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Metals
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Sustainable Gold Production and Recycling
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Sustainable Gold Production and Recycling

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

Deadline for manuscript submissions: 31 July 2024 | Viewed by 7059

Special Issue Editors

Prof. Dr. Bernd Friedrich

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Guest Editor
IME Process Metallurgy and Metal Recycling, RWTH Aachen University, 52056 Aachen, Germany
Interests: pyrometallurgy; process technology; metals; recycling; purification; alloying; WEEE; spent batteries; critical materials; circular economy; electrometallurgy
Special Issues, Collections and Topics in MDPI journals
Dr. Alexander Birich

E-Mail Website
Guest Editor
Institute of Metal Process Engineering and Metal Recycling, RWTH Aachen University, 52072 Aachen, Germany
Interests: hydrometallurgy; precious metals; WEEE; recycling; circular economy

Special Issue Information

Dear Colleagues,

Since its inception in the late 1800s, cyanidation has been the dominant process for gold production worldwide. Due to its simplicity and high cost efficiency, it nearly completely replaced all former processes. The main disadvantage of cyanide is related to environmental issues, which may occur through improper storage and transport or failed tailings management and storage. From a technical aspect, industrial gold recovery becomes more difficult, since most high-grade and easy-to-process ore deposits are already depleted. Gold producers are forced to use increasingly complex and low-grade ores. With regard to these limitations of cyanide, alternative reagents and processes often show better technical characteristics, such as a higher extraction rate, a higher selectivity and lower hazardousness.

From an ecological perspective, the recycling of gold becomes especially important, as it allows for a reduction of more than 99% compared to primary production. While recycling jewellery is already a quite elaborated process, other waste materials show a high potential for optimization. The most important secondary resource stream after jewellery is electronic waste. The dominant pyrometallurgical state-of-the-art process is slow, requires large and expensive facilities, and generates a high amount of emissions. Smaller-scale operations often take place in the informal sector by using aqua regia or mercury to recover gold.

This Special Issue aims to provide an up-to-date view on current industrial gold production and recycling technologies in a worldwide context, considering innovative approaches for gold extraction and refining from the laboratory scale up to industrial applications. A special focus will be placed on the recycling of e-waste and other gold-containing waste streams, which shows important ecological but also economic advantages.

Prof. Dr. Bernd Friedrich
Dr. Alexander Birich
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

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

  • gold
  • hydrometallurgy
  • sustainable production
  • cyanide alternative
  • recycling
  • WEEE
  • e-waste

Published Papers (5 papers)

