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A novel process of extracting precious metals from waste printed circuit boards: Utilization of gold concentrate as a fluxing material
Abstract
Waste printed circuit boards (PCBs) are highly toxic materials because of the hazardous substances that are incorporated into them. An advanced recycling technology based on pyrometallurgical treatment using Au concentrate as a flux material was developed in this study. The benefits of employing roasted gold concentrate (RGC) in the smelting process of waste PCBs were demonstrated through high-temperature experiments. The major oxide compositions of PCBs (CaO, Al2O3, and SiO2) were fluxed using oxidized Au concentrate composed of FetO and SiO2. Quaternary slag systems (CaO-FetO-Al2O3-SiO2) were formed during the smelting process, which rendered the process of separation of oxide impurities from Cu-based alloys easier. Precious metals (Au and Ag) were effectively recovered from waste PCBs and Au concentrate in the form of a metal alloy that required further treatment by leaching and extraction. Residual S in the RGC significantly changed the alloy phases. A large quantity of S was formulated into a matte phase, while a small amount of S was dissolved into a Cu-Fe metal alloy. The subsequent hydrometallurgical process was optional. Electrorefining or pressure leaching could be applied depending on the type of Cu alloy.
... Meanwhile, the excessive use of precious metals in modern industries has greatly contributed to the generation of electronic waste (e-waste) and wastewater, such as in the electricity and electronics industries [5][6][7][8]. Therefore, the importance of recovering gold from secondary resources is highlighted [9][10][11]. ...
... Finally, using ICP-AES, the ion concentration in the filtrate was finally determined. The distribution ratio (D) and the selectivity coefficient (k) were computed using Equations (10) and (11) ...
The recovery of precious metals from secondary resources is significant economically and environmentally. However, their separation is still challenging because they often occur in complex metal ion mixtures. The poor selectivity of adsorbents for gold in complicated solutions prevents further application of adsorption technology. In this study, a Zr-based MOF adsorbent, MIL-161, was synthesized using s-tetrazine dicarboxylic acid (H2STz) as an organic ligand. MIL-161 demonstrated a high adsorption capacity of up to 446.49 mg/g and outstanding selectivity for gold(III) in a simulated electronic waste solution as a result of the presence of sulfur- and nitrogen-containing groups. In addition, the MIL-161 adsorbents were characterized using Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TG), Brunner–Emment–Teller (BET), and X-ray photoelectron spectroscopy (XPS). Additionally, the adsorption kinetics, isotherms, and thermodynamics of the MOF adsorbents were also thoroughly examined. More importantly, the experimental results and DFT calculations indicate that chelation and electrostatic interactions are the main adsorption mechanisms.
... E-waste fundamentally consists of plastics, inert oxides, and metals. The latter are significantly found in circuit boards, primarily encompassing common metals such as Cu, Sn, Fe, Ni, Al, and Zn, while also containing smaller quantities of Mo, Sb, and precious metals like Au and Ag (Zhang et al., 2018;Fu et al., 2019;Gu et al., 2019;Park and Kim, 2019). Given the high presence of elements such as Cu, Fe, Sn, Ni, Ag, and Zn in e-waste, theoretically, it is feasible to utilize circuit board alloys as the primary component in the creation of copperbased brazing metals (Kell, 2009;Guo et al., 2015;Hsu et al., 2019;Rene et al., 2021;Murthy and Ramakrishna, 2022;Shahabuddin et al., 2023). ...
The effects of different contents of e-waste alloy on the microstructure and joint properties of Cu90PSn brazing filler metal was investigated during copper and copper brazing. Microstructure of base metal and brazing filler metal was studied with scanning electronic microscopy (SEM). The properties of brazing joint obtained by adding different electronic waste filler metal for smelting copper alloy were compared together. The results indicated that the fluidity of Cu90PSn brazing filler metal was weakened and the spreading property of Cu90PSn brazing filler metal was damaged after the addition of e-waste copper alloy. The structure of Cu90PSn brazing filler metal is mainly composed of (Cu), Cu3P and (Cu,Sn) compounds. When a small amount of electronic waste copper alloy is added, a trace amount of Fe in the brazing filler metal is distributed in the matrix structure of the filler metal in the form of solid solution. With the increase of copper alloys contents by smelting e-waste, Fe content in Cu90PSn brazing filler metal increases; the granular Fe3P phosphide changes into lamellar form. The Cu3P compound phase changes from continuous large orderly arrangement to discontinuous small block structure. Therefore, adding a trace amount of electronic waste copper alloy to the solder induction brazing copper/copper can obtain a uniform composition of the brazing structure. And the welding performance is not affected. However, As the content of e-waste smelted copper alloy continues to increase, the tensile strength shows a downward trend, which is attributed to the presence of brittle compound Fe3P in the joint.
... 7 An example of WEEE is printed circuit boards (PCBs) that contain various noble metals, which has led to studies concerning the development of recycling techniques for PCBs present in electronic waste. 8,9 The metallic fraction is the most important part of PCBs, due to the presence of economically important metals such as gold (Au), silver (Ag), and copper (Cu). 10 PCBs can contain significant amounts of gold, reaching around 0.03%, which is a very high value, if compared to an average 0.0005% content of Au in ores. ...
Advances in technological development mean that the recovery of rare and strategic metals from secondary sources has become essential, due to the high demand for these metals in the production of electronic equipment. Contributing to this goal, the main purpose of this work was to develop Nylon 6 nanofibers modified with the Cyanex 272 organic extractant, for use in the selective recovery of gold present in printed circuit boards from armored vehicles. The nanofibers were produced by the centrifugation technique, employing the Forcespinning® system. The best extraction conditions for the separation and concentration of gold were 10% Cyanex 272, fixed pH of 1.5, contact time of 15 min, and solid:liquid ratio (S/L) of 1/700. Gold extraction efficiencies above 77% were achieved in this step. In the stripping step, efficiencies exceeding 85% were obtained using 1 M HCl, 1 M thiourea, S/L of 1/50, and contact time of 3 min. The nanofibers were evaluated in terms of their adsorption capacity, stability, and capacity for reuse in successive cycles. The results showed that the Nylon 6/Cyanex 272 nanofibers could be used in several extraction and stripping cycles. These nanofibers provided high selectivity in the recovery of gold when applied using real leachate solutions, in the presence of other metals (lead, tin, zinc, and copper). The use of nanofibers modified with Cyanex 272 was shown to be an effective option for gold recovery, with lower environmental impacts, compared to conventional liquid–liquid extraction methods that require the use of organic solvents.
... These boards typically consist of fiber glass and resin, with thin copper layers on top where electronic components are connected. They also contain hazardous heavy elements such as tin, copper, lead, zinc, nickel, antimony, chromium, strontium, barium, and so on (Oguchi et al., 2013;Park & Kim, 2019;Vermeșan et al., 2019). ...
The main aim of the present investigation is to fabricate waste printed circuit board (WPCB) particles and woven bidirectional flax fiber mat reinforced polymer matrix composite through a hand layup technique followed by vacuum bagging technique and examine its mechanical properties using the Universal Testing Machine (UTM), compression testing machine, and Shore D hardness tester. The WPCB particles with weight percentages of 0, 5, 10, 15, and 20 were used as reinforcement along with five layers of flax fiber mat to improve the adhesion behavior of epoxy resin with reinforcements and thereby improve the properties. The XRF (X‐ray fluorescence) investigation of the prepared WPCB particles confirmed the existence of various toxic elements in the processed printed circuit board (PCB). The scanning electron microscopy (SEM) analysis confirmed the presence of WPCB particles in the composite, along with flax fiber and resin. The tensile, compression, impact test shows that that the 15 wt.% WPCB particles reinforced flax fiber polymer composite gave betters properties, and the reduction of properties was seen thereafter. The percentage of water absorption increased with the weight percentage of the WPCB particles from 0% to 20%. Results indicate that the biodegradable flax fiber composites impregnated with WPCB filler can be utilized for many engineering and domestic applications.
... Instead, thiocyanate-based systems are hazardous and require additional safety measures [9]. Many processes have been investigated worldwide to extract metals from PCBs, mainly on a lab scale and a few on a pilot scale [12][13][14][15][16][17][18][19][20][21][22]. Considering the circular approach of the whole recycling concept, even the recovery of the non-metallic fraction of PCBs has been studied [1]. ...
