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Metals
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Valuable Metal Recycling
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Valuable Metal Recycling

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

Deadline for manuscript submissions: closed (31 August 2017) | Viewed by 105212

Special Issue Editors

Dr. Jae-Chun Lee

E-Mail Website
Guest Editor
1. Resources Recycling, Korea University of Science and Technology, Daejeon 34113, Republic of Korea
2. Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Republic of Korea
Interests: leaching, separation, and purification of metals from primary and secondary resources; material preparation by aqueous processing; recycling of valuable metals from industrial waste and waste electric and electronic equipment (WEEE) by hydrometallurgical routes
Special Issues, Collections and Topics in MDPI journals
Dr. Bong-Gyoo Cho

E-Mail Website
Guest Editor
R&D Center for Valuable Recycling, Korea
Interests: development of recycling processes in commercial scales and help to launch small business recycling companies
Prof. Dr. Kyoungkeun Yoo

E-Mail Website
Guest Editor
Department of Energy and Resources Engineering, Korea Maritime and Ocean University, Busan, Korea
Interests: hydrometallurgy; leaching; recycling; mineral processing; space mining; smart factory

Special Issue Information

Dear Colleagues,

This Special Issue focuses on valuable metal recycling through the recovery or removal of metals from all secondary resources, such as E-waste, scraps, slag, tailings, or other similar materials, contaminated soil, and wastewater, using mineral processing, hydrometallurgical, and pyrometallurgical processes. This Special Issue is open to research supported by the R&D Center for Valuable Recycling, funded by the Ministry of Environment, Korea, but we also welcome any academic and industrial articles related with the above-mentioned research subjects.

Dr. Jae-chun Lee
Dr. Bong-Gyoo Cho
Dr. Kyoungkeun Yoo
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.

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Published Papers (17 papers)

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Editorial

Jump to: Research, Review

4 pages, 185 KiB  
Editorial
Valuable Metal Recycling
by Bong-Gyoo Cho, Jae-chun Lee and Kyoungkeun Yoo
Metals 2018, 8(5), 345; https://doi.org/10.3390/met8050345 - 11 May 2018
Cited by 3 | Viewed by 3099
Abstract
As the global economy grows, demand for metal continues to increase. Unfortunately, metal resources are in limited supply [...]
Full article
(This article belongs to the Special Issue Valuable Metal Recycling)

