Waste Printed Circuit Boards Research Articles

Dioxin Control in the Co-processing of Waste Printed Circuit Board and Copper Concentrate with an Ausmelt Furnace

Dioxin Control in the Co-processing of Waste Printed Circuit Board and Copper Concentrate with an Ausmelt Furnace

Sustainable fermentable sugar production using a glass fiber supported gallium–molybdenum photocatalyst towards bioethanol production: LCA analysis

A waste printed circuit board derived glass fiber supported gallium–molybdenum photocatalyst for sustainable hydrolysis of sugarcane bagasse for bioethanol production is reported.

Effect of e-waste nanofillers on the mechanical, thermal, and wear properties of epoxy-blend sisal woven fiber-reinforced composites

Abstract Lignocellulosic biomass extracted from plants that contain rich amounts of cellulose, hemicellulose, and lignin content can replace synthetic fibers in many engineering applications and is biodegradable. However, e-waste is rapidly evolving into one of the most serious environmental issues in the world owing to the presence of several toxic compounds that can contaminate the environment and pose a threat to human health. Printed circuit boards (PCBs) are one of the major components available in e-waste. In this research work, waste PCB (WPCB) powder is mixed in suitable proportions of 5%, 10%, 15%, and 20% with a lignocellulosic sisal woven fabric fiber mat, and blended with epoxy resin using the vacuum-assisted hand lay-up method. To determine the effect of particle size on the fabricated composites, mechanical, thermal, water absorption, surface roughness, and wear tests were conducted. It was found that the composition that contains 15% nanofiller composites gave better results in mechanical testing than the composition that contains 10% microfiller composites. Pin-on disc wear test and differential scanning calorimetric thermal test results show that 10% microfiller composites show better outcome results than 15% nanofiller composites. Testing values indicate that lignocellulosic sisal fiber composites with WPCB nano- and microfillers can be substituted for many engineering applications instead of being disposed of in landfills.

Process simulation and life cycle assessment of hydrometallurgical recycling routes of waste printed circuit boards

Electronic waste remains a pressing global environmental concern. Addressing the proper treatment and recycling of waste printed circuit boards (WPCBs) is imperative to mitigate environmental pollution and prevent the loss of valuable resources. In this study, a comparative analysis of acidic and alkaline leaching processes for recovering base metals (Cu, Sn, Zn, and Ni) from WPCBs was conducted by process simulation (using HSC software). Life cycle inventories were compiled accordingly. Furthermore, by incorporating an alternative method for precious metal recovery, the life cycles (using openLCA software) of both processes for recovering all metals were examined. The results revealed that while the acidic leaching process showed higher recoveries for base metals and advantages in terms of lower electricity consumption and wastewater generation, it also exhibited a more pronounced environmental impact due to the chemical input in the HNO3 leaching process. Conversely, the alkaline leaching process utilized fewer chemicals, generated less solid waste and off-gases, resulting in a lower overall environmental impact. For recycling 1 t of WPCBs, the acidic leaching process achieved recoveries of 92% for tin, 99% for copper, 79% for zinc, and 94% for nickel, whereas the alkaline leaching process yielded recoveries of 96%, 93%, 78%, and 74% for the corresponding metals. Notably, the alkaline leaching process demonstrated a lower global warming potential of 11,395 kg CO2 eq, compared to the 12,459 kg CO2 eq associated with the acidic leaching process. In the evaluation of the alkaline leaching process, most environmental impacts were found to be lower than for virgin production. As a result, while the acidic leaching process is indeed more efficient in metal recycling, the alkaline leaching process emerges as a stronger contender in terms of environmental sustainability, with great potential for further technical improvements.

Fractional factorial design of ultrasonic-assisted metal recovery from waste printed circuit board

Fractional factorial design of ultrasonic-assisted metal recovery from waste printed circuit board

From E-Waste to High-Value Materials: Sustainable Synthesis of Metal, Metal Oxide, and MOF Nanoparticles from Waste Printed Circuit Boards.

The exponential growth of electronic waste (e-waste) has raised significant environmental concerns, with projections indicating a surge to 74.7 million metric tons of e-waste generated by 2030. Waste printed circuit boards (WPCBs), constituting approximately 10% of all e-waste, are particularly intriguing due to their high content of valuable metals and rare earth elements. However, the presence of hazardous elements necessitates sustainable recycling strategies. This review explores innovative approaches to sustainable metal nanoparticle synthesis from WPCBs. Efficient metal recovery from WPCBs begins with disassembly and the utilization of advanced equipment for optimal separation. Various pretreatment techniques, including selective leaching and magnetic separation, enhance metal recovery efficiency. Green recovery systems such as biohydrometallurgy offer eco-friendly alternatives, with high selectivity. Converting metal ions into nanoparticles involves concentration and transformation methods like chemical precipitation, electrowinning, and dialysis. These methods are vital for transforming recovered metal ions into valuable nanoparticles, promoting sustainable resource utilization and eco-friendly e-waste recycling. Sustainable green synthesis methods utilizing natural sources, including microorganisms and plants, are discussed, with a focus on their applications in producing well-defined nanoparticles. Nanoparticles derived from WPCBs find valuable applications in drug delivery, microelectronics, antimicrobial materials, environmental remediation, diagnostics, catalysis, agriculture, etc. They contribute to eco-friendly wastewater treatment, photocatalysis, protective coatings, and biomedicine. The important implications of this review lie in its identification of sustainable metal nanoparticle synthesis from WPCBs as a pivotal solution to e-waste environmental concerns, paving the way for eco-friendly recycling practices and the supply of valuable materials for diverse industrial applications.

Selective separation of metals from waste printed circuit boards using supergravity-assisted liquation technology

Waste printed circuit boards (WPCBs) are the most crucial components of electronic waste，containing high-value metals that are attractive secondary sources and main recycling targets. This study proposed a combined method of supergravity technology and liquation technology to separate metals from WPCBs. Fe-rich, Cu–Zn and Cu–Sn phases were gradually precipitated and separated in supergravity fields. Two key parameters of separation temperature and gravity coefficient were investigated under different conditions. The optimum temperature was 1100 °C for separating Fe-rich alloy, and 800 °C for separating Cu–Zn and Cu–Sn alloy. Moreover, controlling the gravity coefficient at 600 in this study was deemed the most appropriate and energy-efficient. Under the optimum conditions, the mass fractions of Fe, (Cu + Zn), and (Cu + Sn) in Fe-rich, Cu–Zn, and Cu–Sn alloy reached 81.8 wt%, 95.0 wt%, and 89.9 wt%, respectively. A potential industrial apparatus for the novel method was also proposed. The results demonstrate that the proposed supergravity-assisted liquation method is a promising and optimized approach for selectively separating metals from WPCBs.

A combined and sustainable approach and a novel mechanism for recovering Bi, Au and Ag from high-chloride leachate of waste printed circuit board smelting ash

High-chloride leachate is a solution rich in precious metals that is produced in chloride hydrometallurgy. It has high levels of both rare and precious metals and hazardous chloride ions, and resource recovery from this solution and its safe disposal have become key objectives in the field of hydrometallurgy. In this study, a sustainable process involving "ultrasound-assisted precipitation–Pb powder cementation" was proposed for the stepwise separation and high-value utilization of Bi, Au and Ag obtained from high-chloride leachate. Targeted separation and conversion of Bi were achieved by precipitation–re-acid hydrolysis–ultrasonication-assisted coprecipitation–centrifugal purification. Under the optimal process conditions, the removal rate of Bi reached 99.52%, while the loss rates of Au and Ag were only 4.63% and 8.72%, respectively. Single-factor experiments of Au and Ag cementation by Pb powder showed that the recovery rates of precious metals could be improved by increasing the temperature, raising the solution pH, and applying mechanical force and ultrasonication. A possible reaction mechanism for Au and Ag cementation with Pb powder was proposed based on macroscopic kinetic analysis and microscopic mineral characterization. This work provides technical support and a theoretical basis for the separation and enrichment of rare and precious metals in chloride hydrometallurgy.

A study on waste PCB fibres reinforced concrete with and without silica fume made from electronic waste

This research goal is to appraise the effect of electronic waste on concrete properties by examining the mechanical properties of concrete reinforced with waste printed circuit boards (PCBs). PCB fibres, each 50 mm long, were mixed in varying proportions (1–5% by weight of cement). Silica fume (SF) was used as a 12% weight replacement for cement to conserve the properties of PCB fibre-reinforced concrete while tumbling cement consumption. Following a 28-day curing period, the fresh and hardened characteristics of PCB fibre-reinforced concrete were juxtaposed with those of conventional concrete. The experimental results led to the conclusion that 5% by weight of cement is the most effective proportion of PCB fibres to include in both PCB fibre-reinforced concrete and silica fume-modified PCB fibre-reinforced concrete. The addition of PCB fibres and silica fume significantly increased the mechanical strength of the concrete, making it suitable for high-strength concrete applications. Based on a similar investigational research design, an artificial neural network model was created, and it played a critical role in predicting the mechanical properties of the concrete. The model produced accurate results, with an R-squared (R2) value greater than 0.99.

