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The Royal Society of Arts on the Circular Economy Through the Centuries
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Graphite Separation from Lithium-Ion Battery Black Mass Using Froth Flotation and Quality Evaluation for Reuse as a Secondary Raw Material Including Non-Battery Applications
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Logistic Regression Insights on Pyrolysis vs. Recycling
Journal Description
Recycling
Recycling
is an international, peer-reviewed, open access journal on the recycling and reuse of material resources, including circular economy published bimonthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, ESCI (Web of Science), FSTA, Inspec, AGRIS, and other databases.
- Journal Rank: CiteScore - Q1 (Management, Monitoring, Policy and Law)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 20.9 days after submission; acceptance to publication is undertaken in 4.9 days (median values for papers published in this journal in the first half of 2025).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Impact Factor:
4.6 (2024);
5-Year Impact Factor:
4.9 (2024)
Latest Articles
Developing an Integrated Circular Economy Framework for Nanomaterial-Enhanced Recycled PET (nrPET): Advancing Sustainable and Resilient Road Construction Practices
Recycling 2025, 10(4), 146; https://doi.org/10.3390/recycling10040146 - 22 Jul 2025
Abstract
The rapid growth in plastic consumption, particularly polyethylene terephthalate (PET), has led to a significant increase in plastic waste, posing a major environmental challenge. Developing an integrated circular economy framework for nanomaterial-enhanced recycled PET (nrPET) can be a promising approach to address this
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The rapid growth in plastic consumption, particularly polyethylene terephthalate (PET), has led to a significant increase in plastic waste, posing a major environmental challenge. Developing an integrated circular economy framework for nanomaterial-enhanced recycled PET (nrPET) can be a promising approach to address this issue and advance sustainable and resilient road construction practices. This comprehensive review examines the current use of rPET in road construction, its existing limitations, and the role of nanomaterials in enhancing the performance of these materials. The review explores the mechanisms by which nanomaterials, such as carbon nanotubes, graphene, nanosilica, and clay nanoplatelets, can improve the properties of rPET, leading to more durable, weather-resistant, and cost-effective road materials. Furthermore, the review analyzes the environmental and sustainability benefits of using nrPET in road construction, focusing on carbon footprint reduction, conservation of natural resources, and alignment with circular economy principles. The potential for job creation, social benefits, and support for circular economy initiatives are also discussed. The review then delves into the challenges associated with the implementation of this framework, including technical barriers, economic and market barriers, regulatory and policy challenges, and environmental and safety considerations. Strategies to address these challenges, such as advancements in nanotechnology, scaling up circular economy models, and fostering collaborative research, are presented. Finally, the article proposes a framework and outlines future directions and research opportunities, emphasizing the exploration of emerging nanomaterials, scaling up circular economy models, and encouraging collaborations between researchers, industry stakeholders, policymakers, and communities.
Full article
(This article belongs to the Special Issue Recycled Materials in Sustainable Pavement Innovation)
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Open AccessArticle
Organic Acid Leaching of Black Mass with an LFP and NMC Mixed Chemistry
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Marc Simon Henderson, Chau Chun Beh, Elsayed Oraby and Jacques Eksteen
Recycling 2025, 10(4), 145; https://doi.org/10.3390/recycling10040145 - 21 Jul 2025
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There is an increasing demand for the development of efficient and sustainable battery recycling processes. Currently, many recycling processes rely on toxic inorganic acids to recover materials from high-value battery chemistries such as lithium nickel manganese cobalt oxides (NMCs) and lithium cobalt oxide
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There is an increasing demand for the development of efficient and sustainable battery recycling processes. Currently, many recycling processes rely on toxic inorganic acids to recover materials from high-value battery chemistries such as lithium nickel manganese cobalt oxides (NMCs) and lithium cobalt oxide (LCOs). However, as cell manufacturers seek more cost-effective battery chemistries, the value of the spent battery value chain is increasingly diluted by chemistries such as lithium iron phosphate (LFPs). These cheaper alternatives present a difficulty when recycling, as current recycling processes are geared towards dealing with high-value chemistries; thus, the current processes become less economical. To date, much research is focused on treating a single battery chemistry; however, often, the feed material entering a battery recycling facility is contaminated with other battery chemistries, e.g., LFP feed contaminated with NMC, LCO, or LMOs. This research aims to selectively leach various battery chemistries out of a mixed feed material with the aid of a green organic acid, namely oxalic acid. When operating at the optimal conditions (2% solids, 0.25 M oxalic acid, natural pH around 1.15, 25 °C, 60 min), this research has proven that oxalic acid can be used to selectively dissolve 95.58% and 93.57% of Li and P, respectively, from a mixed LFP-NMC mixed feed, all while only extracting 12.83% of Fe and 8.43% of Mn, with no Co and Ni being detected in solution. Along with the high degree of selectivity, this research has also demonstrated, through varying the pH, that the selectivity of the leaching system can be altered. It was determined that at pH 0.5 the system dissolved both the NMC and LFP chemistries; at a pH of 1.15, the LFP chemistry (Li and P) was selectively targeted. Finally, at a pH of 4, the NMC chemistry (Ni, Co and Mn) was selectively dissolved.