Research

Jump to: Editorial, Review

6 pages, 1345 KiB  
Article
Fabrication of Nickel Nanosized Powder from LiNiO2 from Spent Lithium-Ion Battery
by Shun-Myung Shin, Dong-Won Lee and Jei-Pil Wang
Metals 2018, 8(1), 79; https://doi.org/10.3390/met8010079 - 21 Jan 2018
Cited by 9 | Viewed by 4403
Abstract
In this study, a fabrication of nickel nanoparticles from LNO(LiNiO2), which is a cathode active material, was synthesized by the liquid reduction process of NiSO4, obtained through a leaching and purification process. Hydrazine monohydrate (N2H4·H [...] Read more.
In this study, a fabrication of nickel nanoparticles from LNO(LiNiO2), which is a cathode active material, was synthesized by the liquid reduction process of NiSO4, obtained through a leaching and purification process. Hydrazine monohydrate (N2H4·H2O) was used as a liquid reducing agent and it was added to NiSO4 at a volume ratio of NiSO4:N2H4·H2O = 10:3 and reacted for 10 min to synthesize the nickel hydrazine complex. Sodium hydroxide was added to the nickel hydrazine complex at the weight ratio of NiSO4:NaOH = 10:1.25–1.5 and the reduction reaction was performed at 80 °C for 15 min to synthesize nickel particles. Synthesized nickel particles were agglomerated and had a mean size of 200 nm to 300 nm. Ultrasonic dispersion, which is a physical dispersion method, was conducted. The nickel had particles of 100 nm or less when dispersed for 2 h at an ultrasonic intensity of 40 kHz. In order to prevent the agglomeration of the dispersed particles again, polyvinylpyrrolidone (PVP), an interfacial stabilizer, was added to stabilize the dispersed particles. It was confirmed that the nanoparticles were stably retained when PVP was added in an amount of 1 to 2 wt % based on the weight of the nickel. The purity of nickel recovered was found to be 99.62 wt %. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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1949 KiB  
Article
Application of Co and Mn for a Co-Mn-Br or Co-Mn-C2H3O2 Petroleum Liquid Catalyst from the Cathode Material of Spent Lithium Ion Batteries by a Hydrometallurgical Route
by Sung-Ho Joo, Dong Ju Shin, Chang Hyun Oh, Je-Pil Wang, Jin Tae Park and Shun Myung Shin
Metals 2017, 7(10), 439; https://doi.org/10.3390/met7100439 - 18 Oct 2017
Cited by 6 | Viewed by 4978
Abstract
We investigated the preparation of CMB (cobalt-manganese-bromide) and CMA (cobalt-manganese-acetate) liquid catalysts as petroleum liquid catalysts by simultaneously recovering Co and Mn from spent Li-ion battery cathode material. To prepare the liquid catalysts, the total preparation process for the liquid catalysts consisted of [...] Read more.
We investigated the preparation of CMB (cobalt-manganese-bromide) and CMA (cobalt-manganese-acetate) liquid catalysts as petroleum liquid catalysts by simultaneously recovering Co and Mn from spent Li-ion battery cathode material. To prepare the liquid catalysts, the total preparation process for the liquid catalysts consisted of physical pre-treatments, such as grinding and sieving, and chemical processes, such as leaching, solvent extraction, and stripping. In the physical pre-treatment process, over 99% of Al was removed from material with a size of less than 0.42 mm. In the chemical process, the leaching solution as obtained under the following conditions: 2 mol/L sulfuric acid, 10 vol % H2O2, 0.1 of solid/liquid ratio, and 60 °C. In the solvent extraction process, the optimum concentration of bis (2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272), the equilibrium pH, the degree of saponification, the organic phase/aqueous phase ratio isotherm, and the stripping study for the extraction of Co and Mn were investigated. As a result, Co and Mn were recovered by 0.85 M Cyanex 272 with 50% saponification in counter current two extraction stages. Finally, a CMB and CMA liquid catalyst containing 33.1 g/L Co, 29.8 g/L Mn, and 168 g/L Br and 12.67 g/L Co, 12.0 g/L Mn, and 511 g/L C2H3O2, respectively, was produced by 2 M hydrogen bromide and 50 vol % acetic acid; it was also found that a shortage in the concentration can be compensated with cobalt and manganese salts. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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4778 KiB  
Article
Trajectory Analysis of Copper and Glass Particles in Electrostatic Separation for the Recycling of ASR
