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Engineered Artificial Minerals (EnAMs): A Geo-Metallurgical Tool to Recycle Critical...
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Engineered Artificial Minerals (EnAMs): A Geo-Metallurgical Tool to Recycle Critical Elements from Waste Streams: Synthesis, Characterization, Metallurgical and Mechanical Processing (SPP 2315)

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

Deadline for manuscript submissions: 31 May 2025 | Viewed by 8931

Special Issue Editors

Prof. Dr. Urs Alexander Peuker

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Guest Editor
Institute of Mechanical Process Engineering and Mineral Processing, TU Bergakademie Freiberg, 09599 Freiberg, Germany
Interests: mechanical separation processes; solid liquid separation; recycling and mineral processing; particle-particle interactions; particle characterization
Special Issues, Collections and Topics in MDPI journals
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
Prof. Dr. Ursula Elisabeth Adriane Fittschen

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Guest Editor
Institute of Inorganic and Analytical Chemistry, TU Clausthal, 38678 Clausthal-Zellerfeld, Germany
Interests: elemental and element species determination; materials analysis; phase separation
Prof. Dr. Sandra Breitung-Faes

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Guest Editor
The Fraunhofer Research Group, TH Nürnberg, Wassertorstraße 10, 90489 Nürnberg, Germany
Interests: comminution and separation processes; mechanochemical reactions and co-cristallisation; fine powder handling

Special Issue Information

Dear Colleagues,

The central purpose of this Special Issue is to communicate a wide range of research related to the priority programme SPP 2315 Engineered Artificial Minerals (EnAMs). The programme addresses the slag phase of pyrometallurgical processes as an important source for critical technology elements. When slag solidifies, it either forms a homogeneous amorphous structure or generates crystals. These crystals are be seen as artificial minerals (EnAMs) or ores, and their generation is considered to concentrate diluted elements by orders of magnitude. The SPP 2315 looks at Li-, Ta-, or Cr-containing slag systems. The formation of EnAMs itself depends on the thermodynamics of the complex multicomponent slag system and the processing conditions of the melt, e.g., the temperature profile and gradient during solidification.

The core of the programme includes 18 individual projects at various departments of German universities and research institutes in the fields of process engineering, metallurgy, stochastics, organic chemistry, geochemistry, and thermodynamics.

The idea behind this programme is that the recycling industry currently mainly focuses on recovering the main bulk materials, which leads to the under-recognition and loss of metals essential for advanced technological functions in waste streams, such as Ta and Li incorporated into building materials, Nd and Dy dissolved in iron-based construction materials, and Pd dispersed as dust across various process streams. Consequently, this results in downcycling and the depletion of valuable chemical species, since these species are trapped and lost in the slag structures.

The Engineered Artificial Minerals (EnAMs) concept facilitates the selective concentration and recovery of specific elements from small-scale components and multimaterial composites. With regard to metallurgical processing, where the target element is transferred to slag, this involves an additional two-stage strategy: first, integrating the target element into an artificial mineral phase during pyrometallurgical treatment, and second, liberating and separating this mineral from slag. Understanding and quantifying these processes rely on the in situ monitoring and multidimensional analysis of the EnAMs’ structure.

A holistic approach requires an integrated model and simulation, developing new process models to create digital twins of related processes. This involves an enhanced entropy concept to describe material flows' mixture and structure quantitatively. The approach combines particle and thermochemical metallurgy processes into a digital tool to estimate recycling efforts and link to economic, ecological, and life-cycle assessment models, enabling predictive simulations to find the most efficient recycling concept for each element.

Prof. Dr. Urs Alexander Peuker
Prof. Dr. Bernd Friedrich
Prof. Dr. Ursula Elisabeth Adriane Fittschen
Prof. Dr. Sandra Breitung-Faes
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. Minerals 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 2400 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.

