A review on recovery processes of metals from E-waste: A green perspective

Bioleaching as an Eco-Friendly Nano-Factory for Sustainable Inorganic Waste Management: Current Advancements, Challenges, and Opportunities

Inorganic waste management and metal recovery technology pose significant challenges to the global research community and policymakers. Bioleaching is an economical, eco-friendly, and sustainable technology used for extracting metals and nanoparticles from inorganic waste streams, including e-waste, fly ash, ore, spent batteries, and petroleum catalysts. Valuable metals are recovered from these waste materials by microbial action. Bioleaching occurs by redoxolysis, acidolysis, and complexolysis processes. The present review provides insights into global trends and hazards of e-waste while also discussing the bioleaching of metals and nanoparticles from various inorganic wastes. In addition, the review focuses on the mechanistic pathway of the bioleaching process and computational aspects, such as the response surface method employed for enhanced recovery of metals from solid waste materials. Various physicochemical and biological parameters influencing metal bioleaching, as well as economic impacts and challenges affecting the bioleaching of metals from solid wastes, are discussed.

Quercetin and luteolin complexation with first-row transition metals in purely aqueous solutions: stoichiometry and binding site selectivity

The complexation behaviour of quercetin and luteolin with first-row transition metals (Cr(III), Mn(II), Co(II), Ni(II), and Zn(II)) in aqueous solutions was systematically investigated using potentiometric titrations, UV-Vis and FT-IR spectroscopy, and density functional theory (DFT) calculations. This study aimed to elucidate the stability, stoichiometry, and preferred binding sites of these flavonoid-metal complexes in an entirely aqueous solution at 37 °C as a function of pH under controlled ionic strength. Speciation analysis revealed the formation of 1 : 1, 1 : 2, and 1 : 3 metal-to-ligand complexes, with coordination occurring primarily at the 4,5- or 3,4-binding site, depending on the metal ion and ligand structure. UV-Vis and IR spectral changes confirmed complex formation, while computational modeling provided insights into binding site selectivity and free energy changes associated with coordination. Results highlight the influence of the ligand structure on metal affinity and stability, with quercetin forming more stable complexes than those formed by luteolin owing to the presence of an additional hydroxyl group at position 3. These findings contribute to a deeper understanding of flavonoid-metal interactions, with potential implications for antioxidant activity, metal chelation therapy, and environmental applications.

Bioleaching of uranium from ores and rocks using filamentous fungi

The purpose of this article is to review the role of filamentous fungi in the leaching of uranium from ores and rocks. Fungi produce short-chain fatty acids through the fermentation and partial oxidation of organic compounds. Biomass can be separated from the culture, while organic acids in spent media dissolve and sequester uranium from minerals in ores and rocks. Oxide, carbonate, and silicate ores containing hexavalent uranium are suitable for this treatment. Fungi can maximize the production of short-chain fatty acids. Uranium dissolution and sequestration are attributed mostly to the formation of soluble U(VI)-carboxylate complexes with citric and oxalic acids, although other carboxylic acids can also sequester uranium. The leach solutions maintain a pH level between 1.5 and 3.5, as the low pH facilitates proton attack on the minerals and minimizes the precipitation of metals in the leach solution. Two types of uranium leaching processes using fungi have been tested: one-step leaching, where biomass is not separated before contact with the uranium mineral, and two-step leaching, which employs spent medium after the removal of fungal biomass. Process optimization to the pilot stage has not yet been reported in the literature. To date, this article is the first to review the role of filamentous fungi in uranium bioleaching from ores and rocks.

Decatungstate-Driven Photocatalytic Pathways for Sustainable and Cleaner Recovery of Precious Metals

The recovery of precious metals from waste streams is crucial for sustainable resource utilization but remains hindered by traditional methods involving high toxicity, energy consumption, and environmental pollution. Here, we present a photocatalytic strategy employing hydrothermally synthesized decatungstate ([W10O32]4-) homogeneous ion catalysts to achieve simultaneous oxidation and reduction of precious metals under ambient conditions. This innovative approach integrates solvent-controlled reaction pathways, enabling efficient dissolution and recovery of precious metals from diverse waste sources, including electronic waste (e-waste), platinum membrane electrodes, and platinum-containing catalysts. The decatungstate catalyst exhibits exceptional performance, with an apparent quantum yield of 0.027%-nearly double that of commercial TiO2 (0.014%)-and achieves recovery efficiency of 80%-100% for platinum, surpassing 21 tested photocatalysts. The process adheres to a solid-phase dissolution model and remains against ionic interference. Time-dependent density functional theory (TD-DFT) calculations corroborate experimental UV-vis spectra, while electron-hole pair analyses elucidate atomic and molecular contributions to photocatalytic activity. Density functional theory (DFT) further validates the thermodynamic feasibility of the reaction pathways. By combining high efficiency, ambient operational conditions, and scalability, this work establishes decatungstates as a sustainable benchmark for green precious metal recovery, addressing the limitations of traditional methods and advancing innovation in resource circularity.