by Beom-uk Kim, Oh-hyung Han, Ho-seok Jeon, Sang-ho Baek and Chul-hyun Park
Metals 2017, 7(10), 434; https://doi.org/10.3390/met7100434 - 17 Oct 2017
Cited by 9 | Viewed by 6123
Abstract
Automobile-shredder-residue (ASR) recycling techniques have been widely applied for improving the total recycling rate of end-of-life vehicles. In this study, to obtain useful information for predicting or improving ASR-separation efficiency, trajectory analyses of conductors (copper) and non-conductors (glass) were performed using a lab-scale [...] Read more.
Automobile-shredder-residue (ASR) recycling techniques have been widely applied for improving the total recycling rate of end-of-life vehicles. In this study, to obtain useful information for predicting or improving ASR-separation efficiency, trajectory analyses of conductors (copper) and non-conductors (glass) were performed using a lab-scale induction electrostatic separator. The copper-wire trajectories obtained showed a good agreement depending significantly on the electric field strength and particle size. The observed copper-wire trajectories showed consistent congruity with the coarse-particles simulation (0.5 and 0.25 mm). The observed fine-particles (0.06 mm) trajectory was deflected toward the (−) attractive electrode, owing to the charge density effects due to the particle characteristics and relative humidity. This results in superior separation performance because more copper enters the conductor products bin. The actual dielectric-glass trajectory was deflected toward the (−) attractive electrode, thus showing characteristics similar to conductive-particle characteristics. Through analyses conducted using a stereoscopic microscope, scanning electron microscope, and energy dispersive spectroscope, we found heterogeneous materials (fine ferrous particles and conductive organics) on the glass surface. This demonstrates the separation-efficiency decrease for non-ferrous metals during electrostatic separation in the recycling of ASR. Future work should include a pretreatment process for eliminating impurities from the glass and advanced trajectory-simulation processes. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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1519 KiB  
Communication
Novel Recycling Method for Boron Removal from Silicon by Thermal Plasma Treatment Coupled with Steam and Hydrogen Gases
by Su-Hyun Baek, Hyunjae Lee, Dong-Joon Min, Su-Ji Choi, Byung-Moon Moon and Hyun-Do Jung
Metals 2017, 7(10), 401; https://doi.org/10.3390/met7100401 - 29 Sep 2017
Cited by 5 | Viewed by 4549
Abstract
Boron (B) separation from photovoltaic silicon (Si) remains a research challenge in the recycling field. In this study, a novel B-removal process was developed using thermal plasma treatment coupled with steam and hydrogen gases. Experiments were performed on artificially B-doped Si using various [...] Read more.
Boron (B) separation from photovoltaic silicon (Si) remains a research challenge in the recycling field. In this study, a novel B-removal process was developed using thermal plasma treatment coupled with steam and hydrogen gases. Experiments were performed on artificially B-doped Si using various plasma conditions of mixed argon (Ar)/steam/hydrogen gases and varied refining time. The B concentration in all of the samples decreased with increasing refining time. The use of the plasma mixed with Ar/steam/hydrogen gases resulted in a significant improvement of the efficiency of B removal compared with the Ar/steam plasma refining. In addition, with increasing steam content in the plasma with mixed Ar/steam/hydrogen gases, the B-removal rates increased. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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6548 KiB  
Article
The Effects of Incorporated Sn in Resynthesized Ni-Rich Cathode Materials on Their Lithium-Ion Battery Performance
by Ga-hee Kang, Ko-woon Lee, Kyungjung Kwon and Junho Song
Metals 2017, 7(10), 395; https://doi.org/10.3390/met7100395 - 26 Sep 2017
Cited by 19 | Viewed by 6056
Abstract
LiNixCoyMnz (NCM), one of the most promising candidates for high-capacity cathode materials in Li-ion batteries (LIBs), is synthesized with various amounts of Sn. Sn-incorporated NCM from the resynthesis of NMC in leach liquor containing Sn from spent LIBs [...] Read more.
