Recycling

26 pages, 339 KiB

Open AccessArticle

Pro-Environmental Behavior and Attitudes Towards Recycling in Slovak Republic

by Silvia Lorincová and Mária Osvaldová

Recycling 2025, 10(4), 159; https://doi.org/10.3390/recycling10040159 - 7 Aug 2025

Climate changes have increased interest in the circular economy, an alternative model that seeks to minimize environmental impact and maximize resource reuse. A key element of this model is individuals’ behaviors and attitudes, which determine the overall efficiency of recycling processes. The study [...] Read more.

Climate changes have increased interest in the circular economy, an alternative model that seeks to minimize environmental impact and maximize resource reuse. A key element of this model is individuals’ behaviors and attitudes, which determine the overall efficiency of recycling processes. The study fills the gap by investigating how selected socio-demographic factors affect attitudes and intentions toward recycling and material reuse in the Slovak Republic, by using the Perceived Characteristics of Innovating (PCI) framework. Through a two-way ANOVA, we tested the hypotheses that higher education correlates with stronger recycling attitudes and that women are more willing than men to engage in circular practices. The results show that gender differences in consumer attitudes towards the circular economy do occur, but their magnitude is often conditioned by education level. Education proved to be the strongest predictor of ecological behavior: respondents with higher education reported stronger beliefs in the importance of recycling and a greater willingness to act sustainably. The interaction between gender and education revealed that university-educated women hold the most pronounced pro-environmental attitudes, underscoring the importance of gender-sensitive educational strategies. It is recommended that environmental education and outreach focus on less-educated groups, particularly women, who have high potential to influence their communities. Full article

16 pages, 1369 KiB

Open AccessArticle

Recycling Waste Cottonseed Hulls to Biomaterials for Ammonia Adsorption

by Thomas Klasson, Bretlyn Pancio and Allen Torbert

Recycling 2025, 10(4), 158; https://doi.org/10.3390/recycling10040158 - 6 Aug 2025

Abstract

Ammonia emissions in poultry houses are common and pose health concerns for animals and workers. However, effective control of these emissions with sustainable products is lacking. Therefore, we investigated if an agricultural byproduct, cottonseed hulls, could be recycled through pyrolysis and used to [...] Read more.

Ammonia emissions in poultry houses are common and pose health concerns for animals and workers. However, effective control of these emissions with sustainable products is lacking. Therefore, we investigated if an agricultural byproduct, cottonseed hulls, could be recycled through pyrolysis and used to remove ammonia from air. In this study, the efficacy of ammonia removal was observed using cottonseed hull biomaterials pyrolyzed at seven different temperatures: 250, 300, 350, 400, 500, 600, and 700 °C. In this study, ammonia was passed through a column filled with pyrolyzed material, and ammonia in the filtered air was monitored. The results showed that materials pyrolyzed at intermediate temperatures of 350 and 400 °C were the most efficient at ammonia removal and were able to adsorb approximately 3.7 mg NH₃/g of material. Despite extensive characterization, ammonia adsorption could not be linked to intrinsic material properties. Evaluation of the materials showed that the carbon in the pyrolyzed materials would be stable over time should the spent material be used as a soil amendment. Full article

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21 pages, 19752 KiB

Open AccessArticle

Phase Characterisation for Recycling of Shredded Waste Printed Circuit Boards

by Laurance Donnelly, Duncan Pirrie, Matthew Power and Andrew Menzies

Recycling 2025, 10(4), 157; https://doi.org/10.3390/recycling10040157 - 6 Aug 2025

Abstract

In this study, we adopt a geometallurgical analytical approach common in mineral processing in the characterization of samples of shredded waste printed circuit board (PCB) E-waste, originating from Europe. Conventionally, bulk chemical analysis provides a value for E-waste; however, chemical analysis alone does [...] Read more.

