Recovery of metals and nonmetals from electronic waste by physical and chemical recycling processes

Potential and current practices of recycling waste printed circuit boards: A review of the recent progress in pyrometallurgy

Over the last few decades, a substantial amount of e-waste including waste printed circuit boards (WPCBs) has been produced and is accumulating worldwide. More recently, the rate of production has increased significantly, and this trend has raised some serious concerns regarding the need to develop viable recycling methods. The presence of other materials in the WPCBs, such as ceramics and polymers, and the multi-metal nature of WPCBs all contribute to the increased complexity of any recycling process. Among the viable techniques, pyrometallurgy, with the inherent ability to process the waste independent of its composition, is a promising candidate for both rapid and large-scale treatment. In the present study, firstly, the principles of the pyrometallurgical methods for WPCB recycling are discussed. Secondly, the different unit operations of thermochemical pretreatment including incineration, pyrolysis, and molten salt processing are reviewed. Thirdly, the smelting processes for the recovery of metals from WPCBs, as well as the issues surrounding slag formation and subsequent treatment are explained. Fourthly, alternative methods for the recovery of polymers and ceramics, in addition to metal recycling, are elucidated. Fifthly, emission control techniques and the potential for energy recovery are evaluated.

Do the Main Developers of Electrical and Electronic Equipment Comply with the Precepts of the Circular Economy Concepts? A Patent-Based Approach

The unceasing demand for electronic equipment has led to numerous problems, such as environmental damage and raw material shortages. The adoption of circular production chains and the precepts of the circular economy when designing electronic equipment could minimize these problems by fostering the reuse of resources without loss of quality or value. The scientific literature has many studies on the importance of circular production, but there are no data to demonstrate whether the scientific information produced on the circular economy and circular production is being taken up by industry. This study analyzes whether patent applications for inventions applicable to the production of electronic equipment meet the precepts of the circular economy. To this end, a study of patent documents was conducted. A total of 3638 documents were retrieved. Their analysis revealed that the technologies developed by the leading patent applicants and manufacturers are mainly from the first link in the production chain, materials, and components. The solutions proposed tend to be geared toward equipment efficiency and reduced energy consumption, which may indirectly increase the equipment’s useful life and save energy. Despite the existence of laws and research highlighting the importance of feeding used materials back into the production process, the developers of electronic equipment have not yet turned their attention to the recycling and retrieval of materials for their use as inputs for new components.

A comprehensive review on hazardous aspects and management strategies of electronic waste: Bangladesh perspectives

Electronic waste (e-waste) contains a variety of electronic components e.g., metals, non-metals, plastics, cables, etc. The excessive generation of e-waste has become a significant concern in the last few decades. The current global e-waste generation is 57.4 million metric tons (MMT) per year. Asia produces the highest amount of e-waste (24.9 MMT) followed by America, Europe, Africa, and Oceania. In Bangladesh, e-waste produces from two sources: its own consumption of electronic devices, which is 0.6 MMT, and imported e-waste from ship breaking yards that is 2.5 MMT in 2021. However, inadequate information on the current state of e-waste generation and management systems in Bangladesh has created a void to establish the future direction for proper handling of e-waste. In this work, the Bangladesh perspective of e-waste has been analyzed. The environmental, health economical forfeiture of e-waste has been discussed. The development of government legislations regarding e-waste have been stated. The establishment of e-waste management has been designed by the life cycle assessment (LCA) and material flow analysis (MFA) models. Moreover, a holistic approach for understanding the possible hazards, the economic feasibility of e-waste processing and viable management models for e-waste in Bangladesh was endeavored in this work to propose systematic future directions and recommendations to improve the current e-waste scenario of Bangladesh.

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Collection, recycling, and disposal processes have to be established in Bangladesh.

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E-waste generation in Bangladesh is 3.1 MMT including shipbreaking yards generation.

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Bangladesh has an e-waste business potential of 221 million USD/yr.

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The policies and legislations for e-waste management in Bangladesh are not adequate.

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A combined MFA and LCA model can help decision-making for e-waste management.

Photocatalytic Materials Obtained from E-Waste Recycling: Review, Techniques, Critique, and Update

Waste-derived materials obtained from the recovery and recycling of electronic waste (e-waste) such as batteries and printed circuit boards have attracted enormous attention from academia and industry in recent years, especially due to their eco-friendly nature and the massive increment in e-waste due to technological development. Several investigations in the literature have covered the advances achieved so far. Meanwhile, photocatalytic applications are especially of interest since they maintain mutual benefits and can be used for H2 production from solar water splitting based on semiconductor processing as a proper environmentally friendly technique for solar energy conversion. In addition, they can be utilized to degrade a variety of organic and non-organic contaminations. Nonetheless, to the best of the authors’ knowledge, there has not been any comprehensive review that has specifically been focused on e-waste-derived photocatalytic materials. In this regard, the present work is dedicated to thoroughly discussing the related mechanisms, strategies, and methods, as well as the various possible photocatalysts synthesized from e-wastes with some critiques in this field. This brief overview can introduce modern technologies and promising possibilities for e-waste valorization, photocatalytic processes, and new photocatalytic degradation methods of eco-friendly nature. This paper discusses various e-waste-obtained photocatalytic materials, synthesis procedures, and applications, as well as several types of e-waste, derived materials such as TiO2, ZnO, indium tin oxide, and a variety of sulfide- and ferrite-based photocatalytic materials.

Occurrence, Distribution, and Human Exposure of Emerging Liquid Crystal Monomers (LCMs) in Indoor and Outdoor Dust: A Nationwide Study

Liquid crystal monomers (LCMs) are a class of emerging, persistent, bioaccumulative, and toxic organic pollutants. They are detected in various environmental matrixes that are associated with electronic waste (e-waste) dismantling. However, their occurrence and distribution in indoor and outdoor dust on a national scale remain unknown. In this study, a dedicated target analysis quantified a broad range of 60 LCMs in dust samples collected across China. The LCMs were frequently detected in indoor (n = 48) and outdoor dust (n = 97; 37 sampled concomitantly with indoors dust) from dwellings, and indoor dust from cybercafés (n = 34) and phone repair stores (n = 22), with median concentrations of 41.6, 94.7, 106, and 171 ng/g, respectively. No significant spatial difference was observed for the concentrations of the total LCMs among distinct geographical regions (p > 0.05). The median daily intake values of the total LCMs via dust ingestion, dermal contact, and inhalation were estimated at 1.50 × 10^-2, 2.90 × 10^-2, and 8.57 × 10^-6 ng/kg BW/day for adults and 1.47 × 10^-1, 1.22 × 10^-1, and 2.18 × 10^-5 ng/kg BW/day for children, respectively. These estimates suggested higher exposure risks for children and indicated that dust ingestion and dermal contact significantly contribute to the human intake of LCMs. The microenvironmental pollution levels of LCMs together with the potential exposure risks associated with some of these chemicals are of concern for human health.

