. Considering the MgO-saturated operational condition of the EAF, the viscosity was measured in the MgO-saturated composition at 1823 K with varying FeO and Al2O3 concentrations. An increase in the slag viscosity with decreasing temperature was observed. The activation energy was evaluated, and the change in the thermodynamically equilibrated phase was considered. The changes in the aluminate structure with varying FeO and Al2O3 concentrations were investigated by Fourier-transform infrared spectroscopy, which revealed an increase in the [AlO4] tetrahedral structure with increasing Al2O3 concentration. Depolymerization of the aluminate structure was observed at higher FeO concentrations. The Raman spectra showed the polymerization of the silicate network structure at higher Al2O3 concentrations. By associations between the silicate and aluminate structures, a more highly polymerized slag structure was achieved in the present system by increasing the Al2O3 concentration. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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12 pages, 1201 KiB  
Article
Comparative Studies of Digestion Techniques for the Dissolution of Neodymium-Based Magnets
by Mélodie Bonin, Frédéric-Georges Fontaine and Dominic Larivière
Metals 2021, 11(8), 1149; https://doi.org/10.3390/met11081149 - 21 Jul 2021
Cited by 6 | Viewed by 2489
Abstract
The digestion of neodymium (NdFeB) magnets was investigated in the context of recycling rare earth elements (i.e., Nd, Pr, Dy, and Tb). Among more conventional digestion techniques (microwave digestion, open vessel digestion, and alkaline fusion), focused infrared digestion (FID) was tested as a [...] Read more.
The digestion of neodymium (NdFeB) magnets was investigated in the context of recycling rare earth elements (i.e., Nd, Pr, Dy, and Tb). Among more conventional digestion techniques (microwave digestion, open vessel digestion, and alkaline fusion), focused infrared digestion (FID) was tested as a possible approach to rapidly and efficiently solubilize NdFeB magnets. FID parameters were initially optimized with unmagnetized magnet powder and subsequently used on magnet pieces, demonstrating that the demagnetization and grinding steps are optional. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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14 pages, 4652 KiB  
Article
Leaching of Phosphorus from Quenched Steelmaking Slags with Different Composition
by Ning-Ning Lv, Chuan-Ming Du, Hui Kong and Yao-Hui Yu
Metals 2021, 11(7), 1026; https://doi.org/10.3390/met11071026 - 25 Jun 2021
Cited by 6 | Viewed by 1468
Abstract
Separating P2O5 from steelmaking slag is the key to achieving optimum resource utilization of slag. If the P-concentrating 2CaO∙SiO2–3CaO∙P2O5 solid solution was effectively separated, it can be a potential phosphate resource and the remaining slag [...] Read more.
Separating P2O5 from steelmaking slag is the key to achieving optimum resource utilization of slag. If the P-concentrating 2CaO∙SiO2–3CaO∙P2O5 solid solution was effectively separated, it can be a potential phosphate resource and the remaining slag rich in Fe2O3 and CaO can be reutilized as a flux in steelmaking process. In this study, a low-cost method of selective leaching was adopted, and hydrochloric acid was selected as leaching agent. The dissolution behavior of quenched steelmaking slags with different composition in the acidic solution was investigated and the dissolution mechanism was clarified. It was found that the P dissolution ratio from each slag was higher than those of other elements, achieving an effective separation of P and Fe. The dissolution ratios of P, Ca, and Si decreased as the P2O5 content in slag increased. A higher Fe2O3 content in slag led to a lower P dissolution ratio. Increasing slag basicity facilitated the dissolution of P from slag. The residue mainly composed of matrix phase and the P2O5 content decreased significantly through selective leaching. The P dissolution ratio from slag was primarily determined by the P distribution ratio in the 2CaO∙SiO2–3CaO∙P2O5 solid solution and the precipitation of ferric phosphate in the leachate. The P-concentrating solid solution was effectively separated from quenched steelmaking slag, even though hydrochloric acid was used as leaching agent. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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8 pages, 2079 KiB  
Article
Optimization on Temperature Strategy of BOF Vanadium Extraction to Enhance Vanadium Yield with Minimum Carbon Loss
by Zhen-Yu Zhou and Ping Tang
Metals 2021, 11(6), 906; https://doi.org/10.3390/met11060906 - 2 Jun 2021
Cited by 3 | Viewed by 1777
Abstract
During the vanadium extraction process in basic oxygen furnace (BOF), unduly high temperature is unfavorable to achieve efficient vanadium yield with minimum carbon loss. A new temperature strategy was developed based on industrial experiments. The new strategy applies the selective oxidation temperature between [...] Read more.