The paper describes a small full-scale plant based on the Goldrec 1 process, designed and patented by the University of L'Aquila. The Goldrec 1 hydrometallurgical process can treat printed circuit boards (PCBs) and other gold-containing components of different grades. The first step is a mechanical treatment to reduce the size of the scraps below 2 mm. The extraction of base metals occurs in a first reactor, where elements like Cu, Sn, Al, Fe, and Zn are extracted by a sulfuric acid/hydrogen peroxide solution. After filtration, the solid is leached again with thiourea and ferric sulfate in a sulfuric acid solution to extract gold and silver. The insoluble materials, mainly the plastic fraction, are filtered off. This second solution is sent to an electrolytic cell where gold is recovered as metal powder. The resulting solution undergoes a second electrowinning, where silver is deposited on the cathode. The first pregnant solution undergoes recovery of Cu and Sn. The simulation was developed using lab-scale trial results. The 350 tons PCB/year, running in a batch operating mode, produces around 43.8 kg/y of gold, 85.8 kg/y of silver, 42.4 tons/y of copper, and 7.2 tons/y of tin oxide. The results show that profitability is easily achieved when PCBs are directly collected without cost: the net present value is 10.7 MEuro, with an internal rate of return of 150 % and a discounted payback time of 2 years only.
... Many processes have been investigated worldwide to extract metals from PCBs, mainly on a lab scale and a few on a pilot scale [12][13][14][15][16][17][18][19][20][21][22]. Considering the circular approach of the whole recycling concept, even the recovery of the nonmetallic fraction of PCBs has been studied [1]. ...
The paper describes a small full-scale plant based on the Gold-REC 1 process, designed and patented by the University of L’Aquila; the hydrometallurgical process allows the treatment of printed circuit boards (PCBs). The first step is a mechanical treatment to reduce the size of the scraps below 2 mm. The extraction of base metals occurs in a first reactor by a sulfuric acid/hydrogen peroxide solution. After filtration, the solid is leached again with thiourea and ferric sulfate in a sulfuric acid solution to extract gold and silver. This second solution is sent to an electrolytic cell where gold is recovered as metal powder. The resulting solution undergoes a second electrowinning, where silver is deposited on the cathode. The first pregnant solution undergoes recovery of Cu and Sn. A simulation was developed using lab-scale trial results. The 350 tons PCBs/year, running in a batch operating mode, produces around 43.8 kg/year of gold, 85.8 kg/year of silver, 42.4 tons/year of copper, and 7.2 tons/year of tin oxide. The results show the profitability of the process: the net present value is EUR 10.7 M, with an internal rate of return of 150% and a discounted payback time of 2 years.
... Therefore, secondary recovery of gold from discarded electronic waste is of great significance. However, since the secondary recovered gold solution may contain other metal ions such as copper, when the gold solution is not purified, the recovered gold may contain high metal impurities [4,5]. ...
In this paper, the covalent organic polymer of enaminone was modified by thiourea, and the covalent organic polymer of thiourea (CTOP) was synthesized by simple solvothermal method. At 25 ℃, the adsorption capacity of the polymer for trivalent gold ion is 2372.7 mg/g. In the mixed aqueous solution of divalent cadmium ion, trivalent gold ion, divalent copper ion, divalent cobalt ion and divalent nickel ion, CTOP can only adsorb trivalent gold ion, which indicates that CTOP has high selective adsorption performance for trivalent gold ion. In addition, CTOP material still maintains high adsorption performance after five adsorption cycles, which proves that the adsorption material has good reusability. According to the experimental results of adsorption kinetics and thermodynamics, the adsorption process of CTOP for trivalent gold ions conforms to the quasi second order adsorption model and Langmuir adsorption model, that is, the adsorption process of CTOP for trivalent gold ions is single-layer chemical adsorption. CTOP not only has strong adsorption and selectivity to Au (Ⅲ), but also has good reusability. Therefore, it is an ideal environmental functional material, which can be used to separate and enrich trivalent gold ions in wastewater.
... Mo, Sb, and rare and precious metals, such as, Au and Ag (Jiang et al., 2016), have a comparatively low concentration. The research reports that a number of methods of recovering metal from circuit boards in China and abroad are dominated by physical separation extractive techniques such as magnetic separation, electrical separation, eddy current separation (Zheng et al., 2016;Gu et al., 2019), pyrometallurgy (Park and Kim, 2019;Habibi et al., 2020;Yue et al., 2021), hydrometallurgy (Díaz-Martínez et al., 2019), Bio-hydrometallurgy (Gu, 2016), and other extractive techniques. Due to the characteristics of e-waste, including its large quantity, complicated constituents, great harm, high potential value, and difficulty in treatment (Cao et al., 2003;Zhu et al., 2018), the recovery of valuable metals is the focus of attention for metal resource recovery from e-waste. ...
In order to realize the efficient and comprehensive utilization of e-waste resources and short process preparation of alloy brazing materials, this study has analyzed the microstructure and properties of e-waste recycled brazing alloys by the analysis methods of inductively coupled plasma emission spectrometer, differential scanning calorimeter, scanning electron microscope, metalloscope, X-ray diffractometer, micro-hardness tester. Experimental results showed that phase compositions are significant differences between the alloys prepared by the recycled e-waste and the pure metals. The circuit board recycling alloy mainly consisted of α-Fe dendrites, (Cu, Sn) phases, Sn-rich phases and Cu matrix, while the alloy obtained by pure metals is composed of (Cu, Sn) phase, Sn-rich phase and Cu matrix. The melting temperature of alloy obtained by melting the circuit board is in the range of 985.3°C–1,053.0°C, which was wider and higher than that of alloy obtained by pure metal smelting. The shear strengths of the joints brazed by the brazing alloys prepared by the recycle e-waste and pure metals are 182.21 MPa and 277.02 MPa, respectively. There is little difference in hardness between the two types of brazed joints. In addition, there are a large number of precipitated phases in alloy obtained by the recycled circuit board, owing to the precipitation strengthening mechanism. The main strengthening mechanism of alloy obtained by pure metals is solid-solution strengthening. The paper focused primarily on alloy obtained by melting the circuit board and studying the specific composition, melting temperature, structure, and properties of alloys formed by melting the circuit board and pure metals. Meawhile, the size, morphology and other microstructure evolution of the second phase of brazing alloy were investigated to provide theoretical guidance for the brazing alloy in the subsequent actual production process.
... The major embedded metal values in e-waste materials are present in complex printed circuit boards (PCBs) as plastic-ceramic-metal composites [8][9][10][11]. Several processing routes including physical separation, pyrometallurgical, hydrometallurgical, biohydrometallurgical and supercritical techniques, either individually or in combination, have been proposed and have been extensively investigated to extract value metals from PCBs [12,13]. However, still there remains significant challenges to recover values at an industrial scale primarily because of the heterogeneity of the materials, the rapid changing of technology and the chemistry and structure of the materials. ...
The phase equilibria in the CaO-Al2O3-SiO2 ternary system doped with around 5, 10, 15 and 20 wt% B2O3 was studied using a high-temperature equilibration followed by rapid quenching technique. Fifteen samples with CaO/SiO2 (C/S) ratios of 0.3, 0.6 and 1.0 containing 15.6-19.1 wt% Al2O3 were equilibrated at a range of temperatures close to predicted liquidus phase boundaries within the B2O3-free ternary. Quenched samples were characterised using Scanning Electron Microscopy (SEM) to reveal the equilibrium phase assemblage and Electron Probe Microanalysis (EPMA) to determine the chemistry of individual phases. The liquidus temperatures of the synthetic slags were determined within an uncertainty of ± 10-20 °C. Depending on temperature and composition, anorthite (CaO.Al2O3.2SiO2), pseudowollastonite (CaO.SiO2), gehlenite (2CaO.Al2O3.SiO2) and tridymite (SiO2) crystals were observed in equilibrium with the liquid phase at temperatures below the liquidus. Doping with successively higher amounts of B2O3 caused the boundaries of the initial primary phase fields to shift position, generally resulting in a reduction of the liquidus temperature. The lowest liquidus temperature was 900 °C for slag with initial composition having C/S = 0.6 and 18.8 wt% B2O3 representing a decline of the liquidus by 435 °C compared to the undoped slag. Only one sample (C/S = 1.0, 18.8 wt% B2O3) resulted in an increase in the liquidus temperature due to the expansion of the pseudowollastonite phase field at high B2O3 contents. Based on the experimental results, B2O3 may be a suitable fluxing agent to reduce the smelting temperature in the CaO-Al2O3-SiO2-B2O3 quaternary system. A comparison of results with liquidus data for similar experiments using Na2O flux showed that B2O3 was more effective in lowering the liquidus.
