Waste Printed Circuit Boards Research Articles

Efficient conversion process and mechanism of bromine in bromine-rich saline wastewater

Bromine resources, widely utilized in basic chemical engineering, are considered non-renewable. A substantial amount of Bromine-Rich Saline Wastewater (BRSW), a hazardous waste, is generated during the smelting process of waste printed circuit boards (WPCBs). The efficient conversion of bromine resources is important in BRSW, which contain high concentrations of bromide ions. This study developed a synergistic treatment method utilizing electrolytic manganese anode sludge (EMAS) achieved efficient conversion of Br− to Br2 in BRSW. Optimal technical parameters are determined through single-factor experiments, and the oxidative acid leaching process was optimized using response surface methodology (RSM). The significant influencing factors for Br− conversion were ranked as acidity > anode mud addition amount > temperature > time, resulting in a bromine conversion efficiency of 96.55%. Kinetic studies of bromine conversion in BRSW during the oxidation-acid leaching process indicated a two-stage process: Stage I being a chemical reaction control model and Stage II being a diffusion control model. The reaction mechanism was elucidated, where H+ initially breaks the Mn-O bond in MnO2, exposing O vacancies and forming Mn4+, leading to a redox reaction between free Br− and Mn4+. This research embodies the concept of synergistic solid waste disposal, achieving cost-effectiveness and streamlined preparation of bromine, and providing technical and theoretical support for bromine resource recovery in BRSW.

Potential of metal recovery from printed circuit boards in Brazil.

In this study, the generation of domestic waste electrical and electronic equipment (WEEE) and waste printed circuit board (WPCB) were estimated, from 2015 to 2030. Based on the number of EEE put on the Brazilian market, the possession rate in the Brazilian households and obsolescence amounts of five EEE types were estimated using time series. The results show that, between 2015 and 2030, the quantity of WEEE generated per year will increase from 131.87 kt to 195.22 kt. In this period, WPCB generation will stay around 10% of WEEE generation. Additionally, this study shows that the urban mining potential of the materials recoverable from WPCB can be an important revenue source, with environmental benefits deriving from energy savings and a reduction in CO2 emissions. The results of this study provide a quantitative basis that may help decision makers develop strategic policies for WEEE management, considering material circularity.

Synthesis and characterization of alkali-activated binders with slag and waste printed circuit board

The global production of printed circuit board (PCB) is expected to rise substantially in the next decade due to the advancement in technology. The production of PCB results in generation of hazardous waste of various kinds, and one such waste is the very fine particles of the board material that is generated due to drilling and other preparatory operations. The disposal of such waste in the environment can result in serious consequences which needs attention. Therefore, recycling of waste printed circuit board (WPCB) can mitigate its harmful effects on the environment and also reduce the remediation costs. In this study, the WPCB is used as a substitute to ground granulated blast furnace slag (GGBFS) in development of alkali-activated binder. Alkali-activated binder was synthesized with GGBFS, WPCB, sodium hydroxide sol. (NaOH), and sodium silicate sol. (Na2SiO3). GGBFS was replaced with WPCB at replacement rates of 0%, 10%, 20%, and 30% by volume. Additionally, the effect of varying concentration of NaOH and Na2SiO3 on the physical and mechanical performance of the binder was studied. The developed binders were evaluated for workability, strength, water absorption, and efflorescence properties. Further, to ascertain its safety on the environment, the toxicity characteristic leaching procedure (TCLP) test was also performed. The results indicate that WPCB characteristics are compatible with GGBFS in terms of its particle size distribution. Moreover, the replacement of GGBFS with up to 20% WPCB provides desirable properties for the alkali-activated binder. However, higher replacements are not recommended, since it had detrimental effect on the mechanical performance of the binder. The study revealed that desirable performance can be achieved for binders with 8 M NaOH and with Na2SiO3 to NaOH ratio of 2, and up to 20% GGBFS replaced with WPCB. The results of TCLP test disclose that the contaminant in the leachate from alkali-activated binders with WPCB are within regulatory limits, and do not pose any threat to the environment. Finally, the outcome of this study provides an innovative approach towards formulation of eco-friendly binder for various construction applications such as foundations, buildings, bridges, pavements, etc.

