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Greener Recovery and Separation Processes for REMs and PGMs in...
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Greener Recovery and Separation Processes for REMs and PGMs in Various Matrices

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 (30 June 2021) | Viewed by 28118

Special Issue Editors

Dr. Nomvano Mketo

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Guest Editor
Department of Chemistry, College of Science and Engineering and Technology, Florida Science Campus, University of South Africa, Johannesburg 1710, South Africa
Interests: metal leaching; metal recovery; grenner solvents; nanomaterial; adsorptive removal; microwave-assisted extrcation; ultrasound-assisted extraction; sequential extraction; metal speciation; multivariate optimization
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Philiswa Nosizo Nomngongo

E-Mail Website
Guest Editor
Department of Chemical Sciences, University of Johannesburg, Doornfontein 2028, Gauteng, South Africa
Interests: nanotechnology; nanomaterials; chemometrics; sample preparation; environmental analytical chemistry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Rare earth elements (REEs) and platinum group metals (PGMs) occur naturally in the earth's crust and are generally scattered in small concentration levels. According to IUPAC, REEs includes two metals of group 17 transition metals (Sc and Y) and the 15 lanthanide elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Th, Tm, Yb, and Lu). These metals are commonly dispersed or bonded with various minerals of the earth and their biggest market (80-90% REEs ores) is China. On the other hand, PGMs consists of Au, Ru, Rh, Pd, Os, Ir and Pt transition metals, which can be found in their purest elemental form. South Africa has the largest reserves of PGMs world-wide. Most importantly, these precious metals (REEs and PGMs) are referred to as industrial vitamins and treasury due to their wide technological applications. Furthermore, the demand for these precious metals is gradually increasing mainly due to the advancement in their various industrial applications. However, the mining industry is facing challenges of natural resource depletion and it is predicted that in the near future, there will be no natural sources of these metals. Therefore, several studies have been conducted to recover REEs and PGMs from secondary resources such as spent industrial catalysts, jewellery, magnets, automobile parts, electronic and industrial effluents.

This issue welcomes all the novel developments that describe recovery and separation of REEs and/or PGMs from various matrices using greener solvents (ionic liquids and deep eutectic solvents) and bio-adsorbents. The rationale of using greener solvents and material is based on the implementation of Green Chemistry, which was first reported in the early 1990s. Therefore, development of effective greener processes for recovery and separation of precious elements is urgently required, in order to meet global challenges associated with metal sustainability and to improve industrial economy.

Dr. Nomvano Mketo
Prof. Dr. Philiswa Nosizo Nomngongo
Guest Editors

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Keywords

  • Ionic liquids
  • Deep eutectic solvents
  • Bio-adsorbents
  • Nanomaterials
  • Adsorptive recovery
  • Solid phase extraction
  • Liquid-liquid extraction
  • Microwave assisted extraction (MAE)
  • Ultrasound assisted extraction (UAE)
  • Platinum group metals
  • Rare earth elements
  • Low cost adsorbents

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Published Papers (7 papers)

