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16 pages, 1624 KB

Open AccessArticle

Removal of Residual Ammonium from Weathered Crust Elution-Deposited Rare Earth Ore Tailings by Magnesium Chloride: Kinetics and Mass Transfer

by Jian Feng, Tao Ou, Wuhan Zhang, Xin Deng, Shijun Chen, Xiaoyan Wu, Jianyun Chen, Ruan Chi and Fang Zhou

Separations 2026, 13(8), 225; https://doi.org/10.3390/separations13080225 - 9 Aug 2026

Viewed by 284

Abstract

After in situ leaching of weathered crust elution-deposited rare earth ore (WREO), large amounts of residual ammonium (RA) salts remain in the ore body and slowly release, causing persistent ammonia-nitrogen pollution in surrounding waters. This study proposes using magnesium chloride for in situ [...] Read more.

After in situ leaching of weathered crust elution-deposited rare earth ore (WREO), large amounts of residual ammonium (RA) salts remain in the ore body and slowly release, causing persistent ammonia-nitrogen pollution in surrounding waters. This study proposes using magnesium chloride for in situ elution remediation of closed mines. Column experiments were conducted to evaluate the effects of eluent concentration, liquid–solid ratio, flow rate, pH, and temperature on residual ammonium removal, and a kinetic model was established based on the shrinking unreacted-core model. The results show that increasing Mg²⁺ concentration, temperature, or flow rate accelerates the eluting rate, with temperature being the most influential. A higher liquid–solid ratio in the tested range could enhance the elution efficiency of residual ammonium, but it will substantially raise the production cost. Weakly acidic pH 4–6 favors the reaction, while alkaline conditions inhibit it. Kinetic analysis indicates inner particle diffusion control, with an activation energy of 6.03 kJ/mol and a reaction order of 0.3009. Under optimal conditions of 0.1 mol/L Mg²⁺, 2:1 liquid–solid ratio, 0.6 mL/min, pH 4–6 and room temperature, elution efficiency reaches 95.45%. This work provides theoretical and technical support for green remediation of historical ammonium contamination in WREO. Full article

(This article belongs to the Special Issue Solid Waste Recycling and Strategic Metal Extraction)

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21 pages, 3200 KB

Open AccessArticle

Sustainable Valorization of Coal Gasification Slag via Low-Temperature Alkaline Activation for Efficient Cd²⁺ Removal: Performance, Mechanism, and Life Cycle Assessment

by Haicheng Zhao, Lihui Gao, Xinmeng Jiang and Yijing Zhang

Separations 2026, 13(7), 198; https://doi.org/10.3390/separations13070198 - 8 Jul 2026

Viewed by 546

Abstract

Coal gasification slag (CGS), a massive industrial solid waste, possesses inherent adsorptive potential that remains underutilized due to pore blockage by amorphous siliceous phases. Conventional modification strategies typically rely on energy-intensive high-temperature processes. Herein, we report a facile, low-temperature alkaline activation approach to [...] Read more.

Coal gasification slag (CGS), a massive industrial solid waste, possesses inherent adsorptive potential that remains underutilized due to pore blockage by amorphous siliceous phases. Conventional modification strategies typically rely on energy-intensive high-temperature processes. Herein, we report a facile, low-temperature alkaline activation approach to transform CGS into a high-efficiency adsorbent (denoted NCGS) for Cd²⁺ removal. Sodium hydroxide (NaOH) solution was employed under mild conditions (90 °C) to selectively etch siliceous species, thereby generating a porous architecture and enriching surface oxygen-containing functionalities. Orthogonal experimental design identified optimal synthesis parameters (1 mol/L NaOH, solid–liquid ratio of 1:30 g/mL, 12 h), yielding NCGS with significantly enhanced textural properties. The adsorption isotherm was well described by the Langmuir model, with a maximum capacity of 87.06 mg/g at pH 6.0, while kinetic studies indicated the adsorption process could be described by pseudo-second-order kinetic model. Comprehensive characterization via SEM-EDS, FTIR, and XPS elucidated a multi-mechanistic adsorption pathway mainly involving ion exchange (Na⁺/Cd²⁺) and coordination complexation. Life cycle assessment analysis revealed that NCGS production generates 11.23 kg CO₂ eq emissions, with transportation accounting for 88%. This study presents an energy-saving and environmentally friendly strategy to unlock the adsorptive potential of CGS, providing a highly promising waste-based adsorption material for the remediation of Cd²⁺-contaminated water. Full article

(This article belongs to the Special Issue Solid Waste Recycling and Strategic Metal Extraction)

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19 pages, 11084 KB

Open AccessArticle

Preferential Lithium Recovery and Temperature-Regulated Stepwise Desorption of Transition Metals from Simulated Spent NCM111 Leachate Using NaA Zeolite

by Qian Cheng, Yongxiang Wang, Xiangyu Liu, Wenxi Zhang and Panfeng Gao

Separations 2026, 13(5), 132; https://doi.org/10.3390/separations13050132 - 28 Apr 2026

Cited by 1 | Viewed by 710

Abstract

Recycling spent lithium-ion batteries (LIBs) is critical for resource sustainability and carbon neutrality. This work presents a green strategy in which NaA zeolite is used to preferentially recover lithium from leachate of spent NCM111 batteries, combined with temperature-regulated stepwise separation of transition metals. [...] Read more.