During the vanadium extraction process in basic oxygen furnace (BOF), unduly high temperature is unfavorable to achieve efficient vanadium yield with minimum carbon loss. A new temperature strategy was developed based on industrial experiments. The new strategy applies the selective oxidation temperature between carbon and vanadium (Tsl) and the equilibrium temperature of vanadium oxidation and reduction (Teq) for the earlier and middle-late smelting, respectively. Industrial experiments showed 56.9 wt% of V was removed together with carbon loss for 5.6 wt% only in the earlier smelting. Additionally, 30 wt% of vanadium was removed together with carbon loss by 13.4 wt% in middle-late smelting. Applicability analyses confirmed Teq as the high-limit temperature, vanadium removal remains low and carbon loss increased sharply when the molten bath temperature exceeded Teq. With the optimized temperature strategy, vanadium removal increased from 69.2 wt% to 92.3 wt% with a promotion by 23 wt%. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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12 pages, 3414 KiB  
Article
Study on the Extraction and Separation of Zinc, Cobalt, and Nickel Using Ionquest 801, Cyanex 272, and Their Mixtures
by Wensen Liu, Jian Zhang, Zhenya Xu, Jie Liang and Zhaowu Zhu
Metals 2021, 11(3), 401; https://doi.org/10.3390/met11030401 - 1 Mar 2021
Cited by 8 | Viewed by 3328
Abstract
Both Cyanex 272 (bis (2,4,4-trimethylpentyl) phosphinic acid) and Ionquest 801 (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) are commonly used for metal extraction and separation, particularly for zinc, cobalt, and nickel, which are often found together in processing solutions. Detailed metal extractions of zinc, cobalt, [...] Read more.
Both Cyanex 272 (bis (2,4,4-trimethylpentyl) phosphinic acid) and Ionquest 801 (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) are commonly used for metal extraction and separation, particularly for zinc, cobalt, and nickel, which are often found together in processing solutions. Detailed metal extractions of zinc, cobalt, and nickel were studied in this paper using Cya-nex 272, Ionquest 801, and their mixtures. It was found that they performed very similarly in zinc selectivity over cobalt. Cyanex 272 performed much better than Ionquest 801 in cobalt separation from nickel. However, very good separation of them was also obtained with Ionquest 801 at its low concentration with separation factors over 4000, indicating high metal loading of cobalt can significantly suppress nickel extraction. Slop analysis proved that two moles of dimeric extractants were needed for one mole extraction of zinc and cobalt, but three moles were needed for the extraction of one mole nickel. A synergistic effect was found between Cyanex 272 and Ionquest 801 for three metal extractions with the synergistic species of M(AB) determined by the Job’s method. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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18 pages, 9482 KiB  
Article
Hydrometallurgical Leaching of Copper Flash Furnace Electrostatic Precipitator Dust for the Separation of Copper from Bismuth and Arsenic
by Michael Caplan, Joseph Trouba, Corby Anderson and Shijie Wang
Metals 2021, 11(2), 371; https://doi.org/10.3390/met11020371 - 23 Feb 2021
Cited by 8 | Viewed by 2871
Abstract
Flash furnace electrostatic precipitator dust (FF-ESP dust) is a recycle stream in some primary copper production facilities. This dust contains high amounts of copper. In some cases, the FF-ESP dust contains elevated levels of bismuth and arsenic, both of which cause problems during [...] Read more.
