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Minerals
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Recycling of Mining and Solid Wastes
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Recycling of Mining and Solid Wastes

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

Deadline for manuscript submissions: 30 June 2025 | Viewed by 8879

Special Issue Editors

Prof. Dr. Weslei Monteiro Ambros

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Guest Editor
Mineral Processing Laboratory, Federal University of Rio Grande do Sul, 9500 Bento Gonçalves Avenue, Porto Alegre 91501-970, Brazil
Interests: mineral processing; extractive metallurgy; urban mining; gravity separation; granular materials; mass and energy balances
Special Issues, Collections and Topics in MDPI journals
Dr. Irineu Antonio Schadach Brum

E-Mail Website
Guest Editor
Mineral Processing Laboratory, Federal University of Rio Grande do Sul, 9500 Bento Gonçalves Avenue, Porto Alegre 91501-970, Brazil
Interests: waste recycling; emerging pollutants; mineral processing; froth flotation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The diminishing ore grades pose increasingly significant economic and sustainability challenges for primary extraction from ores. Simultaneously, each year witnesses the establishment of new records for solid waste production, and long-forgotten waste dumps are now being recognized as valuable reservoirs of raw materials. This shift has given rise to a prominent trend: the growing interest in extracting raw materials, particularly the scarcer ones, from secondary resources. This evolving field is now commonly referred to as "urban mining."

Within this context, this Special Issue is dedicated to the compilation and presentation of the latest advancements in the processing and extraction of raw materials from mining and solid waste. We cordially invite original research, comprehensive reviews, and technical papers addressing the treatment of mining and metallurgical waste sources (including waste rocks, tailings, slags, dust, and sludges) as well as solid waste widespread generated (plastics, construction and demolition waste, waste from electrical and electronic equipment, biomass, etc.). We are committed to providing a comprehensive platform for discussing these emerging challenges and opportunities in the field of solid waste recycling, fostering a deeper understanding of sustainable resource extraction from secondary resources.

In anticipation of your valuable contributions to this Special Issue, we look forward to collectively advancing our knowledge of sustainable waste recycling. Your insights are vital in shaping the future of resource management and environmental sustainability in a world where secondary resources play an increasingly critical role. We invite you to share the rich possibilities that the recycling of mining and solid wastes present, forging a path toward a more resource-efficient and sustainable future.

Prof. Dr. Weslei Monteiro Ambros
Dr. Irineu Antonio Schadach Brum
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.

Keywords

  • recycling
  • secondary resources
  • solid wastes
  • urban mining
  • mining wastes
  • metallurgical wastes
  • construction and demolition waste
  • e-waste

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Published Papers (7 papers)

