Thermal degradation and pollutant emission from waste printed circuit boards mounted with electronic components

Lagging pollution of polycyclic aromatic hydrocarbons in the rebuilt e-waste site: From the perspective of characteristics, sources, and risk assessment

Little information is known regarding how the lagged pollution of polycyclic aromatic hydrocarbon (PAH) influenced the environment and human health after an e-waste dismantling site was rebuilt. This study investigated the characteristics, sources, and risk assessment of PAHs in a rebuilt e-waste site and its surrounding farmland by analyzing the samples of soil, dust, water, and vegetable. Concentrations of PAHs in soil, vegetable and water in the rebuilt site were relatively higher than in its surrounding farmland. The concentrations in surface soils, soil columns, dust, vegetables, and water varied from 55.4 to 3990 ng g-1, 1.65 to 5060 ng g-1, 2190 to 2420 ng g-1, 2670 to 10,300 ng g-1, and 46.8 to 110 μg L-1 in the e-waste site, respectively. On the farmland, PAH concentrations in surface soils, vegetables, and water ranged from 41.5 to 2760 ng g-1, 506 to 7640 ng g-1, and 56.6 to 89.2 μg L-1, respectively. A higher proportion of high-molecular-weight PAHs (HMW-PAHs) appeared in all multimedia compared with low-molecular-weight PAHs (LMW-PAHs). Diagnostic ratio together with positive matrix factorization (PMF) revealed that vehicle emission was the primary source in this area, and the activity of e-waste disposal was another important source in the rebuilt e-waste site. Based on the deterministic health risks, people working in the reconstructed e-waste site were exposed to low risks, whereas the residents living near the surrounding farmland were exposed to low risk. Sensitivity analyses indicated that exposure frequency and PAH concentrations were the main factors that influenced exposure risk. This study provides valuable insight into the comprehension of the lagging pollution effects of PAH on the environment and human health after the e-waste site was rebuilt.

A novel subcritical water synergistic co-treatment of brominated epoxy resin and copper-based spent catalysts: debromination, phenol production, and copper recovery

In this study, a high-efficiency co-treatment strategy for brominated epoxy resin (BER) and copper-based spent catalyst (CBSC) was developed by using subcritical water (SubCW) process. Multivalent species of copper released from CBSC could accelerate the electron transfer of the SubCW system and efficiently catalyze radical reactions to promote the debromination and decomposition of BER, and had an effect on the capture and binding of bromine species. Meanwhile, the formation of HBr by the BER debromination resulted in a decrease in the system pH and markedly enhanced the leaching/recovery of Cu from CBSC. The optimal conditions of the SubCW co-treatment process were as follows: reaction temperature of 350 °C, solid-to-liquid ratio of 1:30 g/mL, BER-to-CBSC mass ratio of 10:1 g/g, and reaction time of 60 min. Under the optimal conditions, 97.12 % of the Br could be removed from BER by the SubCW co-treatment process and a high-purity phenol (64.09 %) could be obtained in the oil phase product, and 86.44 % of Cu in the CBSC could be leached and recovered. The introduction of CBSC significantly changed the decomposition path of BER. Compared to the SubCW process without CBSC, bromine-free oils products could be obtained by the co-treatment process of BER and CBSC at low-temperature. This study provided a novel understanding of resource conversion mechanism of BER and CBSC in subcritical water medium via the synergistic effect between the two different waste streams to improve treatment efficiency and synchronously recover high-value products.

A computer vision-based system for real-time component identification from waste printed circuit boards

With an exponential increase in consumers' need for electronic products, the world is facing an ever-increasing economic and environmental threat of electronic waste (e-waste). To minimize their adverse effects, e-waste recycling is one of the pivotal factors that can help in minimizing the environmental pollution andto increase recovery of valuable materials. For instance, Printed Circuit Boards (PCBs), while they have several valuable elements, they are hazardous too; and therefore, they form a large chunk of e-waste being generated today. Thus, in recycling PCBs, Electronic Components (ECs) are segregated at first, and separately processed for recovering key elements that could be re-used. However, in the current recycling process, especially in developing nations, humans manually screen ECs, which goes on to affect their health. It also causes losses of valuable materials. Therefore, automated solutions need to be adopted for both to classify and to segregate ECs from waste PCBs. The study proposes a robust EC identification system based on computer vision and deep learning algorithms (YOLOv3) to automate sorting process which would help in further processing. The study uses a publicly available dataset, and a PCB dataset which reflect challenging recycling environments like lighting conditions, cast shadows, orientations, viewpoints, and different cameras/resolutions. The outcome of YOLOv3 detection model based on training of both datasets presents satisfactory classification accuracy and capability of real-time competent identification, which in turn, could help in automatically segregating ECs, while leading towards effective e-waste recycling.

Mechanochemical debromination of allyl 2,4,6-tribromophenyl ether (TBP-AE): optimization of the operational conditions

Allyl 2,4,6-tribromophenyl ether (TBP-AE) is a flame retardant that is added to plastics to improve their fire resistance. This kind of additive is hazardous to both human health and the environment. As any other BFRs, TBP-AE resists photo-degradation in the environment and hence materials laden with TBP-AE are to be dibrominated to avoid environmental pollution. Mechanochemical degradation of TBP-AE is a promising approach with potential industrial applications since it does not require high temperatures nor it generates any secondary pollutants. A planetary ball milling simulation experiment was designed to study TBP-AE's mechanochemical debromination. To report products from the mechanochemical process, a variety of characterization techniques were used. The characterization methods included gas chromatography-mass spectrometry (GC-MS), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) with energy-dispersive X-ray analysis (EDX). The effects of various co-milling reagent types, co-milling reagent concentrations with raw material, time, and revolution speed on mechanochemical debromination efficiency have been thoroughly investigated. The Fe/Al2O3 mixture entails the highest debromination efficiency of 23%. However, when using a Fe/Al2O3 mixture, neither the reagent concentration nor the revolution speed influenced the debromination efficiency. In case of using only Al2O3, the next viable reagent, it was revealed that while increasing the revolution, speed improved debromination efficiency to a certain point, and increasing it any further left the debromination efficiency unchanged. In addition, the results showed that an equal mass ratio of TBP-AE to Al2O3 promoted degradation more than an increase in the ratio of Al2O3 to TBP-AE. The addition of ABS polymer largely inhibits the reaction between Al2O3 and TBP-AE, which hindered alumina's ability to capture organic bromine, causing a significant decrease in the debromination efficiency when model of waste printed circuit board (WPCB) is considered.

Enhanced bromine fixation and tar lightweighting in co-pyrolysis of non-metallic fractions of waste printed circuit boards with Bayer red mud

A co-pyrolysis process for non-metallic fractions (NMFs) from WPCBs with Bayer red mud (RM) is proposed to upgrade pyrolysis products in this study. High bromine fixation efficiency was realized, and higher content of lightweight pyrolysis tar was obtained. The mechanism of catalytic pyrolysis and simultaneous bromine fixation of NMFs by RM was investigated by experiments and theoretical calculations. The three inorganic components of Fe₂O₃, CaCO₃ and Al₂O₃ in RM played key roles in the catalytic pyrolysis of NMFs, and their order of catalytic debromination effect was CaCO₃ > Fe₂O₃ > Al₂O₃. By adding 15 wt% RM, the pyrolysis solid residue could fix 89.55 wt% bromine, compared with 35.42 wt% of NMFs without adding RM, due to the formation of FeBr₂ and CaBr₂ from Fe₂O₃ and CaCO₃ in RM, respectively. Tar lightweighting was realized by reducing the energy barrier of the direct decomposition of tetrabromobisphenol A (TBBPA) in NMFs. The order of effect of the three key components on the tar lightweighting was Fe₂O₃ > Al₂O₃ > CaCO₃. The content of lightweight tar in the tar obtained by catalytic pyrolysis of NMFs with 15 wt% RM was 44.29% higher than that in the tar obtained by direct pyrolysis of NMFs. This work provides a theoretical guidance for the low-cost and eco-friendly recycling of e-wastes by co-pyrolysis with RM.

Comprehensive characterization and environmental implications of spent telecommunication printed circuit boards: Towards a cleaner and sustainable environment

The management and prevention of environmental risks associated with spent telecommunications printed circuit boards (STPCBs) is a concerning issue worldwide. Recycling might be proposed as a proper method to overcome this issue. Despite knowing that, choosing a sustainable method is challenging because of STPCBs complexity. This problem was overcome by analyzing STPCBs using different analytical methods and metal speciation. Understanding these data is essential in selection strategies to maximize selective recycling of metals and to minimize environmental impact. This research focused on characterizing STPCBs based on their structural, morphological, physiochemical, surface, and thermal properties. The accurate measurement of metal contents, indicating 187,900 mg kg^-1 Cu, 22,540 mg kg^-1 Pb, 1320 mg kg^-1 Ag, and 205 mg kg^-1 Au elements, plus other base metals, revealed a remarkable potential value in STPCBs. The results of structural analyses indicated that the powder has a crystalline structure and consists of Cu, Sn and Pb phases as well as different functional groups. In addition, after evaluating the zeta potential of the sample, the isoelectric pH of the sample was observed to be 5.6, which indicates that the powder particles have a negative surface in an environment with a pH higher than this value. Further, the metal speciation via sequential extraction procedure was performed, which showed that a unique harsh recycling strategy is required due to the stable structure of STPCBs. According to the results of this analysis, the global contamination factor (GCF) value was 83.48, which indicates STPCBs have a high degree of contamination. Leaching tests and environmental criteria were also conducted on this waste. The findings suggest that STPCBs needs pretreatments before landfilling to lower the concentration of toxic metals. Also, waste extraction test was the most aggressive procedure to assess mobility. Achieving this information is considered an essential step to choosing the most efficient recycling methods that minimize environmental impact while maximizing selective recycling of metals.

Toward Sustainable Wearable Electronic Textiles

Smart wearable electronic textiles (e-textiles) that can detect and differentiate multiple stimuli, while also collecting and storing the diverse array of data signals using highly innovative, multifunctional, and intelligent garments, are of great value for personalized healthcare applications. However, material performance and sustainability, complicated and difficult e-textile fabrication methods, and their limited end-of-life processability are major challenges to wide adoption of e-textiles. In this review, we explore the potential for sustainable materials, manufacturing techniques, and their end-of-the-life processes for developing eco-friendly e-textiles. In addition, we survey the current state-of-the-art for sustainable fibers and electronic materials (i.e., conductors, semiconductors, and dielectrics) to serve as different components in wearable e-textiles and then provide an overview of environmentally friendly digital manufacturing techniques for such textiles which involve less or no water utilization, combined with a reduction in both material waste and energy consumption. Furthermore, standardized parameters for evaluating the sustainability of e-textiles are established, such as life cycle analysis, biodegradability, and recyclability. Finally, we discuss the current development trends, as well as the future research directions for wearable e-textiles which include an integrated product design approach based on the use of eco-friendly materials, the development of sustainable manufacturing processes, and an effective end-of-the-life strategy to manufacture next generation smart and sustainable wearable e-textiles that can be either recycled to value-added products or decomposed in the landfill without any negative environmental impacts.

Oxidative and pyrolytic decomposition of an evaporated stream of 2,4,6-tribromophenol over hematite: A prevailing scenario during thermal recycling of e-waste

Brominated flame retardants (BFRs) constitute a major load in the polymeric fraction of e-waste. Degradation of BFRs-laden plastics over transition metal oxides is currently deployed as a mainstream strategy in the disposal and treatment of the non-metallic segment of e-waste. However, interaction of pyrolysis's products of BFRs with transition metal oxides is well-known to facilitate the formation of notorious pollutants. Despite recent progress to comprehend the germane chemistry of this interaction, several important pertinent aspects remain to be addressed. To fill in this gap, an integrated experimental and simulation account of the pyrolytic and oxidative decomposition of a gaseous stream of 2,4,6-tribromophenol (TBP) over hematite (Fe2O3) has been reported herein. TBP is utilized as a model compounds of BFRs as their most common formulations include brominated phenolic rings. Overall, hematite entails a rather low cracking capacity under pyrolytic conditions. Analysis of condensate products indicates that oxidative degradation of a gaseous stream of TBP results mainly in the formation of brominated alkanes such as bromoethane and bromo-pentane. Likewise, Ion chromatography (IC) measurements disclosed a noticeable reduction in the concentrations of escaped HBr. Transformation of iron oxides into iron bromides (possibly in the form of FeBr2) during pyrolysis and combustion operations is evident through XRD measurements. Density functional theory (DFT) calculations map out important reactions pathways that operate in the initial degradation of the TBP molecule. From a broader perspective, outlined results shall be instrumental to precisely assess the effectiveness of using iron oxides in thermal catalytic recycling of e-waste and the likely emission of brominated toxicants.

