Recycling

19 pages, 5375 KB

Open AccessArticle

Using Marble Waste in the Production of Concrete and Pervious Paver Blocks

by Ana Carolina Valdevieso Buzzo, Maria Eliana Camargo Ferreira, Willian Luís de Oliveira, José Eduardo Gonçalves, Luiz Fernando Belchior Ribeiro and Natália Ueda Yamaguchi

Recycling 2026, 11(2), 38; https://doi.org/10.3390/recycling11020038 - 6 Feb 2026

Abstract

This study aimed to evaluate the technical and environmental feasibility of producing concrete paver blocks and pervious concrete paver blocks by incorporating marble waste to evaluate its filler effect within the cementitious matrix. The methodology included the characterization of marble waste, the production [...] Read more.

This study aimed to evaluate the technical and environmental feasibility of producing concrete paver blocks and pervious concrete paver blocks by incorporating marble waste to evaluate its filler effect within the cementitious matrix. The methodology included the characterization of marble waste, the production of test specimens with the control (0%), 10%, 20%, and 30% of cement replacement, and the execution of performance tests, supplemented by statistical analyses. The results indicated that marble waste replacement significantly impacted the properties. In terms of pervious concrete paver block permeability, the highest rates were observed in the control and 30% treatments. For water absorption, concrete paver blocks showed higher values at a maximum of 20%, while pervious concrete paver blocks maintained statistically analogous values for 10% and 20%. Regarding compressive strength, the concrete paver block formulation with 10% marble waste was statistically compatible with the control. It is concluded that the incorporation of marble waste into concrete and pervious concrete paver blocks is environmentally advantageous as it valorizes an industrial waste. However, mix design optimization is essential, given that excessive replacement (above 10%) resulted in a reduction in compressive strength. Full article

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

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13 pages, 1797 KB

Open AccessArticle

Mechanochemical Recycling of Tire-Derived Styrene–Butadiene Rubber Using a Regeneration Agent

by Matheus Silva de Oliveira, Leila Lea Yuan Visconte and Elen Beatriz Acordi Vasques Pacheco

Recycling 2026, 11(2), 37; https://doi.org/10.3390/recycling11020037 - 6 Feb 2026

Abstract

Mechanochemical regeneration aims to selectively cleave the crosslinked network of vulcanized rubber. In this study, a tire-grade styrene–butadiene rubber (SBR) compound was vulcanized and then subjected to mechanochemical regeneration using a zinc (II) dithiocarbamate complex (ZNIBU) at 6, 8, and 10 phr. The [...] Read more.

Mechanochemical regeneration aims to selectively cleave the crosslinked network of vulcanized rubber. In this study, a tire-grade styrene–butadiene rubber (SBR) compound was vulcanized and then subjected to mechanochemical regeneration using a zinc (II) dithiocarbamate complex (ZNIBU) at 6, 8, and 10 phr. The regenerated materials were subsequently revulcanized, and their properties were assessed before and after both processing steps. The regenerated (non-revulcanized) samples exhibited reduced crosslink density and increased swelling, indicating effective network cleavage by the regenerator. After revulcanization, the compounds presented higher hardness (23%) but lower tensile strength (75%) and tear strength (25%) compared to the virgin vulcanizate. Overall, ZNIBU proved highly effective for the mechanochemical regeneration of SBR, with optimum performance observed at 8 phr. Full article

(This article belongs to the Special Issue Celebrating 10 Years of Recycling: Shaping the Future of Waste Management)

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22 pages, 8313 KB

Open AccessArticle

A Technical Feasibility Assessment of Chemically Recycling PET Fibers Through Glycolysis to Produce Functional Oligoesters

by Elaine Meireles Senra, Ana Carolina da Silva Guimarães, Renan Henriques Gonçalves de Almeida, Ana Lúcia Nazareth da Silva, José Carlos Costa da Silva Pinto, Christine Rabello Nascimento and Elen Beatriz Acordi Vasques Pacheco

Recycling 2026, 11(2), 36; https://doi.org/10.3390/recycling11020036 - 5 Feb 2026

Abstract

This study investigated the chemical recycling of poly(ethylene terephthalate) (PET) fiber residues from two sources—high-molar mass mooring ropes and low-molar mass textile-grade fibers—to produce functional oligomers. Glycolysis was carried out using polyethylene glycol (PEG400) as the depolymerizing agent, and two catalysts were assessed, [...] Read more.

