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Metals
Special Issues
Separation and Leaching for Metals Recovery
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Separation and Leaching for Metals Recovery

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

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 67644

Special Issue Editor

Prof. Dr. Jaeryeong Lee

E-Mail Website
Guest Editor
Department of Energy and Resources Engineering (ENRE), Kangwon National University, Chuncheon 24341, Korea
Interests: urban mine; recycling technology; dismantling; grinding; physical separation; hydrometallurgy; purification; rare metals
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In recent decades, the interest in urban mines has been gradually increasing. As a result, the industrial scale and case for commercialization have also been increasing dramatically. Raw materials in the urban mining industry can be divided mainly into industrial waste (including scrap) and municipal waste (including end-of-life products). Unfortunately, the current recycling research and metal recovery rates for municipal waste are much lower compared to industrial waste. This may be the result of a shortage of economic feasibility, the variety in compositions (such as non-metal and organic materials), and the lower content of metals in the municipal wastes. Municipal waste having these characteristics is not directly processed for metal recovery, and first requires separation and concentration using a separation pretreatment.

Therefore, further research is needed on the recovery and recycling of metal components from municipal wastes using a leaching process, as well as separation processes such as unit separation, dismantling/detaching, thermal decomposition, and physical separation (also referred to as mineral processing). This research could form the basis for the development of commercialization processes for municipal wastes and in addition to realization of a sustainable society through the continuous growth of the urban mining industry.

This Special Issue aims to address the latest research on not only leaching processes but also separation processes for waste with low-content metals (including end-life products), in order to achieve economic feasibility. Moreover, research articles will focus on the development of integrated environmentally friendly and cost-effective separation and leaching processes for the recovery of valuable metals.

Prof. Dr. Jaeryeong Lee
Guest Editor

Manuscript Submission Information

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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

  • urban mine
  • municipal waste
  • recycling
  • end-life product
  • separation process
  • leaching process
  • hydrometallurgical processes
  • unit separation
  • dismantling/detaching
  • thermal decomposition
  • mineral processing
  • low content of metals
  • environmentally friendly
  • cost-effective

Published Papers (17 papers)

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Research

17 pages, 4608 KiB  
Article
Leaching Kinetics of Rare Earth Elements in Phosphoric Acid from Phosphate Rock
by Zhili Li, Zhihao Xie, Jie Deng, Dongsheng He, Hengqin Zhao and Huan Liang
Metals 2021, 11(2), 239; https://doi.org/10.3390/met11020239 - 1 Feb 2021
Cited by 12 | Viewed by 2882
Abstract
Phosphate rock has been considered as one of the most significant secondary rare-earth resource, and the utilization of rare earth elements (REEs) in phosphate rock has attracted increasing attention. In this study, the leaching kinetics of REEs from a phosphate ore from China [...] Read more.
Phosphate rock has been considered as one of the most significant secondary rare-earth resource, and the utilization of rare earth elements (REEs) in phosphate rock has attracted increasing attention. In this study, the leaching kinetics of REEs from a phosphate ore from China was studied with the variation of temperature and phosphoric acid concentration under the conditions: ratio of liquid to solid of 12 mL/g, stirring speed of 120 r/min, and phosphate particle size of −0.074 mm amounts 61.1%. The results suggest that there were two distinct stages in leaching process and kinetics of both stages followed shrinking core model. At fast reaction stage, the semi-empirical equation describing the kinetics was 1 − 3(1 − α)2/3 + 2(1 − α) = 1.885CH3PO40.89exp(−11220/8.31T)t. The semi-empirical equation for slow reaction stage was 1 − 3(1 − α)2/3 + 2(1 − α) = 0.299CH3PO42.50exp(−18720/8.31T)t. Using shrinking core model and time-to-a-given-fraction method, we found that leaching rate of fast reaction stage was controlled by solid product layer diffusion, and both solid product layer diffusion and chemical reaction determined slow reaction stage. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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13 pages, 4201 KiB  
Article
Selective Recovery of Copper from Industrial Sludge by Integrated Sulfuric Leaching and Electrodeposition
by Ha Bich Trinh, Jaeryeong Lee, Seunghyun Kim, Jae-chun Lee, Juan Carlos Fuentes Aceituno and Seokhoon Oh
Metals 2021, 11(1), 22; https://doi.org/10.3390/met11010022 - 27 Dec 2020
Cited by 9 | Viewed by 2959
Abstract
The metal-containing sludge generated from the printed circuit boards (PCBs) manufacturing has been recycled as a secondary resource of copper (Cu) rather than being treated as a hazardous solid waste. However, it should consider the complexity of processing and using of oxidizing or [...] Read more.
