Waste Printed Circuit Boards Research Articles

NOx removal and copper recovery from the leaching process for waste printed circuit boards: performance evaluation and potential environmental impact assessment.

Resource recovery is crucial for small- and medium-sized enterprises to attain a circular economy. The economic benefits of recovering precious metals from electronic waste, such as waste printed circuit boards (WPCBs), are hindered by secondary pollutant emissions from pretreatment processes. This study aims to recover copper from the WPCB acid leaching process and reduce NOx emissions through the use of a high gravity rotating packed bed (RPB). The results indicate that the copper recovery ratio increases to 99.75% through the displacement reaction between iron powder and copper nitrate. The kinetic analysis of copper dissolution was employed to simulate the NOx emissions during acid leaching, with an R-squared value of 0.872. Three oxidants, including H2O2(aq), ClO2(aq), and O3(g), with pH adjusted to different NaOH concentrations, were used to remove NOx. The greatest NOx removal rate was achieved using a 0.06M NaOH solution, with a removal rate of 91.2% for ozone oxidation at a 152-fold gravity level and a gas-to-liquid (G/L) ratio of 0.83. The gas-side mass transfer coefficients (KGa) for NOx range from 0.003 to 0.012 1/s and are comparable to previous studies. The results of a life cycle analysis indicate that the NOx removal rate, nitric acid recycling rate, and copper recovery rate are 85%, 80%, and 100%, respectively, reducing the environmental impact on the ecosystem, human health, and resource depletion by 10% compared to a scenario with no NOx removal.

Evaluating glycine as an alternative lixiviant for copper recovery from waste printed circuit boards

Current hydrometallurgical processing routes for copper recovery from waste printed circuit boards (PCBs) utilise strong mineral acids, which pose environmental hazards. Glycine has been proposed as an alternate lixiviant with a lower environmental impact. This study aimed to investigate the effectiveness of glycine as lixiviant for copper dissolution from waste PCBs. Bench scale laboratory leaching tests were performed to investigate the effect of key process variables such as temperature, oxidant type and lixiviant concentration on the rate, extent and selectivity of copper leaching.In the presence of oxygen as oxidant, the glycine concentration did not have a significant effect on the rate or extent of copper leaching in the range 1 M to 2 M. Increasing the temperature from 25 °C to 60 °C increased copper dissolution after 22 h from 29.6% to 81.2% when using a glycine concentration of 1 M. When air instead of oxygen was used as oxidant, the copper dissolution achieved with 1 M glycine after 22 h at 60 °C decreased by 43.9 percentage points to 37.3%, due to the lower concentration of dissolved oxygen in the system. Using hydrogen peroxide instead of oxygen as oxidant, did not improve the overall extent of copper leaching achieved.Leaching with 1 M glycine and oxygen as oxidant at 60 °C is proposed as the most feasible operating conditions within the ranges investigated, because these conditions yielded the highest copper dissolution (81.2%) with relatively low (1.3%) gold co-extraction.

Copper recovery from waste printed circuit boards with small peptides enhanced by ultrasound

Waste printed circuit boards (WPCBs) are one of the most critical and valuable components in electronic equipment. WPCBs contain many metals (Cu accounts for more than 90%), which are a potential secondary resource to overcome metal scarcity. The recovery of metals from WPCBs is significant for environmental protection and resource reuse. This investigation presents a simple and sustainable approach to leach Cu from WPCBs with small peptides enhanced by ultrasound. Various leaching parameters, including initial small peptides concentration, temperature and initial H2O2 volume fraction have a highly significant influence. The maximum Cu leaching were 95.4 ± 0.1%, 92.5 ± 0.1% and 87.4 ± 0.1% by glutathione (GSH), glycylglycine (GG), and glycyl-L-glutamine (GLG), which caused by the differences of small peptides functional groups. The Cu leaching by ultrasound exhibited 2.1–3.9 folds higher than without ultrasound treatment. The kinetic analysis showed that the Cu leaching from WPCBs was mainly controlled by diffusion and chemical reactions. The coordination numbers of copper-chelating GSH (CC-GSH), copper-chelating GG (CC-GG), and copper-chelating GLG (CC-GLG) were measured by simulation experiments. The hydroxyl, carboxyl, amino and sulfhydryl groups are the main reasons for the complexation of small peptides and Cu2+, which was confirmed by the characterization of copper-chelating small peptides (CCPs) crystal. The Cu leaching with small peptides enhanced by ultrasound potentially represents an innovative technology with significant advantages in metals extraction and time efficiency. Furthermore, the results provide perspectives and new insights into the preparation of CCPs and the industrial application of modified leaching residues.

