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Advances in Recycling of Valuable Metals—2nd Edition

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

Deadline for manuscript submissions: 30 October 2024 | Viewed by 11134

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Special Issue Editors

Dr. Denise Crocce Romano Espinosa

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Department of Chemical Engineering, Polytechnic School, University of Sao Paulo, São Paulo 05508-080, Brazil
Interests: hydrometallurgy; separation process; electrodialysis; reverse osmosis; ultrafiltration; microfiltration; solvent extraction; recycling processes; circular economy; SDGs; net-zero emission
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Prof. Dr. Daniel Assumpcao Bertuol

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Department of Chemical Engineering (DEQ), Universidade Federal de Santa Maria, Santa Maria, Brazil
Interests: recycling processes; leaching; liquid-liquid extraction; separation and purification process; pyrolysis; mechanical processing; nanofibers; supercritical fluids

Dr. Amilton Botelho Junior

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Special Issue Information

Dear Colleagues,

The interest in urban mining to recover critical metals has increased in recent decades. Among them are cobalt, lithium, rare earth elements, gallium, germanium, hafnium, indium, niobium, platinum group metals, tantalum, titanium, vanadium, tungsten, and strontium.

The insertion of metals into society through increasingly complex electronic equipment adds even greater pressure on extractive processes from primary sources. For instance, printed circuit boards are becoming increasingly complex, as well as the replacement of technologies (fluorescent lamps for LED or LCD TVs for LED and OLED).

At the same time, the decrease in metal content in ores results in the increased generation of mining waste, which can also be used as a secondary source of other critical metals. For example, bauxite is the main ore for making alumina, and the Bayer process residue (also known as red mud) contains critical and valuable metals, such as titanium, zirconium, and rare earth elements (including scandium, yttrium, lanthanum, and cerium).

For this reason, recycling processes, used to obtain critical metals from urban mining and industrial waste, are important to supply critical metals. However, as the residues are becoming more complex, further research is necessary to develop new recycling approaches toward a circular economy model and achieve the Sustainable Development Goals from the United Nations.

This Special Issue aims to address the most recent developments in recycling processes to obtain critical and valuable metals from secondary sources by performing pyro- and hydrometallurgical techniques, which includes pyrolysis, roasting, smelting, calcination, leaching (inorganic and organic acids and alkali), ion exchange separation (resins and solvent extraction), precipitation, ionic liquids, deep eutectic solvents, supercritical fluids, nanohydrometallurgy, and biohydrometallurgy. Moreover, research articles will focus on the techniques and processes used to achieve the Sustainable Development Goals.

We gladly invite you to submit your work to this Special Issue.

Dr. Denise Crocce Romano Espinosa
Prof. Dr. Daniel Assumpcao Bertuol
Dr. Amilton Botelho Junior
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

recycling process
hydrometallurgy
pyrometallurgy
critical metals
circular economy
SDGs
WEEE

Published Papers (5 papers)

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Research

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14 pages, 2746 KiB

Open AccessArticle

Towards Sustainable Battery Recycling: A Carbon Footprint Comparison between Pyrometallurgical and Hydrometallurgical Battery Recycling Flowsheets