A Microbial-Centric View of Mobile Phones: Enhancing the Technological Feasibility of Biotechnological Recovery of Critical Metals

End-of-life (EoL) mobile phones represent a valuable reservoir of critical raw materials at higher concentrations compared to primary ores. This review emphasizes the critical need to transition from single-material recovery approaches to comprehensive, holistic strategies for recycling EoL mobile phones. In response to the call for sustainable techniques with reduced energy consumption and pollutant emissions, biohydrometallurgy emerges as a promising solution. The present work intends to review the most relevant studies focusing on the exploitation of microbial consortia in bioleaching and biorecovery processes. All living organisms need macro- and micronutrients for their metabolic functionalities, including some of the elements contained in mobile phones. By exploring the interactions between microbial communities and the diverse elements found in mobile phones, this paper establishes a microbial-centric perspective by connecting each element of each layer to their role in the microbial cell system. A special focus is dedicated to the concepts of ecodesign and modularity as key requirements in electronics to potentially increase selectivity of microbial consortia in the bioleaching process. By bridging microbial science with sustainable design, this review proposes an innovative roadmap to optimize metal recovery, aligning with the principles of the circular economy and advancing scalable biotechnological solutions for electronic waste management.

Evaluating e-waste mitigation strategies based on industry 5.0 enablers: An integrated scenario-based BWM and F-VIKOR approach

Electronic waste (e-waste) is the fastest-growing type of solid waste. According to the United Nations (UN), e-waste costs the global economy around $37 billion annually. Indeed, e-waste impedes UN Sustainable Development Goals (SDGs). Toward sustainable e-waste management, Industry 5.0 (I5.0) can offer a comprehensive solution by integrating the core principles of sustainability, resilience, and human-centricity into the technological advancements of Industry 4.0 (I4.0). However, no earlier study has systematically investigated the link between e-waste mitigation and I5.0. To bridge this crucial gap, an evaluation of e-waste Mitigation Strategies (MSs) grounded on I5.0 enablers is conducted in this research endeavor. Initially, ten e-waste MSs and fifteen I5.0 enablers are formulated, with a foundation on pertinent policies and existing literature. Then, an integrated scenario-based Best-Worst Method (scenario-based BWM) and Fuzzy Vlse Kriterijumsk Optimizacija Kompromisno Resenje (F-VIKOR) framework is proposed for decision-making. By harmonizing fuzzy and scenario-based methodologies, this novel framework proficiently navigates both epistemic uncertainties and randomness. The scenario-based BWM analyzes the I5.0 enablers to determine their respective weights, while the F-VIKOR method is deployed to assess the e-waste MSs through the lens of the I5.0 enablers' relative significance. A case study conducted in India applied the proposed approach, showing 'sustainability' and 'control emission' as paramount I5.0 dimension and enabler, respectively. Notably, the MS 'adoption of take-back practices at top management' emerges as a linchpin for fostering sustainable e-waste management practices. The research findings are elucidated through an economic lens and juxtaposed with existing studies, with sensitivity analysis reinforcing the credibility of the results. The implications of this study offer practical insights and policy considerations crucial for all key stakeholders within the e-waste management ecosystem.

Recycling Lithium-Ion Batteries-Technologies, Environmental, Human Health, and Economic Issues-Mini-Systematic Literature Review

Global concerns about pollution reduction, associated with the continuous technological development of electronic equipment raises challenge for the future regarding lithium-ion batteries exploitation, use, and recovery through recycling of critical metals. Several human and environmental issues are reported, including related diseases caused by lithium waste. Lithium in Li-ion batteries can be recovered through various methods to prevent environmental contamination, and Li can be reused as a recyclable resource. Classical technologies for recovering lithium from batteries are associated with various environmental issues, so lithium recovery remains challenging. However, the emergence of membrane processes has opened new research directions in lithium recovery, offering hope for more efficient and environmentally friendly solutions. These processes can be integrated into current industrial recycling flows, having a high recovery potential and paving the way for a more sustainable future. A second method, biolexivation, is eco-friendly, but this point illustrates significant drawbacks when used on an industrial scale. We discussed toxicity induced by metals associated with Li to iron-oxidizing bacteria, which needs further study since it causes low recycling efficiency. One major environmental problem is the low efficiency of the recovery of Li from the water cycle, which affects global-scale safety. Still, electromembranes can offer promising solutions in the future, but there is needed to update regulations to actual needs for both producing and recycling LIB.

