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Separations
Special Issues
Solid Waste Recycling and Strategic Metal Extraction
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Solid Waste Recycling and Strategic Metal Extraction

A special issue of Separations (ISSN 2297-8739). This special issue belongs to the section "Separation Engineering".

Deadline for manuscript submissions: 20 October 2025 | Viewed by 4492

Special Issue Editors

Dr. Lihui Gao

E-Mail Website
Guest Editor
School of Environment and Spatial Informatics, China University of Mining and Technology, Xuzhou 221116, China
Interests: extraction of strategic metal resources; adsorption; wastewater treatment
Special Issues, Collections and Topics in MDPI journals
Dr. Daoguang Teng

E-Mail Website
Guest Editor
1. Zhongyuan Critical Metals Laboratory, Zhengzhou University, Zhengzhou, China
2. School of Chemical Engineering, Zhengzhou University, Zhengzhou, China
3. The Key Lab of Critical Metals Minerals Supernormal Enrichment and Extraction, Ministry of Education, Zhengzhou, China
Interests: enrichment and extraction of critical rare metals; utilization of coal-based solid waste/secondary metallurgical resources/urban mining resources; intensification of separation processes
Special Issues, Collections and Topics in MDPI journals
Dr. Shulei Li

E-Mail Website
Guest Editor
National Engineering Research Center of Coal Preparation and Purification, China University of Mining and Technology, Xuzhou 221116, China
Interests: utilization of solid waste resources; wastewater treatment; separation; flotation
Special Issues, Collections and Topics in MDPI journals
Dr. Chunlin He

E-Mail Website
Guest Editor
School of Resources, Environment and Materials, Guangxi University, Nanning, China
Interests: adsorbent material; enrichment and extraction of key metals

Special Issue Information

Dear Colleagues,

This Special Issue of Separations delves into advanced separation technologies for the valorization of solid waste and the enrichment of rare earth elements (REEs). This Special Issue invites contributors to submit innovative research, review articles, and case studies that highlight a comprehensive array of methodologies, including, but not limited to, the value-added utilization of biomass, synthesis of adsorption materials, and efficient enrichment and extraction of REEs. The focus of this Special Issue is on developing processes that are efficient, environmentally friendly, and economically viable to achieve resource recovery from solid waste and meet the growing demand for REEs.

Dr. Lihui Gao
Dr. Daoguang Teng
Dr. Shulei Li
Dr. Chunlin He
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. Separations 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

  • solid waste
  • biomass
  • adsorption material
  • wastewater treatment
  • strategic metal resources

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Published Papers (4 papers)

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Research

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20 pages, 2946 KB  
Article
Iron Recovery from Turkish and Romanian Bauxite Residues Through Magnetic Separation: Effect of Hydrothermal Processing and Separation Conditions
by Panagiotis Angelopoulos, Paschalis Oustadakis, Nikolaos Kountouris, Michail Samouhos, Georgios Anastassakis and Maria Taxiarchou
Separations 2025, 12(9), 252; https://doi.org/10.3390/separations12090252 - 17 Sep 2025
Viewed by 327
Abstract
This study investigates the potential of two low-iron-grade bauxite residue (BR) samples, containing up to 27.4 wt.% Fe and originating from alumina plants in Romania and Turkey, for the recovery of iron concentrate via wet magnetic separation. The methodology involved the hydrothermal reduction [...] Read more.
This study investigates the potential of two low-iron-grade bauxite residue (BR) samples, containing up to 27.4 wt.% Fe and originating from alumina plants in Romania and Turkey, for the recovery of iron concentrate via wet magnetic separation. The methodology involved the hydrothermal reduction of the residues, aiming to transform the hematite/goethite (Fe3+) phases into magnetite (Fe2+/Fe3+) and enhance their magnetic susceptibility. The effect of hydrothermal treatment, magnetic induction value (up to 1600 Gs), and slurry dispersion on iron recovery and iron grade were investigated. An optimum magnetic fraction was obtained, containing 44.4 wt.% elemental iron (Feelem) and achieving 98% iron recovery. These results demonstrate a significant improvement compared to the magnetic fraction derived from the respective non-reduced sample, which showed a maximum of 29.7 wt.% Fe grade and 59.7% recovery. Furthermore, silicon and sodium are primarily distributed in the non-ferrous fraction. The application of sonication to enhance slurry dispersion during magnetic separation did not have a positive impact on the process. In addition to iron recovery, an aspect of considerable potential is the reutilization of the Al-rich liquor generated during hydrothermal treatment of the BR. Its reintroduction into the Bayer process circuit could contribute to improved material utilization and enhanced overall process efficiency. Full article
(This article belongs to the Special Issue Solid Waste Recycling and Strategic Metal Extraction)
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21 pages, 3513 KB  
Article
Alkali-Resistant Ion-Imprinted Chitosan–Mesoporous Silica Composite for Efficient and Selective Gallium Separation
by Zhifang Lv, Shiqiao Yang, Jiangyan Wu, Guixia Fan, Guosheng Li, Yijun Cao, Peng Li and Daoguang Teng
Separations 2025, 12(9), 226; https://doi.org/10.3390/separations12090226 - 24 Aug 2025
Viewed by 511
Abstract
Efficient and selective separation of gallium (Ga(III)) from alkaline industrial waste streams remains a significant challenge due to the coexistence of chemically similar ions such as Al(III) and V(V). In this study, a novel ion-imprinted chitosan-based adsorbent (CS/(H-CGCS)-Ga-IIP) was synthesized via a hybrid [...] Read more.
Efficient and selective separation of gallium (Ga(III)) from alkaline industrial waste streams remains a significant challenge due to the coexistence of chemically similar ions such as Al(III) and V(V). In this study, a novel ion-imprinted chitosan-based adsorbent (CS/(H-CGCS)-Ga-IIP) was synthesized via a hybrid cross-linking strategy using glutaraldehyde and siloxane-modified chitosan. The optimized material exhibited a high adsorption capacity of 106.31 mg·g−1 for Ga(III) at pH 9, with fast adsorption kinetics reaching equilibrium within 60 min. Adsorption behavior followed the pseudo-second-order kinetic and Langmuir isotherm models, and thermodynamic analysis indicated a spontaneous and endothermic process. In simulated Bayer mother liquor systems, the material demonstrated outstanding selectivity and a distribution coefficient ratio kd-Ga/kd-Al = 146.9, highlighting its strong discrimination ability toward Ga(III). Mechanistic insights from SEM-EDS, FTIR, and XPS analyses revealed that Ga(III) adsorption occurs via electrostatic interaction, ligand coordination, and structural stabilization by the siloxane network. The material maintained good adsorption performance over three regeneration cycles, indicating potential for reuse. These findings suggest that CS/(H-CGCS)-Ga-IIP is a promising candidate for the sustainable recovery of gallium from complex alkaline waste streams such as Bayer process residues. Full article
(This article belongs to the Special Issue Solid Waste Recycling and Strategic Metal Extraction)
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Review