Low Temperature Pyrolysis and Exfoliation of Waste Printed Circuit Boards: Recovery of High Purity Copper Foils

Although several techniques have been developed to extract copper from waste printed circuit boards (PCBs), there remain several challenges regarding energy consumption, local area contamination and environmental damage. A novel technique has been developed for extracting copper foils from waste PCBs based on low temperature pyrolysis followed by exfoliation to overcome these issues. The standard pretreatment steps of removing electronic components from PCBs and mechanical processing/size-reduction/powdering, etc., were minimized in this study. Several unsorted ‘as received’ PCBs were heat treated in the temperature range 750–850 °C for 5–20 min. in an argon atmosphere. Brittle dark chars and other residues on the heat-treated specimens were scrapped off to separate copper foils and other residuals. Most of the electronic components mounted on PCBs had dropped off during the heat treatment. Good-quality copper foils were recovered in all cases; the purity of copper was in excess of 85 wt.%. Key impurities present were Pb, Sn and Zn with typical concentrations less than 4 wt.%. Key features of the technique include minimizing energy intensive pre-treatment processes and waste handling, low pyrolysis temperatures and short heating times. This energy-efficient approach has the potential to enhance resource recovery while reducing the loss of materials, local area contamination and pollution near e-waste processing facilities.

Highly efficient and eco-friendly process for selective recovery of copper from waste printed circuit boards via pyrolysis and ammoniacal solvoleaching

This study proposes a process combining pyrolysis and ammoniacal solvoleaching to selectively recover Cu from waste printed circuit boards (WPCBs). Optimal pyrolysis conditions were determined by investigating parameters such as temperature, heating rate, N2 flow rate, holding time and particle size. Under the conditions: 500 °C temperature, 20 °C/min heating rate, 0.3 L/min N2 flow rate, 10 min time and +9.50 mm particle size, ∼25% of weight loss was obtained. The pyrolyzed mass underwent further physical separation process involving impact crushing, magnetic- and gravity separations to enrich metals into a concentrate. Copper in the resulting concentrate was selectively extracted using a one-stage ammoniacal leaching and solvent extraction process (ammoniacal solvoleaching), employing an oxime-based organic extractant, LIX 84-I with a small volume of NH4OH. Ammoniacal solvoleaching was optimized by considering parameters such as stirring speed, time, LIX 84-I concentration, volume of aqueous ammonia, temperature and pulp density. Under the following conditions: 500 rpm, 0.3/0.3/10 (g/mL/mL) of sample/NH4OH/LIX 84-I (0.8 M), 3 h time and 25 °C temperature, quantitative Cu dissolution was achieved after two-stage solvoleaching. Cu solvoleaching followed the Avrami model, with an activation energy of 28.95 kJ/mol in the temperature range 15–45 °C (298–318 K) for the mixed control mechanism. LIX 84-I could be recycled without loss of extraction performance. Cu concentration was further enriched during stripping stage using H2SO4. A flowsheet for the sustainable metal recovery from WPCBs was developed.

Organophosphate flame retardants in air from formal e-waste recycling workshops in China: Size-distribution, gas-particle partitioning and exposure assessment