The metal-containing sludge generated from the printed circuit boards (PCBs) manufacturing has been recycled as a secondary resource of copper (Cu) rather than being treated as a hazardous solid waste. However, it should consider the complexity of processing and using of oxidizing or precipitation agents to dissolve and separate Cu from other impurities, especially iron (Fe). This study has combined the dissolution and separation step in one stage by integrated acid leaching and electrodeposition to simplify the recovery process, while maintaining the high efficiency of separation. The chemistry of acid leaching and electrodeposition of the metals demonstrated that the metals (Cu and Fe) in the sludge sample were dissolved in the H2SO4 electrolyte, and Cu could be selectively deposited on the cathode based on the different potential conditions to reduce it on the cathode. The important factors affecting the deposition of Cu were investigated, finding the optimal conditions (current density 15 mA/cm2, H2SO4 100 g/L, Cu 20 g/L, at 45 °C, and for 6 h) which could completely recover Cu from the electrolyte in a selective manner. The obtained copper product possessed a high purity of >99% with adequately uniform morphology and an acceptable consumption of energy (1.7 kWh/kg). It is an effective and simple approach to reclaim the value metal copper from the industrial waste in one single stage of integrated extraction and refining. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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17 pages, 5680 KiB  
Article
Complete Extraction of Amorphous Aluminosilicate from Coal Fly Ash by Alkali Leaching under Atmospheric Pressure
by Andrei Shoppert, Dmitry Valeev, Irina Loginova and Leonid Chaikin
Metals 2020, 10(12), 1684; https://doi.org/10.3390/met10121684 - 16 Dec 2020
Cited by 21 | Viewed by 3488
Abstract
One of the potential sources of alumina and mesoporous silica is the coal-fired thermal plants waste known as the coal fly ash (CFA). The studies of the alumina extraction from CFA are often focused on the preliminary desilication, but the efficiency of the [...] Read more.
One of the potential sources of alumina and mesoporous silica is the coal-fired thermal plants waste known as the coal fly ash (CFA). The studies of the alumina extraction from CFA are often focused on the preliminary desilication, but the efficiency of the alkali desilication is low due to formation of the desilication product—Na6[Al6Si6O24]·Na2X (DSP). This research is focused on the possibility of CFA desilication without formation of DSP using a leaching process with higher liquid to solid ratios (L/S) and alkali concentrations. The experimental data were analyzed using an artificial neural network (ANN) machine learning method and a shrinking core model (SCM). The investigation of the CFA morphology, chemical and phase composition before and after leaching were carried out by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray diffraction (XRD). The present work shows that it is possible to avoid formation of DSP if using the L/S ratio >20 and concentration of Na2O—400 g/L during CFA leaching. The kinetics analysis by SCM showed that the process is limited by the surface chemical reaction at T <100 °C, and by diffusion through the product layer at T >100 °C, respectively. The SEM images of the solid residue after NaOH leaching under conditions that prevent the DSP formation show mullite particles with an acicular structure. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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9 pages, 3519 KiB  
Article
Leaching Behavior of Gold and Silver from Concentrated Sulfide Ore Using Ammonium Thiosulfate
by Mooki Bae, Sookyung Kim, Jeongsoo Sohn, Donghyo Yang and Hyunju Lee
Metals 2020, 10(8), 1029; https://doi.org/10.3390/met10081029 - 1 Aug 2020
Cited by 8 | Viewed by 4267
Abstract
Ammonium thiosulfate is an alternative lixiviant for the hydrometallurgical treatment of sulfide gold ores. The present study is primarily focused on ammonium thiosulfate leaching of gold (Au) and silver (Ag) from the sulfide ore (Sunshin mine in Korea). The main chemical composition of [...] Read more.
