Recycling

In view of the increasing demand for secondary aluminum, which is intended to partially replace the very energy- and resource-intensive primary aluminum production, effective treatment methods can maintain the high quality level of light metal castings. The transition from a linear to a circular economy can result in an accumulation of oxides or carbides in aluminum. Therefore, melt purification is crucial, especially as foundries aim to increase the use of often dirty end-of-life scrap. Nonmetallic inclusions in the melt can impact its flowability and mechanical properties. As the purity of the melt increases, its flow length also tends to increase. Available assessment methods like reduced pressure test or K-mold are capable of ensuring high levels of purity. This study demonstrates the implication of inclusions originating from dirty scrap. An experimental test run deals with various scrap contents in an AlSi7Cu0.5Mg alloy and shows correlations between impurity and performance, expressed by flowability and mechanical properties. These performance indicators have been connected to inclusion and porosity rates. In conclusion, these findings emphasize the need for further extensive research on contaminants in the field of scrap melting and the development of methods for easy-to-handle assessment methods. Full article

The escalating use of plastic materials in agricultural practices has substantially increased the amount of plastic waste directed to landfills, leading to significant environmental and ecological challenges. Conventional disposal methods have been found to release hazardous pollutants, including microplastics and toxic chemicals, exacerbating these concerns. This study aims to address the environmental impact of agricultural plastic waste by exploring advanced reprocessing technologies and characterising the processed waste to assess its physical, mechanical, and thermal properties. Synthetic polymer-based bale twine (BT) waste, commonly used in livestock farming, was processed using an economically viable melting machine developed by Ritchie Technology. The BT and processed bale twine (PrBT) were analysed to understand their properties. Fourier transmission infrared spectroscopy revealed that the waste primarily consisted of polypropylene (PP). Thermal analysis indicated that the melting temperature of the PrBT was 162.49 °C, similar to virgin PP. Additionally, tensile testing revealed that the PrBT had an ultimate strength of 13.06 MPa and a Young’s modulus of 434.07 MPa. The PrBT was further transformed into a bench that can be applicable in outdoor applications. Furthermore, the PrBT was extruded into 3D printable filament. Therefore, it is evident that bale twine waste can be given a second life through an economically viable technology. Full article

The increasing global demand for raw materials underscores the importance of lightweight construction and sustainable material use, drawing attention to composite techniques like galvanic coating of plastics. To support recycling efforts, the development of efficient separation and material recovery processes is critical, particularly for end-of-life products containing metal-plated polymers. This study investigates the recyclability of metallized polymer foams and coated polymers through comminution, focusing on the potential for effective separation of metal and polymer components. Cu-ABS samples showed 27% of the products in the 8–10 mm fraction and 48% in the 10–16 mm fraction during primary comminution, while Cu-PUR achieved a more even distribution. Microscopic analyses revealed decoating rates of up to 95% for Cu-ABS compared to 19% for Cu-PUR. The comminution energy required for Cu-PUR was three times higher, with a fivefold lower decoating rate than solid materials. Particles larger than 200 µm exhibited interlocking, complicating the separation process. These findings highlight the need for optimized recycling processes to enable efficient raw material recovery and support a circular economy. Full article

A silver-rich lead alloy was obtained through the recycling of two metallurgical wastes: these are lead paste obtained from spent lead–acid batteries and a jarosite residue obtained from the hydrometallurgical production of zinc. Mixtures of both wastes were pyrometallurgically treated with sodium carbonate in a silicon carbide crucible at 1200 °C. The alloy and slag produced were analyzed by atomic absorption spectrometry, X-ray diffraction, and scanning electron microscopy with energy-dispersive spectra. High silver recovery was obtained in a Pb-Ag alloy for a mixture ratio of 30% Na₂CO₃–40% lead paste–30% jarosite, reaching a silver grade of 126 ppm. The slags produced for the highest jarosite content allow the compound formation of Na₂(SO₄) and Na₂Fe(SO₄)₂, which have high sulfur-fixing, avoiding SO₂ release and contributing to the minimization of atmospheric pollution. The novel pyrometallurgical route addresses not only the valorization of precious metals such as silver and lead but also the reduction in accumulated industrial waste. Full article