... If the nonmetallic fraction is detoxified and reused, additional raw materials can be saved . Zeng et al., 2015), spent LiNi x Mn y Co z O 2 (A 2 ) Hu et al., 2017), WPCBs (B) (Han et al., 2020;Jadhao et al., 2020;Huang et al., 2020;Arshadi et al., 2020;Pereira et al., 2020;Liu et al., 2020;Yken et al., 2020;Jha et al., 2020;Panda et al., 2020;Amato et al., 2020;Yao et al., 2020;Guo et al., 2020;Xing et al., 2020;Qiu et al., 2020;Zhou et al., 2020;Park and Kim, 2019;Xiu et al., 2019;Hossain et al., 2019;Rigoldi et al., 2019), IBA (C 1 , C 2 ), and IFA (D 1 , D 2 ) (Dontriros et al., 2020;K.Z. Yan et al., 2020;van de Wouw et al., 2020). ...
Metal-containing solid wastes can induce serious environmental pollution if managed improperly, but contain considerable resources. The detoxification and resource recoveries of these wastes are of both environmental and economic significances, being indispensable for circular economy. In the past decades, attempts have been made worldwide to treat these wastes. Crushing and grinding-based treatments have been increasingly applied, the operating apparatus and parameters of which depend on the waste type and treatment purpose. Based on the relevant studies, the applications of crushing and grinding on four major types of solid wastes, namely spent lithium-ion batteries (LIBs) cathode, waste printed circuit boards (WPCBs), incineration bottom ash (IBA), and incineration fly ash (IFA) are here systematically reviewed. These types of solid wastes are generated in increasing amounts, and have the potentials to release various organic and inorganic pollutants. Despite of the widely different texture, composition, and other physicochemical properties of the solid wastes, crushing and grinding have been demonstrated to be universally applicable. For each of the four wastes, the technical route that involving crushing and grinding is described with the advantages highlighted. The crushing and grinding serve either mainstream or auxiliary role in the processing of the solid wastes. This review summarizes and highlights the developments and future directions of crushing and grinding-based treatments.
... As shown in Table 1 and Figure 3a obtained by the thermodynamic calculation software of FactSage 7.2 (version 7.2, Thermfact/CRCT and GTT-Technologies, Montreal, Canada and Ahern, Germany), the RM was an excellent flux agent for the SAC smelting-collection process since it contains SiO 2, Al 2 O 3 , TiO 2 , and Fe t O. A previous study found that a multicomponent slag with more than five different oxides generally complicates slag design and hinders a clear expectation of the physicochemical properties of slag [28]. Restricting the number of oxides can effectively facilitate slag design for the smelting process. ...
Co-treatment for two kinds of hazardous solid waste is an effective method to reduce cost and increase recycle efficiency of value resource. This work developed an integrated process based on capture of red mud (RM) and a one-step heat-treatment process to efficiently recover PGMs from spent auto-catalysts (SAC) and reuse RM simultaneously. Firstly, the iron oxide in RM was reduced to metallic iron to capture PGMs by the reduction process, without the addition of an extra reducing agent, since SAC contained abundant organic volatiles. Then, the mixed waste of SAC and RM was melted under high temperature with additives of CaO and H3BO3. More than 99% of PGMs can be extracted under the optimal conditions of 40–50 wt% of RM addition, 14 wt% of H3BO3 addition, 0.7–0.8 of basicity, 1500 °C of temperature, and 40 min of holding time. In addition, PGM content in obtained glassy slag was less than 1 g/t. The mechanism of iron trapping PGMs was also discussed in detailed, which mainly contained two stages: migration of PGMs and separation of PGM-bearing alloy and slag phases. Besides, the obtained glassy slag was further prepared into glass-ceramic by a one-step heat-treatment process. It was found that the prepared glass-ceramic has good thermostability and an excellent stabilizing effect on heavy metals. Overall, the results indicated that the developed integrated smelting–collection process is an efficient and promising method for the reutilization of SAC and RM.
... However, it is not easy to separate precious metals from waste devices. Indeed, pyrometallurgy requires high energy consumption, while hydrometallurgy applied on WEEE needs specific operating parameters in order to be selective [13][14][15]. An example is given by the Printed Circuit Boards (PCB), which contain up to 60 different metals simultaneously [16], including base metals, copper layers, precious and rare earths metals [17]. ...
The intensive exploitation of resources on a global level has led to a progressive depletion of mineral reserves, which were proved to be insufficient to meet the high demand for high-technological devices. On the other hand, the continuous production of Waste from Electrical and Electronic Equipment (WEEE) is causing serious environmental problems, due to the complex composition of WEEE, which makes the recycling and reuse particularly challenging. The average metal content of WEEE is estimated to be around 30% and varies depending on the manufacturing period and brand of production. It contains base metals and precious metals, such as gold and palladium. The remaining 70% of WEEEs is composed of plastics, resins, and glassy materials. The recovery of metals from WEEEs is characterized by two main processes well represented by the literature: Pyrometallurgy and hydrometallurgy. Both of them require the pre-treatment of WEEEs, such as dismantling and magnetic separation of plastics. In this work, the selective adsorption of precious metals has been attempted, using copper, gold, and palladium aqueous solutions and mixtures of them. A screening on different adsorbent materials such as granular activated carbons and polymers, either as pellets or foams, has been performed. Among these, PolyEther Block Amide (PEBA) was elected as the most performing adsorbent in terms of gold selectivity over copper. Spent PEBA has been then characterized using scanning electron microscope, coupled with energy dispersive spectroscopy, demonstrating the predominant presence of gold in most analyzed sites, either in the pellet or foam form.
... Several other processes were investigated to recover metals from PCBs [6][7][8][9][10][11][12][13][14], but, considering the circular approach of the full recycling concept, even the recovery of the non-metallic fraction of PCBs was studied [10]. Debromination is a necessary treatment before any other recycling process. ...
The present paper is focused on the extraction of gold from high-grade e-waste, i.e., spent electronic connectors and plates, by leaching and electrowinning. These connectors are usually made up of an alloy covered by a layer of gold; sometimes, in some of them, a plastic part is also present. The applied leaching system consisted of an acid solution of diluted sulfuric acid (0.2 mol/L) with thiourea (20 g/L) as a reagent and ferric sulfate (21.8 g/L) as an oxidant. This system was applied on three different high-grade e-waste, namely: (1) Connectors with the partial gold-plated surface (Au concentration—1139 mg/kg); (2) different types of connectors with some of which with completely gold-plated surface (Au concentration—590 mg/kg); and (3) connectors and plates with the completely gold-plated surface (Au concentration—7900 mg/kg). Gold dissolution yields of 52, 94, and 49 % were achieved from the first, second, and third samples, respectively. About 95 % of Au recovery was achieved after 1.5 h of electrowinning at a current efficiency of only 4.06 % and current consumption of 3.02 kWh/kg of Au from the leach solution of the third sample.
... They contain valuable metals such as copper (Cu), gold (Au), silver (Ag), tin (Sn) etc. Based on the contained compositions, the CaO-Al 2 O 3 -SiO 2 (CAS) slag system is the most relevant to the recovery of metals from waste PCBs [4]. The CAS system is a highly refractory system requiring elevated temperatures to create a liquid slag. ...