Mechanistic insights into catalysis of in-situ iron on pyrolysis of waste printed circuit boards: Comparative study of kinetics, products, and reaction mechanism

Pyrolysis is a potential recovery method for waste printed circuit boards (WPCBs), but the organic brominated products are toxic and hazardous. Iron has been used as a catalyst for debromination from pyrolysis oil, but the effects of in-situ iron on WPCBs pyrolysis is still not well understood. Herein, the pyrolysis mechanism for laminates of PCBs in the absence and presence of iron was studied via analyzing pyrolysis characteristics, kinetics, and products. According to the thermogravimetry experiments, pyrolysis of all samples could be divided into four stages, and iron accelerated the pyrolysis reaction by decreasing the activation energy as calculated using the Starink method. Volatiles released during the heating process were continuously determined by TG-FTIR-MS, and products generated at different pyrolysis temperatures were collected and characterized. The obtained results exhibited that iron promoted the generation of gaseous products and facilitated the conversion of organic bromides to inorganic bromides. Therefore, retaining iron was beneficial to energy saving and environmental protection for WPCBs pyrolysis. In addition, the decomposition mechanisms of brominated epoxy resin with and without iron were proposed. This work would contribute to the improvement and application of WPCBs pyrolysis technology.

Removal of Bromine from the non-metallic fraction in printed circuit board via its Co-pyrolysis with alumina

The effectiveness of a recycling approach of the printed circuit board (PCBs), and, thus, the quality of polymeric constituents, primarily rests on the capacity to eliminate the bromine content (mainly as HBr). HBr is emitted in appreciable quantities during thermal decomposition of PCB-contained brominated flame retardants (BFRs). The highly corrosive, yet relatively reactive HBr, renders recovery of bromine-free hydrocarbons streams from brominated polymers in PCBs very challenging. Via combined experimental and theoretical frameworks, this study explores the potential of deploying alumina (Al₂O₃) as a debromination agent of Br-containing hydrocarbon fractions in PCBs. A consensus from a wide array of characterization techniques utilized herein (ICP-OES, IC, XRD, FTIR, SEM-EDX, and TGA) clearly demonstrates the transformation of alumina upon its co-pyrolysis with the non-metallic fractions of PCBs, into aluminum bromides and oxy-bromides. ICP-OES measurements disclose the presence of high concentration of Cu in the non-metallic fraction of PCB, along with minor levels of selected valuable metals. Likewise, elemental ionic analysis by IC demonstrates an elevated concentration of bromine in washed alumina-PCBs pyrolysates, especially at 500 °C. The Coats-Redfern model facilitates the derivation of thermo-kinetic parameters underpinning the thermal degradation of alumina-PCB mixtures. Density functional theory calculations (DFT) establish an accessible reaction pathway for the HBr uptake by the alumina surface, thus elucidating chemical reactions governing the observed alumina debromination activity. Findings from this study illustrate the capacity of alumina as a HBr fixation agent during the thermal treatment of e-waste.