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

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

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.

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.

Effective electronic waste valorization via microwave-assisted pyrolysis: investigation of graphite susceptor and feedstock quantity on pyrolysis using experimental and polynomial regression techniques.

Waste printed circuit board (WPCB) was subjected to microwave-assisted pyrolysis (MAP) to investigate the energy and pyrolysis products. In MAP, pyrolysis experiments were conducted, and the effects of WPCB to graphite mass ratio on three-phase product yields and their compositions were analyzed. In addition, the role of the initial WPCB mass (10, 55, and 100 g) and susceptor loading (2, 22, and 38 g) on the quality of product yield was also evaluated. By using design of experiments, the effects of graphite susceptor addition and WPCB feedstock quantity was investigated. A significant liquid yield of 38.2 wt.% was achieved at 38g of graphite and 100g of WPCB. Several other operating parameters, including average heating rate, pyrolysis time, microwave energy consumption, specific microwave power used, and product yields, were optimized for the MAP of WPCB. Pyrolysis index (PI) was calculated at the blending of fixed quantity WPCB (100g) and various graphite quantities in the following order: 2g (21) > 20g (20.4) > 38g (19.5). The PI improved by increasing the WPCB quantity (10, 55, and 100g) with a fixed quantity of graphite. This work proposes the product formation and new reaction pathways of the condensable compounds. GC-MS of the liquid fraction from the MAP of WPCBs without susceptor resulted in the generation of phenolic with 46.1% relative composition. The addition of graphite susceptor aided in the formation of phenolic and the relative composition of phenolics was found to be 83.6%. The area percent of phenol increased from 42.8% (without susceptor) to 78.6% (with susceptor). Without a susceptor, cyclopentadiene derivative was observed in a very high composition (~ 31 area %).

Enhancing Debromination Efficiency through Introducing Water Vapor Atmosphere to Overcome Limitations of Conventional Pyrolysis.

Bromine removal is significant in the recycling of waste printed circuit boards (WPCBs). This study found that the critical factors limiting the debromination efficiency of conventional pyrolysis are the formation of coke impeding mass transfer and conversion of bromine into less volatile species, such as coking-Br and copper bromide. According to frontier molecular orbital analysis and thermodynamic equilibrium analysis, C-O bonds of resin are sites prone to electrophilic reactions and copper bromide in residue may undergo hydrolysis; therefore, introducing H2O during pyrolysis was a feasible method for thorough debromination. Through pyrolysis in a water vapor atmosphere, the diffusion limitation of debromination was overcome, and resin was converted into light components; thereby, rapid and deep removal of bromine was achieved. The result indicated that 99.7% of bromine was removed, and the residue could be used as a clean secondary resource. According to life-cycle assessment, pyrolysis of WPCBs in water vapor could be expected to reduce 77 Kt of CO2 emission and increase financial benefits by 60 million dollars, annually.

The fate of bromine during microwave-assisted pyrolysis of waste printed circuit boards

Bromine control is imperative for efficient treatment and products utilization during pyrolysis of waste printed circuit boards (WPCBs). This study investigated Br-species in products from microwave-assisted auger pyrolysis of WPCBs, and discussed synergetic evolution mechanisms, release kinetics and thermodynamics of Br-containing pollutants with different kinds of mineral species (alkaline earth, alkali, and transition metals). Results indicated that heavy Br-containing volatiles release (e.g., brominated phenols) was dominated at 320–520 °C. Brominated phenols released Br* to react with small-molecule groups to form light Br-containing products (e.g., HBr, CH3Br, and CH3CH2Br) at >520 °C. K2CO3 efficiently suppressed Br-containing pollutants emissions (∼50% reduction) and promoted bromine fixation in char (∼33.49% increase). With K2CO3 addition, bromine evolution mechanism is largely dehydrobromination and neutralization reactions when bromine bonds with aliphatic carbon with an adjacent aliphatic hydrogen. Negatively charged oxygen of K2CO3 attacks bromine and causes C-Br scission when bromine bonds with CH3* or aromatic carbon. The chemical reaction models (CRM3–CRM5) are best fitted with bromine evolution and the activation energy of WPCBs-KC reached the lowest (149.83–192.19 kJ/mol). Furthermore, bromine control strategy in WPCBs pyrolysis products toward environmental and economic sustainability were suggested, which created less environmental impact and maximum resource recovery.