Ammonium thiosulfate is an alternative lixiviant for the hydrometallurgical treatment of sulfide gold ores. The present study is primarily focused on ammonium thiosulfate leaching of gold (Au) and silver (Ag) from the sulfide ore (Sunshin mine in Korea). The main chemical composition of the concentrate was Au (84 ppm), Ag (852 ppm), Fe (18.9%), Si (23.2%), and S (21.1%). The effects of various parameters on the process, such as leaching time (1–4 h), ammonium thiosulfate concentration (0.05–0.5 M), copper sulfate (CuSO4), concentration (0.05–0.25 M), solid to liquid ratio (0.2–0.5), and reaction temperature (40–60 °C) were systematically examined. Optimum Au leaching efficiency (>99%) was obtained under the following leaching conditions: 0.5 M ammonium thiosulfate with 0.05 M CuSO4 concentration, 0.2 S/L ratio at 60 °C for 2 h. The results indicate that the behavior of Ag was similar to that of Au. Almost complete dissolution of Ag occurred under following leaching conditions: 0.5 M ammonium thiosulfate with 0.05 M CuSO4 concentration at 60 °C for 4 h. This study would be useful in understanding the eco-friendly leaching systems of Au and Ag during the hydrometallurgical process of sulfide gold ore. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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10 pages, 3198 KiB  
Article
The Separation of Aluminum and Stainless-Steel Scraps Using Vibrating Mixed-Size Ball Bed
by Hyunjin Na, Kyoungkeun Yoo, Manis Kumar Jha and Carlito Baltazar Tabelin
Metals 2020, 10(7), 868; https://doi.org/10.3390/met10070868 - 30 Jun 2020
Cited by 10 | Viewed by 3769
Abstract
Dry gravity separation using a vibrating zirconia ball bed is proposed in this study to separate aluminum (Al) and stainless steel (STS) scraps obtained from spent hard disk drive recycling. The effects of zirconia ball sizes and vibrating power (vibration amplitude) on the [...] Read more.
Dry gravity separation using a vibrating zirconia ball bed is proposed in this study to separate aluminum (Al) and stainless steel (STS) scraps obtained from spent hard disk drive recycling. The effects of zirconia ball sizes and vibrating power (vibration amplitude) on the separation efficiency of Al and STS scraps were investigated. The zirconia balls moved down at the center of the vessel and rose with the wall during the vibration test. Although more STS scraps sunk than Al scraps did, the separation efficiency was not maintained because Al scraps also sunk along with balls’ movement. The separation efficiency increased to 86.6% using 1-mm zirconia balls with a 2.5-mm vibration amplitude at 4 min, but it decreased rapidly by ball moving. Therefore, when a ball bed of mixed sizes (2:1 ratio of 1 and 3 mm) was used and arranged, whereby the 3-mm zirconia balls were above the 1-mm ball bed, the separation efficiency increased to 100% for more than 2 min. This dramatic improvement was because the 3-mm ball bed acted as a barrier to prevent sunken STS scraps from rising, and Al scrap cannot sink through the 3-mm ball bed. These results indicate that the separation of Al and STS scraps could be achieved successfully using the dry gravity separation method. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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12 pages, 3467 KiB  
Article
Solvent Extraction of Sc(III) by D2EHPA/TBP from the Leaching Solution of Vanadium Slag
by Xuejiao Cao, Ting-an Zhang, Weiguang Zhang and Guozhi Lv
Metals 2020, 10(6), 790; https://doi.org/10.3390/met10060790 - 14 Jun 2020
Cited by 10 | Viewed by 3573
Abstract
The solvent extraction of scandium by the mixture of di-(2-ethylhexyl) phosphate (D2EHPA) and tri-n-butyl phosphate (TBP) has been investigated in the acidic leaching solution of vanadium slag. Thermodynamic analysis of the species distribution diagrams on the Sc-S-H2O system showed that scandium [...] Read more.