Novel and Sustainable Materials for the Separation of Lithium, Rubidium, and Cesium Ions from Aqueous Solutions in Adsorption Processes-A Review

The growing demand for alkali metals (AMs), such as lithium, cesium, and rubidium, related to their wide application across various industries (e.g., electronics, medicine, aerospace, etc.) and the limited resources of their naturally occurring ores, has led to an increased interest in methods of their recovery from secondary sources (e.g., brines, wastewater, waste leachates). One of the dynamically developing research directions in the field of separation of AMs ions from various aqueous solutions is the search for novel, efficient, and "green" materials that could be used in adsorption processes, also on a larger industrial scale. This review concerns the latest achievements (mainly from 2023 to 2024) in the development of innovative adsorption materials (e.g., ion sieves, aluminum-based adsorbents, mineral adsorbents, composites, resins) for the separation of Li+, Cs+, and Rb+ ions from solutions, with particular emphasis on their most important advantages and limitations, as well as their potential impact on the environment.

Carbazole-Phosphazene Based Polymer for Efficient Extraction of Gold and Precious Elements from Electronic Waste

The continuous advancement of industry and technology has significantly increased electronic waste, which contributes to the depletion of valuable metal reserves. Therefore, it is crucial to recycle precious metals in electronic waste effectively and sustainably. This study introduces a novel approach by applying a carbazole-phosphazene-based polymer, EBE-06, in a two-stage leaching method for efficient metal extraction. In the first leaching stage, tin is selectively separated using an acid solution at a controlled pH. In the second stage, valuable metals such as gold are recovered through adsorption onto EBE-06. The polymer exhibited a 99% gold adsorption rate within 1 h, independent of pH, and a maximum adsorption capacity of 1.787 g of gold per gram of polymer. The desorption process yielded 95% efficiency, with the polymer maintaining 94% efficiency over three cycles of use.

Recent advances in bioleaching and biosorption of metals from waste printed circuit boards: A review

Electronic waste, commonly known as "e-waste", refers to electrical or electronic equipment that has been discarded. E-waste, especially waste-printed circuit boards (WPCBs), must be handled carefully; as they can cause serious environmental pollution and threaten the health of local residents. The most abundant metal in WPCBs is copper, in addition to gold, aluminum, nickel, and lead, with grades that are tens or even hundreds of times higher than those of natural deposits. Due to the superiority of biorecovery methods in terms of their environmental friendliness, low capital investment and low operating costs, this study focuses on recent advances in the bioleaching and biosorption of metals from WPCBs. First, the principles, methods, and efficiency of bioleaching are reviewed in detail, particularly acidolysis, redoxolysis, and complexolysis. Additionally, six major factors (microbes, pH, temperature, nutrients, aeration, and substrate) affecting bioleaching are analyzed. The principles, kinetics, and isotherms of biosorption are then reviewed, and the factors influencing biosorption, including temperature and pH, are elaborated on. Hybrid recovery with biorecovery is explored, as these integrated strategies are conducive to achieving selective and efficient metal recovery. Finally, we discuss the advantages and disadvantages of the bioleaching and biosorption processes for metal recovery from WPCBs, particularly in terms of recovery efficiency, recovery time, and cost. Furthermore, future developments in biorecovery are also examined, along with useful ideas on how to accomplish energy-efficient metal recovery from WPCBs in the future.

Selective recovery of Co(II), Mn(II), Cu(II), and Ni(II) by multiple step batch treatments with nanocellulose products

The recovery of Co(II), Mn(II), Ni(II), and Cu(II) from black mass e-waste solutions through cellulose nanofibers (CNFs) and nanocrystals (CNCs) was investigated. These materials were synthetized by TEMPO-oxidation followed by high-pressure homogenization, and acid hydrolysis, respectively. The NC characterization included the measurement of consistency, cationic demand, carboxylic content, dissolved amorphous cellulose, and transmittance at λ = 600 nm. These parameters revealed a high transmittance of the NC solutions and a large presence of anionic groups on the surface. The high surface area and charge of the NC justify their high interaction with the cationic metals. Results indicate that short contact times (even 1 min) and low sorbent doses (10 mg/L) at acidic pHs (2 to 4) implied remarkable sorption capacities in most cases with more than 1 g/g of sorption capacity of Co(II), Mn(II), and Cu(II) in single-step sorption tests. Such levels of sorption capacities exceed by at least one order of magnitude most of the literature values of metal recovery applying cellulosic materials. Isotherm modeling through a combination of Langmuir and Freundlich models suggested that both sorption and surface precipitation occurred. A novel procedure following multiple-step batch operation was applied for Mn(II) sorption. This new method was applied as a five-step process, leading to a fourfold and 18-fold increase of sorption capacity onto CNCs and CNFs, respectively, compared to the single-step process. Therefore, this process shows an innovative way to implement the multiple-step batch sorption with NC as an efficient and environmentally friendly solution for critical metal recovery from e-waste leachates.

