Recovery of Precious Metals, Rare Earth Elements and Special Metals from Spent Secondary Products

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Processing and Extractive Metallurgy".

Deadline for manuscript submissions: closed (15 April 2021) | Viewed by 32595

Special Issue Editors

School of Biomolecular and Chemical Sciences, Department of Chemistry, Nelson Mandela University, Port Elizabeth 6031, Africa
Interests: base metals; PGMs; hydrometallurgy; desulfurization; denitrogenation; functional materials
Special Issues, Collections and Topics in MDPI journals
Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8565, Japan
Interests: adsorbent; wastewater treatment; PGMs; resource recycling
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

The global demand for precious metals, in chemical, petrochemical, electrical and electronic products, medical and dentistry applications, jewelry and automobile industries, against the dwindling natural deposits; demands the development of more efficient recovery methods, as well as a move towards urban mining. The latter is becoming more attractive due to the high yields compared with extraction from primary ores. Current recovery rates of precious metals and REEs from spent products are low and there is a need to drive towards a closed-loop recycling system. However; the heterogeneous nature of such secondary sources of precious metals and REEs demands the development of robust methods for the recovery of strategic metals. This Special Issue will contribute to the knowledge gap in the characterization and recycling of precious metals and REEs from spent secondary materials. Spent secondary materials include catalytic converters, electronic boards, magnet scraps, fluorescent lamps, CRTs, LCDs, PV cells, solar panels, batteries, and fly ash, among others.

Prof. Dr. Zenixole Tshentu
Dr. Durga Parajuli
Guest Editors

Manuscript Submission Information

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Keywords

  • precious metals
  • REEs
  • spent products
  • metal scrap
  • urban mining

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Published Papers (10 papers)

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Editorial

Jump to: Research, Review

2 pages, 155 KiB  
Editorial
Editorial for the Special Issue on “Recovery of Precious Metals, Rare Earth Elements and Special Metals from Spent Secondary Products”
by Zenixole R. Tshentu and Durga Parajuli
Minerals 2022, 12(4), 481; https://0-doi-org.brum.beds.ac.uk/10.3390/min12040481 - 14 Apr 2022
Cited by 1 | Viewed by 1294
Abstract
The global demand for precious metals in chemical, petrochemical, electrical and electronic products, for medical and dentistry applications, as well as jewelry and automobile industries, when set against the dwindling natural deposits, demands the development of more efficient recovery methods as well as [...] Read more.
The global demand for precious metals in chemical, petrochemical, electrical and electronic products, for medical and dentistry applications, as well as jewelry and automobile industries, when set against the dwindling natural deposits, demands the development of more efficient recovery methods as well as a move towards urban mining [...] Full article