In this study, we adopt a geometallurgical analytical approach common in mineral processing in the characterization of samples of shredded waste printed circuit board (PCB) E-waste, originating from Europe. Conventionally, bulk chemical analysis provides a value for E-waste; however, chemical analysis alone does not provide information on the textural variability, phase complexity, grain size, particle morphology, phase liberation and associations. To address this, we have integrated analysis using binocular microscopy, manual scanning electron microscopy, phase, textural and compositional analyses by automated (SEM-EDS), phase analysis based on (Automated Material Identification and Classification System (AMICS) software, and elemental analysis using micro-XRF. All methods used have strengths and limitations, but an integration of these analytical tools allows the detailed characterization of the texture and composition of the E-waste feeds, ahead of waste reprocessing. These data can then be used to aid the design of optimized processing circuits for the recovery of the key payable components, and assist in the commercial trading of e-scrap. Full article

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18 pages, 7363 KiB

Open AccessArticle

Agronomic Evaluation of Compost Formulations Based on Mining Tailings and Microbial Mats from Geothermal Sources

by María Jesús Puy-Alquiza, Miren Yosune Miranda Puy, Raúl Miranda-Avilés, Pooja Vinod Kshirsagar and Cristina Daniela Moncada Sanchez

Recycling 2025, 10(4), 156; https://doi.org/10.3390/recycling10040156 - 5 Aug 2025

Abstract

This study, conducted in Mexico, evaluates the agricultural potential of three compost formulations BFS1, BFS2, and BFS3 produced from mining tailings and thermophilic microbial mats and collected from geothermal environments. The physicochemical characterization included pH, electrical conductivity (EC), macronutrients (N, P, K, Ca, [...] Read more.

This study, conducted in Mexico, evaluates the agricultural potential of three compost formulations BFS1, BFS2, and BFS3 produced from mining tailings and thermophilic microbial mats and collected from geothermal environments. The physicochemical characterization included pH, electrical conductivity (EC), macronutrients (N, P, K, Ca, Mg, and S), micronutrients (Fe, Zn, B, Cu, Mn, Mo, and Ni), organic matter (OM), and the carbon-to-nitrogen (C/N) ratio. All composts exhibited neutral pH values (7.38–7.52), high OM content (38.5–48.4%), and optimal C/N ratios (10.5–13.9), indicating maturity and chemical stability. Nitrogen ranged from 19 to 21 kg·t⁻¹, while potassium and calcium were present in concentrations beneficial for crop development. However, EC values (3.43–3.66 dS/m) and boron levels (>160 ppm) were moderately high, requiring caution in saline soils or with boron-sensitive crops. A semi-quantitative Compost Quality Index (CQI) ranked BFS3 highest due to elevated OM and potassium content, followed by BFS1. BFS2, while rich in nitrogen, scored lower due to excessive boron. One-way ANOVA revealed no significant difference in nitrogen (p > 0.05), but it did reveal significant differences in potassium (p < 0.01) and boron (p < 0.001) among formulations. These results confirm the potential of mining tailings—microbial mat composts are low-cost, nutrient-rich biofertilizers. They are suitable for field crops or as components in nursery substrates, particularly when EC and boron are managed through dilution. This study promotes the circular reuse of geothermal and industrial residues and contributes to sustainable soil restoration practices in mining-affected regions through innovative composting strategies. Full article

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31 pages, 1741 KiB

Open AccessReview

Recycled Concrete Aggregate in Asphalt Mixtures: A Review

by Juan Gabriel Bastidas-Martínez, Hugo Alexander Rondón-Quintana and Luis Ángel Moreno-Anselmi

Recycling 2025, 10(4), 155; https://doi.org/10.3390/recycling10040155 - 2 Aug 2025

Abstract

Effective management and handling of construction and demolition waste (CDW) can yield significant technical and environmental benefits for road pavement construction. This article aims to provide a comprehensive and up-to-date chronological review of studies on the mechanical performance of asphalt mixtures—primarily hot mix [...] Read more.

Effective management and handling of construction and demolition waste (CDW) can yield significant technical and environmental benefits for road pavement construction. This article aims to provide a comprehensive and up-to-date chronological review of studies on the mechanical performance of asphalt mixtures—primarily hot mix asphalt (HMA)—incorporating recycled concrete aggregate (RCA). Since the main limitation of RCA is the presence of residual adhered mortar, the review also includes studies that applied various surface treatments (mechanical, chemical, and thermal, among others) to enhance mixture performance. The article summarizes the experimental procedures used and highlights the key findings and conclusions of the reviewed research. Although the results are varied and sometimes contradictory—mainly due to the source variability and heterogeneity of RCA—the use of these materials is technically viable. Moreover, their application can provide environmental, social, and economic advantages, particularly in the construction of low-traffic roadways. Finally, the article identifies research gaps and offers recommendations for future researches. Full article