The solvent extraction of scandium by the mixture of di-(2-ethylhexyl) phosphate (D2EHPA) and tri-n-butyl phosphate (TBP) has been investigated in the acidic leaching solution of vanadium slag. Thermodynamic analysis of the species distribution diagrams on the Sc-S-H2O system showed that scandium mainly exists as Sc3+ and Sc(SO4)+, and sulfur mainly exists as HSO4− in the actual leaching solution of vanadium slag (pH = −0.75). The extraction process was studied to optimize various parameters such as the extractant concentration, dosage of TBP, phase ratio, and stirring speed. The results indicated that 83.64% of scandium and less than 2% of co-extracted elements were extracted under optimal conditions. Then, over 95% of the co-extracted elements and less than 1.1% of scandium were scrubbed from the loaded organic phase by 4.0 mol/L of HCl. Finally, 87.20% of scandium was stripped with 2 mol/L of NaOH and 1 mol/L of NaCl at a stripping O/A of 1:1. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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15 pages, 4961 KiB  
Article
Preparation of Doped Iron Phosphate by Selective Precipitation of Iron from Titanium Dioxide Waste Acid
by Weiguang Zhang, Ting-an Zhang, Liuliu Cai, Guozhi Lv and Xuejiao Cao
Metals 2020, 10(6), 789; https://doi.org/10.3390/met10060789 - 14 Jun 2020
Cited by 7 | Viewed by 3691
Abstract
In view of the current situation where the acid resources and valuable components in titanium dioxide waste acid cannot be effectively extracted and are prone to secondary pollution, the research team proposed a new technology of step extraction and comprehensive utilization of titanium [...] Read more.
In view of the current situation where the acid resources and valuable components in titanium dioxide waste acid cannot be effectively extracted and are prone to secondary pollution, the research team proposed a new technology of step extraction and comprehensive utilization of titanium dioxide waste acid. In this paper, the preparation of doped iron phosphate from waste acid by selective precipitation was studied. The thermodynamics of selective precipitation, the effect of the reaction temperature, the initial pH value, the molar ratio of P/Fe, and the dispersant on the precipitation process were investigated in detail. The thermodynamics results show that iron(II) in titanium dioxide waste acid is oxidized and is preferentially precipitated with phosphoric acid to form iron(III) phosphate, when compared with other impurity ions. The experimental results show that the optimal precipitation condition is a temperature of 60 °C, an initial pH value of 2.5, an optimal P/Fe molar ratio of 1.1, and a dispersant polyethylene glycol at 5 mL (Per 50 mL of waster acid). After calcination, the precipitate mainly consists of iron phosphate and a small amount of aluminum phosphate. Meanwhile, the utilization ratios of iron and phosphorus were 98.81% and 98.39%, respectively. Moreover, the mass percentage of Fe2O3 and P2O5 and the molar ratio of Fe/P were 99.13% and 1.03, which basically met the requirements of the iron phosphate precursor. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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15 pages, 5248 KiB  
Article
Recovery of Cerium Oxide Abrasive from an Abrasive–Glass Polishing Waste through Alkaline Roasting Followed by Water Leaching
by Li-Pang Wang, Pei-Hsin Liu and Yan-Jhang Chen
Metals 2020, 10(6), 752; https://doi.org/10.3390/met10060752 - 5 Jun 2020
Cited by 3 | Viewed by 3332
Abstract
Abrasive–glass polishing waste is generated from the polishing process of glass components by using cerium oxide abrasive, which contains the cerium oxide abrasive and the polished glass. This study attempted to recover the cerium oxide abrasive from the abrasive–glass polishing waste through removing [...] Read more.