Recycling spent lithium-ion batteries (LIBs) is critical for resource sustainability and carbon neutrality. This work presents a green strategy in which NaA zeolite is used to preferentially recover lithium from leachate of spent NCM111 batteries, combined with temperature-regulated stepwise separation of transition metals. Benefiting from the distinct hydrated ionic radii and charge density between Li⁺ and divalent metal ions, NaA zeolite selectively adsorbs Ni²⁺, Co²⁺ and Mn²⁺, leaving Li⁺ in the raffinate. Under optimized conditions, two-stage adsorption achieves 95.6%, 96.7% and 99.7% removal of Ni²⁺, Co²⁺ and Mn²⁺, respectively, with 11% Li⁺ co-adsorption. Thermodynamic analysis reveals that the adsorption process is endothermic and thermodynamically spontaneous. The interaction strength between metal ions and NaA zeolite follows the order Ni²⁺ > Co²⁺ > Mn²⁺, and ion exchange is identified as the dominant mechanism. It is determined that 96.8% of Mn²⁺ can be recovered at 0 °C, followed by the desorption of 93.5% of Co²⁺ at 90 °C, and the sequential separation of Mn, Co and Ni is realized. Three consecutive adsorption–desorption cycles demonstrate the acceptable reusability of the Ni-loaded NaA adsorbent. High-purity Li₂CO₃ (purity 96.7%, yield 93.5%), MnO₂ (purity 99.3%, yield 98.4%) and Co₃O₄ (purity 98.8%, yield 97.6%) are obtained from the corresponding solutions. This approach provides a scalable closed-loop pathway for full-component recovery of valuable metals from spent LIBs. Full article

(This article belongs to the Special Issue Solid Waste Recycling and Strategic Metal Extraction)

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19 pages, 5532 KB

Open AccessArticle

Multi-Parameter Synergistic Effects on Fine Coal Slurry Sedimentation in High-Gravity Fields: A CFD Study

by Lingyun Liu, Huikuan Pan, Wei Ge and Chuilei Kong

Separations 2025, 12(11), 320; https://doi.org/10.3390/separations12110320 - 16 Nov 2025

Cited by 1 | Viewed by 986

Abstract

This study addresses the technical challenges of conventional coal slurry sedimentation equipment in handling fine coal particles, such as poor settling performance and strong dependence on chemical reagents, by designing a novel high-gravity sedimentation and dewatering device. Solid–liquid centrifugal separation was simulated on [...] Read more.

This study addresses the technical challenges of conventional coal slurry sedimentation equipment in handling fine coal particles, such as poor settling performance and strong dependence on chemical reagents, by designing a novel high-gravity sedimentation and dewatering device. Solid–liquid centrifugal separation was simulated on the CFD-Fluent platform using the Eulerian–Eulerian method, with the solid volume fraction and effective deposition thickness adopted as key indicators of particle settling performance. The settling behavior and flow field characteristics of particles with different sizes (0.045–0.5 mm) were elucidated under varying centrifugal radii (400–800 mm) and rotational speeds (400–1200 r·min⁻¹), thereby providing a solid theoretical foundation for the parameter optimization of centrifugal settling processes for fine particles. The results indicate that increasing the centrifugal radius and rotational speed strengthens the centrifugal field effect, markedly enhancing the dynamic pressure gradient and interphase slip velocity. Under high-speed (ω = 1200 r·min⁻¹) and large-radius (R = 800 mm) conditions, the dynamic pressure of fine particles (0.045 mm) reached 7.52 MPa with a radial velocity of 0.79 m·s⁻¹, effectively compensating for the settling disadvantage of fine particles, promoting solid–liquid separation, and ensuring the stable deposition of coal particles. Meanwhile, as particle size increases, a distinct deposition thickness can be formed under different operating conditions, demonstrating that particle size is the dominant factor governing deposition behavior. The study elucidates the intrinsic mechanism of how multiple parameters—rotational speed, centrifugal radius, and coal particle size—synergistically influence particle deposition characteristics. By regulating these parameters to accommodate different particle sizes, the findings provide valuable insights for the parameter optimization of centrifugal settling processes for fine particles. Full article

(This article belongs to the Special Issue Solid Waste Recycling and Strategic Metal Extraction)

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20 pages, 2946 KB

Open AccessArticle

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

Cited by 2 | Viewed by 2010

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 (Fe_elem) 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

Open AccessArticle

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

Cited by 5 | Viewed by 1838

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 k_d-Ga/k_d-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

Open AccessEditor’s ChoiceReview

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 8 | Viewed by 3668

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

Open AccessReview

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 6 | Viewed by 6707

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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