This study investigated the chemical recycling of poly(ethylene terephthalate) (PET) fiber residues from two sources—high-molar mass mooring ropes and low-molar mass textile-grade fibers—to produce functional oligomers. Glycolysis was carried out using polyethylene glycol (PEG400) as the depolymerizing agent, and two catalysts were assessed, zinc acetate and lithium octoate, with the latter reported on for the first time in this application. Reactions were performed for 180 min under mechanical stirring, inert atmosphere, reflux, and controlled heating. The resulting oligomers were characterized by Fourier-transform infrared spectroscopy (FTIR), hydroxyl and acidity indices, and thermogravimetric analysis (TGA). Both PET feedstocks showed high reactivity toward glycolysis. Monitoring the reactions by acidity index indicated that conversion reached equilibrium at approximately 120 min. ATR-FTIR confirmed the formation of ester and hydroxyl groups, consistent with oligomer structures. Glycolysis of PET derived from mooring ropes produced oligoesters with hydroxyl values of 228 and 242 mgKOH/g for zinc acetate and lithium octoate, respectively, and molar masses of 1296 and 1338 g/mol for zinc acetate and lithium octoate, respectively. These values are suitable for subsequent syntheses such as polyester polyol production. Full article

(This article belongs to the Special Issue Celebrating 10 Years of Recycling: Shaping the Future of Waste Management)

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24 pages, 9743 KB

Open AccessArticle

Data-Efficient Polymer Classification Using Spectra Simulation and Bayesian Optimization

by Alexander Pletl, Roman-David Kulko, Andreas Hanus and Benedikt Elser

Recycling 2026, 11(2), 35; https://doi.org/10.3390/recycling11020035 - 3 Feb 2026

Abstract

Plastic recycling represents an essential element of strategies aimed at lowering global carbon emissions while supporting a circular plastics economy. However, the effectiveness of current plastic sorting systems remains limited by data scarcity, spectral variability, and the complexity of real world waste streams. [...] Read more.

Plastic recycling represents an essential element of strategies aimed at lowering global carbon emissions while supporting a circular plastics economy. However, the effectiveness of current plastic sorting systems remains limited by data scarcity, spectral variability, and the complexity of real world waste streams. This study introduces a CNN-based polymer classification framework that integrates physics-informed spectral simulation, adaptive data augmentation, and Bayesian hyperparameter optimization to enable robust classification under data limited conditions. Our framework combines near-infrared (NIR) spectral data from technical scale measurements with synthetically generated spectra. With only 100 measured spectra per polymer, the proposed framework achieves average balanced accuracies of 0.9739 in multi-target polymer classification tasks. By using technical scale spectral data, this study bridges the gap between laboratory model development and real sorting conditions. Full article

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25 pages, 2696 KB

Open AccessArticle

Recycled Lignocellulosic Resources for Circular Bioeconomy Applications: Heat-Treated Eucalyptus Fibers in Polyester Composites

by Douglas Lamounier Faria, Tamires Galvão Tavares Pereira, Danillo Wisky Silva, Mário Vanoli Scatolino, Julio Soriano, Thiago de Paula Protásio and Lourival Marin Mendes

Recycling 2026, 11(2), 34; https://doi.org/10.3390/recycling11020034 - 3 Feb 2026

Abstract

The pursuit of alternatives to nonrenewable materials has stimulated the development of sustainable materials with improved performance, particularly polymer composites reinforced with plant-based fibers. In this study, eucalyptus fibers were thermally treated and evaluated as eco-friendly reinforcements for polyester composites, aiming to enhance [...] Read more.

The pursuit of alternatives to nonrenewable materials has stimulated the development of sustainable materials with improved performance, particularly polymer composites reinforced with plant-based fibers. In this study, eucalyptus fibers were thermally treated and evaluated as eco-friendly reinforcements for polyester composites, aiming to enhance their physical and mechanical properties. The fibers were subjected to heat treatments between 140 and 230 °C in a Macro-ATG oven, followed by analyses of anatomical characteristics and chemical composition. Composites containing 25% fiber reinforcement were produced using an orthophthalic unsaturated polyester matrix catalyzed with methyl ethyl ketone peroxide, with untreated fibers used as references. Thermal treatment induced significant modifications in fiber morphology and composition, including increases in cell wall fraction at 170 and 200 °C and higher cellulose contents at 140 and 170 °C. Mechanical performance was assessed through tensile, flexural (modulus of rupture—MOR), modulus of elasticity (E_B), and impact tests. Composites reinforced with heat-treated fibers exhibited lower apparent density and, notably, those treated at 230 °C showed markedly reduced water absorption and enhanced tensile strength compared with the control. Overall, treatment at 230 °C proved most effective, highlighting the potential of thermally modified eucalyptus fibers as viable reinforcements for high-performance, bio-based polymer composites. Full article

(This article belongs to the Special Issue Celebrating 10 Years of Recycling: Shaping the Future of Waste Management)

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47 pages, 2159 KB

Open AccessReview

A Review of Current and Emerging Strategies for Recycling Waste: Bicycle Tires and Inner Tubes

by Xiao Yuan Chen and Denis Rodrigue

Recycling 2026, 11(2), 33; https://doi.org/10.3390/recycling11020033 - 2 Feb 2026

Abstract

Bicycle tires and inner tubes constitute a growing waste stream mainly composed of natural rubber, butyl rubber, synthetic elastomers, carbon black, and reinforcing materials. Their multi-material structure and highly crosslinked networks make their recycling challenging, yet efficient recovery is essential for advanced circular [...] Read more.