Abrasive–glass polishing waste is generated from the polishing process of glass components by using cerium oxide abrasive, which contains the cerium oxide abrasive and the polished glass. This study attempted to recover the cerium oxide abrasive from the abrasive–glass polishing waste through removing the polished glass by alkaline roasting using sodium hydroxide (NaOH) followed by water leaching. The experimental results indicated that the polished glass in the abrasive–glass polishing waste could be fully removed under the optimal alkaline roasting and water leaching conditions of roasting temperature of 450 °C, mass ratio of polishing waste to NaOH of 1:1, roasting time of 30 min, leaching pH of 3, leaching temperature of 25 °C, and liquid–solid ratio of 25 mL/g. The characteristics including elemental composition, particle size distribution, mineralogical phases, and morphology of the recovered cerium oxide abrasive obtained under the optimal conditions were similar to those of the original unused one, which was suitable to be reused for polishing again. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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8 pages, 1672 KiB  
Article
Improvement of Copper Metal Leaching in Sulfuric Acid Solution by Simultaneous Use of Oxygen and Cupric Ions
by Kyoungkeun Yoo, Yujin Park, Sanghyeon Choi and Ilhwan Park
Metals 2020, 10(6), 721; https://doi.org/10.3390/met10060721 - 28 May 2020
Cited by 14 | Viewed by 10222
Abstract
A new concept for copper (Cu) metal leaching by the simultaneous use of cupric ions (Cu2+) and oxygen (O2) was proposed to improve Cu metal leaching in sulfuric acid. According to this concept, Cu2+ oxidizes Cu metal into [...] Read more.
A new concept for copper (Cu) metal leaching by the simultaneous use of cupric ions (Cu2+) and oxygen (O2) was proposed to improve Cu metal leaching in sulfuric acid. According to this concept, Cu2+ oxidizes Cu metal into cuprous ion (Cu+), and O2 oxidizes Cu+ into Cu2+. The improvement in Cu leaching efficiency from Cu metal was investigated experimentally in the sulfuric acid solution using Cu2+ and O2 simultaneously. Furthermore, the result was compared with that for the sulfuric acid solution containing neither Cu2+ nor O2 and with the sulfuric acid solution without Cu2+ and O2. When both Cu2+ and O2 were used in the leaching solution, the leaching rate of Cu from Cu metal powder was higher than at other leaching conditions, and the leaching efficiency of Cu increased to more than 99.9% in 1 mol/L sulfuric acid solution at 400 rpm and 50 °C with ≤75 µm Cu metal powder, 1% pulp density, 10,000 mg/L initial Cu2+ concentration, and 100 cc/min O2 introduction. These results indicated that the leaching of Cu from Cu metal could be accelerated by adding Cu2+ and O2 in the sulfuric acid solution. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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14 pages, 2958 KiB  
Article
Leaching of Oxide Copper Ores by Addition of Weak Acid from Copper Smelters
by Giselle Araya, Norman Toro, Jonathan Castillo, Danny Guzmán, Alexis Guzmán, Pía Hernández, Ricardo I. Jeldres and Rossana Sepúlveda
Metals 2020, 10(5), 627; https://doi.org/10.3390/met10050627 - 11 May 2020
Cited by 8 | Viewed by 3664
Abstract
In this study, weak acid in the curing and leaching stages of copper ore was incorporated, and we analyzed its effect on the dissolution of copper and final impurities. The weak acid corresponds to a wastewater effluent from sulfuric acid plants produced in [...] Read more.
In this study, weak acid in the curing and leaching stages of copper ore was incorporated, and we analyzed its effect on the dissolution of copper and final impurities. The weak acid corresponds to a wastewater effluent from sulfuric acid plants produced in the gas treatment of copper smelting processes. This effluent is basically water with high acidity (pH-value low at 1), which contains several toxic elements and some valuable metals. The results indicated that there is no positive or negative effect on the incorporation of the weak acid in the curing stage, while the case of the leaching stage is favored. Toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) toxicity tests were performed on the solid leaching residues, determining that they accomplish the stability ranges of the impurities (Pb, Cd, Hg, Cr, Ba, Se, As, and Ag). Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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13 pages, 2781 KiB  
Article
The Manufacture of Synthetic Rutile by Solvent Extraction of Tri-Alkyl Phosphine Oxide from HCl Leaching Solution of Soda-Roasted Ilmenite Ore
by Sung-Ho Joo, Dong Ju Shin, Dongseok Lee, Jungshin Kang, Min-seuk Kim, Hoseok Jeon, Jin-Tae Park and Shun Myung Shin
Metals 2020, 10(5), 588; https://doi.org/10.3390/met10050588 - 29 Apr 2020
Cited by 1 | Viewed by 2423
Abstract
To manufacture TiO2, a high-purity synthetic rutile, the recovery of Ti was investigated using a hydro-metallurgical process. Using a feed solution containing 32050 mg/L Ti, 110 mg/L Si, 88 mg/L Nb, 2614 mg/L Fe, and 130 mg/L Zr, solvent-extraction experiments were [...] Read more.