An automatic sorting system for electronic components detached from waste printed circuit boards

Recycling e-waste makes for eliminating the pollution to environment and recovering critical materials as one of resource. Printed circuit boards (PCBs) serve as the important part in all e-waste, containing valuable but hazardous elements to be recycled when they reach the end of life. For the recycling of waste PCB, the electronic components (ECs) are liberated from base board and to be treated separately for element recovery. Due to the diverse element composition, ECs deserve to be further classified and sorted to improve the efficiency of recycling, achieving the concept of accurate recovery. Currently, the recycling industry only roughly screen the ECs manually by labors, which increases the risk of health for exposure to the hazardous environment. Automatic solutions are necessary for replacing labors to classify and sort the waste ECs, thus safeguarding them against the hazards of factory environment. In this work, the YOLO-V3, an emerging image detection algorithm, is utilized to train the self-made dataset and classify the ECs into specific categories. To avoid surface damage that weakens the accuracy of object detection, the technology process of detaching the ECs is improved by building a nitrogen atmosphere during the desoldering process, which delivers great protection effects on ECs. Results of YOLO-V3 detection model present satisfactory classification capability for all the classes of ECs and a smart on-line sorting system is proposed to automatically separate the ECs detached from WPCB.

Dismantling of Printed Circuit Boards Enabling Electronic Components Sorting and Their Subsequent Treatment Open Improved Elemental Sustainability Opportunities

This critical review focuses on advanced recycling strategies to enable or increase recovery of chemical elements present in waste printed circuit boards (WPCBs). Conventional recycling involves manual removal of high value electronic components (ECs), followed by raw crushing of WPCBs, to recover main elements (by weight or value). All other elements remain unrecovered and end up highly diluted in post-processing wastes or ashes. To retrieve these elements, it is necessary to enrich the waste streams, which requires a change of paradigm in WPCB treatment: the disassembly of WPCBs combined with the sorting of ECs. This allows ECs to be separated by composition and to drastically increase chemical element concentration, thus making their recovery economically viable. In this report, we critically review state-of-the-art processes that dismantle and sort ECs, including some unpublished foresight from our laboratory work, which could be implemented in a recycling plant. We then identify research, business opportunities and associated advanced retrieval methods for those elements that can therefore be recovered, such as refractory metals (Ta, Nb, W, Mo), gallium, or lanthanides, or those, such as the platinum group elements, that can be recovered in a more environmentally friendly way than pyrometallurgy. The recovery methods can be directly tuned and adapted to the corresponding stream.

Volatile organic compounds in an e-waste dismantling region: From spatial-seasonal variation to human health impact

The dismantling of electrical and electronic waste (e-waste) can release various Volatile organic compounds (VOCs), impacting the surrounding ambient environment. We investigated the spatio-temporal characteristics and health risks of the ambient VOCs emitted in a typical e-waste dismantling region by conducting multi-site sampling campaigns in four seasons. The pollution of benzene, toluene, ethylbenzene, and xylenes (BTEX) in the e-waste dismantling park has relation to e-waste dismantling by seasonal trend analysis. The highest concentrations of most VOCs occurred in winter and autumn, while the lowest levels were observed in summer and spring. The spatial distribution map revealed the e-waste dismantling park to be a hotspot of BTEX, 1,2-dichloropropane (1,2-DCP), and 1,2-dichloroethane (1,2-DCA), while two major residential areas were also the hotspots of BTEX. The e-waste emission source contributed 20.14% to the total VOCs in the e-waste dismantling park, while it was absent in the major residential and rural areas. The cancer risk assessment showed that six VOCs exceeded 1.0 × 10^-6 in the e-waste dismantling park, while only three or four compounds exceeded this risk in other areas. The noncancer risks of all compounds were below the safety threshold. This study supplements the existing knowledge on VOC pollution from e-waste dismantling and expands the research scope of chemical pollution caused by e-waste.

Application of plasma technology for treating e-waste: A review

This review details the current information on e-waste treatment using plasma technology. The current status of e-waste treatment via plasma technology from the scientific literature is presented herein, namely, moist paste battery, galvanic sludge, resin, printed circuit board, and semiconductor industries. The concept of plasma technology, classification of e-waste, contaminants of e-waste (metals, metalloids, and VOCs), and vitrification of the final product are presented herein. This review paper focuses on fusing flux agents to vitrify e-waste. Furthermore, this paper covers laboratory-scale investigations, plasma technology benefits, and reuse of material from plasma post-treatment. The use of plasma technology combined with flux agents could be recommended to eliminate contaminants from e-waste. Materials from plasma post-treatment may also be applied in environmental reuse applications.