Removal of iron from waste printed circuit board dust: surfactant assisted magnetic separation versus selective leaching routes

Removal of iron from waste printed circuit board dust: surfactant assisted magnetic separation versus selective leaching routes

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

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

Selective extraction of gold from strong acid E-waste leachate through H+-triggered cascade reaction of thiolated β-cyclodextrin

Recycling precious metals from the increasing amount of e-waste is significant for the sustainability of strategic metal resources. However, few technologies have been reported for efficient and highly selective recovery of precious metals from the strong acidic e-waste leachate. Herein, we demonstrated a simply synthesized thiolated β-cyclodextrin (T-CD) that can recover gold from multi-metal coexistence solutions at pH 2 with an exceptional adsorption capacity of 1890.98 mg/g, and a superior selectivity coefficient about 5×104. The recognition of Au3+ by sulfhydryl groups on T-CD and the hydrolysis of T-CD triggered by H+ were proved to be the critically important contributors to the highly selective recovery of gold from strong acid wastewater. In addition, T-CD can directly and effectively extract gold from actual waste PCB leachate, allowing the acidic solution to be recycled five times. This work provides a new guidance for the direct recovery of rare metals from strongly acidic wastewater.

Environmentally Friendly Synthesis of Copper Oxide Nanoparticles from Waste Printed Circuit Boards as Photocatalyst in the Photodegradation of Tetracycline

Environmentally Friendly Synthesis of Copper Oxide Nanoparticles from Waste Printed Circuit Boards as Photocatalyst in the Photodegradation of Tetracycline

A sustainable route for the recovery of metals from waste printed circuit boards using methanesulfonic acid

The rapid increase in electronic waste (e-waste) generation and its unsustainable management pose a threat to the environment and human well-being. However, various valuable metals are present in e-waste, which makes it a potential secondary source to recover metals. Therefore, in the present study, efforts were made to recover valuable metals (Cu, Zn, and Ni) from waste printed circuit boards (WPCB) of computers using methanesulfonic acid (MSA). MSA is contemplated as a biodegradable green solvent and has a high solubility for various metals. The effect of various process parameters (MSA concentration, H2O2 concentration, stirring speed, liquid to solid ratio, time, and temperature) was investigated on metal extraction to optimize the process. At the optimized process conditions, 100% extraction of Cu and Zn was achieved, while Ni extraction was around 90%. The kinetic study for metal extraction was performed using a shrinking core model and findings showed that MSA-aided metal extraction is a diffusion-controlled process. Activation energies were found to be 9.35, 10.89, and 18.86 kJ/mol for Cu, Zn, and Ni extraction, respectively. Furthermore, the individual recovery of Cu and Zn was achieved using the combination of cementation and electrowinning, which resulted in 99.9% purity of Cu and Zn. The current study proposes a sustainable solution for the selective recovery of Cu and Zn from WPCB.

