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To fulfill the different aspects of green chemistry and to achieve full use of the secondary resources (waste printed circuit boards (WPCB)), the necessity of developing green methods for recovery of precious metals (Au, Pd, and Ag) is highly demanded. In this study, a novel environment-friendly physical separation approach; the combination of crus...
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... the first step of separation procedure, a Richard Mozley Limited (Redruth, UK) hydrocyclone ( Fig. 1) was utilized to separate valuable metals through a continuous classification of solid particles according to their different size, shape, and density characteristics ( Bai et al., 2009b;Ghadirian et al., 2015). Hydrocyclone consists of a cylindrical section at the top and a conical base. In this method, the suspension is fed through a ...
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... the next step, the dilution-gravity separation (DGM) (Ren Y. et al., 2017) of underflow samples from the hydrocyclone step was performed. In the DGM, the underflow suspended solution was initially transferred into clean glass beaker and diluted by ultrapure water until 1000 mL (Fig. 1). Thereafter, the diluted suspension was mechanically stirred with a propeller stirrer at 500 rpm at 22 C for 5 min. Afterwards, 900 mL of supernatant including float sample was transferred to another beaker and subsequently filtered using a Buchner system and Whatman paper (grade 42 filter paper whatman®, UK). The rest of the solution ...
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... separation (DMG). Since more fiber rods were separated in the float fraction, fewer fiber rods can be seen in the sink sample. These results are in parallel with the RRB model and particle size distribution experimental results in Fig. 9. EDS maps were acquired from the initial feed and the optimum separated sample (UF2.2P3 À Sink). According to Fig. 10, precious metals are distributed homogeneously in the samples. Fig. 10a and 10.b illustrate that Ca, Al, and Si are the fiber rods' main components. The Cu, Fe, Sn, Pb, and Ag elemental phase distribution in the optimum separated sample (UF2.2P3 À Sink) confirms the separation of coarser grains at the end of the process which was ...
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... fewer fiber rods can be seen in the sink sample. These results are in parallel with the RRB model and particle size distribution experimental results in Fig. 9. EDS maps were acquired from the initial feed and the optimum separated sample (UF2.2P3 À Sink). According to Fig. 10, precious metals are distributed homogeneously in the samples. Fig. 10a and 10.b illustrate that Ca, Al, and Si are the fiber rods' main components. The Cu, Fe, Sn, Pb, and Ag elemental phase distribution in the optimum separated sample (UF2.2P3 À Sink) confirms the separation of coarser grains at the end of the process which was indicated in the particle size distribution analysis. Finally, in order to ...
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... (UF2.2P3 À Sink) confirms the separation of coarser grains at the end of the process which was indicated in the particle size distribution analysis. Finally, in order to obtain a better understanding of the subject, the selected processes for the efficient separation of valuable metals are addressed with a simplified flowchart represented in Fig. ...
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... The application of 21st-century solvents-ionic liquids (ILs)-in the recycling of metals has been popular for many years [3]. E-waste generated globally is a source of many metals, such as Cu, Zn, Ni, Al, Fe, Pb, and Sn, as well as precious metals (Au, Ag, Pd, and Pt), and rare earth metals (Y, Eu, Ce, Gd, and La) [8][9][10][11]. The most popular methods for recycling metals from WPCBs 4 ] with the addition of H 2 O 2 , after the primary extraction with 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM] [BF 4 ]) [44]. The extraction of Cu, Ag, and Au from WPCBs was presented with 1-butyl-3-methylimidazolium bis{(trfluoromethyl)sulfonyl}amide ([BMIM][NTf 2 ]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF 6 ]), and trihexyltetradecylphosphonium chloride, also known as Cyphos 101 ([P 6,6,6,14 ][Cl]), after preliminary leaching with (H 2 SO 4 + H 2 O 2 ) and (35% HCl + 55% HNO 3 ) [45]. ...
