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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Green Materials".

Deadline for manuscript submissions: 25 April 2026 | Viewed by 4413

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Prof. Dr. Natalia Howaniec

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Department of Energy Saving and Air Protection, Central Mining Institute–National Research Institute, Pl. Gwarkow 1, 40-166 Katowice, Poland
Interests: environmental engineering; waste valorization; hydrogen economy; sustainable energy systems; renewable energy; carbon materials; thermochemical conversion of solid materials; gasification; adsorption
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Special Issue Information

Dear Colleagues,

The sustainable management of natural resources remains one of the principal economic and environmental challenges. Efforts to address this complex issue range from the development and implementation of cost-effective and more resource- and energy-efficient production technologies to the recovery and reuse of waste materials. Considerable progress has been made so far with the adaptation of circular economy principles, but further advancements and the creation of a more interdisciplinary approach are still needed in this field.

This Special Issue aims to provide a platform for researchers and practitioners from various scientific disciplines, involved in common efforts to reduce natural resource demand and waste volume while reusing and recycling solid, liquid, and gaseous waste materials of industrial, municipal, and agricultural origins, to present recent advances in this field.

Authors are invited to contribute full research and review papers, as well as communications, to this Special Issue.

Prof. Dr. Natalia Howaniec
Guest Editor

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Keywords

waste
valorization
utilization
reuse
recycling
circular economy

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Published Papers (6 papers)

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Research

20 pages, 4502 KB

Open AccessArticle

Transforming Waste into Value: The Role of Recovered Carbon Fibre and Oil Shale Ash in Enhancing Cement-Based Structural Composites

by Regina Kalpokaitė-Dičkuvienė, Inga Stasiulaitiene, Arūnas Baltušnikas and Samy Yousef

Materials 2025, 18(24), 5636; https://doi.org/10.3390/ma18245636 - 15 Dec 2025

Viewed by 181

Abstract

Economic and technological factors necessitate the use of alternative fuels during oil shale combustion, a process that generates substantial amounts of solid waste with varying ash compositions. This study evaluates the potential of two such waste materials: (i) fly ash derived from the combustion of oil shale (a fine particulate residue from burning crushed shale rock, sometimes combined with biomass), and (ii) short carbon fibres recovered from the pyrolysis (a process of decomposing materials at high temperatures in the absence of oxygen) of waste wind turbine blades. Oil shale ash from two different sources was investigated as a partial cement replacement, while recycled short carbon fibres (rCFs) were incorporated to enhance the functional properties of mortar composites. Results showed that carbonate-rich ash promoted the formation of higher amounts of monocarboaluminate (a crystalline hydration product in cement chemistry), leading to a refined pore structure and increased volumes of reaction products—primarily calcium silicate hydrates (C–S–H, critical compounds for cement strength). The findings indicate that the mineralogical composition of the modified binder (the mixture that holds solid particles together in mortar), rather than the fibre content, is the dominant factor in achieving a dense microstructure. This, in turn, enhances resistance to water ingress and improves mechanical performance under long-term hydration and freeze–thaw exposure. Life cycle assessment (LCA, a method to evaluate environmental impacts across a product’s lifespan) further demonstrated that combining complex binders with rCFs can significantly reduce the environmental impacts of cement production, particularly in terms of global warming potential (−4225 kg CO₂ eq), terrestrial ecotoxicity (−1651 kg 1,4-DCB), human non-carcinogenic toxicity (−2280 kg 1,4-DCB), and fossil resource scarcity (−422 kg oil eq). Overall, the integrative use of OSA and rCF presents a sustainable alternative to conventional cement, aligning with principles of waste recovery and reuse, while providing a foundation for the development of next-generation binder systems. Full article

(This article belongs to the Special Issue Advances in Waste Materials’ Valorization)

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23 pages, 8791 KB

Open AccessArticle

Preliminary Assessment of Commercial Antibacterial Finishes on Knitted Fabrics from Recycled Cotton and Polyester

by Muhammad Sajid Faheem, Hafsa Jamshaid, Rajesh Kumar Mishra, Adeel Abbas, Miroslav Muller, Jiri Urban and Michal Penc