by Gert Van Hoof, Bénédicte Robertz and Bart Verrecht

Metals 2023, 13(12), 1915; https://doi.org/10.3390/met13121915 - 21 Nov 2023

Viewed by 3304

Abstract

The expected large growth in electric mobility presents challenges, such as requiring a very large amount of critical raw materials like nickel, cobalt, and lithium. Due to this expected growth significant amounts of production scrap from cell and battery manufacturing will be generated. Over the next decade, increasingly larger amounts of Li-ion batteries from electric vehicles will also reach their end-of-life. Hence, in order to close the loop, the development and industrialization of sustainable battery recycling flowsheets are key so that both production scrap and end-of-life batteries can be recycled back to their ‘battery grade’ building blocks. Battery recycling flowsheets are typically categorized into two categories: (1) ‘Pyro-Hydro’, a combination of battery smelting in a pyrometallurgical process, followed by the further refining of the alloy via hydrometallurgy; and (2) ‘(Thermo)mechanical-Hydro’, a combination of (thermo)mechanical pretreatment and further hydrometallurgical refining of the resulting black mass. In this paper, a carbon footprint analysis is presented comparing these two battery recycling approaches: ‘Pyro-Hydro’ and ‘Thermomechanical-Hydro’, taking into account the impact of the latest evolutions in process technology and efficiency. To facilitate this comparison, a prospective LCA was carried out for the respective flowsheets. The quantitative analysis shows that ‘Pyro-Hydro’ leads to the lowest overall carbon footprint but also that both ‘Pyro-Hydro’ and ‘Thermomechanical-Hydro’ flowsheets have their challenges and opportunities for decarbonization. The inclusion of the fate of side streams such as graphite and electrolyte in the analysis is shown to be critically important in order to gain an objective and complete view. Full article

(This article belongs to the Special Issue Advances in Recycling of Valuable Metals—2nd Edition)

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18 pages, 4119 KiB

Open AccessArticle

An Experimental Study on the Kinetics of Leaching Ion-Adsorbed REE Deposits with Different Concentrations of Magnesium Sulfate

by Min Han, Dan Wang, Yunzhang Rao, Wei Xu and Wen Nie

Metals 2023, 13(11), 1906; https://doi.org/10.3390/met13111906 - 18 Nov 2023

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Abstract

As an important substitute for ammonium-free leaching, magnesium sulfate is applied as a leaching agent for the mining of ion-adsorbed REE (rare earth element) deposits. Upon deriving the equation regulating the leaching kinetics on the basis of the REE “shrinking core model” during the leaching process of magnesium sulfate, we conducted leaching experiments of natural particle-sized REE deposits by applying magnesium sulfate with concentrations of 1%, 2%, 3% and 4%. Hence, the leaching efficiencies and mass transfer rates were obtained. The results show that the hybrid control equation

\frac{μ δ}{D_{1}} α + \frac{3 μ r}{2 D_{2}} [1 - \frac{2}{3} {α - (1 - α)}^{\frac{2}{3}}] = \frac{3 C_{0} M}{ρ r}

is applicable for describing the leaching process when the concentration of magnesium sulfate is 1%; when the concentrations reach 2%, 3% and 4%, the external diffusion control equation

α = k t

is appropriate to describe the leaching processes. The leaching efficiency of REE deposits reaches over 90%, specifically, 94.65%, 97.24% and 97.98%, when the concentration of magnesium sulfate is 2%, 3% and 4%, respectively. The maximum mass transfer rate appears when the concentration of magnesium sulfate is 4%, and the leaching time is reduced by 1.96 times compared to 1% concentration of magnesium sulfate. The results provide a favorable theoretical basis for the green and efficient extraction of ion-adsorbed REEs. Full article

(This article belongs to the Special Issue Advances in Recycling of Valuable Metals—2nd Edition)

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19 pages, 4754 KiB

Open AccessArticle

Efficient Gallium Recovery from Aqueous Solutions Using Polyacrylonitrile Nanofibers Loaded with D2EHPA

by Bibiane Nardes Segala, Bruno München Wenzel, Nicholas P. Power, Satheesh Krishnamurthy, Daniel Assumpção Bertuol and Eduardo Hiromitsu Tanabe