Developing an efficient recycling route for spent single-use medical devices is essential for recovering precious metals. The proposed complete hydrometallurgical route goes through the initial pyrolysis and acid digestion steps, expanding upon our previous relevant work in the field, followed by solvent extraction, stripping, and precipitation procedures. In this study, a complete hydrometallurgical process was developed for the recovery of gold, platinum, iridium, and tantalum, separating them from other metals, i.e., from iron, chromium, and nickel, also present in the examined medical devices, i.e., (i) diagnostic electrophysiology catheters, containing gold, (ii) diagnostic guide wires, containing platinum and iridium alloys, and (iii) self-expanding stents, containing tantalum. This study reports the experimental results of selecting an efficient extractant, stripping, and precipitation agent, along with the effects of key factors that influence each consecutive step of the process, i.e., agent concentration, aqueous to organic phase ratio, contact time, and pH, using simulated metal solutions and also applying the obtained optimal conditions to the treatment of real sample solutions. For the selective separation of gold, Aliquat 336 was used to extract it in the organic phase; it was then stripped using a thiourea solution and precipitated by utilizing an iron sulfate (II) solution and proper pH adjustment. The selective separation of platinum was achieved by using Aliquat 336 for the organic phase extraction and a perchlorate acid solution for stripping it back into the aqueous solution and adding a sodium bromate solution to precipitate it. Due to the similar chemical behavior, the selective recovery of iridium followed the same processes as that of platinum, and the separation between them was achieved through selective precipitation, as heating the solution and adjusting the pH value resulted in the selective precipitation of iridium. Lastly, the selective recovery of tantalum consists of extraction by using Alamine 336, then stripping it back to the aqueous phase by using sodium chloride, and precipitation by using potassium salt solution and proper pH adjustment. A total recovery of 88% for Au, 86% for Pt, 84% for Ir, and 80% for Ta was obtained, thus achieving a high uptake of precious metals from the examined real spent/waste samples. Full article

The increasing volume of municipal solid waste (MSW), including biodegradable plant residues such as pruning, leaf, and kitchen wastes, presents a substantial environmental challenge due to the limited availability of landfill space and the resulting environmental contamination. Sustainable waste management practices, encompassing recycling and waste-to-energy conversion through biological or thermochemical processes, are imperative. In the Municipality of Athens, Greece, significant quantities of green waste generated from public and private gardening activities provide a valuable opportunity for energy recovery and landfill waste reduction. In accordance with Directive 2008/98/EC, Athens emphasizes waste prevention, reuse, recycling, and recovery. This study examined alternative bio-waste and green waste management systems, using examples from Europe, focusing on the Athens Directorate of Urban Green Spaces and Urban Wildlife. This paper discusses methods for assessing the energy value of pruning residues, providing a definitive disposal framework. Additionally, it presents a technoeconomic study of one of the municipal swimming pools in the Municipality of Athens, investigating the production and distribution of thermal energy to meet the heating needs of the pool facilities. This research identified key constraints and their impact on decision-making, highlighting the potential for alternative green waste management strategies. It advocates modern recycling techniques in line with national and community legislation, which have significant environmental and economic benefits. Full article

