Metals

Editorial

Jump to: Research, Review

4 pages, 185 KiB

Open AccessEditorial

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 3405

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

Open AccessArticle

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 11 | Viewed by 4773

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)

► Show Figures

Figure 1

1949 KiB

Open AccessArticle

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 5390

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)

► Show Figures

Figure 1

4778 KiB

Open AccessArticle

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 6495

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)

► Show Figures

Figure 1

1519 KiB

Open AccessCommunication

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 4883

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)

► Show Figures

Figure 1

6548 KiB

Open AccessArticle

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 6535

Abstract

LiNi_xCo_yMn_z (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.

LiNi_xCo_yMn_z (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)

► Show Figures

Figure 1

1902 KiB

Open AccessArticle

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 4053

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 TU_24hr and 14.25 TU_48hr, 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)

► Show Figures

Figure 1

3206 KiB

Open AccessArticle

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 22 | Viewed by 7016

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, CaCO₃production 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)

► Show Figures

Graphical abstract

4904 KiB

Open AccessArticle

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 29 | Viewed by 6024

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)

► Show Figures

Figure 1

4646 KiB

Open AccessArticle

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 42 | Viewed by 8004

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)

► Show Figures

Graphical abstract

3969 KiB

Open AccessArticle

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 15 | Viewed by 4922

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)

► Show Figures

Figure 1

10099 KiB

Open AccessArticle

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 7121

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)

► Show Figures

Figure 1

2749 KiB

Open AccessArticle

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 16 | Viewed by 6656

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)

► Show Figures

Figure 1

3109 KiB

Open AccessArticle

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 11 | Viewed by 6324

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)

► Show Figures

Graphical abstract

Review

Jump to: Editorial, Research

696 KiB

Open AccessFeature PaperReview

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 62 | Viewed by 9104

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)

► Show Figures

Figure 1

1415 KiB

Open AccessReview

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 132 | Viewed by 16330

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)

► Show Figures

Figure 1

3026 KiB

Open AccessFeature PaperReview

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 - 6 Jun 2017

Cited by 48 | Viewed by 8071

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)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Valuable Metal Recycling

Share This Special Issue

Special Issue Editors

Special Issue Information

Benefits of Publishing in a Special Issue

Published Papers (17 papers)

Editorial

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI