Chitosan-thioglycolic acid composite cross-linked with glutaraldehyde for selective recovery of Au(III) ions from e-waste leachate via reduction-coupled adsorption and incineration.

The recovery of gold (Au) from electronic waste (e-waste) has gained significant attention due to its high Au content and economic feasibility compared to natural ores. This study presents a facile, single-step approach to prepare the chitosan-thioglycolic acid composite crosslinked with glutaraldehyde (CS-TGA-GA) and demonstrates its unique capability for precious metal management, which is a less investigated application area for thiolated chitosan materials. The novel cost-effective biosorbent CS-TGA-GA demonstrated a very high adsorption capacity of 1351.9 ± 96 mg/g and selectivity for Au(III) from an acidic e-waste solution at pH 1 and 298 K. The high adsorption capacity and selectivity of the sorbent can be attributed to the abundance of -NH2, -OH, and -SH groups present on its surface. Various characterizations, such as scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy, as well as sorption experiments, including pH, kinetic, and isotherm studies, were performed. The kinetic data align with a pseudo-second-order model and the isotherm data can be well expressed by the Freundlich model. The CS-TGA-GA composite effectively facilitated the conversion of Au(III) to Au(0), leading to the formation of Au nanoparticles that aggregated in the reaction vessel over time. Subsequently, the Au-loaded CS-TGA-GA underwent an incineration procedure, yielding recovered Au with a purity of 99.6%, as measured by X-ray fluorescence. In addition to its large uptake capacity, acid stability, and recyclability, the prepared sorbent showed a highly selective uptake of Au(III) ions in a solution containing various metal ions leached from waste printed circuit boards. These results highlight the potential of CS-TGA-GA as an adsorbent for the recovery of Au from e-waste leachate, thereby contributing to sustainable resource management.

Estimation of the uncertainty of metal content in a batch of waste printed circuit boards from computer motherboards.

Electronic wastes are a valuable resource due to their critical and precious metal content. To include these wastes in recycling or recovery chains, it is necessary to precisely determine their metal content. Because analysing the whole sample of a batch of electronic waste is not practical, different preparation and sampling or subsampling steps are necessary. Sampling induces an error in the composition of the final sample compared to that of the initial batch, which finally leads to uncertainty in the final metal content measurement as compared to the "actual" batch metal content. The aim was to characterize the uncertainty in metal content of a batch of 372 kg of WPCB. Thirty-nine metals were analysed and thirty-two were considered: base, precious, rare-earths and critical metals. An empirical method (i.e. replicated measurement tests) was thus applied, based on statistical calculations according to Eurachem Guidelines. Uncertainty arising during the 3 different stages of the preparation process (primary, secondly and tertiary sampling steps) was calculated. For the analysed given weight (0.5 g), the shredding efficiency, which directly affects metal particle size distribution, was found to be the most important factor influencing the uncertainty. Uncertainties in base metal content, which is often concentrated in the coarsest particles, arose mainly from the last preparation step (tertiary sampling). Conversely, precious metals and rare-earths were finely ground during the 3 preparation steps, which led to low uncertainties, despite their low concentration in the waste (<337 mg/t for precious and < 35 mg/t for rare-earths).

Copper leaching from ultrasonically treated milled waste printed circuit boards: investigation of parameters optimization and kinetics.

Waste printed circuit boards (WPCBs) encompass abundant metals (gold, silver, and copper), along with other harmful materials including brominated epoxy resins, plastics, and heavy metals (lead, mercury, and cadmium). Direct burning and landfilling of WPCBs may cause severe health issues and impair the environment. Therefore, sustainable treatment of WPCBs is necessary to recover valuable metals and remove hazardous materials before disposal. The present work investigates the separation of copper-rich metallic fractions from the WPCBs by the combination of hammer milling and ultrasonic irradiation. Initially, discarded mobile phone PCBs are pre-processed and shortened into 1 × 1 cm2. Downscaled WPCBs are fed into the hammer mill to obtain the fine ground powder. The Powdered WPCBs are further processed through ultrasonic treatment to acquire metal-rich fraction. XRD, SEM-EDS, and ICP/AAS analysis revealed that the current technique can efficiently separate the metal-rich fraction without using toxic solvents. Results show the enhancement of copper fraction from 42.73 to 87 wt. % after ultrasonic treatment of WPCBs ground powder. Further, nitric acid leaching has been implemented to metal-rich fractions, and the parameters have been optimized for copper leaching with the assistance of response surface methodology (RSM) of the design of experiments (DOE). Quantitative dissolution (98.96%) of copper occurred using 3.5 M nitric acid within 3 h at 30 °C with 50 GPL pulp density and 500 rpm agitation speed. Finally, the kinetics of the leaching process were studied to conform the kinetics model. Moreover, the activation energy for diffusion (19.075 kJ/mole) and reaction kinetics model (13.29 kJ/mole) has also been calculated. The low energy consumption due to room temperature pre-treatment and effective leaching ensures the industrial feasibility of the proposed process.

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.

Copper recovery from waste printed circuit boards using pyrite as the bioleaching substrate.

Waste printed circuit boards (WPCBs) can be bioleached for Cu recovery, but lack of substrate for the bioleaching culture. In this study, using pyrite as a bacterial substrate for bioleaching WPCBs and recovering Cu was explored. The results showed that the WPCBs bioleaching using pyrite as the bacterial substrate was feasible. Mechanical crushing was a suitable WPCBs pretreatment method. The optimal WPCBs and pyrite pulp densities were respectively found to be 1.25% (w/v) and 1.0% (w/v), and the suitable nitrogen source ratio ((NH4)2SO4: (NH4)2HPO4) was deemed as 2 g/L: 2 g/L, achieving a Cu2+ leaching efficiency of 95.60 ± 1.57% in 14 d. Copper in the bioleaching solution can be directly recovery via electrodeposition. The Cu recovery efficiency in 60 min was up to 92.19 ± 1.35% under the optimal condition that the initial Cu2+ concentration and pH were respectively set at 7.34 g/L and 2.75, and the current density was set at 200 A/m2. Copper was found as the dominant metal in the cathode deposits, existing in the form of Cu and Cu2O. This work provided a novel approach for bioleaching WPCBs and recovering Cu.

Highly selective recovery of gold and silver from E-waste via stepwise electrodeposition directly from the pregnant leaching solution enabled by the MoS2 cathode.

The recycling of electronic waste, i.e., waste Printed Circuit Boards (WPCBs), provides substantial environmental and economic advantages. In fact, the concentration of valuable precious and base metals in WPCBs is even higher compared to those found in mined ores. Nevertheless, it is still challenging to selectively extract precious metals with low concentrations from the pregnant leaching solution, due to the co-deposition of base metals, like Cu, which have higher concentrations. In this research, stepwise recovery of precious metals and copper directly from WPCBs thiosulfate leaching solution was facilitated by the Ti cathode coated with MoS2 (MoS2/Ti). The in-situ enrichment of Au(S2O3)23- and Ag(S2O3)23- at the surface of MoS2 enables the high efficiency and selectivity of electrodeposition, which has been confirmed through COMSOL Multiphysics simulations and visualization. As a result, the first-step electrodeposition at 0.6 V recovered 92.44 % Au and 98.18 % Ag without any co-deposition of Cu. Subsequently, the second-step recovery employed a constant current of 0.03 A, achieving 100 % recovery of copper within 12 h. Furthermore, this study optimized the reduction potential, NH3·H2O concentration, and S2O32- concentration for the stepwise electrodeposition process. These findings provide valuable insights for establishing a closed loop circular economy in the electronics industry.

New insights into brominated epoxy resin type WPCBs pyrolysis mechanisms: Integrated experimental and DFT simulation studies.

Pyrolysis is a recycling technology for waste circuit boards (WPCBs) with a wide range of applications. In this research, the brominated epoxy resin (BER) type WPCBs were taken as the research object, and the optimal pyrolysis process parameters were determined. Combined with experiments and density functional theory (DFT) calculations, the pyrolysis gaseous generation pattern and product distribution of BER type WPCBs were analyzed, and the generation mechanism of phenol, bromide and other pyrolysis products was investigated in depth. The results of the study showed that the pyrolysis rate of WPCBs exceeded 95 % under optimal reaction conditions. In the initial phase of the pyrolysis of WPCBs, the BER's CO bonds and a portion of Ph-Br bonds will be broken, leading to the production of intermediates such propylene oxide, bisphenol A, isopropyl alcohol, tetrabromobisphenol A and HBr. Among them, propylene oxide can generate ethylene oxide through free radical reaction. In the second stage, intermediates such as bisphenol A undergo homolytic cleavage and radical addition to form phenols, bromides, alcohols, ketones and other pyrolysis products.

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.

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 38 g of graphite and 100 g 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 (100 g) and various graphite quantities in the following order: 2 g (21) > 20 g (20.4) > 38 g (19.5). The PI improved by increasing the WPCB quantity (10, 55, and 100 g) 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.

Recovery of precious metals from waste printed circuit boards though bioleaching route: A review of the recent progress and perspective.

