Recycling Of Waste Printed Circuit Boards Research Articles

Drivers and Pathways for the Recovery of Critical Metals from Waste-Printed Circuit Boards.

The ever-increasing importance of critical metals (CMs) in modern society underscores their resource security and circularity. Waste-printed circuit boards (WPCBs) are particularly attractive reservoirs of CMs due to their gamut CM embedding and ubiquitous presence. However, the recovery of most CMs is out of reach from current metal-centric recycling industries, resulting in a flood loss of refined CMs. Here, 41 types of such spent CMs are identified. To deliver a higher level of CM sustainability, this work provides an insightful overview of paradigm-shifting pathways for CM recovery from WPCBs that have been developed in recent years. As a crucial starting entropy-decreasing step, various strategies of metal enrichment are compared, and the deployment of artificial intelligence (AI) and hyperspectral sensing is highlighted. Then, tailored metal recycling schemes are presented for the platinum group, rare earth, and refractory metals, with emphasis on greener metallurgical methods contributing to transforming CMs into marketable products. In addition, due to the vital nexus of CMs between the environment and energy sectors, the upcycling of CMs into electro-/photo-chemical catalysts for green fuel synthesis is proposed to extend the recycling chain. Finally, the challenges and outlook on this all-round upgrading of WPCB recycling are outlined.

Surface characteristic driven in waste printed circuit boards flotation: Floatability mechanism of resin and glass fiber in non-metallic component

To alleviate the environmental crisis caused by electrical waste, green reverse flotation of waste printed circuit boards (WPCBs) has been an appealing approach. Unfortunately, whether the floatability of non-metallic particles (NMPs) is caused by resin or glass fiber has not been confirmed. The floatability of NMPs, glass fiber particles in NMPs, pure resin particles and pure glass fiber particles were studied to determine the contribution to the floatability of NMPs. Firstly, the surface morphology of NMPs was analyzed by SEM, the results show that glass fiber and resin are locked together, leading to confusion in the mechanism of flotation. FTIR results show that the hydrophobic functional groups in NMPs are mainly derived from resins. Secondly, the floatability of each sample was also characterized by contact angle (CA) and wrap angle. The results show that NMPs and pure resin particles have excellent floatability with CA of 77.31º and 85.19º, while pure glass fiber particles have strong hydrophilicity with CA of 0º. The wrap angles of pure resin particles and pure glass fiber particles are 245º and 76º, respectively. Furthermore, the flotation results show that accumulated float yield of pure resin reach 100% within 120 s. The cumulative yield of pure glass fiber particles and NMPs after combustion is 6.22% and 12.52%, respectively. This study reveals the flotation mechanism of NMPs in WPCBs, proves that resin is the cause of the floatability of NMPs, which provides a guidance for the subsequent efficient recycling of WPCBs.

Waste remediation: Low-temperature synthesis of hybrid Cu(OH)2/CuO and CuO nanostructures from spent printed circuit boards and their dye degradation studies.

The demand for environmentally friendly and sustainable resource utilization techniques for recycling waste printed circuit boards is significant due to their status as valuable secondary resources, containing high-purity copper and precious metals. In this context, Cu(OH)2/CuO and CuO nanostructures were fabricated using alkaline precipitation and low-temperature aging methods using the strip solution originated from laboratory-scale spent mobile phone printed circuit board recovery process. XRD, FTIR, FESEM-EDX, and TEM were utilized to characterize the as-recovered nanoproducts. A hybrid structure of Cu(OH)2/CuO was formed at 70°, and monoclinic CuO phase was formed at 80°C aging time. The results show that Cu(OH)2/CuO nanoflakes have an average crystallite size of 24.06nm and a particle width of 22 ± 3nm. Cu(OH)2/CuO nanoflakes formed at 70°C aging temperature and 24-h residence time have finer crystallite and particle sizes than CuO-ridged nanospheres formed at 80°C aging temperature. The optical band gap energy of Cu(OH)2/CuO and CuO nanostructures formed was found to be 2.28eV and 2.22eV, respectively. The hybrid Cu(OH)2/CuO nanostructure photocatalyzed the decomposed 97.28% rhodamine blue using a visible light source, whereas the CuO nanostructure degraded only 14.64% rhodamine blue dye under similar conditions. A surfactant-less hybrid structure is developed without the use of any chemical precursor. Thus, a high value-added product is produced using one waste material to remove another waste in wastewater treatment.