This study employed dynamic material flow analysis (MFA) and mass balance principles to examine copper flows in Indonesia, Malaysia, the Philippines, Thailand, and Vietnam from 1960 to 2020, with projections extending to 2050 using five shared socioeconomic pathway (SSP) scenarios. We applied the secondary resources classification framework to assess secondary copper resources and their recoverability in these countries. The results indicated that total copper stocks across these countries would continue to rise, with Indonesia’s copper stock projected to reach around 5000–12,000 kt by 2050, the highest among the five nations. In 2022, Malaysia had the highest per capita copper stock at 100 kg/person, although all countries were expected to remain below the per capita stock levels seen in major copper-consuming developed countries by 2050. Copper demand was projected to increase by 118–238 kt annually from 2023 to 2050, leading to a significant rise in end-of-life copper scrap. By 2050, secondary copper reserves in Indonesia were estimated to reach 4096 kt, with similar growth trends observed in other countries (3898 kt in Thailand, 3290 kt in Vietnam, 3096 kt in Malaysia, and 2564 kt in the Philippines). This highlights both the potential for resource recovery and the need for improved waste management. If recycling rates increase to 80–90%, secondary reserves could meet up to 42–65% of the copper demand in 2050. However, current recycling rates remain well below this potential, underscoring the urgent need for better waste management systems. This study emphasizes the balance between economic development and resource sustainability, offering critical insights for policymakers to improve recycling efficiency and reduce reliance on primary copper sources. Full article

The use of pyrolyzed carbon fibers (pCFs) in the secondary raw material market is growing, but potential applications for pCFs are limited by their wool-like appearance. Common solutions are further processing into fiber mats or shredding and adding the fibers during compounding in twin-screw extruders (TSEs). In the latter process, the initial fiber length is usually reduced to less than 1 mm during compounding and further reduced during injection molding. Hence, this paper presents an alternative compounding approach by investigating if internal mixers (IMs) are suitable for retaining pCFs after compounding longer. First, the influence of the mixing sequence for adding pCFs to the mixing process of the resulting fiber length was investigated. Second, a design of experiments was carried out using a laboratory IM, considering the process parameters of rotational speed, mixing time, coupling agent content, initial fiber length, and chamber filling level. Third, the results obtained were scaled up and applied to a production-scale IM. Important findings are that the melting of the matrix polymer should occur before fibers are added. This results in fiber contents of 20 wt.%. To achieve higher fiber contents, small amounts of carbon fiber must be added during the melting process. The process parameters investigated had no significant influence on the resulting fiber length. Compounding with IM is suitable for an initial fiber length of up to 24 mm. A composite with carbon fibers from industrial offcuts (rCFs) prepared by TSE compounding was used to compare the mechanical properties of the injection-molded samples due to the non-availability of composites with pyrolyzed fibers. Compounding resulted in an improvement in the weight-average fiber length from 226 µm (TSE) to 540 µm (IM). However, this fiber length could not be preserved during injection molding, resulting in similar mechanical properties of both, the pCF composites prepared by an IM and the commercially available rCF composites. Full article

The construction, demolition, and renovation industries are among the largest contributors to global carbon emissions and waste. With decreased landfill capacities, increased waste diversion targets, resource shortages, and the recognition that material waste is critical to climate change, diverting demolition waste is now a significant priority in waste management. Deconstructing a structure and reusing its building components can significantly reduce the environmental burdens imposed. However, to optimize the reuse of building materials and components for their environmental, societal, and economical benefits, the reclamation procedure must be undertaken in a more rational and robust manner. There are currently gaps in frameworks and tools that involve the assessment of reusable building components in demolition projects. This paper develops a reclamation framework to assess the viability of recovering and reusing building components. The framework first describes a process for conducting a technical audit and uses an assessment tool to suggest a level of deconstruction based on the physical parameters of the building circumstances. The framework complements this initial outcome by then assessing additional comprehensive parameters, such as the cost, the heritage value, and the available timeframe to arrive at a suggested outcome of actions, which can range from complete demolition and basic material recovery to deliberately removing salvageable items. The framework is then applied to an older, detached office building as a conceptual case study for demonstration. The recommended level of deconstruction appears appropriate based on the visual assessment of the structure. The result of this paper promotes the circular economy and supports the United Nations Sustainable Development Goals (UN SDGs) by presenting a notably more insightful and guided approach to capturing deconstruction waste. Full article