Publisher’s Notice

As stated above, the central purpose of this Special Issue is to present research from "Engineered Artificial Minerals (EnAMs): A Geo-Metallurgical Tool to Recycle Critical Elements from Waste Streams: Synthesis, Characterization, Metallurgical and Mechanical Processing (SPP 2315)". Given this purpose, the Guest Editors’ contribution to this Special Issue may be greater than standard Special Issues published by MDPI. Further details on MDPI's Special Issue guidelines can be found here: https://www.mdpi.com/special_issues_guidelines. The Editorial Office and Editor-in-Chief of Minerals has approved this and MDPI’s standard manuscript editorial processing procedure (https://www.mdpi.com/editorial_process) will be applied to all submissions. As per our standard procedure, Guest Editors are excluded from participating in the editorial process for their submission and/or for submissions from persons with whom a potential conflict of interest may exist. More details on MDPI’s Conflict of Interest policy for reviewers and editors can be found here: https://www.mdpi.com/ethics#_bookmark22.

Keywords

  • metallurgical recycling
  • pyrometallurgy
  • mineral processing
  • grain size distribution
  • crushing, milling, breakage and liberation
  • mechanical sorting
  • flotation, magnetic separation, density separation, electrostatic separation
  • flow sheet simulation
  • DEM-modelling and simulation
  • thermodynamic modelling and simulation
  • phase equilibrium and crystallization
  • metallurgical slags
  • Controlled Solidification
  • e-waste and spent batteries

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Published Papers (6 papers)