Research

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14 pages, 3921 KiB  
Article
Recovery of Platinum Group Metals from Leach Solutions of Spent Catalytic Converters Using Custom-Made Resins
by Pulleng Moleko-Boyce, Hlamulo Makelane, Mbokazi Z. Ngayeka and Zenixole R. Tshentu
Minerals 2022, 12(3), 361; https://0-doi-org.brum.beds.ac.uk/10.3390/min12030361 - 16 Mar 2022
Cited by 9 | Viewed by 3899
Abstract
Platinum group metals (PGMs) play a key role in modern society as they find application in clean technologies and other high-tech equipment. Spent catalytic converters as a secondary resource contain higher PGM concentrations and the recovery of these metals via leaching is continuously [...] Read more.
Platinum group metals (PGMs) play a key role in modern society as they find application in clean technologies and other high-tech equipment. Spent catalytic converters as a secondary resource contain higher PGM concentrations and the recovery of these metals via leaching is continuously being improved but efforts are also directed at the purification of individual metal ions. The study presents the recovery of PGMs, namely, rhodium (Rh), platinum (Pt) and palladium (Pd) as well as base metals, namely, zinc (Zn), nickel (Ni), iron (Fe), manganese (Mn) and chromium (Cr) using leachates from spent diesel and petrol catalytic converters. The largest amount of Pt was leached from the diesel catalytic converter while the petrol gave the highest amount of Pd when leached with aqua regia. Merrifield beads (M) were functionalized with triethylenetetramine (TETA), ethane-1,2-dithiol (SS) and bis((1H-benzimidazol-2-yl)methyl)sulfide (NSN) to form M-TETA, M-SS and M-NSN, respectively, for recovery of PGMs and base metals from the leach solutions. The adsorption and loading capacities of the PGMs and base metals were investigated using column studies at 1 M HCl concentration. The loading capacity was observed in the increasing order of Pd to be 64.93 mmol/g (M-SS), 177.07 mmol/g (M-NSN), and 192.0 mmol/g (M-TETA), respectively, from a petrol catalytic converter. The M-NSN beads also had a much higher loading capacity for Fe (489.55 mmol/g) compared to other base metals. The finding showed that functionalized Merrifield resins were effective for the simultaneous recovery of PGMs and base metals from spent catalytic converters. Full article
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16 pages, 2279 KiB  
Article
High-Gradient Magnetic Separation of Compact Fluorescent Lamp Phosphors: Elucidation of the Removal Dynamics in a Rotary Permanent Magnet Separator
by Peter Boelens, Zhe Lei, Björn Drobot, Martin Rudolph, Zichao Li, Matthias Franzreb, Kerstin Eckert and Franziska Lederer
Minerals 2021, 11(10), 1116; https://0-doi-org.brum.beds.ac.uk/10.3390/min11101116 - 12 Oct 2021
Cited by 10 | Viewed by 1966
Abstract
In an ongoing effort towards a more sustainable rare-earth element market, there is a high potential for an efficient recycling of rare-earth elements from end-of-life compact fluorescent lamps by physical separation of the individual phosphors. In this study, we investigate the separation of [...] Read more.
In an ongoing effort towards a more sustainable rare-earth element market, there is a high potential for an efficient recycling of rare-earth elements from end-of-life compact fluorescent lamps by physical separation of the individual phosphors. In this study, we investigate the separation of five fluorescent lamp particles by high-gradient magnetic separation in a rotary permanent magnet separator. We thoroughly characterize the phosphors by ICP-MS, laser diffraction analysis, gas displacement pycnometry, surface area analysis, SQUID-VSM, and Time-Resolved Laser-Induced Fluorescence Spectroscopy. We present a fast and reliable quantification method for mixtures of the investigated phosphors, based on a combination of Time-Resolved Laser-Induced Fluorescence Spectroscopy and parallel factor analysis. With this method, we were able to monitor each phosphors’ removal dynamics in the high-gradient magnetic separator and we estimate that the particles’ removal efficiencies are proportional to (d2·χ)1/3. Finally, we have found that the removed phosphors can readily be recovered easily from the separation cell by backwashing with an intermittent air–water flow. This work should contribute to a better understanding of the phosphors’ separability by high-gradient magnetic separation and can simultaneously be considered to be an important preparation for an upscalable separation process with (bio)functionalized superparamagnetic carriers. Full article
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18 pages, 2385 KiB  
Article
The Behaviour of Rare Earth Elements from South African Coal Fly Ash during Enrichment Processes: Wet, Magnetic Separation and Zeolitisation
by Mero-Lee Ursula Cornelius, Alechine Emmanuel Ameh, Chuks Paul Eze, Olanrewaju Fatoba, Asel Sartbaeva and Leslie Felicia Petrik
Minerals 2021, 11(9), 950; https://0-doi-org.brum.beds.ac.uk/10.3390/min11090950 - 31 Aug 2021
Cited by 11 | Viewed by 3881
Abstract