The recycling of metals from waste printed circuit boards (WPCBs) has been presented as a solid–liquid extraction process using two deep eutectic solvents (DESs) and four ionic liquids (ILs). The extraction and separation of Cu(II), Ag(I), and other metals, such as Al(III), Fe(II), and Zn(II), from the solid WPCBs (after the physical, mechanical, and thermal pre-treatments) with different solvents are demonstrated. Two popular DESs were used to recover valuable metal ions: (1) choline chloride + malonic acid, 1:1, and (2) choline chloride + ethylene glycol, 1:2. The extraction efficiencies of DES 1 after two extraction and two stripping stages were only 15.7 wt% for Cu(II) and 17.6 wt% for Ag(I). The obtained results were compared with those obtained with four newly synthetized ILs as follows: didecyldimethylammonium propionate ([N10,10,1,1][C2H5COO]), didecylmethylammonium hydrogen sulphate ([N10,10,1,H][HSO4]), didecyldimethylammonium dihydrogen phosphate ([N10,10,1,1][H2PO4]), and tetrabutylphosphonium dihydrogen phosphate ([P4,4,4,4][H2PO4]). Various additives, such as didecyldimethyl ammonium chloride surfactant, DDACl; hydrogen peroxide, H2O2; trichloroisocyanuric acid, TCCA; and glycine or pentapotassium bis(peroxymonosulphate) bis(sulphate), PHM, were used with ILs during the extraction process. The solvent concentration, quantity of additivities, extraction temperature, pH, and solid/liquid, as well as organic/water ratios, and the selectivity and distribution ratios were described for all of the systems. The utilization of DESs and the new ILs with different additives presented in this work can serve as potential alternative extractants. This will help to compare these extractants, additives, extraction efficiency, temperature, and time of extraction with those of others with different formulas and procedures. The metal ion content in aqueous and stripped organic solutions was determined by the ICP-MS or ICP-OES methods. The obtained results all show that solvent extraction can successfully replace traditional hydrometallurgical and pyrometallurgical methods in new technologies for the extraction of metal ions from a secondary electronic waste, WPCBs.
... The shape, size, and distribution of the particles affect the quality of particle separation and the effectiveness of the approach. Figure 2 shows the effect of the particle size enrichment method on the efficiency of the recovery of different metals from WPCBs [23,27,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. The enrichment techniques are specialized processes used after particle size reduction to separate the metals from the non-metals. ...
... The shape, size, and distribution of the particles affect the quality of particle separation and the effectiveness of the approach. Figure 2 shows the effect of the particle size enrichment method on the efficiency of the recovery of different metals from WPCBs [23,27,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. According to Figure 2, there is a trend indicating that the e-waste particle size required to obtain an efficiency between 90-100% is between 0.75-8 mm, but most processes opt for a fine grind of less than 1 mm. ...
... Effect of particle size on the recovery efficiency of precious metals[23,27,[32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. ...
The exponential growth of electronic waste (e-waste) has raised significant environmental concerns, with projections indicating a surge to 74.7 million metric tons of e-waste generated by 2030. Waste printed circuit boards (WPCBs), constituting approximately 10% of all e-waste, are particularly intriguing due to their high content of valuable metals and rare earth elements. However, the presence of hazardous elements necessitates sustainable recycling strategies. This review explores innovative approaches to sustainable metal nanoparticle synthesis from WPCBs. Efficient metal recovery from WPCBs begins with disassembly and the utilization of advanced equipment for optimal separation. Various pretreatment techniques, including selective leaching and magnetic separation, enhance metal recovery efficiency. Green recovery systems such as biohydrometallurgy offer eco-friendly alternatives, with high selectivity. Converting metal ions into nanoparticles involves concentration and transformation methods like chemical precipitation, electrowinning, and dialysis. These methods are vital for transforming recovered metal ions into valuable nanoparticles, promoting sustainable resource utilization and eco-friendly e-waste recycling. Sustainable green synthesis methods utilizing natural sources, including microorganisms and plants, are discussed, with a focus on their applications in producing well-defined nanoparticles. Nanoparticles derived from WPCBs find valuable applications in drug delivery, microelectronics, antimicrobial materials, environmental remediation, diagnostics, catalysis, agriculture, etc. They contribute to eco-friendly wastewater treatment, photocatalysis, protective coatings, and biomedicine. The important implications of this review lie in its identification of sustainable metal nanoparticle synthesis from WPCBs as a pivotal solution to e-waste environmental concerns, paving the way for eco-friendly recycling practices and the supply of valuable materials for diverse industrial applications.
... Their findings revealed a peak in enrichment within the −212 + 100 µm range, accompanied by a significant decrease below this threshold. Bilesan et al. [143] conducted an extensive study on liberation to determine the ideal hydrocyclone configuration for concentrating the metal fraction found in discarded computer motherboards, achieving up to 87 wt % metal recovery in the concentrate. Their results also revealed that a significant portion of precious metals (73 wt % gold, 66 wt % palladium, and 33 wt % silver), as well as aluminum (Al) and calcium (Ca), accumulated in the −75 µm fraction after sieving. ...