Bicycle tires and inner tubes constitute a growing waste stream mainly composed of natural rubber, butyl rubber, synthetic elastomers, carbon black, and reinforcing materials. Their multi-material structure and highly crosslinked networks make their recycling challenging, yet efficient recovery is essential for advanced circular economy practices. This review summarizes the current and emerging strategies for recycling bicycle tires and inner tubes. It first outlines the materials and additives present in tire casings and butyl inner tubes, which determine their recycling behavior. Mechanical pre-processing methods, including shredding, grinding, and fiber/steel separation, are presented as essential feedstock preparation steps. Thermochemical approaches, such as pyrolysis and thermolysis, are discussed with emphasis on producing value-added fractions, including pyrolysis oil, recovered carbon black, and fuels. Solvent-based feedstock recycling and chemical dissolution are highlighted as promising routes for selective recovery of rubber polymers and additives. Physical, chemical, and biological devulcanization methods are also reviewed for their potential to restore partial processability to reuse reclaimed rubber. Finally, current and prospective applications of recycled materials are discussed, and key challenges with future research needs are identified, including improving devulcanization efficiency, expanding collection systems, and increasing the value of recovered products. Full article

(This article belongs to the Special Issue Celebrating 10 Years of Recycling: Shaping the Future of Waste Management)

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18 pages, 2226 KB

Open AccessArticle

Valorizing the Organic Fraction of Municipal Solid Waste (OFMSW) as Composite Panels for Construction or Furniture

by Cecilia Solís, Armin Kriele, Borja Oliver-Tomas, Martin Hitzl, Juan Carlos Guerrero Ramos, José Luis Millá Tamarit, Alicia Marco Aleixandre, Rosa Maria Pérez Campos, Arturo Valero and Michael Renz

Recycling 2026, 11(2), 32; https://doi.org/10.3390/recycling11020032 - 2 Feb 2026

Abstract

Residual lignocellulosic biomass represents a major resource to be incorporated into the circular economy, with up to 1400 Mt/y in EU27. Due to its complex composition of three biopolymers (cellulose, hemicellulose and lignin) combined with its seasonal and regional variability and high water [...] Read more.

Residual lignocellulosic biomass represents a major resource to be incorporated into the circular economy, with up to 1400 Mt/y in EU27. Due to its complex composition of three biopolymers (cellulose, hemicellulose and lignin) combined with its seasonal and regional variability and high water content, its valorization involves manifold challenging aspects. Herein a three-step procedure is presented to transform this type of biomass into solid composite panels: hydrothermal carbonization (HTC), dry thermal treatment and curing a phenolic resin. HTC triggers chemical dehydration of the polysaccharide part of the lignocellulose and breaks up the cell structure of the plants. This facilitates the diffusion of the water and its separation by filtration, which is more energy efficient than evaporation. HTC and thermal treatment induce chemical changes that concentrate the carbon content and make the material suitable for crosslinking with a phenolic resin, achieving a 90% renewable content. The composite panels are competitive with products of the particle and fiberboard sector with respect to tensile strength and screw withdrawal resistance. Hence, the products can be employed for construction or in the furniture industry. Full article

(This article belongs to the Topic Circular Materials Engineering: Waste Valorization and Sustainable Applications)

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20 pages, 1824 KB

Open AccessArticle

Recycling of Plastic Waste: How the Conditions of Thermal Cracking and the Composition of Plastic Mixtures Affect Product Yield

by Ulyana A. Frolova, Khoshim Kh. Urazov, Nikita N. Sviridenko and Ekaterina N. Kolobova

Recycling 2026, 11(2), 31; https://doi.org/10.3390/recycling11020031 - 2 Feb 2026

Abstract

This study examines the effect of different heat treatment conditions on different mixtures of plastic waste to produce fuel fractions. The mixtures included polypropylene, polystyrene, polyethylene terephthalate, low-density polyethylene, and high-density polyethylene in various ratios. The experiments revealed optimal process parameters, including the [...] Read more.