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Graphical abstract
Open AccessArticle
Zero-Shot Learning for Sustainable Municipal Waste Classification
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Dishant Mewada, Eoin Martino Grua, Ciaran Eising, Patrick Denny, Pepijn Van de Ven and Anthony Scanlan
Recycling 2025, 10(4), 144; https://doi.org/10.3390/recycling10040144 - 21 Jul 2025
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Automated waste classification is an essential step toward efficient recycling and waste management. Traditional deep learning models, such as convolutional neural networks, rely on extensive labeled datasets to achieve high accuracy. However, the annotation process is labor-intensive and time-consuming, limiting the scalability of
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Automated waste classification is an essential step toward efficient recycling and waste management. Traditional deep learning models, such as convolutional neural networks, rely on extensive labeled datasets to achieve high accuracy. However, the annotation process is labor-intensive and time-consuming, limiting the scalability of these approaches in real-world applications. Zero-shot learning is a machine learning paradigm that enables a model to recognize and classify objects it has never seen during training by leveraging semantic relationships and external knowledge sources. In this study, we investigate the potential of zero-shot learning for waste classification using two vision-language models: OWL-ViT and OpenCLIP. These models can classify waste without direct exposure to labeled examples by leveraging textual prompts. We apply this approach to the TrashNet dataset, which consists of images of municipal solid waste organized into six distinct categories: cardboard, glass, metal, paper, plastic, and trash. Our experimental results yield an average classification accuracy of 76.30% with Open Clip ViT-L/14-336 model, demonstrating the feasibility of zero-shot learning for waste classification while highlighting challenges in prompt sensitivity and class imbalance. Despite lower accuracy than CNN- and ViT-based classification models, zero-shot learning offers scalability and adaptability by enabling the classification of novel waste categories without retraining. This study underscores the potential of zero-shot learning in automated recycling systems, paving the way for more efficient, scalable, and annotation-free waste classification methodologies.
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Open AccessArticle
Turning Waste into Wealth: Sustainable Amorphous Silica from Moroccan Oil Shale Ash
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Anas Krime, Sanaâ Saoiabi, Mouhaydine Tlemcani, Ahmed Saoiabi, Elisabete P. Carreiro and Manuela Ribeiro Carrott
Recycling 2025, 10(4), 143; https://doi.org/10.3390/recycling10040143 - 20 Jul 2025
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Moroccan oil shale ash (MOSA) represents an underutilized industrial by-product, particularly in the Rif region, where its high mineral content has often led to its neglect in value-added applications. This study highlights the successful conversion of MOSA into amorphous mesoporous silica (AS-Si) using
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Moroccan oil shale ash (MOSA) represents an underutilized industrial by-product, particularly in the Rif region, where its high mineral content has often led to its neglect in value-added applications. This study highlights the successful conversion of MOSA into amorphous mesoporous silica (AS-Si) using a sol–gel process assisted by polyethylene glycol (PEG-6000) as a soft template. The resulting AS-Si material was extensively characterized to confirm its potential for environmental remediation. FTIR analysis revealed characteristic vibrational bands corresponding to Si–OH and Si–O–Si bonds, while XRD confirmed its amorphous nature with a broad diffraction peak at 2θ ≈ 22.5°. SEM imaging revealed a highly porous, sponge-like morphology composed of aggregated nanoscale particles, consistent with the nitrogen adsorption–desorption isotherm. The material exhibited a specific surface area of 68 m2/g, a maximum in the pore size distribution at a pore diameter of 2.4 nm, and a cumulative pore volume of 0.11 cm3/g for pores up to 78 nm. DLS analysis indicated an average hydrodynamic diameter of 779 nm with moderate polydispersity (PDI = 0.48), while a zeta potential of –34.10 mV confirmed good colloidal stability. Furthermore, thermogravimetric analysis (TGA) and DSC suggested the thermal stability of our amorphous silica. The adsorption performance of AS-Si was evaluated using methylene blue (MB) and ciprofloxacin (Cipro) as model pollutants. Kinetic data were best fitted by the pseudo-second-order model, while isotherm studies favored the Langmuir model, suggesting monolayer adsorption. AS-Si could be used four times for the removal of MB and Cipro. These results collectively demonstrate that AS-Si is a promising, low-cost, and sustainable adsorbent derived from Moroccan oil shale ash for the effective removal of organic contaminants from aqueous media.
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Open AccessArticle
Incorporating Recyclates Derived from Household Waste into Flexible Food Packaging Applications: An Environmental Sustainability Assessment
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Trang T. Nhu, Anna-Sophie Haslinger, Sophie Huysveld and Jo Dewulf
Recycling 2025, 10(4), 142; https://doi.org/10.3390/recycling10040142 - 17 Jul 2025
Abstract
Integrating recyclates into food packaging is key towards circularity while meeting functionality and safety requirements; however, associated environmental impacts remain underexplored. This gap was addressed through a cradle-to-gate life cycle assessment, using the Environmental Footprint method, along with substitution and cut-off approaches for
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Integrating recyclates into food packaging is key towards circularity while meeting functionality and safety requirements; however, associated environmental impacts remain underexplored. This gap was addressed through a cradle-to-gate life cycle assessment, using the Environmental Footprint method, along with substitution and cut-off approaches for handling the multifunctionality of recycling. Recyclates were derived from polyethylene (PE)-rich household food packaging waste, purified via delamination-deinking. Firstly, results show that shifting from virgin multi-material to mono-material multilayer structures with or without recyclates, while maintaining functionality, offers environmental benefits. Secondly, recyclates should sufficiently substitute virgin materials in quantity and quality, decreasing the need for primary plastics and avoiding recyclate incorporation without functionality. Otherwise, thicker laminates are obtained, increasing processability challenges and environmental impacts, e.g., 12% for particulate matter, and 14% for mineral-metal resource use when the recycle content rises from 34 to 50%. Thirdly, a fully closed loop for flexible food packaging is not yet feasible. Key improvements lie in reducing residues generated during recycling, especially in delamination-deinking, lowering energy use in recompounding, and using more efficient transport modes for waste collection. Further research is essential to optimise the innovative technologies studied for flexible food packaging and refine them for broader applications.
Full article
(This article belongs to the Special Issue Challenges and Opportunities in Plastic Waste Management)
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Open AccessArticle
Expansion of Mechanical Biological Residual Treatment Plant with Fermentation Stage for Press Water from Organic Fractions Involving a Screw Press
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Rzgar Bewani, Abdallah Nassour, Thomas Böning, Jan Sprafke and Michael Nelles
Recycling 2025, 10(4), 141; https://doi.org/10.3390/recycling10040141 - 16 Jul 2025
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A three-year optimization study was conducted at a mechanical biological treatment plant with the aim of enhancing organic fractions recovery from mechanically separated fine fractions (MSFF) of residual waste using a screw press. The study aimed to optimize key operating parameters for the
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A three-year optimization study was conducted at a mechanical biological treatment plant with the aim of enhancing organic fractions recovery from mechanically separated fine fractions (MSFF) of residual waste using a screw press. The study aimed to optimize key operating parameters for the employed screw press, such as pressure, liquid-to-MSFF, feeding quantity per hour, and press basket mesh size, to enhance volatile solids and biogas recovery in the generated press water for anaerobic digestion. Experiments were performed at the full-scale facility to evaluate the efficiency of screw press extraction with other pretreatment methods, like press extrusion, wet pulping, and hydrothermal treatment. The results indicated that hydrolysis of the organic fractions in MSFF was the most important factor for improving organic extraction from the MSFF to press water for fermentation. Optimal hydrolysis efficiency was achieved with a digestate and process water-to-MSFF of approximately 1000 L/ton, with a feeding rate between 8.8 and 14 tons per hour. Increasing pressure from 2.5 to 4.0 bar had minimal impact on press water properties or biogas production, regardless of the press basket size. The highest volatile solids (29%) and biogas (50%) recovery occurred at 4.0 bar pressure with a 1000 L/ton liquid-to-MSFF. Further improvements could be achieved with longer mixing times before pressing. These findings demonstrate the technical feasibility of the pressing system for preparing an appropriate substrate for the fermentation process, underscoring the potential for optimizing the system. However, further research is required to assess the cost–benefit balance.
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Open AccessReview
Sustainable Alkali-Activated and Geopolymer Materials: What Is the Future for Italy?
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Laura Ricciotti, Daniele Lucariello, Valeria Perrotta, Antonio Apicella and Raffaella Aversa
Recycling 2025, 10(4), 140; https://doi.org/10.3390/recycling10040140 - 15 Jul 2025
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Using innovative and sustainable materials has become crucial for developed countries. Reusing waste as a secondary raw material in industrial processes central to the circular economy could enhance environmental sustainability and support local economies. Building materials such as Portland cement have a significant
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Using innovative and sustainable materials has become crucial for developed countries. Reusing waste as a secondary raw material in industrial processes central to the circular economy could enhance environmental sustainability and support local economies. Building materials such as Portland cement have a significant environmental impact due to greenhouse gas emissions and construction and demolition waste (CDW), which is challenging to recycle. Research into sustainable alternatives is, therefore, essential. The European Union has set ambitious targets to reduce greenhouse gas emissions by 55% by 2030 and achieve climate neutrality by 2050. The National Recovery and Resilience Plan (PNRR) supports the green transition in Italy by promoting sustainable materials like geopolymers. These ceramic-like materials are based on aluminosilicates obtained through the chemical activation of waste rich in silica and aluminosilicate compounds. Though promising, these materials require further research to address challenges like long-term durability and chemical variability. Collaboration between scientific research and industry is essential to develop specific protocols and suitable infrastructures. This article provides a critical review of the advancements and challenges in using alkali-activated waste as construction binders, focusing on Italy, and encourages the exploration of alternative sustainable materials beyond conventional Portland cement.