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Research

13 pages, 1524 KiB  
Article
The New Paradigm Caused by Regulation (EU) 2024/1252 on the Upcycling of Landfilled Ferrous Slags—Case Study: Iron and Steel Slag Dumps in Romania
by Andrei-Lucian Timiș, Ion Pencea, Zbynek Karas, Philipp Gründken, Adrian Priceputu, Constantin Ungureanu, Florentina Niculescu, Ramona-Nicoleta Turcu, Gheorghe Iacob and Dragoș-Florin Marcu
Minerals 2025, 15(3), 260; https://doi.org/10.3390/min15030260 - 1 Mar 2025
Viewed by 796
Abstract
Romania has some huge ferrous slag stockpiles that are secondary resources of minerals. Although a sizable portion of ferrous slags is recycled for use in building roads and other infrastructure, a sizable portion is still dumped. By November 2026, Member States must submit [...] Read more.
Romania has some huge ferrous slag stockpiles that are secondary resources of minerals. Although a sizable portion of ferrous slags is recycled for use in building roads and other infrastructure, a sizable portion is still dumped. By November 2026, Member States must submit information on the quantity of critical raw materials (CRMs) in their secondary resources, as well as the quantification techniques employed, in accordance with Regulation (EU) 2024/1252. Therefore, the XRFS reliable measurements carried on ferrous slags were addressed to prevent dissipative loss of CRMs in cases where an improper slag recycling route is operated. The main novelty of this paper is the method of ensuring the reliability of the XRFS results based on weighted arithmetic mean and on the maximum likelihood approach. Secondly, the XRFS measurements carried on ferrous slags demonstrate that they contain CRMs like Ba, Sr, Y, etc.; however, below the minimum cut-off grade for CRMs, recovery XRFS cannot detect light CRMs. Our preliminary LIBS measurements on ferrous slags disclosed the presence of Li and Be. The drawbacks of the XRFS technique impose further research to develop an integrated XRFS, LIBS, and XRD procedure for comprehensive and trustworthy CRMs screening in extractive waste piles. Full article
(This article belongs to the Special Issue Recycling of Mining and Solid Wastes)
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27 pages, 11136 KiB  
Article
Dry Magnetic Separation and the Leaching Behaviour of Aluminium, Iron, Titanium, and Selected Rare Earth Elements (REEs) from Coal Fly Ash
by Amanda Qinisile Vilakazi, Alan Shemi and Sehliselo Ndlovu
Minerals 2025, 15(2), 119; https://doi.org/10.3390/min15020119 - 25 Jan 2025
Viewed by 965
Abstract
Coal fly ash (CFA) is a commercially viable source of alumina comparable to traditional bauxite deposits. Due to its high silica content and alumina in the refractory mullite phase, the most suitable processing technique is the sinter-H2SO4 leach process. However, [...] Read more.
Coal fly ash (CFA) is a commercially viable source of alumina comparable to traditional bauxite deposits. Due to its high silica content and alumina in the refractory mullite phase, the most suitable processing technique is the sinter-H2SO4 leach process. However, this process is energy-intensive, has low selectivity for Al, and generates a secondary solid waste residue. To develop a sustainable process that is economically attractive, Al can be extracted with REEs, Ti, and Fe as saleable products, while secondary solid waste is regenerated for further applications to achieve high-value and high-volume utilisation of CFA. This study focused on the potential extraction of selected REEs (Ce, La, Nd, Y, and Sc), Al, Ti, and Fe, using dry magnetic separation and the sinter-H2SO4 leach process. XRD analysis showed that CFA is predominantly amorphous with crystalline mullite, quartz, and magnetite/hematite. Further analysis using SEM-EDS and TIMA showed Al-Si-rich grains as the predominant phase, with discrete REE-bearing grains (phosphates and silicates) and Fe-oxide (magnetite/hematite) grains. Traces of REEs, Ti, Ca, Si, and Fe were also found in the Al-Si-rich grains. Discrete Fe-oxide was recovered using dry magnetic separation, and up to 65.9% Fe was recovered at 1.05 T as the magnetic fraction (MF). The non-magnetic fraction (non-MF) containing quartz, mullite, and amorphous phase was further processed for preliminary leaching studies. The leaching behaviour of Al, Ti, Fe, and the selected REEs was investigated using the direct H2SO4 and sinter-H2SO4 leaching processes. The maximum extraction efficiency was observed using the sinter-H2SO4 leach process at 6 M H2SO4, a 1:5 solid-to-liquid ratio, 70 °C, and a residence time of 10 h, yielding 77.9% Al, 62.1% Fe, 52.3% Ti, and 56.7% Sc extractions. The extraction efficiencies for Ce, La, Nd, and Y were relatively lower at 23.2%, 27.6%, 11.3%, and 11.2%, respectively. Overall, the results demonstrate that the extraction of REEs using the sinter-H2SO4 leach process is strongly influenced by the complex CFA phase composition and the possible formation of insoluble calcium sulphates. Appreciable extraction of Al, Fe, Ti, and Sc was also observed, suggesting a potential two-step leaching process for the extraction of REEs as a feasible option for the industrial recovery of multiple saleable products. Full article
(This article belongs to the Special Issue Recycling of Mining and Solid Wastes)
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14 pages, 2879 KiB  
Article
Extraction of Gold from Tailings Using Ethaline Deep Eutectic Solvent