This study examines the effect of different heat treatment conditions on different mixtures of plastic waste to produce fuel fractions. The mixtures included polypropylene, polystyrene, polyethylene terephthalate, low-density polyethylene, and high-density polyethylene in various ratios. The experiments revealed optimal process parameters, including the heating rate, process temperature, process duration, and environment, as well as the composition of the plastic waste mixture. This made it possible to extract more than 80% of the liquid, while gasoline and diesel fractions amounted to 35.7 and 30.5% wt., respectively. A detailed analysis of the gasoline fraction and diesel fuel obtained by cracking has demonstrated favorable properties confirming their potential as alternative sources of hydrocarbons or fuel components. A detailed study of the characteristics of the initial coke, as well as coke after alkaline treatment and calcination, revealed conditions conducive to the formation of porous carbon structures with a high specific surface area. The use of coke obtained from a mixture of plastic waste as a cracking additive slows down gas formation (by 1–5 ± 0.2% wt.) and increases the yield of low-boiling fractions (by 8.4 ± 0.4% wt.). Alkaline treatment of coke slows down its formation by increasing the specific area of micropores (from 154.8 to 219.1–286.5 m²/g) and decreasing the specific area of mesopores (from 311.2 to 76.4–187.3 m²/g), and also increases the yield of gasoline fractions. The results indicate effective ways to recycle plastic waste into valuable fuels and carbon materials, contributing to the development of technologies for sustainable waste management and resource recovery. Full article

(This article belongs to the Special Issue Celebrating 10 Years of Recycling: Shaping the Future of Waste Management)

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34 pages, 2273 KB

Open AccessReview

Mobile Pyrolysis Systems for Decentralized Biomass Valorization: Technologies, Products, and Applications

by Catarina Nobre, Santa Margarida Santos, José Copa Rey, Andrei Longo, Bruna Rijo, Roberta Panizio, Paulo Brito and Cecilia Mateos-Pedrero

Recycling 2026, 11(2), 30; https://doi.org/10.3390/recycling11020030 - 2 Feb 2026

Abstract

Mobile pyrolysis systems offer a practical pathway for the decentralized valorization of biomass waste, addressing the high logistical and economic burdens of transporting low-density, moisture-rich feedstocks to centralized facilities. By operating directly at the source, these systems convert diverse agricultural and forestry residues [...] Read more.

Mobile pyrolysis systems offer a practical pathway for the decentralized valorization of biomass waste, addressing the high logistical and economic burdens of transporting low-density, moisture-rich feedstocks to centralized facilities. By operating directly at the source, these systems convert diverse agricultural and forestry residues into biochar, bio-oil, pyrogas, and wood vinegar, while reducing transport volumes and associated emissions. Reported mobile reactors process between 4 kg per batch and 10 t/day, achieving biochar yields of 33–44 wt.% at 400 °C and bio-oil yields of 55–68 wt.% in fast pyrolysis at 500–550 °C, demonstrating performance comparable to stationary installations. This review synthesizes current mobile pyrolysis technologies, including reactor configurations, feedstock suitability, operational constraints, and recent advances in automation, real-time monitoring, and machine learning-based optimization. The agricultural and industrial applications of pyrolysis products are examined, with emphasis on soil health enhancement, biopesticide activity, renewable gas generation, and carbon sequestration. Emerging international projects and commercial efforts are highlighted, illustrating growing interest in flexible, low-carbon pyrolysis solutions for rural waste management and distributed bioresource utilization, while outlining the technological gaps that remain to be addressed. Full article

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16 pages, 667 KB

Open AccessArticle

Operational Flexibility Through Hydraulic Retention Time and Its Influence on Mesophilic AD of Fattening/Finishing Phase

by Inês Silva, Nuno Lapa, Henrique Ribeiro and Elizabeth Duarte

Recycling 2026, 11(2), 29; https://doi.org/10.3390/recycling11020029 - 2 Feb 2026

Abstract

Anaerobic digestion (AD) is a proven and promising technology for recovering energy from biowastes, such as pig slurry (PS) from the fattening/finishing phase. The mechanisms of AD are widely studied, and nowadays, it is of the utmost importance to investigate strategies that give [...] Read more.

Anaerobic digestion (AD) is a proven and promising technology for recovering energy from biowastes, such as pig slurry (PS) from the fattening/finishing phase. The mechanisms of AD are widely studied, and nowadays, it is of the utmost importance to investigate strategies that give end-users the confidence to choose this technology and to adapt it to their reality, promoting the energy transition and circular economy. This study investigated how collection and storage period affect PS samples, and how hydraulic retention time (HRT) (15 versus 20 days) influences AD performance and stability. Seasonality was the primary factor influencing feedstock characteristics. Samples presented no significant differences during the storage period. A 20-day HRT led to higher digestate pH, total ammonia nitrogen (TAN), and free ammonia nitrogen (FAN) concentrations, which can cause process instability and methanogenesis inhibition. However, 20-day HRT led to a specific methane production that was 7% higher and to a methane quality (expressed in % v/v CH₄) that was 6% higher than 15-day HRT. Overall, methane quality, digestate pH, TAN, and FAN values may be considered key points that need to be monitored to prevent the AD system from being compromised. Nevertheless, these results provide the operational freedom to choose either HRT, allowing reduced reactor volume and investment. Full article