The recovery of valuable and critical metals from electronic wastes (ewaste)
via the pyrometallurgical route has some challenges including high processing
temperatures. Designing appropriate slag systems based on the major elemental
components in e-waste could bring operational advantages by lowering the liquidus
temperature. In this study, the quaternary slag system CaO–Al2O3–SiO2–Na2Owas
investigated to determine the liquidus temperature and phase equilibria of slags relevant
to e-waste smelting. The slags were thermally equilibrated at different temperatures
inside a vertical tube furnace followed by rapid quenching. The quenched slags
were examined by SEM to observe the phase formed and the equilibrium compositions
were determined using energy dispersive (ED) spectrometry. The liquidus
temperature of the slags in the anorthite (CaO·Al2O3·2SiO2) phase field was significantly
decreased with increasing levels of Na2O. The slag composition moved
towards the pseudo wollastonite (CaO·SiO2) region upon the addition of Na2O.
... Printed circuit boards (PCBs) are an integral part of most electronic equipment and, on average, comprise 40% metals, 30% plastics, and 30% ceramics [2]. Effective utilization of waste PCBs offers tremendous recycling potential for the recovery of base metals (Cu, Ni, Fe, Sn, Pb) and precious metal (Au, Ag) values [3][4][5]. Poor recovery of the base and precious metals is a significant challenge for physical processing as they deport to the fine fraction as a by-product during size reduction. Froth flotation is an effective method for recycling the fine PCB particles due to their hydrophobic nature. ...
The recovery of metals from discarded printed circuit boards using environmentally-friendly physical routes is gaining importance. Physical separation of metal values from non-metallic constituents exploits various characteristics of crushed powder such as density, liberation, shape, size, and wettability. However, the generation of fines during grinding/crushing of the printed circuit boards is an unavoidable but essential by-product. The fine fractions are discarded due to the higher amounts of non-metallic fraction and poor separation of metallic values. In this study, the flotation process was studied to separate metallic and non-metallic values without the addition of external additives from the fine fraction of printed circuit boards (< 212 µm). The natural hydrophobic response of plastic and organic matter in fines stabilized the froth without additional reagents. The difference in tapped density for tailing (~ 0.5 g/cm3) and concentrate (~ 2.7 g/cm3) fraction ensures good separation. The metallic fraction increases from 14.3% in the feed to 91.7% in the concentrate. Recovery for metallic values was observed as ~ 72.3% with a purity of ~ 92% and comprised 77.9% Cu, 8.3% Sn, and 5.5% Pb.
This significant accumulation of waste printed circuit boards (PCBs) is becoming an increasingly alarming problem, both in terms of the environment and the utilization of metal resources. The current methods for recovering metals from waste PCBs mainly include mechanical treatment, pyrometallurgy, and hydrometallurgy. However, these methods have more or less serious shortcomings. More importantly, they are poorly adapted to stringent environmental regulations. In this context, there is an urgency to develop simple and environmentally friendly methods for metal recovery from PCB waste. Deep eutectic solvents (DESs), a family of green designable solvents, have emerged in recent years and have attracted increasing interest due to their ease of preparation, high biodegradability, low toxicity, and high tunability. This chapter provides a brief overview of waste PCBs and the methods currently used in the industry to recover metals from waste PCBs. The characteristics of DESs and their recent applications in metal recovery are highlighted. The advantages and disadvantages of these metal recovery methods are comprehensively compared in terms of economic benefits, environmental impact, and process complexity. Finally, the chapter concludes by outlining the challenges of DES application in future metal recovery.
The improper disposal of discarded electronic and electrical equipment raises environmental and health concerns, spanning air pollution to water and soil contamination, underscoring the imperative for responsible management practices. This review explores the complex composition of discarded printed circuit boards (DPCBs), crucial components in electronic devices. Comprising substrates, electronic elements and solder, DPCBs showcase a heterogeneous structure with metal (30.0-50.0%) and non-metal (50.0-70.0%) fractions. Notably abundant in precious metals such as Au, Ag, and Pd, DPCBs offer a compelling avenue for recycling initiatives. The inclusion of heavy metals and flame retardants adds complexity, necessitating environmentally sound disposal methods. Ongoing research on smart disassembly, utilising 3D image recognition technology, underscores the importance of accurate identification and positioning of electronic components (ECs). The targeted approach of smart disassembly, centred on valuable components, highlights its significance, albeit with challenges in equipment costs and capacity limitations. In mechanical disassembly, techniques such as grinding and heat application are employed to extract ECs, with innovations addressing gas emissions and damage induced by overheating. Chemical disassembly methods, encompassing epoxy resin delamination and tin removal, present promising recovery options, whilst the integration of chemical and electrochemical processes shows potential. Efficient sorting, encompassing both manual and automated methods, is imperative post-disassembly, with smart sorting technologies augmenting accuracy in the identification and categorisation of ECs. In addition, explorations into NH3/NH4+ solutions for selective metal recovery underscore challenges and stress the necessity for meticulous process optimisation in environmentally sustainable PCB recycling. Challenges and future perspectives have also been expounded.
While e-waste poses significant environmental and health risks, it also harbors valuable metals like gold, ripe for recycling. However, extracting gold from e-waste carries its own ecological footprint. Therefore, employing tools like Life Cycle Assessment (LCA) to evaluate environmental impacts and identify mitigation measures is imperative. This research addresses critical gaps in the literature surrounding gold recovery from e-waste. It covers a range of methods, including hydrometallurgical and pyrometallurgical (well-established) to mechanical and biotechnological (less explored for gold recovery), rectifying the imbalance in methodological attention. This study also prioritizes environmental assessment, elevating LCA to a central investigative focus for understanding the sustainability of gold recovery from e-waste. Notably, there is a paucity of consistent and systematic comparisons between diverse gold recovery methods from e-waste in existing literature. While some publications touch on environmental aspects, comprehensive LCA investigations are lacking. Thus, this research explicitly bridges this gap through a comparative LCA, evaluating mechanical, hydrometallurgical, pyrometallurgical, electrochemical, and biotechnological methods and contrasting them with conventional mining (baseline method). The results highlight significant reductions in damage to human health, with the mechanical and electrochemical methods leading the way with a noteworthy 98% reduction compared to the baseline. The hydrometallurgical and pyrometallurgical methods also demonstrate substantial decreases of 83% and 92%, respectively. Though the biotechnological method exhibits a comparatively lower reduction of 60%, it represents a significant advancement in curbing damage to human health. Regarding ecosystem quality, the mechanical and electrochemical methods excel with exceptional reductions of over 99%, while the biotechnological, hydrometallurgical, and pyrometallurgical methods collectively achieve a decrease of approximately 99% compared to the baseline. Across the board, all evaluated methods manifest substantial reductions in total weighted environmental impacts, amounting to an approximate 99% reduction. The biotechnological method does entail the highest exergy demand, signifying greater energy consumption, while the mechanical method demonstrates the lowest exergy consumption. Considering feasibility and scalability, the electrochemical and mechanical methods emerge as the most favorable options for sustainable gold recovery. These methods demonstrate promising results in reducing environmental impacts and are well-suited for practical implementation.
Due to the rarity of gold as a noble metal, efficient and selective Au (III) ions adsorption is critical for gold recovery. Since gold is thiophilic, in this paper, a new covalent thiourea organic polymer (CTOP) was prepared by introducing thiourea reactive groups into the covalent organic polymer of enaminone and applied to the adsorption of Au (III) ions in aqueous solution. The synthesis of the new material was confirmed by SEM, TEM, XRD, and XPS tests. Thanks to the abundant thiourea chelating sites in the CTOP, the total adsorption capacity of the material for Au (III) ions is up to 2372.7 mg/g. In addition, in mixed ionic solutions containing Au (III), Cu (II), Co (II), Cd (II), and Ni (II), it has strong selective adsorption performance for Au (III). It is worth mentioning that the CTOP material still maintains high adsorption performance after five adsorption cycles, which proves that the adsorption material has good reusability. The adsorption kinetics were investigated using pseudo-first-order and pseudo-second-order kinetic models, and the results showed that the adsorption was chemisorption. According to the experimental results of adsorption kinetics and thermodynamics, the adsorption process of CTOP for Au (III) ions conforms to the quasi-secondary adsorption model and the Langmuir adsorption model. We believe that the study of efficient adsorption of Au (III) ions by this new covalent thiourea organic polymer is of great significance for the development of gold recovery technology.