LiNixCoyMnz (NCM), one of the most promising candidates for high-capacity cathode materials in Li-ion batteries (LIBs), is synthesized with various amounts of Sn. Sn-incorporated NCM from the resynthesis of NMC in leach liquor containing Sn from spent LIBs is characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, particle strength tests, and electrochemical tests. Sn-incorporated NCM has a globular form, and the uniform distribution of Sn inside cathode materials is confirmed. As Sn is introduced, the (003) diffraction peak tends to shift to a smaller angle and particle breaking strength increases. It is found that Sn-incorporated cathode active materials have better cycle performance and rate capability than pristine cathode active material although the discharge capacity slightly decreases. Because there is a trade-off between decreased discharge capacity and improved cycling and rate performance, the incorporation of Sn in resynthesized NCM should be carefully designed and conducted. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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1902 KiB  
Article
Environmental Compatibility of Lightweight Aggregates from Mine Tailings and Industrial Byproducts
by Won Jung Ju, Doyun Shin, Hyunsik Park and Kyoungphile Nam
Metals 2017, 7(10), 390; https://doi.org/10.3390/met7100390 - 25 Sep 2017
Cited by 7 | Viewed by 3670
Abstract
A lightweight aggregate was produced by sintering the mixture of gold mine tailings, red mud, and limestone at 1150 °C. The physical (i.e., skid resistance, abrasion resistance, and bond strength) and environmental (i.e., leachability) feasibility of this aggregate was assessed to consider its [...] Read more.
A lightweight aggregate was produced by sintering the mixture of gold mine tailings, red mud, and limestone at 1150 °C. The physical (i.e., skid resistance, abrasion resistance, and bond strength) and environmental (i.e., leachability) feasibility of this aggregate was assessed to consider its potential use as a construction material for bicycle lanes. The skid resistance (British pendulum number of 71) and bond strength (1.5 N·mm−2) of the aggregate were found to be appropriate for this use. However, the abrasion loss value of the aggregate was found to be 290 mg, which exceeds the limit of Korean Standard KS F 281 (200 mg). Heavy metals were found to not leach from the aggregate in various leaching tests. These include Korean (Korea Standard Method for Solid Waste), American (Toxic Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure (SPLP)), and European (BS EN 12457-1) leaching tests, despite the raw materials containing significant amounts of Pb, As, and F. However, leachate extracted from the aggregate exhibited an aquatic toxicity to Daphnia magna of 13.94 TU24hr and 14.25 TU48hr, most likely due to a high pH and Ca concentration originating from the free CaO present in the aggregate. The data suggests that the physical properties of the reconstructed aggregate are appropriate for use in bicycle lane construction, however the dissolution of Ca and the pH level of the leachate need to be controlled to protect aquatic ecosystems. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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3206 KiB  
Article
An Eco-Friendly Neutralization Process by Carbon Mineralization for Ca-Rich Alkaline Wastewater Generated from Concrete Sludge
by Jongchan Yoo, Heeyoung Shin and Sangwoo Ji
Metals 2017, 7(9), 371; https://doi.org/10.3390/met7090371 - 13 Sep 2017
Cited by 18 | Viewed by 6435
Abstract
Waste-concrete recycling processes using wet-based crushing methods inevitably generate a large amount of alkaline concrete sludge, as well as wastewater, which contains abundant Ca ions. The Ca-rich alkaline wastewater must then be neutralized for reuse in the waste-concrete recycling process. In this study, [...] Read more.