Materials 2025, 18(23), 5319; https://doi.org/10.3390/ma18235319 - 25 Nov 2025

Cited by 2 | Viewed by 311

Abstract

Recycled materials are employed in several areas to reduce the environmental burden. Therefore, recycling textiles is a vast domain being investigated by several researchers. Functionalization of textiles using active nanomaterials is a growing area of interest nowadays. However, functionalized textiles with antibacterial properties still do not employ the incorporation of recycled materials. The huge consumer need for different types of functional textiles necessitates a focus on recycled textiles in this area. Hence, this research focuses on the development of metal oxide nanoparticle-functionalized antibacterial textiles using recycled cotton and polyester yarns. Two different finishes have been used with a 50:50 ratio. Using a two-fold approach, antibacterial finishes were applied during both the yarn and fabric stages to analyze the differences in performance. Agar plate qualitative antibacterial analysis revealed efficient antibacterial function both before and after commercial laundering. However, thermo-physiological comfort properties were found to be variable for recycled yarn types and finishing stages. The air permeability of fabric-finished specimens was found to be about 47% lower than yarn-finished specimens owing to reduced porosities. However, the overall moisture management capability (OMMC) index was found to be 21% higher than that of yarn-finished specimens. Among serviceability parameters, bursting strength was found to decrease with increasing concentration, as the finishing treatments made the yarns crispier which eventually compromised yarn strength. Full article

(This article belongs to the Special Issue Advances in Waste Materials’ Valorization)

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26 pages, 8765 KB

Open AccessArticle

Assessment of the Potential for Producing Geopolymer-Based Granulates as a Substitute for Natural Aggregates

by Magdalena Cempa, Jerzy Korol and Agnieszka Klupa

Materials 2025, 18(23), 5275; https://doi.org/10.3390/ma18235275 - 21 Nov 2025

Viewed by 462

Abstract

This study presents the development and evaluation of a technology for producing geopolymer-based granulates, which act as sustainable substitutes for natural aggregates by utilizing waste materials. The technology is demonstrated to be energy-efficient compared to other manufactured aggregate processes (such as sintering), as it relies on a cold-bonding process and achieves self-hardening at room temperature. The granulation of geopolymer materials using an intensive counter-current mixer represents an innovative solution in the field of producing substitutes for natural aggregates. Coal fly ash (CFA) was used as the primary aluminosilicate precursor, with composite regrind from decommissioned wind turbine blades (CR) and steelmaking dust (SD) tested as additives. Reactive solids and alkaline activator liquids were mixed and granulated in a single operation using an intensive counter-current mixer; moistening and surface powdering were applied to improve granule sphericity. The granules were cold-cured at room temperature and characterized after 28 days by grain size distribution, crushing resistance, water absorption, abrasion (micro-Deval), SEM/EDS and leaching tests. The results indicate that the additives significantly improved the mechanical performance: PM + PK granules reached crushing strengths > 6 MPa, while CFA + SD granules reached > 11 MPa, exceeding many commercial lightweight aggregates (such as LECA or Lytag), as detailed in the paper. The CFA + CR granulates exhibited a compact microstructure and the effective immobilization of several heavy metals, whereas the CFA + DS samples demonstrated the excessive leaching of Cr, Pb and Mo. The process achieved a high solid-to-liquid ratio (>2.0), reducing activator consumption. Composite regrind is recommended as a promising additive. Full article

(This article belongs to the Special Issue Advances in Waste Materials’ Valorization)

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23 pages, 9151 KB

Open AccessArticle

Durability Considerations in Replacing Blast Furnace Slag with Low-Grade Calcined Clay and Natural Pozzolan in Quaternary Cements

by Juan Manuel Etcheverry, Laurent Detemmerman, Krist Degezelle, Vadim Grigorjev, Laurena De Brabandere and Nele De Belie