Analysis of environmental sustainability of e-waste in developing countries - a case study from Pakistan

The electronic waste generation rate is increasing drastically at a rate of 3 to 5% per year in developing countries. The aim of this study is to analyze the environmental sustainability and economic benefits of such e-waste management in the developing economies like Pakistan. The life cycle assessment (LCA) method has been employed for streamlined impact analysis of the end-of-life processing of e-waste focusing mainly on laptop computers and liquid crystal display (LCD) desktop computers in Pakistan. The method of cumulative exergy extraction from the natural environment (CEENE) has also been deployed for the relative assessment of resources' consumption of e-waste recycling versus landfilling scenario. The determined impact scores are 1.79E + 03 kg CO₂ eq., 7.19E-07 kg CFC-11 eq., 1.02E + 03 kg 1,4-DCB, 7.13E + 01 kg 1,4-DCB, and 3.41E-03 kg Cu eq. in climate change potential, stratospheric ozone depletion, ecotoxicity potential, human noncarcinogenic potential, and mineral resource depletion impact categories, respectively. The results of CEENE analysis reveal that approximately 80% of the impact on natural resources is reduced by the efficient recycling of e-waste. The comparative assessment of respective scores for current and target material weight recovery (MWR) indicators represented that by increasing the MWR indicator by 33.8% for laptop computers and by 27.2% for LCD computers, the country will achieve an annual economic benefit of US $191.56 million. This is greatly significant for a transitional shift towards e-waste revalorization while realizing the objectives of sustainable resource consumption. Innovative improvement measures ensuring economically feasible, energy-efficient, and environment friendly waste collection, treatment, and recycling practices present an invaluable opportunity for developing countries.

Precious and critical metals from wasted LED lamps: characterization and evaluation

LED lamps already conquered the market of general lighting and are expected to generate a substantial stream of e-waste in the coming years. The challenge of recycling LED lamps have emerged, and it is essential to address both environmental and economic aspects to achieve a circular economy. LED lamps contain precious and critical metals, which can be found in electrical components and in the LED itself, making them a prospective waste for recycling initiatives. However, data about the concentration and distribution of these metals in the LED lamp's components are still scarce and uncertain. This work aims to characterise the various components of different brands of LED lamps to provide novel data on the precious and critical metals' amounts. Gold and silver were found in all brands of lamp, and we highlight the occurrence of gold in all analysed components, in concentrations between 0.01% and 0.07%, which is relevant to the economic viability of future recycling routes (gold and silver can contribute with USD 4340.00 per ton of LED lamps). The critical metals gallium, yttrium, and cerium were found in LEDs, while cobalt, barium, gallium, antimony, and manganese were found in printed circuit boards (PCBs). Additionally, the elements lead, cadmium, and arsenic were characterised due to their association with environmental and human toxicity.

Metals extraction processes from electronic waste: constraints and opportunities

The skyrocketing demand and progressive technology have increased our dependency on electrical and electronic devices. However, the life span of these devices has been shortened because of rapid scientific expansions. Hence, massive volumes of electronic waste (e-waste) is generating day by day. Nevertheless, the ongoing management of e-waste has emerged as a major threat to sustainable economic development worldwide. In general, e-waste contains several toxic substances such as metals, plastics, and refractory oxides. Metals, particularly lead, mercury, nickel, cadmium, and copper along with some valuable metals such as rare earth metals, platinum group elements, alkaline and radioactive metal are very common; which can be extracted before disposing of the e-waste for reuse. In addition, many of these metals are hazardous. Therefore, e-waste management is an essential issue. In this study, we critically have reviewed the existing extraction processes and compared among different processes such as physical, biological, supercritical fluid technologies, pyro and hydrometallurgical, and hybrid methods used for metals extraction from e-waste. The review indicates that although each method has particular merits but hybrid methods are eco-friendlier with extraction efficiency > 90%. This study also provides insight into the technical challenges to the practical realization of metals extraction from e-waste sources.

The Physical Characterization and Terminal Velocities of Aluminium, Iron and Plastic Bottle Caps in a Water Environment

Aluminium, iron and plastic are materials which are extensively used at both industry and individual levels. However, significant amounts of aluminium, iron and plastic end up in the environment. Specifically, bottle caps made of these materials are often thrown away, with or without bottles, and appear among the common plastic debris entering the world’s oceans and beaches. More than 20 million bottle caps and lids have been identified during beach-cleaning campaigns over the last 30 years. To recover bottle caps from the shores, conventional technologies can be used. In this paper, the physical properties of used metal and plastic bottle caps were examined and related to the settling and rising velocities of the caps, as well as their drag coefficients and hydrodynamic modes in water environments, with respect to gravity separation. The sample contained aluminium, iron, high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) bottle caps. The findings revealed that the density differences between the bottle caps resulted in the terminal settling velocities of aluminium and iron particles, which were significantly higher than the rising velocities of the plastic caps. The results allowed us to design a flowsheet for bottle cap recovery from beach coasts in order to reduce environmental impact and produce add-on plastic and metal products.

A review on the utilization of waste material in asphalt pavements

Recycling of waste and disposal has become a vital environmental issue that creates serious concern worldwide. The use of waste material in pavement structure is one of the essential initiative for the future towards sustainable environment. This study imparts a review on waste materials such as plastic waste, crumb rubber, glass fibre, steel slag, crushed concrete and Low Density Polyethylene (LDPE) and their use in asphalt pavements. The waste materials act as modifiers and have the capability to upgrade the performance of pavement and provide green technology with eco-friendly environment. Utilization of waste material as an asphalt binder  enhanced the engineering properties of asphalt pavements. It may be regarded as a smart strategy for sustainable development as it is cost-effective, economical, efficiency and productivity. Moreover, it approached to minimize the pollution. Further, many researchers have investigated the outcomes of asphalt pavement with waste and observed that it achieved the properties and performance of asphalt mixtures while reducing pavement damage, failure and deformation.