Waste-concrete recycling processes using wet-based crushing methods inevitably generate a large amount of alkaline concrete sludge, as well as wastewater, which contains abundant Ca ions. The Ca-rich alkaline wastewater must then be neutralized for reuse in the waste-concrete recycling process. In this study, the feasibility of a carbon mineralization process for the neutralization of alkaline wastewater was considered from both environmental and economic perspectives. The optimal reaction time, efficiency of Ca removal and CO2 sequestration as a function of the CO2 gas flow rate were assessed. The carbon mineralization process resulted in sequestering CO2 (85–100% efficiency) and removing Ca from the solution (84–99%) by precipitating pure CaCO3. Increasing the gas flow rate reduced the reaction time (65.0 down to 3.4 min for 2.5 L of solution), but decreased CO2 sequestration (from 463.3 down to 7.3 mg CO2 for 2.5 L of solution). Optimization of the gas flow rate is essential for efficient CO2 sequestration, Ca removal, CaCO3 production and, therefore, successful wastewater neutralization following the wet-based crushing process. The method presented here is an eco-friendly and economically viable substitute for dealing with alkaline wastewater. It may also provide a practical guide for the design of carbon mineralization processes for the neutralization of alkaline solutions containing large amounts of Ca. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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4904 KiB  
Article
Effect of Pyrite on Thiosulfate Leaching of Gold and the Role of Ammonium Alcohol Polyvinyl Phosphate (AAPP)
by Xiaoliang Liu, Bin Xu, Xin Min, Qian Li, Yongbin Yang, Tao Jiang, Yinghe He and Xi Zhang
Metals 2017, 7(7), 278; https://doi.org/10.3390/met7070278 - 19 Jul 2017
Cited by 28 | Viewed by 5578
Abstract
The effect of pyrite and the role of ammonium alcohol polyvinyl phosphate (AAPP) during gold leaching in ammoniacal thiosulfate solutions were investigated using pure gold foils. The results showed that pyrite catalyzed the decomposition and also significantly increased the consumption of thiosulfate. This [...] Read more.
The effect of pyrite and the role of ammonium alcohol polyvinyl phosphate (AAPP) during gold leaching in ammoniacal thiosulfate solutions were investigated using pure gold foils. The results showed that pyrite catalyzed the decomposition and also significantly increased the consumption of thiosulfate. This detrimental effect became more severe with increasing pyrite content. Further, the presence of pyrite also substantially slowed the gold leaching kinetics and reduced the overall gold dissolution. The reduction in gold dissolution was found to be caused primarily by the surface passivation of the gold. The negative effects of pyrite, however, can be alleviated by the addition of AAPP. Comparison of zeta potentials of pyrite with and without AAPP suggests that AAPP had adsorbed on the surface of the pyrite and weakened the catalytic effect of pyrite on the thiosulfate decomposition by blocking the contact between the pyrite and thiosulfate anions. AAPP also competed with thiosulfate anions to complex with the cupric ion at the axial coordinate sites, and thus abated the oxidation of thiosulfate by cupric ions. Moreover, the indiscriminate adsorption of AAPP on the surfaces of gold and passivation species prevented the passivation of the gold surface by surface charge and electrostatic repulsion. Therefore, AAPP effectively stabilized the thiosulfate in the solution and facilitated the gold leaching in the presence of pyrite. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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4646 KiB  
Article
An Efficient Approach for Lithium and Aluminum Recovery from Coal Fly Ash by Pre-Desilication and Intensified Acid Leaching Processes
by Shenyong Li, Shenjun Qin, Lianwei Kang, Jianjun Liu, Jing Wang and Yanheng Li
Metals 2017, 7(7), 272; https://doi.org/10.3390/met7070272 - 14 Jul 2017
Cited by 36 | Viewed by 7246
Abstract
A novel technique was developed for the recovery of lithium and aluminum from coal fly ash using a combination of pre-desilication and an intensified acid leaching process. The main components of the high-aluminum fly ash were found to be Al2O3 [...] Read more.