Urban mining has emerged as a concept that goes beyond conventional recycling, as it aims to tackle both the challenges of solid waste generation and management, as well as the scarcity of primary resources. Gravity concentration has gained increasing attention as a promising method for addressing crucial challenges in urban mining applications. In this sense, this review provides a comprehensive and up-to-date overview of gravity concentration in urban mining processes, covering principles, techniques, current applications, recent advancements, challenges, and opportunities. Emphasis was placed on shifting from the commonly found literature focus on ore processing to solid waste processing. Three types of solid waste, namely plastics, construction and demolition waste (CDW), and waste from electrical and electronic equipment (WEEE), were chosen for a more in-depth examination due to their massive production and widespread generation. Discussions also considered the potential of gravity concentration to address the unique challenges in their processing and explored possibilities for future developments.
... Hydrocyclones are an integral part of the available technology for the separation of non-homogeneous suspensions, not only in traditional fields like chemical engineering but also in emerging fields of biology (He et al., 2022), environmental protection and secondary utilization (Bilesan et al., 2021). Theoretically, as long as there are appropriate size or density differences between the discrete phases and the medium, hydrocyclones can always accelerate the separation process using a cyclonic force field (Svarovsky, 1984). ...
... [1] In this context, secondary "urban" ores such as electronic wastes are of particular interest as their Au content is one to two order of magnitude greater than in mined ores. [2,3] For example, waste printed circuit boards (PCBs) contain on average 224 ppm of Au [4] compared to 18 ppm in ores, [5] with Au representing over 50 % of the inherent metal value of PCBs. [2] The resource perspective for the globally generated secondary raw materials of e-waste in 2019 is estimated at 57 × 10 9 US$, of which only 10 × 10 9 US$ are currently being valorised to some extent. ...
... Typical metal contents are 10-27% copper (Cu), 2-8% aluminium (Al), 1-4% lead (Pb), 1-8% iron (Fe), 1-6% tin (Sn) and <0.1% precious metals (Au; 10-1600 ppm, Ag: 20-200x103 ppm, Pd: 5-970 ppm). 3 There are i) mechanical/physical [4][5][6][7] , ii) thermal 8,9 , and iii) chemical [10][11][12][13][14] , iv) physicochemical techniques 15 and their combinations [16][17][18] applied to recover the targeted metallic fraction from PCBs. Physical methods include dismantling; screening; shape separation; flotation; jigging; air, electrostatic, magnetic, eddy-current and density-based separation. ...
... The studies in the literature attempted to recover metallic contents by gravity methods are jigging, sorting on aero-tables, sink-float separation. 6,7,[22][23][24] Bilesan et al. 7 used hydrocyclone to recover PMs and Cu and reported 72% total separation efficiency of copper. In the other study 23 on pneumatic separation method followed by electrostatic/magnetic separation, copper recovery was 57% for 0.3-0.6 mm size fraction. ...
... The studies in the literature attempted to recover metallic contents by gravity methods are jigging, sorting on aero-tables, sink-float separation. 6,7,[22][23][24] Bilesan et al. 7 used hydrocyclone to recover PMs and Cu and reported 72% total separation efficiency of copper. In the other study 23 on pneumatic separation method followed by electrostatic/magnetic separation, copper recovery was 57% for 0.3-0.6 mm size fraction. ...
In recent years, there has been a growing focus on the reuse of metallic components from waste electrical and electronic equipment (WEEE) which refers to electrical and electronic equipment that has become obsolete, stopped working, or developed defects during production. In this research, shaking table was selected as a gravity concentration tool for the recovery of copper from the light components. The flowsheet included comminution, gravimetric concentration and physical/chemical characterization of feed material and products. The process parameters were deck angle (degrees), motion frequency (Hz), wash water rate (Lpm), and particle size diameter. The Box Behnken Design (BBD) was used to optimize the performance of the wet shaking table and to identify the ideal combination of its operating parameters. By analysing the experimental design, it was found that the optimal settings for deck angle, motion frequency, wash water rate, and particle size diameter were 2 degrees, 50 Hz, 12 Lpm, and -500+300 mm, respectively. These optimal settings were located near the central points of the experimental design, suggesting that the actual optimal point could be within the design space.
... From these, waste printed circuit boards (PCBs) represent the most economically attractive portion and account for about 3% of the total e-waste [9]. Therefore, PCBs recycling is a business opportunity with a high potential to obtain revenue from growth in the extraction and reuse of precious and base metals, such as gold, silver, and copper [10]. In addition, PCBs contain one of the highest concentrations of rare and precious metals (RPM). ...