To manufacture TiO2, a high-purity synthetic rutile, the recovery of Ti was investigated using a hydro-metallurgical process. Using a feed solution containing 32050 mg/L Ti, 110 mg/L Si, 88 mg/L Nb, 2614 mg/L Fe, and 130 mg/L Zr, solvent-extraction experiments were conducted with alkyl phosphine oxide in conjunction with diluents such as kerosene and xylene. The results showed that the extraction mechanism of both diluents was very similar to slope analysis, which had a value of 1.9; however, the extraction equilibrium constant value of organic–metallic species in xylene as a diluent was lower than in kerosene as a diluent. This result affected the stripping efficiency of Ti in particular; therefore, xylene was selected as a diluent. To recover Ti ion from a leaching solution, a series of experiments was conducted, such as the McCabe–Thiele method and countercurrent simulation test for extraction and stripping of Ti. As a result, Ti and impurities such as Fe and Zr were extracted to 99.9% from Si and Nb under optimal conditions using countercurrent four-stage extraction, with 1 M Cyanex 923 at a ratio of organic phase/ aqueous phase=3. In the stripping test, Ti was selectively stripped to 90.1% from Fe and Zr in the organic phase by 1 M HCl. The obtained powder, which was hydrolyzed from an impurity-free solution, was analyzed to a purity of 99.9% by inductively coupled plasma. The TiO2, which has a spherical shape and a diameter of approximately 2 µm according to SEM, was evident by XRD. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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14 pages, 2983 KiB  
Article
Extraction of Lead and Zinc from a Rotary Kiln Oxidizing Roasting Cinder
by Junhui Xiao, Kai Zou, Wei Ding, Yang Peng and Tao Chen
Metals 2020, 10(4), 465; https://doi.org/10.3390/met10040465 - 2 Apr 2020
Cited by 9 | Viewed by 4644
Abstract
In this study, sulfuric acid leaching and gravity shaking-table separation by shaking a table are used to extract lead and zinc from a Pb-Zn oxidizing roasting cinder. The oxidizing roasting cinder—containing 16.9% Pb, 30.5% Zn, 10.3% Fe and 25.1% S—was obtained from a [...] Read more.
In this study, sulfuric acid leaching and gravity shaking-table separation by shaking a table are used to extract lead and zinc from a Pb-Zn oxidizing roasting cinder. The oxidizing roasting cinder—containing 16.9% Pb, 30.5% Zn, 10.3% Fe and 25.1% S—was obtained from a Pb-Zn sulfide ore in the Hanyuan area of China by a flotation-rotary kiln oxidizing roasting process. Anglesite and lead oxide were the main Pb-bearing minerals, while zinc sulfate, zinc oxide and zinc ferrite were the main Zn-bearing minerals. The results show that a part of lead contained in lead oxide is transformed to anglesite, and a 3PbO·PbSO4·H2O-dominated new lead mineral phase after acid leaching. A zinc leaching efficiency of 96.7% was obtained under the leaching conditions used: a leaching temperature of 55 °C; a leaching time of 90 min; a sulfuric acid dosage of 20%; a sulfurous acid dosage of 4%; a cinder particle size of <0.3 mm; and a solid-liquid ratio of R = 1:4. After the gravity shaking-table separation, a lead concentrate with 50.2% Pb, 2.33% Zn and lead recovery of 86.0% was produced. The main chemical compounds in leaching residue are anglesite, 3PbO·PbSO4·H2O, SiO2 and ZnFe2O4, while the main chemical compounds in lead concentrate are anglesite, 3PbO·PbSO4·H2O and SiO2. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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13 pages, 3509 KiB  
Article
Selective Copper Recovery by Acid Leaching from Printed Circuit Board Waste Sludge
by Ha Bich Trinh, Seunghyun Kim and Jaeryeong Lee
Metals 2020, 10(2), 293; https://doi.org/10.3390/met10020293 - 23 Feb 2020
Cited by 9 | Viewed by 5444
Abstract
The most challenging issue associated with recycling the sludge generated from printed circuit boards (PCBs) is the separation of copper (Cu) from iron (Fe), using multi-stage leaching, or adding oxidizing and precipitating agents. Herein we investigated simple acid leaching to effectively extract copper [...] Read more.