(This article belongs to the Special Issue Biomass Revival: Rethinking Waste Recycling for a Greener Future)

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28 pages, 4871 KB

Open AccessArticle

Ultrasound-Assisted Depolymerization Process of Kraft Lignin by Laccase–Mediator System from Industrial Black Liquor

by Florian Teuffo, Xavier Trivelli, Stéphane Menuel, Loubna Firdaous, Muriel Bigan and Rénato Froidevaux

Recycling 2026, 11(2), 28; https://doi.org/10.3390/recycling11020028 - 2 Feb 2026

Abstract

The recycling of industrial biomass waste, such as black liquor rich in lignin from the pulp and paper industry, represents a sustainable strategy to reduce environmental impact and promote resource valorization. Enzymatic depolymerization of lignin is considered a promising approach due to the [...] Read more.

The recycling of industrial biomass waste, such as black liquor rich in lignin from the pulp and paper industry, represents a sustainable strategy to reduce environmental impact and promote resource valorization. Enzymatic depolymerization of lignin is considered a promising approach due to the high specificity of lignin-degrading enzymes. However, lignin’s poor solubility in aqueous and acidic conditions, combined with its structural complexity and recalcitrance, limits its enzymatic reactivity. In this study, Trametes versicolor laccase was used to depolymerize lignin following a sonication pretreatment designed to improve its solubility and reactivity. Response surface methodology (RSM) identified lignin concentration and sonication time as the most influential parameters for optimizing pretreatment efficiency. The enzymatic depolymerization process revealed a competition between condensation and depolymerization reactions. Characterization of the reaction products using GPC, FTIR, and NMR confirmed the formation of lignin-derived aromatic compounds. These findings highlight the effectiveness of sonication as a pretreatment method to enhance enzymatic lignin degradation. Future research will focus on integrating depolymerization and product separation processes to limit lignin repolymerization and increase the yield of depolymerized aromatic products. Full article

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35 pages, 1099 KB

Open AccessReview

Review of Reagent-Free Electronic Waste Recycling: Technology, Energy, Materials and Spatial Effects

by Natalya Kulenova, Marzhan Sadenova and Stanislav Boldyryev

Recycling 2026, 11(2), 27; https://doi.org/10.3390/recycling11020027 - 1 Feb 2026

Abstract

The rapid increase in e-waste has become a significant global concern, influenced by swift technological advancements, shorter product lifecycles, and rising consumer demand. This situation leads to considerable environmental and health hazards, primarily due to the presence of toxic materials, energy demands, and [...] Read more.

The rapid increase in e-waste has become a significant global concern, influenced by swift technological advancements, shorter product lifecycles, and rising consumer demand. This situation leads to considerable environmental and health hazards, primarily due to the presence of toxic materials, energy demands, and the inadvertent loss of valuable resources when waste is not adequately managed. This review synthesises contemporary theories related to sustainable e-waste management, featuring concepts such as principles of the circular economy, energy efficiency and innovative recycling technologies. The review explores a range of actions, including regulatory strategies, mechanical pre-treatment methods, focusing on reagent-free recovery techniques, and the utilisation of digital solutions to enhance traceability and operational efficiency. The findings indicate substantial improvements in formal e-waste collection rates in areas with strong legislative frameworks, enhanced metal recovery efficiencies through refined hydrometallurgical and pyrometallurgical techniques and minimised environmental footprints through reagent-free and energy-conserving practices. The review emphasises the importance of viewing e-waste recycling not just as a waste management issue but as a fundamental element of resource security and sustainable industrial practices. By assessing recent developments, this work advocates for closed-loop recycling as an essential driver in the global shift towards a resilient, low-carbon, energy-efficient and circular economy. Full article

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18 pages, 5981 KB

Open AccessArticle

Material Performance and Processing Behavior of Polyolefin Waste in Mechanical Recycling

by Yamila V. Vazquez, Cristina Pavon, Juan Vicente Miguel Guillem, Juan López-Martínez and María Dolores Samper

Recycling 2026, 11(2), 26; https://doi.org/10.3390/recycling11020026 - 1 Feb 2026

Abstract

This study investigates the processability and performance limits of high-density polyethylene (HDPE) recovered from mixed polyolefin waste under realistic mechanical recycling conditions. The waste stream was processed by extrusion and injection molding, with parameters actively adapted. ATR-FTIR and DSC analysis confirmed HDPE as [...] Read more.