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

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

Increasing the Added Value of Copper and Silver Metal from Printed Circuit Board Waste Using a Knelson Concentrator with Variations in Size and Centrifugal Force

The use of technology in Indonesia has resulted in an increasing demand for electronic and electrical goods, including printed circuit board (PCB) waste. Currently, PCB waste amounts to 20-50 million tons and continues to grow annually. Given that the composition of PCB waste consists of approximately 40% metals such as Ag, Cu, Fe, Au, Sn, and Mn, recycling PCB FR-2 waste can significantly increase its added value. One effective method is employing a concentration technique to recover these metals. This study aims to investigate the impact of particle size and centrifugal force variations on the content and recovery of Cu and Ag metals in PCB FR-2 waste using a Knelson concentrator. The concentration process involved three size variations: -63+100, -100+150, and-150#, along with three centrifugal force values: 60, 90, and 120 G Force. The results indicate that the size variation-100+150# and a centrifugal force value of 90 G Force exhibited effectiveness in recovering Cu and Ag metals, with a minimal mass loss of 3.9%. The Cu and Ag levels reached 67.49% and 0.18%, respectively, with recovery rates of 53.22% and 39.96%.

Evaluation of the effect of physical and chemical factors in the recovery of Cu, Pb and Fe from waste PCB through acid leaching

Electronic waste recycling is a strategy that contributes to implement a circular economy model which include reuse, component and raw material recovery and minimum final deposition. Given the importance of reincorporating the components of electronic devices into the productive chain and a correct recovery for some hazardous metals such as lead contained in such residues. This study is focused on the effect of maximum available content (MAC) of metal, sulfuric acid initial concentration, agitation velocity, and oxidising agent on the recovery of copper, lead and iron from electronic waste through acid leaching. A solid-state characterization before and after treatment and electrochemical analysis was carried out to analyse MCA effects and surface chemistry. It was found that sub-millimetric particles show a better available extraction percentage in case of copper and iron, being opposite for lead. Presence of hydrogen peroxide enhance the extraction efficiency, however, this cause iron and lead precipitation, therefore it is inefficient for metals recovery as well as for reagent consumption. The presence of calcium salts reacts producing gypsum, which reduces the extraction yield of copper at particle size below 250 μm.

Life cycle analysis on sequential recovery of copper and gold from waste printed circuit boards

Informal recycling activities of waste printed circuit boards, such as pyrolysis and landfilling, cause severe environmental harm to society. Pyrolysis of resin and polymer fraction leads to the generation of toxic effluents, and landfilling causes the leaching of heavy metals into the groundwater. A sustainable and eco-friendly way to recover base and precious elements will be an economically attractive option. Current research studied the cradle-to-gate environmental impacts of the sequential recovery of copper and gold through delamination, leaching, solvent extraction, electrowinning and cementation from waste printed circuit boards with the help of life cycle assessment.GaBi software was utilized to assess environmental impacts such as global warming, abiotic depletion (fossil), acidification potential and human toxicity potential during the process. Inventory data was collected by conducting several experiments and from optimizing parameters for recycling and separating 4.53 g of copper and 2.25 mg of gold from 16 g of component-free waste printed circuit boards. Results indicate that the chemical pre-treatment or delamination process for separating metal clads from the non-metallic fraction is primarily involved in the impact category. The higher impact during delamination is due to electricity consumption. The proposed study also corroborates the industrial viability of recycling valuable metals from waste printed circuit boards to minimize the environmental impacts. The outcomes of this work could be beneficial in creating the environmental guiding principle for WPCBs recycling plants.

Recycling and sustainable applications of waste printed circuit board in concrete application and validation using response surface methodology

The present investigation aims to examine the mechanical and durability properties of concrete that has been reinforced with a waste printed circuit board (WPCB) towards a low-carbon built environment. It assessed the fresh and hardened characteristics of the low-carbon concrete reinforced with WPCB fibres, after a curing period of 7 and 28 days. The evaluation was done by quantifying slump, compressive strength, split tensile strength, flexural strength, sorptivity, rapid, and acid tests. It further analysed eleven discrete concrete mixes with WPCB fibres at a weight percentage ranging from 1 to 5% in the cement mixture. The results indicate that incorporating WPCB fibre into concrete improves its mechanical strength. The results revealed that incorporating 5% WPCB fibre yielded the most favourable outcomes. The properties of WPCB fibre-reinforced concrete have been theoretically validated through Response Surface Methodology (RSM), which employs various statistical and mathematical tools to analyse the experimental data. The results derived from RSM were compared with the experimental results. It was found that the RSM model demonstrated a high level of accuracy (R2 ≥ 0.98) in validating the mechanical properties of WPCB fibre concrete. The statistical model exhibited no indication of prediction bias and demonstrated a statistically significant outcome, with a p-value below 0.5.