Research trend and dynamical development of focusing on the global critical metals: a bibliometric analysis during 1991-2020

Critical metals are indispensable to a world seeking to transition away from carbon. Yet their extraction, processing, and application leave an unsustainable global environment and climate change footprint. To capture the development dynamics and research emphases of critical metals throughout their life cycle, this paper adopts bibliometrics to analyze the various stages of global critical metal flow in multiple dimensions to reveal the hot issues and future strategic trends. The research results indicate that the number of research papers on critical metals is annually rising, with remarkably rapid growth after 2010. Judging from the number of articles published by the authors and the citations, among the authors, Kawakita, Poettgen, Anwander, Inoue, and Dongmei Cui have a significant influence on critical metal research fields. The institutions with the most research on critical metals are universities, not research institutes. In addition, the focus has extended from a single discipline to the interdisciplinary development of multiple disciplines. Analysis of keywords shows that "rare metals" and "precious metals" are the most popular metals among the researched metals. The researched buzzwords of critical metals are disappearing, convergent, and merging over time. The research has focused on the mining and the whole life cycle process of extraction, treatment, and application. Based on the above characteristics, this paper tries to understand the dynamic development and evolution of global critical metals from multiple dimensions, resorting to giving a reference for follow-up-related research scholars.

Iodine‐Catalysed Dissolution of Elemental Gold in Ethanol

Gold is a scarce element in the Earth's crust but indispensable in modern electronic devices. New, sustainable methods of gold recycling are essential to meet the growing eco‐social demand of gold. Here, we describe a simple, inexpensive, and environmentally benign dissolution of gold under mild conditions. Gold dissolves quantitatively in ethanol using 2‐mercaptobenzimidazole as a ligand in the presence of a catalytic amount of iodine. Mechanistically, the dissolution of gold begins when I₂ oxidizes Au⁰ and forms a [Au^II₂]⁻ species, which undergoes subsequent ligand‐exchange reactions and forms a stable bis‐ligand Au^I complex. H₂O₂ oxidizes free iodide and regenerated I₂ returns back to the catalytic cycle. Addition of a reductant to the reaction mixture precipitates gold quantitatively and partially regenerates the ligand. We anticipate our work will open a new pathway to more sustainable metal recycling with the utilization of just catalytic amounts of reagents and green solvents.

A Biodegradable and Recyclable Piezoelectric Sensor Based on a Molecular Ferroelectric Embedded in a Bacterial Cellulose Hydrogel

Currently, various electronic devices make our life more and more safe, healthy, and comfortable, but at the same time, they produce a large amount of nondegradable and nonrecyclable electronic waste that threatens our environment. In this work, we explore an environmentally friendly and flexible mechanical sensor that is biodegradable and recyclable. The sensor consists of a bacterial cellulose (BC) hydrogel as the matrix and imidazolium perchlorate (ImClO₄) molecular ferroelectric as the functional element, the hybrid of which possesses a high sensitivity of 4 mV kPa^-1 and a wide operational range from 0.2 to 31.25 kPa, outperforming those of most devices based on conventional functional biomaterials. Moreover, the BC hydrogel can be fully degraded into glucose and oligosaccharides, while ImClO₄ can be recyclable and reused for the same devices, leaving no environmentally hazardous electronic waste.

Examination of metal sorting and concentration technology in landfill mining -with focus on gravity and magnetic force sorting

The study focuses on the recovery of the minor metals contained in waste landfills. We have previously reported on the method of investigating the existing chemical morphology of each element in landfills, creating a high-concentration zone for a specific element, and non-destructively exploring the position of that within the block. In this study, a method for concentrating useful metals from landfills was examined, using samples taken from a concentrated zone. Specifically, the efficiency of physical sorting using gravity and a magnetic force was examined with samples collected from landfills mainly composed of incinerator ash. In the gravity sorting method, the resulting metal concentration is large when the heavy liquid specific gravity is 2.5 or 2.75 g/cm3 and above. Currently, sorting using a heavy liquid with a specific gravity of 2.75-3.0 g/cm3 is effective for increasing the metal concentration of the sample. Magnetic force sorting can efficiently separate metals and non-metals, and is effective as a pretreatment for a more advanced concentration stage. Various substances are mixed within the landfill waste, and several stages of sorting and concentration treatments are required to extract useful minor metals. A physical sorting method, such as the use of gravity or magnetic force is effective for the initial stage processing. Furthermore, when the metal to be extracted has been determined, a more effective concentration method based on the chemical form and characteristics of the target metal will be further examined for these pretreated samples.

Gravity and Electrostatic Separation for Recovering Metals from Obsolete Printed Circuit Board

This study proposed an evaluation of enrichment processes of obsolete Printed Circuit Boards (PCBs), by means of gravity and electrostatic separation, aiming at the recovery of metals. PCBs are the most important component in electronic devices, having high concentrations of metals and offering a secondary source of raw materials. Its recycling promotes the reduction in the environmental impacts associated with its production, use, and disposal. The recovery method studied started with the dismantling of the PCB, followed by a comminution and granulometric classification. Subsequent magnetic, gravity, and electrostatic separations were performed. After the separations, a macroscopic visual evaluation and chemical analysis were carried out, determining the metal content in the concentrate products. The results obtained from gravity separation showed a product with metallic concentrations of 89% and 76% for particle sizes of 0.3−0.6 mm and 0.6−1.18 mm, respectively. In electrostatic separation, the product obtained was 88% for the lower particle size (<0.3 mm) and 62% for particles sizes >1.18 mm.

Biologically engineered microbes for bioremediation of electronic waste: Wayposts, challenges and future directions

In the face of a burgeoning stream of e-waste globally, e-waste recycling becomes increasingly imperative, not only to mitigate the environmental and health risks it poses but also as an urban mining strategy for resource recovery of precious metals, rare Earth elements, and even plastics. As part of the continual efforts to develop greener alternatives to conventional approaches of e-waste recycling, biologically assisted degradation of e-waste offers a promising recourse by capitalising on certain microorganisms' innate ability to interact with metals or degrade plastics. By harnessing emerging genetic tools in synthetic biology, the evolution of novel or enhanced capabilities needed to advance bioremediation and resource recovery could be potentially accelerated by improving enzyme catalytic abilities, modifying substrate specificities, and increasing toxicity tolerance. Yet, the management of e-waste presents formidable challenges due to its massive volume, high component complexity, and associated toxicity. Several limitations will need to be addressed before nascent laboratory-scale achievements in bioremediation can be translated to viable industrial applications. Nonetheless, vested groups, involving both start-up and established companies, have taken visionary steps towards deploying microbes for commercial implementation in e-waste recycling.

Waste electrical and electronic equipments as urban mines in Burkina Faso: Characterization and release of metal particles

Like other developing countries, Burkina Faso is one of the preferential destinations for second-hand electrical and electronic equipments (EEE). At the end of their life, these EEEs are classified as waste electrical and electronic equipment (WEEE) including Printed Circuit Boards (PCB). A particle size reduction is realized for the release of metals by shredding and grinding to obtain particles smaller 1.5 mm. A granulometric sorting was realized and nine granulometric portions were obtained. Particles were characterized by optical microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (EDS). The experiments confirmed that the fractions contained polymers, glass fibers and metals under the form of single metals or alloys. The release of metal was efficient for particles with a size smaller than 0.71 mm. Three digestion procedures were experimented on four components to assess the impact on metals leaching. Microwave-assisted digestion method was the best procedure, compared to the analysis methods ISO 11466: 1995, and method 3050B, adapted. The characterization by Inductively coupled plasma atomic emission spectroscopy (ICP-AES) of these PCBs exhibited important amounts of precious metals (Ag, Au, Pd) and other metals in greater quantities (Cu, Pb, Ni, Co, etc.), leading to their qualification as "Urban Mines" calling for their recovery. The characterization of metals in each granulometric portion is realized. Precious and others metals were distributed in all granulometric size portions. So granulometric size reduction was not efficient for metal separation and recovery from PCBs and alternative methods should be investigated for selective precious metal recovery.