by Marema Jack Khuduwe, Alan Shemi and Sehliselo Ndlovu
Minerals 2024, 14(12), 1239; https://doi.org/10.3390/min14121239 - 5 Dec 2024
Viewed by 1497
Abstract
For over a century, cyanidation has been a highly effective method for extracting gold from gold-bearing sources. However, due to environmental, health, and safety concerns associated with this process, considerable efforts have been devoted to exploring the use of alternative, less toxic, and [...] Read more.
For over a century, cyanidation has been a highly effective method for extracting gold from gold-bearing sources. However, due to environmental, health, and safety concerns associated with this process, considerable efforts have been devoted to exploring the use of alternative, less toxic, and environmentally friendly reagents. In this study, a comparative cyanide and ethaline deep eutectic solvent (DES) leaching study of gold from the Witwatersrand gold tailings was undertaken. A Statistical Design of Experiments (DOE) was used for the screening and optimization of significant process factors to achieve optimal gold extraction. The factors investigated include the reagent concentration, leaching time, pulp density, and solution temperature. The subsequent gold recovery from leach solutions was undertaken using activated carbon (AC). Mineralogical analysis by X–ray diffraction (XRD) showed that the tailings consisted of quartz (72.13%), muscovite (7.49%), chlorite (2.65%), pyrophyllite (1.50%), clinochlore (1.30%), and other trace minerals. Mineral liberation analysis (MLA) employing the Sparse Liberation–Dual Zoom (SPL-DZ) method showed that gold was associated with iron oxides (Fe2O3, Fe3O4). Fire assay analysis (FAA) showed that the bulk tailings had a grade of 0.32 g/t Au. Ethaline was found to be the most efficient reagent, achieving up to 71.9% gold extraction, thereby exceeding the 46.9% gold extraction obtained via the cyanidation process. Moreover, gold recovery using AC from ethaline leach solution was 75%. The high gold extraction from tailings using ethaline suggests a potentially feasible alternative to the traditional cyanidation process, particularly for the processing of gold locked in iron oxide phases, offering the advantages of low toxicity, cost-effectiveness, and ease of preparation. Full article
(This article belongs to the Special Issue Recycling of Mining and Solid Wastes)
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17 pages, 3748 KiB  
Article
Iron Oxide-Bearing Wastes as Media for Supporting Biodegradation of BTEX
by Safaa A. Al-Obaidi, Pallavee Srivastava, Gordon Webster, Andrew J. Weightman and Devin Sapsford
Minerals 2024, 14(12), 1231; https://doi.org/10.3390/min14121231 - 3 Dec 2024
Viewed by 926
Abstract
Two common iron oxide-bearing wastes—a drinking water treatment residual and a passive mine water treatment sludge (MWTS)—were utilised with and without modification as media in microcosm experiments to treat artificial benzene, toluene, ethylbenzene, and xylene (BTEX)-contaminated wastewater. In all cases, the removal of [...] Read more.
Two common iron oxide-bearing wastes—a drinking water treatment residual and a passive mine water treatment sludge (MWTS)—were utilised with and without modification as media in microcosm experiments to treat artificial benzene, toluene, ethylbenzene, and xylene (BTEX)-contaminated wastewater. In all cases, the removal of BTEX was observed over the 160-day experiments, with benzene being the most recalcitrant. The solubilisation of iron was observed, which, alongside the syntropic relationship between the methanogens and firmicutes, allowed several anaerobic processes to occur, including iron reduction in concert with the biodegradation of BTEX. Nitrogen sparging prior to microcosm establishment, compared to aeration, was seen to lead to the greater subsequent removal of BTEX, indicating that anaerobic conditions favoured removal. The rates of BTEX removal indicated that these iron oxide-bearing wastes, an abundant waste stream, may be an interesting candidate for cost-effective media for BTEX remediation in applications such as permeable reactive barriers. Full article
(This article belongs to the Special Issue Recycling of Mining and Solid Wastes)
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23 pages, 5122 KiB  
Article
Selective Leaching of Lithium and Beyond: Sustainable Eggshell-Mediated Recovery from Spent Li-Ion Batteries
by Hossein Shalchian, Maryam Khalili, Alireza Kiani-Rashid, Behzad Nateq and Francesco Vegliò
Minerals 2024, 14(11), 1120; https://doi.org/10.3390/min14111120 - 4 Nov 2024
Viewed by 1050
Abstract
This study introduces an innovative strategy for the selective leaching of lithium from spent Li-ion batteries. Based on thermodynamic assessments and exploiting waste eggshells as a source of calcium carbonate, an impressive 38% of lithium was dissolved selectively through mechanical milling and water [...] Read more.
This study introduces an innovative strategy for the selective leaching of lithium from spent Li-ion batteries. Based on thermodynamic assessments and exploiting waste eggshells as a source of calcium carbonate, an impressive 38% of lithium was dissolved selectively through mechanical milling and water leaching, outperforming conventional thermochemical methods. Afterwards, a hydrogen peroxide-assisted sulfuric acid leaching was also implemented to solubilize targeted elements (Mn, Co, Ni, and Li), with an exceptional 99% efficiency in Mn removal from the leachate using potassium permanganate and a pH range of 1.5 to 3.5. Selective separations of Co and Ni were then facilitated utilizing CYANEX 272 and n-heptane. This comprehensive study presents a promising and sustainable avenue for the effective recovery of Li and associated co-elements from spent lithium batteries. Full article