Comparative study of raw and HNO3-modified porous carbon from waste printed circuit boards for sulfadiazine adsorption: Experiment and DFT study

A huge amount of waste printed circuit boards (WPCBs) was produced while the electronic manufacturing industry developed rapidly. WPCBs mainly consist of organic compounds, which makes it possible to prepare them into porous carbon as valuable adsorbent. However, WPCBs are also rich in valuable metals. Cu makes up the most of these metals. It is worth studying whether the residual metal will affect the application of carbon materials. In this study, the porous active carbon (AC) was prepared from WPCBs as an adsorbent. Sulfadiazine (SD), a widely detected antibiotic contaminant, was used as a target pollutant. Nitric acid (HNO3) was used to modify AC (AC-HNO3) to remove the residual Cu. The experiment results showed that the adsorption kinetics of SD by AC (k = 0.0025) and AC-HNO3 (k = 0.0029) can be described better using a pseudo-second-order kinetic equation. The adsorption isotherms of AC and AC-HNO3 on SD could be fitted by the Langmuir model. AC had a larger adsorption capacity than AC-HNO3. Density functional theory (DFT) calculation results suggested that the −OH group and Cu on the surface of AC could be the adsorption sites and promote the SD adsorption. This work provides practical methods to recycle WPCBs into wealth and realized waste control by waste.

Recovery of Copper and Gold from Waste Printed Circuit Boards Using Monosodium Glutamate Supplemented with Hydrogen Peroxide

This study aimed to recover copper and gold from a waste printed circuit board (WPCB) using monosodium glutamate (MSG) supplemented with a clean oxidizer(s) under 30 °C, 150 rpm, and an initial pH of 7.00. The solder mask of WPCBs needed to be removed before leaching. At the first leaching, 93% of copper was selectively leached from solder–mask–free WPCBs within 3 h using 0.75 M MSG with 0.50% (w/v) H2O2. Then, gold (86%) was extracted from the first residue for 3 h by 1 M MSG with 0.25% (w/v) H2O2. In the downstream process, 98–100% copper could be directly recovered within 5–6 h from the first leachate by electrowinning (EW). However, gold in the second leachate required separation and purification processes before EW. At 4 h, 98% gold was adsorbed onto the activated carbon. Most impurities were removed from gold-loaded activated carbon by pre-elution using 0.05 M EDTA for 0.5 h without gold release. Afterward, 99% gold was eluted by diluted aqua-regia within an hour. Finally, the gold could be harvested perfectly using EW for 2 h. This complete copper and gold recycling process delivers an innovative concept for hydrometallurgical study and has the potential to develop into a practical industry.

Cost-effective and eco-friendly copper recovery from waste printed circuit boards using organic chemical leaching

Electronic waste generation is indeed a global concern; therefore, appropriate management and recycling are becoming highly significant. Printed circuit boards (PCBs) are significant portion of e-waste; contains a large number of valuable metals, rendering this material an important recovery resource. Among all other metals, the high Copper concentration of PCB residues, which is often ten times higher than that of rich-content rocks, makes these residues an appealing secondary source of Cu recovery. The primary goal of this study is to develop a simple and economical method for recovering Cu from waste PCBs. To leach metals, a combination of citric acid, acetic acid, and hydrogen peroxide (H2O2) was utilized. The influence of systemic factors such as citric acid concentration, acetic acid concentration, and H2O2 concentration on Cu leaching process was investigated. The results proved that the combination of citric acid, acetic acid, and H2O2 has increased the leaching efficiency of copper. More copper was dissolved when leaching with 0.5–1.5 M citric acid, 2.5–7.5%, and 2.5–7.5% H2O2 at 30 °C; however the individual acids produces less amount of Cu such as 26.86 ppm, 22.33 ppm, and 6.28 ppm whereas, high amount of Cu is obtained from the leaching solution containing 1 M citric acid, 5% acetic acid and 5% H2O2 with 325.89 ppm respectively. Thus, the combination of these acids and can be used as standardized method for leaching of Cu. These findings suggest that organic acids can replace inorganic acids as eco-friendly lixiviants for waste management.

Debromination with Bromine Recovery from Pyrolysis of Waste Printed Circuit Boards Offers Economic and Environmental Benefits.