Rare earth elements (REEs) are essential raw materials in a variety of industries including clean energy technologies such as electric vehicles and wind turbines. This places an ever-increasing demand on global rare earth element production. Coal fly ash (CFA) possesses appreciable levels of [...] Read more.
Rare earth elements (REEs) are essential raw materials in a variety of industries including clean energy technologies such as electric vehicles and wind turbines. This places an ever-increasing demand on global rare earth element production. Coal fly ash (CFA) possesses appreciable levels of REEs. CFA, a waste by-product of coal combustion, is therefore a readily available source of REEs that does not require mining. CFA valorisation to zeolites has been achieved via various synthesis pathways. This study aimed to evaluate one such pathway by monitoring how REEs partition during CFA processing by the wet, magnetic separation process and zeolitisation. South African CFA was subjected to wet, magnetic separation and subsequent zeolitisation of the nonmagnetic fraction (NMF); solid products were characterised by XRD, SEM, XRF and LA-ICP-MS. The wet, magnetic separation process resulted in the partitioning of a specific set of transition metals (such as Fe, Mn, Cr, V, Ni, Zn, Cu, Co and Mo) into the magnetic fraction (MF) of CFA, while REEs partitioned into the NMF with a total REE content of 530.2 ppm; thus, the matrix elements of CFA were extracted with ease. Zeolitisation resulted in a solid zeolite product (hydroxysodalite) with a total REE content of 537.6 ppm. The process of zeolitisation also resulted in the selective enrichment of Ce (259.1 ppm) into the solid zeolite product (hydroxysodalite), while other REEs were largely partitioned into the liquid phase. CFA valorisation by wet, magnetic separation and zeolitisation therefore allowed for the partitioning of REEs into various extraction products while recovering the matrix elements of CFA such as Fe, Si and Al. The findings of this study highlight the geopolitical importance of REEs in terms of the development of alternative processes for REE recovery from waste and alternative sources, which may potentially give countries that employ and develop the technology a key advantage in the production of REEs for the global market. Full article
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16 pages, 5022 KiB  
Article
Extraction of REEs (Ce, Tb, Y, Eu) from Phosphors Waste by a Combined Alkali Roasting–Acid Leaching Process
by Bing-Xuan He, Yong Liang, Lue-Wei Xu, Long-Bin Shao, De-Gang Liu, Fei Yang and Guan-Jie Liang
Minerals 2021, 11(4), 437; https://0-doi-org.brum.beds.ac.uk/10.3390/min11040437 - 20 Apr 2021
Cited by 6 | Viewed by 2088
Abstract
Rare Earth (RE) phosphors waste contains valuable rare Earth elements (REEs), such as cerium, terbium, yttrium, and europium. In industry, the process of NaOH roasting followed by acid leaching is usually used to extract the REEs from the waste in China. Using this [...] Read more.
Rare Earth (RE) phosphors waste contains valuable rare Earth elements (REEs), such as cerium, terbium, yttrium, and europium. In industry, the process of NaOH roasting followed by acid leaching is usually used to extract the REEs from the waste in China. Using this process, the leaching efficiencies of cerium and terbium are clearly lower than those of other REEs, which results in uneven extraction of REEs in the waste and low total REE leaching efficiency. The key reason is that the trivalent cerium and terbium in the waste are oxidized into RE oxides during NaOH roasting, which are difficult to dissolve in acid solution. To solve this problem, an optimized process of controlling the oxygen concentration during NaOH roasting is proposed in this paper. The influences of the oxygen concentration, roasting temperature, roasting time, mass ratio of waste phosphor to NaOH, HCl solution concentration, acid leaching temperature, acid leaching time, and liquid–solid ratio on the REE leaching efficiency were investigated. Under the optimum conditions, the leaching efficiencies of cerium and terbium increased dramatically and the total REE leaching efficiency is 99.11%. Full article
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10 pages, 1091 KiB  
Article
Application of Green Solvents for Rare Earth Element Recovery from Aluminate Phosphors
by Clive H. Yen and Rui Cheong
Minerals 2021, 11(3), 287; https://0-doi-org.brum.beds.ac.uk/10.3390/min11030287 - 10 Mar 2021
Cited by 4 | Viewed by 2329
Abstract
Two processes applying green solvents for recovering rare earth elements (REEs) from different types of aluminate phosphors are demonstrated in this report. For magnesium aluminate-type phosphors, a pretreatment with peroxide calcination was implemented first, and then followed by a supercritical fluid extraction (SFE) [...] Read more.