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.

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.

A sustainable printed circuit board derived hierarchically porous carbon/polyaniline composites for supercapacitors

The hierarchically porous carbon/polyaniline electrodes derived from the nonmetallic part of waste printed circuit board have been synthesized by a convenient carbonization and activation method. A detailed analysis of the morphology, structure, and electrochemical performances of as-prepared composites is presented. As expected, the balanced specific surface area and porous structure manifest their remarkable electrochemical performances. Apparently, the multiple synergistic effects are crucial to simultaneously achieving high capacity and significantly increased stability. As a result, the electrodes display exceptional rate capability, superior cyclic stability, and high specific capacitance (520.0 F/g at 1 A/g). Furthermore, the asymmetrical device possesses an improved energy density of 9.3 Wh/kg with a power density of 62.4 W/kg in H2SO4 electrolyte. Moreover, a potential mechanism contributing to the superior performance of hierarchically porous carbon/polyaniline composites has been studied in detail. Noteworthy, this study provides a feasible strategy for recycling waste printed circuit boards. Importantly, this approach will provide a path toward the rational synthesis and design of electrode materials for supercapacitors that take both high-performance and cost-effective into account.

Bioleaching of Typical Electronic Waste-Printed Circuit Boards (WPCBs): A Short Review.

The rapid pace of innovations and the frequency of replacement of electrical and electronic equipment has made waste printed circuit boards (WPCB) one of the fastest growing waste streams. The frequency of replacement of equipment can be caused by a limited time of proper functioning and increasing malfunctions. Resource utilization of WPCBs have become some of the most profitable companies in the recycling industry. To facilitate WPCB recycling, several advanced technologies such as pyrometallurgy, hydrometallurgy and biometallurgy have been developed. Bioleaching uses naturally occurring microorganisms and their metabolic products to recover valuable metals, which is a promising technology due to its cost-effectiveness, environmental friendliness, and sustainability. However, there is sparse comprehensive research on WPCB bioleaching. Therefore, in this work, a short review was conducted from the perspective of potential microorganisms, bioleaching mechanisms and parameter optimization. Perspectives on future research directions are also discussed.

Sustainable development in WPCBs treatment for production of bituminous waterproofing materials

Due to the rapidly increasing use of electrical devices, e-waste became one of the major threats to the environment. Waste printed circuit boards (WPCBs) are an integral part of electrical devices, thus the interest in their recycling is growing. Recycling of WPCBs can be performed by applying hydrometallurgical or pyrometallurgical processes, as well as vacuum pyrolysis. The main advantages of vacuum pyrolysis are eco-friendliness, economic viability and efficiency in extracting present noble metals, while pyrolysis oil occurs as a by-product. Pyrolysis oil poses a tremendous threat to the environment, due to the possibility of its spillage into water, as well as a potential release into the air and soil. Because of this, the pyrolysis oil was subjected to chemical treatment with different reagents, such as sodium hydroxide, calcium oxide, sulfuric acid and maleic anhydride, with the intent to solidify the material and remove unpleasant odors. Incorporation of the solidified materials into bitumen, at 2.5, 5, 7.5, and 10 wt.% addition, was performed to obtain waterproofing materials. The obtained solidified and bituminous water-resistant materials were subjected to various test methods: FTIR spectroscopy, physicochemical and mechanical properties of bitumen, etc. which showed that all the tested characteristics are in accordance with values prescribed by the current standard. Toxicity Leaching Procedure (TCLP) confirmed non-hazardous characteristics of the obtained materials, except for the ones with added solidified pyrolysis oil, with Sodium hydroxide, that showed higher leaching of the phenol constituent.

Reveal the Release and Transformation Mechanism of Polybrominated Diphenyl Ethers during the Crushing of Waste Printed Circuit Boards Based on the Experimental Monitoring and Theoretical Simulation

Waste printed circuit boards (WPCBs) are not only valuable recourses but also hazardous materials. Mechanical crushing is an essential pretreatment for WPCB recycling. Polybrominated diphenyl ether...

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.