The world is rapidly transitioning to a carbon-neutral society to combat CO2-induced climate change. To become carbon-neutral, the conventional fossil-fuel-based technologies need to be replaced with low-carbon technologies including renewable energy technologies (e.g., solar power, wind power, etc.) as well as electric vehicles (EVs); however, the latter is more intensive towards materials, minerals, and metals compared to the former. As primary/natural mineral resources have been depleting, the development of green and sustainable chemical/physical technologies for metal extraction from secondary resources (e.g., E-wastes, scrap alloys, metallurgical slag/residues, mine tailings, etc.) is becoming an important issue to maintain a robust and stable supply chain of metals. Moreover, recycling of the secondary resources is essential to achieve a circular economy that reduces their negative environmental impacts.
The development of recycling methods should be encouraged for the reduction of current waste production near to zero. Besides, this could help boost circular economy while also supplying the metals needed for a low-carbon future as well as avoiding loss of materials in landfills and ponds. Therefore, the aim of this special issue is to review the latest green processes and technologies to improve sustainability by using the efficient, non-toxic and environmental-friendly techniques of physical and chemical processing for the recycling of solid wastes, which include metal-containing industrial process residues (e-wastes, scrap alloys, smelter and steel plant slags, spent cutting tools, catalysis, PV panels, REE magnets, fluorescent lamps, bauxite residues, fly ashes and concentrator tailings).
To prevent CO2-induced climate change, the world is quickly moving toward a carbon- neutral society by using electric vehicles, renewable energy sources, and other energy sources, which demand more resources than traditional ones in terms of materials, minerals, and metals. In this regard, recycling processes of rare earth elements (REEs), metals, plastic, and glass from secondary sources with a zero-waste strategy have become more important in order to reduce environmental damage and bring them into the economy when primary mineral resources are running out. Therefore, in this Research Topic, studies on effective, non-hazardous, long-term, and ecological recycling processes of solid wastes, including by-products from industrial processes containing metals have been compiled.
Ilmenite mud generated in the sulfate process for titanium dioxide pigment production is a secondary titanium resource with a high content of silica, iron oxides, and sulfur. However, the ilmenite mud is mostly landfilled. We propose roasting and high-temperature smelting processes to investigate the reduction behavior of ilmenite mud waste. Sulfur is present in ilmenite mud in the form of sulfates, and is completely removed via roasting. The phases in the roasted ilmenite mud were titanium dioxide, pseudobrookite, and silica. The roasted ilmenite was smelted to recover iron, silicon, and titanium. All the iron oxides were reduced to metallic iron. As a result, the carbothermic reduction of titanium dioxide occurred, and titanium carbide was formed. Silica was first converted into mullite using alumina and then reduced to form liquid silicon, which was combined with metallic iron to form an iron-silicon alloy. After a reduction time of 60 min, most of the silica was converted into the iron-silicon alloy, and the alloy and titanium carbide were completely separated.
Waste printed circuit boards smelting ash (WPCBs-SA), which is generated in the waste printed circuit boards (WPCBs) smelting process, is considered hazardous waste because it contains substantial amounts of highly...
The effect of the addition of Al2O3 on the viscosity of the iron-compound bearing CaO-SiO2-Al2O3-MgO slags with different SiO2 content (= 30, 40, and 50 wt%) was investigated at high temperatures. The addition of Al2O3 increased the viscosity of iron-compound bearing calcium-aluminosilicate melts. The addition of Al2O3 to the slag at low-SiO2 content (= 30 wt%) increased the fraction of Fe²⁺ at a fixed iron content because Fe³⁺ cations prefer to exist as tetrahedral unit, i.e., Fe³⁺ [IV], in the melt. On the other hand, the addition of Al2O3 to the slag at high-SiO2 content (= 50 wt%) increased the fraction of Fe³⁺ at a fixed iron content due to the preference of octahedrally coordinated Fe³⁺ [VI] in the slag. Although the redox equilibrium reaction of iron in the CaO-SiO2-Al2O3-FetO-MgO system was strongly affected by the basicity of the melt, the addition of Al2O3 polymerized silicate networks regardless of the SiO2 content in the slags. The activation energy for the viscous flow of the slags had a linear correlation with the non-bridged oxygen per tetrahedron (NBO/T) in the aluminosilicate network. Therefore, the viscosity of the iron-compound bearing calcium-aluminosilicate melt was determined by the degree of polymerization within the aluminosilicate networks.
Waste printed circuit boards (WPCBs) are identified to be the most complex recycling materials among waste electrical and electronic equipment (WEEE). Slurry electrolysis with acidic system can directly separate and recover copper from WPCBs while current efficiency and purity were generally reduced due to deposition of impurity metals and the hydrogen evolution during recovery process. In ammonia-based system, copper can be selectively extracted and copper (II) ammine complexes generally react with metallic copper to form copper (I) ammine complexes, promoting current efficiency and purity. Therefore, an efficient ammonia-ammonium carbonate slurry electrolysis system is proposed for high purity copper recycling from waste printed circuit boards of mobile phones (WPCB-MPs). The factors affecting copper current efficiency and recovery rate are systematically discussed. These results indicate that appropriate increasing NH3·H2O, (NH4)2CO3, Cu²⁺, NaCl concentration, solid-to-liquid ratio, current density and reaction time could effectively increase copper recovery rate and current efficiency. The current efficiency and recovery rate of copper are 95.2 and 90.4%, respectively under the optimum test conditions of 20 g/L Cu²⁺, 0.25 mol/L (NH4)2CO3, 4 mol/L NH3·H2O, 30 g/L solid-to-liquid ratio, 1 mol/L NaCl, 20 mA/cm², 3 h. Moreover, copper could be recovered at the cathode with a purity of 99.97%. Compared with acidic system, this study provides an efficient approach to recover high purity copper from WPCB-MPs, showing a prospective future for WEEE resource recycling.
El objetivo de este artículo es revisar el contexto mundial, y especialmente el colombiano, respecto al manejo de los residuos de equipos eléctricos y electrónicos, su aprovechamiento, recuperación y los principales métodos para la extracción de metales base y preciosos de alto valor agregado. Para ello, se realizó una revisión bibliográfica para obtener las cantidades de residuos, sus componentes principales y los métodos de extracción de metales base y preciosos; para Colombia, se realizó un estudio de caso, en el que, mediante un proceso de hidrometalurgia aplicado a teléfonos celulares, se calcularon las cantidades de metales base y preciosos que se pueden obtener. Se encontró que solo se aprovecha el 15,5 % de los residuos electrónicos en el mundo, que los principales componentes reciclables son el hierro (Fe), el cobre (Cu), el aluminio (Al), el plomo (Pb), el níquel (Ni), la plata (Ag), el oro (Au) y el paladio (Pd), y que el uso de los residuos electrónicos como fuente de metales podría reducir el consumo de energía entre 60 % y 95 %. Para el estudio de caso en Colombia, se encontró que se podrían obtener 3,8 t/año de Cu, 3,5 t/año de Fe, 56,5 kg/año de Ag, 6 kg/año de Pd y 10 kg/año de Au. Se concluye que es viable la recuperación de metales a partir de residuos eléctricos y electrónicos y que se deben buscar alternativas para aprovecharlos debido a su potencial valor agregado.
Phase equilibria of CaO-Al2O3-SiO2-Na2O slags were studied by thermal equilibration and quenching. The primary phases of the quenched slags were identified, and their equilibrium compositions determined by electron probe microanalysis. Liquidus temperatures of the slags were bracketed within an uncertainty of ± 10–20°C. Anorthite (CaO·Al2O3·2SiO2), gehlenite (2CaO·Al2O3·SiO2), pseudowollastonite (CaO·SiO2), and larnite (2CaO·SiO2) were observed as primary phases. Progressive doping by Na2O substantially changed the slag liquidus temperature, shifting the primary phase from anorthite to pseudowollastonite and larnite, and gehlenite to larnite. The liquidus temperature decreased significantly with increasing Na2O in slags with CaO/SiO2 (C/S) ratios of 0.3 and 0.6, while the liquidus temperature increased for slags with a C/S ratio of 1.0. The solid solubility of Na2O in the phases was quantified. Finally, the relevance of the phase equilibria study of the CaO-Al2O3-SiO2-Na2O system was discussed with regard to the optimum design of smelting with a focus on value recovery from e-waste.