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Research

15 pages, 2150 KiB  
Article
Application of Ion Exchange for Recovery of Noble Metals
by Karolina Goc, Joanna Kluczka, Grzegorz Benke, Joanna Malarz, Karolina Pianowska and Katarzyna Leszczyńska-Sejda
Minerals 2021, 11(11), 1188; https://doi.org/10.3390/min11111188 - 26 Oct 2021
Cited by 20 | Viewed by 4008
Abstract
The production of noble metals has started to shift towards using different types of wastes. The leaching solutions collected during the processing of waste have low concentrations of noble metals; therefore, it forces the use of sorption methods in recovery technology. This work [...] Read more.
The production of noble metals has started to shift towards using different types of wastes. The leaching solutions collected during the processing of waste have low concentrations of noble metals; therefore, it forces the use of sorption methods in recovery technology. This work focused on recovering noble metals with a technological solution, obtained during the processing of waste from refining processes. The research consisted of a set of experiments using a batch method that enabled determination of the parameters of the process and selection of the leading resins. Sorption isotherms were determined and kinetic studies were conducted, along with the preliminary elution tests with the use of different eluents. Cementation experiments were the final part of the research. During the experiments, it was concluded that the leading resins for the sorption of noble metals were Puromet MTS9200, Puromet MTS9850, and Lewatit K 6362. The volume ratio Vr:Vs = 1:10 and the reaction time 15–30 min could be used as basic conditions to conduct the experiments in the column; the solution of thiourea in hydrochloric acid can be used as an eluting agent from which noble metals could be cemented using powder zinc. Full article
(This article belongs to the Special Issue Greener Recovery and Separation Processes for REMs and PGMs in Various Matrices)
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14 pages, 2193 KiB  
Article
Simultaneous Determination of REEs in Coal Samples Using the Combination of Microwave-Assisted Ashing and Ultrasound-Assisted Extraction Methods Followed by ICP-OES Analysis
by Mceliseni C. Zuma, Philiswa N. Nomngongo and Nomvano Mketo
Minerals 2021, 11(10), 1103; https://doi.org/10.3390/min11101103 - 8 Oct 2021
Cited by 16 | Viewed by 2616
Abstract
The world during the COVID-19 pandemic has led to extensive use of virtual activities by means of electronic devices, which are made up of rare earth elements (REEs). This means that quantitative knowledge of REEs in various resources is crucial for the development [...] Read more.
The world during the COVID-19 pandemic has led to extensive use of virtual activities by means of electronic devices, which are made up of rare earth elements (REEs). This means that quantitative knowledge of REEs in various resources is crucial for the development of effective recovery methods. Therefore, this report describes a simple microwave assisted ashing followed by ultrasound-assisted extraction (MAA-UAE) for quantitative determination of REEs in coal samples using inductively coupled plasma-optical emission spectroscopy (ICP-OES). Firstly, coal samples were ashed at 55 °C for 4.5 h to form white ashes, which were then treated with dilute HNO3 acid under ultrasonication to enhance the extraction of REEs. The quantitative recoveries (86–120%) of REEs were obtained when 1 mol L−1, 0.1 g, 40 °C, 20 min, and high frequency were applied for [HNO3], sample mass, ultrasonic bath temperature, extraction time, and ultrasonic bath frequency, respectively. The method detection limits of the proposed MAA-UAE method were between 0.0075 and 0.59 µg g−1 with satisfactory precision (<5%). The concentration levels of REEs in South African coals ranged from 1.4 to 105 µg g−1, suggesting that this coal can be a resource for REEs. Full article
(This article belongs to the Special Issue Greener Recovery and Separation Processes for REMs and PGMs in Various Matrices)
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19 pages, 4029 KiB  
Article
Recovery of Palladium and Gold from PGM Ore and Concentrate Leachates Using Fe3O4@SiO2@Mg-Al-LDH Nanocomposite
by Nkositetile Raphael Biata, Silindokuhle Jakavula, Richard Motlhaletsi Moutloali and Philiswa Nosizo Nomngongo
Minerals 2021, 11(9), 917; https://doi.org/10.3390/min11090917 - 25 Aug 2021
Cited by 5 | Viewed by 4594
Abstract
In this work, we developed a core–shell nanostructured magnetic composite by functionalizing layered double hydroxide (Mg-Al-LDH) microspheres with Fe3O4@SiO2, for the recovery of Au(III) and Pd(II). The magnetic Fe3O4 nanoparticles provided effective magnetic separation [...] Read more.