Turning Solid Waste into Catalysts: A Path for Environmental Solutions

Waste, often overlooked, stands out as a prime source of valuable products, meeting the demand for natural resources. In the face of environmental challenges, this study explores the crucial role of waste-derived catalysts in sustainable practices, emphasizing the transformative potential of solid waste materials. Carbon-based catalysts sourced from agricultural, municipal, and industrial waste streams can be transformed into activated carbon, biochar, and hydrochar which are extensively used adsorbents. Furthermore, the paper also highlights the potential of transition metal-based catalysts derived from spent batteries, electronic waste, and industrial byproducts, showcasing their efficacy in environmental remediation processes. Calcium-based catalysts originating from food waste, including seashells, eggshells, bones, as well as industrial and construction waste also find an extensive application in biodiesel production, providing a comprehensive overview of their promising role in sustainable and eco-friendly practices. From mitigating pollutants to recovering valuable resources, waste-derived catalysts exhibit a versatile role in addressing waste management challenges and promoting resource sustainability. By transforming waste into valuable catalysts, this study champions a paradigm shift towards a more sustainable and resource-efficient future.

Challenges of E-Waste Dismantling in China

Electronic and electrical products have deeply permeated all aspects of life, bringing a lot of convenience to individuals. However, the generation of e-waste after their end-of-life has resulted in serious risks both to the ecological environment and human health due to a lack of scientific and effective recycling and treatments. As two major types of components in e-waste, heavy metals and plastics can not only directly enter the human body via inhalation, ingestion, and skin absorption, but also accumulate in the human body indirectly through the food chain. E-waste is full of resources such as valuable metals like gold, silver, and copper that are often discarded incorrectly. Environmental and health risks derived from unregulated e-waste dismantling activities may be finally addressed through the application of advanced e-waste recycling technology, policy support of governments, legislation on recycling laws and regulations, and the improvement of public environmental protection awareness. This review gives a brief overview of the history, current situation, and future development of e-waste in China, which may provide novel thinking and approaches to e-waste management in the world.

Sustainable upcycling of copper from waste printed circuit boards with the assistance of tannic acid and Fe3+ to a magnetic heterogeneous catalyst

The recovery and upcycling of metals from electronic waste into functional materials for wastewater treatment is a win-win strategy for simultaneously realizing electronic waste recycling and wastewater purification. This study focused on converting Cu from waste printed boards (PCBs), a common Cu-rich electronic waste, into CuFe2O4 supported on a mesoporous carbon framework (PCFT) with the assistance of Fe3+ and tannic acid (TA). Compared to the PCF prepared without TA, the resulting PCFT exhibited excellent magnetic properties, high crystallinity, lower interfacial transfer resistance, more abundant oxygen vacancies (OV), and lower metal leaching. Moreover, PCFT can serve as a superior heterogeneous catalyst to activate peroxymonosulfate to remove reactive brilliant blue KN-R from wastewater, and its catalytic activity was markedly higher than that of CFT synthesized with Cu(NO3)2·3H2O, which may be due to its higher specific surface area and more abundant OV. The combined results of scavenging experiments, electron paramagnetic resonance analysis, and electrochemical measurements implied that both radical and nonradical processes promoted the elimination of KN-R; however, •OH and SO4•- were not the major contributors. Furthermore, the PCFT exhibited high adaptability to pH and water matrices, confirming its practical application potential. These findings provide a novel strategy for the upcycling of metals from electronic waste.

Biotechnological Approaches for Metal Recovery from Electronic Wastes

The disposal of electronic waste (EW) in open landfills has caused several toxic environmental effects. The harmful metallic components released in the environment due to deposition of EW act as hazards for living systems. EW management has been widely studied in recent days across the world. Though, several processes are implemented in extraction, recycling and recovery of heavy metals from the EW, most of them are not effective in recovering the precious metals. Various chemical processes are executed for efficient extraction of precious metals from e-wastes. Though the techniques are easy to process and rapid, however, the chemical leaching also has detrimental environmental consequences. Biological approaches, on the other hand, solves the purpose for efficient and environmentally friendly recovery of precious metals. Thus, both resource recovery as well as remediation can be targeted simultaneously. Biotechnological methods offer sustainable and efficient solutions for metal recovery from electronic wastes, presenting a viable alternative to traditional methods. Continued advancements in this field hold significant promise for addressing the growing e-waste challenge.

Classification of Electronic Waste Components through X-ray and Neutron-Based Imaging Techniques

In modern society, the amount of e-waste is growing year by year. Waste electronic items are complex, highly heterogeneous systems, containing organic material as well as several exotic, valuable, toxic, mostly metallic elements. In this study, the potential of X-ray and neutron radiography to reveal the inner structure of various complex e-waste was investigated. The images obtained using the two techniques were evaluated together to investigate the possibility of a more efficient segmentation of the individual components. The advantages and limitations of the two methods were identified for the studied waste types. X-ray radiography was found to be preferable for the identification of small metallic parts and for revealing the internal structure of e-waste with thick plastic coatings. Neutron radiography allowed for the identification of several components that did not provide sufficient contrast with X-ray imaging due to their similar X-ray attenuation compared to their surroundings. The combination of the two methods opens up new opportunities and could provide much more effective segmentation than either method alone.