Solid waste disposal methods within indigenous communities present unique challenges and opportunities for sustainable development. However, the current knowledge on solid waste management focuses on formal waste collection systems, neglecting the practices and sustainability aspects of solid waste management in indigenous communities. Thus, it becomes imperative to undertake research studies that evaluate the sustainability of these practices as they play a pivotal role in ensuring sustainable development. The current study systematically evaluates the views and judgments associated with the sustainability aspects of indigenous waste management practices in the rural communities of South Africa using the Analytic Hierarchy Process (AHP) model. The data analysis was carried out using the AHP model. The findings of this study showed that the rural communities of Bushbuckridge Local Municipality prioritize the sustainability of the environment (weight: 0.590) over the economic (weight: 0.240) and social sustainability (weight: 0.165) based on the AHP evaluative framework. The validity of the priorities was tested through the computed degree of consistency (<10%) and an eigenvalue of 5.107. Furthermore, according to the assessment in the current study, the AHP evaluative framework dominantly prioritizes the sub-criteria of environmental sustainability (composting) at a responding rate of over 70% almost across all indigenous communities except for Acornhoek (30%), Casteel (25%), and Mambumbu (24%). Likewise, the sub-criterion of social sustainability, which is associated with communal cleaning labor, was found to be of extreme importance (60%), outperforming taboos (10%) that are anchored in cultural and spiritual beliefs. With a response rate > 50%, waste trading proved to be of economic efficacy. Using the AHP model to evaluate the sustainability aspects associated with indigenous solid waste management practices addresses a substantial gap in the comprehension of the role of indigenous knowledge towards sustainability in the discipline of solid waste management. However, it also offers a valuable sustainability perception that is associated with indigenous waste disposal methods that local governments and policymakers should include for consideration in integrated waste management plans. This can lead to the development of waste disposal programs that are well-coordinated and in accordance with indigenous sustainable waste management practices that advance the circular economy and promote environmental protection. Full article

This study investigates the effects of aging and recycling on the optical properties of paperboard, which is key to advancing circular economy practices in packaging. Methods included deinking flotation of cardboard made from sea algae and eco-conventional cardboard of unexposed and exposed samples in a xenon test chamber. Optical measurements were performed on the obtained laboratory paper sheets. Measurements for the chromatic coefficients ΔL*, Δa* and Δb*, as well as the CIE whiteness from comparison of the fluorescent component in the cardboard, were carried out under two light sources, D65 and UV. Regression analysis was used to quantify the statistical significance of these changes over time, i.e., in the aging process. The results revealed significant effects of both aging and recycling on the chromatic coefficients, with ΔL* and Δa* decreasing, while Δb* initially increased before decreasing. The influence of the fluorescent component is reduced by recycling the samples. Opacity measurements showed an initial increase in values that decreased with the aging of the samples, which indicates structural changes in the material. This research contributes to the circular economy by providing insight into the durability and optical properties of recycled cardboard, helping to develop sustainable packaging solutions. Full article

As more countries emphasize the importance of the circular economy, recycling resources from waste has become increasingly crucial. This study proposes a novel separation process for SmCo magnets, which can separate and recover metals by precipitation, thus reducing the amount of solvent used. The precipitation process involved the use of Na₂SO₄, NH₄OH, and H₂C₂O₄ to separate Sm, Fe, Cu, and Co, resulting in high precipitation efficiencies of 96.11%, 99.97%, 93.81%, and 98.15%, respectively. Moreover, the recovered metals can be directly used to create magnets after calcination, making this process a step towards achieving a circular economy. Full article

Municipal solid waste (MSW) is a growing problem worldwide posing a variety of environmental and human health impacts. Despite recycling being one major strategy to alleviate MSW production, the effectiveness of recycling has been equivocally dependent on local policy implementation and citizen environmental behavior. To enhance recycling effectiveness in Hong Kong, the government has established Green@Community, a unified community-based network for recycling and public environmental education. Since its establishment, the number of visitors to and the amount of recyclable materials collected at the network increased steadily over time. Our study is the very first to investigate the effectiveness of this territory-wide recycling network. Through a questionnaire survey, we found that respondents’ recycling traits were stronger if they have accrued gift tokens through participating in recycling activities. Visiting a Green@Community facility could also enhance knowledge of the types of acceptable recyclables, and respondents who had visited a Green@Community facility agreed that education and publicity could increase the recycling rate in Hong Kong. These findings highlighted the effectiveness and uniqueness of this community-based recycling network, its role in raising recycling knowledge, and its implications for policymakers and urban planners of densely populated cities to leverage society’s recycling participation, but also called for more efforts on developing, promoting, and incentivizing the usage of such a network to further enhance recycling and alleviate MSW production in Hong Kong. Full article