In this work, we developed a core–shell nanostructured magnetic composite by functionalizing layered double hydroxide (Mg-Al-LDH) microspheres with Fe3O4@SiO2, for the recovery of Au(III) and Pd(II). The magnetic Fe3O4 nanoparticles provided effective magnetic separation of the adsorbent from aqueous solutions. While silica protected the Fe3O4 nanoparticles, increased the adsorption sites and the stability of the material. Finally, Mg-Al-LDH was chosen because of its large anion sorption capacities which lead to the improved adsorption capacity of Fe3O4@SiO2@ Mg-Al-LDH nanocomposite. The morphology and structural composition of the nanocomposite were characterized using various analytical techniques. It was satisfactorily established that silica was coated on iron oxide and layered double hydroxide was immobilized on Fe3O4@SiO2. Parameters affecting adsorption of the composite towards Au(III) and Pd(II), such as effects of sample pH, mass of adsorbent, extraction time, eluent type and concentration were investigated using response methodology based on central composite design. Maximum adsorption capacities of Fe3O4@SiO2@ Mg-Al-LDH for Au(III) and Pd(II) were 289 mg g−1 and 313 mg g−1, respectively. Under optimum conditions, the proposed method displayed good analytical performance suggesting that the adsorbent is a good candidate for quantitative extraction of Au(III) and Pd(II) from secondary sources. Additionally, %recoveries ranging from 85%–99.6% were obtained revealing that Fe3O4@SiO2@ Mg-Al-LDH could selectively extract Au(III) and Pd(II) from leaching solutions of SARM 107 PGM ore and SARM 186 PGM concentrate. Full article
(This article belongs to the Special Issue Greener Recovery and Separation Processes for REMs and PGMs in Various Matrices)
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19 pages, 9455 KiB  
Article
Towards Sustainability Pathway with Bio-Derived Platinum and Palladium Catalyst for Furfural Hydrogenation—A Novel Greener Approach in Catalysis
by Babatunde J. Akinbile, Leah C. Matsinha, Banothile C. E. Makhubela and Abayneh A. Ambushe
Minerals 2021, 11(8), 895; https://doi.org/10.3390/min11080895 - 19 Aug 2021
Cited by 5 | Viewed by 3084
Abstract
The use of living plants to recover precious metals with potential catalytic activity is still at the infant stage. In this study, selective hydrogenation of furfural to furfuryl alcohol using novel bio-ore catalysts recovered from the end stage of phytomining process is demonstrated. [...] Read more.
The use of living plants to recover precious metals with potential catalytic activity is still at the infant stage. In this study, selective hydrogenation of furfural to furfuryl alcohol using novel bio-ore catalysts recovered from the end stage of phytomining process is demonstrated. The phytomining process was carried out in the green house by artificially contaminating cassava (Manihot esculenta) plant with 500 mg/L palladium (Pd) and platinum (Pt) solutions for a period of eight weeks. After harvesting, concentrations of metals as high as 78 ± 0.047 and 1276 ± 0.036 µg/g of Pd and Pt, respectively, were detected in the calcinated root of cassava. The produced bio-ore catalysts; @PdCassCat and @PtCassCat were fully characterized with the following techniques: transmission electron microscopy (TEM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), powder X-ray diffraction (pXRD), N2-sorption, and UV-visible spectroscopy techniques and directly applied as catalysts for hydrogenation of furfural to furfuryl alcohol. The reaction was conducted under an optimized condition (furfural (10 mmol), triethylamine (Et3N) (10 mmol), formic acid (20 mmol), temperature (160 °C), catalyst amount (40 mg)) realizing a yield of 76.5% and 100% furfuryl alcohol using @PdCassCat and @PtCassCat, respectively. The catalytic activities of the @PdCassCat and @PtCassCat were excellent as well as recyclable up to four and five times, respectively. Full article
(This article belongs to the Special Issue Greener Recovery and Separation Processes for REMs and PGMs in Various Matrices)
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18 pages, 5690 KiB  
Article
Adsorption of Selected Heavy and Precious Metals from Simulated Wastewater Using Fabricated Polyacrylonitrile (PAN) and Poly(4-Vinylpyridine) (P4VP) Monoliths
by Keziah E. Liebenberg, Abayneh A. Ambushe and Orpah Zinyemba
Minerals 2021, 11(8), 884; https://doi.org/10.3390/min11080884 - 16 Aug 2021
Cited by 1 | Viewed by 2290
Abstract
Adsorption has become an attractive method for the extraction and recovery of metals from wastewater effluents. This study involved the fabrication of mesoporous neat polyacrylonitrile (PAN) monoliths and composite polymer monoliths of PAN and poly-4-vinylpyridine (P4VP) as adsorbents for toxic elements (As(V), Cr(VI)) [...] Read more.