Electronic-Waste-Driven Pollution of Liquid Crystal Monomers: Environmental Occurrence and Human Exposure in Recycling Industrial Parks

Liquid crystal monomers (LCMs) in liquid crystal displays (LCDs) may be released into the environment, especially in electronic waste (e-waste) recycling industrial parks with a high pollution risk. However, little has been known about the environmental release and human exposure to LCMs until now. Herein, a total of 45 LCMs were detected in LCDs of commonly used smartphones and computers by high-resolution mass spectrometry with suspect screening analysis. Fluorinated biphenyls and their analogs were the dominant LCMs. Based on available standards of the screening results and previous studies, 55 LCMs were quantified in samples from an e-waste recycling industrial park in Central China. The LCMs were frequently detected in outdoor dust (n = 43), workshop #1 indoor dust (n = 53), and hand (n = 43) and forehead wipes (n = 43), with median concentrations of 6950 ng/g, 67,400 ng/g, 46,100 ng/m², and 62,100 ng/m², respectively. The median estimated daily intake values of the LCMs via dust ingestion and dermal absorption were 48.3 and 16.5 ng/kg body weight/day, respectively, indicating a high occupational exposure risk of these compounds. In addition, 16 LCMs were detected in the serum of eight elderly people (≥60 years old) with over 5 years of experience in e-waste dismantling operations, resulting in a total concentration range of 3.9-26.3 ng/mL.

Assessment of precious metals positioning in waste printed circuit boards and the economic benefits of recycling

In this study, the distribution of precious metals in waste printed circuit boards was investigated and the economic value of recycling was assessed. Contacts of pins, slots, interfaces and the board surface in waste printed circuit boards were analyzed, and three types of precious metals were detected. The content of gold, silver and palladium ranged from 179.86 mg/kg to 3694.51 mg/kg, 809 mg/kg to 12320.51 mg/kg and 96.25 mg/kg to 117.49 mg/kg, respectively. Gold was distributed wildly in contacts of many slots and all interfaces, while contacts of only two interfaces (the cable and USB) contained palladium. The highest content of Au was found in contacts of the cable. Silver mainly concentrated on pins (metal foil contacts) of electronic components and its highest content was found in microchips. The economic value of recyclable precious metals in 1 t waste printed circuit boards was up to 2292.94 dollars, of which Au contributed 98%. This study indicates the prominent economic benefits of precious metal recovery from waste printed circuit boards. Moreover, the scientific information provide guidance for the directional and accurate recovery of precious metals from waste printed circuit boards.

Environmental Nanoparticles Reach Human Fetal Brains

Anthropogenic ultrafine particulate matter (UFPM) and industrial and natural nanoparticles (NPs) are ubiquitous. Normal term, preeclamptic, and postconceptional weeks(PCW) 8–15 human placentas and brains from polluted Mexican cities were analyzed by TEM and energy-dispersive X-ray spectroscopy. We documented NPs in maternal erythrocytes, early syncytiotrophoblast, Hofbauer cells, and fetal endothelium (ECs). Fetal ECs exhibited caveolar NP activity and widespread erythroblast contact. Brain ECs displayed micropodial extensions reaching luminal NP-loaded erythroblasts. Neurons and primitive glia displayed nuclear, organelle, and cytoplasmic NPs in both singles and conglomerates. Nanoscale Fe, Ti, and Al alloys, Hg, Cu, Ca, Sn, and Si were detected in placentas and fetal brains. Preeclamptic fetal blood NP vesicles are prospective neonate UFPM exposure biomarkers. NPs are reaching brain tissues at the early developmental PCW 8–15 stage, and NPs in maternal and fetal placental tissue compartments strongly suggests the placental barrier is not limiting the access of environmental NPs. Erythroblasts are the main early NP carriers to fetal tissues. The passage of UFPM/NPs from mothers to fetuses is documented and fingerprinting placental single particle composition could be useful for postnatal risk assessments. Fetal brain combustion and industrial NPs raise medical concerns about prenatal and postnatal health, including neurological and neurodegenerative lifelong consequences.

E-waste it wisely: lessons from Africa

E-waste is the world’s fastest growing and most valuable domestic waste stream. The increasing production of e-waste is driving elevated levels of export from developed to developing countries. Although countries worldwide are actively recognising the issues around e-waste and introducing policies, legislation or regulations governing e-waste, a large fraction of e-waste, goes undocumented at its end-of-life. Much of the global e-waste is accumulating in open dumpsites in several African countries. Using available data, we calculate the total e-waste in Africa (locally produced plus imported e-waste) for 2019 to be between 5.8 and 3.4 metric tonnes (Mt). This is believed to be an underestimate, large data gaps exist, hindering more precise estimates. The data is further complicated by, sometimes intentional, differences in labelling and reporting between formal and intermittent informal importers. Based on the available data, the main African recipients of e-waste are Nigeria, Ghana, and Tanzania, with Kenya, Senegal and Egypt featuring as countries of concern. The lack of proper waste management in the recipient developing countries, leads to environmental contamination and human exposure. A coordinated, regional and global, approach is needed in tackling e-waste. Regulatory frameworks, together with monitoring and compliance mechanisms need to be developed, financed, and enforced.

An Overview of Modified Chitosan Adsorbents for the Removal of Precious Metals Species from Aqueous Media

This mini-review provides coverage of chitosan-based adsorbents and their modified forms as sustainable solid-phase extraction (SPE) materials for precious metal ions, such as gold species, and their complexes in aqueous media. Modified forms of chitosan-based adsorbents range from surface-functionalized systems to biomaterial composites that contain inorganic or other nanomaterial components. An overview of the SPE conditions such as pH, temperature, contact time, and adsorbent dosage was carried out to outline how these factors affect the efficiency of the sorption process, with an emphasis on gold species. This review provides insight into the structure-property relationships for chitinaceous adsorbents and their metal-ion removal mechanism in aqueous media. Cross-linked chitosan sorbents showed a maximum for Au(III) uptake capacity (600 mg/g), while S-containing cross-linked chitosan display favourable selectivity and uptake capacity with Au(III) species. Compared to industrial adsorbents such as activated carbon, modified chitosan sorbents display favourable uptake of Au(III) species, especially in aqueous media at low pH. In turn, this contribution is intended to catalyze further research directed at the rational design of tailored SPE materials that employ biopolymer scaffolds to yield improved uptake properties of precious metal species in aqueous systems. The controlled removal of gold and precious metal species from aqueous media is highly relevant to sustainable industrial processes and environmental remediation.