Flash furnace electrostatic precipitator dust (FF-ESP dust) is a recycle stream in some primary copper production facilities. This dust contains high amounts of copper. In some cases, the FF-ESP dust contains elevated levels of bismuth and arsenic, both of which cause problems during the electrorefining stages of copper production. Because of this, methods for separation of copper from bismuth and arsenic in FF-ESP dust are necessary. Hydrometallurgical leaching using a number of lixiviants, including sulfuric acid, sulfurous acid, sodium hydroxide, and water, were explored. Pourbaix diagrams of copper, bismuth, and arsenic were used to determine sets of conditions which would thermodynamically separate copper from bismuth and arsenic. The data indicate that water provides the best overall separation between copper and both bismuth and arsenic. Sodium hydroxide provided a separation between copper and arsenic. Sulfurous acid provided a separation between copper and bismuth. Sulfuric acid did not provide any separations between copper and bismuth or copper and arsenic. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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10 pages, 1879 KiB  
Article
Hydrometallurgical Recovery of Cu and Zn from a Complex Sulfide Mineral by Fe3+/H2SO4 Leaching in the Presence of Carbon-Based Materials
by María Luisa Álvarez, José Manuel Fidalgo, Gabriel Gascó and Ana Méndez
Metals 2021, 11(2), 286; https://doi.org/10.3390/met11020286 - 6 Feb 2021
Cited by 11 | Viewed by 3313
Abstract
Chalcopyrite, the main ore of copper, is refractory in sulfuric media with slow dissolution. The most commonly employed hydrometallurgical process for the oxidation of chalcopyrite and copper extraction is the sulfuric acid ferric sulfate system The main objective of the present work is [...] Read more.
Chalcopyrite, the main ore of copper, is refractory in sulfuric media with slow dissolution. The most commonly employed hydrometallurgical process for the oxidation of chalcopyrite and copper extraction is the sulfuric acid ferric sulfate system The main objective of the present work is to study the use of cheap carbon-based materials in the leaching of copper and zinc from a sulfide complex mineral from Iberian Pyrite Belt (IPB). The addition effect of commercial charcoal (VC) and two magnetic biochars (BM and HM) that were obtained by pyrolysis of biomass wastes was compared to that of commercial activated carbon (AC). The experimental results performed in this work have shown that the presence of carbon-based materials significantly influences the kinetics of chalcopyrite leaching in the sulfuric acid ferric sulfate media at 90 °C. The amount of copper and zinc extracted from IPB without the addition of carbon-based material was 63 and 72%, respectively. The highest amount of extracted zinc (>90%) was obtained with the addition of VC and AC in IPB/carbon-based material ratio of 1/0.25 w/w. Moreover, it is possible to recover more than 80% of copper with the addition of VC in a ratio 1/0.25 w/w. Moreover, an optimization of the properties of the carbon-based material for its potential application as catalyst in the leaching of metals from sulfide is necessary. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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11 pages, 3506 KiB  
Article
Enhanced Cementation of Co2+ and Ni2+ from Sulfate and Chloride Solutions Using Aluminum as an Electron Donor and Conductive Particles as an Electron Pathway
by Sanghyeon Choi, Sanghee Jeon, Ilhwan Park, Mayumi Ito and Naoki Hiroyoshi
Metals 2021, 11(2), 248; https://doi.org/10.3390/met11020248 - 2 Feb 2021
Cited by 8 | Viewed by 2170
Abstract
Cobalt and nickel have become important strategic resources because they are widely used for renewable energy technologies and rechargeable battery production. Cementation, an electrochemical deposition of noble metal ions using a less noble metal as an electron donor, is an important option to [...] Read more.
Cobalt and nickel have become important strategic resources because they are widely used for renewable energy technologies and rechargeable battery production. Cementation, an electrochemical deposition of noble metal ions using a less noble metal as an electron donor, is an important option to recover Co and Ni from dilute aqueous solutions of these metal ions. In this study, cementation experiments for recovering Co2+ and Ni2+ from sulfate and chloride solutions (pH = 4) were conducted at 298 K using Al powder as electron donor, and the effects of additives such as activated carbon (AC), TiO2, and SiO2 powders on the cementation efficiency were investigated. Without additives, cementation efficiencies of Co2+ and Ni2+ were almost zero in both sulfate and chloride solutions, mainly because of the presence of an aluminum oxide layer (Al2O3) on an Al surface, which inhibits electron transfer from Al to the metal ions. Addition of nonconductor (SiO2) did not affect the cementation efficiencies of Co2+ and Ni2+ using Al as electron donor, while addition of (semi)conductors such as AC or TiO2 enhanced the cementation efficiencies significantly. The results of surface analysis (Auger electron spectroscopy) for the cementation products when using TiO2/Al mixture showed that Co and Ni were deposited on TiO2 particles attached on the Al surface. This result suggests that conductors such as TiO2 act as an electron pathway from Al to Co2+ and Ni2+, even when an Al oxide layer covered on an Al surface. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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15 pages, 3219 KiB  
Article
Recovery of Cobalt from the Residues of an Industrial Zinc Refinery
by Laurence Boisvert, Keven Turgeon, Jean-François Boulanger, Claude Bazin and Georges Houlachi
Metals 2020, 10(11), 1553; https://doi.org/10.3390/met10111553 - 22 Nov 2020
Cited by 9 | Viewed by 2596
Abstract
The electrolytic production of metallic zinc from processing zinc sulfide concentrates generates a residue containing cadmium, copper, and cobalt that need to be removed from the electrolytic zinc solution because they are harmful to the zinc electro-winning process. This residue is commonly sent [...] Read more.