How to realize the high value-added utilization of scrap copper from e-waste is a meaningful topic. In the study, an Ohno Continuous Casting (OCC) process is an existing method you applied to purify the copper. Based on the model of diffusion-controlled grain growth kinetics, the redistribution of impurity of tin in the scrap copper were studied under the different continuous casting speed and mold temperature. On the centerline, macrosegregation in the axial direction of the tin was more obvious with the decrease of continuous casting speed. The small continuous casting rate was beneficial to the segregation and enrichment of tin. The axial segregation gradually decreased with the increase of the mold temperature. The flattening of the liquid–solid interface resulted in a weakening of the solute enrichment at the root of the interface with the increase of temperature. Morphology, electron backscattered diffraction (EBSD) analysis showed the structure of single crystal copper. The range of resistance of single crystal copper was from 5 × 10⁻⁶ to 3 × 10⁻⁵ Ω m. Obviously, the resistance of the single crystal copper was significantly smaller than that of ordinary copper wire (9.0 × 10⁻³ Ω m). This study provided a key theoretical and practical basis for the high value-added reuse of copper in e-waste.
The present review covers achievements in the development and application of phosphorous-containing extractants for varios metals. The extractants based on industrial organophosphorus compounds, chelating compounds, ionic liquids, as well as polymers and copolymers bearing phosphorus-containing groups capable of complexing metals have been considered. Especial attention was paid to the efficiency and selectivity of these classes of compounds in the recovery of used metals from industrial wastewater, soil, and ashes via liquid-liquid, supercritical fluid, solid-phase, and synergistic extractions.
The bibliography includes 184 references published within the last 10 years (2010−2020).
Interest in the recoveryRecoveryof Rare EarthRare earthsElementsRare earth elements (REEs) has increased significantly in the last few years. There has been a concomitant increase in research and in process developmentProcess development for REE recoveryRecovery [1]. Antisolvent crystallizationCrystallization has the potential to recover REE from solution at high yields and with minimal waste. However, antisolvent addition generally results in uncontrolled primary nucleation and very small product crystals. A better approach could be to carry out the crystallizationCrystallization in fluidized bed reactors. Therefore, our approach in this work was to focus on the development of a novel process for the recoveryRecovery of REE by combining antisolvent crystallizationCrystallization and a fluidised bed process. Thermodynamic modellingThermodynamic modelling showed that, when ethanol is added to a Nd2(SO4)3 or Dy2(SO4)3 solution as an antisolvent, the only solid products formed were the REE sulphate salts. Since the solubilities of the REE sulphate salts at any of the Organic/Aqueous (O/A) ratios are of similar orders of magnitude to those of salts that have been successfully recovered in a fluidised reactor process, an antisolvent, fluidised reactor process is potentially suitable for REE sulphate salts. Batch experimentsBatch experiment showed that the yields are sufficiently high for a viable process. At the same time, the micrographs show that the nature of the formed crystals are such that they are likely to form uniform and robust coatings on seed particles in and fluidised bed reactor Fluidised Bed Reactor process. Therefore, our preliminary conclusion is that this REE system is well suited for further investigation in a combined antisolvent crystallizationCrystallization and fluidised bed process.
The waste printed circuit board smelting ash (WPCB-SA) produced in the waste printed circuit board smelting process is a hazardous material that not only contains valuable metals, but also contains a large amount of toxic and harmful inorganic bromides. The utilization of metals has received considerable attention in previous studies, but the recovery of hazardous bromides requires further study. In this article, a new idea of converting inorganic bromine in WPCB-SA by traditional sulfated roasting is proposed. Debromination kinetics under simulated experimental conditions are discussed, and kinetic equations are established. The kinetic results show that during low-temperature sulfated roasting, the conversion of Br in CuBr and PbBr2 conforms to the chemical reaction diffusion model and diffusion control the product layer model, respectively. A possible reaction mechanism is also proposed. Our research shows that the conversion of Br in CuBr is divided into three processes: covalent bond decomposition, hydrogen ion form acid, copper ion form salt, and HBr oxidation conversion, whereas the conversion of Br in PbBr2 is divided into two processes: sulfuric acid ionization, lead ion form salt and HBr oxidation conversion. This work provides the theoretical basis for the improvement and application of inorganic bromide recovery technology in WPCB-SA.
The recycling of waste printed circuit board (WPCBs) is of great significance for saving resources and protecting the environment. In this study, the WPCBs were pyrolyzed by microwave and the contained valuable metals Cu, Sn and Pb were recovered from the pyrolyzed WPCBs. The effect of pyrolysis temperature and time on the recovery efficiency of valuable metals was investigated. Additionally, the characterization for morphology and surface elemental distribution of pyrolysis residues was carried out to investigate the pyrolysis mechanism. The plastic fiber boards turned into black carbides, and they can be easily separated from the metals by manual. The results indicate that 91.2 %, 96.1 % and 94.4 % of Cu, Sn and Pb can be recovered after microwave pyrolysis at 700 °C for 60 minutes. After pyrolysis, about 79.8 wt% solid products, 11.9 wt% oil and 8.3 wt% gas were produced. These gas and oil can be used as fuel and raw materials of organic chemicals, respectively. This process provides an efficient and environmentally friendly technology for recovering valuable metals from WPCBs.
Present research reports a novel and feasible process to recover Ag and generate concentrate of precious metals (Au, Pd and Pt) from waste ICs present in PCBs of computers. Initially, depopulated ICs were pulverized and beneficiated to obtain metallic concentrate, which contained (per ton) 7 Kg Ag, 5 Kg Au, 110 g Pd and 4 g Pt along with Cu, Pb, Fe and Ni. Leaching was carried out and found that at optimized condition i.e. 3 M HNO3, temperature 80 °C, pulp density 50 g/L and mixing time 1 h, >90% of Ag, Cu, Pb and Ni were leached leaving Au, Pt and Pd in the residue. From the leach liquor, Ag was precipitated using 1 M KCl in 30 min and other metals were recovered by precipitation, solvent extraction and cementation methods. All wastes (solid/ liquid) generated during process development could be treated using standard environmental procedure.
Waste printed circuit boards (WPCBs) are considered as the most complicated and valuable component among e-waste. Slurry electrolysis can separate and recover metals from the extremely complex WPCBs. To promote its industrial application, a 5000 mL scale experiment was conducted to confirm industrial feasibility. Those results showed that copper and total metal recovery rates were 94.5 % and 75.2 % under the optimized conditions (30 g/L WPCBs, 10 g/L CuSO4·5H2O, 30 g/L NaCl, 190 g/L H2SO4, 30 g/L H2O2, 298 K temperature, 250 r/min stirring speed, 300 A/m² and 8 h). The copper purity was 92.9 %, and SEM-EDS analyses indicated the main dendritic metals recovered were copper and lead. USEtox toxicity potential evaluation results demonstrated human toxicity and ecotoxicity of WPCBs sharply decreased after treatment. A cost analysis of this process indicated that the 1.9 return from 1 kg WPCBs. Thus, slurry electrolysis has a promising industrial future for e-waste recycling/utilization.
The circularity represents the key strategy of the modern economy, where the waste becomes a raw material, ready to be reprocessed for a second life. In this context, the main aim of the present work was the development of a sustainable process for the recovery of Cu and Zn from end-of-life printed circuit boards (PCBs). The exploitation of this hazardous waste produces a double effect: the recovery of metals, suitable for the current metal market, and the avoided disposal of scraps produced worldwide. The process allowed to exceed the limits of several approaches reported in the literature, mainly due to the highest consumptions (both energy and raw materials) and the loss of Zn content. The best identified conditions, suitable for the treatment of both chemical and bio- leach liquor included: the Fe precipitation with sodium hydroxide, followed by the Cu cementation with Zn (Zn/Cu molar ratio of 1.1) and a final Zn precipitation with oxalic acid (O.A./Zn molar ratio of 1.5). The metals showed recovery efficiencies higher than 95% and purities up to 95%. An efficient recirculation system contributes to the sustainability growth, as confirmed by the carbon footprint assessment, towards the implementation of a zero waste treatment. Future perspective should include the further exploitation of the residue, rich in precious metals.