The most challenging issue associated with recycling the sludge generated from printed circuit boards (PCBs) is the separation of copper (Cu) from iron (Fe), using multi-stage leaching, or adding oxidizing and precipitating agents. Herein we investigated simple acid leaching to effectively extract copper and limit iron dissolution. Selective copper leaching was achieved with all the acids studied, including HCl, HNO3, and H2SO4. The lower concentration of acid solutions resulted in a larger difference in leachabilities between Cu and Fe. Among three leachates, the H2SO4 solution performed effectively on the selective leaching of Cu and Fe. Adjusting the pulp density to 4% and the H2SO4 concentration at ~0.2 M, accomplished ~95% Cu leaching and reduced the Fe extraction to less than 5%. Kinetic studies revealed that Cu leaching followed the ash diffusion-controlled mechanism. Aactivation energy (Ea) of 9.8 kJ/mol was determined for the first 10 min of leaching. Further, leaching up to 60 min corresponded to a mixed control model, increasing the Ea to 20.9 kJ/mol. The change in the control model with regard to the two leaching stages can be attributed to the Cu hydroxide and metal phases present in the original sample. A simple, economically attractive H2SO4 acid leaching process was demonstrated, recovering Cu efficiently and selectively from PCBs waste sludge under moderate conditions. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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13 pages, 3161 KiB  
Article
Removal of Phosphorus from High-Phosphorus Manganese Ores by Ammonia-Ammonium Carbonate Leaching Method
by Zhongbing Tu, Xiaoping Liang, Yu Wang and Chengbo Wu
Metals 2019, 9(12), 1354; https://doi.org/10.3390/met9121354 - 16 Dec 2019
Cited by 5 | Viewed by 3530
Abstract
High-phosphorus manganese ores provide an important source of manganese, which is regarded as an irreplaceable material in the steel industry. The ammonia-ammonium carbonate leaching method was proposed for the removal of phosphorus and extracting manganese from high-phosphorus manganese ore, both effectively and environmentally. [...] Read more.
High-phosphorus manganese ores provide an important source of manganese, which is regarded as an irreplaceable material in the steel industry. The ammonia-ammonium carbonate leaching method was proposed for the removal of phosphorus and extracting manganese from high-phosphorus manganese ore, both effectively and environmentally. To explore the dissolution behavior of phosphorus and manganese in the ammonia-ammonium carbonate solution, the effect of the ammonia-to-ammonium carbonate concentration ratio, the leaching temperature, and the liquid-to-solid ratio on manganese extraction and dephosphorization rate were investigated. In addition, the composition of precipitated manganiferous sample, which was obtained from high-phosphorus manganese ores by ammonia-ammonium carbonate leaching process, was also studied. The results indicated that more than 99.2% phosphorus was removed and more than 83.5% of manganese was extracted by ammonia-ammonium carbonate leaching under the following conditions: ammonia to ammonium carbonate concentrations: 14:2 mol/L; liquid/solid ratio: 5:1 mL/g; leaching temperature: 25 °C; The precipitated manganiferous sample has little impurities, Mn% is 44.12%, P% is 0.02%, P/Mn = 0.00045. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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10 pages, 2721 KiB  
Article
Investigation on the Effect of Roasting and Leaching Parameters on Recovery of Gallium from Solid Waste Coal Fly Ash
by Jing Huang, Yingbin Wang, Guanxuan Zhou and Yu Gu
Metals 2019, 9(12), 1251; https://doi.org/10.3390/met9121251 - 22 Nov 2019
Cited by 14 | Viewed by 2805
Abstract
Coal fly ash (CFA) provides important resources of gallium, which is regarded as an irreplaceable material in many technologies. A prospective roasting reagent assisted acid leaching process was proposed for the purpose of extracting gallium. The extraction efficiency of gallium by NaF (sodium [...] Read more.