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Open AccessArticle
Simulation-Based RF-ICP Torch Optimization for Efficient and Environmentally Sustainable Radioactive Waste Management
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Roman Stetsiuk, Mustafa A. Aldeeb and Hossam A. Gabbar
Recycling 2025, 10(4), 139; https://doi.org/10.3390/recycling10040139 - 15 Jul 2025
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This study examines methods to improve the energy efficiency of radiofrequency inductively coupled plasma (RF-ICP) torches for radioactive waste treatment, with a focus on surpassing the typical energy efficiency limit of approximately 70%. To improve energy efficiency and plasma performance, this research investigates
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This study examines methods to improve the energy efficiency of radiofrequency inductively coupled plasma (RF-ICP) torches for radioactive waste treatment, with a focus on surpassing the typical energy efficiency limit of approximately 70%. To improve energy efficiency and plasma performance, this research investigates the transition from axial gas flow to vortex gas flow patterns using COMSOL Multiphysics software v6.2. Key plasma parameters, including energy efficiency, number of gas vortices, heat transfer, and temperature distribution, were analyzed to evaluate the improvements. The results indicate that adopting a vortex flow pattern increases energy conversion efficiency, increases heat flux, and reduces charge losses. Furthermore, optimizing the torch body design, particularly the nozzle, chamber volume, and gas entry angle, significantly improves plasma properties and energy efficiency by up to 90%. Improvements to RF-ICP torches positively impact waste decomposition by creating better thermal conditions that support resource recovery and potential material recycling. In addition, these improvements contribute to reducing secondary waste, mitigating environmental risks, and fostering long-term public support for nuclear technology, thereby promoting a more sustainable approach to waste management. Simulation results demonstrate the potential of RF-ICP flares as a cost-effective and sustainable solution for the thermal treatment of low- to intermediate-level radioactive waste.
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Open AccessArticle
An Experimental Investigation into the Performance of Concrete and Mortar with Partial Replacement of Fine Aggregate by Printed Circuit Board (PCB) E-Waste
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Srinivasan Krishnan, Sai Gopal Krishna Bhagavatula, Jayanarayanan Karingamanna and Mini K. Madhavan
Recycling 2025, 10(4), 138; https://doi.org/10.3390/recycling10040138 - 12 Jul 2025
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The increasing accumulation of E-waste presents significant environmental challenges, particularly its disposal and resource management. The present study investigates the potential of printed circuit boards (PCBs) as a partial replacement for fine aggregates in cement mortar and concrete. The replacement levels of PCBs
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The increasing accumulation of E-waste presents significant environmental challenges, particularly its disposal and resource management. The present study investigates the potential of printed circuit boards (PCBs) as a partial replacement for fine aggregates in cement mortar and concrete. The replacement levels of PCBs ranged from 0 to 35 wt% in cement mortar and from 0 to 30 wt% in concrete, aiming to improve the qualities of both mixes. The specimens were cured for 7 and 28 days, respectively, followed by tests to evaluate the flowability and static mechanical properties. The performance of the developed mortar/concrete was analyzed under aggressive environmental conditions by conducting various durability tests. Properties such as acoustic and thermal conductivity were also evaluated to check the suitability of the developed material for its multifunctionality. Test results revealed that the optimal replacement percentages of fine aggregate by PCBs in mortar and concrete mixes were 25 wt% and 20 wt%, respectively. A decline in mechanical properties was observed after a further increase in replacement level. The results demonstrate the feasibility of E-waste integration in cement and mortar as a sustainable waste management solution.
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Open AccessArticle
Selective Ammonium Recovery from Livestock and Organic Solid Waste Digestates Using Zeolite Tuff: Efficiency and Farm-Scale Prospects
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Matteo Alberghini, Giacomo Ferretti, Giulio Galamini, Cristina Botezatu and Barbara Faccini
Recycling 2025, 10(4), 137; https://doi.org/10.3390/recycling10040137 - 8 Jul 2025
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Implementing efficient strategies for the circular recovery and reuse of nutrients from wastewaters is mandatory to meet the Green Deal objectives and Sustainable Development Goals. In this context we investigated the use of zeolitic tuff (containing chabazite and phillipsite) in the selective recovery
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Implementing efficient strategies for the circular recovery and reuse of nutrients from wastewaters is mandatory to meet the Green Deal objectives and Sustainable Development Goals. In this context we investigated the use of zeolitic tuff (containing chabazite and phillipsite) in the selective recovery and reuse of N from various anaerobic liquid digestates in view of their implementation in farm-scale treatment plants. We tested the method on three livestock digestates and two municipal organic solid waste digestates. Adsorption isotherms and kinetics were assessed on each digestate, and a large set of parameters, including (i) contact time, (ii) initial NH4+ concentration, (iii) presence of competing ions, (iv) total solids content, and (vi) separation methods (microfiltration and clarification), were considered in the experimental design. Our results showed that the adsorption mechanism can be explained by the Freundlich model (R2 up to 0.97), indicating a multilayer and heterogeneous adsorption, while the kinetic of adsorption can be explained by the pseudo-second-order model, indicating chemical adsorption and ion exchange. The efficiency in the removal of NH4+ was indirectly related to the K+ and total solids content of the digestate. Maximum NH4+ removal exceeded 90% in MSW-derived digestates and 80% within 60 min in livestock-derived digestates at a 5% solid/liquid ratio. Thermodynamic parameters confirmed favorable and spontaneous adsorption (ΔG up to −7 kJ⋅mol−1). Farm-scale projections estimate a nitrogen recovery potential of 1.2 to 16 kg N⋅day−1, depending on digestate type and process conditions. These findings support the application of natural zeolitic tuffs as a low-cost, chemical-free solution for ammonium recovery, contributing to sustainable agriculture and circular economy objectives.