(This article belongs to the Special Issue Recycled Materials in Sustainable Pavement Innovation)

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30 pages, 2603 KiB

Open AccessReview

Sugarcane Industry By-Products: A Decade of Research Using Biotechnological Approaches

by Serafín Pérez-Contreras, Francisco Hernández-Rosas, Manuel A. Lizardi-Jiménez, José A. Herrera-Corredor, Obdulia Baltazar-Bernal, Dora A. Avalos-de la Cruz and Ricardo Hernández-Martínez

Recycling 2025, 10(4), 154; https://doi.org/10.3390/recycling10040154 - 2 Aug 2025

Abstract

The sugarcane industry plays a crucial economic role worldwide, with sucrose and ethanol as its main products. However, its processing generates large volumes of by-products—such as bagasse, molasses, vinasse, and straw—that contain valuable components for biotechnological valorization. This review integrates approximately 100 original [...] Read more.

The sugarcane industry plays a crucial economic role worldwide, with sucrose and ethanol as its main products. However, its processing generates large volumes of by-products—such as bagasse, molasses, vinasse, and straw—that contain valuable components for biotechnological valorization. This review integrates approximately 100 original research articles published in JCR-indexed journals between 2015 and 2025, of which over 50% focus specifically on sugarcane-derived agroindustrial residues. The biotechnological approaches discussed include submerged fermentation, solid-state fermentation, enzymatic biocatalysis, and anaerobic digestion, highlighting their potential for the production of biofuels, enzymes, and high-value bioproducts. In addition to identifying current advances, this review addresses key technical challenges such as (i) the need for efficient pretreatment to release fermentable sugars from lignocellulosic biomass; (ii) the compositional variability of by-products like vinasse and molasses; (iii) the generation of metabolic inhibitors—such as furfural and hydroxymethylfurfural—during thermochemical processes; and (iv) the high costs related to inputs like hydrolytic enzymes. Special attention is given to detoxification strategies for inhibitory compounds and to the integration of multifunctional processes to improve overall system efficiency. The final section outlines emerging trends (2024–2025) such as the use of CRISPR-engineered microbial consortia, advanced pretreatments, and immobilization systems to enhance the productivity and sustainability of bioprocesses. In conclusion, the valorization of sugarcane by-products through biotechnology not only contributes to waste reduction but also supports circular economy principles and the development of sustainable production models. Full article

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Graphical abstract

19 pages, 4487 KiB

Open AccessArticle

Recycling Volcanic Lapillus as a Supplementary Cementitious Material in Sustainable Mortars

by Fabiana Altimari, Luisa Barbieri, Andrea Saccani and Isabella Lancellotti

Recycling 2025, 10(4), 153; https://doi.org/10.3390/recycling10040153 - 1 Aug 2025

Abstract

This study investigates the feasibility of using volcanic lapillus as a supplementary cementitious material (SCM) in mortar production to improve the sustainability of the cement industry. Cement production is one of the main sources of CO₂ emissions, mainly due to clinker production. [...] Read more.

This study investigates the feasibility of using volcanic lapillus as a supplementary cementitious material (SCM) in mortar production to improve the sustainability of the cement industry. Cement production is one of the main sources of CO₂ emissions, mainly due to clinker production. Replacing clinker with SCMs, such as volcanic lapillus, can reduce the environmental impact while maintaining adequate mechanical properties. Experiments were conducted to replace up to 20 wt% of limestone Portland cement with volcanic lapillus. Workability, compressive strength, microstructure, resistance to alkali-silica reaction (ASR), sulfate, and chloride penetration were analyzed. The results showed that up to 10% replacement had a minimal effect on mechanical properties, while higher percentages resulted in reduced strength but still improved some durability features. The control sample cured 28 days showed a compressive strength of 43.05 MPa compared with 36.89 MPa for the sample containing 10% lapillus. After 90 days the respective values for the above samples were 44.76 MPa and 44.57 MPa. Scanning electron microscopy (SEM) revealed good gel–aggregate adhesion, and thermogravimetric analysis (TGA) confirmed reduced calcium hydroxide content, indicating pozzolanic activity. Overall, volcanic lapillus shows promise as a sustainable SCM, offering CO₂ reduction and durability benefits, although higher replacement rates require further optimization. Full article