The rapid proliferation of electronic waste (e-waste), including waste printed circuit boards (WPCBs), has exerted immense pressure on the environment. The recovery of precious metals from WPCBs not only serves as an effective means of alleviating this environmental burden but also generates economic value. This review focuses on bioleaching, an environmentally friendly method for extracting precious metals from WPCBs. Under various conditions, this method has achieved leaching rates of 30%-73% for Au and 33.8%-90% for Ag. However, there is a relative scarcity of studies on the bioleaching of precious metals from WPCBs. In this paper, we provide an overview of the current status of bioleaching for precious metals from WPCBs and describe the underlying mechanisms. We also briefly outline the influence of various process factors on leaching efficiency. While this review underscores the considerable potential of bioleaching in WPCBs applications, certain limitations hinder the engineering-scale application of the technology. Consequently, this paper describes the current enhanced processes for enhancing leaching efficiency. Overall, this review can serve as a valuable reference for future research endeavors, ultimately promoting the widespread utilization of bioleaching for the recovery of precious metals from WPCBs.

High Value-Added Reutilization of Waste-Printed Circuit Boards Non-Metallic Components in Sustainable Polymer Composites.

The reutilization non-metallic components from a waste-printed circuit board (WPCB) has become one of the most significant bottlenecks in the comprehensive reuse of electronic wastes due to its low value and complex compositions, and it has received great attention from scientific and industrial researchers. To effectively address the environmental pollution caused by inappropriate recycling methods, such as incineration and landfill, extensive efforts have been dedicated to achieving the high value-added reutilization of WPCB non-metals in sustainable polymer composites. In this review, recent progress in developing sustainable polymer composites based on WPCB non-metallic components was systematically summarized. It has been demonstrated that the WPCB non-metals can serve as a promising reinforcing and functional fillers to significantly ameliorate some of the physical and chemical properties of polymer composites, such as excellent mechanical properties, enhanced thermal stability, and flame retardancy. The recovery strategies and composition of WPCB non-metals were also briefly discussed. Finally, the future potentials and remaining challenges regarding the reutilization of WPCB non-metallic components are outlined. This work provides readers with a comprehensive understanding of the preparation, structure, and properties of the polymer composites based on WPCB non-metals, providing significant insights regarding the high value-added reutilization of WPCB non-metals of electronic wastes.

Eco-friendly approach for enhancing the floatability of non-metallic components in waste printed circuit boards: Adding gutter oil during dry grinding.

Waste printed circuit boards (WPCBs) are an attractive secondary resource that is challenging to dispose of due to its complexity. Reverse flotation is an effective method to remove non-metallic particles (NMPs) to obtain metals from WPCBs. Nevertheless, the removal of NMPs is usually inadequate in the present flotation practice. Thus, to provide a clean approach to improve the removal efficiency of NMPs, the method of adding gutter oil during dry grinding process was adopted to enhance the hydrophobic sites on the surface of NMPs to improve the floatability. The surface morphology of NMPs was analyzed by SEM, the results show that the rough morphology inhibited the adhesion of bubbles, while water occupied the cracks and pores, making it challenging for collector adsorption, which result in unstable particle-bubble adhesion. The results of FTIR indicate that both NMPs and gutter oil have -CH3, -CH2, -C = O, -C-O functional groups, which promotes the adsorption of gutter oil on the surface of NMPs. The contact angle (CA) results show that the adsorption of gutter oil on the particle surface is conducive to the formation of enhanced CA. Furthermore, the flotation enhancement effect was verified by flotation kinetic experiments. The accumulated floats yield of NMPs conditioned by gutter oil during grinding is increased from 67.05% (NMPs without conditioning) to 95.02%, and the resin recovery is increased by 31.10%. It is demonstrated that dry grinding with gutter oil can strengthen the floatability of NMPs, which provides a potential approach to increase the flotation efficiency of WPCBs.

Genesis of copper oxide nanoparticles from waste printed circuit boards and evaluation of their photocatalytic activity.

Discarded Printed Circuit Boards (PCBs) are one of the secondary resources of high-purity copper, and precious materials, which if disposed off inappropriately may present several environmental risks. This study focuses on the production of copper oxide nanoparticles (CuO NPs) from reclaimed copper via a facile precipitation route to obtain a value-added nanoproduct. The synthesis involved the dissolution of downsized PCBs, leaching of Cu into the solution phase and the precipitation of nanoparticles (NPs) in an alkaline medium. XRD analysis confirmed the as-synthesized NPs were monoclinic CuO of size 19.23 nm without any impurity. HRTEM analysis confirmed that the NPs were nearly round spheres with average particle size of 19.973 ± 6.036 nm. The NPs have a specific surface area of 200 m2/g and mesoporous structure with mean pore diameter of 18.051 nm. The CuO NPs photocatalyzed the degradation of Congo Red under visible light irradiation. Hence, the PCB e-waste was utilized to produce nanomaterials with added-values, decreasing environmental problems.