Recycling precious metals from secondary resources is of great environmental and economic significance. In this study, the Zr-based MOFs UiO-66-NH2 was synthesized and used to adsorb Au (III) in aqueous solution. The ultrafine particle size (∼50 nm), excellent crystallinity and huge specific surface area (1039.2 m2 ·g-1) were verified by transmission electron microscope (TEM), powder X-ray diffraction (PXRD) and surface area analysis. About 50 % Au (III) was adsorbed within 6 min and the maximum adsorption capacity at 298 K reached up to 650 mg·g-1, showing superiority to traditional adsorbents. The general order kinetics model and Liu equation were suitable to describe the adsorption process, which was spontaneous, endothermic and driven by the increasing system entropy. Electrostatic attraction between -NH3+ and Au (III) anions and inner complexation to Zr-OH played a vital role in adsorption. Au (Ⅲ) was reduced to Au° by amino groups via redox reaction certified by X-ray photoelectron spectroscopy (XPS), PXRD and high-resolution transmission electron microscopy (HRTEM) analysis. Moreover, UiO-66-NH2 displayed high selectivity, robust stability and excellent reusability, making it an ideal candidate for gold recycling in industrial practice.
In the ten years from 2003 to 2013 global mine production of copper has increased by
over 23% to meet demand while the weighted average head grade has dropped from 0.9
to 0.7% Cu. These divergent trends of increasing demand and declining economic grades
will extend the life of many existing mines and improve the viability of marginal and/or
complex copper deposits. Against that context this paper outlines hydrometallurgical
copper sulphide leaching options as alternatives to the more conventional
pyrometallurgical processing route of copper sulphides.
Three copper sulphide leaching and refining processes are discussed: total pressure
oxidation, ferric sulphate leaching and copper chloride leaching. The effect of mineralogy
on the choice of processing technology is discussed as well as some of the unit processes
used. Additionally, possible benefits that a hydrometallurgical process may offer over an
existing pyrometallurgical route are discussed. Subsequently, two very important aspects
to the development of projects involving the leaching of copper sulphides are discussed.
Finally, a number of conclusions are presented that will be useful to keep in mind when
considering projects involving the leaching of copper sulphides.
The development of the recycling technologies for waste electrical and electronic equipment (WEEE) has entered a new stage. The WEEE disposing technologies have evolved from simple disassembly, classification and sorting to high value-added utilization technologies. In the past decade, some modified and novel technologies have been developed to recover metals from WEEE. This paper focuses on the recycling of metals from WEEE. The recycling principle, separating process, and optimized operating parameters of existing technologies are summarized and discussed in detail. Based on traditional recycling technologies of WEEE, pyrometallurgical technology and some mild extracting reagent, such as chloride medium, ammonia–ammonium and non-cyanide lixiviants can effectively recycle metals. Compared with the conventional acid and cyanide leaching, they have vast improvements in aspect of environmental protection. More than 98% of Cu and 70% of Au can be extracted. In addition, electrochemical technology, supercritical technology, vacuum metallurgical technology, etc. are also applied to recycle WEEE. The recovery rate of Cu and Pb under optimum conditions is around 84.2% and 89.4% respectively in supercritical water oxidation (SCWO) combined with electrokinetic (EK) technology. Vacuum technology has good environmental performance due to its avoiding discharge of waste water. Other new technologies such as ultrasound technology, mechanochemical technology, and molten salt oxidation technology have also been tried to recycle metals from WEEE. Regrettably, although many endeavors to develop recycling technologies have been attempted, these technologies are still relatively single and limited because WEEE is a complex system. Hence, the shortages and defects of each technology are discussed from the perspective of technological promotion and environmental protection. Furthermore, the outlook about the further development of recycling technologies for metals from WEEE is presented.
The useful life of electrical and electronic equipment (EEE) has been shortened as a consequence of the advancement in technology and change in consumer patterns. This has resulted in the generation of large quantities of electronic waste (e-waste) that needs to be managed. The handling of e-waste including combustion in incinerators, disposing in landfill or exporting overseas is no longer permitted due to environmental pollution and global legislations. Additionally, the presence of precious metals (PMs) makes e-waste recycling attractive economically. In this paper, current metallurgical processes for the extraction of metals from e-waste, including existing industrial routes, are reviewed. In the first part of this paper, the definition, composition and classifications of e-wastes are described. In the second part, separation of metals from e-waste using mechanical processing, hydrometallurgical and pyrometallurgical routes are critically analyzed. Pyrometallurgical routes are comparatively economical and eco-efficient if the hazardous emissions are controlled. Currently, pyrometallurgical routes are used initially for the segregation and upgrading of PMs (gold and silver) into base metals (BMs) (copper, lead and nickel) and followed by hydrometallurgical and electrometallurgical processing for the recovery of pure base and PMs. For the recycling of e-waste in Australia, challenges such as collection, transportation, liberation of metal fractions, and installation of integrated smelting and refining facilities are identified.
With the new legislation for Waste Electrical and Electronic Equipment (WEEE) coming up in Europe and similar developments in other parts of the world, a substantial increase of end-of-life electronic equipment to be treated will take place on a global scale. In this context, often much attention is placed on logistical issues, dismantling and shredding/pre-processing of electronic-scrap, while the final, physical metals recovery step in a smelter is often just taken for granted. However, a state-of-the-art smelter and refinery process has a major impact on recycling efficiency, in terms of elements and value that are recovered as well as in terms of overall environmental performance. Besides copper and precious metals, modern integrated smelters recover a large variety of other elements, and can make use of organics such as plastics to substitute coke as a reducing agent and fuel as an energy source. Umicore has recently completed major investments at its Hoboken Works, completely shifting the plants focus from mining concentrates to recyclable materials and industrial by-products. Based on complex Cu/Pb/Ni metallurgy, the plant has been developed to the globally most advanced full-scale processor of various precious metals containing fractions from electronic scrap, generating optimum metal yields for precious and special metals at increased productivity and minimised environmental impact. Especially the interface between pre-processing (shredding/sorting) and integrated smelting offers additional optimisation potential, which can lead to a substantial increase in overall (precious) metals yields.
This paper reviews a series of alternative lixiviant systems for the recovery of gold from ores and concentrates. For over 100 years, cyanide has been the leach reagent of choice in gold mining because of its high gold recoveries, robustness and relatively low costs. The environmental damages resulting from its mismanagement, however, have initiated widespread research aimed at identifying and developing less toxic leaching agents. The most widely-researched alternative lixiviants for gold ores are examined in this paper, but it is evident that none has yet made any significant inroad into the dominant position of cyanide as the reagent of choice at the vast majority of gold mines worldwide.
Informal recycling is a new and expanding low cost recycling practice in managing Waste Electrical and Electronic Equipment (WEEE or e-waste). It occurs in many developing countries, including China, where current gaps in environmental management, high demand for second-hand electronic appliances and the norm of selling e-waste to individual collectors encourage the growth of a strong informal recycling sector. This paper gathers information on informal e-waste management, takes a look at its particular manifestations in China and identifies some of the main difficulties of the current Chinese approach. Informal e-waste recycling is not only associated with serious environmental and health impacts, but also the supply deficiency of formal recyclers and the safety problems of remanufactured electronic products. Experiences already show that simply prohibiting or competing with the informal collectors and informal recyclers is not an effective solution. New formal e-waste recycling systems should take existing informal sectors into account, and more policies need to be made to improve recycling rates, working conditions and the efficiency of involved informal players. A key issue for China's e-waste management is how to set up incentives for informal recyclers so as to reduce improper recycling activities and to divert more e-waste flow into the formal recycling sector.
In recent years, due to the large amount of waste electrical and electronic equipment. Researchers need to search for a method to solve the harmless disposal of waste printed circuit boards (WPCBs) as soon as possible. Considering that WPCBs contain metals and polymeric materials, they have been considered to be an important urban mineral resource. The recycling of WPCBs has been widely studied. Published research shows that pyrometallurgical processing is an economic and effective method to achieve WPCBs harmless recycling and resource utilization. This paper summarizes and analyzes the research results of pyrometallurgical processing for the recycling of WPCBs in recent years, and recovery processes such as incineration, pyrolysis, plasma and molten salt are discussed. Some proposals against the existing problems during pyrometallurgical processing process were presented. We hope that this paper can provide some certain assistances to policy makers, other researchers and the practitioners in the WPCB recycling enterprise.