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23 pages, 4356 KiB

Open AccessArticle

Quantifying Cotton Content in Post-Consumer Polyester/Cotton Blend Textiles via NIR Spectroscopy: Current Attainable Outcomes and Challenges in Practice

by Hana Stipanovic, Gerald Koinig, Thomas Fink, Christian B. Schimper, David Lilek, Jeannie Egan and Alexia Tischberger-Aldrian

Recycling 2025, 10(4), 152; https://doi.org/10.3390/recycling10040152 - 1 Aug 2025

Abstract

Rising volumes of textile waste necessitate the development of more efficient recycling systems, with a primary focus on the optimization of sorting technologies. Near-infrared (NIR) spectroscopy is a state-of-the-art method for fiber identification; however, its accuracy in quantifying textile blends, particularly common polyester/cotton [...] Read more.

Rising volumes of textile waste necessitate the development of more efficient recycling systems, with a primary focus on the optimization of sorting technologies. Near-infrared (NIR) spectroscopy is a state-of-the-art method for fiber identification; however, its accuracy in quantifying textile blends, particularly common polyester/cotton blend textiles, still requires refinement. This study explores the potential and limitations of NIR spectroscopy for quantifying cotton content in post-consumer textiles. A lab-scale NIR sorter and a handheld NIR spectrometer in complementary wavelength ranges were applied to a diverse range of post-consumer textile samples to test model accuracies. Results show that the commonly assumed 10% accuracy threshold in industrial sorting can be exceeded, especially when excluding textiles with <35% cotton content. Identifying and excluding the range of non-linearity significantly improved the model’s performance. The final models achieved an RMSEP of 6.6% and bias of −0.9% for the NIR sorter and an RMSEP of 3.1% and bias of −0.6% for the handheld NIR spectrometer. This study also assessed how textile characteristics—such as color, structure, product type, and alkaline treatment—affect spectral behavior and model accuracy, highlighting their importance for refining quantification when high-purity inputs are needed. By identifying current limitations and potential sources of errors, this study provides a foundation for improving NIR-based models. Full article

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20 pages, 1701 KiB

Open AccessArticle

Life Cycle Assessment of Biomass Waste and Coal Co-Firing: Advancing Circular Economy in Energy Production

by Stiven J. Sofán-Germán, Miguel E. Doria-Oviedo, Jesus D. Rhenals-Julio and Jorge M. Mendoza-Fandiño

Recycling 2025, 10(4), 151; https://doi.org/10.3390/recycling10040151 - 1 Aug 2025

Abstract

This study uses life cycle analysis (LCA) to evaluate the environmental impacts of co-firing bituminous coal with agricultural biomass waste, such as coconut and rice husks, emphasising circular economy principles. Seven experimental scenarios with different coal-to-biomass ratios were designed, ranging from pure coal [...] Read more.

This study uses life cycle analysis (LCA) to evaluate the environmental impacts of co-firing bituminous coal with agricultural biomass waste, such as coconut and rice husks, emphasising circular economy principles. Seven experimental scenarios with different coal-to-biomass ratios were designed, ranging from pure coal to pure biomass. The results show that Scenario B (100% rice husk) achieved the best overall environmental performance, with the lowest global warming potential (300 kg CO₂ equivalent), eutrophication potential (4.742 kg PO₄ equivalent), and smog formation potential (0.012 kg C₂H₄ equivalent). Additionally, Scenario F (15% biomass mix) recorded the lowest acidification potential (57.39 kg SO₂ eq), indicating that even partial substitution can yield significant environmental benefits. In contrast, Scenario C (100% coal) exhibited the highest acidification (164.08 kg SO₂ eq) and eutrophication (8.82 kg PO₄ eq) potential. Overall, the results demonstrate that co-firing biomass waste significantly reduces pollutant emissions compared to burning coal alone. This study highlights the effectiveness of biomass waste co-firing in mitigating environmental impacts, promoting resource recovery, and supporting a sustainable energy transition within a circular economy framework. Full article

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17 pages, 9519 KiB

Open AccessArticle

Lead Recovery from Flue Dust by Using Ultrasonic-Enhanced Hydrogen Peroxide Water Washing

by Tian Wang, Yuxi Xie, Phan Duc Lenh, Thiquynhxuan Le and Libo Zhang

Recycling 2025, 10(4), 150; https://doi.org/10.3390/recycling10040150 - 1 Aug 2025

Abstract

An ultrasonic-enhanced hydrogen peroxide water-washing process was developed to recover lead from raw flue dust (RFD) under neutral conditions. At optimal parameters (40 °C, 30 min, 4 mL H₂O₂, liquid-to-solid ratio 2:1, 240 W ultrasound), the Pb mass fraction [...] Read more.