The electrolytic production of metallic zinc from processing zinc sulfide concentrates generates a residue containing cadmium, copper, and cobalt that need to be removed from the electrolytic zinc solution because they are harmful to the zinc electro-winning process. This residue is commonly sent to other parties that partly recover the contained elements. These elements can generate revenues if recovered at the zinc plant site. A series of laboratory tests were conducted to evaluate a method to process a zinc plant residue with the objective of recovering cobalt into a salable product. The proposed process comprises washing, selective leaching, purifying and precipitation of cobalt following its oxidation. The process allows the production of a cobalt rich hydroxide precipitate assaying 45 ± 4% Co, 0.8 ± 0.2% Zn, 4.4 ± 0.7% Cu, and 0.120 ± 0.004% Cd at a 61 ± 14% Co recovery. Replicating the whole process with different feed samples allowed the identification of the critical steps in the production of the cobalt product; one of these critical steps being the control of the oxidation conditions for the selective precipitation step. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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23 pages, 5368 KiB  
Article
Evaluation of the Use of Electric Arc Furnace Slag and Ladle Furnace Slag in Stone Mastic Asphalt Mixes with Discarded Cellulose Fibers from the Papermaking Industry
by Juan María Terrones-Saeta, Jorge Suárez-Macías, Francisco Javier Iglesias-Godino and Francisco Antonio Corpas-Iglesias
Metals 2020, 10(11), 1548; https://doi.org/10.3390/met10111548 - 21 Nov 2020
Cited by 13 | Viewed by 2561
Abstract
The construction sector is one of the most demanding of raw materials that exist at present. In turn, the greenhouse gas emissions that it produces are important. Therefore, at present there are several lines of research in which industrial by-products are incorporated for [...] Read more.
The construction sector is one of the most demanding of raw materials that exist at present. In turn, the greenhouse gas emissions that it produces are important. Therefore, at present there are several lines of research in which industrial by-products are incorporated for the manufacture of bituminous mixtures and the reduction of CO2 emissions, framed inside the circular economy. On the base of the aforementioned, in this research, bituminous mixtures of the Stone Mastic Asphalt type were developed with electric arc furnace slag, ladle furnace slag and discarded cellulose fibers from the papermaking industry. To this end, the waste is first characterized physically and chemically, and its properties evaluated for use in bituminous mixtures. Later, different groups of samples are conformed with conventional materials and with the waste in order to be able to compare the physical and mechanical properties of the obtained bituminous mixtures. The physical tests carried out were bulk density, maximum density and void index, as well as the Marshall test for the evaluation of the strength and plastic deformations of all the bituminous mixtures manufactured. The study and evaluation of the results showed that the incorporation of slag makes it possible to absorb a greater percentage of bitumen and obtain better mechanical properties, while maintaining a similar deformation and void content. Therefore, it is feasible to use the mentioned slags to create sustainable, resistant and suitable pavements for important traffic. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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19 pages, 3751 KiB  
Article
Selective Recovery of Molybdenum over Rhenium from Molybdenite Flue Dust Leaching Solution Using PC88A Extractant
by Ali Entezari-Zarandi, Dariush Azizi, Pavel Anatolyevich Nikolaychuk, Faïçal Larachi and Louis-César Pasquier
Metals 2020, 10(11), 1423; https://doi.org/10.3390/met10111423 - 26 Oct 2020
Cited by 10 | Viewed by 3028
Abstract
Selective solvent extraction of molybdenum over rhenium from molybdenite (MoS2) flue dust leaching solution was studied. In the present work, thermodynamic calculations of the chemical equilibria in aqueous solution were first performed, and the potential–pH diagram for the Mo–Re– [...] Read more.