Environmental and economic performance analysis of recycling waste printed circuit boards using life cycle assessment

Recycling precious elements from the electronic waste could be an environmental friendly way to avoid likely ecological damages caused by leaching of heavy metals and toxic elements as well as an economically attractive option to recover valuable materials that would otherwise be wasted. This research assessed the environmental and economic performance of recovering nine metal elements (aluminum (Al), copper (Cu), gold (Au), lead (Pb), nickel (Ni), silver (Ag), tin (Sn), zinc (Zn), and iron (Fe)) and two non-metal materials (resin and glass-fiber) from the waste printed circuit boards (PCBs), one of the vital components of electronic-waste (e-waste). SimaPro software was used to assess the environmental performance of recycling waste PCBs. Data were collected from recycling plants in Taichung City, Taiwan, and Eco-invent database was also used in the study. The impacts of metal recycling from PCBs were compared with the impacts caused by the mining of respective metals from their natural ores. Among the analyzed elements, only the recovery of Au from waste PCBs proved to have less environmental impacts than the mining from the natural ore. Among 16 environmental impact categories (ILCD midpoint 2011+ method of impact analysis) considered in the present study, cancer and non-cancer human toxicity were the most affected categories followed by minerals, fossils, and resource extraction. However, the economic analysis showed that the recycling of all elements from waste PCBs had a net positive benefit. When considering both the environment and economic performance, the recycling of Au proved to be a beneficial option.

Waste-Printed Circuit Board Recycling: Focusing on Preparing Polymer Composites and Geopolymers

The waste from end-of-life electrical and electronic equipment has become the fastest growing waste problem in the world. The difficult-to-treat waste-printed circuit boards (WPCBs), which are nearly 3–6 wt % of the total electronic waste, generate great environmental concern nowadays. For WPCB treatment and recycling, the mechanical–physical method has turned out to be more technologically and economically feasible. In this work, the mechanical–physical treatment and recycling technologies for WPCBs were investigated, and future research was directed as well. Removing electric and electronic components (EECs) from WPCBs is critical for their crushing and metal recovery; however, environmentally friendly and high-efficiency removal techniques need be developed. Concentrated metals rich in Cu, Al, Au, Pb, and Sn recovered from WPCBs need be further refined to add to their economic values. The low value-added nonmetallic fraction of waste-printed circuit boards (NMF-WPCBs) accounts for approximately 60 wt % of the WPCBs. From the perspective of environmental management, a zero-waste approach to recycling them should be developed to gain values. Preparing polymer composites and geopolymers offers many advantages and has potential applications in various fields, especially as construction and building materials. However, the mechanical and thermal properties of NMF-WPCBs composites should be further improved for preparing polymer composites. Surface modification or filler blending could be applied to improve the interfacial comparability between NMF-WPCBs and the polymer matrix. The NMF-WPCBs shows potential in preparing cement mortar and geological polymers, but the environmental safety resulting from metals needs to be taken into account. This study will provide a significant reference for the industrial recycling of NMF-WPCBs.

Biotechnological recycling of critical metals from waste printed circuit boards

AbstractCritical metals are key raw materials for new generation clean energy production. The extraction of critical metals often follows the difficult processing of primary ores and they are many times recovered as the companion metals. With the depletion of primary reserves, the focus has now shifted to processing the urban mines, like electronic (e‐)waste. Among the different types of e‐waste, the waste printed circuit boards (WPCBs) are the major reservoir of high‐value critical metals and are usually treated by the traditional pyro‐ and/or hydro‐metallurgical techniques. However, the application of microbial activities in metals recycling is rapidly emerging as a green technology in comparison to smelter or chemical processing. The application of microorganisms (bacteria/fungi) in WPCBs’ recycling is being increasingly explored in order to meet the parallel objectives of resource recovery and pollution mitigation. Therefore, the present article assesses the current frontiers in bioleaching of critical metals from WPCBs and contains discussions on process fundamentals, challenges, and perspectives. The applicability of microbial recycling of WPCBs at a higher scale in terms of a circular economy and urban mining notion, the techno‐economic analysis, and environmental sustainability in comparison to the chemical processing route are also discussed. © 2020 Society of Chemical Industry

Separating and recycling metal mixture of pyrolyzed waste printed circuit boards by a combined method