(This article belongs to the Special Issue Recycling of Mining and Solid Wastes)
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20 pages, 4378 KiB  
Article
A Comparison Study on the Recovery of REEs from Red Mud by Sulfation Roasting–Water Leaching and Citric Acid Leaching
by Hossein Shalchian, Mohsen Hajizadeh Navakh, Ionela Birloaga, Abolfazl Babakhani and Francesco Vegliò
Minerals 2024, 14(10), 1044; https://doi.org/10.3390/min14101044 - 18 Oct 2024
Viewed by 1209
Abstract
In this study, the recovery of rare earth elements (REEs) from red mud (bauxite residue) was explored through a combination of citric acid leaching and sulfation roasting–water leaching processes, introducing an innovative approach to the field. The research uniquely investigates the influence of [...] Read more.
In this study, the recovery of rare earth elements (REEs) from red mud (bauxite residue) was explored through a combination of citric acid leaching and sulfation roasting–water leaching processes, introducing an innovative approach to the field. The research uniquely investigates the influence of citric acid on the leaching behavior of REEs and impurities in both untreated red mud and red mud subjected to sulfation roasting, providing a direct comparison of these methodologies. A novel aspect of this study is the evaluation of solvent extraction efficiency using DEHPA, highlighting the selective recovery of REEs over impurities from both citric acid and water-leaching solutions. Furthermore, a comprehensive phase analysis using X-ray diffraction (XRD) was conducted to track the transformations of minerals during the sulfation roasting process, an original contribution to the literature. The findings revealed that over 85% of REEs and major elements such as Fe, Al, Ca, and Ti dissolved in water after sulfation at 105 °C, while iron and titanium dissolution significantly decreased following roasting at 725 °C. Importantly, terbium, neodymium, and gadolinium extraction efficiencies were notably affected by roasting temperature. Citric acid leaching results demonstrated that the direct leaching of red mud leads to higher leaching efficiency than leaching it after the roasting process. Solvent extraction demonstrated lower terbium and neodymium recovery from citric acid solutions compared to water leaching solution. Finally, stripping experiments illustrated that 6M H2SO4 solution is capable of stripping more than 80% of rare earth elements, except terbium. Full article
(This article belongs to the Special Issue Recycling of Mining and Solid Wastes)
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14 pages, 3808 KiB  
Article
Recovery of Demolished House Rocks from Construction and Demolition Waste with Water Jigs
by Artur Bressanelli Teixeira, Hassan Barkat, Carlos Hoffmann Sampaio and Josep Oliva Moncunill
Minerals 2024, 14(1), 39; https://doi.org/10.3390/min14010039 - 29 Dec 2023
Cited by 2 | Viewed by 1500
Abstract
The European Union (EU) is responsible for generating quantities ranging from 310 to almost 700 million tons of construction and demolition waste (CDW) per year. Consisting of over 70% inert material (concrete, ceramics, plaster, bricks, and rocks), CDW can be recycled for various [...] Read more.
The European Union (EU) is responsible for generating quantities ranging from 310 to almost 700 million tons of construction and demolition waste (CDW) per year. Consisting of over 70% inert material (concrete, ceramics, plaster, bricks, and rocks), CDW can be recycled for various uses, and studies on the concentration of the materials of interest are necessary to improve the management of this material and reduce waste. In CDW recycling plants in Spain, there is a significant presence of limestone from old houses (a common material used in civil construction before new construction materials and technologies emerged) that were demolished and mixed with CDW that can be recovered for use as aggregates in concretes with process density concentration processes such as water jigging. The jigging process is based on the difference in density between materials, allowing the concentration of the densest material at the bottom of the jig. Concrete, conventional construction bricks, and rocks from old houses were taken separately and then were crushed and mixed based on binary and ternary tests, and each test was performed in this study by applying the jigging separation method. The physical characterization tests of these materials was carried out to observe the jigging performance in the concentration of rocks as well as the aggregates present in concrete. Binary tests (with two different materials) and ternary tests (with three different materials) were carried out to analyze the concentration of particles with a density greater than 2.55 g/cm3. The efficiency of jigging in the concentration of these materials was proven, and products were generated with more than 70% recovery of this material, with a concentration comprised of more than 95% rocks and concrete. Full article
(This article belongs to the Special Issue Recycling of Mining and Solid Wastes)
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