Performance of electronic waste based mixed metal oxide as novel oxygen carriers for chemical looping co-combustion of high ash coal and rice straw

Electronic waste (e-waste) is one of the major pollutants accumulated due to its huge demand and short lifespan. Hence, it is essential to reuse and extract the value added components from e-waste. In this context, firstly, a printed circuit board (PCB) is used to produce calorific valuable gases by pyrolysis and gasification reactions. Secondly, the resultant residue of PCB is combusted to extract metals such as iron, copper, nickel etc. as oxygen carriers for the chemical looping combustion (CLC) process. CLC is an emerging and appealing technology for producing rich CO₂ that can be directly sent for sequestration. In the present study, a detailed investigation is performed to ensure the reactivity of the e-waste based metal oxide with high ash coal, rice straw and their blends in the CLC process. CO₂ yield, gas conversion, and char conversion are evaluated to assess the performance of the co-combustion based CLC process. It is found that 90.9% CO₂ yield, 94.1% gas conversion and 93.2% char conversion can be obtained using the blends of coal and rice straw in the first cycle of the CLC operation. Further, a reduction of 5% to 7% of these parameters is evaluated at the end of the third consecutive cycle of CLC operations. The interaction between coal and rice straw is further studied by evaluating their synergistic effects, char-oxygen carrier interaction and kinetic parameters using a thermogravimetric analyzer under N₂ and CO₂ atmosphere. The co-combustion process has reduced the activation energy by 13.4% at 800-1000 °C under CO₂ atmosphere.

In-situ, Ex-situ, and nano-remediation strategies to treat polluted soil, water, and air - A review

Nanotechnology, as an emerging science, has taken over all fields of life including industries, health and medicine, environmental issues, agriculture, biotechnology etc. The use of nanostructure molecules has revolutionized all sectors. Environmental pollution is a great concern now a days, in all industrial and developing as well as some developed countries. A number of remedies are in practice to overcome this problem. The application of nanotechnology in the bioremediation of environmental pollutants is a step towards revolution. The use of various types of nanoparticles (TiO₂ based NPs, dendrimers, Fe based NPs, Silica and carbon nanomaterials, Graphene based NPs, nanotubes, polymers, micelles, nanomembranes etc.) is in practice to diminish environmental hazards. For this many In-situ (bioventing, bioslurping, biosparging, phytoremediation, permeable reactive barrier etc.) and Ex-situ (biopile, windrows, bioreactors, land farming etc.) methodologies are employed. Improved properties like nanoscale size, less time utilization, high adaptability for In-situ and Ex-situ use, undeniable degree of surface-region to-volume proportion for possible reactivity, and protection from ecological elements make nanoparticles ideal for natural applications. There are distinctive nanomaterials and nanotools accessible to treat the pollutants. Each of these methods and nanotools depends on the properties of foreign substances and the pollution site. The current designed review highlights the techniques used for bioremediation of environmental pollutants as well as use of various nanoparticles along with proposed In-situ and Ex-situ bioremediation techniques.

Biosorption and Bioleaching of Heavy Metals from Electronic Waste Varied with Microbial Genera

Industrialization and technological advancements have led to the exploitation of natural resources and the production of hazardous wastes, including electronic waste (E-waste). The traditional physical and chemical techniques used to combat E-waste accumulation have inherent drawbacks, such as the production of harmful gases and toxic by-products. These limitations may be prudently addressed by employing green biological methods, such as biosorption and bioleaching. Therefore, this study was aimed at evaluating the biosorption and bioleaching potential of seven microbial cultures using E-waste (printed circuit board (PCB)) as a substrate under submerged culture conditions. The cut pieces of PCB were incubated with seven microbial cultures in liquid broth conditions in three replicates. Atomic absorption spectroscopy (AAS) analysis of the culture biomass and culture filtrates was performed to evaluate and screen the better-performing microbial cultures for biosorption and bioleaching potentials. The best four cultures were further evaluated through SEM, energy-dispersive X-ray spectroscopy (EDX), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) studies to identify the possible culture that can be utilized for the biological decontamination of E-waste. The study revealed the highest and differential ability of Pleurotus florida and Pseudomonas spp. for biosorption and bioleaching of copper and iron. This can be attributed to bio-catalysis by the laccase enzyme. For both P. florida and Pseudomonas spp. on the 20th day of incubation, laccase exhibited higher specific activity (6.98 U/mg and 5.98 U/mg, respectively) than other microbial cultures. The biomass loaded with Cu2+ and Fe2+ ions after biosorption was used for the desorption process for recovery. The test cultures exhibited variable copper recovery efficiencies varying between 10.5 and 18.0%. Protein characterization through SDS-PAGE of four promising microbial cultures exhibited a higher number of bands in E-waste as compared with microbial cultures without E-waste. The surface topography studies of the E-waste substrate showed etching, as well as deposition of vegetative and spore cells on the surfaces of PCB cards. The EDX studies of the E-waste showed decreases in metal element content (% wt/% atom basis) on microbial treatment from the respective initial concentrations present in non-treated samples, which established the bioleaching phenomenon. Therefore, these microbial cultures can be utilized to develop a biological remediation method to manage E-waste.

Selective Chelating Resin for Copper Removal and Recovery in Aqueous Acidic Solution Generated from Synthetic Copper-Citrate Complexes from Bioleaching of E-waste

This research focused on batch experiment using a new generation of chelating resins via an ion exchange process to describe the metabolic adsorption and desorption capacity onto iminodiacetic acid/Chelex 100, bis-pyridylmethyl amine/Dowex m4195, and aminomethyl phosphonic/Lewatit TP260 functional groups in bioleaching. The results showed that Dowex m4195 had the highest performance of adsorption capacity for copper removal in both H+-form and Na+-form. Results for Lewatit TP260 and Chelex 100 revealed lower adsorption performance than results for Dowex m4195. The investigation of desorption from chelating resins was carried out, and it was found that 2 M ammonium hydroxide concentration provided the best desorption capacity of about 64.86% for the H+-form Dowex m4195 followed by 52.55% with 2 M sulfuric acid. Lewatit with 2 M hydrochloric acid gave the best desorption performance in Na+-form while Chelex 100 using hydrochloric at 1 M and 2 M provided similar results in terms of the H+-form and Na+-form. As aspects of the selective chelating resins for copper (II) ions in aqueous acidic solution generated from synthetic copper-citrate complexes from bioleaching of e-waste were considered, H+-form Dowex m4195 was a good performer in adsorption using ammonium hydroxide for the desorption. However, chelating resins used were subsequently reused for more than five cycles with an acidic and basic solution. It can be concluded from these results that selective chelating resins could be used as an alternative for the treatment of copper (II) ions contained in e-waste or application to other divalent metals in wastewater for sustainable water and adsorbent reuse as circular economy.