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Open AccessArticle
Thermodynamic Assessment of the Pyrometallurgical Recovery of a Pb-Ag Alloy from a Mixture of Ammonium Jarosite–Lead Paste Wastes
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Jose Enrique Sanchez Vite, Alejandro Cruz Ramírez, Manuel Eduardo Flores Favela, Ricardo Gerardo Sánchez Alvarado, José Antonio Romero Serrano, Margarita García Hernández, Teresita del Refugio Jiménez Romero and Juan Cancio Jiménez Lugos
Recycling 2025, 10(4), 136; https://doi.org/10.3390/recycling10040136 - 8 Jul 2025
Abstract
A previously pyrometallurgical process, developed to obtain a Pb-Ag alloy and a slag rich in sulfur from the recycling of a mixture of industrial wastes of jarosite and lead paste, was thermodynamically assessed at 1200 °C. The industrial jarosite sourced from a Mexican
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A previously pyrometallurgical process, developed to obtain a Pb-Ag alloy and a slag rich in sulfur from the recycling of a mixture of industrial wastes of jarosite and lead paste, was thermodynamically assessed at 1200 °C. The industrial jarosite sourced from a Mexican zinc hydrometallurgical plant corresponded to an ammonium jarosite with a measurable silver content. The specific heat capacity (Cp) of the ammonium jarosite was obtained from TGA and DSC measurements, as well as the thermodynamic functions of enthalpy, entropy, and Gibbs free energy. The Cp was successfully modeled using polynomial regression, with a second-degree polynomial employed to describe the low-temperature behavior. The thermodynamic data generated were input into the thermodynamic software FactSage 8.2 for modeling of the lead paste–ammonium jarosite-Na2CO3-SiC system and represented by stability phase diagrams. The thermodynamic assessment of the pyrometallurgical process predicted compounds formed at high temperatures, showing that a Pb-Ag alloy and a slag rich in Na, S, and Fe (NaFeS2 and NaFeO2) were obtained. The compounds formed evidence of the effective sulfur retention in the slag, which is crucial for mitigating SO2 emissions during high-temperature treatments. The experimental compounds, after solidification, were determined by X-ray diffraction measurements to be Na2Fe(SO4)2 and Na2(SO4), which reasonably match the thermodynamic assessment. The heat capacity of the ammonium jarosite provides essential thermodynamic insights into the compositional complexities of industrial waste, which are particularly relevant for thermodynamic modeling and process optimization in pyrometallurgical systems aimed at metal recovery and residue valorization.
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(This article belongs to the Topic Sustainable Recycling and Reuse of Industrial By-Products or Waste from Geo-Resource Exploitation)
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Open AccessArticle
Mass Distribution of Organic Carbon, S-Containing Compounds and Heavy Metals During Flotation of Municipal Solid Waste Incineration Fly Ash
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Weifang Chen, Peng Li, Shuyue Zhang and Yifan Chen
Recycling 2025, 10(4), 135; https://doi.org/10.3390/recycling10040135 - 8 Jul 2025
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Flotation was investigated to treat incineration fly ash with diesel, kerosene, TX-100, or SDS as a collector and methyl isobutyl carbinol (MIBC) or 2-Octyl alcohol as a frother. Fly ash was separated into light and residual materials. Comparison of yield, carbon and sulfur
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Flotation was investigated to treat incineration fly ash with diesel, kerosene, TX-100, or SDS as a collector and methyl isobutyl carbinol (MIBC) or 2-Octyl alcohol as a frother. Fly ash was separated into light and residual materials. Comparison of yield, carbon and sulfur removal showed that kerosene and MIBC showed the best performance. The results revealed that flotation was a method that could simultaneously achieve the removal of organics and S-containing compounds. Specifically, approximately 7.63–9.45% of the total mass was collected as light material, which was enriched with organic carbon. Contents of organic carbon reached 14.35 wt%–14.56 wt% in the light materials from those of 2.74 wt%–3.52 wt% in the original fly ash. Elemental analysis further proved that sulfur was also accumulated in light material. Approximately 78.84–81.69% of the organic carbon and 80.47–82.66% of the sulfur were removed. Decarbonization was primarily achieved through the flotation of organic materials, while desulfurization resulted from both flotation and the dissolution of soluble salts. Furthermore, the contents of the chloride and heavy metals in the residual fly ash also decreased. Particle size analysis showed that flotation was effective in the removal of smaller particles, and those particles were also rich in heavy metals. Overall, by selecting the right collector and frother, flotation was also able to reduce the leaching toxicity of heavy metals. The residual fly ash was safe for further disposal. Organic carbon, sulfur and heavy metals were accumulated in the light materials, which accounted for less than 10% of the original mass. The portion of fly ash needing further treatment was therefore greatly reduced.