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Research

0 pages, 5949 KiB  
Communication
Economic Aspects of Mechanical Pre-Treatment’s Role in Precious Metals Recovery from Electronic Waste
by Ervins Blumbergs, Andrei Shishkin, Karlis Markus, Vera Serga, Dmitri Goljandin, Artur Klauson, Vitalijs Abramovskis, Janis Baronins, Aleksej Zarkov and Vladimir Pankratov
Metals 2024, 14(1), 95; https://doi.org/10.3390/met14010095 - 13 Jan 2024
Viewed by 1164
Abstract
Printed circuit boards (PCBs) make up 3 to 5% of all electronic waste. The metal content of spent PCBs can reach 40%. They usually contain valuable metals, such as Ag, Au, and Pd, as well as other metals such as Cu, Sn, Pb, [...] Read more.
Printed circuit boards (PCBs) make up 3 to 5% of all electronic waste. The metal content of spent PCBs can reach 40%. They usually contain valuable metals, such as Ag, Au, and Pd, as well as other metals such as Cu, Sn, Pb, Cd, Cr, Zn, Ni, and Mn. However, the metallic part of a whole PCB is 40–60% including the Cu layers between the fiberglass–polymer layers. The paper describes the economics of the valuable metal (Ag, Au, Pd)-containing concentrate preparation from a raw PCB. We considered the influence of the pre-treatment method of PCBs before the extraction of valuable metals on the extraction self-cost change. The disintegration method is based on the high-energy impact of the particles of the material to be ground, thus causing the separation of the metallic components of the PCB. In the course of the work, single and double direct grinding using the method of disintegration was studied. For the calculation, the test batch of 10,000 kg of two types of PCB was taken for estimation of the self costs and potential profit in the case of complete valuable metals (Ag, Au, Pd) plus Cu extraction. It was shown that from 10,000 kg of studied PCB, it is possible to obtain 1144 and 1644 kg of metal-rich concentrate, which should be further subjected to electro-hydrochlorination for metals leaching. The novelty of this research lies in the fact that a technical and economic analysis has been carried out on a newly developed combined technology for processing electronic waste. This included mechanical processing and electrochemical leaching with the help of the active chlorine that is formed in situ. The real (not specially selected or prepared) waste PCBs were used for the process’s economical efficiency evaluation. The main findings showed that despite the high content of Cu in the studied PCBs, the commercial value was insignificant in relation to the total income from the Ag, Au, and Pd sale. A correlation was established between the self-cost decrease after separative disintegration of PCBs by metal content increase (by specific metals such as Au, Ag, Pd, and Cu) with the metal potential yield after extraction. Full article
(This article belongs to the Special Issue Sustainable Gold Production and Recycling)
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25 pages, 5489 KiB  
Article
Investigation of the Impact of Electrochemical Hydrochlorination Process Parameters on the Efficiency of Noble (Au, Ag) and Base Metals Leaching from Computer Printed Circuit Boards
by Vera Serga, Aleksej Zarkov, Andrei Shishkin, Maksims Melnichuks and Vladimir Pankratov
Metals 2024, 14(1), 65; https://doi.org/10.3390/met14010065 - 05 Jan 2024
Viewed by 926
Abstract
The development of environmentally friendly and energy-saving processes for recycling electronic waste (e-waste) is still relevant today. The research presented in this work relates to hydrometallurgy, namely, the electrochemical leaching of metals from e-waste under the action of alternating current (AC) into hydrochloric [...] Read more.
The development of environmentally friendly and energy-saving processes for recycling electronic waste (e-waste) is still relevant today. The research presented in this work relates to hydrometallurgy, namely, the electrochemical leaching of metals from e-waste under the action of alternating current (AC) into hydrochloric acid solutions of electrolytes, and can be used for leaching both noble and non-ferrous metals from secondary raw materials. The main object of the study was disintegrator-crushed mixed computer PCBs metal-rich powders with a particle size (d) of <90 µm. The impact of such leaching process parameters as temperature (Tel) and composition of the electrolyte solution, AC density (i) on the electrodes, experiment duration (tex) while maintaining a constant electrolyte temperature (60 °C, 70 °C, and 80 °C) on the metal (Au, Ag, Cu, Al, Ni, Pb, Sn, Ti, Zn, and Fe) leaching efficiency has been studied. In addition, under similar experimental conditions, but without external control of Tel, the kinetics of metal leaching from raw material powders obtained via PCBs single and double crushing in a disintegrator has been also presented. Comparison of raw material powders obtained from different batches of the source material showed both the variability of its chemical composition and the different kinetics of Au and Ag leaching under the same experimental conditions. The optimal conditions for pretreatment of the raw material obtained by single crushing in a disintegrator (CHCl = 6 mol·L−1, i = 0.88 A·cm−2, tex = 1 h, solid-to-liquid ratio—8.6 g·L−1 and without external control of Tel) were determined. It has been shown that this electrochemical pretreatment is accompanied by transition of only base metals into the electrolyte solution, making it possible to significantly reduce their concentration in the final solution. Under pretreatment conditions, the following degree of metal leaching (RMe) has been established: RCu = 98.2%, RAl = 62.8%, RNi = 53.4%, RPb = 93.2%, RSn = 98.0%, RTi = 88.5%, RZn = 61.6%, and RFe = 78.8%. As a result of a subsequent two-hour electrochemical treatment of a solid residue, the degree of leaching of gold and silver was 73.6% and 86.7%, respectively. The presented results provide a broader understanding of the possibility of using the proposed electrochemical hydrochlorination method for noble and base metals leaching from waste PCBs. The novelty and practical value of this research is a validation of the developed technology in laboratory conditions using the real batch of the PCBs. This approach may also be useful to researchers involved in the recycling of other types of secondary raw materials. Full article