Various metals and semiconductors containing printed circuit boards (PCBs) are abundant in any electronic device equipped with controlling and computing features. These devices inevitably constitute e-waste after the end of service life. The typical construction of PCBs includes mechanically and chemically resistive materials, which significantly reduce the reaction rate or even avoid accessing chemical reagents (dissolvents) to target metals. Additionally, the presence of relatively reactive polymers and compounds from PCBs requires high energy consumption and reactive supply due to the formation of undesirable and sometimes environmentally hazardous reaction products. Preliminarily milling PCBs into powder is a promising method for increasing the reaction rate and avoiding liquid and gaseous emissions. Unfortunately, current state-of-the-art milling methods also lead to the presence of significantly more reactive polymers still adhered to milled target metal particles. This paper aims to find a novel and double-step disintegration–milling approach that can provide the formation of metal-rich particle size fractions. The morphology, particle fraction sizes, bulk density, and metal content in produced particles were measured and compared. Research results show the highest bulk density (up to 6.8 g·cm−3) and total metal content (up to 95.2 wt.%) in finest sieved fractions after the one-step milling of PCBs. Therefore, about half of the tested metallic element concentrations are higher in the one-step milled specimen and with lower adhered plastics concentrations than in double-step milled samples.
... Non-metallic fractions are generated, and volume reduction is not significant. [20][21][22] Pyrometallurgy Significant volume reduction, high treatment efficiency. ...
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.
... As a matter of fact, in order to get an ideal separation result, different pretreatment techniques are included in these methods to obtain a mixture of metal and non-metal components [29]. Pretreatment methods include microwave irradiation, physicochemical method, pyrolysis, and so on. ...
Accumulation of electronic waste (e-waste) will place a heavy burden on the environment without proper treatment; however, most ingredients contained in it are useful, and it could bring great economic benefits when recycled. A three-phase alternating current (AC) arc plasma pyrolysis device was designed for resourcing treatment of waste printed circuit boards (WPCBs). This paper focuses on the analysis of plasma pyrolysis gas products, and the results showed that the plasma could operate stably, and overcame the problems of the poor continuity and low energy of single-arc discharge. Air-plasma would generate NOx contaminants, burn the organics, and oxidize the metals; therefore, air had not been selected as a working gas. Ar-plasma can break the long chains of organic macromolecules to make a combustible gas. Moreover, the strong adhesion between the metals and fiberglass boards would be destroyed, which facilitates subsequent separation. Ar/H2-plasma promoted the decrease of carbon dioxide and the increase of combustible small molecular hydrocarbons in the pyrolysis product compared with Ar-plasma, and the increase of the H2 flow rate or plasma power intensified that promotion effect. The percentage of other components, except the hydrogen of CO2, CO, CH4, C2H4, and C3H6, accounted for 55.7%, 34.2%, 5.6%, 4.5%, and 0% in Ar-plasma, and changed to 35.0%, 29.0%, 11.2%, 24.3%, and 0.5% in Ar/H2-plasma. Ar/H2-plasma could provide a highly chemically active species and break chemical bonds in organic macromolecules to produce small molecules of combustible gas. This laboratory work presents a novel three-phase AC arc plasma device and a new way for recycling WPCBs with high value.
... An effective recycling of these materials is essential to keep them available for the manufacturing of new products, conserving natural resources, and being a great contribution to the circular economy, removing waste from its disposal and reinserting it in the production cycle. Thus, the proper management of electronic waste is essential to guarantee access for future generations of electronic products, to preserve natural resources and human 2 of 11 health, to protect working conditions, to reduce the environmental impacts associated with production, and to use and dispose of electronic equipment [4]. ...
This study proposed an evaluation of enrichment processes of obsolete Printed Circuit Boards (PCBs), by means of gravity and electrostatic separation, aiming at the recovery of metals. PCBs are the most important component in electronic devices, having high concentrations of metals and offering a secondary source of raw materials. Its recycling promotes the reduction in the environmental impacts associated with its production, use, and disposal. The recovery method studied started with the dismantling of the PCB, followed by a comminution and granulometric classification. Subsequent magnetic, gravity, and electrostatic separations were performed. After the separations, a macroscopic visual evaluation and chemical analysis were carried out, determining the metal content in the concentrate products. The results obtained from gravity separation showed a product with metallic concentrations of 89% and 76% for particle sizes of 0.3–0.6 mm and 0.6–1.18 mm, respectively. In electrostatic separation, the product obtained was 88% for the lower particle size (<0.3 mm) and 62% for particles sizes >1.18 mm.