Thermodynamic Rarity Assessment of Mobile Phone PCBs: A Physical Criticality Indicator in Times of Shortage

Rising prices in energy, raw materials, and shortages of critical raw materials (CRMs) for renewable energies or electric vehicles are jeopardizing the transition to a low-carbon economy. Therefore, managing scarce resources must be a priority for governments. To that end, appropriate indicators that can identify the criticality of raw materials and products is key. Thermodynamic rarity (TR) is an exergy-based indicator that measures the scarcity of elements in the earth’s crust and the energy intensity to extract and refine them. This paper uses TR to study 70 Mobile Phone (MP) Printed Circuit Boards (PCBs) samples. Results show that an average MP PCB has a TR of 88 MJ per unit, indicating their intensive use of valuable materials. Every year the embedded TR increases by 36,250 GWh worldwide -similar to the electricity consumed by Denmark in 2019- due to annual production of MP. Pd, Ta and Au embedded in MP PCBs worldwide between 2007 and 2021 contribute to 90% of the overall TR, which account for 75, 600 and 250 tones, respectively, and increasing by 11% annually. This, coupled with the short lifespan of MP, makes PCBs an important potential source of secondary resources.

A Review on Global E-Waste Management: Urban Mining towards a Sustainable Future and Circular Economy

The trending need for smarter electrical and electronic equipment (EEE) is surging globally by the year and is giving rise to huge amounts of outdated EEE going into landfills. This has caused enormous threats to our environment and the health of living beings due to its unsustainable ways of collection, treatment and disposal of waste EEE or E-waste. With increasing E-waste, the formal sectors lack infrastructure, technology and expertise required to collect and process the E-waste in an environmentally sound manner. This article is intended to bring out the global best practices in the field of E-waste management, to shed light on the importance of policy implementation, technology requirement and social awareness to arrive at a sustainable and circular economy. Although about 71% of the world’s populace has incorporated E-waste legislation, there is a need to enforce and implement a common legal framework across the globe. The article explains the gap created among the stakeholders and their knowledge on the roles and responsibilities towards a legalized E-waste management. It further explains the lack of awareness on extended producer responsibility (EPR) and producer responsibility schemes. Despite various legislations in force, numerous illegal practices such as acid leaching, open incineration, illegal dumping carried out by the informal sector are causing harm to the environment, natural resources and the safety of unorganized and unskilled labor. The article discusses the crucial need for awareness amongst stakeholders, consumer behavior and the global challenges and opportunities in this field to achieve a low-carbon, circular economy. To conclude, the article highlights the importance of common legal framework, EPR and licenses, transformation of the informal sector, benchmark technologies, responsibilities of various stakeholders and entrepreneurial opportunities to enhance the formal capacity. The article wholly advocates for transparency, accountability and traceability in the E-waste recycling chain, thus creating a greener environment and protecting our planet and natural resources for future generations.

Electronic wastes: A near inexhaustible and an unimaginably wealthy resource for water splitting electrocatalysts

E-wastes comprise complex combinations of potentially toxic elements that cause detrimental effects of the environmental contamination; besides their posing threat, most of the products also contain valuable and recoverable materials (Li, Au, Ag, W, Se, Te, etc.), which make them distinct from other forms of industrial wastes. Most of these value-added elements which are primarily employed in electronic goods are disposed of by incineration and land-filling. This is a serious issue besides just environmental pollution, as IUPAC recognized that such ignorance of or poor attention to e-waste recycling has put several elements in the periodic table to the list of endangered elements. Recycling these wastes utilized for electrocatalytic water splitting to produce H₂. These recovered e-wastes materials are used as electrocatalysts for the water-splitting, additives to enhance reaction kinetics, and substrate electrodes as well. Recycling and recovery of value-added materials in the view of applying them to electrocatalytic water splitting with endangered elements' perspective have not been covered by any recent review so far. Hence, this review is dedicated to discussing the opportunities available with recycling e-wastes, types of value-added materials that can be recovered for water splitting, strategies exploited, and prospects are discussed in details.

A review on recent advancements in recovery of valuable and toxic metals from e-waste using bioleaching approach

This review is intent on the environmental pollution generated from printed circuit boards and the methods employed to retrieve valuable and hazardous metals present in the e-wastes. Printed circuit boards are the key components in the electronic devices and considered as huge e-pollutants in polluting our surroundings and the environment as a whole. Composing of toxic heavy metals, it causes serious health effects to the plants, animals and humans in the environment. A number of chemical, biological and physical approaches were carried out to recover the precious metals and to remove the hazardous metals from the environment. Chemical leaching is one of the conventional PCBs recycling methods which was carried out by using different organic solvents and chemicals. Need of high cost for execution, generation of secondary wastes in the conventional methods, forces to discover the advanced recycling methods such as hydrometallurgical, bio-metallurgical and bioleaching processes to retrieve the valuable metals generate through e-wastes. Among them, bioleaching process gain extra priority due to its higher efficiency of metal recovery from printed circuit boards. There are different classes of microorganisms have been utilized for precious metal recovery from the PCBs through bioleaching process such as chemolithoautotrophy, heterotrophy and different fungal species including Aspergillus sp. and Penicillium sp. The current status and scope for further studies in printed circuit boards recycling are discussed in this review.

Recovery of high-grade copper from metal-rich particles of waste printed circuit boards by ball milling and sieving

In this paper, a method of ball milling and sieving is proposed for recovery of high-grade copper from waste printed circuit boards (WPCBs). The effects of the milling time on the metals grade and recovery of the Cu, Sn and Pb during mechanical treatment were investigated. The results showed that, after 3 cycles of ball milling and sieving, the content of Cu was enriched to 94.72 wt.% from the initial 74.22 wt.% with a high recovery rate of 86.78%. Moreover, the contents of Sn and Pb were enriched to 28.27 wt.% and 18.86 wt.% from 10.13 wt.% and 6.63 wt.% in the by-products, respectively. However, excessive grinding occurred when the milling time was longer than 3 h and led to a sharp decrease in Cu recovery. The X-ray diffraction (XRD) patterns indicated that the metal phases mainly comprised pure Cu, Sn, Pb in the WPCB particles, while a Cu-Sn alloy was formed during the milling process, and the Cu-Sn alloy was also enriched in the tailings. The results presented here establish that ball milling and sieving is an alternative approach to recovering high-grade copper from WPCBs.

