Recycling Of Printed Circuit Boards Research Articles

Applying Circular Thermoeconomics for Sustainable Metal Recovery in PCB Recycling

The momentum of the Fourth Industrial Revolution is driving increased demand for certain specific metals. These include copper, silver, gold, and platinum group metals (PGMs), which have important applications in renewable energies, green hydrogen, and electronic products. However, the continuous extraction of these metals is leading to a rapid decline in their ore grades and, consequently, increasing the environmental impact of extraction. Hence, obtaining metals from secondary sources, such as waste electrical and electronic equipment (WEEE), has become imperative for both environmental sustainability and ensuring their availability. To evaluate the sustainability of the process, this paper proposes using an exergy approach, which enables appropriate allocation among co-products, as well as the assessment of exergy losses and the use of non-renewable resources. As a case study, this paper analyzes the recycling process of waste printed circuit boards (PCBs) by disaggregating the exergy cost into renewable and non-renewable sources, employing different exergy-based cost allocation methods for the mentioned metals. It further considers the complete life cycle of metals using the Circular Thermoeconomics methodology. The results show that, when considering the entire life cycle, between 47% and 53% of the non-renewable exergy is destroyed during recycling. Therefore, delaying recycling as much as possible would be the most desirable option for minimizing the use of non-renewable resources.

Use of electrodialysis to produce and recycle on-site raw materials for waste printed circuit board recycling process. I. HBr and KOH electrosynthesys

Use of electrodialysis to produce and recycle on-site raw materials for waste printed circuit board recycling process. I. HBr and KOH electrosynthesys

Printed circuit board recycling: a focus on a novel, efficient and sustainable process for spent critical metals recovery

Printed circuit board recycling: a focus on a novel, efficient and sustainable process for spent critical metals recovery

Mechanically Robust Reversibly Cross‐Linked Polymers with Closed‐Loop Recyclability for Use in Flexible Printed Circuit Boards

AbstractIt remains a huge challenge to efficiently recycle the printed circuit boards (PCBs) because of the diversity and complexity of the PCBs in terms of material composition. The recycling of PCBs highly depends on the design of the polymers that make up the polymer substrates and conductive pastes. Herein, closed‐loop recyclable plastics for use as the polymer substrates and for the preparation of the conductive pastes are fabricated by dynamically cross‐linking phenylboronic acid‐functionalized poly(methylmethacrylate) (PMMA‐B) and poly(urea‐urethane) (PUU‐B) with boroxines. The closed‐loop recyclable plastic, which is denoted as PMMA‐PUU exhibits a breaking strength of 71.0 MPa and Young's modulus of 1.8 GPa. Because of the dynamic nature of boroxines, the PMMA‐PUU0.6 plastic can be depolymerized in the N, N‐dimethylacetamide/ethanol mixture solvent. The depolymerized PMMA and PUU can be efficiently recovered in high yields and purity through their solubility differences in selective solvents. Conductive pastes suitable for printing of electrical circuits are fabricated through complexation of Ag particles with PMMA‐PUU. PCBs composed of PMMA‐PUU substrates and PMMA‐PUU‐based conductive pastes are flexible, healable, and recyclable. The closed‐loop recycling of the PCBs enables the collection of highly purified Ag particles, PMMA‐B, and PUU‐B monomers even when the PCBs are mixed with polymer wastes.

Life cycle assessment in the recycling of waste printed circuit boards and lithium-ion batteries: systematic literature review

This research aims to analyze life cycle assessment (LCA) studies covering recycling of printed circuit boards (PCB) and lithium-ion batteries from waste electrical and electronic equipment. The method of systematic literature review was used in addition to structured content analysis, to extract relevant data from 22 peer-reviewed scientific articles. The results show that the research topic is expanding, indicating an increased trend in research in the future. Most lca studies are focused on contexts of developed countries, indicating a research need in developing countries. The results of the content analysis point that most studies carried out LCA of PCB recycling, indicating that investigations in lithium-ion battery recycling processes are scarce in the literature. The treatment methods with the highest number of lca studies are pyrometallurgical and hydrometallurgical. New techniques such as bioleaching, physical recycling, relitiation, and functional recycling have been found, however, it is needed to perform more studies on the environmental impacts of these recycling methods.