Materials 2025, 18(21), 5048; https://doi.org/10.3390/ma18215048 - 5 Nov 2025

Viewed by 573

Abstract

Belgium and the EU-27 face a shortage of suitable supplementary cementitious materials (SCMs) capable of supporting high levels of Portland cement substitution. To reduce CO₂ emissions from the cement industry, blended cements incorporating low-grade calcined clay, limestone, and lava (a natural pozzolan) are investigated. Calcined clay is combined with limestone to produce a limestone–calcined clay cement (LC3). The reactivity of these new blends is assessed using isothermal calorimetry and compared to a reference blend with ground-granulated blast-furnace slag (GGBFS). Results show that mixtures with calcined clay develop slightly lower 28-day strength than those with GGBFS, while blends with lava exhibit strength gains only at later ages due to delayed pozzolanic activity. Overall, concrete made with low-grade calcined clay and lava achieves comparable compressive strength to the reference (CEM III/A), but with higher capillary porosity, leading to increased water absorption, drying shrinkage, and reduced freeze–thaw resistance. Despite these durability limitations, the sustainability assessment reveals that the LC3 mix with low-grade clay and lava has a lower global warming potential per unit strength at 28 days than CEM III/A and is competitive with CEM III/B. Full article

(This article belongs to the Special Issue Advances in Waste Materials’ Valorization)

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20 pages, 3907 KB

Open AccessArticle

Valorizing Organic Waste: Selenium Sulfide Production Mediated by Sulfate-Reducing Bacteria

by Shahrzad Safinazlou, Ahmad Yaman Abdin, Eduard Tiganescu, Rainer Lilischkis, Karl-Herbert Schäfer, Claudia Fink-Straube, Muhammad Jawad Nasim and Claus Jacob

Materials 2025, 18(12), 2784; https://doi.org/10.3390/ma18122784 - 13 Jun 2025

Viewed by 931

Abstract

Selenium sulfide, the active ingredient of traditional antidandruff shampoos, is industrially produced from selenium dioxide (SeO₂) and hydrogen sulfide (H₂S) under acidic conditions. This reaction can also be carried out with natural H₂S and H₂S generated by sulfate-reducing bacteria (SRB). These bacteria are robust and, by relying on their conventional growth medium, also thrive in “waste” materials, such as a mixture of cabbage juice and compost on the one side, and a mixture of spoiled milk and mineral water on the other. In these mixtures, SRB are able to utilize the DL-lactate and sulfate (SO₄²⁻) present naturally and produce up to 4.1 mM concentrations of H₂S in the gas phase above a standard culture medium. This gas subsequently escapes the fermentation vessel and can be collected and reacted with SeO₂ in a separate compartment, where it yields, for instance, pure selenium sulfide, therefore avoiding the need for any cumbersome workup or purification procedures. Thus “harvesting” H₂S and similar (bio-)gases produced by the fermentation of organic waste materials by suitable microorganisms provides an elegant avenue to turn dirty waste into valuable clean chemical products of considerable industrial and pharmaceutical interest. Full article

(This article belongs to the Special Issue Advances in Waste Materials’ Valorization)

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20 pages, 2984 KB

Open AccessArticle

Comparative LCA Analysis of Selected Recycling Methods for Carbon Fibers and Socio-Economic Analysis

by Nikolina Poranek, Krzysztof Pikoń, Natalia Generowicz-Caba, Maciej Mańka, Joanna Kulczycka, Dimitrios Marinis, Ergina Farsari, Eleftherios Amanatides, Anna Lewandowska, Marcin Sajdak, Sebastian Werle and Szymon Sobek

Materials 2025, 18(11), 2660; https://doi.org/10.3390/ma18112660 - 5 Jun 2025

Cited by 5 | Viewed by 1266

Abstract

Carbon fiber is essential in many industries. Since primary production is highly energy-intensive, recycling technologies are being sought. A goal of the research was to develop at a laboratory scale a chemical recycling method aimed at recovering carbon fiber. Two variants of the method have been established and environmentally compared with a primary production version. Methods: The life cycle assessment methodology has been used to assess and quantify the environmental impacts. The cradle to gate analysis was performed with the functional unit defined as a production of 1 kg of carbon fiber. Results: The best environmental option turned out to be a developed chemical recycling technology named Scenario 1. It is a solvolysis performed using an ambient-pressure-operated batch reactor connected to a reflux condenser and an inert gas supply tank, using an ethylene glycol and potassium hydroxide solution. The worst case appeared to be the second variant of the chemical recycling, named Scenario 2 (plasma-enhanced nitric acid solvolysis). Conclusions: In Scenario 1, a production of the ethylene glycol was recognized as a key environmental driver, while in Scenarios 2 and 3 the energy-related impact was the most influential. Full article

(This article belongs to the Special Issue Advances in Waste Materials’ Valorization)

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