This study investigates the processability and performance limits of high-density polyethylene (HDPE) recovered from mixed polyolefin waste under realistic mechanical recycling conditions. The waste stream was processed by extrusion and injection molding, with parameters actively adapted. ATR-FTIR and DSC analysis confirmed HDPE as the matrix, contaminated with minor fractions of polypropylene (PP), PET, and polyurethane (PU). The reprocessed material exhibited a single melting peak at 132 °C and a melt flow rate (MFR) of 9.9 ± 0.6 g 10 min⁻¹, indicative of moderate degradation. Mechanical testing revealed reduced tensile strength and elongation at break compared to virgin HDPE, indicating compositional heterogeneity and poor interfacial adhesion. Field emission scanning electron microscopy (FESEM) revealed dispersed inclusions and microvoids acting as stress concentrators, consistent with reduced ductility. Crucially, progressive reduction of back pressure during processing optimization was essential for stabilizing melt flow and minimizing shear-induced degradation. This adjustment enabled consistent mold filling despite the material’s variability. The results demonstrate that mixed HDPE waste can be successfully valorized for non-structural applications such as plastic lumber or pallets, providing a sustainable pathway for recycling heterogeneous streams without costly pre-treatment or compatibilization. Full article

(This article belongs to the Topic Advances and Innovations in Waste Management)

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28 pages, 2189 KB

Open AccessArticle

A Comparative Evaluation of Three Valorisation Pathways for Waste Electric Arc Furnace Slag to Improve Its Use as an Eco-Logical Binder

by Bruno Machini, Diogo Simões, Pedro Humbert, Julieta António and João Almeida

Recycling 2026, 11(2), 25; https://doi.org/10.3390/recycling11020025 - 1 Feb 2026

Abstract

The urgent need to reduce greenhouse gas emissions and enhance resource circularity is driving the cement and construction industry to explore alternatives to clinker-based binders. Electric arc furnace slag (EAFS), a major steelmaking by-product, is currently underutilised as a binder due to its [...] Read more.

The urgent need to reduce greenhouse gas emissions and enhance resource circularity is driving the cement and construction industry to explore alternatives to clinker-based binders. Electric arc furnace slag (EAFS), a major steelmaking by-product, is currently underutilised as a binder due to its low intrinsic reactivity. This study provides a comparative evaluation of three distinct valorisation pathways for the same EAFS—use as a supplementary cementitious material (SCM), as a precursor for alkali-activated binders, and as a component in accelerated carbonation systems—thereby highlighting its multifunctional and more ecological binding potential. A comprehensive physicochemical characterisation was conducted, followed by mechanical performance assessment under different curing regimes. When used as an SCM, partial cement replacement resulted in no loss of mechanical performance and a compressive strength increase of up to 8.9% at 10% replacement, demonstrating its suitability for structural applications. Under accelerated carbonation, specimens with 50% replacement of cement and sand achieved compressive strengths of 46.7 MPa, comparable to the non-carbonated reference (47 MPa), indicating full strength recovery despite high substitution levels. Full replacement systems based on alkali activation or carbonation of EAFS achieved moderate compressive strengths (~10 MPa), suitable for non-structural applications, with clear potential for improvement through optimisation of activation and curing conditions. Overall, this work demonstrates that EAFS can be effectively valorised through multiple reaction routes, supporting its role as a versatile and low-carbon resource for sustainable cementitious materials. Full article

(This article belongs to the Special Issue Celebrating 10 Years of Recycling: Shaping the Future of Waste Management)

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16 pages, 3259 KB

Open AccessArticle

Demulsification of Oily Sludge Using Ozone Micro–Nanobubbles in Aqueous Media

by Lingli Wang, Xiaoqi Hu, Tianzhi Wang, Fawei Lin, Yuehua Li, Xiangqi Meng and Manuel Fiallos

Recycling 2026, 11(2), 24; https://doi.org/10.3390/recycling11020024 - 1 Feb 2026

Abstract

Oily sludge is a complex emulsified waste consisting of water, oil, and solid particles. Conventional treatments are often inefficient, energy-intensive, and prone to causing secondary pollution. This study proposes a green demulsification technology based on ozone micro–nanobubbles (O₃MNBs) by constructing an [...] Read more.

Oily sludge is a complex emulsified waste consisting of water, oil, and solid particles. Conventional treatments are often inefficient, energy-intensive, and prone to causing secondary pollution. This study proposes a green demulsification technology based on ozone micro–nanobubbles (O₃MNBs) by constructing an experimental system to analyze its effects and mechanisms of action on oily sludge treatment. The O₃MNBs exhibited a mean particle size of 831 nm and generated a substantial amount of hydroxyl radicals (·OH, 250.4 μmol·L⁻¹) in situ. Compared with conventional aeration, the dissolved ozone concentration and residence time in water of O₃MNBs increased by 192% and 213%, respectively. During bubble collapse, intense pressure waves and high-speed microjets were generated to disrupt sludge aggregates, promoting the dispersion of sludge particles while simultaneously stripping oil films. Thus, the oil removal rate reached 41.5%, demonstrating the high demulsification efficiency of O₃MNBs. Furthermore, ozone and ·OH attacked alkane C-H bonds in the oil phase, oxidizing hydrophobic films into hydrophilic products and decomposing surfactants that stabilize emulsions. This process promoted oil droplet coalescence and degradation into small organic molecules. After O₃MNB treatment, the absorption peak of alkane C-H bonds gradually reduced, while a new C=O absorption peak appeared. This study provides a theoretical foundation and technical support for environmentally sustainable treatment of oily sludge by O₃MNB application, offering an effective alternative to chemical demulsification without secondary pollution. Full article