A novel technique was developed for the recovery of lithium and aluminum from coal fly ash using a combination of pre-desilication and an intensified acid leaching process. The main components of the high-aluminum fly ash were found to be Al2O3 and SiO2, and the Al/Si ratio increased from 1.0 to 1.5 after desiliconization. The lithium content of the coal fly ash met national recycling standards. The optimal acid leaching conditions, under which the leaching efficiencies of lithium and aluminum were 82.23% and 76.72%, respectively, were as follows: 6 mol/L HCl, 1:20 solid to liquid ratio, 120 °C and 4 h. During the hydrochloric acid pressure leaching process, spherical particles of desilicated fly ash were decomposed into flakes. Part of the mullite phase was dissolved, and most of the glass phase leached into the liquor. The generation of the silicates hindered lithium transport, which decreased the leaching rate of lithium. This work suggests that the preprocessing is a promising option for effective recovery of high-aluminum and fly ash-associated lithium. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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3969 KiB  
Article
Leaching Kinetics of Hemimorphite in Ammonium Chloride Solution
by Duoqiang Zhao, Shenghai Yang, Yongming Chen, Chaobo Tang, Jing He and Hao Li
Metals 2017, 7(7), 237; https://doi.org/10.3390/met7070237 - 28 Jun 2017
Cited by 14 | Viewed by 4521
Abstract
The leaching kinetics of hemimorphite (Zn4Si2O7(OH)2·H2O) in ammonium chloride solution was presented in detail. Effects of stirring speed (150–350 rpm), leaching temperature (75–108 °C), particle size of hemimorphite (45–150 μm), and the concentration [...] Read more.
The leaching kinetics of hemimorphite (Zn4Si2O7(OH)2·H2O) in ammonium chloride solution was presented in detail. Effects of stirring speed (150–350 rpm), leaching temperature (75–108 °C), particle size of hemimorphite (45–150 μm), and the concentration of ammonium chloride (3.5–5.5 mol/L) on the zinc extraction rate were studied. The zinc extraction rate enhanced slightly with the increase in stirring speed, but increased significantly with an increase in the leaching temperature and ammonium chloride concentration. Zinc extraction was enhanced significantly in the first 60 min with decreasing particle size, but had little effect on the leaching process after 60 min. Scanning electron microscopy (SEM) analysis showed that some silica gel formed in the leaching process was not separated from the hemimorphite surface, but covered some of the active particle surface. The Elovich equation successfully described the leaching kinetics of hemimorphite in ammonium chloride solution with an apparent activation energy of 405.14 kJ/mol at temperatures of 75–90 °C and 239.61 kJ/mol at temperatures of 95–108 °C, which is characteristic for a chemically-controlled process. Silica gel is generated at temperatures of 75–90 °C and decomposed into silica at temperatures of 95–108 °C. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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10099 KiB  
Article
Separation and Recovery of Iron and Rare Earth from Bayan Obo Tailings by Magnetizing Roasting and (NH4)2SO4 Activation Roasting
by Yan Zhou, He Yang, Xiang-xin Xue and Shuai Yuan
Metals 2017, 7(6), 195; https://doi.org/10.3390/met7060195 - 27 May 2017
Cited by 24 | Viewed by 6571
Abstract
A novel approach for recovery of iron and rare earth elements (REEs) from Bayan Obo tailings of Baotou, China, was developed by combining magnetizing roasting, magnetic separation, (NH4)2SO4 activation roasting, and water leaching. Thermodynamic analysis of carbothermal reduction [...] Read more.
A novel approach for recovery of iron and rare earth elements (REEs) from Bayan Obo tailings of Baotou, China, was developed by combining magnetizing roasting, magnetic separation, (NH4)2SO4 activation roasting, and water leaching. Thermodynamic analysis of carbothermal reduction was conducted to determine the temperature of magnetizing roasting, and it agreed well with the experimental results. The maximum recovery of Fe reached 77.8% at 600 °C, and the grade of total Fe in the magnetic concentrate was 56.3 wt. %. An innovative approach, using water to leach REEs after (NH4)2SO4 activation roasting, was used to extract REEs from magnetic separation tailings. The main influence factors of the leaching recovery during (NH4)2SO4 activation roasting, were investigated with the mass ratio of (NH4)2SO4 to magnetic separation tailings, roasting temperature and roasting time. The leaching recoveries of La, Ce and Nd reached 83.12%, 76.64% and 77.35%, respectively, under the optimized conditions: a mass ratio of 6:1, a roasting temperature of 400 °C and a roasting time of 80 min. Furthermore, the phase composition and reaction process during the (NH4)2SO4 activation roasting were analyzed with X-ray diffraction (XRD), energy dispersive X-ray spectroscopy & scanning electron microscopy (EDS-SEM) and thermogravimetry & differential scanning calorimetry (TG-DSC), and the leaching solution and leaching residue were also characterized. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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2749 KiB  