Marine materials as innovative metal sorbents suitable for applications in wastewater treatments

The growing interest for urban mining strategies has pushed the research towards innovative strategies for metal recovery from electronic waste. Nevertheless, the treatment of the resulting metal-rich wastewater is still an issue. In this context, the present paper shows a method to use the capacity of Ulva algae to adsorb metals for the treatment of a synthetic solutions which simulates that resulting from a printed circuit board recycling process. The experiments considered a copper‑zinc‑iron system, showing a copper adsorption capacity of biomaterial up to 65 mg/g, at pH 5, favoured by iron presence. The process needs a short time (around 15 min) and it is suitable to be performed in a fixed-bed column able to treat more than 30 L of copper-contaminated wastewater, decreasing the energetic costs for mixing (compared to the typical slurry-reactor configuration) with an almost completed metal removal. The sustainability of the process is further improved by the selection of a macroalga which often accumulates on beaches (becoming a waste to remove) complying with the circular economy pillars.

Exploring the pretreatment routes of waste printed circuit boards for enhanced metal recovery

Obsolete printed circuit boards (PCBs) have been identified as secondary resources of valuable metals (Au, Ag, Cu, etc.) at the same time environmental contaminants in case of improper dumping, landfilling, and open burning. Therefore, the recycling of waste PCBs is very essential for recovering these metals, maintaining the circular economy, and also for protecting our environment. The present work investigates two pretreatment routes; delamination of waste printed circuit boards (WPCBs) by Dimethylacetamide (DMA) and ultrasonic treatment of milled waste printed circuit boards (WPCBs) for the separation of metallic fractions. Initially, discarded mobile WPCBs are preprocessed and the attached components were removed by a heating gun. Bare WPCBs were shear cut and shortened into 1 × 1 cm2. In the former case, effective delamination of WPCBs has been achieved by DMA at optimized conditions 150 °C, 16 h with a solid–liquid ratio of 3:10. In the later process, downsized WPCBs were fed into the hammer mill to obtain the powder. The Powdered WPCBs were further processed through ultrasonic cleaner to acquire metal-rich fractions. The delaminated metallic fractions, hammer milled powder and ultrasonically separated metallic powder were dissolved into aqua regia to get metal concentration. Moreover, XRD and SEM-EDS analysis revealed that the same metals were present in directly milled, ultrasonically cleaned powder and delaminated metallic fractions. However, an increased weight % of a few metals was observed in the case of ultrasonically cleaned powder and it was further confirmed using ICP-MS and AAS analysis. The current study revealed that the ultrasonic-assisted process is a faster and more cost-effective process.

Waste to wastewater treatment: Synthesis of CuO nanoparticles from discarded printed circuit boards for the removal of Methylene Blue under visible light

Owing to the swift advancements in the electronic industry and the increased demand, electronic equipment has a reduced lifespan in both developed and developing country markets, causing the generation of tons of electronic waste. The improper disposal of discarded Printed Circuit Boards (PCBs) can pose various environmental risks, despite the fact that they are a valuable source of high-purity copper and precious materials. Consequently, there is a significant demand for the recycling of waste PCBs using environmentally friendly and appropriate sustainable resource utilization methods. In this study the metallic clads separated from downsized PCBs are leached into the solution phase and precipitation with an alkaline medium is done to recover Copper Oxide nanoparticles (CuO NPs). The XRD analysis provided confirmation that the synthesized nanoparticles were monoclinic CuO, free from any impurities. FTIR confirmed that the synthesized product is pure CuO. The surface morphology of the synthesized CuO was revealed through FESEM, which showed irregular morphology. Further confirmation of this was obtained through TEM analysis. Additionally, the direct band gap was measured to be 1.93 eV. The as-synthesized nanoparticles are utilized for the degradation of Methylene Blue when exposed to visible light. Hence e-waste can be useful to produce value-added product to solve environmental problem as well as reducing the problematic e-waste, preserving naturally occurring ores.

Life cycle assessment of e-waste management system in Australia: Case of waste printed circuit board (PCB)

Electronic waste (e-waste) is one of the fastest-growing waste streams globally. Recycling is one of the environment-friendly waste management strategies that creates a net environmental gain in recovering valuable materials. In some countries, downstream recycling (high-value material recovery) is done overseas, and Australia is one of them. Waste printed circuit board (PCB) is a critical component of various electronic equipment, and it contains metals such as copper, tin, gold, aluminium, iron, silver, and others. Waste PCB, as apart of e-waste is mainly recycled overseas in Australia. However, the overall environmental impacts of recycling the waste stream overseas have yet to be investigated. The benefits of recovering the material in Australia have yet to be extensively understood from a supply chain perspective. This study aims to develop multiple scenarios using lifecycle assessment (LCA) methodology to identify the best possible solution for waste PCB disposal (final sink) derived from e-waste. Using SimaPro and Ecoinvent databases, four scenarios have been developed, along with a baseline scenario where waste PCB is recycled overseas. Receipe 2016 impact assessment methodology was utilized for the analysis, and results of the study showed that Scenario 2 (integrated material and energy recovery) is the best approach for waste PCB recycling in Australia, while landfill and direct incineration were the identified two worst scenarios in terms of final disposal option. When choosing local recycling over overseas recycling of waste PCB (material recovery only), it was found that impact categories such as global warming (human health) and fossil resource scarcity were reduced by 53% and 98%, respectively. In addition, the net positive environmental gain could be achieved for human non-carcinogenic toxicity by 7.16% when the waste stream is recycled in Australia. Uncertainty analysis of the study showed that in almost all major impact categories, material and energy recovery together scored high compared to scenarios when only material recovery was considered. This study is the first systematic attempt to characterize system-level lifecycle environmental impact assessment for waste PCB recycling. Future policies and regulations should focus on data transparency and availability across the value chain, local infrastructure development, and resource circularity. This study will add value to decision-making, policy on investment and future policy planning. It will also help industry and researchers develop optimized recycling-focused low-emission resource recovery supply chains.

Assessment of Mass and Energy Balance of Waste Printed Circuit Board Recycling through Hydrogen Reduction in Black Copper Smelting Process

Due to growing concern over environmental impacts and the pressure to lower carbon footprints in the metals industry, hydrogen (H2) has gained attention as a promising alternative for the replacement of carbon as a reductant and fuel. This paper evaluates the potential use of hydrogen as an energy source and reducing agent during the processing of waste printed circuit boards (waste PCBs) from e-waste through black copper smelting. The effect of the use of carbon and hydrogen during the reduction–oxidation process was analysed and compared from the perspective of thermodynamics and heat balance. The thermodynamic analyses of waste-PCB processing were carried out using the FactSage thermochemical package for the smelting process at temperatures from 1473 K to 1673 K (1200–1400 °C). The results show that the CO2 emissions can be reduced by 73% when hydrogen is used as the reducing agent. A minimum of 10 wt% of waste PCBs in the feed material can be used to replace the necessary carbon to supply heat for the reduction process. The addition of waste PCBs can increase the volume of slag and affect the composition of the off gas.

Repair and recycling of PCBs and their components based on obsolescence index: a domestic electrical appliances case study.

Population expansion and improving living standards, particularly in developed nations, have led to an increase in the usage of domestic electrical equipment, worldwide energy consumption, and CO2 emissions per capita. To limit the usage of non-reusable components and the amount of garbage that must be transferred at the end of a product's life cycle, longer-lasting electrical domestic appliances are a pillar of the circular economy. In recent years, the complexity of printed circuit boards (PCBs) used in the manufacture of modern electrical devices has increased, leading to an increase in device failures. This study focuses on the maintenance and recycling of domestic electrical appliance components and printed circuit boards. The proposed methodology for PCB repair is defined as a sequential quadratic programming (SQP) problem implemented in MATLAB environment and successfully tested to a variety of domestic appliances such as refrigerator, dishwasher and washing machine. The possibility of recycling metal parts of electronic components, which were replaced after PCBs' repair was also studied. Metals' percentage concentration of PCB electronic components for three customer's budgets considering metals and valuable metals recovery as given from the corresponding average metal recovery and calculated from different recycling procedures presented in the literature. The results of the proposed procedure in terms of valuable metals gave 38.4078ppm of silver. We also compared the suggested procedure with other works in terms of environmental perspective considering four measures, namely the gross energy requirement (GER), the global warming potential (GWP), the acidification potential (AP), and the solid waste burden (SWB). In terms of economic perspective and considering the existence of silver (Ag) in the electronic components, the recommended method gave comparable amount of money. Finally, a comparison of different recycling works from a technical viewpoint is also conducted. Moreover, a reparability index of domestic electrical appliances is introduced to further quantify the results of the proposed algorithm.

Techno-economic analysis of waste PCB recycling in Australia

Detailed techno-economic assessment of different scenarios of waste printed circuit board (PCB) metallurgical processing was carried out in the context of Australia. The results show that the cost of recycling waste PCB through black copper smelting at a small scale (10,000 tonnes/year) is estimated to be AU$ 5.33/kg waste PCB, with a likely revenue ranging from AU$7.3 to AU$9.3/kg waste PCB. The result also shows that a small-scale centralised recycling facility could provide a cumulative net benefit of AU$ 175 million with 76% IRR (Internal Rate of Return) over 20 years of plant life. The NPV (Net Present Value) of the scenario is highly sensitive to waste input capacity, feed material composition and the metal market price. Overall, the current study suggests that a small local waste PCB recycling plant is highly likely to be economically viable in the context of Australia based on the current assumptions in this study.