Bromine is an important resource that is widely used in medical, automotive, and electronic industries. Waste electronic products containing brominated flame retardants can cause serious secondary pollution, which is why catalytic cracking, adsorption, fixation, separation, and purification have gained significant attention. However, the bromine resources have not been effectively reutilized. The application of advanced pyrolysis technology could help solve this problem via converting bromine pollution into bromine resources. Coupled debromination and bromide reutilization during pyrolysis is an important field of research in the future. This prospective paper presents new insights in terms of the reorganization of different elements and adjustment of bromine phase transition. Furthermore, we proposed some research directions for efficient and environmentally friendly debromination and reutilization of bromine: 1) precise synergistic pyrolysis should be further explored for efficient debromination, such as using persistent free radicals in biomass, polymer hydrogen supply, and metal catalysis, 2) rematching of Br elements and nonmetal elements (C/H/O) will be a promising direction for synthesizing functionalized adsorption materials, 3) oriented control of the bromide migration path should be further studied to obtain different forms of bromine resources, and 4) advanced pyrolysis equipment should be well developed.

A Newly Acidophilic Bacterium Acidomyces acidothermus Was Isolated to Efficiently Bioleach Copper from Waste Printed Circuit Boards (WPCBs)

An acidophilic metal-resistant bacterial strain, Acidomyces acidothermus (A. acidothermus), was isolated and identified by morphology, physiology, biochemistry, and 16S rDNA. A. acidothermus culture conditions were optimized by response surface methodology (RSM). Results showed that with a temperature of 40 °C, a pH of 3 in a 9k medium, and a rotation speed of 140 r/min, the copper leaching rate reached the highest value of 39.8%. Furthermore, SEM images and a heatmap of differential metabolites indicated that A. acidothermus adsorbed on the surface of WPCBs and extracellular polymeric substances (EPS), mainly D-glucuronic acid, were secreted, suggesting the highly efficient mechanism of copper recovery from WPCBs.

Study on particle characteristics and metal distribution of waste printed circuit boards based on a shear crusher

The crushing process plays an important role in the separation and purification process of waste printed circuit boards (PCBs). In this work, the fine crushing of waste PCBs was conducted to investigate particle characteristics and metal distribution using a shear crusher. The results demonstrated that a better crushing was obtained with the feed concentration of 183 g/L and crushing time of 60 s. Meanwhile, the coarse and fine particles presented the characteristics of higher circularity and smaller aspect ratio than medium-size particles for waste PCBs. Main metal elements such as Cu, Al, Zn and Fe were distributed in waste PCBs with various particle sizes, and these total metal content in the coarse crushed products was obviously higher than that in the fine crushed products. Overall, waste PCBs can be effectively crushed to a desirable product for subsequent separation and purification process using a shear crusher. • The fine crushing of waste PCBs was conducted using a shear crusher. • Particle shape characteristics and metal distribution were observed. • Coarse and fine PCB particles had the higher circularity and smaller aspect ratio. • Selective crushing of waste PCBs was confirmed under a higher shear crushing.

Copper recovery from leach solution of waste printed circuit boards by pulse current electrodeposition

Copper recovery from leach solution of waste printed circuit boards by pulse current electrodeposition

Upcycling of waste printed circuit boards into metallic pyrolytic carbon for supercapacitor electrode

Upcycling of waste printed circuit boards into metallic pyrolytic carbon for supercapacitor electrode

Electrorefining and electrodeposition for metal separation and purification from polymetallic concentrates after waste printed circuit board smelting