In order to understand the organophosphate flame retardants (OPFRs) pollution and evaluate the inhalation exposure risk in formal e-waste recycling facilities, the air concentrations, particle size distribution and gas-particle partitioning of OPFRs in four typical workshops were investigated. The total Σ15OPFR concentrations inside workshops were in the range of 64.7–682 ng/m3, with 5.80–23.4 ng/m3 in gas phase and 58.8–658 ng/m3 in particle phase. Triphenyl phosphate (TPHP) and tris(2-chloroisopropyl) phosphate (TCIPP) were main analogs, both of which contributed to 49.0–85.7% of total OPFRs. In the waste printed circuit boards thermal treatment workshop, the OPFRs concentration was the highest, and particle-bound OPFRs mainly distributed in 0.7–1.1 μm particles. The proportions of TPHP in different size particles increased as the decrease of particle size, while TCIPP presented an opposite trend. The gas-particle partitioning of OPFR analogs was dominated by absorption process, and did not reach equilibrium state due to continuous emission of OPFRs from the recycling activities. The deposition fluxes of OPFRs in respiratory tract were 65.7–639 ng/h, and the estimated daily intake doses of OPFRs were 8.52–76.9 ng/(kg·day) in four workshops. Inhalation exposure was an important exposure pathway for e-waste recycling workers, and deposition fluxes of size-segregated OPFRs were mainly in head airways region.

Exploration of polymer inclusion membrane for nickel recovery from waste printed circuit boards

In this study, the selective recovery of nickel ions from waste printed circuit boards (WPCBs) solution through polymer inclusion membranes (PIMs) containing 5-nonylsalicylaldoxime (ACORGA M5640) as extracting agent and polyvinyl chloride (PVC) as base polymer has been explored. The proposed method utilizes combined process of solvent extraction and PIMs route for the recovery of nickel. As a first step, the copper was solvent extracted using ACORGA M5640 by the previously developed method by our group and further the raffinate of first stage is utilized as feed phase for the nickel recovery. The consequence of carrier concentration on transportation of nickel, pH of feed solution and effect of acidity of stripping agent has also been investigated. The increase in carrier concentration increases the nickel removal efficiency from feed phase to strip phase. Moreover, the increase in concentration of strip phase also increases the nickel ion flux. 99.77 % nickel was selectively recovered from leach liquor using PIMs containing 50 % of ACORGA M5640. Further, PIMs stability and transport studies has been carried out to know the feasibility of its use in recycling of electronic waste.

Pneumatic separation and process simulation of waste printed circuit boards pyrolysis residue

In this study, the application of Z-shape pneumatic separator for separating metal and nonmetal particles in pyrolysis residue of waste printed circuit boards was investigated, and the flow field characteristics and particle motion behavior in the separator were revealed through flow field simulation. The pneumatic separation results indicated that pre-screening significantly enhanced the separation efficiency of metals and nonmetals in pyrolysis residue. The simulation results showed that the large gradient of airflow velocity distribution and the turbulent flow field within the Z-shape separation cavity are beneficial for dispersing particles and reducing the influence between particles of different properties, thus enhancing separation efficiency. Using Rocky DEM for modeling of different shapes and properties of particles, and then combined with ANSYS Fluent can better simulate the particle separation behavior in the pneumatic separator.

Pyrolysis Behavior of Waste Printed Circuit Boards in a Vertical Fixed Bed

Pyrolysis Behavior of Waste Printed Circuit Boards in a Vertical Fixed Bed

Unveiling Pyrolysis Mechanisms of Waste Printed Circuit Boards Through Multiphysics Simulation

The pyrolysis process of waste printed circuit board (WPCB) with high economic benefit has been a black box problem, limiting the upgrading of pyrolysis processes. The resourcefulness and hazardous nature of WPCB will make it necessary for it to be treated properly. Multiphysics model was built to simulate the whole processes of WPCB pyrolysis and contaminants’ release. The circuit board samples containing six components were selected for pyrolysis in a tube furnace at a rate of 10[Formula: see text]C/min from room temperature to 600[Formula: see text]C, and the residual rate of Br- was determined by the oxygen bomb method. The results showed that the difference in temperature distribution could be attributed to thermal conductivity and surface area. Heat distribution would be more even from the inner material in areas where holes existed. The assembly method would affect the stress distribution around the components. Thermal stress at the pins might cause the separation of components from the substrate. The concentration of brominated contaminants was influenced by the material and assembly method. The instantaneous concentration around the pin was 3–4 times compared to the bare substrate, which was beneficial for the release and control of brominated organics. This study provided the research method for the in-depth understanding of the pyrolysis process of complex materials; and provided a basis for the upgrading of related processes.