Two processes applying green solvents for recovering rare earth elements (REEs) from different types of aluminate phosphors are demonstrated in this report. For magnesium aluminate-type phosphors, a pretreatment with peroxide calcination was implemented first, and then followed by a supercritical fluid extraction (SFE) process. Supercritical carbon dioxide (sc-CO2) provides an effective and green medium for extracting REEs from dry materials. With the addition of a complex agent, tri-n-butyl phosphate-nitric acid complex, highly efficient and selective extraction of REEs using supercritical carbon dioxide can be achieved. The highest extraction efficiency was 92% for europium from the europium doped barium magnesium aluminate phosphor (BAM), whereas the highest extraction selectivity was more than 99% for the REEs combined from the trichromatic phosphor. On the other hand, for strontium aluminate type phosphors, a direct acid leaching process is suggested. It was found out that acetic acid, which is considerably green, could have high recovery rate for dysprosium (>99%) and europium (~83%) from this strontium aluminate phosphor materials. Nevertheless, both green processes showed promising results and could have high potential for industrial applications. Full article
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21 pages, 5642 KiB  
Article
Impact of Grinding of Printed Circuit Boards on the Efficiency of Metal Recovery by Means of Electrostatic Separation
by Tomasz Suponik, Dawid M. Franke, Paweł M. Nuckowski, Piotr Matusiak, Daniel Kowol and Barbara Tora
Minerals 2021, 11(3), 281; https://0-doi-org.brum.beds.ac.uk/10.3390/min11030281 - 09 Mar 2021
Cited by 14 | Viewed by 3541
Abstract
This paper analyses the impact of the method of grinding printed circuit boards (PCBs) in a knife mill on the efficiency and purity of products obtained during electrostatic separation. The separated metals and plastics and ceramics can be used as secondary raw materials. [...] Read more.
This paper analyses the impact of the method of grinding printed circuit boards (PCBs) in a knife mill on the efficiency and purity of products obtained during electrostatic separation. The separated metals and plastics and ceramics can be used as secondary raw materials. This is in line with the principle of circular economy. Three different screen perforations were used in the mill to obtain different sizes of ground grains. Moreover, the effect of cooling the feed to cryogenic temperature on the final products of separation was investigated. The level of contamination of the concentrate, intermediate, and waste obtained as a result of the application of fixed, determined electrostatic separation parameters was assessed using ICP-AES, SEM–EDS, XRD, and microscopic analysis as well as specific density. The yields of grain classes obtained from grinding in a knife mill were tested through sieve analysis and by using a particle size analyser. The test results indicate that using a knife mill with a 1 mm screen perforation along with cooling the feed to cryogenic temperature significantly improves the efficiency of the process. The grinding products were characterised by the highest release level of the useful substance—metals in the free state. The purity of the concentrate and waste obtained from electrostatic separation was satisfactory, and the content of the intermediate, in which conglomerates of solid metal–plastic connections were present, was very low. The yield of concentrate and waste amounted to 26.2% and 71.0%, respectively. Their purity, reflected in the content of the identified metals (valuable metals), was at the level of 93.3% and 0.5%, respectively. In order to achieve effective recovery of metals from PCBs by means of electrostatic separation, one should strive to obtain a feed composed of grains <1000 μm and, optimally, <800 μm. Full article
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8 pages, 2634 KiB  
Article
Characteristics of Metals Leached from Waste Printed Circuit Boards Using Acidithiobacillus ferrooxidans
by Jinsung An
Minerals 2021, 11(2), 224; https://0-doi-org.brum.beds.ac.uk/10.3390/min11020224 - 22 Feb 2021
Cited by 4 | Viewed by 2271
Abstract
The aim of this study was to compare leaching characteristics of metals from printed circuit boards (PCBs), taken from waste electrical and electronic equipment in the presence and in the absence of the iron-oxidizing bacteria, Acidithiobacillus ferrooxidans. A. ferrooxidans not only increases the [...] Read more.
The aim of this study was to compare leaching characteristics of metals from printed circuit boards (PCBs), taken from waste electrical and electronic equipment in the presence and in the absence of the iron-oxidizing bacteria, Acidithiobacillus ferrooxidans. A. ferrooxidans not only increases the leached concentration of Cu from the PCBs, but also inhibits the components of the 0K medium and leached Cu from forming precipitates such as libethenite (Cu2(PO4)(OH)), thereby assisting Cu recovery from the PCBs. In addition, the leached concentration of Pb from PCBs decreased in the presence of A. ferrooxidans, due to Pb forming amorphous precipitates. It is expected that Pb is not highly toxic to A. ferrooxidans. Consequently, A. ferrooxidans can be used as a cost-effective and environmentally friendly way to leach out valuable metals from PCBs as low-grade urban ore. Full article
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Review