(This article belongs to the Special Issue Advanced Wastewater Treatment and Resource Recovery: Pathways to Circular Valorization)

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23 pages, 2207 KB

Open AccessArticle

Integrated Optimization Framework for a RF-ICP Plasma-Based System for Solid Waste Treatment

by Roman Stetsiuk, Mustafa A. Aldeeb and Hossam A. Gabbar

Recycling 2026, 11(2), 23; https://doi.org/10.3390/recycling11020023 - 28 Jan 2026

Abstract

Waste management remains a major challenge worldwide, as rapidly expanding urban populations put greater pressure on traditional disposal methods such as landfilling and incineration. Plasma-based waste treatment offers an innovative, sustainable waste-to-energy solution capable of converting a wide range of waste types. Although [...] Read more.

Waste management remains a major challenge worldwide, as rapidly expanding urban populations put greater pressure on traditional disposal methods such as landfilling and incineration. Plasma-based waste treatment offers an innovative, sustainable waste-to-energy solution capable of converting a wide range of waste types. Although plasma technologies provide significant environmental benefits, such as greatly reducing waste volume and emissions compared to conventional approaches, their widespread adoption faces notable economic hurdles. Primary among these is high operational cost due to system inefficiencies. These costs mainly arise from energy losses within the plasma torch, energy consumed during plasma torch tuning with the plasma reactor, and power inefficiencies when processing unsuitable waste loads. These issues not only increase costs but also impact process stability, which can influence stakeholder support and the technology’s commercial potential. Optimizing the process through simulation presents an effective approach to overcoming this inefficiency. However, relying solely on these advanced tools can be time-consuming and requires substantial domain expertise, creating a bottleneck in design and optimization. This paper introduces a new integrated platform combining COMSOL Multiphysics v6.2, Ansys Fluent 2024 R1, and Aspen Plus v12.1 to address these challenges. Using a genetic algorithm, the platform automates the complex task of designing an optimal plasma torch, optimizes it for peak performance, and dynamically adjusts plasma conditions. This intelligent optimization system aims to maximize energy output and process efficiency, directly tackling key cost-related issues. Full article

(This article belongs to the Special Issue Celebrating 10 Years of Recycling: Shaping the Future of Waste Management)

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26 pages, 3890 KB

Open AccessArticle

An Integrated Leach–Extract–Strip Process for Yttrium Recovery from Spent Fluorescent Lamps: Kinetic Assessment and Solid–Liquid Extraction with D2EHPA-Impregnated XAD-7

by Pedro Adrián Martínez-Montoya, Mónica Corea-Téllez, Ricardo Gerardo Sánchez-Alvarado, Teresita del Refugio Jiménez-Romero, Jorge Luis Gutiérrez-Estrada, Margarita García-Hernández and Angel de Jesús Morales-Ramírez

Recycling 2026, 11(1), 22; https://doi.org/10.3390/recycling11010022 - 19 Jan 2026

Abstract

Growing demand for rare earth elements (REEs) necessitates the development of efficient recycling strategies from secondary sources. This work presents a complete hydrometallurgical process for recovering yttrium (Y) from spent fluorescent lamps, emphasizing the efficient coupling of a conventional acid leaching with a [...] Read more.

Growing demand for rare earth elements (REEs) necessitates the development of efficient recycling strategies from secondary sources. This work presents a complete hydrometallurgical process for recovering yttrium (Y) from spent fluorescent lamps, emphasizing the efficient coupling of a conventional acid leaching with a solid–liquid extraction system. Multi-stage sulfuric acid leaching (2 M, 65 °C, an S/L ratio of 0.25 g/L) achieved a cumulative yttrium dissolution of 71.11% over four stages, with individual stage recoveries (based on initial yttrium content) of 44.2%, 21.56%, 7.19%, and 0.68%. Kinetic and spectroscopic analyses (FTIR, SEM-EDS) revealed that the leaching rate is controlled by diffusion through an in situ formed sulfate-rich layer (CaSO₄, Na₂SO₄), as described by the Z-L-T (Zhuravlev–Leshokin–Templeman) model (Ea = 35.5 kJ mol⁻¹). The resulting leachate was subjected to solid–liquid extraction using Amberlite XAD-7 resin impregnated with D₂EHPA. Under optimal conditions, the extraction process was highly efficient, yielding over 99% yttrium recovery at an optimal pH of 0.75 with a low resin dosage of 0.1 g/L. Furthermore, the solvent-impregnated resins exhibited excellent reusability over five consecutive extraction–stripping cycles, maintaining a single-cycle stripping efficiency above 70% and a cumulative recovery exceeding 97%. This study validates the technical feasibility of an integrated leach–extract–strip process based on impregnated resins as an alternative approach for yttrium recycling from electronic waste, potentially supporting the development of a circular economy. Full article