Architectural Decoration of Bioleached NiFeP Surfaces by Co3O4 Flowers for Efficient Electrocatalytic Hydrogen Generation

In the quest for sustainable hydrogen production via water electrolysis, the development of high-performance, noble-metal-free catalytic systems is highly desired. Herein, we proposed an innovative strategy for the development of an electrocatalyst by refining the surface characteristics of a NiFeP alloy through microbiological techniques and subsequent enrichment of active sites by tailoring 3D hierarchical flower-like structures with intact and interconnected two-dimensional (2D) Co3O4. The resultant 3D Co3O4@NiFeP-5/24h has a porous structure comprised of intercrossed nanoparticles covering the entirety of the catalytic surface. This design ensures comprehensive electrolyte ion penetration and facilitates the release of gas bubbles while reducing bubble adhesion rates. Remarkably, the Co3O4@NiFeP-5/24h electrode demonstrates superior hydrogen evolution (HER) performance in an alkaline medium, characterized by its high stability, low overpotential (106 mV at a current density of 10 mA cm-2), and reduced Tafel slope (98 mV dec-1). Besides, the minimized interfacial contact resistance among the phases of electrode and electrolyte emphasizes the high HER performance of the 3D Co3O4@NiFeP-5/24h electrode. The innovative design and fabrication strategy employed herein holds significant potential for advancing the field of water-splitting electrocatalysis, offering a promising path toward the rational design and development of noble-metal-free electrocatalysts.

Physicochemical reactions in e-waste recycling

Electronic waste (e-waste) recycling is becoming a global concern owing to its immense quantity, hazardous character and the potential loss of valuable metals. The many processes involved in e-waste recycling stem from a mixture of physicochemical reactions, and understanding the principles of these reactions can lead to more efficient recycling methods. In this Review, we discuss the principles behind photochemistry, thermochemistry, mechanochemistry, electrochemistry and sonochemistry for metal recovery, polymer decomposition and pollutant elimination from e-waste. We also discuss how these processes induce or improve reaction rates, selectivity and controllability of e-waste recycling based on thermodynamics and kinetics, free radicals, chemical bond energy, electrical potential regulation and more. Lastly, key factors, limitations and suggestions for improvements of these physicochemical reactions for e-waste recycling are highlighted, wherein we also indicate possible research directions for the future.

Heterogeneous CuxO Nano-Skeletons from Waste Electronics for Enhanced Glucose Detection

Electronic waste (e-waste) and diabetes are global challenges to modern societies. However, solving these two challenges together has been challenging until now. Herein, we propose a laser-induced transfer method to fabricate portable glucose sensors by recycling copper from e-waste. We bring up a laser-induced full-automatic fabrication method for synthesizing continuous heterogeneous CuxO (h-CuxO) nano-skeletons electrode for glucose sensing, offering rapid (< 1 min), clean, air-compatible, and continuous fabrication, applicable to a wide range of Cu-containing substrates. Leveraging this approach, h-CuxO nano-skeletons, with an inner core predominantly composed of Cu2O with lower oxygen content, juxtaposed with an outer layer rich in amorphous CuxO (a-CuxO) with higher oxygen content, are derived from discarded printed circuit boards. When employed in glucose detection, the h-CuxO nano-skeletons undergo a structural evolution process, transitioning into rigid Cu2O@CuO nano-skeletons prompted by electrochemical activation. This transformation yields exceptional glucose-sensing performance (sensitivity: 9.893 mA mM-1 cm-2; detection limit: 0.34 μM), outperforming most previously reported glucose sensors. Density functional theory analysis elucidates that the heterogeneous structure facilitates gluconolactone desorption. This glucose detection device has also been downsized to optimize its scalability and portability for convenient integration into people's everyday lives.

Assessing the environmental impacts of copper cathode production based on life cycle assessment

The demand for copper is growing considerably in parallel with economic and technological development. The rate increase in copper consumption in Iran increases pressure on the numerous unexploited mines in southeast Iran and causes the environmental crisis alongside the northern Levar wind in this area. Given this, this study systematically explored the environmental impacts of a one-ton copper cathode processing operation from a cradle-to-gate perspective, using life cycle assessment (LCA). Moreover, the release of greenhouse gases and the energy consumption during the copper cathode production were also assessed. The results indicated that sulfuric acid use in the smelting and extraction stages, metal leaching from tailings, and CO2 dominated more than 50% of contributions to freshwater and marine ecotoxicity, human toxicity, and global warming. The energy analysis revealed 88.92% of crude oil use especially for the electrowinning stage, which should be promoted technologically. For global warming, the indirect CO2 emission from electricity consumption using fossil fuels was the main contributor (94.56%). Therefore, shifting from conventional energy systems to renewable energy systems could alleviate the overall environmental impact. For a 0.57-ton sulfuric acid effluent per one ton of copper cathode production, its treatment and reuse in the process is recommended. Summing up, the results of this study provide the environmental hot spots for copper cathode production for further investigation. Integr Environ Assess Manag 2024;20:1180-1190. © 2023 SETAC.