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Research

14 pages, 20689 KiB  
Article
Enhancing Lithium Recovery from Slag Through Dry Forced Triboelectric Separation: A Sustainable Recycling Approach
by Mehran Javadi, Cindytami Rachmawati, Annett Wollmann, Joao Weiss, Hugo Lucas, Robert Möckel, Bernd Friedrich, Urs Peuker and Alfred P. Weber
Minerals 2024, 14(12), 1254; https://doi.org/10.3390/min14121254 - 10 Dec 2024
Viewed by 678
Abstract
The increasing use of lithium-containing materials highlights the urgent need for their recycling to preserve resources and protect the environment. Lithium-containing slags, produced during the pyrometallurgical process in lithium-ion battery recycling, represent an essential resource for lithium recovery efforts. While multiple methods for [...] Read more.
The increasing use of lithium-containing materials highlights the urgent need for their recycling to preserve resources and protect the environment. Lithium-containing slags, produced during the pyrometallurgical process in lithium-ion battery recycling, represent an essential resource for lithium recovery efforts. While multiple methods for lithium recycling exist, it is crucial to emphasize environmentally sustainable approaches. This study employs dry forced triboelectrification (FTC) to recover valuable components from slag powder, commonly known as engineered artificial minerals (EnAMs). The FTC method is used to change the charge of the target material and achieve a neutral state while other materials remain charged. The downstream electrostatic separator enables the charged particles to be separated from the target material, which in this study is lithium aluminate. The results show that the method is effective, and lithium aluminate can be successfully enriched. Full article
(This article belongs to the Special Issue Engineered Artificial Minerals (EnAMs): A Geo-Metallurgical Tool to Recycle Critical Elements from Waste Streams: Synthesis, Characterization, Metallurgical and Mechanical Processing (SPP 2315))
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21 pages, 7190 KiB  
Article
Experimental and Simulation Studies on the Mn Oxidation State Evolution of a Li2O-MnOx-CaO-SiO2 Slag Analogue
by Sven Hampel, Iyad Alabd Alhafez, Alena Schnickmann, Sophie Wunderlich, Haojie Li, Michael Fischlschweiger, Thomas Schirmer, Nina Merkert and Ursula E. A. Fittschen
Minerals 2024, 14(9), 868; https://doi.org/10.3390/min14090868 - 26 Aug 2024
Viewed by 895
Abstract
This manuscript presents the results from the synthesis and characterization of a slag analogue with a nominal composition of 17 wt% LiMnO2 and 83 wt% Ca2SiO4 encountering fairly high cooling rates in order to study the evolution of Mn-species. [...] Read more.
This manuscript presents the results from the synthesis and characterization of a slag analogue with a nominal composition of 17 wt% LiMnO2 and 83 wt% Ca2SiO4 encountering fairly high cooling rates in order to study the evolution of Mn-species. The Mn species was also simulated from 1223 K to 1773 K using a thermodynamic model, assuming a homogeneous melt. The micro-composition including the Mn species of the solidified slag was determined experimentally, and was used as basis for molecular dynamics (MD) simulation. The MD simulation provides information on structure and viscosity at high temperatures, which are otherwise difficult to access. These parameters significantly influence oxidation state of redox-active elements and the solidified product. The micro-composition analyzed by electron probe micro analysis (EPMA) and synchrotron-based micro-X-ray fluorescence (micro-XRF) showed that Mn-rich and Ca-Si-rich phases are separated. While the Mn-O phases did not contain noticeable Ca, the Ca2SiO4 phase had incorporated 0.6 wt% of Mn. The slag solidified into round-shaped and droplet-shaped grains of a Li-Mn-oxide, some Mn3O4 and Ca2SiO4. The powder X-ray diffraction (PXRD) confirmed the formation of larnite; the identity of the Li-Mn-oxide, however, remained inconclusive. The Mn oxidation state (OS) was identified using synchrotron-based micro-X-ray absorption near edge spectroscopy (micro-XANES). The Mn-O grains matched well with Li-Mn-oxides and a Mn OS: +3, e.g., LiMn3+O2. Small areas matching hausmannite (Mn2+Mn23+O4) were also identified. The OS of Mn in the silicate phase could not be identified. For comparison, a slowly cooled slag analogue with similar composition, but higher Si content, was also subjected to micro-XANES. The slowly cooled slag formed long Mn-rich needles in a matrix of large calcium silicate crystals. The Mn-rich crystals matched well with the XANES spectrum of a Mn3+ Li-oxide like LiMn3+O2. At the rim of the needles, the Mn-spectra matched well the hausmannite (Mn2+Mn23+O4) reference. In the silicate phases, Mn had an OS: +2, unambiguously. The melt structure at different temperatures of two compositions, i.e., LiMn3+O2 and Ca2SiO4, was simulated using molecular dynamics (MD). They serve as model compositions, assuming a heterogeneous melt. The results show significant different degrees of polymerization and viscosity. Information from MD simulations can support the identification of potentially different oxygen permeability and with that prediction of oxidation states. The bulk composition was identified by inductively coupled plasma optical emission spectrometry (ICP-OES), bulk structure by PXRD and bulk species by lab-XANES. The synchrotron micro analysis including micro-XRD were performed at the microfocus beamline I18 at the Diamond Light Source. Pure reference compounds were prepared and characterized with the same multi-modal approach. Full article
