Circular Economy最新文献

The treatment and utilisation of agricultural and rural solid wastes are important initiatives to advance high-quality agricultural development and improve rural living environment in a concerted manner. We identified the general background and need of agricultural andrural solid wastes in China, and elucidated the main sources and classified the agricultural and rural solid wastes; we grouped the wastes according to their source, value, components, and form, and described the basic characteristics of agricultural and rural solid wastes, namely, diversity, spatio-temporal fluctuations, and consistency of collection. Based on this, the technical pathways of agricultural and rural solid waste co-processing were systematically summarised for a circular economy based on the construction concept of ‘zero-waste city’ in China, including conversion to fertilisers and energy, value enhancement, and volume reduction. Three main models were developed, namely, the mixed fermentation of agricultural and rural solid wastes for fertiliser production, mixed pyrolysis/gasification/incineration for energy production, and urban-rural integrated waste treatment. Subsequently, we systematically analysed the main framework, fundamental characteristics, and applicable scenarios of the three models. We established the foundations and strategies for the co-processing and efficient utilisation of agricultural and rural solid wastes.

Coal-fired power generation resulted in a shortage of conventional fossil fuels and an increase in greenhouse gas emissions. The co-firing of coal and biomass waste in coal-fired boilers was a promising strategy to supplement the energy source and reduce greenhouse gases. However, the co-firing mechanism and potential problems were not well understood. Therefore, the differences between coal and biomass in properties such as proximate and ultimate composition, components in ash and the calorific value were first discussed. Next, compared with the combustion of coal alone, this review analyzed the discrepancies and corresponding issues of co-firing in combustion behaviors and products such as ash and gaseous pollutants. Finally, this review outlined how operational conditions could affect the co-firing performance.

Despite progress in plastic waste recycling technologies, global plastic waste recycling rates remain disappointing. This issue not only suggests an underutilization of existing recycling technologies but also hinders resource utilization, the circular economy, and sustainable manufacturing. Several studies have proposed to address this issue, such as by evaluating the efficiency of recycling technologies based on the volume of recycled waste. However, such single-indicator methods often overlook other critical factors and, thus, may not provide holistic assessments. Additionally, existing methods for evaluating or comparing different recycling technologies are often complex and time-consuming. Meanwhile, several other studies have proposed hundreds of indicators for assessing the effectiveness and suitability of recycling technologies, which often complicates the selection process. Consequently, recyclers and other stakeholders often struggle to select effective and suitable recycling technologies for different plastic waste types and under specific conditions. To address these challenges, we propose the recycling technology selection framework (RTSF), a simple tool that enables easy visualization of relevant recycling indicators under five key pillars: economic, technical, environmental, social, and policy. By allowing recyclers and stakeholders to quickly identify, select, and visualize factors of interest from a large pool, the RTSF enables qualitative comparison and enhances the evaluation of the effectiveness and suitability of multiple plastic recycling technologies. Lastly, the RTSF can serve as a preliminary tool and be used in conjunction with other approaches to enhance the effectiveness of plastic recycling technologies.

The co-smelting of electronic waste (e-waste) in copper/lead pyrometallurgical processes is widely recognized as the preferred solution for sustainable development. However, aluminum and halogen elements in e-waste causes new challenges. To address this, the slag chemistry of high Al₂O₃-containing slag was studied, and the distribution behaviors of Au, Ag, Sn, and other elements in the copper alloy/slag/gas system were investigated in the presence of halogen elements (F/Cl/Br) using the equilibration method. The industrial practice of electronic waste smelting was modeled using METSIM, and the material and energy balances of one industrial process were obtained. Under the conditions of electronic waste smelting, the solubility of Al₂O₃ in the FexO–SiO₂–Al₂O₃–CaO slag system decreased with increasing CaO content. When the CaO content was 20 wt%, and the Fe/SiO₂ mass ratio was 0.62–0.95, the solubility of Al₂O₃ in the slag reached 20 wt%. When 1%–10% CaF₂ was added, 93% of Au entered the metal phase. When the same amount of CaCl₂ or CaBr₂ was added, up to 32% Au entered the gas phase. When CaF₂ was added to the system, 22%–49% of Ag entered the gas phase. However, when CaCl₂ or CaBr₂ was added, 3%–34% of Ag entered the gas phase. The proportion of tin in the gas and slag phases increased with increasing temperature or the addition of halides. The METSIM simulation results showed that under optimized conditions, the crude copper contained more than 90 wt% copper, the discharged slag contained approximately 0.5 wt% copper, and the recovery rates of copper, gold, and silver were ≥98%. The heat generated from raw materials and fuel accounted for the largest part of the heat income, representing 65.32% of the total.