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Open AccessArticle
Evaluation of Plastic Waste Degradation Using Terahertz Spectroscopy for Material Recycling
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Hitomi Sonohata, Gaku Manago, Shun Seike, Hidetoshi Kitawaki and Tadao Tanabe
Recycling 2025, 10(4), 134; https://doi.org/10.3390/recycling10040134 - 5 Jul 2025
Abstract
In Japan, the majority of waste plastics are classified into three categories: approximately 22% are used for material recycling, 3% are used for chemical recycling, and 62% are used for thermal recycling. Thermal recycling is not considered true recycling in the EU, however.
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In Japan, the majority of waste plastics are classified into three categories: approximately 22% are used for material recycling, 3% are used for chemical recycling, and 62% are used for thermal recycling. Thermal recycling is not considered true recycling in the EU, however. To achieve a decarbonized society, Japan must increase the share of material recycling. The accurate identification of plastic materials is essential in this regard, and while near-infrared (NIR) spectroscopy is commonly employed in analyses, it cannot be used to assess degradation levels. Plastics characterized by different degrees of degradation can reduce the quality of recycled products and require additional treatment. In this study, we irradiated artificially degraded polyethylene and polypropylene samples using Fourier transform infrared (FTIR) spectroscopy and terahertz (THz) waves and subsequently compared them with undegraded samples. Our results provide experimental confirmation that THz waves can be used to determine the degree of plastic degradation. When combined with NIR-based material identification, this method could enhance the precision and efficiency of plastic recycling, contributing to a more sustainable recycling system.
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(This article belongs to the Special Issue Challenges and Opportunities in Plastic Waste Management)
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Open AccessArticle
Sustainable Mortar with Waste Glass and Fly Ash: Impact of Glass Aggregate Size and Life-Cycle Assessment
by
Vimukthi Fernando, Weena Lokuge, Hannah Seligmann, Hao Wang and Chamila Gunasekara
Recycling 2025, 10(4), 133; https://doi.org/10.3390/recycling10040133 - 4 Jul 2025
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This study investigates the use of Glass Fine Aggregate (GFA) and Fly Ash (FA) in mortar for Alkali–Silica Reaction (ASR) mitigation through a multidimensional evaluation. GFA was used to replace river sand in 20% increments up to 100%, while FA replaced cement at
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This study investigates the use of Glass Fine Aggregate (GFA) and Fly Ash (FA) in mortar for Alkali–Silica Reaction (ASR) mitigation through a multidimensional evaluation. GFA was used to replace river sand in 20% increments up to 100%, while FA replaced cement at 10%, 20%, and 30%. Three GFA size ranges were considered: <1.18 mm, 1.18–4.75 mm, and a combined fraction of <4.75 mm. At 100% replacement, <1.18 mm GFA reduced ASR expansion to 0.07%, compared to 0.2% for <4.75 mm and 0.46% for 1.18–4.75 mm GFA. It also improved long-term strength by 25% from 28 days to 6 months due to pozzolanic activity. However, refining GFA to below 1.18 mm increased environmental impacts and resulted in a 4.2% increase in energy demand due to the additional drying process. Incorporating 10% FA reduced ASR expansion to 0.044%, had no significant effect on strength, and decreased key environmental burdens such as toxicity by up to 18.2%. These findings indicate that FA utilisation offers greater benefits for ASR mitigation and environmental sustainability than further refining GFA size. Therefore, combining <4.75 mm GFA with 10% FA is identified as the optimal strategy for producing durable and sustainable mortar with recycled waste glass.
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Open AccessReview
A Review of the Progress in Molecular Dynamics Simulation of Calcium Aluminosilicate Hydrate: From Structure and Properties to Applications
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Xiaohuan Jing, Daqiang Cang, Mohammed Ramadan, Alaa Mohsen and Lingling Zhang
Recycling 2025, 10(4), 132; https://doi.org/10.3390/recycling10040132 - 2 Jul 2025
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Recyclable aluminum-containing industrial solid waste can be used as supplementary cementitious materials (SCMs) to replace cement (30–50%), thereby reducing CO2 emissions during cement production and improving the mechanical properties and durability of concrete. Therefore, the use of SCMs in building materials presents
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Recyclable aluminum-containing industrial solid waste can be used as supplementary cementitious materials (SCMs) to replace cement (30–50%), thereby reducing CO2 emissions during cement production and improving the mechanical properties and durability of concrete. Therefore, the use of SCMs in building materials presents significant potential. Due to the presence of the aluminum phase in the SCMs, the hydration products of cements blended with SCMs are changed. Compared to the primary hydration product of conventional cement, calcium silicate hydrate (CSH), the main hydration product of cement blended with SCMs is calcium aluminosilicate hydrate (CASH), which exhibits a more complex molecular structure. Understanding the role of Al in C-A-S-H at the atomic scale facilitates mechanistic insights and promotes the sustainable utilization of SCMs in eco-friendly construction. Molecular dynamics enables the rapid and accurate structural analysis and property prediction of materials. Therefore, this paper presents a systematic review of molecular dynamics simulations of CASH and discusses the role of Al in the molecular structure, dynamic, and mechanical behavior of CASH. It also analyzes the interfacial properties of CASH composites, the immobilization and transport of ions in CASH, and the temperature effect on the structure and properties of CASH. Finally, the challenges and perspectives for molecular dynamics simulation of CASH are presented.