(This article belongs to the Special Issue Engineered Artificial Minerals (EnAMs): A Geo-Metallurgical Tool to Recycle Critical Elements from Waste Streams: Synthesis, Characterization, Metallurgical and Mechanical Processing (SPP 2315))
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17 pages, 5124 KiB  
Article
In Situ Hydrophobization of Lithium Aluminate Particles for Flotations by Dry Grinding in the Presence of Punicines
by Frédéric Steiner, Ali Zgheib, Maximilian Hans Fischer, Lukas Büttner, Andreas Schmidt and Sandra Breitung-Faes
Minerals 2024, 14(7), 650; https://doi.org/10.3390/min14070650 - 25 Jun 2024
Cited by 1 | Viewed by 1661
Abstract
The engineered artificial mineral (EnAM) lithium aluminate (LiAlO2) is a promising candidate for the recycling of lithium from slags, which can originate from the reprocessing of batteries, for example. Derivatives of the natural product Punicine (1-(2′,5′-dihydroxyphenyl)-pyridinium) from Punica granatum have been [...] Read more.
The engineered artificial mineral (EnAM) lithium aluminate (LiAlO2) is a promising candidate for the recycling of lithium from slags, which can originate from the reprocessing of batteries, for example. Derivatives of the natural product Punicine (1-(2′,5′-dihydroxyphenyl)-pyridinium) from Punica granatum have been proven to be effective switchable collectors for the flotation of this mineral as they react to light. In the present study, three Punicines were added to a planetary ball mill before grinding LiAlO2 to particle sizes suitable for flotation. We investigated the influence of Punicine and two derivatives with C10 and C17 side chains on the grinding results at different grinding times and conditions as well as on the yields in flotations. SEM images of the particles, IR and ICP–OES measurements provided insights into the Punicine–particle interactions. They showed that Punicines not only prevent the formation of hydrophilic and thus undesirable lithium aluminate hydroxide hydrate (LiAl2(OH)7 ▪ x H2O) surfaces in this process, as is unavoidable in aqueous flotation without this pretreatment, they also prevent the undesired release of lithium cations into the aqueous phase. Due to considerable hydrophobization of the particle surface of LiAlO2, nearly quantitative recovery rates of this engineered artificial mineral are achieved using the process described here. Full article
(This article belongs to the Special Issue Engineered Artificial Minerals (EnAMs): A Geo-Metallurgical Tool to Recycle Critical Elements from Waste Streams: Synthesis, Characterization, Metallurgical and Mechanical Processing (SPP 2315))
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15 pages, 4931 KiB  
Article
Stabilization of Mn4+ in Synthetic Slags and Identification of Important Slag Forming Phases
by Alena Schnickmann, Danilo Alencar De Abreu, Olga Fabrichnaya and Thomas Schirmer
Minerals 2024, 14(4), 368; https://doi.org/10.3390/min14040368 - 30 Mar 2024
Cited by 5 | Viewed by 1172
Abstract
The expected shortage of Li due to the strong increase in electromobility is an important issue for the recovery of Li from spent Li-ion batteries. One approach is pyrometallurgical processing, during which ignoble elements such as Li, Al and Mn enter the slag [...] Read more.
The expected shortage of Li due to the strong increase in electromobility is an important issue for the recovery of Li from spent Li-ion batteries. One approach is pyrometallurgical processing, during which ignoble elements such as Li, Al and Mn enter the slag system. The engineered artificial mineral (EnAM) strategy aims to efficiently recover critical elements. This study focuses on stabilizing Li-manganates in a synthetic slag and investigates the relationship between Mn4+ and Mg and Al in relation to phase formation. Therefore, three synthetic slags (Li, Mg, Al, Si, Ca, Mn, O) were synthesized. In addition to LiMn3+O2, Li2Mn4+O3 was also stabilized. Both phases crystallized in a Ca-silicate-rich matrix. In the structures of Li2MnO3 and LiMnO2, Li and Mn can substitute each other in certain proportions. As long as a mix of Mn2+ and Mn3+ is present in the slag, spinels form through the addition of Mg and/or Al. Full article
(This article belongs to the Special Issue Engineered Artificial Minerals (EnAMs): A Geo-Metallurgical Tool to Recycle Critical Elements from Waste Streams: Synthesis, Characterization, Metallurgical and Mechanical Processing (SPP 2315))
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36 pages, 5708 KiB  
Article
Behavior of Tantalum in a Fe-Dominated Synthetic Fayalitic Slag System—Phase Analysis and Incorporation
by Thomas Schirmer, Jessica Hiller, Joao Weiss, Daniel Munchen, Hugo Lucas, Ursula E. A. Fittschen and Bernd Friedrich
Minerals 2024, 14(3), 262; https://doi.org/10.3390/min14030262 - 29 Feb 2024
Cited by 3 | Viewed by 1760
Abstract
Pyrometallurgical processes produce slags that may contain valuable elements because of their high oxygen affinity. However, the concentration is extremely low, which causes losses. In fact, these elements, for example, tantalum and rare earth elements, are less than 1% recycled. To return such [...] Read more.
