Environmentally friendly synthesis of copper nanoparticles from waste printed circuit boards

Copper recovery by solvent extraction for nanoparticle synthesis from waste motherboards

Printed circuit boards, which make up part of waste from electrical and electronic equipment, contain elements that can be economically reused, such as copper, silver, gold, and nickel, as well as metals that are harmful to the environment and health, such as lead, mercury, and cadmium. Thus, through recycling this scrap, materials that would otherwise be discarded can be reinserted as secondary raw materials to produce new consumer goods through urban mining. In this context, the synthesis of nanoparticles shows promise as it allows the reinsertion of these materials in the manufacture of new products. Therefore, this study used obsolete computer motherboards as a secondary material to obtain copper to produce nanoparticles of this metal. From a solution based on the leach liquor of this scrap, a purification route using solvent extraction was defined and applied to the real leach liquor. Applying the hydroxyoxime extractant at a dilution of 20% (v/v) in kerosene, A/O of 1/1, 298 K, and 0.25 h of contact during extraction, and stripping in H2SO4 (2 M), 298 K, 0.25 h, W/O ratio of 3/1, and two theoretical countercurrent stages, a solution containing more than 95% of the copper in the leach liquor could be obtained with less than 1% of contaminants. From this purified liquor, nanoparticles containing copper and metallic copper oxides and hydroxides were produced, with an average size of 84 nm, at pH 11, 3 h of hot stirring, volume of 0.015 L of ascorbic acid (0.50 M) and 0.015 L of precursor solution (0.03 M Cu), and temperature (343 K).

Synthesis of Cu and CuO nanoparticles from e-waste and evaluation of their antibacterial and photocatalytic properties

Waste printed circuit boards (WPCBs) contain a plethora of valuable metals, considered an attractive secondary resource. In the current research, a hydrometallurgical process combined ammonia/ammonium chloride leaching and reduction (using L-ascorbic acid) to recover copper and its oxide (CuO) as nanosized particles from WPCBs was investigated. The results of leaching indicated that 96.7% of copper could be recovered at a temperature of 35 °C for a leaching duration of 2 h with ammonium chloride and ammonia concentration of 2 mol/L at a solid:liquid ratio of 1:10 g/cm3. The synthesized particles exhibit spherical and distorted sphere morphology with average particle size of 460 nm and 50 nm for Cu and CuO NPs, respectively. The antibacterial activity of Cu, CuO, and a (1:1) blend of both (Cu/CuO) has been examined against five different bacterial and fungal strains. The highest zone of inhibition was measured as 21.2 mm for Cu NPs toward Escherichia coli and 16.7 mm for Cu/CuO blend toward Bacillus cereus bacteria. The highest zone of inhibition was measured as 13 mm and 13.8 mm for Cu/CuO blend toward Fusarium proliferatum and Penicillium verrucosum fungi. Cu/CuO blend showed notable photocatalytic activity towards Rhodamine B dye under visible light irradiation with 96% degradation rate within 120 min. Using the process developed in this study, copper and its oxide as nanoparticles can be produced from WPCBs and used for multifunctional applications.

E-waste recycled materials as efficient catalysts for renewable energy technologies and better environmental sustainability

Waste from electrical and electronic equipment exponentially increased due to the innovation and the ever-increasing demand for electronic products in our life. The quantities of electronic waste (e-waste) produced are expected to reach 44.4 million metric tons over the next five years. Consequently, the global market for electronics recycling is expected to reach $65.8 billion by 2026. However, electronic waste management in developing countries is not appropriately handled, as only 17.4% has been collected and recycled. The inadequate electronic waste treatment causes significant environmental and health issues and a systematic depletion of natural resources in secondary material recycling and extracting valuable materials. Electronic waste contains numerous valuable materials that can be recovered and reused to create renewable energy technologies to overcome the shortage of raw materials and the adverse effects of using non-renewable energy resources. Several approaches were devoted to mitigate the impact of climate change. The cooperate social responsibilities supported integrating informal collection and recycling agencies into a well-structured management program. Moreover, the emission reductions resulting from recycling and proper management systems significantly impact climate change solutions. This emission reduction will create a channel in carbon market mechanisms by trading the CO2 emission reductions. This review provides an up-to-date overview and discussion of the different categories of electronic waste, the recycling methods, and the use of high recycled value-added (HAV) materials from various e-waste components in green renewable energy technologies.