Article
Preparation of Highly Pure Vanadyl Sulfate from Sulfate Solutions Containing Impurities of Iron and Aluminum by Solvent Extraction Using EHEHPA
by Dan Li, Desheng Chen, Guozhi Zhang, Hongxin Zhao, Tao Qi, Weijing Wang, Lina Wang and Yahui Liu
Metals 2017, 7(3), 106; https://doi.org/10.3390/met7030106 - 22 Mar 2017
Cited by 13 | Viewed by 6119
Abstract
The preparation of highly pure vanadyl sulfate from sulfate solutions containing impurities of iron and aluminumwas investigated by solvent extraction with 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (EHEHPA) and tri-n-butyl phosphate (TBP) as the phase modifier. The extraction and stripping conditions of [...] Read more.
The preparation of highly pure vanadyl sulfate from sulfate solutions containing impurities of iron and aluminumwas investigated by solvent extraction with 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (EHEHPA) and tri-n-butyl phosphate (TBP) as the phase modifier. The extraction and stripping conditions of vanadium (IV) and its separation from iron and aluminum were optimized. Under the optimal extraction conditions, the extraction of vanadium (IV) and iron were 68% and 53%, respectively, while only 2% aluminum was extracted in a single contact, suggesting good separation of vanadium (IV) from aluminum. Sulfuric acid solution was used for the stripping. Nearly 100% vanadium (IV) and 95% aluminum were stripped, while only 10% iron was stripped under the optimal stripping conditions in a single contact, suggesting good separation of vanadium (IV) from iron. After five stages of extraction and stripping, highly pure vanadyl sulfate containing 76.5 g/L V (IV) with the impurities of 12 mg/L Fe and 10 mg/L Al was obtained, which is suitable for the electrolyte of a vanadium redox flow battery. Organic solution was well regenerated after stripping by oxalic acid solution to remove the remaining iron. The mechanism of vanadium (IV) extraction using EHEHPA was also discussed based on the Fourier transform infrared spectroscopy (FT-IR) analysis. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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3109 KiB  
Article
Urban Mining and Electrochemistry: Cyclic Voltammetry Study of Acidic Solutions from Electronic Wastes (Printed Circuit Boards) for Recovery of Cu, Zn, and Ni
by Ma. Isabel Reyes‐Valderrama, Eleazar Salinas‐Rodríguez, J. Fabian Montiel‐Hernández, Isauro Rivera‐Landero, Eduardo Cerecedo‐Sáenz, Juan Hernándezvila and Alberto Arenas‐Flores
Metals 2017, 7(2), 55; https://doi.org/10.3390/met7020055 - 13 Feb 2017
Cited by 9 | Viewed by 5739
Abstract
We report potentiodynamic studies to characterize copper, nickel and zinc leaching solutions from electronic waste. The metals were leached using oxygen and sulfuric acid (pH = 1.5). As is known, reduction potentials are determined using thermodynamics laws, and metal recovery strategies from electronic [...] Read more.
We report potentiodynamic studies to characterize copper, nickel and zinc leaching solutions from electronic waste. The metals were leached using oxygen and sulfuric acid (pH = 1.5). As is known, reduction potentials are determined using thermodynamics laws, and metal recovery strategies from electronic waste are usually considered according these thermodynamic values. Pourbaix‐type diagrams are not appropriate to plan strategies in electrochemical processing. Therefore, knowledge of electrode potentials for the metal deposit/dissolution process is the basis for the selective recovery planning. For this reason, potentiodynamic studies, specifically cyclic voltammetry, are revealed as a good way to decide the best conditions for the process of electrochemical recovery of metals from electronic waste, which is also cost‐efficient and has no interference from strange ions, such as lead, in this case. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Review