Selective solvent extraction of molybdenum over rhenium from molybdenite (MoS2) flue dust leaching solution was studied. In the present work, thermodynamic calculations of the chemical equilibria in aqueous solution were first performed, and the potential–pH diagram for the Mo–Re–SO42−–H2O system was constructed. With the gained insight on the system, 2-ethylhexyl phosphonic acid mono-(2-ethylhexyl)-ester (PC88A) diluted in kerosene was used as the extractant agent. Keeping constant the reaction temperature and aqueous-to-organic phase ratio (1:1), organic phase concentration and pH were the studied experimental variables. It was observed that by increasing the acidity of the solution and extractant concentration, selectivity towards Mo extraction increased, while the opposite was true for Re extraction. Selective Mo removal (+95%) from leach solution containing ca. 9 g/L Mo and 0.5 g/L Re was achieved when using an organic phase of 5% PC88A at pH = 0. No rhenium was coextracted during 10 min of extraction time at room temperature. Density functional theory (DFT) calculations were performed in order to study the interactions of organic extractants with Mo and Re ions, permitting a direct comparison of calculation results with the experimental data to estimate selectivity factors in Mo–Re separation. For this aim, PC88A and D2EHPA (di-(2-ethylhexyl) phosphoric acid) were simulated. The interaction energies of D2EHPA were shown to be higher than those of PC88A, which could be due to its stronger capability for complex formation. Besides, it was found that the interaction energies of both extractants follow this trend considering Mo species: MoO22+ > MoO42−. It was also demonstrated through DFT calculations that the interaction energies of D2EHPA and PC88A with species are based on these trends, respectively: MoO22+ > MoO42− > ReO4− and MoO22+ > ReO4− > MoO42−, in qualitative agreement with the experimental findings. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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16 pages, 2047 KiB  
Article
Hydrometallurgical Process and Economic Evaluation for Recovery of Zinc and Manganese from Spent Alkaline Batteries
by Lan-Huong Tran, Kulchaya Tanong, Ahlame Dalila Jabir, Guy Mercier and Jean-François Blais
Metals 2020, 10(9), 1175; https://doi.org/10.3390/met10091175 - 1 Sep 2020
Cited by 16 | Viewed by 5193
Abstract
An innovative, efficient, and economically viable process for the recycling of spent alkaline batteries is presented herein. The developed process allows for the selective recovery of Zn and Mn metals present in alkaline batteries. The hydrometallurgical process consists of a physical pre-treatment step [...] Read more.
An innovative, efficient, and economically viable process for the recycling of spent alkaline batteries is presented herein. The developed process allows for the selective recovery of Zn and Mn metals present in alkaline batteries. The hydrometallurgical process consists of a physical pre-treatment step for separating out the metal powder containing Zn and Mn, followed by a chemical treatment step for the recovery of these metals. Sulfuric acid was used for the first leaching process to dissolve Zn(II) and Mn(II) into the leachate. After purification, Mn was recovered in the form of MnO2, and Zn in its metal form. Furthermore, during the second sulfuric acid leaching, Na2S2O5 was added for the conversion of Mn(IV) to Mn(II) (soluble in the leachate), allowing Mn to be recovered as MnCO3. Masses of 162 kg of Zn metal and 215 kg of Mn (both in the form of MnO2 and MnCO3) were recovered from one ton of spent alkaline batteries. The direct operating costs (chemicals, labor operation, utilities, energy) and indirect costs (amortization, interest payment) required for a plant treating 8 tons of spent batteries per day was calculated to be $CAD 726 and $CAD 534 per ton, respectively, while the total revenue from the sale of the metals was calculated at $CAD 1359.6 per ton of spent batteries. The development of this type of cost-effective industrial process is necessary for a circular economy, as it contributes to addressing environment- and energy-related issues, and creates opportunities for the economic utilization of metals. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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9 pages, 2663 KiB  
Article
Removal of Metallic Iron from Reduced Ilmenite by Aeration Leaching
by Qiuyue Zhao, Maoyuan Li, Lei Zhou, Mingzhao Zheng and Ting’an Zhang
Metals 2020, 10(8), 1020; https://doi.org/10.3390/met10081020 - 29 Jul 2020
Cited by 4 | Viewed by 3027
Abstract
Aeration leaching was used to obtain synthetic rutile from a reduced ilmenite. The reduced ilmenite, obtained from the carbothermic reduction of ilmenite concentrate in a rotary kiln at about 1100 °C, contained 62.88% TiO2 and 28.93% Metallic iron. The particle size was [...] Read more.