Preliminary strategy and product analysis of microwave pyrolysis of waste printed circuit board

AbstractIn this study, microwave pyrolysis of waste printed circuit boards (WPCBs) was carried out in an inert atmosphere, and the effects of pyrolysis temperature and nitrogen flow rate on the yield and composition of pyrolysis products were investigated. With the increase of pyrolysis temperature, the yield of liquid product increases gradually, and the yield of solid product decreases gradually. At 600°C, the yield of each phase tends to be stable. When the temperature continues to rise, the content of H2 and CO decreases, and the content of C6 ~ C9 in the liquid product decreases. Microwave heating promotes the pyrolysis of brominated epoxy resin, which helps to improve the recovery rate of valuable substances and reduce the environmental impact of waste treatment. This study demonstrates that the microwave pyrolysis of WPCBs in nitrogen atmosphere has great potential in the green recovery process.

A review on metal extraction from waste printed circuit boards (wPCBs)

A review on metal extraction from waste printed circuit boards (wPCBs)

X-ray transmission imaging of waste printed circuit boards for value estimation in recycling using machine learning.

The growing amount of electronic waste is a global challenge: on one hand, it poses a threat to the environment as it may contain toxic or hazardous substances, on the other hand it is a valuable 'urban mine' containing metals like gold and copper. Thus, recycling of electronic waste is not only a measure to reduce environmental pollution but also economically reasonable as prices for raw materials are rising. Within electronic waste, printed circuit boards (PCBs) occupy a prominent position, as they contain most of the valuable material. One important step in the overall recycling process is the evaluation and the value estimation for further treatment of the waste PCBs (WPCBs). In this article, we introduce a method for value estimation of entire WPCBs based on component detection. The value of the WPCB is then predicted by the value of the detected components. This approach allows a flexible application to different situations. In the first step, we created a dataset and labelled the components of 104 WPCBs using different component classes. The component detection is performed on dual energy X-ray images by the deep neural object detection network 'YOLO v5'. The dataset is split into a training, validation and test subset and standard performance measures as precision, recall and F1-score of the component detection are evaluated. Representative samples from all component classes were selected and analysed for the valuable materials to provide the ground truth of the value estimation in the subsequent step.

Pyrolytic urban mining of waste printed circuit boards: an enviro-economic analysis.

E-waste, a global environmental concern resulting from supply chain inefficiency, also offers the opportunity to recover valuable materials, including general and rare earth metals. Waste printed circuit boards (WPCBs) are integral components of e-waste that contains substantial amounts of precious metals, making them a valuable waste category. Pyrolysis has emerged as a promising method for material recovery from WPCBs. Hence, pyrolytic urban mining of WPCBs offers an excellent avenue for resource recovery, redirecting valuable materials back into the supply chain. Under the current study, experimental investigation has been conducted to explore the recovery of materials from WPCBs through pyrolysis followed by process simulation, economic analysis, and life cycle assessment (LCA). An Aspen Plus simulation was conducted to model the pyrolysis of WPCBs and subsequent product recovery using a non-equilibrium kinetic model, which represents a unique approach in this study. Another distinct aspect is the comprehensive assessment of environmental and economic sustainability. The economic analysis has been carried out using Aspen economic analyzer whereas the LCA of WPCB pyrolysis has been conducted using the SimaPro software. The experimental investigation reveals yield of solid residues are about 75-84 wt.%, liquid yields of 6-13 wt.%, and gas yields of 4-21 wt.%, which is in well agreement with the Aspen Plus simulation results. The economic analysis for an e-waste pyrolysis plant with an annual feed rate of 2000 t reveals that the total capital cost of a pyrolysis plant is nearly $51.3 million, whereas the total equipment cost is nearly $2.7 million and the total operating cost is nearly $25.6 million. The desired rate of return is 20% per year and the payback period is 6years with a profitability index of 1.25. From the LCA, the major impact categories are global warming, fossil resource scarcity, ozone formation in human health, ozone formation in terrestrial ecosystems, fine particulate matter formation, and water consumption. The findings of this study can serve as a guideline for e-waste recyclers, researchers, and decision-makers in establishing circular economy.