An ultrasonic-enhanced hydrogen peroxide water-washing process was developed to recover lead from raw flue dust (RFD) under neutral conditions. At optimal parameters (40 °C, 30 min, 4 mL H₂O₂, liquid-to-solid ratio 2:1, 240 W ultrasound), the Pb mass fraction in the solid residue increased from 41.68% in the RFD to 68.11%, accompanied by a Pb recovery rate of 97.1%. These values are significantly higher than those obtained under identical conditions without ultrasound (64.07% and 95.93%, respectively). Ultrasound promotes de-agglomeration and generates •OH radicals that accelerate the oxidation of PbSO₃ to insoluble PbSO₄ while concurrently removing impurity cadmium. This research offers a green and efficient alternative to traditional lead recovery methods, fostering sustainable development in the metallurgical industry. Full article

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21 pages, 2332 KiB

Open AccessArticle

Evaluation of Spent Catalyst from Fluid Catalytic Cracking in Fly Ash and Blast Furnace Slag Based Alkali Activated Materials

by Yolanda Luna-Galiano, Domigo Cabrera-Gallardo, Mónica Rodríguez-Galán, Rui M. Novais, João A. Labrincha and Carlos Leiva Fernández

Recycling 2025, 10(4), 149; https://doi.org/10.3390/recycling10040149 - 1 Aug 2025

Abstract

The objective of this work is to evaluate how spent catalyst from fluid catalytic cracking (SCFCC) affects the physical, mechanical and durability properties of fly ash (FA) and blast furnace slag (BFS)-based alkali-activated materials (AAMs). Recycling of SCFCC by integrating it in a [...] Read more.

The objective of this work is to evaluate how spent catalyst from fluid catalytic cracking (SCFCC) affects the physical, mechanical and durability properties of fly ash (FA) and blast furnace slag (BFS)-based alkali-activated materials (AAMs). Recycling of SCFCC by integrating it in a AAM matrix offers several advantages: valorization of the material, reducing its disposal in landfills and the landfill cost, and minimizing the environmental impact. Mineralogical, physical and mechanical characterization were carried out. The durability of the specimens was studied by performing acid attack and thermal stability tests. Mass variation, compressive strength and porosity parameters were determined to assess the durability. BFS- and FA-based AAMs have a different chemical composition, which contribute to variations in microstructure and physical and mechanical properties. Acid neutralization capacity was also determined to analyse the acid attack results. Porosity, including the pore size distribution, and the acid neutralization capacity are crucial in explaining the resistance of the AAMs to sulfuric acid attack and thermal degradation. Herein, a novel route was explored, the use of SCFCC to enhance the durability of AAMs under harsh operating conditions since results show that the compositions containing SCFCC showed lower strength decay due to the lower macroporosity proportions in these compositions. Full article

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33 pages, 3709 KiB

Open AccessReview

A Review of Methods and Data on the Recycling of Plastics from the European Waste Stream of Electric and Electronic Equipment

by Nicolas Nève, Xavier Mackré-Delannoy, Bruno Fayolle, Matthieu Gervais, Stéphane Pompidou, Carole Charbuillet, Cyrille Sollogoub and Nicolas Perry

Recycling 2025, 10(4), 148; https://doi.org/10.3390/recycling10040148 - 28 Jul 2025

Abstract

Plastics make up a significant proportion of the stream of the European Waste of Electric and Electronic Equipment (WEEE), yet the use of recycled plastic materials is very low in new manufactured products. A description of the WEEE waste stream in Europe is [...] Read more.