(This article belongs to the Topic Converting and Recycling of Waste Materials)

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18 pages, 9896 KB

Open AccessArticle

Experimental Investigation of Temperature Distribution and Evolution in Hot Recycled Asphalt Mixtures with Different Reclaimed Asphalt Pavement Contents

by Quan Liu, Huanting Lei, Jiangyu Liu, Yuting Han and Jiantao Wu

Recycling 2026, 11(1), 21; https://doi.org/10.3390/recycling11010021 - 19 Jan 2026

Abstract

Temperature homogeneity assumes a crucial role in the manufacture of asphalt mixtures due to its impact on mechanical formation and mixing homogeneity. The existence of reclaimed asphalt pavement (RAP) exacerbates its impact on temperature inhomogeneity. To address this, the RAP contents of 20%, [...] Read more.

Temperature homogeneity assumes a crucial role in the manufacture of asphalt mixtures due to its impact on mechanical formation and mixing homogeneity. The existence of reclaimed asphalt pavement (RAP) exacerbates its impact on temperature inhomogeneity. To address this, the RAP contents of 20%, 40%, and 60%, combined with RAP preheated temperatures of 353 K, 373 K, and 393 K, were taken into consideration to examine the thermal transition and evolution of temperature for the recycled asphalt mixtures in the mixing. Thermal images captured within the range of 30 s to 120 s were used to monitor the temperature evolution of the recycled asphalt mixtures during the mixing. To quantitatively assess the level of thermal non-uniformity, a Relative Thermal Equilibrium Temperature Index (RETI) was introduced. This index reflects the degree of deviation from ideal thermal equilibrium within the recycled mixtures. Based on the RETI calculation, complete temperature homogeneity cannot be attained until the end of the mixing of hot recycled asphalt mixtures. However, a prolongation of the mixing time or an elevation in the RAP preheated temperature can expedite the thermal equilibrium process of recycled asphalt mixtures. Additionally, the RAP contents also exerted a crucial influence on the thermal equilibrium process of the recycled asphalt mixtures. Full article

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

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17 pages, 4305 KB

Open AccessArticle

Performance and Leaching Behavior of Hybrid Geopolymer–Cement Mortars Incorporating Copper Mine Tailings and Silt

by Dionella Jitka B. Quinagoran, James Albert Narvaez, Joy Marisol Maniaul, John Kenneth A. Cruz, Djoan Kate T. Tungpalan, Eduardo R. Magdaluyo, Jr. and Karlo Leandro D. Baladad

Recycling 2026, 11(1), 20; https://doi.org/10.3390/recycling11010020 - 16 Jan 2026

Abstract

Mine waste remains a persistent challenge for the minerals industry, posing significant environmental concerns if not properly managed. The 1996 Marcopper Mining Disaster in Marinduque, Philippines, left a legacy of mine tailings that continue to threaten local ecosystems and communities. This study investigates [...] Read more.

Mine waste remains a persistent challenge for the minerals industry, posing significant environmental concerns if not properly managed. The 1996 Marcopper Mining Disaster in Marinduque, Philippines, left a legacy of mine tailings that continue to threaten local ecosystems and communities. This study investigates the valorization and stabilization of Marcopper river sediments laden with mine tailings using a combined geopolymerization and cement hydration approach. Hybrid mortar samples were prepared with 7.5%, 15%, 22.5%, and 30% mine tailings by weight, utilizing potassium hydroxide (KOH) as an alkaline activator at concentrations of 1 M and 3 M, combined with Ordinary Portland Cement (OPC). The mechanical properties of the hybrid geopolymer cement mortars were assessed via unconfined compression tests, and their crystalline structure, phase composition, surface morphology, and chemical bonding were also analyzed. Static leaching tests were performed to evaluate heavy metal mobility in the geopolymer matrix. The compression tests yielded strength values ranging from 24.22 MPa to 53.99 MPa, meeting ASTM C150 strength requirements. In addition, leaching tests confirmed the effective encapsulation and immobilization of heavy metals, demonstrating the potential of this method for mitigating the environmental risks associated with mine tailings. Full article

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