Porous Polypyrrolidines for Highly Efficient Recovery of Precious Metals through Reductive Adsorption Mechanism.

The recycling and utilization of precious metals have emerged as a critical research focus in advancing the development of the circular economy. Among numerous methods for recovering precious metals such as gold, adsorbents with both high adsorption selectivity and capacity have become key technologies. This article incorporated the N-phenylpyrrolidine into a flexible porous polynorbornene backbone to create a class of distinctive porous organic polymers, named BIT-POP-14-BIT-POP-17. Through a reductive capture mechanism, the reductive adsorption sites of N-phenylpyrrolidine coordinate selectively with precious metals, the reduced metal is captured by the hierarchically porous polymers with flexible backbone. This approach leads to remarkable gold recovery efficiency, achieving a record of 2321mgg-1 at ambient conditions, and 3020mgg-1 under UV light, surpassing the theoretical limit. The porous polymers are filled in a column for a continuous uptake of gold from waste printed circuit boards (PCBs), showing recovery efficiency toward gold as high as 95% after 84h. Overall, this work offers a new perspective on designing novel adsorbents for precious metal recovery, providing inspiration for researchers to explore novel adsorption modes and contribute to the advancement of the circular economy.

Electrocatalytic degradation of ofloxacin by self-doped copper/carbon cathode materials derived from waste printed circuit boards

Using residual copper metal from waste circuit boards, ordered carbon materials containing copper (PCBs-Cu-800) were synthesized by self-doping for the electrocatalytic degradation of ofloxacin (OFL). Although PCBs-Cu-800 has a smaller specific surface area, its efficiency in degrading OFL was higher than that of carbon materials without copper (PCBs-800), reaching 95.9 % within 2 h. The PCBs-Cu-800 electrode can generate a large amount of H2O2 in the initial stage of degradation, thereby increasing the amount of hydroxyl radicals (·OH) generated and removing OFL. Density functional theory simulations were used to calculate the adsorption energies of O2 on both materials, demonstrating that the self-doped copper model was more prone to O2 adsorption, and elucidating the excellent electrocatalytic performance of PCBs-Cu. The residual copper metal in the raw material is important in the electrocatalytic processes. This study presents an environmentally friendly catalytic material capable of effectively degrading OFL in solution using waste circuit boards and further expands the application scope of advanced electrochemical oxidation technology in wastewater treatment.

Mechanism of PGMs capture from spent automobile catalyst by copper from waste printed circuit boards with simultaneous pollutants transformation

The traditional pyrometallurgical recycling of nano-sized platinum group metals (PGMs) from spent automotive catalysts (SACs) is an energy-intensive process that requires the addition of large quantities of copper capture and slag-forming reagents. Similarly, pyro-recycling of valuable metals from waste printed circuit boards (WPCBs) is also an energy- and reagent-intensive process that and carries a risk of pollution emissions. Based on the complementarity of composition and similarity of recycling process, synergistic pyro-recycling of SACs and WPCBs allow copper in WPCBs to capture PGMs in SACs and oxides from two waste form slag jointly, which offers benefits of enhanced metal recovery, reduced reagent and energy consumption, and suppressed pollutant emissions. However, the mechanisms of PGMs capture and pollutant transformation in co-smelting remain unknown. Here, we investigated the sub-processes mechanisms of slag formation, brominates fixation, multi-metal distribution and kinetic settlement. Oxides in both wastes support SiO2-Al2O3-CaO slag formation with low melting point and viscosity, where CaO suppresses the emission of brominated pollutants. Copper (50–100 μm) from WPCBs facilitates nano-sized PGMs in SACs recovery through capture and settlement. The results of demonstration experiments indicated a recovery rate of 94.6 %, 96.8 %, 97.2 %, and 98.1 % for Cu, Pt, Pd, and Rh, respectively, with a debromination efficiency exceeding 98 %. The theoretical analysis provides support for the establishment of a synergistic pyro-recycling process for SACs and WPCBs and provides insights into the potential for a greener and more efficient co-recycling of multi urban mines.