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.

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.

Ultrasound-enhanced catalytic degradation of simulated dye wastewater using waste printed circuit boards: catalytic performance and artificial neuron network-based simulation.

Recent developments of heterogeneous advanced oxidation for refractory organic contaminants and catalysts made of solid waste have attracted much attention. In this work, waste printed circuit board (wPCB) was used for catalytic degradation of simulated textile wastewater enhanced by ultrasound. Catalytic degradation of rhodamine B (RhB) and methylene blue (MB) was conducted in the presence of H2O2. Effect of ultrasound, wPCB, H2O2, pH, and dye concentration was investigated by single factor experiments. The growing catalytic efficiency was determined by ultrasound. The removal efficiency of MB and RhB are influenced by wPCB, H2O2, pH, and dye concentration. Degradation efficiency is accelerated with increasing wPCB dosage and H2O2 and decreasing dye concentration. Effective degradation of MB and RhB is obtained under broader pH region, attractively at neutral pH. Under optimal conditions, MB removal reaches 98.83% at 90 min while RhB removal reaches 99.57% at 80 min. Hydroxyl radicals play an important role in catalytic process. Tentative mechanism for catalytic degradation of MB and RhB are discussed based on multiple characterizations. Superior reusability of wPCB proves that wPCB is highly durable catalyst. Due to low cost and high efficiency, wPCB is attractive as effective catalyst for treatment of organic wastewater. Artificial neuron network-based (ANN) simulation, as a widely used artificial intelligence algorithm, was one of preferred methods for the wastewater treatment due to its unique properties in solving complex processes. An ANN model was designed for the prediction of the performance of ultrasound-enhanced catalytic degradation with a high R value (0.99).

Enhanced cleaner flotation behavior of non-metallic particles in waste printed circuit boards: From the perspective of particle size.

Flotation is an attractive method for separating the different components of waste printed circuit boards (WPCBs) due to its cleanliness and efficiency. Non-metallic particles (NMPs) with good floatability usually need to be floated, however, it is difficult to achieve complete removal. The effect of particle size on the flotation behavior of NMPs, which is usually ignored in previous studies, is concerned in this paper. Flotation tests and kinetic analysis were carried out to reveal the effect of reagent dosage on flotation characteristics of particles in narrow size fractions. As the fineness decreases, the particles are more likely to be floated. Equally, the finer the particle size, the lower the reagent dosage required to achieve the maximum recovery. For 1-0.5 mm and -0.045 mm, the maximum recovery increased from 42.16% (1500 g/t MIBC) to 97.31% (100 g/t MIBC). Therefore, the feasibility of reducing particle size by grinding to improve floatability was verified. The results show that the reduction of particle size can significantly promote its efficiency of being floated. After grinding treatment, -0.045 mm yields in each size fraction (1-0.5, 0.5-0.25, 0.25-0.125, 0.125-0.074, 0.074-0.045 mm) increased by 22.10%, 28.42%, 30.90%, 64.56%, 89.32%, resulting in an increase of 37.71%, 13.12%, 2.82%, 7.82% and 2.00% in maximum recovery, respectively. It is also proved that the particle size, rather than the resin content, has a more significant effect on the floatability of NMPs.

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.

Research on the pyrolysis characteristics and mechanisms of waste printed circuit boards at fast and slow heating rates.

The pyrolysis treatment of waste printed circuit boards (WPCBs) shows great potential for sustainable treatment and hazard reduction. In this work, based on thermogravimetry (TG), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and density functional theory (DFT), the thermal weight loss, product distribution, and kinetics of WPCBs pyrolysis were studied by single-step and multi-step pyrolysis at fast (600 °C/min) and slow (10 °C/min) heating rates. The heating rates of TG and Py-GC/MS were the same for each group of experiments. In addition, the bond dissociation energy (BDE) of WPCBs polymer monomers was calculated by DFT method. Compared with slow pyrolysis, the final weight loss of fast pyrolysis is reduced by 0.76 wt%. The kinetic analysis indicates that the activation energies of main pyrolysis stages range from 98.29 kJ/mol to 177.59 kJ/mol. The volatile products of fast pyrolysis are mainly phenols and aromatics. With the increase of multi-step pyrolysis temperature, the order of the escaping volatiles is phenols, hydrocarbyl phenols, aromatics, and benzene (or diphenyl phenol). The pyrolysis residue of WPCBs may contains phenolics and polymers. Based on the free radical reactions, the mechanism and reaction pathways of WPCBs pyrolysis were deduced by the DFT. Moreover, a large amount of benzene is produced by pyrolysis, and its formation mechanism was elaborated.