(This article belongs to the Special Issue Sustainable Gold Production and Recycling)
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19 pages, 11377 KiB  
Article
Fast Gold Recovery from Aqueous Solutions and Assessment of Antimicrobial Activities of Novel Gold Composite
by Tamara Tadić, Bojana Marković, Zorica Vuković, Plamen Stefanov, Danijela Maksin, Aleksandra Nastasović and Antonije Onjia
Metals 2023, 13(11), 1864; https://doi.org/10.3390/met13111864 - 09 Nov 2023
Viewed by 1046
Abstract
A novel porous gold polymer composite was prepared by the functionalization of a glycidyl methacrylate-based copolymer (pGME) with ethylene diamine (pGME-en), and activation by gold (pGME-en/Au), in a simple batch adsorption procedure in an acid solution, at room temperature. Detailed characterization of the [...] Read more.
A novel porous gold polymer composite was prepared by the functionalization of a glycidyl methacrylate-based copolymer (pGME) with ethylene diamine (pGME-en), and activation by gold (pGME-en/Au), in a simple batch adsorption procedure in an acid solution, at room temperature. Detailed characterization of the pGME-en before and after activation was performed. The main focuses of this research were the design of a method that can enable the recovery of gold and the reuse of this multipurpose sorbent as an antimicrobial agent. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis pointed out amine groups as the primary binding sites for Au activation, while hydroxyl groups also contributed to the chelation reaction. pGME-en exhibited fast gold adsorption with an adsorption half-time of 5 min and an equilibrium time of 30 min. The maximal adsorption capacity was about 187 mg/g. The analysis of sorption experimental data with a non-linear surface reaction and diffusion-based kinetic models revealed the pseudo-second-order and Avrami model as the best fit, with unambiguous control by liquid film and intra-particle diffusion. The biological activity studies against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, and Candida albicans revealed moderate activity of pGME-en/Au against different bacterial and fungal species. pGME-en/Au was stable in a saline solution, with a release of approximately 2.3 mg/g after 24 h. Full article
(This article belongs to the Special Issue Sustainable Gold Production and Recycling)
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11 pages, 424 KiB  
Article
Experimenting with Dimethyl Sulfoxide to Leach Gold from a Colombian Artisanal Gold Ore
by Pariya Torkaman, Akihiro Yoshimura, Leslie M. Lavkulich and Marcello M. Veiga
Metals 2023, 13(11), 1855; https://doi.org/10.3390/met13111855 - 06 Nov 2023
Viewed by 1237
Abstract
The diverse uses of gold and its crucial role in the global economy are growing, particularly during cycles of economic crises. The broad use of cyanide by conventional gold-mining companies and mercury by artisanal miners poses environmental and health concerns for local communities. [...] Read more.
The diverse uses of gold and its crucial role in the global economy are growing, particularly during cycles of economic crises. The broad use of cyanide by conventional gold-mining companies and mercury by artisanal miners poses environmental and health concerns for local communities. This article introduces an innovative gold-leaching process using a non-toxic organic reagent, dimethyl sulfoxide (DMSO), a water-free lixiviant that extracts gold from ores/concentrates in combination with copper halides. The results of laboratory experiments using dimethyl sulfoxide and a sample of high-grade gold ore from Colombia show that 96.5% of the gold was extracted in 2 h at room temperature. The typical cyanidation process using 5 g/L of CN− at pH 10.5 on the same ore sample obtained 97% gold extraction in 24 h at ambient temperature. The gold extracted using DMSO was precipitated by adding a mild acidic solution, and the reagent can be recycled via distillation and reused in repeating cycles. The results show that DMSO can be used as a promising agent for gold leaching, offering a straightforward, cost-effective, and eco-friendly procedure with minimal chemical waste. Full article
(This article belongs to the Special Issue Sustainable Gold Production and Recycling)
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20 pages, 5355 KiB  
Article
Sensitivity of Gold Lixiviants for Metal Impurities in Leaching of RAM Printed Circuit Boards
by Alexander Birich, Zixi Gao, Dzeneta Vrucak and Bernd Friedrich
Metals 2023, 13(5), 969; https://doi.org/10.3390/met13050969 - 17 May 2023
Cited by 1 | Viewed by 2058
Abstract
The importance of gold recovery from waste printed circuit boards is continuously increasing due to raising gold prices and demand as well as the need for innovative and flexible recycling methods for this complex waste stream. The state-of-the-art recycling process aims at the [...] Read more.
The importance of gold recovery from waste printed circuit boards is continuously increasing due to raising gold prices and demand as well as the need for innovative and flexible recycling methods for this complex waste stream. The state-of-the-art recycling process aims at the pyrometallurgical recovery of noble metals, mainly using a copper collector. Different technical limitations justify the application of a hydrometallurgical process alternative for recovering gold. The direct application of gold lixiviants on comminuted PCBs is hardly possible due to the high concentration of metal impurities. As a solution, most researchers propose hydrometallurgical separation of disturbing base metals prior to gold extraction. For this, different leaching systems with aggressive chemicals can be applied, often leaving residual base metal concentrations behind. Within this study, two different leaching parameter sets were investigated to separate base metals and determine the impact of residual base metals on subsequent gold recovery. The gold lixiviants that were applied for comparison were thiosulfate, thiourea, iodine-iodide, NBS, and cyanide. It was found that thiosulfate and thiourea are less sensitive than other lixiviants to metal impurities. When base metals are separated completely, gold recovery is strongly improved, and cyanide also achieves a good gold recovery. Full article
(This article belongs to the Special Issue Sustainable Gold Production and Recycling)
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