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26 pages, 7085 KB  
Review
Advances in Electrolytic Manganese Residue: Harmless Treatment and Comprehensive Utilization
by Weijian Yu, Xiaoya Li, Wenting Xu, Qingjun Guan, Fujia Zhou, Jiani Zhang, Li Wang, Yanxiu Wang and Honghu Tang
Separations 2025, 12(7), 180; https://doi.org/10.3390/separations12070180 - 7 Jul 2025
Cited by 1 | Viewed by 825
Abstract
Electrolytic manganese residue (EMR) is a byproduct of electrolytic manganese production, rich in soluble pollutants such as manganese and ammonia nitrogen. Traditional stockpiling methods result in contaminant leaching and water pollution, threatening ecosystems. Meanwhile, EMR has significant resource-recovery potential. This paper systematically reviews [...] Read more.
Electrolytic manganese residue (EMR) is a byproduct of electrolytic manganese production, rich in soluble pollutants such as manganese and ammonia nitrogen. Traditional stockpiling methods result in contaminant leaching and water pollution, threatening ecosystems. Meanwhile, EMR has significant resource-recovery potential. This paper systematically reviews the harmless process and resource technology of EMR, efficiency bottlenecks, and the current status of industrial applications. The mechanisms of chemical leaching, precipitation, solidification, roasting, electrochemistry, and microorganisms were analyzed. Among these, electrochemical purification stands out for its efficiency and environmental benefits, positioning it as a promising option for broad industrial use. The mechanisms of chemical leaching, precipitation, solidification, roasting, electrochemistry, and microorganisms were analyzed, revealing the complementarity between building materials and chemical materials (microcrystalline glass) in scale and high-value-added production. But the lack of impurity separation accuracy and market standards restricts its promotion. Finally, it proposes future directions for EMR resource utilization based on practical and economic considerations. Full article
(This article belongs to the Special Issue Solid Waste Recycling and Strategic Metal Extraction)
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26 pages, 948 KB  
Review
Antimony Recovery from Industrial Residues—Emphasis on Leaching: A Review
by Marinela Panayotova, Serhii Pysmennyi and Vladko Panayotov
Separations 2025, 12(6), 156; https://doi.org/10.3390/separations12060156 - 8 Jun 2025
Cited by 1 | Viewed by 2430
Abstract
Antimony (Sb) is a metalloid widely used in different areas—from the cutting-edge renewable energy technologies to “classical” lead acid batteries. Its availability in primary sources is limited, and these sources are geographically unevenly distributed worldwide. Antimony use will increase in the future. That [...] Read more.
Antimony (Sb) is a metalloid widely used in different areas—from the cutting-edge renewable energy technologies to “classical” lead acid batteries. Its availability in primary sources is limited, and these sources are geographically unevenly distributed worldwide. Antimony use will increase in the future. That is why Sb is included in the critical raw material lists of the European Union and the USA. In order to mitigate the future Sb shortage, Sb recovery from industrial residues is worth considering. This paper presents the availability of Sb in nonferrous metals extraction waste and the applicability of the hydrometallurgical route for Sb recovery from such sources. Leaching is emphasized. The use of acidic and alkaline leaching methods, their recent modifications, and the effect of different process parameters (reagents’ type, solid-to-liquid ratio, temperature, and the addition of oxidizing reagents) are highlighted. The use of new leaching systems, such as deep eutectic solvents and non-aqueous solutions, is presented. Initial attempts to apply bioleaching are described. Finally, some proposals for future investigations are given. Full article
(This article belongs to the Special Issue Solid Waste Recycling and Strategic Metal Extraction)
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