Greener reactants, renewable energies and environmental impact mitigation strategies in pyrometallurgical processes: A review

Abstract

Metals and alloys are among the most technologically important materials for our industrialized societies. They are the most common structural materials used in cars, airplanes and buildings, and constitute the technological core of most electronic devices. They allow the transportation of energy over great distances and are exploited in critical parts of renewable energy technologies. Even though primary metal production industries are mature and operate optimized pyrometallurgical processes, they extensively rely on cheap and abundant carbonaceous reactants (fossil fuels, coke), require high power heating units (which are also typically powered by fossil fuels) to calcine, roast, smelt and refine, and they generate many output streams with high residual energy content. Many unit operations also generate hazardous gaseous species on top of large CO₂ emissions which require gas-scrubbing and capture strategies for the future. Therefore, there are still many opportunities to lower the environmental footprint of key pyrometallurgical operations. This paper explores the possibility to use greener reactants such as bio-fuels, bio-char, hydrogen and ammonia in different pyrometallurgical units. It also identifies all recycled streams that are available (such as steel and aluminum scraps, electronic waste and Li-ion batteries) as well as the technological challenges associated with their integration in primary metal processes. A complete discussion about the alternatives to carbon-based reduction is constructed around the use of hydrogen, metallo-reduction as well as inert anode electrometallurgy. The review work is completed with an overview of the different approaches to use renewable energies and valorize residual heat in pyrometallurgical units. Finally, strategies to mitigate environmental impacts of pyrometallurgical operations such as CO₂ capture utilization and storage as well as gas scrubbing technologies are detailed. This original review paper brings together for the first time all potential strategies and efforts that could be deployed in the future to decrease the environmental footprint of the pyrometallurgical industry. It is primarily intended to favour collaborative work and establish synergies between academia, the pyrometallurgical industry, decision-makers and equipment providers.

Graphical abstract

Highlights

A more sustainable production of metals using greener reactants, green electricity or carbon capture is possible and sometimes already underway. More investments and pressure are required to hasten change.

Discussion

Is there enough pressure on the aluminum and steel industries to meet the set climate targets?The greenhouse gas emissions of existing facilities can often be partly mitigated by retrofitting them with green technologies, should we close plants prematurely to build new plants using greener technologies?Since green or renewable resources presently have limited availability, in which sector should we use them to maximize their benefits?

Analytical and reclamation technologies for identification and recycling of precious materials from waste computer and mobile phones

Waste electrical and electronic equipment (WEEE) is one of the world's fastest-growing class of waste. WEEE contain a large amount of precious materials that have aroused the interest to develop new recycling technologies. Hence, effective recycling strategies are extremely necessary to promote the proper handling of these materials as well as for environmentally sound recovery of secondary raw resource. This paper reviews important existing methods and emerging technologies in WEEE management, with special emphasis in characterization, extraction and reclamation of precious materials from waste computer and mobile phones. Traditional pyrometallurgical and hydrometallurgical technologies still play a central role in the recovery of metals. More recently, emerging greener recycling technologies using microorganisms (i.e. biometallurgical), plasma arc fusion method and pretreatments (i.e. ultrasound and mechanochemical technologies) combined with other recycling methods (e.g. hydrometallurgical), and using less toxic solvents such as ionic liquids (ILs) and deep eutectic solvents (DESs) have also been attempted to recycle metals from computer and mobile phone scrap. The role of analytical method development, especially using spectroanalytical methods for chemical inspection and e-waste sorting process at industrial applications is also discussed. This confirmed that most direct sampling techniques such as laser-induced breakdown spectroscopy (LIBS) and X-ray fluorescence (XFR) have several advantages over traditional sorting methods including rapid analytical response, without use of chemical reagents or waste generation, and greater reclamation of precious and critical materials in the WEEE stream.

Review on the Use of Heavy Metal Deposits from Water Treatment Waste towards Catalytic Chemical Syntheses

The toxicity and persistence of heavy metals has become a serious problem for humans. These heavy metals accumulate mainly in wastewater from various industries' discharged effluents. The recent trends in research are now focused not only on the removal efficiency of toxic metal particles, but also on their effective reuse as catalysts. This review discusses the types of heavy metals obtained from wastewater and their recovery through commonly practiced physico-chemical pathways. In addition, it covers the advantages of the new system for capturing heavy metals from wastewater, as compared to older conventional technologies. The discussion also includes the various structural aspects of trapping systems and their hypothesized mechanistic approaches to immobilization and further rejuvenation of catalysts. Finally, it concludes with the challenges and future prospects of this research to help protect the ecosystem.

Industrial wastewater treatment: Current trends, bottlenecks, and best practices

Rapid urbanization and industrialization have inextricably linked to water consumption and wastewater generation. Mining resources from industrial wastewater has proved to be an excellent source of secondary raw materials i.e., proficient for providing economic and financial benefits, clean and sustainable resilient environment, and achieving sustainable development goals (SDGs). Treatment of industrial wastewater for reusable resources has become a tedious task for decision-makers due to several bottlenecks and barriers, such as inefficient treatment options, high-cost expenditure, poor infrastructure, lack of financial support, and technical know-how. Most of the existing methods are conventional and fails to provide an economic benefit to the industries and have certain disadvantages. Also, the untreated industrial wastewater is discharged into the open drains, lakes, and rivers that lead to environmental pollution and severe health hazards. This paper has consolidated information about the current trends, opportunities, bottlenecks, and best practices associated with wastewater treatment and scope for the advancement in the existing technologies. Along with the efficient resource recovery, the wastewater could be ideally explored in the development of value-added materials, energy, and product recovery. The concepts, such as the circular economy (CE), partitions-release-recover (PRR), and transforming wastewater into bio factory are anticipated to be more convenient options to tackle the industrial wastewater menace.

Miniaturization of Anthracene-Containing Nonapeptides for Selective Precipitation/Recovery of Metallic Gold from Aqueous Solutions Containing Gold and Platinum Ions

The separation and recovery of noble metals is increasingly of interest, in particular the recovery of gold nanocrystals, which have applications in medicine and industry. Typically, metal recovery is performed using liquid–liquid extraction or electrowinning. However, it is necessary to develop noble metal recovery systems providing high selectivity in conjunction with a one-pot setup, ready product recovery, and the use of dilute aqueous solutions. In prior work, our group developed a selective gold recovery process using peptides. This previous research showed that RU065, a nonapeptide containing an anthracene moiety (at a concentration of 2.0 × 10−4 M), is capable of selective reduction of HAuCl4 to recover gold from a solution of HAuCl4 and H2PtCl6, each at 5.0 × 10−5 M. However, peptide molecules are generally costly to synthesize, and therefore it is important to determine the minimum required structural features to design non-peptide anthracene derivatives that could reduce operational costs. In this study, we used RU065 together with 23 of its fragment peptides and investigated the selective precipitation/recovery of metallic gold. RU0654–8, a fragment peptide comprising five amino acid residues (having two lysine, one L-isoleusine, and one L-alanine residue (representing six amide groups) along with an L-2-anthrylalanine residue) provided an Au/Pt atomic ratio of approximately 8, which was comparable to that for the full-length original RU065. The structural features identified in this study are expected to contribute to the design of non-peptide anthracene derivatives for low-cost, one-pot selective gold recovery.