The global tuna canning industry generates substantial volumes of by-products, comprising 50% to 70% of the total processed material. Traditionally, these by-products have been utilized in low-value products such as fish oils and fishmeal. However, there is significant potential to extract high-value compounds from these by-products, such as calcium phosphates (CaP), which can have pharmaceutical, agricultural and biotechnological applications. This work explores the potential of tuna canning by-products, particularly mineral-rich fractions (central skeleton, head and fish bones) as sources of calcium phosphates (CaP), offering a sustainable alternative to conventional synthetic derivatives within a circular bioeconomy framework. By-products from two of the most exploited species (yellowfin and skipjack) were subjected to enzymatic hydrolysis and chemical extraction, followed by controlled calcination to obtain CaP. The content of organic matter, nitrogen, total proteins, lipids and amino acids in the cleaned bones, as well as the main chemical bonds, structure and elemental composition (FT-Raman, XRD, XRF) were evaluated. Results indicated that the highest recovery yield of wet bones was achieved using the chemical method, particularly from the dorsal and caudal fins of yellowfin tuna. The proximal composition, with ash content ranging from 52% to 66% and protein content varying between 30% and 53%, highlights the potential of tuna skeleton substrates for plant growth formulations. Furthermore, variations in crystalline structures of the substrates revealed significant differences depending on the by-product source and species. XRD and Raman results confirmed a monophase calcium phosphate composition in most samples from both species, primarily based on hydroxyapatite (central skeleton, caudal and dorsal fin) or whitlockite/β-tricalcium phosphate (viscera), whereas the heads exhibited a biphasic composition. Comparing the species, yellowfin tuna (YF) exhibited a hydroxyapatite structure in the branchial arch and scales, while skipjack (SKJ) had a biphasic composition in these same regions. Full article

Over the last two decades, the use of bioreactors filled with aged refuse extracted from closed areas of landfills has proven to be a viable alternative for the treatment of different types of wastewater. This study presents the results obtained during the evaluation of aged refuse used as filling material for a downflow bioreactor during the removal of the organic load present in wastewater generated in the wet processing of coffee. The tests were carried out over a period of 120 days, with 15 days to start up and stabilize the bioreactor and 105 days to perform treatability tests. The aged refuse, once extracted, was dried and sifted to a particle size of less than 50 mm. The bioreactor used had a cylindrical geometry (Ø = 0.20 m, and h = 3.40 m), and it was fed with hydraulic loads of 50, 100, and 150 L m⁻³ d⁻¹. The analysis of the data obtained shows that the system studied achieves the removal of 98.3% of the initial organic load when fed with 150 L m⁻³ d⁻¹. This showcases recycling aged refuse as a technically viable alternative to treat the wastewater generated during coffee processing. Also, the evaluated system has the advantage of needing a short period of time to achieve its stabilization, which turns out to be of great value, especially in its possible use in the treatment of residual water generated in the harvest of agricultural products where the period of harvest is very short. Full article

This study addresses the global issue of recycling used vehicle tires, typically burned out or trimmed to be reused in playground floors or road banks. In this study, we explore a novel environmentally responsive approach to decomposing and recovering the carbon black particles contained in tires (25–30 wt.%) by vacuum pyrolysis. Given that carbon black is well known for its UV protection in plastics, the objective of this research is to provide an ecological alternative to commercial carbon black of fossil origin by recycling the carbon black (rCB) from used tires. In our research, we create a composite material using rCB and high-density polyethylene (HDPE). In this article, we present the environmental aging studies carried out on this composite material. The topographic evolution of the samples with aging and the oxidation kinetics of the surface and through the thickness were studied. The Beer–Lambert law is used to relate the oxidative index to the characteristic depth of the samples. The UV photons are observed to penetrate up to 54% less with the addition of 6 wt.% of rCB compared to virgin HDPE. In this work, the addition of rCB as filler for HDPE used for outdoor applications has demonstrated to be an antioxidant for UV protection and a good substitute for commercial carbon black for industrial goods. Full article