Can e-waste recycling provide a solution to the scarcity of rare earth metals? An overview of e-waste recycling methods

Recycling e-waste is seen as a sustainable alternative to compensate for the limited natural rare earth elements (REEs) resources and the difficulty of accessing these resources. Recycling facilitates the recovery of valuable products and minimizes emissions during their transportation. Numerous studies have been reported on e-waste recycling using various techniques, including thermo-, hydro- and biometallurgical approaches. However, each approach still has technical, economic, social, or environmental limitations. This review highlights the potential of recycling e-waste, including outlining the current unutilized potential of REE recycling from different e-waste components. An in-depth analysis of e-waste generation on a global scale and Australian scenario, along with various hazardous impacts on ecosystem and human health, is reported. In addition, a comprehensive summary of various metal recovery processes and their merits and demerits is also presented. Lifecycle analysis for recovering REEs from e-waste indicate a positive environmental impact when compared to REEs produced from virgin sources. In addition, recovering REEs form secondary sources eliminated ca. 1.5 times radioactive waste, as seen in production from primary sources scenario. The review outcome demonstrates the increasing potential of REE recycling to overcome critical challenges, including issues over supply security and localized dependency.

An in-depth analysis and review of management strategies for E-waste in the south Asian region: A way forward towards waste to energy conversion and sustainability

The soaring rise of electronic and electrical waste (E-waste) leads to significant challenges to the South Asian region, urging for incorporating comprehensive assessment and management strategies. The research dives into the intricacies of E-waste and examines how regulatory barriers, public ignorance, and the limited lifespan of electronic devices all contribute to the significant production of E-waste. This study emphasizes the vital need for ongoing and appropriate management practices by bringing attention to the short lifespan of electronic devices and the resulting generation of E-waste. This work also addresses the increased risks that people who live close to informal recycling sites for electronic waste face, as well as the dangerous substances that are found in them and how they harm the environment and human health. Furthermore, in order to promote circular economies and increase productivity, the study assesses management practices in both developed and developing nations, placing special emphasis on component reuse and recycling. Along with addressing the grave consequences of the illicit E-waste trade on the environment, particularly in developing nations, this review attempts to enlighten stakeholders and policymakers about the vital need for coordinated efforts to address the issues related to E-waste in the South Asian region by offering insights into E-waste assessment and management techniques.

Risk control of heavy metal in waste incinerator ash by available solidification scenarios in cement production based on waste flow analysis

Incineration is a common method in municipal solid waste management, which has several advantages such as reducing the volume of waste, but with concerns about exhaust gas and ash management. In this study, heavy metals in bottom ash, secondary furnace ash and fly ash of two waste incinerators in Tehran and Nowshahr were analyzed and its control in cement production was investigated. For this purpose, twelve monthly samples of three types of incinerator ash were analyzed. By combining the studied ashes in the raw materials, the quantity of metals in the cement was analyzed. Finally, by investigating four scenarios based on quantitative variations in the routes of municipal solid waste, ash quantity and the related risk caused by its heavy metals were studied. The results showed that the concentration of heavy metals in the three ash samples of the studied incinerators was 19,513-23,972 µg/g and the composition of the metals included Hg (less than 0.01%), Pb (2.93%), Cd (0.59%), Cu (21.51%), Zn (58.7%), As (less than 0.01%), Cr (15.88%), and Ni (0.91%). The best quality of produced cement included 20% ash and 10% zeolite, which was the basis of the next calculations. It was estimated that the reduction of the release of metals into the environment includes 37 gr/day in best scenario equal to 10.6 tons/year. Ash solidification can be considered as a complementary solution in waste incinerator management.

Negative-carbon recycling of copper from waste as secondary resources using deep eutectic solvents

Copper plays a crucial role in the low-carbon transformation of global communities with prevalent use of electric vehicles. This study proposed an environmentally friendly approach that utilizes a deep eutectic solvent (DES), choline chloride-ethylene glycol (ChCl-EG), as green solvent for the selective extraction of copper from scrap materials. With hydrogen peroxide as an oxidizing agent, the copper species from the printed circuit boards (PCBs) scraps were efficiently leached by the DES through oxidation-complexation reactions (conditions: 25 min, 20 °C, and 5 wt% H2O2). Molecular dynamics and density functional theory were performed to simulate the intricate cascade of interactions between copper species and hydrogen bond donors/acceptors of DES, providing insights into the mechanistic processes involved. Copper was selectively recovered from the DES leachate containing impurities (e.g., Pb2+, Sn2+, and Al3+) through electrodeposition via a diffusion-controlled reaction under a constant potential mode. A comprehensive life cycle assessment of the process demonstrated that the utilisation of DES in the extraction of copper from waste PCBs could result in significant reduction in carbon dioxide emissions (-93.6 kg CO2 eq of 1000 kg waste PCBs), thus mitigating the carbon footprint of global copper use through the proposed solvometallurgical recycling process of secondary resources.