Elemental mercury removal by copper-containing brominated pyrolytic chars derived from waste printed circuit boards

Waste printed circuit boards (WPCBs) containing brominated flame retardants (BFRs) would result in serious environmental pollution without pertinent treatments. However, bromine-containing materials have been proven highly efficient for elemental mercury removal (Hg0). This work proposes a win–win strategy of a cost-effective Hg0 removal method and a highly efficient utilization of WPCB-derived chars. Diverse copper-containing brominated pyrolytic chars of WPCBs were prepared in a fixed bed reactor at 500–700 °C tailored for Hg0 removal from coal-fired flue gas. The resulting copper-containing pyrolytic chars were proven to have a high Hg0 removal efficiency. Various characterizations and adsorption curves insights into the impacts of copper, sorbent weights, pyrolysis and adsorption temperatures, on Hg0 removal efficiency of WPCB-derived chars. The results indicate that copper in WPCBs enhances the fixation of the bromine elements in pyrolytic chars, resulting in improved Hg0 removal performance. The optimal pyrolysis and adsorption temperatures for pyrolytic chars are 600 °C and 140 °C, respectively. Under optimized conditions, a Hg0 removal efficiency exceeding 90 % is realized after 30 min of adsorption. Notably, the results indicating the Hg0 adsorption capacity of WPCB-derived chars rivals that of commercial activated carbons and significantly surpasses that of biochar. Both adsorption kinetics and characterizations affirm that chemisorption is the predominant adsorption method. The C-Br bond and CuO emerge as crucial active sites facilitating the oxidation of Hg0.

Effective and selective recovery of Au(III) from WPCBs using quaternary phosphonium adsorbent synthesized by adjusting steric hindrance

With the gradual depletion of natural gold ore, waste printed circuit boards (WPCBs) have become one of the most attractive alternatives to gold ore. Here, a series of quaternary phosphonium adsorbents with a large size were successfully synthesized by adjusting the number of functional groups and carbon chain length of functional monomers, which can be used for selective recovery of gold(III) from WPCBs leaching solution. The quaternary phosphonium adsorbent (PS-TEP) prepared by the nucleophilic substitution reaction between triethyl phosphine with the smallest volume and chloromethylated polystyrene (PS-Cl) exhibited the best gold loading capacity (617.90 mg g−1). The adsorption mechanism of gold(III) on PS-TEP surface mainly involves anion exchange between AuCl4− and Cl− in the adsorbent. The charge level of the H atom closest to –CH2–P+ group directly determines the strength of the interaction between the adsorbent and the gold ion. Multiwfn and VMD programs visually confirm the weak interaction between PS-TEP+ and AuCl4−. After 5 adsorption-stripping cycles, the adsorption rate of gold(III) in solution remained at about 99 %. In addition, PS-TEP exhibited good gold(III) selectivity in both simulated and actual WPCBs gold leaching solutions. These results indicate that the large-particle PS-TEP with high capacity is suitable for selective gold recovery from WPCBs leaching solution.

Survey of diverse hydrometallurgy techniques for recovering and extracting valuable metals from PCB waste: an overview

Survey of diverse hydrometallurgy techniques for recovering and extracting valuable metals from PCB waste: an overview