Morphology, Phase and Chemical Analysis of Leachate after Bioleaching Metals from Printed Circuit Boards.

The article presents the assessment of solutions and dried residues precipitated from solutions after the bioleaching process of Printed Circuit Boards (PCB) utilizing the Acidithiobacillus ferrooxidans. The obtained dried residues precipitated from bioleaching solution (leachate) and control solution were tested using morphology, phase, and chemical composition analysis, with particular emphasis on the assessment of crystalline and amorphous components. The analysis of the dried residues from leachate after bioleaching as well as those from the sterile control solution demonstrated a difference in the component oxidation—the leachate consisted of mainly amorphous spherical particles in diameter up to 200 nm, forming lacy aggregates. In the specimenform control solution larger particles (up to 500 nm) were observed with a hollow in the middle and crystalline outer part (probably Fe2O3, CuFeS2, and Cu2O). The X-ray diffraction phase analysis revealed that specimen obtained from leachate after bioleaching consisted mainly of an amorphous component and some content of Fe2O3 crystalline phase, while the dried residue from control solution showed more crystalline components. The share of the crystalline and amorphous components can be related to efficiency in dissolving metals during bioleaching. Obtained results of the investigation confirm the activity and participation of the A. ferrooxidans bacteria in the solubilization process of electro-waste components, with their visible degradation–acceleration of the reaction owing to a continuous regeneration of the leaching medium. The performed investigations allowed to characterize the specimen from leachate and showed that the application of complementary cross-check of the micro (SEM and S/TEM) and macro (ICP-OES and XRD) methods are of immense use for complete guidance assessment and obtained valuable data for the next stages of PCBs recycling.

LPViT: A Transformer Based Model for PCB Image Classification and Defect Detection

PCB (printed circuit board) is an extremely important component of all electronic products, which has greatly facilitated human life. Meanwhile, tons of PCBs in the waste streams become a waste of resources, which puts the recycling and reuse of PCBs in urgent need. In the manufacturing and recycling of electronic products, the classification of PCBs, recognition of sub-components, and defect detection have been the key technology. Traditional manual detection and classification are subjective and rely on individuals’ experience. With the development of artificial intelligence, lots of research efforts have been dedicated to the automated detection and recognition of PCBs. In this paper, we propose a transformer-based model, LPViT, for defect detection and classification of PCBs. We conduct the defect detection task on the dataset DeepPCB, which consists of six different types of PCB defects. Defect detection benefits both manufacturing and recycling of PCBs. Among many electronic products, a group of affordable, general-purpose, and small-size PCBs is very popular, which are referred to as micro-PCBs. The classification and recognition of those PCBs will greatly facilitate the recycling and reuse process. We conduct the classification task on a dataset called <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">micro-PCB</b> , which includes 12 types of popular, general-purpose, affordable, and small PCBs. Through comparative experiments, our system demonstrates its advantage in both classification and defect detection tasks.

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.

Recovering valuable metals from Waste Printed Circuit Boards (WPCB): A short review

In the modern era, metal usage can be traced in almost anything from simple household tools to complex electronic equipment. About 95 % of the electronic equipment surrounding us is built using components containing valuable metals, such as gold, silver, copper, palladium, and rare earths. Recycling electronic equipment offers a much richer resource than extracting metals from their respective ores. Printed circuit boards (PCBs) form about 3–6 % of the total electronic waste yet contain considerable quantities of precious metals. Most of the electronic waste (e-waste) that is disposed of, such as computers, mobile phones, televisions, printers, etc., are equipped with PCBs. These products are equipped with printed circuit boards(PCB) which are rich in valuable metals, including copper, aluminium, and gold. Recycling e-waste, especially PCBs, provides a route for economical and profitable extraction of valuable metals other than mining. Waste PCBs can be recycled using mechanical, pyrometallurgical, hydrometallurgical, electrometallurgical, and biometallurgical processes. In this review, the different technologies available for PCB recycling are compared, their limitations are highlighted to appreciate an environmentally friendly recovery of metals from the WPCBs. The PCBs feature a complex composition; therefore, it requires an intricate and novel approach to extract the specific metals. The review briefly analyses the different methods and techniques to extract the constituent elements and serves as a reliable reference for recycling WPCBs.