Coal fly ash (CFA) provides important resources of gallium, which is regarded as an irreplaceable material in many technologies. A prospective roasting reagent assisted acid leaching process was proposed for the purpose of extracting gallium. The extraction efficiency of gallium by NaF (sodium fluoride) roasting followed by HNO3 (nitric acid) leaching process was demonstrated. The effect of roasting temperature, roasting time, the NaF-CFA mass ratio, acid leaching temperature, acid leaching time, and acid concentration were investigated. The results revealed that under optimal conditions (roasting temperature of 800 °C, roasting time of 10 min, acid leaching in 2 mol/L HNO3 for 1 h, and the NaF-CFA mass ratio of 0.75:1), 94% of gallium was extracted. Compared to previous studies, the process is a cost-effective method which can greatly shorten reaction time. It can reduce environmental pollution as it requires fewer acid reagents with low concentration and additives. It is expected to provide a method for the extraction of gallium from CFA. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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13 pages, 1483 KiB  
Article
Effects of Solid Content and Substrate Concentration on Bioleaching of Heavy Metals from Sewage Sludge Using Aspergillus niger
by Shen-Yi Chen and Sheng-Ying Wang
Metals 2019, 9(9), 994; https://doi.org/10.3390/met9090994 - 9 Sep 2019
Cited by 9 | Viewed by 2976
Abstract
The presence of heavy metals in sewage sludge not only affects the performance of sludge anaerobic digestion process but also restricts the land application of treated sewage sludge. Therefore, a fungi-mediated bioleaching process for simultaneous metal leaching and sludge digestion by Aspergillus niger [...] Read more.
The presence of heavy metals in sewage sludge not only affects the performance of sludge anaerobic digestion process but also restricts the land application of treated sewage sludge. Therefore, a fungi-mediated bioleaching process for simultaneous metal leaching and sludge digestion by Aspergillus niger was developed to treat the sewage sludge containing heavy metals in this study. The effects of two important parameters, sludge solid content and substrate (sucrose) concentration, on the performance of fungal bioleaching were investigated in this study. The results showed that the rate of pH reduction increased with increasing sludge solid contents and sucrose concentrations. In this study, the efficiency of metal removal decreases in the order of Mn > Zn > Ni > Pb. The efficiencies of metal leaching and solid degradation (SS and VSS) were found to be decreased with an increase of sludge solid content and a decrease of sucrose concentration. At 2 days of reaction time, the maximum efficiency of metal solubilization was 95, 56, 21 and 13% for Mn, Zn, Ni and Pb, respectively. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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11 pages, 2600 KiB  
Article
Destruction of Cyanide and Removal of Copper from Waste Printed Circuit Boards Leach Solution Using Electro-Generated Hypochlorite Followed by Magnetite Adsorption
by Mooki Bae, Hyunju Lee, Sookyung Kim and Kyoungkeun Yoo
Metals 2019, 9(9), 963; https://doi.org/10.3390/met9090963 - 2 Sep 2019
Cited by 9 | Viewed by 2803
Abstract
The removal of the cyanide and copper (Cu) from the waste printed circuit boards (WPCBs) cyanide leach solution through the alkaline chlorination using electro-generated hypochlorite (NaOCl) followed by magnetite (Fe3O4) adsorption is investigated. The efficiency of the destruction of [...] Read more.
The removal of the cyanide and copper (Cu) from the waste printed circuit boards (WPCBs) cyanide leach solution through the alkaline chlorination using electro-generated hypochlorite (NaOCl) followed by magnetite (Fe3O4) adsorption is investigated. The efficiency of the destruction of cyanide and precipitation of Cu was increased with increasing the concentration of free available chlorine in NaOCl. More than 99% of free cyanide and 76% of Cu were removed under the following conditions: concentration of chlorine in electro-generated NaOCl, 5.2 g/L; volume ratio of NaOCl/leach solution, 1; pH, ~9.8; ambient temperature for 12 h. Then, magnetite adsorption for selective removal of remaining Cu (50.5 mg/L) was selected and more than 99% of copper ion was successfully removed with dosage 10g/100mL, shaking speed 150 rpm within 30 min. The results revealed that the alkaline chlorination using electro-generated NaOCl followed by magnetite adsorption could completely remove the cyanide and Cu, remaining Au in the final solution. Full article
(This article belongs to the Special Issue Separation and Leaching for Metals Recovery)
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