Preparation and performance characteristics of an environmentally-friendly agglomerant to improve the dry dust removal effect for filter material

The incomplete and uneven dust removal of a pulse filter greatly reduces the dust removal efficiency, which affects the efficiency, service life, and running resistance of dust removers. Therefore, due to improve the pulse cleaning effect, an agglomerant developed by free radical polymerization was added during dust removal. The optimal process conditions were determined by measuring the viscosity, surface tension, and atomization effect of the agglomerant solution. The phases, chemical composition, surface morphology, and morphology of the agglomerant and coal dust were characterized by infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. Molecular dynamics simulations were used to study the interaction mechanism between the agglomerant and coal dust. Finally, the dust removal performance under water mist conditions and agglomerate solution atomization was tested using a pulse filter. The results showed that a 0.3 % agglomerant solution effectively reduced the surface tension of the solution and displayed good wetting and bonding properties. Compared with water misting, the agglomerant solution subjected to an atomization rate of 2400 m³/h prolonged the filtration period, reduced the filtration resistance, and reduced the dust emission concentration. These results have important theoretical and practical significance for improving the dust removal effect of pulse filters.

Recent advances in surface and interface design of photocatalysts for the degradation of volatile organic compounds

Photocatalysis has attracted wide attention in eliminating volatile organic compounds (VOCs). This paper pays attention to the relationship between structure and performance of photocatalysts based on the fact that catalytic reactions arise on the surface of catalysts and the interface structure of photocatalysts plays key role in transfer efficiency of charges carriers. This review summarizes various surface/interface designs including unsaturated coordination such as oxygen vacancies, surface halogenations, and heterojunctions, homojunctions, facets, etc., as well as the application in photocatalytic degradation of VOCs. This paper reviews the influence of surface and interface properties of materials on VOCs molecules, effective strategies to promote the decomposition of VOCs from the perspectives of VOCs activation, reaction barrier etc., and presents various methods of photocatalyst design appropriately. The degradation path of highly toxic benzene VOCs are also summarized. In addition, the possible problems and suggestions for photocatalytic degradation of VOCs are proposed.

Biodegradable Materials and Green Processing for Green Electronics

There is little question that the "electronic revolution" of the 20th century has impacted almost every aspect of human life. However, the emergence of solid-state electronics as a ubiquitous feature of an advanced modern society is posing new challenges such as the management of electronic waste (e-waste) that will remain through the 21st century. In addition to developing strategies to manage such e-waste, further challenges can be identified concerning the conservation and recycling of scarce elements, reducing the use of toxic materials and solvents in electronics processing, and lowering energy usage during fabrication methods. In response to these issues, the construction of electronic devices from renewable or biodegradable materials that decompose to harmless by-products is becoming a topic of great interest. Such "green" electronic devices need to be fabricated on industrial scale through low-energy and low-cost methods that involve low/non-toxic functional materials or solvents. This review highlights recent advances in the development of biodegradable materials and processing strategies for electronics with an emphasis on areas where green electronic devices show the greatest promise, including solar cells, organic field-effect transistors, light-emitting diodes, and other electronic devices.

Effect of shell powder on removal of metals and volatile organic compounds (VOCs) from resin in an atmospheric-pressure microwave plasma reactor

Resin has been widely used for thermosetting printed circuit boards (PCBs) and is a key part of e-waste from scrap PCBs. It requires appropriate treatment because of its harmful elements (metals and metalloids) and organic compounds that are toxic to human health and the environment. The purpose of this study is to eliminate volatile organic compounds (VOCs) and elements (metals and metalloids) in resin via the use of powdered snail shell (Babylonia formosae) in an atmospheric-pressure microwave plasma reactor. Shell powder plays a significant role in the destruction of benzene and toluene with removal efficiency 98.8 % and 100 %, respectively, compared to quartz sand with removal efficiency 44.9 %. A high ratio of shell powder increases the inertization of metals and metalloids by more than 96 %. The crystalline structures of these materials are dominated by calcite formations (CaCO₃), confirming the elimination of metals and metalloids. Raman spectroscopy shows that the shell powder vitrifies these elements. The use of shell powder is thus recommended to degrade hazardous substances and to vitrify elements from resin in plasma pyrolysis.