Assessment of Pre-Treatment Techniques for Coarse Printed Circuit Boards (PCBs) Recycling

Waste electrical and electronic equipment or e-waste generation has been skyrocketing over the last decades. This poses waste management and value recovery challenges, especially in developing countries. Printed circuit boards (PCBs) are mainly employed in value recovery operations. Despite the high energy costs of generating crushed and milled particles of the order of several microns, those are employed in conventional hydrometallurgical techniques. Coarse PCB pieces (of order a few centimetres) based value recovery operations are not reported at the industrial scale as the complexities of the internal structure of PCBs limit efficient metal and non-metal separation. Since coarse PCB particles’ pre-treatment is of paramount importance to enhance metal and non-metal separations, thermal, mechanical, chemical and electrical pre-treatment techniques were extensively studied. It is quite evident that a single pre-treatment technique does not result in complete metal liberation and therefore several pre-treatment flowsheets were formulated for coarse PCB particles. Thermal, mechanical and chemical pre-treatments integrated flowsheets were derived and such flowsheets are seldom reported in the e-waste literature. The potential flowsheets need to be assessed considering socio-techno-economic considerations to yield the best available technologies (BAT). In the wider context, the results of this work could be useful for achieving the United Nations sustainable development goals.

Design-of-experiment analysis of non-destructive detachment of electric parts from printed circuit boards of mobile phones using a cross-flow shredder

For minor metal recycling from electric parts, detachment without breakage (non-destructive detachment) of the electric parts from printed circuit boards (PCBs) is required. A cross-flow shredder (CFS), a drum-type chain mill, is often used in PCB recycling, but the effects of its individual features (e.g., chain thickness) on the non-destructive detachment of the PCB parts have yet to be understood. In this study, a CFS suited to the design-of-experiment (DoE) approach was developed; 27 different experimental conditions were evaluated, with three repetitions under each condition for a single PCB crushing, and the effect of nine CFS factors on the non-destructive detachment of parts from the PCBs of mobile phones was investigated. It was revealed that two factors (rotation rate and vent screen) have a statistically significant influence on such non-destructive detachment, and two other factors (chain-wall distance and crushing time) have a significant influence on related results such as the overcrushing of boards (PCBs after parts detachment) and powder generation. Based on these results, a future perspective on CFS improvement is presented.

Estimating Recycling Return of Integrated Circuits Using Computer Vision on Printed Circuit Boards

The technological growth of the last decades has brought many improvements in daily life, but also concerns on how to deal with electronic waste. Electrical and electronic equipment waste is the fastest-growing rate in the industrialized world. One of the elements of electronic equipment is the printed circuit board (PCB) and almost every electronic equipment has a PCB inside it. While waste PCB (WPCB) recycling may result in the recovery of potentially precious materials and the reuse of some components, it is a challenging task because its composition diversity requires a cautious pre-processing stage to achieve optimal recycling outcomes. Our research focused on proposing a method to evaluate the economic feasibility of recycling integrated circuits (ICs) from WPCB. The proposed method can help decide whether to dismantle a separate WPCB before the physical or mechanical recycling process and consists of estimating the IC area from a WPCB, calculating the IC’s weight using surface density, and estimating how much metal can be recovered by recycling those ICs. To estimate the IC area in a WPCB, we used a state-of-the-art object detection deep learning model (YOLO) and the PCB DSLR image dataset to detect the WPCB’s ICs. Regarding IC detection, the best result was obtained with the partitioned analysis of each image through a sliding window, thus creating new images of smaller dimensions, reaching 86.77% mAP. As a final result, we estimate that the Deep PCB Dataset has a total of 1079.18 g of ICs, from which it would be possible to recover at least 909.94 g of metals and silicon elements from all WPCBs’ ICs. Since there is a high variability in the compositions of WPCBs, it is possible to calculate the gross income for each WPCB and use it as a decision criterion for the type of pre-processing.

Reaction mechanisms of waste printed circuit board recycling in copper smelting: The impurity elements

Feeding Waste Printed Circuit Boards (WPCBs) into existing pyrometallurgical processes is developing as an easy-to-adapt and efficient way to recycle them. To fulfill sustainability and circular economy targets, kinetics and distributions are the key factors when recovering metals and trace elements from WPCBs. We investigated the reaction mechanisms and distribution behavior of impurity elements Sb, As and Bi between copper matte and slag at a typical smelting temperature of 1300 °C both in air and argon atmospheres. Laboratory-scale heat-quench experiments indicated that vaporization can effectively eliminate arsenic in the matte phase, but not antimony or bismuth either in air or in an argon atmosphere. Sufficient contact time between the gas and matte phase is also needed to transfer the trace elements into gas and slag. In this work, kinetic data and distribution ratios of these impurity elements in the matte and slag phase were calculated. They can be used in process development for WPCB recycling and, equally, when using complex copper concentrates with high As, Sb, and Bi contents. The results also complement CFD models to simulate flash smelting processes more precisely.