Aeration leaching was used to obtain synthetic rutile from a reduced ilmenite. The reduced ilmenite, obtained from the carbothermic reduction of ilmenite concentrate in a rotary kiln at about 1100 °C, contained 62.88% TiO2 and 28.93% Metallic iron. The particle size was about 200 μm and the size distribution was uniform. The effects of NH4Cl and HCl concentrations, stirring speed, and aeration leaching time on the extent of removal of metallic iron from the reduced ilmenite were studied at room temperature. The results revealed that aeration leaching is feasible at room temperature. When using the NH4Cl system, the metallic iron content was reduced to 1.98% in synthetic rutile, but the TiO2 content only reached 69.16%. Higher NH4Cl concentration did not improve the leaching. Using 2% NH4Cl with 3% HCl, we were able to upgrade the synthetic rutile to 75%, with a metallic iron content as low as 0.14% and a total iron content of about 4%. Synthetic rutile could be upgraded to about 90% using HCl solution alone. HCl and NH4Cl are both effective on the aeration leaching process. However, within the scope of this experiment, hydrochloric acid is more efficient in aeration leaching. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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15 pages, 5243 KiB  
Article
Recovery of Rubidium and Cesium Resources from Brine of Desalination through t-BAMBP Extraction
by Wei-Sheng Chen, Cheng-Han Lee, Yi-Fan Chung, Ko-Wei Tien, Yen-Jung Chen and Yu-An Chen
Metals 2020, 10(5), 607; https://doi.org/10.3390/met10050607 - 8 May 2020
Cited by 35 | Viewed by 4447
Abstract
50 billion cubic meters of brine every year creates ecological hazards to the environment. In order to reuse brine efficiently, rubidium and cesium were recovered in this experiment. On the other hand, the main impurities which were needed to be eliminated in brine [...] Read more.
50 billion cubic meters of brine every year creates ecological hazards to the environment. In order to reuse brine efficiently, rubidium and cesium were recovered in this experiment. On the other hand, the main impurities which were needed to be eliminated in brine were lithium, sodium, potassium, calcium, and magnesium. In the procedure, seawater was distilled and evaporated first to turn into simulated brine. Perchloric acid was then added into simulated brine to precipitate potassium perchlorate which could reduce the influence of potassium in the extraction procedure. After that, t-BAMBP and ammonia were separately used as extractant and stripping agent in the extraction and stripping procedures to get rubidium hydroxide solutions and cesium hydroxide solutions. Subsequently, they reacted with ammonium carbonate to get rubidium carbonate and cesium carbonate. In a nutshell, this study shows the optimal parameters of pH value to precipitate potassium perchlorate. Besides, pH value in the system, the concentration of t-BAMBP and ammonia, organic phase/aqueous phase ratio (O/A ratio), reaction time, and reaction temperature in solvent extraction step were investigated to get high purities of rubidium carbonate and cesium carbonate. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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Review

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22 pages, 2885 KiB  
Review
Separation of Radioactive Elements from Rare Earth Element-Bearing Minerals
by Adrián Carrillo García, Mohammad Latifi, Ahmadreza Amini and Jamal Chaouki
Metals 2020, 10(11), 1524; https://doi.org/10.3390/met10111524 - 17 Nov 2020
Cited by 38 | Viewed by 8423
Abstract
Rare earth elements (REE), originally found in various low-grade deposits in the form of different minerals, are associated with gangues that have similar physicochemical properties. However, the production of REE is attractive due to their numerous applications in advanced materials and new technologies. [...] Read more.
Rare earth elements (REE), originally found in various low-grade deposits in the form of different minerals, are associated with gangues that have similar physicochemical properties. However, the production of REE is attractive due to their numerous applications in advanced materials and new technologies. The presence of the radioactive elements, thorium and uranium, in the REE deposits, is a production challenge. Their separation is crucial to gaining a product with minimum radioactivity in the downstream processes, and to mitigate the environmental and safety issues. In the present study, different techniques for separation of the radioactive elements from REE are reviewed, including leaching, precipitation, solvent extraction, and ion chromatography. In addition, the waste management of the separated radioactive elements is discussed with a particular conclusion that such a waste stream can be employed as a valuable co-product. Full article
(This article belongs to the Special Issue Recovery and Recycling of Valuable Metals)
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