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Open AccessArticle
Development of Sustainable Composite Sandwich with Wood Waste and Natural Fibers for Circular Economy Applications
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Sofia Gomes, Paulo Santos and Tânia M. Lima
Recycling 2025, 10(4), 131; https://doi.org/10.3390/recycling10040131 - 2 Jul 2025
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Sustainability and the circular economy are increasingly recognized as global priorities, particularly in industrial waste management. This study explores the development of a sustainable composite material using wood waste and natural fibers, contributing to circular economy practices. Sandwich panels were manufactured with a
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Sustainability and the circular economy are increasingly recognized as global priorities, particularly in industrial waste management. This study explores the development of a sustainable composite material using wood waste and natural fibers, contributing to circular economy practices. Sandwich panels were manufactured with a green epoxy resin matrix, incorporating wood waste in the core and flax fibers in the outer layers. Mechanical tests on the sandwich panel revealed a facing bending stress of 92.79 MPa and a core shear stress of 2.43 MPa. The panel demonstrated good compressive performance, with an edgewise compressive strength of 61.39 MPa and a flatwise compressive strength of 96.66 MPa. The material’s viscoelastic behavior was also characterized. In stress relaxation tests (from an initial 21 MPa), the panel’s stress decreased by 20.2% after three hours. The experimental relaxation data were successfully fitted by the Kohlrausch–Williams–Watts (KWW) model for both short- and long-term predictions. In creep tests, the panel showed a 21.30% increase in displacement after three hours under a 21 MPa load. For creep behavior, the KWW model was preferable for short-term predictions, while the Findley model provided a better fit for long-term predictions.
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Open AccessArticle
Efficiency Determination of Water Lily (Eichhornia crassipes) Fiber Delignification by Electrohydrolysis Using Different Electrolytes
by
R. Sanchez-Torres, E. Onofre Bustamante, T. Pérez López and A. C. Espindola-Flores
Recycling 2025, 10(4), 130; https://doi.org/10.3390/recycling10040130 - 1 Jul 2025
Abstract
Nowadays, biomass use has increased due to it being the most abundant raw material on the planet, and treating it is a difficult task, as a result of the number of existing methods and the applications’ diversification. This research work shows the results
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Nowadays, biomass use has increased due to it being the most abundant raw material on the planet, and treating it is a difficult task, as a result of the number of existing methods and the applications’ diversification. This research work shows the results obtained using different delignification methods (physical and chemical) on water lily ((Eichhornia crassipes) fiber lignocellulosic biomass including a seldom exploited method, known as “electrohydrolysis” in order to determinate the removal efficiency of lignin and hemicellulose. The characterization of the physicochemical and morphological properties of the water lily (Eichhornia crassipes) fiber before and after the pretreatments were applied were by means of Fourier Transform Infrared (FT-IR), X-ray diffraction (XRD) and optical microscopy (OM). The results of FT-IR show a significant decrease in the bands associated with lignin and hemicellulose. By XRD, it was determined that the crystallinity of the cellulose increased by 60% for the treated samples with respect to the reference, and an increase in the surface roughness of the samples was observed by OM. In conclusion, it was determined that electrochemistry delignification is an efficient, environmentally friendly methodology to remove the soluble sugars, opening the possibility to use the water lily (Eichhornia crassipes) fiber to produce a green concrete.