Waste printed circuit boards (WPCBs) contain a variety of valuable and hazardous materials. Recycling WPCBs is an important subject not only for environmental protection but also for sustainable development of resources. In this work, a new method combined low-temperature alkaline smelting with liquid-liquid phase separation is proposed to separate and recycle metal mixture in pyrolysis residue of WPCBs of mobile phones. During the low-temperature alkaline smelting process, amphoteric metals Al, Pb, Si, Sn, and Zn are firstly separated and recycled from the metal mixture with the separation rates of 99.5%, 81.6%, 97.8%, 88.4% and 95.7%, respectively. To separate the remaining metal mixture mainly containing elements Cu, Fe, Cr, Ni, Au and Ag, a liquid-liquid phase separation system is designed. As a result, the noble metals Au and Ag are concentrated in the copper-rich substance to form a high-value group, while the elements Ni and Cr distribute in the iron-rich substance. The iron-rich substance can be reused in the liquid-liquid phase separation process. In the super-gravity field, the recycling rates of the metals Au, Ag, Cr and Ni reach 98.1%, 99.8%, 95.6% and 75.4%, respectively. Furthermore, the iron-rich substance can be reused back to the liquid-liquid separation system. The copper-rich substance enriched by the noble metals can be efficiently recovered with low energy consumption and less pollution. This work provides an environmentally friendly and efficient route for separating and recycling the metal mixture in WPCBs.

Reverse flotation efficiency and mechanism of various collectors for recycling waste printed circuit boards

Reverse flotation was used to recover metal components from waste printed circuit boards (PCBs). The micro-morphology and chemical composition analysis of raw materials indicated that waste PCBs are mainly composed of glass fibers, ceramics and valuable metals. The effects of collector dosage and temperature on flotation efficiency were investigated and evaluated. The flotation results using various collectors showed that the efficient recovery of metal components could be achieved via reverse flotation with the diesel oil (DO) dosage of 370–1110 g/t, composite collector (CC) dosage of 370–740 g/t and laurylamine (LAM) dosage of 740 g/t, respectively. The suitable temperature should be controlled at around 20 °C for these collectors. The results also indicated that the selectivity of DO for nonmetal particles was stronger than that of CC and LAM. In summary, reverse flotation is a feasible and environmental approach for disposal of waste PCBs.

High-resolution continuum source graphite furnace atomic absorption spectrometry determination of ecotoxic and precious metals in printed circuit boards of waste mobile phones after selective sorption

Waste printed circuit boards (PCBs) contain high amounts of valuable precious metals (PMs) as well as ecotoxic elements (TE). Recycling waste PCBs enables the recovery of precious metals minimize harm to the environment caused by discarded electronics.This study established a benign and effective process for selective recovery of Au, Pt, Pd and ecotoxic elements such as As, Cd, Cr, Pb, Sb from waste PCBs. Pre-treating waste PCBs with a mixture of HCl and H2O2 in autoclave was fast and efficient decomposition. In order to recover PMs and TE from obtained PCB solutions, two sorbents were synthesized. 0.1 M HCl is sufficient for extraction of 96–100 % of TE and 3 M HCl is used for extraction of 100 % of PMs from PCB-solutions. The developed approach of transferring analyte into a solution is characterized as highly productive and make it possible to avoid any impact of matrices upon selectivity extraction and to determine analyte with high accuracy.The concentrations of analytes in five PCB samples were found in range of 10−6 - 10-1 % wt by HR-CS GFAAS method. HR-CS-GFAAS limits of determination and upper limits of analyte content determination were (μg·mL-1) 0.0008 and 0.1 (Au); 0.0008 and 0.1 (Pd); 0.001 and 0.8 (Pt); 0.0005 and 0.3 (As); 0.00006 and 0.01 (Cd); 0.0002 and 0.03 (Cr); 0.0005 and 0.1 (Pb); 0.0005 and 0.25 (Sb).The obtained data will be useful for the development of processes for the recycling of analytes from waste mobile phones.