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696 KiB  
Review
Magnetic Adsorbents for the Recovery of Precious Metals from Leach Solutions and Wastewater
by Elham Aghaei, Richard Diaz Alorro, Ashly N. Encila and Kyoungkeun Yoo
Metals 2017, 7(12), 529; https://doi.org/10.3390/met7120529 - 27 Nov 2017
Cited by 55 | Viewed by 8235
Abstract
Precious metals which include the platinum group, gold, and silver, play indispensable roles in high technology industries of the modern world due to their outstanding physical and chemical properties. As a result of diminishing availability of mineral sources, increasing demand, and environmental concerns, [...] Read more.
Precious metals which include the platinum group, gold, and silver, play indispensable roles in high technology industries of the modern world due to their outstanding physical and chemical properties. As a result of diminishing availability of mineral sources, increasing demand, and environmental concerns, the recovery of precious metals from both leaching and industrial waste solutions is becoming a very important technology. Magnetic solid phase extraction (MSPE) is a technique that has received substantial consideration in the separation and recovery of precious metals because of the many advantages it offers compared to conventional methods. This technique is based on the extraction of different analytes from solutions using solid adsorbents with magnetic properties. This review focuses on different types of magnetic adsorbents, the main procedures used for synthesis, characterization and their application in precious metals recovery based on recently published literatures. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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1415 KiB  
Review
A Review of Thiosulfate Leaching of Gold: Focus on Thiosulfate Consumption and Gold Recovery from Pregnant Solution
by Bin Xu, Wenhao Kong, Qian Li, Yongbin Yang, Tao Jiang and Xiaoliang Liu
Metals 2017, 7(6), 222; https://doi.org/10.3390/met7060222 - 15 Jun 2017
Cited by 118 | Viewed by 12987
Abstract
Thiosulfate leaching is a promising alternative to cyanidation, and the main hindrances for its wide commercial application are the high thiosulfate consumption and the difficult recovery of dissolved gold. In this review, the four solutions to reduce the consumption of thiosulfate, including the [...] Read more.
Thiosulfate leaching is a promising alternative to cyanidation, and the main hindrances for its wide commercial application are the high thiosulfate consumption and the difficult recovery of dissolved gold. In this review, the four solutions to reduce the consumption of thiosulfate, including the control of reaction conditions, the use of additives, the generation of thiosulfate in situ, and the replacement of traditional cupric-ammonia catalysis, are introduced and evaluated after the presentation of background knowledge about thiosulfate consumption. The replacement of cupric-ammonia catalysis with other metals, such as nickel- and cobalt-based catalysts, is proposed. The reason is that it not only reduces thiosulfate consumption observably via decreasing the redox potential of leach solution significantly but also is beneficial to gold recovery mainly owing to eliminating the interference of cuprous thiosulfate [Cu(S2O3)3]5−. Based on the comparative analysis for five common recovery techniques of rare-noble metals from pregnant leach solution, ion-exchange resin adsorption is considered to be the most appropriate to recover aurothiosulfate [Au(S2O3)2]3− because the resin can be employed in the form of resin-in-leach/pulp and, furthermore, is able to be eluted and regenerated simultaneously at ambient temperature. At last, how to reduce the process cost of the resin adsorption technique is discussed. In order to simplify the complex two-stage elution process for loaded resins, the traditional catalysis is suggested to be replaced. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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Review
Bio-Reclamation of Strategic and Energy Critical Metals from Secondary Resources
by Sadia Ilyas, Min-Seuk Kim, Jae-Chun Lee, Asma Jabeen and Haq Nawaz Bhatti
Metals 2017, 7(6), 207; https://doi.org/10.3390/met7060207 - 06 Jun 2017
Cited by 43 | Viewed by 7415
Abstract
Metals with an average crustal abundance of <0.01 ppm, which are high in supply shortage due to soaring demand, can, under the excessive environmental risk and <1% recycling rate of their production, be termed as ‘critical’ in a limited geo-boundary. A global trend [...] Read more.
Metals with an average crustal abundance of <0.01 ppm, which are high in supply shortage due to soaring demand, can, under the excessive environmental risk and <1% recycling rate of their production, be termed as ‘critical’ in a limited geo-boundary. A global trend to the green energy and low carbon technologies with geopolitical scenario is challenging for the sustainable reclamation of these metals from secondary resources. Among the available processes, bio-reclamation can be a sustainable technique for extracting and concentrating these metals. Therefore, in the present paper, the potential reclamation of critical metals (including rare earth elements, precious metals, and a common nuclear fuel element, uranium) via their interaction with microbe/s has been reviewed. Full article
(This article belongs to the Special Issue Valuable Metal Recycling)
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