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17 pages, 6098 KiB  
Review
Rare Earths’ Recovery from Phosphogypsum: An Overview on Direct and Indirect Leaching Techniques
by Jean-Luc Mukaba, Chuks Paul Eze, Omoniyi Pereao and Leslie Felicia Petrik
Minerals 2021, 11(10), 1051; https://0-doi-org.brum.beds.ac.uk/10.3390/min11101051 - 28 Sep 2021
Cited by 29 | Viewed by 4496
Abstract
The need for rare earths elements (REEs) in high tech electrical and electronic based materials are vital. In the global economy, deposits of natural REEs are limited except for countries such as China, which has prompted current attempts to seek alternative resources of [...] Read more.
The need for rare earths elements (REEs) in high tech electrical and electronic based materials are vital. In the global economy, deposits of natural REEs are limited except for countries such as China, which has prompted current attempts to seek alternative resources of REEs. This increased the dependence on major secondary rare earth-bearing sources such as scrap alloy, battery waste, spent catalysts, fly ash, spent magnets, waste light-emitting diodes (LEDs), and phosphogypsum (PG) for a substantial recovery of REEs for use. Recycling of REEs from these alternative waste sources through hydrometallurgical processes is becoming a sustainable and viable approach due to the low energy consumption, low waste generation, few emissions, environmentally friendliness, and economically feasibility. Industrial wastes such as the PG generated from the production of phosphoric acid is a potential secondary resource of REEs that contains a total REE concentration of over 2000 mg/kg depending upon the phosphate ore from which it is generated. Due to trace concentration of REEs in the PG (normally < 0.1% wt.) and their tiny and complex occurrence as mineral phases the recovery process of REE from PG would be highly challenging in both technology and economy. Various physicochemical pre-treatments approaches have been used up to date to up-concentrate REEs from PG prior to their extraction. Methods such as carbonation, roasting, microwave heating, grinding or recrystallization have been widely used for this purpose. This present paper reviews recent literature on various techniques that are currently employed to up-concentrate REs from PG to provide preliminary insight into further critical raw materials recovery. In addition, the advantages and disadvantages of the different strategies are discussed as avenues for realization of REE recovery from PG at a larger scale. In all the different approaches, recrystallization of PG appears to show promising advantages due to both high REE recovery as well as the pure PG phase that can be obtained. Full article
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28 pages, 6491 KiB  
Review
Status of Recovery of Strategic Metals from Spent Secondary Products
by Luthando Xolo, Pulleng Moleko-Boyce, Hlamulo Makelane, Nobathembu Faleni and Zenixole R. Tshentu
Minerals 2021, 11(7), 673; https://0-doi-org.brum.beds.ac.uk/10.3390/min11070673 - 24 Jun 2021
Cited by 19 | Viewed by 4965
Abstract
The need to drive towards sustainable metal resource recovery from end-of-cycle products cannot be overstated. This review attempts to investigate progress in the development of recycling strategies for the recovery of strategic metals, such as precious metals and base metals, from catalytic converters, [...] Read more.
The need to drive towards sustainable metal resource recovery from end-of-cycle products cannot be overstated. This review attempts to investigate progress in the development of recycling strategies for the recovery of strategic metals, such as precious metals and base metals, from catalytic converters, e-waste, and batteries. Several methods for the recovery of metal resources have been explored for these waste streams, such as pyrometallurgy, hydrometallurgy, and biohydrometallurgy. The results are discussed, and the efficiency of the processes and the chemistry involved are detailed. The conversion of metal waste to high-value nanomaterials is also presented. Process flow diagrams are also presented, where possible, to represent simplified process steps. Despite concerns about environmental effects from processing the metal waste streams, the gains for driving towards a circular economy of these waste streams are enormous. Therefore, the development of greener processes is recommended. In addition, countries need to manage their metal waste streams appropriately and ensure that this becomes part of the formal economic activity and, therefore, becomes regulated. Full article
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