Pyrometallurgical processes produce slags that may contain valuable elements because of their high oxygen affinity. However, the concentration is extremely low, which causes losses. In fact, these elements, for example, tantalum and rare earth elements, are less than 1% recycled. To return such technologically important elements to the material cycle, pyrometallurgically is used to enrich them in the simplest possible compounds within the slag, which have favorable properties for recovery (morphology, crystal size, magnetic properties), allowing further mechanical separation. The purpose of modification of the slag system is to obtain engineered artificial minerals” (EnAM), a process in which targeted minerals with high element concentration are formed. In this article, this approach is investigated using tantalum-rich fayalitic slag, since this slag is commonly found in the industry for the pyrometallurgical treatment of waste electric and electronic equipment. Synthetic fayalitic slags in reducing environment under different cooling rates were produced with Ta addition. The characterization of the produced samples was carried out using powder X-ray diffraction (PXRD) and electron probe microanalysis (EPMA). Additionally, the speciation of Fe and Ta was accessible through X-ray absorption near-edge structure (XANES) spectroscopy. EPMA also provided a semiquantitative assessment of the Ta distribution in these individual compounds. In these slags, tantalum accumulated in perovskite-like oxidic and silicate compounds as well as in magnetic iron oxides. The enrichment factor is highest in tantalite/perovskite-type oxides (FexTayO6, CaxFeyTazO3) with up to 60 wt.% Ta and ‘tantalomagnetite’ (FeII(FeIII(2-5/3x)Tax)O4) with a maximum of ~30 wt.% Ta (only fast cooling). This is followed by a perovskite-like silicon containing oxide (XYO3) with 12–15 wt.% Ta (only slow cooling), and a hedenbergite-like compound (XYZ2O6) with a varying content of 0.3–7 wt.%. The Ta concentration in pure Fe, Fe(1-x)O, hercynitic spinel and hematite is negligible. Despite the very low phase fraction, the most promising EnAM compound is nevertheless perovskite-like tantalum oxide, as the highest enrichment factor was obtained. Tantalum-rich magnetite-like oxides also could be promising. Full article
(This article belongs to the Special Issue Engineered Artificial Minerals (EnAMs): A Geo-Metallurgical Tool to Recycle Critical Elements from Waste Streams: Synthesis, Characterization, Metallurgical and Mechanical Processing (SPP 2315))
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18 pages, 8984 KiB  
Article
Characterisation of the Grain Morphology of Artificial Minerals (EnAMs) in Lithium Slags by Correlating Multi-Dimensional 2D and 3D Methods
by Cindytami Rachmawati, Joao Weiss, Hugo Ignacio Lucas, Erik Löwer, Thomas Leißner, Doreen Ebert, Robert Möckel, Bernd Friedrich and Urs Alexander Peuker
Minerals 2024, 14(2), 130; https://doi.org/10.3390/min14020130 - 25 Jan 2024
Cited by 3 | Viewed by 1771
Abstract
Slags from the metallurgical recycling process are an important source of resources classified as critical elements by the EU. One example is lithium from Li-ion battery recycling. In this context, the thermodynamic properties of the recycled component system play a significant role in [...] Read more.
Slags from the metallurgical recycling process are an important source of resources classified as critical elements by the EU. One example is lithium from Li-ion battery recycling. In this context, the thermodynamic properties of the recycled component system play a significant role in the formation of the Li-bearing phases in the slag, in this case, LiAlO2. LiAlO2 crystal formation could be engineered and result in varying sizes and occurrences by different metallurgical processing conditions. This study uses pure ingredients to provide a synthetic model material which can be used to generate the valuable phase in the slag, or so-called engineered artificial minerals (EnAMs). The aim is to investigate the crystallisation of LiAlO2 as an EnAM by controlling the cooling conditions of the model slag to optimise the EnAM formed during crystallisation. Characterisation of the EnAMs is an important step before further mechanically processing the material to recover the valuable element Li, the Li-bearing species, respectively. Investigations are conducted using powder X-ray diffraction (XRD), X-ray fluorescence (µXRF), and X-ray Computer Tomography (XCT) on two different artificial lithium slags from MnO-Al2O3-SiO2-CaO systems with different cooling temperature gradients. The result shows the different EnAM morphology along the height of the slag, which is formed under different slag production conditions in a semi-pilot scale experiment of 5 kg. Based on the different EnAM morphologies, three defined qualities of the EnAM are identified: granular, dendritic, and irregular-shape EnAM. Full article
(This article belongs to the Special Issue Engineered Artificial Minerals (EnAMs): A Geo-Metallurgical Tool to Recycle Critical Elements from Waste Streams: Synthesis, Characterization, Metallurgical and Mechanical Processing (SPP 2315))
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