Anaerobic digestion sludge technology is a green and efficient method of treating sludge. However, the presence of humic acid (HA) in sludge can inhibit methanogenic efficiency, and it is necessary to reduce its impact on biogas production by removal or pretreatment. HA, a graphene oxide material can be used to produce high-performance energy-storage materials. Thus, this study examined the sludge source of HA as a precursor, and different electrode materials were prepared by varying the reaction conditions. The structure and electrochemical properties of the electrode materials were analyzed. The results showed that the electrode material prepared using KOH as an activator at 700 °C exhibited optimal performance, with a high specific surface area (1480.53 m²·g⁻¹), pore volume (0.943 cm³·g⁻¹), specific capacitance (185.9 F·g⁻¹), and equivalent series resistance (0.73 Ω). The material maintained 97.8% of its specific capacitance after 1000 cycles at a current density of 1 A·g⁻¹ with benign cycle stability. This study confirmed that the production of HA as an electrode material at a low cost with good performance presents significant prospects.

The collection rate is a difficult and important issue in the management of polyethylene terephthalate (PET) bottle waste, as it is related to the behavior of the community to participate and comply with the system established by the government. One system that has been shown to increase the collection rate of PET bottle waste is the deposit–refund scheme (DRS). We tested residents’ intention to participate in the DRS using the theory of planned behavior and complemented it with several important variables that could influence the model. The method used is partial least square-structural equation modeling. The result of the study is that all the variables studied were positively influenced according to their respective paths. Nevertheless, environmental awareness is the latent variable with the strongest positive effect on attitude, and attitude has the strongest positive effect on intention. Public information is the latent variable that positively influences all variables related to intention. The proposed model can be applied globally to identify factors that influence recycling participation, particularly for DRS, and help achieve sustainable development goals while initiating a circular economy by recycling plastic bottle waste.

Cities are the core of social interactions and resource consumption in our current times. However, urban systems are still largely based on linear activities in which resources are discarded after usage. Current practices around waste reduce possibilities of circularity, mainly due to low percentages of sorting and recycling practices in high- and middle-income countries and landfill practices in middle- and low-income countries. This resulted in a continuous increase in urban waste and negative environmental impact over the last decades. The development of circular practices and innovations, such as additive manufacturing, is crucial to modify the current supply chain and return valuable discarded materials to urban industries. Additive manufacturing is a novel technology based on the creation of objects layer by layer involving the use of a diverse range of materials. Several materials such as plastics, metal or concrete, for example, can be transformed into functional products for cities. Based on a literature review, this paper showcases the potential of urban waste for 3D printing with a main focus on recycling practices at the end of the supply chain. This paper aims to examine the current knowledge, regulations, and practices in circularity and additive manufacturing in the urban context, to identify opportunities and practices for material recovery applications, and showcase applications for additive manufacturing at the last stage of the supply chain. Furthermore, it identifies the needs for further research that could support the implementation and diffusion of additive manufacturing in society.

Mining activities tend to generate various waste including tailings, waste water and waste rock. Efficient management and disposal of these waste materials are critical to minimize their environmental impact and ensure the sustainable operation of mining activities. A huge number of tailings are produced all around the world each year. Generally, part of the tailings is used for underground backfilling and another part is discharged to the tailings dam. The former can provide underground support while the latter tends to cause some environmental problems because the tailings are generally mixed with some chemicals. Regarding this, enhancing the circular use of tailings is crucial to guarantee the sustainable mining engineering. In this study, the feasibility of using fine-grained tailings to make non-burning hollow bricks for underground windbreaks is investigated. A two-stage experiment was implemented where the first stage experiment indicated the threshold of water content, the ratio of cement and tailings and the ratio of fine-grained and rod-mill tailings. In addition, it can be indicated that the addition of polyethylene fibers would increase the compressive strength of hollow bricks in some extent. The second-stage experiment was conducted with no rod-mill tailing added and it can be found that when the ratio of cement and tailings is equal or higher than 1:6, fiber content is more significant in improving brick strength but when this value is lower, the ratio of cement is more important than fiber factors. When the ratio of cement and fine-grained tailings is 1:8 with 0.5 g/kg and 12 mm polypropylene fiber added, the hollow brick is capable of achieving strength of 1.4 MPa for 28 days curation with the price of 0.50 RMB/block. This proportioning scheme is the least expensive while meeting the strength of the windbreak wall for the Fan Kou lead–zinc mine. Finally, it can be indicated that the usage of fine-grained tailings to make underground windbreak wall is feasible and thus provide a new scenario to circular usage of tailings. In addition, other proportioning schemes proposed in this study perhaps can meet more engineering requirements so as to provide more alternatives for circular use of tailings.