Synthesis and Characterization of Ferrous and Copper Nanoparticles from E-Waste Using Biological Reduction by Lichen-Associated Bacteria and Their Application in Antifouling Activity

The largest and fastest growing industry in the world is electronic industries and the generation of waste are emerging problem. Electronic wastes are the source of precious metals that contributes 40 to 50 times more than the ore extracted from mines. The recycling of the waste is very important as it can protect the earth's natural resources. There are various methods for recycling e-waste such as chemical, fire, physical, and mechanical method. Currently, chemical treatment is in practice for recycling but, due to the usage of inorganic chemicals, it gives more environmental issues. Therefore, this paper used the biological method to prepare the nanoparticle from e-waste as it is an eco-friendly method. The copper and ferrous nanoparticle was extracted from the e-waste and biologically reduced using lichen-associated bacterial such as Parmotrema tintorum and P. recticulatum. The characteristics of these nanoparticles such as size, shape, and functional group were analyzed using UV, PSA, SEM, and FTIR respectively. The size of the synthesized particle was in the range of 10-100 nm using PSA. At the 2.5% concentration, the synthesis of ferrous nanoparticles was confirmed by the peak value obtained at 430 nm and 540 nm for copper nanoparticles. The antifouling properties of synthesized nanoparticles were analyzed by colliding them with the paint and applying to the iron surface. In recent research, the nanomaterials were able to use to reduce the fouling activity, also prevent harmful effects to the other marine species and the resistance of some microorganisms to antifoulants. This study helps to prevent environmental contaminants by using the copper and ferrous nanoparticle substances synthesized from the e-waste materials with the help of bacterial reduction.

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.

Utilising problematic waste to detect toxic gas release in the environment: fabricating a NiO doped CuO nanoflake based ammonia sensor from e-waste

Using problematic electronic waste to synthesise high-purity nanomaterials can enable sustainable production and create opportunities to divert waste from landfills. Reported here is a simple strategy for the controllable synthesis of in situ NiO doped CuO nanoflakes from waste flexible printed circuit boards (FPCBs) using a chemothermal microrecycling process, and the nanomaterial is then utilised for an ammonia (NH₃) sensor at room temperature. Characterisation of the nanoflakes confirmed the purity of the CuO phase with a monoclinic structure without the formation of the Cu₂O phase. The NiO doped CuO 2D nanoflakes made of an assembly of 1D nanorods with a high surface area of 115.703 m² g^-1 are selectively synthesised from the waste FPCBs and have outstanding gas sensing characteristics such as a high response, a fast response (11.7 s) and a recovery time of (21.5 s), good stability, and superior selectivity towards 200 ppm of NH₃ gas at room temperature (RT, 20 °C). From a broader perspective, the process opens up exciting new avenues explore the production of toxic gas sensing functional materials from toxic and problematic waste.

Selective recovery of gold from dilute aqua regia leachate of waste printed circuit board by thiol-modified garlic peel

Garlic peel (GP) was chemically modified by using thiourea under hydrothermal treatment, which could selectively adsorb gold ions from the 1/10 dilute aqua regia media directly without needing the dangerous evaporation operation. The synthetic chloroauric solution and practical leach liquor of the waste PCB (printed circuit board) powder in dilute aqua regia were employed to assess the adsorption performance on the thiol-GP and the commercial quaternary ammonia anion resin of D201, respectively. It was experimentally confirmed that the adsorption efficiency of gold onto the thiol-GP and D201 resin both reached 100%, and the maximum adsorption capacity of thiol-GP gel was evaluated as 42.59 mg Au/g that was much larger than that of D201 resin (3.33 mg Au/g). The thiol-GP gel adsorption efficiency of other coexisting base metal ions like Cu²⁺, Ni²⁺, Al³⁺, and Fe³⁺ from dilute aqua regia leach liquor of the waste PCB powder was near zero, and only gold could be enriched by selective adsorption onto the thiol-GP gel. At least 3 cycles of adsorption/elution could be obtained without decreasing the adsorption efficiency drastically. The adsorbed gold on the thiol-GP was able to be eluted effectively by using the mixture solution of 0.1 M thiourea and 0.1 M hydrochloric acid, and finally the solid gold could be recovered by sodium borohydride through a reduction process. This study demonstrated a green, environmentally friendly, low-cost, and efficient method for selective recovery of gold from the dilute leach liquor (aqua regia) of waste circuit boards.