Recovery of non-metallic useable materials from e-waste

Tremendous amounts of electric and electronic wastes (e-waste) are generated daily, and their indiscriminate disposal may cause serious environmental pollution. The recovery of non-metallic materials from e-waste is a strategy to not only reduce the volume of e-waste but also avoid pollutant emissions produced by indiscriminate disposal of e-waste. Pyrolysis, sub/supercritical water treatment, chemical dissolution, and physical treatment (e.g., ball milling, flotation, and electrostatic separation) are available methods to recover useable non-metallic materials (e.g., resins, fibers, and various kinds of polymers) from e-waste. The e-waste-derived materials can be used to manufacture a large variety of industrial and consumer products. In this regard, this work attempts to compile relevant knowledge on the technologies that derive utilizable materials from different classes of e-waste. Moreover, this work highlights the potential of the e-waste-derived materials for various applications. Current challenges and perspectives on e-waste upcycling to useable materials are also discussed.

Driving sustainable circular economy in electronics: A comprehensive review on environmental life cycle assessment of e-waste recycling

E-waste, encompassing discarded materials from outdated electronic equipment, often ends up intermixed with municipal solid waste, leading to improper disposal through burial and incineration. This improper handling releases hazardous substances into water, soil, and air, posing significant risks to ecosystems and human health, ultimately entering the food chain and water supply. Formal e-waste recycling, guided by circular economy models and zero-discharge principles, offers potential solutions to this critical challenge. However, implementing a circular economy for e-waste management due to chemical and energy consumption may cause environmental impacts. Consequently, advanced sustainability assessment tools, such as Life Cycle Assessment (LCA), have been applied to investigate e-waste management strategies. While LCA is a standardized methodology, researchers have employed various routes for environmental assessment of different e-waste management methods. However, to the authors' knowledge, there lacks a comprehensive study focusing on LCA studies to discern the opportunities and limitations of this method in formal e-waste management strategies. Hence, this review aims to survey the existing literature on the LCA of e-waste management under a circular economy, shedding light on the current state of research, identifying research gaps, and proposing future research directions. It first explains various methods of managing e-waste in the circular economy. This review then evaluates and scrutinizes the LCA approach in implementing the circular bioeconomy for e-waste management. Finally, it proposes frameworks and procedures to enhance the applicability of the LCA method to future e-waste management research. The literature on the LCA of e-waste management reveals a wide variation in implementing LCA in formal e-waste management, resulting in diverse results and findings in this field. This paper underscores that LCA can pinpoint the environmental hotspots for various pathways of formal e-waste recycling, particularly focusing on metals. It can help address these concerns and achieve greater sustainability in e-waste recycling, especially in pyrometallurgical and hydrometallurgical pathways. The recovery of high-value metals is more environmentally justified compared to other metals. However, biometallurgical pathways remain limited in terms of environmental studies. Despite the potential for recycling e-waste into plastic or glass, there is a dearth of robust background in LCA studies within this sector. This review concludes that LCA can offer valuable insights for decision-making and policy processes on e-waste management, promoting environmentally sound e-waste recycling practices. However, the accuracy of LCA results in e-waste recycling, owing to data requirements, subjectivity, impact category weighting, and other factors, remains debatable, emphasizing the need for more uncertainty analysis in this field.

Fungal bioleaching of metals from WPCBs of mobile phones employing mixed Aspergillus spp.: Optimization and predictive modelling by RSM and AI models

In the present study, optimization and prediction models for fungal bioleaching for effective metal extraction from waste printed circuit boards (WPCBs) of mobile phones were developed employing central composite design (CCD) of response surface methodology (RSM), and two artificial intelligence (AI) models, i.e., artificial neural network (ANN) and, support vector machine (SVM), respectively. Two continuous process parameters, such as pH (4-9) and pulp density (1-10 g/L), and the bioleaching approaches, viz., one-step and two-step, were experimentally optimized for the extraction of targeted metals, i.e., Cu, Ni, and Zn from WPCBs by mixed cultures of Aspergillus niger and Aspergillus tubingensis. Datasets were then used for predictive modelling using AI tools. Results showed that the highest simultaneous bioleaching of Cu, Ni, and Zn, with an extraction efficacy of about 86%, 51%, and 100%, respectively, achieved at an optimal condition of pH 5.7 and pulp density of 3 g/L following the two-step bioleaching approach. Effective metal extraction in the two-step approach could be attributed to the abundant production of organic acids with a content of about 16.3 g/L, 8.4 g/L, and 0.5 g/L of citric acid, oxalic acid, and malic acid, respectively. Further, the predictive modelling revealed that the ANN model was found to predict the fungal bioleaching responses more accurately as compared to the SVM model with R2 values exceeding 0.96 for all targeted metals. This research demonstrates the applicability of the optimization and prediction models for efficient metal extraction from WPCBs using mixed Aspergillus spp. following the two-step approach.