Recovering full metallic resources from waste printed circuit boards: A refined review

Abstract Huge environment stresses and economic benefits promoted the vigorous development of recovery technology of waste printed circuit boards. However, the recovery technologies of metals from waste printed circuit boards were lack of systematicness, definiteness, and full-value. In this paper, we have systematically reviewed the literature, compared the advantages and limitations of various recycling methods, and established a complete framework for recycling waste printed circuit boards (PCBs). Then, an integrated, definite, and systematic recovery route of full renewable metals from waste printed circuit board was proposed. The recovery route included temperature-control crushing, magnetic separation, high voltage electrostatic separation, vacuum gasification and condensation, electrolysis, and bioleaching. This will raise people’s attention to recycling in an environment-friendly, energy-saving and value-added way, providing new ideas and entry points for future e-waste recycling. Finally, the perspective of the recovery route of full metals from waste printed circuit boards were looked forward. This review will contribute to the industrialization of metallic resources recycle and energy saving.

Facile and Cost-Effective Approach for Copper Recovery from Waste Printed Circuit Boards via a Sequential Mechanochemical/Leaching/Recrystallization Process.

The recovery of copper (Cu0) from waste printed circuit boards (WPCBs) is a great challenge as a result of its heterogeneous structural properties, with a mixture of metals, epoxy resin, and fiberglass. In this study, a three-step sequential process, including mechanochemical processing, water leaching, and recrystallization, for Cu0 recovery from WPCB powder is reported. Potassium persulfate (K2S2O8), instead of acid/alkali reagents, was employed as the sole reagent in the cupric sulfate (CuSO4) regeneration process. Complete oxidation of Cu0 in the WPCBs to copper oxide (CuO) and CuSO4 was first achieved during mechanochemical processing with K2S2O8 as the solid oxidant, and the K2S2O8 was simultaneously converted to sulfate compounds [K3H(SO4)2] via a solid-solid reaction with epoxy resin (C nH mO y) as the hydrogen donator under mechanical force. The rapid leaching of Cu species in the forms of CuO and CuSO4 was therefore easily realized with pure water as a nontoxic leaching reagent. The kinetics of the leaching process of Cu species was confirmed to follow the shrinking nucleus model controlled by solid-film diffusion. Finally, CuSO4·5H2O was successfully separated by cooling crystallization of the hot saturated solution of sulfate salt [K2Cu(SO4)2·6H2O]. An efficient conversion of Cu0 to CuSO4·5H2O product, for WPCB recycling, was therefore established.

Improvement of the crushing effect of waste printed circuit boards by co-heating swelling with organic solvent

The crushing is a crucial unit operation for recycling waste printed circuit boards. In this study, dimethylacetamide was used to improve the crushing efficiency of waste printed circuit boards. The sectional morphology of the printed circuit boards was observed by scanning electron microscopy after a swelling treatment, the result showed the metal-nonmetal interface appeared noticeable cracks. The mechanical properties of material was measured by dynamometer, the results indicated that the destructive load of treated printed circuit boards was reduced by 115.32 N. The yield and metal grade of the crushed products were determined for each fraction. For the −0.074 mm fraction, the swelling treatment reduced the yield by 8.19% versus the regular treatment. For the −0.5 + 0.25 mm fraction, the grade of copper was increased by 7.35% after the swelling treatment. In addition, the main trace elements of the electrical components can be enriched in the coarse fraction. An analysis of the infrared spectra of the organic solvent before and after the swelling treatment revealed that the compositions of the organic solvent and the resins remained unchanged with this treatment. The swelling process of printed circuit boards was illustrated by the non-uniform effects of thermal expansion of materials and the interaction of organic solvent with nonmetal. Further, the hydrogen bonds between the dimethylacetamide and the resin molecules were expressed by a molecular structure diagram. Overall, this method can achieve metal liberation and enrichment in the coarse fraction, reducing the generation of fine particles and organic solvent can also be recycled. Thus, this study provides an alternative approach to improve the crushing efficiency of waste printed circuit boards.

Decomposition of LCD screen inverter by pyrolysis

PCBs (Printed Circuit Boards) are important parts of electronic equipment and their use increases with technology development. Recycling of waste PCBs is challenging due to their complex structure and receives wide concerns as the amount of this type of waste is growing rapidly. In the article, the experiment of pyrolysis carried out with electronic waste sample was presented. The material employed in the present work was inverter of the LCD screen that it the example of the multilayer PCB. The correlation between pyrolysis temperature and gas emission from the system, which is associated with epoxy resin decomposition, is presented in the article.