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(This article belongs to the Special Issue Biomass Revival: Rethinking Waste Recycling for a Greener Future)
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Open AccessArticle
Sustainable Mobile Phone Waste Management: Behavioral Insights and Educational Interventions Through a University-Wide Survey
by
Silvia Serranti, Riccardo Gasbarrone, Roberta Palmieri and Giuseppe Bonifazi
Recycling 2025, 10(4), 129; https://doi.org/10.3390/recycling10040129 - 1 Jul 2025
Abstract
Mobile phone waste management is a growing environmental challenge, with improper disposal contributing to resource depletion, pollution and missed opportunities for material recovery. This study presents the findings of a dual-purpose survey (11,163 respondents) conducted in a wide academic context in Italy, aimed
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Mobile phone waste management is a growing environmental challenge, with improper disposal contributing to resource depletion, pollution and missed opportunities for material recovery. This study presents the findings of a dual-purpose survey (11,163 respondents) conducted in a wide academic context in Italy, aimed at both assessing mobile phones disposal behaviors and knowledge and raising awareness through structured educational prompts about sustainable e-waste management. The results reveal significant behavioral patterns and knowledge gaps across demographic groups. While most respondents (90.6%) own one phone, males tend to have more than females. Phones are replaced every 3–5 years by 48.8% of users and every 1–3 years by 36.7%, with students tending to replace them earlier. Only 20.2% replace their phone when irreparable while 46% replace them due to high repair costs. A large majority (92.3%) store old devices at home, forming an estimated urban mine of 29,799 unused phones. The awareness of hazardous components is higher than that of critical raw materials, with males more informed than females and students in scientific fields displaying greater awareness than those in humanities and health disciplines. The awareness of official take-back programs is particularly low, especially among younger generations. Notably, 90% reported increased awareness from the educational survey and 93.1% expressed willingness to use an on-campus e-waste collection system. These results highlight the role of universities as catalysts for sustainable behavior, supporting the design of targeted educational strategies and policy actions in line with circular economy principles and Sustainable Development Goal 12 “Responsible consumption and production”.
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(This article belongs to the Special Issue Sustainability Education for Recycling: Multidisciplinary Approaches and Innovative Practices)
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Open AccessArticle
From Waste to Product: New Circularity by Recovering Polypropylene from Mixed Commercial Waste
by
Maximilian Julius Enengel, Julia Roitner, Lisa Kandlbauer, Tatjana Lasch, Markus Lehner and Renato Sarc
Recycling 2025, 10(4), 128; https://doi.org/10.3390/recycling10040128 - 27 Jun 2025
Abstract
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To meet the EU’s ambitious recycling targets, it is crucial to expand mechanical recycling to include currently underutilized waste streams, such as mixed commercial waste (MCW), which today achieves a recycling rate of only 3–5%. This study addresses the challenge of recovering polypropylene
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To meet the EU’s ambitious recycling targets, it is crucial to expand mechanical recycling to include currently underutilized waste streams, such as mixed commercial waste (MCW), which today achieves a recycling rate of only 3–5%. This study addresses the challenge of recovering polypropylene (PP) from MCW and demonstrates a viable process to do so. The goal was to develop and test industrial-scale process concepts to extract PP and transform it into high-quality recyclate. Two process concepts were developed and tested at industrial scale to extract PP as a pre-concentrate. The recovered material was further sorted, shredded, washed, and granulated, ultimately reaching End-of-Waste status. Material analysis confirmed that the resulting PP granulate meets all relevant quality standards. A total of 456.8 kg of this recyclate was processed into market-ready products. To the best of the authors’ knowledge, this is the first demonstration of plastic products made entirely from MCW. By covering the full value chain—from waste to final product—this study highlights a viable and scalable approach for integrating complex waste streams into high-quality material cycles, thereby contributing to circular economy strategies.
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Open AccessArticle
Rebound Effect Generated by Waste HDPE in Hot Asphalt Mixtures
by
David Sepúlveda-Valdez, Julio Calderón-Ramírez, Ricardo Cota-Ramírez, José Manuel Gutiérrez-Moreno, Marco Montoya-Alcaraz, Leonel García-Gómez and Atondo Sánchez-Atondo
Recycling 2025, 10(4), 127; https://doi.org/10.3390/recycling10040127 - 26 Jun 2025
Abstract
The feasibility of using high-density polyethylene (HDPE) waste in hot asphalt mixtures was analyzed, with particular focus on the rebound effect generated during compaction. Traditional asphalt mixtures without additives were evaluated alongside mixtures modified with varying percentages of HDPE waste (0.5%, 0.62%, 1%,
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The feasibility of using high-density polyethylene (HDPE) waste in hot asphalt mixtures was analyzed, with particular focus on the rebound effect generated during compaction. Traditional asphalt mixtures without additives were evaluated alongside mixtures modified with varying percentages of HDPE waste (0.5%, 0.62%, 1%, 4%, and 5%) through the dry method. In this method, crushed HDPE was incorporated as an aggregate within the asphalt mixture structure, added prior to the introduction of the asphalt binder. Laboratory tests assessed compaction, specific gravity (Gmb and Gmm), void content, and resistance to permanent deformation via the Hamburg wheel tracking test. The results indicated that high percentages of HDPE (4% and 5%) triggered a rebound effect that hindered proper compaction of the mixtures, thereby compromising structural integrity. Conversely, mixtures with lower HDPE percentages (0.5% and 0.62%) exhibited better compaction, although they remained comparable to the traditional mixtures without plastic. In conclusion, HDPE does not constitute a viable option for enhancing the properties of asphalt mixtures at high percentages due to elastic behavior during compaction, which introduces densification irregularities. However, some benefits were observed in mixtures with low HDPE percentages, including improvements in stability and resistance to deformation. Nonetheless, these advantages are insufficient to justify replacing traditional asphalt mixtures.
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(This article belongs to the Special Issue Recycled Materials in Sustainable Pavement Innovation)
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