In order to be able to recycle composite components made of polymer and metal, which are used in the automotive industry, the joints must be broken. The success of the separation is influenced by the stress and also by the joining mechanism between the polymer and the metal. Here, force-fit and form-fit connected components are produced and crushed in a rotor impact mill with two different rotors. The results show that the crushing results differ significantly for the different rotors and for the various joining processes. In short, the hammer-type rotor provides much finer and better-separated fragments and the force-fit joints enable a better separation of metal and polymers. The additional cooling of the samples also changes the result in a way, where deep cooling significantly improves the separation of the metal and the polymer. Different types of polymers also led to a different separation result with both rotors. Full article

The discharge of metal-loaded mining-influenced waters can significantly pollute downstream water bodies for many kilometers. Addressing this issue at the earliest discharge point is crucial to prevent further contamination of the natural environment. Additionally, recovering metals from these discharges and other sources of contamination can reduce the environmental impacts of mining and support the circular economy by providing secondary raw materials. This study focused on optimizing zinc recovery from mining-influenced water in the Freiberg mining region in Germany, where significant loads of zinc are released into the Elbe River. By employing pretreatment techniques, conducting 100 mL scale ion-exchange column experiments, and refining the regeneration process, we aimed to identify optimal conditions for efficient zinc removal and recovery. Initial tests showed that aminophosphonic functionalized TP 260 resin had a high affinity for aluminum, occupying 93% of the resin’s capacity, while zinc capacity was limited to 0.2 eq/L. To improve zinc recovery, selective precipitation of aluminum at pH 6.0 was introduced as a pretreatment step. This significantly increased the zinc loading capacity of the resin to 1 eq/L. Under optimal conditions, a concentrated zinc solution of 18.5 g/L was obtained with 100% recovery. Sulfuric acid proved more effective than hydrochloric acid in eluting zinc from the resin. Further analysis using SEM-EDX revealed residual acid on the resin, indicating a need for additional study on long-term resin performance and capacity variation. The research also highlighted the environmental impact of the Freiberg mining area, where three drainage galleries currently contribute nearly 85 tons of zinc annually to the Elbe River. This study underscores the feasibility of efficient zinc recovery from these point sources of pollution using advanced ion-exchange processes, contributing to circular economy efforts and environmental conservation. Full article

Pressmud, a by-product of sugarcane processing, is typically disposed of through incineration or landfilling, though it has considerable potential in organic agriculture. This study explored the composting of pressmud through bioaugmentation using specific bacterial strains. Two experimental setups were created: E2 with a cellulolytic and phosphorus-solubilizing strain, Bacillus amyloliquefaciens-ASK11, and E3 with a nitrogen-fixing strain, Bacillus megaterium-ASNF3. A control setup (E1) was also maintained without bacterial augmentation. Results indicated that the Bacillus-enhanced composts in E2 and E3 showed significant increases of 129% and 83% in nitrogen and of 49% and 91% in phosphorus contents, respectively, after 60 days. Additionally, organic matter decomposition improved by 49–50% in the bioaugmented setups after 60 days. FTIR analysis revealed organic phosphate peaks and P-O-C stretching bands at 1025 cm⁻¹ in the E2 compost, while a nitrogen vibration band at 3849 cm⁻¹ in E3 indicated significantly higher nitrogen content compared to the control. The Bacillus-enriched pressmud compost not only accelerated the composting process but also enhanced nutrient levels, positioning it as a promising biofertilizer for rehabilitating barren lands. Full article