Multi metal recycling from waste printed circuit boards (WPCBs) is attractive for resource conservation and sustainability. While smelting is commonly adopted to produce polymetallic concentrates from WPCBs, current processes cost oxidation smelting and fire refining followed by electrorefining to deport co-existing base metals and recover copper, which can cause substantial metal losses, long steps, and lack of effective methods for subsequent base metal recycling. Here, direct electrorefining of polymetallic concentrates (Cu-Ni-Fe-Pb-sn-Au-Ag) combined with electrodeposition was investigated to realize multi metal separation and purification. It was found that direct electrorefining of concentrates in H2SO4/CuSO4 electrolyte at 0.4 V realized >98% base metal dissolution and copper production (∼99% purity), serving as a combined metal leaching and copper electrowinning procedure. PbSO4-SnO2-Cu5FeS4 precipitate was formed in anode slime, with Ag-Au enriched by 8.5–61 times. Analysis on subsequent selective metal electrodeposition revealed the blocking effect of Zn2+ and overlapped potential region of Fe2+-Ni2+, emphasizing the importance of Zn and Fe pre-separation during smelting and chemical precipitation. Electrodeposition experiments demonstrated high selectivity for Cu and Ni at 0.05 and −0.7 V, where Ni2+ shows complex electroreduction behaviors. The proposed process can serve as an alternative feasible route for multi metal recycling from WPCBs.

Eco-friendly recovery of base and precious metals from waste printed circuit boards by step-wise glycine leaching: Process optimization, kinetics modeling, and comparative life cycle assessment

Glycine as a green alternative to cyanide for gold leaching is a promising reagent to put a curb on the environmental footprints of conventional hydrometallurgical processes. This work was designed to investigate the step-wise glycine leaching of the base and precious metals from waste printed circuit boards (WPCBs) as one of the most dominant and problematic e-wastes in today's world. Using response surface methodology, selective copper extraction reached 99.96% recovery at the optimum condition of 0.5 M glycine, 1% v/v H2O2, 20 g/l pulp density, and ambient temperature. Copper sulfide was then recovered from the leach solution via precipitation by sodium hydrosulfide. Gold leaching in the glycine + permanganate system was thoroughly studied with an emphasis on the process's kinetics mechanisms. It was revealed that gold leaching in the glycine and permanganate system starts with a rapid phase followed by a slower chemically controlled phase. At the optimum condition of 4 g/l glycine, 2 g/l potassium permanganate, and room temperature, 96.17% of the gold was selectively extracted. By using 3 g/L activated carbon, about 100% of the gold was separated from the leach solution. Comparative life cycle assessment revealed that in the proposed process, the main contributor to most of the environmental impact categories is glycine. Replacing the first step of glycine copper leaching with nitric acid can substantially reduce the environmental footprints of the process to a lower level than many other proposed recycling routes.

Ag recovery from waste printed circuit boards of cell phone for synthesis of Ag nanoparticles and their antibacterial activity

Ag recovery from waste printed circuit boards of cell phone for synthesis of Ag nanoparticles and their antibacterial activity

Co-Pyrolysis Behavior, Kinetic and Mechanism of Waste-Printed Circuit Board with Biomass

Waste-printed circuit boards (WPCBs) account for approximately 3–6 wt% of total electronic waste. Due to their content of thermosetting materials and added brominated fire retardants, their recycling and disposal is difficult and not eco-friendly. Pyrolysis as a thermal degradation process may assist in the solution of this problem. In addition, using biomass as an additive can upgrade the bio-oil and fix bromines in the char. In this study, cotton stalk (CS) is chosen as an additive and kinetic of the pyrolysis of three samples namely: PCB, CS, and CS:PCB (50:50) were investigated by the thermogravimetric analyzer (TGA) at heating rates of 5, 10, and 15 K/min. Three non-isothermal methods: FWO, KAS, and Starink were found in good agreement with the TGA data; however, the FWO method was more efficient in the description of the degradation mechanism of solid-state reactions. For CS and CS:PCB (50:50), α was increased from 0.2 to 0.9 with the FWO method, and calculated Eα values were found in the range of 121.43–151.88 and 151.60–105.67 kJ/mol in zone 1, while 197.06–79.22 and 115.90–275.06 kJ/mol in zone 2, respectively. Whereas, for PCB in zone 1, Eα values were found to be in the range of 190.23–93.88 kJ/mol. The possible decomposition mechanism was determined by the Criado method, which was in agreement with the mechanism model for reaction order n = 3. The oil product was also analyzed using Fourier-Transform Infrared Spectroscopy analysis.