Adsorption has become an attractive method for the extraction and recovery of metals from wastewater effluents. This study involved the fabrication of mesoporous neat polyacrylonitrile (PAN) monoliths and composite polymer monoliths of PAN and poly-4-vinylpyridine (P4VP) as adsorbents for toxic elements (As(V), Cr(VI)) and the recovery of PGMs(Ru(III), Rh(III), Pd(II)) from simulated wastewater solutions. Fabrication of the mesoporous polymer monoliths was conducted using the non-solvent induced phase separation method (NIPS). The monoliths were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer–Emmett–Teller (BET). Adsorption studies were conducted using crushed monoliths saturated in 1 mg·L−1 simulated wastewater solutions. Spectroscopic analyses of the resulting filtrates were conducted using inductively coupled plasma-optical emission spectrometry (ICP-OES). In this study, the NIPS method was successfully optimized and mesoporous PAN, as well as composite polymer monoliths, were successfully fabricated. A concentration of 1 mg·L−1 of Ru(III) and Pd(II) was completely adsorbed by both monoliths. The mesoporous composite polymer monoliths exhibited the highest adsorption capacity for Rh(III), As(V), and Cr(VI). The mesoporous polymer monoliths showed great potential for use as wastewater cleaning aids as well as remediators of precious metals. Full article
(This article belongs to the Special Issue Greener Recovery and Separation Processes for REMs and PGMs in Various Matrices)
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16 pages, 4339 KiB  
Article
Preliminary Study on Gold Recovery from High Grade E-Waste by Thiourea Leaching and Electrowinning
by Nicolò Maria Ippolito, Ionela Birloaga, Francesco Ferella, Marcello Centofanti and Francesco Vegliò
Minerals 2021, 11(3), 235; https://doi.org/10.3390/min11030235 - 25 Feb 2021
Cited by 22 | Viewed by 6266
Abstract
The present paper is focused on the extraction of gold from high-grade e-waste, i.e., spent electronic connectors and plates, by leaching and electrowinning. These connectors are usually made up of an alloy covered by a layer of gold; sometimes, in some of them, [...] Read more.
The present paper is focused on the extraction of gold from high-grade e-waste, i.e., spent electronic connectors and plates, by leaching and electrowinning. These connectors are usually made up of an alloy covered by a layer of gold; sometimes, in some of them, a plastic part is also present. The applied leaching system consisted of an acid solution of diluted sulfuric acid (0.2 mol/L) with thiourea (20 g/L) as a reagent and ferric sulfate (21.8 g/L) as an oxidant. This system was applied on three different high-grade e-waste, namely: (1) Connectors with the partial gold-plated surface (Au concentration—1139 mg/kg); (2) different types of connectors with some of which with completely gold-plated surface (Au concentration—590 mg/kg); and (3) connectors and plates with the completely gold-plated surface (Au concentration—7900 mg/kg). Gold dissolution yields of 52, 94, and 49% were achieved from the first, second, and third samples, respectively. About 95% of Au recovery was achieved after 1.5 h of electrowinning at a current efficiency of only 4.06% and current consumption of 3.02 kWh/kg of Au from the leach solution of the third sample. Full article
(This article belongs to the Special Issue Greener Recovery and Separation Processes for REMs and PGMs in Various Matrices)
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21 pages, 6435 KiB  
Article
Separation of Radionuclides from a Rare Earth-Containing Solution by Zeolite Adsorption
by Deniz Talan and Qingqing Huang
Minerals 2021, 11(1), 20; https://doi.org/10.3390/min11010020 - 26 Dec 2020
Cited by 16 | Viewed by 4022
Abstract
The increasing industrial demand for rare earths requires new or alternative sources to be found. Within this context, there have been studies validating the technical feasibility of coal and coal byproducts as alternative sources for rare earth elements. Nonetheless, radioactive materials, such as [...] Read more.
The increasing industrial demand for rare earths requires new or alternative sources to be found. Within this context, there have been studies validating the technical feasibility of coal and coal byproducts as alternative sources for rare earth elements. Nonetheless, radioactive materials, such as thorium and uranium, are frequently seen in the rare earths’ mineralization, and causes environmental and health concerns. Consequently, there exists an urgent need to remove these radionuclides in order to produce high purity rare earths to diversify the supply chain, as well as maintain an environmentally-favorable extraction process for the surroundings. In this study, an experimental design was generated to examine the effect of zeolite particle size, feed solution pH, zeolite amount, and contact time of solid and aqueous phases on the removal of thorium and uranium from the solution. The best separation performance was achieved using 2.50 g of 12-µm zeolite sample at a pH value of 3 with a contact time of 2 h. Under these conditions, the adsorption recovery of rare earths, thorium, and uranium into the solid phase was found to be 20.43 wt%, 99.20 wt%, and 89.60 wt%, respectively. The Freundlich adsorption isotherm was determined to be the best-fit model, and the adsorption mechanism of rare earths and thorium was identified as multilayer physisorption. Further, the separation efficiency was assessed using the response surface methodology based on the development of a statistically significant model. Full article
(This article belongs to the Special Issue Greener Recovery and Separation Processes for REMs and PGMs in Various Matrices)
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