Recycling of the waste battery: Effect of waste battery on property of asphalt and environmental impact evaluation

A waste battery is a kind of hazardous solid waste, and traditional recycling methods can cause serious environmental pollution. In this paper, a pilot study was conducted to reduce the leaching of heavy metals in waste battery power (WBP) by using the wrapping effect of asphalt and explored the feasibility of adding waste battery as a modifier to asphalt. The main components of WBP are determined through microscopic experiments, and its compatibility with asphalt and microscopic mechanism are analyzed; The influence of WBP on asphalt properties are analyzed through routine tests and mixture tests; The leaching test of toxicity is used to analyze the impact of WBP and WBP modified asphalt on the environment. The experimental results indicate that WBP is mainly composed of MnO2, C, and ZnO; There are many wrinkles and grooves on the surface of WBP, which can effectively adsorb asphalt during the modification process, produce anchoring effect, and have good compatibility with asphalt; The components of waste battery adsorb the aging light components in asphalt through their folds and swelling, so that the proportion of heavy components is relatively increased, improving the property indicators of asphalt; From the perspective of engineering property, WBP modified asphalt mixture has strong resistance to deformation and water damage. The leaching concentration of heavy metal ions from bare WBP in soil seriously exceeded the standard. In contrast, when WBP was added to asphalt, the cumulative leaching concentration of heavy metal ions was significantly reduced due to the wrapping effect of asphalt, and the WBP leaching toxicity was greatly suppressed; The method of recycling waste battery and adding it to asphalt as a modifier can prevent the release of heavy metal ions from waste battery into the environment and reduce the risk of the total environmental harm to soil, groundwater and human health.

Review on the gentle hydrometallurgical treatment of WPCBs: Sustainable and selective gradient process for multiple valuable metals recovery

The metal resource crisis and the inherent need for a low-carbon circular economy have driven the rapid development of e-waste recycling technology. High-value waste printed circuit boards (WPCBs) are an essential component of e-waste. However, WPCBs are considered hazardous to the ecosystem due to the presence of heavy metals and brominated organic polymers. Therefore, achieving the recycling of metals in WPCBs is not only a strategic requirement for building a green ecological civilization but also an essential guarantee for achieving a safe supply of mineral resources. This review systematically analyzes the hydrometallurgical technology of metals in WPCBs in recent years. Firstly, the different unit operations of pretreatment in the hydrometallurgical process, which contain disassembly, crushing, and pre-enrichment, were analyzed. Secondly, environmentally friendly hydrometallurgical leaching systems and high-value product regeneration technologies used in recent years to recover metals from WPCBs were evaluated. The leaching techniques, including cyanidation, halide, thiourea, and thiosulfate for precious metals, and inorganic acid, organic acid, and other leaching methods for base metals such as copper and nickel in WPCBs, were outlined, and the leaching performance and greenness of each leaching system were summarized and analyzed. Eventually, based on the advantages of each leaching system and the differences in chemical properties of metals in WPCBs, an integrated and multi-gradient green process for the recovery of WPCBs was proposed, which provides a sustainable pathway for the recovery of metals in WPCBs. This paper provides a reference for realizing the gradient hydrometallurgical recovery of metals from WPCBs to promote the recycling metal resources.

Environmental biotechnology and the involving biological process using graphene-based biocompatible material

Biotechnology is a promising approach to environmental remediation but requires improvement in efficiency and convenience. The improvement of biotechnology has been illustrated with the help of biocompatible materials as biocarrier for environmental remediations. Recently, graphene-based materials (GBMs) have become promising materials in environmental biotechnology. To better illustrate the principle and mechanisms of GBM application in biotechnology, the comprehension of the biological response of microorganisms and enzymes when facing the GBMs is needed. The review illustrated distinct GBM-microbe/enzyme composites by providing the GBM-microbe/enzyme interaction and the determining factors. There are diverse GBM modifications for distinct biotechnology applications. Each of these methods and applications depends on the physicochemical properties of GBMs. The applications of these composites were mainly categorized as pollutant adsorption, anaerobic digestion, microbial fuel cells, and organics degradation. Where information was available, the strategies and mechanisms of GBMs in improving application efficacies were also demonstrated. In addition, the biological response, from microbial community changes, extracellular polymeric substances changes to biological pathway alteration, may become important in the application of these composites. Furthermore, we also discuss challenges facing the environmental application of GBMs, considering their fate and toxicity in the ecosystem, and offer potential solutions. This research significantly enhances our comprehension of the fundamental principles, underlying mechanisms, and biological pathways for the in-situ utilization of GBMs.