Photocatalytic Materials Obtained from E-Waste Recycling: Review, Techniques, Critique, and Update

Waste-derived materials obtained from the recovery and recycling of electronic waste (e-waste) such as batteries and printed circuit boards have attracted enormous attention from academia and industry in recent years, especially due to their eco-friendly nature and the massive increment in e-waste due to technological development. Several investigations in the literature have covered the advances achieved so far. Meanwhile, photocatalytic applications are especially of interest since they maintain mutual benefits and can be used for H2 production from solar water splitting based on semiconductor processing as a proper environmentally friendly technique for solar energy conversion. In addition, they can be utilized to degrade a variety of organic and non-organic contaminations. Nonetheless, to the best of the authors’ knowledge, there has not been any comprehensive review that has specifically been focused on e-waste-derived photocatalytic materials. In this regard, the present work is dedicated to thoroughly discussing the related mechanisms, strategies, and methods, as well as the various possible photocatalysts synthesized from e-wastes with some critiques in this field. This brief overview can introduce modern technologies and promising possibilities for e-waste valorization, photocatalytic processes, and new photocatalytic degradation methods of eco-friendly nature. This paper discusses various e-waste-obtained photocatalytic materials, synthesis procedures, and applications, as well as several types of e-waste, derived materials such as TiO2, ZnO, indium tin oxide, and a variety of sulfide- and ferrite-based photocatalytic materials.

Morphology, Phase and Chemical Analysis of Leachate after Bioleaching Metals from Printed Circuit Boards

The article presents the assessment of solutions and dried residues precipitated from solutions after the bioleaching process of Printed Circuit Boards (PCB) utilizing the Acidithiobacillus ferrooxidans. The obtained dried residues precipitated from bioleaching solution (leachate) and control solution were tested using morphology, phase, and chemical composition analysis, with particular emphasis on the assessment of crystalline and amorphous components. The analysis of the dried residues from leachate after bioleaching as well as those from the sterile control solution demonstrated a difference in the component oxidation—the leachate consisted of mainly amorphous spherical particles in diameter up to 200 nm, forming lacy aggregates. In the specimenform control solution larger particles (up to 500 nm) were observed with a hollow in the middle and crystalline outer part (probably Fe2O3, CuFeS2, and Cu2O). The X-ray diffraction phase analysis revealed that specimen obtained from leachate after bioleaching consisted mainly of an amorphous component and some content of Fe2O3 crystalline phase, while the dried residue from control solution showed more crystalline components. The share of the crystalline and amorphous components can be related to efficiency in dissolving metals during bioleaching. Obtained results of the investigation confirm the activity and participation of the A. ferrooxidans bacteria in the solubilization process of electro-waste components, with their visible degradation–acceleration of the reaction owing to a continuous regeneration of the leaching medium. The performed investigations allowed to characterize the specimen from leachate and showed that the application of complementary cross-check of the micro (SEM and S/TEM) and macro (ICP-OES and XRD) methods are of immense use for complete guidance assessment and obtained valuable data for the next stages of PCBs recycling.

Leaching of Copper from Waste-Printed Circuit Boards (PCBs) in Sulfate Medium Using Cupric Ion and Oxygen

In the present paper, the leaching of copper from printed circuit boards (PCBs) using sulfuric acid with Cu2+ and O2 is proposed. The effects of various process parameters such as agitation speed, temperature, the type and the flow rate of gas, initial Cu2+ concentration, and pulp density were investigated to examine the dissolution behavior of Cu from PCBs in 1 mol/L sulfuric acid. The kinetic studies were performed using the obtained leaching data. The leaching rate of Cu from PCBs was found to be higher on addition of Cu2+ and O2 to the leachant in comparison with the addition of O2 or both Cu2+ and N2 in the leachant. The leaching efficiency of Cu was found to be increased with increasing agitation speed, temperature, O2 flow rate, and initial Cu2+ concentration and decreasing pulp density. The 96% of Cu leaching efficiency was obtained under the following conditions: sulfuric acid concentration, 1 mol/L; temperature, 90 °C; agitation speed, 600 rpm; pulp density, 1%; initial Cu2+ concentration, 10,000 mg/L; and O2 flow rate, 1000 cc/min. The leaching data and analyses indicate that the Cu leaching from PCBs followed the reaction-controlled model satisfactorily and determined that the activation energy was found to be 23.8 kJ/mol. Therefore, these results indicate that the sulfuric acid solution with Cu2+ and O2 as a mild leach medium without strong oxidants such as HNO3, H2O2, and Fe3+ is valid for Cu leaching from PCBs.