Metals 2023, 13(9), 1545; https://doi.org/10.3390/met13091545 - 1 Sep 2023

Cited by 1 | Viewed by 1159

Abstract

Centrifugal spinning was utilized in producing polyacrylonitrile (PAN) nanofibers loaded with extractant di-(2-ethylhexyl) phosphoric acid (D2EHPA) for efficient adsorption recovery of gallium from aqueous solutions. The adsorption experimental data were best fitted by a pseudo-second-order kinetic model and the BET equilibrium isotherm model. Optimal adsorption performance by the PAN/D2EHPA nanofibers exhibited an adsorption capacity of 33.13 mg g⁻¹ for the recovery of gallium at pH 2.5 and 55 °C. The thermodynamic parameters demonstrated that adsorption was endothermic, spontaneous, and favorable. The stability and reusability of the nanofibers was assessed, demonstrating retention of structural and functional integrity for the nanofibers over five cycles of an adsorption/desorption process, whilst retaining adsorption efficiency. The results demonstrate that PAN/D2EHPA nanofibers have excellent potential for utilization in an efficient adsorption process for gallium recovery, offering significant positive environmental impact over conventional liquid–liquid extraction methods. Full article

(This article belongs to the Special Issue Advances in Recycling of Valuable Metals—2nd Edition)

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16 pages, 2706 KiB

Open AccessArticle

Structure Investigation of La, Y, and Nd Complexes in Solvent Extraction Process with Liquid Phosphine Oxide, Phosphinic Acid, and Amine Extractants

by Amilton Barbosa Botelho Junior, Natália Olim Martins da Silva, Jorge Alberto Soares Tenório and Denise Crocce Romano Espinosa

Metals 2023, 13(8), 1434; https://doi.org/10.3390/met13081434 - 10 Aug 2023

Cited by 2 | Viewed by 954

Abstract

The main challenge in separating REEs through hydrometallurgical processes is their chemical similarities. Despite the literature widely presenting the possibilities for organic extractants, there is a lack of evaluation of the structures formed between the REEs and the extractants. The present study aimed to evaluate different extractants (neutral, anionic, and acid extractants) for separating La, Y, and Nd. The extraction efficiencies were evaluated, and the structure investigation was carried out in FT-IR. From the results obtained, it is clear that the extraction order is Alamine 336 <<< Cyanex 272 < Cyanex 923, where both acid extractants were more selective for Y than for La and Nd. The extraction achieved 99% at pH 5.0 in nitric acid media, and a Y/La ratio of 2 and a Y/Nd ratio of 4 using Cyanex 923. The present study also elucidated the organometallic complexation between Cyanex 923 and Cyanex 272 with Y and La, which may improve separation processes to obtain critical metals from primary and secondary sources. Full article

(This article belongs to the Special Issue Advances in Recycling of Valuable Metals—2nd Edition)

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Review

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25 pages, 3577 KiB

Open AccessReview

Sustainable Recovery, Recycle of Critical Metals and Rare Earth Elements from Waste Electric and Electronic Equipment (Circuits, Solar, Wind) and Their Reusability in Additive Manufacturing Applications: A Review

by Vasileios Stratiotou Efstratiadis and Nikolaos Michailidis

Metals 2022, 12(5), 794; https://doi.org/10.3390/met12050794 - 4 May 2022

Cited by 14 | Viewed by 4082

Abstract

The demand for high-efficiency, low-energy consumption materials, with high durability and stability, has led to the rapid increase of the demand and prices of Rare Earth Elements (REE). The REE monopoly of some countries has held the shift of humanity towards sustainability and renewable energy sources back. The isolation, recovery, and recycle of REE from waste electric and electronic equipment (WEEE) constitute the disengagement strategy and can lead to significant economic benefits, via sustainability. The introduction of critical raw materials (RM), derived from WEEE, as additives to filaments used for the synthesis of composite materials, employed by Additive Manufacturing (AM) applications, has tremendous potential for the performance and the commercialization of the final products by adding unique characteristics, such as antibacterial properties, enhanced mechanical and magnetic properties, and thermal and electrical conductivity. The low cost of the recycled RM, the small numbers of process stages, and the inception of a zero-waste paradigm, present its upscalability, with a realistic view to its industrial employment. Although there are many articles in literature that have reviewed WEEE recycle, a comprehensive review on the conditions, parameters, procedure flow charts, and novel properties of the final composite materials with regards to every RM is missing. Full article

(This article belongs to the Special Issue Advances in Recycling of Valuable Metals—2nd Edition)

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