Plastics make up a significant proportion of the stream of the European Waste of Electric and Electronic Equipment (WEEE), yet the use of recycled plastic materials is very low in new manufactured products. A description of the WEEE waste stream in Europe is given, with a focus on the plastic materials commonly found in WEEE that include four principal polymers: polypropylene (PP), polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS) and polystyrene (PS). Furthermore, the legislative aspects related to WEEE and plastics recycling in Europe are complex, and numerous norms have been dictated by the European Commission. These norms are crucial to the sector of polymer recycling and production in Europe. Moreover, an overview of the entire treatment chain is presented. More specifically, each step of a typical recycling chain is introduced, with a focus on the sorting of plastics and the separation of polymers. Lastly, the influence of contaminants in the plastic fraction is discussed, both in terms of polymer particles and unwanted additives. By showing the impact of the purity rate on the mechanical properties of recycled plastics, the consequences of inadequate end-of-life treatment for WEEE-plastics is highlighted, hence linking the quality of recycled plastics to the separation step and the re-compounding of recycled granulates. Full article

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Graphical abstract

22 pages, 3056 KiB

Open AccessArticle

Recycled Glass and Plastic Waste in Sustainable Geopolymer Systems for Affordable Housing Solutions

by Zhao Qing Tang, Yat Choy Wong, Yali Li and Eryadi Kordi Masli

Recycling 2025, 10(4), 147; https://doi.org/10.3390/recycling10040147 - 27 Jul 2025

Abstract

The increasing demand for sustainable construction materials has driven research into low-carbon geopolymers that mitigate both cement-related emissions and plastic and glass waste accumulation. This study explores the development of geopolymer concrete incorporating fly ash (FA), slag (S), and FA + S blends, [...] Read more.

The increasing demand for sustainable construction materials has driven research into low-carbon geopolymers that mitigate both cement-related emissions and plastic and glass waste accumulation. This study explores the development of geopolymer concrete incorporating fly ash (FA), slag (S), and FA + S blends, with 10% recycled crushed glass (RCG) and recycled plastic waste (RPW) as partial coarse aggregate replacements. Compressive strength testing revealed that FA + S-based geopolymers (25FA + S) with 100% ordinary Portland cement (OPC) replacement achieved a 7-day strength of 24.6 MPa, representing a 98% improvement over control specimens. Slag-based geopolymers demonstrated water absorption properties comparable to OPC, indicating enhanced durability. Microstructural analyses using SEM, XRD, and EDS confirmed the formation of a dense aluminosilicate matrix, with slag promoting FA reactivity and reinforcing interfacial transition zone (ITZ). These effects contributed to superior mechanical performance and water resistance. Despite minor shrinkage-induced cracking, full OPC replacement with S or FA + S geopolymers outperformed control specimens, consistently exceeding the target strength of 15 MPa required for low-impact, single-story housing applications within seven days. These findings underscore the potential of geopolymer systems for rapid and sustainable construction, offering an effective solution for reducing carbon footprints and repurposing industrial waste. Full article

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26 pages, 796 KiB

Open AccessArticle

Developing an Integrated Circular Economy Framework for Nanomaterial-Enhanced Recycled PET (nrPET): Advancing Sustainable and Resilient Road Construction Practices

by Demiss A. Belachew and Walied A. Elsaigh

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 [...] Read more.

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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21 pages, 3984 KiB

Open AccessArticle

Organic Acid Leaching of Black Mass with an LFP and NMC Mixed Chemistry

by 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

Abstract

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 [...] Read more.

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. Full article

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15 pages, 677 KiB

Open AccessArticle

Zero-Shot Learning for Sustainable Municipal Waste Classification

by 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

Abstract

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 [...] Read more.

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. Full article

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16 pages, 2206 KiB

Open AccessArticle

Turning Waste into Wealth: Sustainable Amorphous Silica from Moroccan Oil Shale Ash

by 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

Abstract

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 [...] Read more.

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. Full article

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26 pages, 2472 KiB

Open AccessArticle

Incorporating Recyclates Derived from Household Waste into Flexible Food Packaging Applications: An Environmental Sustainability Assessment

by 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 [...] Read more.

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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19 pages, 1165 KiB

Open AccessArticle

Expansion of Mechanical Biological Residual Treatment Plant with Fermentation Stage for Press Water from Organic Fractions Involving a Screw Press

by 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

Abstract

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 [...] Read more.

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. Full article

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