Advanced utilization of copper in waste printed circuit boards: Synthesis of nano-copper assisted by physical enrichment

The copper in the waste printed circuit boards (WPCBs) is cleanly recycled by physical methods and presented in the form of nano copper particles by hydrometallurgical, which provides environmental approach to the advanced utilization of metal copper. Copper in WPCBs was first pre-concentrated by gradient enrichment process including gravity separation, mechanical grinding and flotation. The leaching method was then used to dissolve copper from the flotation concentrate in ammoniacal/ammonium salt solutions. Subsequently, reduction treatment was conducted to synthesize nano-copper from leaching solution. The enrichment results of the clean physical separation process show that the grade of copper increased from 16.22% to -38.05% by gravity separation, and the grade of copper further increased to 72.62 % by flotation after dissociation, which avoids overgrinding of low value components. Copper nanoparticles can be prepared effectively, and the recovery of copper in the leaching process reaches 99 %. The particle size of copper nanoparticles obtained by ascorbic acid reduction is tens of nanometers, and the surface of copper nanoparticles is smooth and nearly spherical. The present study proposes an environmentally friendly process of preparing nano-copper from the copper in WPCBs.

Waste-Derived Nanoparticles: Synthesis Approaches, Environmental Applications, and Sustainability Considerations

For the past few decades, a plethora of nanoparticles have been produced through various methods and utilized to advance technologies for environmental applications, including water treatment, detection of persistent pollutants, and soil/water remediation, amongst many others. The field of materials science and engineering is increasingly interested in increasing the sustainability of the processes involved in the production of nanoparticles, which motivates the exploration of alternative inputs for nanoparticle production as well as the implementation of green synthesis techniques. Herein, we start by overviewing the general aspects of nanoparticle synthesis from industrial, electric/electronic, and plastic waste. We expand on critical aspects of waste identification as a viable input for the treatment and recovery of metal- and carbon-based nanoparticles. We follow-up by discussing different governing mechanisms involved in the production of nanoparticles, and point to potential inferences throughout the synthesis processes. Next, we provide some examples of waste-derived nanoparticles utilized in a proof-of-concept demonstration of technologies for applications in water quality and safety. We conclude by discussing current challenges from the toxicological and life-cycle perspectives that must be taken into consideration before scale-up manufacturing and implementation of waste-derived nanoparticles.

Flotation dynamics of metal and non-metal components in waste printed circuit boards

Flotation is an effective and clean separation technology to realize the recovery of metal in waste printed circuit boards (WPCBs). The flotation kinetic of metal and non-metal components was concerned in this study. In addition, the loading of bubbles, the collision and shedding of particles and bubbles were used to assist in proving the particle dynamics results. By analyzing the force on the particles, the load of bubbles on particles was analyzed, and the appropriate volume ratio of bubbles to particles was 1.5-8.0, depending on the particle density. Moreover, Clift model and Schiller-Naumann model has high fitting accuracy for the final bubble velocity. In addition, metal particles have greater settling velocity, which results in shorter collision time with bubbles. In the process of bubble-particle rising, the shedding probability gradually decreases, and the shedding probability of metal particles is much higher than that of non-metal particles. The results of flotation kinetics show that the removal of impurity particles represented by silicon mainly occurs in the initial stage of flotation process. The loss of copper increases with flotation time and collector dosage. This study reveals the flotation kinetics of particles from the perspectives of bubble loading, bubble-particle collision and shedding.

Mechanical activation to enhance the natural floatability of waste printed circuit boards

The metal in the waste printed circuit boards (WPCBs) is an excellent secondary metal resource. WPCBs were ground to dissociate, and impurities in the dissociated product were removed by gradient flotation to recover valuable metals in this study. The effects of crushing methods on size composition and dissociation state of the crushed products were studied. Then the gradient flotation experiment was designed to verify the natural floatability of ground materials. Grinding test shows that impact crushing has greater grinding fineness (-0.074 mm) than shear crushing, which is 42.14% and 26.18% respectively with 5 min grinding. The flotation test results illustrate that the natural floatability of impurities increases with the grinding fineness, that is, the yield of floats increases without flotation reagents. For impact crushing and shear crushing, the floats yields are 38.48% and 31.75% respectively, accompanied by 70.53% and 65.46% impurity removal for ground materials with 5 min grinding. Subsequently, 21.61% and 26.35% of impurities can be further removed with the aid of collector. Finally, the recovery of Cu in concentrate reaches 67.84% and 65.75%, respectively. FT-IR proves that the excellent floatability of particles is caused by the significant hydrophobic group. Mechanical grinding has been proved to have double effects of improving dissociation and natural floatability.