Optimization of elemental recovery from electronic wastes using a mild oxidizer

In this work, metals were recovered from electronic wastes under optimized conditions. The columnar extraction was used to increase the contact between the leachate solution and solid-state wastes. Industrial metals were recovered by an electrochemical process using a regenerated mild oxidizer under optimized operating parameters to enrich the metal concentrations and reduce waste generation. The maximum recovery rate (1.135 mg·min^-1) was recorded under the optimized conditions (160 A·m^-2 current density, 7 mL·min^-1 leachate flow rate, and 0.8 mol·L^-1 ferric concentration). The selective columnar extraction process was employed to extract gold, wherein the highest extraction efficiency (69.39%) was obtained under optimized conditions of 0.7 mol·L^-1 thiourea, 0.6 mol·L^-1 hydrochloric acid, 0.8 mol·L^-1 ferric chloride, 120 min circulation time, and 6 mL·min^-1 leachate flow rate. The adsorption process was used for the recovery of gold, which was investigated under the kinetic as well as equilibrium adsorption processes. The adsorption curves conformed to the Langmuir model and followed the first-order kinetics. The adsorption rate decreased with the increasing values of pH, temperature, adsorbent size, while the rate increased with the stirring speed and adsorbent quantity. Finally, acidic extraction under anaerobic and optimal conditions was performed to extract and selectively recover rare-earth elements. The rare-earth elements were initially precipitated in their sulfate forms and subsequently transformed into corresponding hydroxides and oxides. The total recovery efficiencies for cerium and neodymium were found to be 91.7% and 86.7%, respectively.

Novel trends in the thermo-chemical recycling of plastics from WEEE containing brominated flame retardants

The amount of plastics from waste electric and electronic equipment (WEEE) has enormously increased nowadays, due to the rapid expansion and consumption of electronic devices and their short lifespan. This, in combination with their non-biodegradability, led to the need to explore environmentally friendly solutions for their safe disposal. One main obstacle when recycling plastics from WEEE is that they usually comprise harmful additives such as brominated flame retardants (BFRs) that need to be removed before or during their recycling. This paper reviews existing techniques for the recycling of plastics from WEEE and focuses specifically on the advantages, disadvantages, and challenges of pyrolysis as an environmentally friendly method for the production of value-added materials (monomers, hydrocarbons, phenols, etc.). Current technological trends available for the recycling of plastics containing brominated flame retardants are reviewed in an attempt to provide insights for future research on the sustainable management of plastics from WEEE. Emphasis is given on conventional pyrolysis, where a pretreatment step for the debromination of products is applied. This is required since brominated compounds treated at high temperatures may result in the production of harmful to health compounds such as dioxins. All current pretreatment methods (solvent extraction, supercritical fluid technology, etc.) are presented and compared in detail. Co-pyrolysis is also investigated, as it seems to be a very interesting approach, since no catalysts or solvents are used, and at the same time, more plastic wastes can be consumed as feedstock. Furthermore, catalytic pyrolysis along with key parameters, such as the type of the catalyst or pyrolysis temperature, are fully analyzed. Catalysts affect the products' distribution and enhance the removal of bromine from pyrolysis oils. Finally, an emerging technique, that of microwave-assisted pyrolysis, is also highlighted, as it offers many advantages over conventional pyrolysis. Of course, there are some impediments, such as the operational costs or other difficulties as regards the industrial implementation of the mentioned techniques that need to be overcome through future works.

Simple and near-zero-waste processing for recycling gold at a high purity level from waste printed circuit boards

This work proposes an efficient and simple hydrometallurgical process based on a chlorination step followed by an ion-exchange step for recycling gold (Au) from a waste printed circuit boards (WPCBs) enriched in Au resulting from a first leaching step under mild oxidizing conditions for extracting Cu and other base metals. Under optimized [3.5 mol/L HCl and 0.46 mol/L NaClO, with a liquid/solid (L/S) ratio of 40, at 40 °C for 3 h with agitation] leaching conditions, 95% Au was extracted from the residue originating a multi-metal solution containing 1.0% Au. Subsequently, Au (initial concentration: 38 µmol/L) present in the multimetal-leached solution was purified in continuous mode using two strong anionic exchange resins: DOW™ XZ-91419.00 and Purogold™ A194. Both resins were suitable in purifying Au from the multimetal-leaching solution, with at least 70% of Au recovered relative to the initial residue. When the DOW™ XZ-91419.00 resin was used, a solution containing 1.7 mmol/L Au with a purity grade of 94% was obtained, with Pb and Sn being the major contaminants (3.3 and 2.4%, respectively). For Purogold™ A194 resin, a solution containing 0.73 mmol/L Au with a purity grade of 92% was achieved; Ag, Pb and Pd were the major contaminants (1.4, 3.6 and 1.8%, respectively). In conclusion, this work demonstrates a novel hydrometallurgical strategy for recycling Au with a high grade from WPCBs, minimizing the number of leaching and purification steps and the amount of waste created.

Electronic Waste Low-Temperature Processing: An Alternative Thermochemical Pretreatment to Improve Component Separation

The production of electronic waste due to technological development, economic growth and increasing population has been rising fast, pushing for solutions before the environmental pressure achieves unprecedented levels. Recently, it was observed that many extractive metallurgy alternatives had been considered to recover value from this type of waste. Regarding pyrometallurgy, little is known about the low-temperature processing applied before fragmentation and subsequent component separation. Therefore, the present manuscript studies such alternative based on scanning electron microscopy characterization. The sample used in the study was supplied by a local recycling center in Rio de Janeiro, Brazil. The mass loss was constant at around 30% for temperatures higher than 300 °C. Based on this fact, the waste material was then submitted to low-temperature processing at 350 °C followed by attrition disassembling, size classification, and magnetic concentration steps. In the end, this first report of the project shows that 15% of the sample was recovered with metallic components with high economic value, such as Cu, Ni, and Au, indicating that such methods could be an interesting alternative to be explored in the future for the development of alternative electronic waste extraction routes.