This chapter discusses the converting of copper matte that is the second half of the smelting/converting sequence by which most Cu–Fe sulfide concentrates are made into metallic copper. The process oxidizes the Fe and S from molten smelting furnace matte with oxygen-enriched air or air to produce molten metallic copper. It is most often carried out in the cylindrical Peirce–Smith converter, which blows the blast into molten matte through submerged tuyeres. The main raw material for converting is molten Cu–Fe–S matte from smelting. Other raw materials include silica flux, air, and industrial oxygen. Several Cu-bearing materials are recycled to the converter, such as solidified Cu-bearing reverts and copper scrap. The products of the process are: Molten blister copper (99% Cu, 0.02% S and 0.6% O), which is sent forward to fire refining for final S and O removal, then anode casting: molten Fe-silicate slag (4–8% Cu), which is sent to Cu recovery, then discard; SO2-bearing offgas, which is treated for heat, dust, and SO2 capture. All of the heat for converting comes from Fe and S oxidation. Peirce–Smith converting is a batch process. It produces SO2 intermittently and captures it somewhat inefficiently.
Gold solubility in the CaO-SiO2-Al2O3-MgOsat slag system was measured at 1773 K (1500 °C) under a CO2–CO atmosphere over a wide range of compositions, i.e., 8 to 40 mass pct CaO, 26 to 50 mass pct SiO2, and 0 to 36 mass pct Al2O3, to determine the dissolution mechanism of gold in the CaO-based metallurgical slags. Gold solubility in the present slag system increased with increasing oxygen partial pressure and increasing activity of CaO. From the thermodynamic analysis, the dissolution mechanism of gold into the (alumino-)silicate melts is proposed as follows according to the activity of basic oxide, which indicates that the predominant species of gold is dependent on slag basicity.
The enthalpy change for the dissolution of gold into the CaO-SiO2-Al2O3-MgOsat slag system was measured to be about −80 kJ/mol, indicating that the gold dissolution is exothermic. From the iso-Au solubility contours, the dominant factor affecting the gold dissolution behavior is the (CaO + MgO)/SiO2 ratio, whereas the influence of Al2O3 was negligible. Consequently, less basic slags and higher processing temperatures, in conjunction with a strongly reducing atmosphere, are recommended to increase gold recovery during pyro-processing of Au-containing e-wastes.
Recycling metals from wastes is essential to a resource-efficient economy, and increasing attention from researchers has been devoted to this process in recent years, with emphasis on mechanochemistry technology. The mechanochemical method can make technically feasible the recycling of metals from some specific wastes, such as cathode ray tube (CRT) funnel glass and tungsten carbide waste, while significantly improving recycling efficiency. Particle size reduction, specific surface area increase, crystalline structure decomposition and bond breakage have been identified as the main processes occurring during the mechanochemical operations in the studies. The activation energy required decreases and reaction activity increases, after these changes with activation progress. This study presents an overall review of the applications of mechanochemistry to metal recycling from wastes. The reaction mechanisms, equipment used, method procedures, and optimized operating parameters of each case, as well as methods enhancing the activation process are discussed in detail. The issues to be addressed and perspectives on the future development of mechanochemistry applied for metal recycling are also presented.
The rapid proliferation of electronic devices in the last two decades has compelled the researchers to find a remedy for one of the most toxic and hazardous waste materials – the waste Printed Circuit Boards. Numerous articles have been published demonstrating the process routes for recycling of this toxic but otherwise useful waste due to nearly 30% metal content. In this paper, more than 150 related articles mostly published in the last 15 years and covering the broad areas like characterization of waste Printed Circuit Boards, health hazards associated with the processing and the different routes of recycling have been analyzed to provide a comprehensive overview on this topic. Physical separation processes employing electrostatic separator, magnetic separator, froth floatation, etc., has been reviewed for separation of metals and non-metals, along with useful utilizations of the non-metallic materials. The recovery of metals from this waste material through pyrometallurgical, hydrometallurgical or bio-hydrometallurgical routes is also critically discussed.
In recent era, more and more electric and electronic equipment wastes (e-wastes) are generated that contain both toxic and valuable materials in them. Most studies focus on the extraction of valuable metals like Au, Ag from e-wastes. However, the recycling of metals such as Pb, Cd, Zn and organics has not attracted enough attentions. Vacuum metallurgy separation (VMS) processes can reduce pollution significantly using vacuum technique. It can effectively recycle heavy metals and organics from e-wastes in an environmentally friendly way, which is beneficial for both preventing the heavy metal contaminations and the sustainable development of resources. VMS can be classified into several methods, such as vacuum evaporation, vacuum carbon reduction and vacuum pyrolysis. This paper respectively reviews the state-of-art of these methods applied to recycling heavy metals and organics from several kinds of e-wastes. The method principle, equipment used, separating process, optimized operating parameters and recycling mechanism of each case are illustrated in details. The perspectives on the further development of e-wastes recycling by VMS are also presented.
In Australia, the use of plastics has increased tremendously over the last few decades, but less than 20% of the waste plastics are recycled. The rest is usually landfilled, which poses major environmental problems. The solution to this problem involves the development of novel environmentally-benign technologies that would utilise these waste materials. This work investigates the reduction of EAF slags (47% FeO) by blends of metallurgical coke with High-Density Polyethylene (HDPE) plastics at 1 550°C. The experiments were conducted in a laboratory-scale horizontal tube furnace, and were coupled with off-gas analysis using an infrared gas analyser and a multiple gas chromatographic analyser. The results indicate that the rate of FeO reduction in slags is significantly higher when the coke/plastics blends were used compared to pure coke, with the maximum rate of reduction (Blend 4) being over twice that of coke. Moreover, the CO 2 content in the off-gas was observed to decrease (by ̃75%) with increase in the polymer content of the blend. Additionally, the degree of carburisation and the removal of sulphur from the metal improved considerably when the coke was blended with plastics. The observed improvements in the rates of reduction, carburisation and desulphurisation are attributed to the reactions of hydrogen evolved from the waste plastics at these high temperatures.
In the view points of resource recycling and environment protection it is necessary to extract the valuable metals from waste electric and electronic scraps (WEES) which contain considerable amounts of valuable metals such as copper, tin, gold, and silver. In present work, a novel process to extract valuable metals such as copper and tin from WEES by smelting with the addition of waste copper slag as a slag formative has been developed. The process uses only waste copper slag without using any additional flux components as slag formatives. In each set of experiment, crushed WEES were melted with waste copper slag for 30 min at 1623 K in air atmosphere. Based on proposed process flow-sheet, up to 90% of copper and 80% of tin contained in the raw materials were extracted as a Cu-Fe-Sn alloy phase at the input ratio of 50 : 50 of WEES and waste copper slag. [doi: 10.2320/matertrans.M2009062]
Waste electrical and electronic equipment (WEEE) has received extensive attention as a secondary source of metals. Because WEEE also contains toxic substances such as heavy metals, appropriate management of these substances is important in the recycling and treatment of WEEE. As a basis for discussion toward better management of WEEE, this study characterizes various types of WEEE in terms of toxic metal contents. The fate of various metals contained in WEEE, including toxic metals, was also investigated in actual waste treatment processes. Cathode-ray tube televisions showed the highest concentration and the largest total amount of toxic metals such as Ba, Pb, and Sb, so appropriate recycling and disposal of these televisions would greatly contribute to better management of toxic metals in WEEE. A future challenge is the management of toxic metals in mid-sized items such as audio/visual and ICT equipment because even though the concentrations were not high in these items, the total amount of toxic metals contained in them is not negligible. In the case of Japan, such mid-sized WEEE items as well as small electronic items are subject to municipal solid waste treatment. A case study showed that a landfill was the main destination of toxic metals contained in those items in the current treatment systems. The case study also showed that changes in the flows of toxic metals will occur when treatment processes are modified to emphasize resource recovery. Because the flow changes might lead to an increase in the amount of toxic metals released to the environment, the flows of toxic metals and the materials targeted for resource recovery should be considered simultaneously.
In Korea due to rapid economical growth followed by urbanisation, breakage of large traditional families into small nuclear families, continuous changes in equipment features and capabilities causes tremendous increase in sale of new electrical and electronic equipment (EEE) and decrease in sale of used EEE. Subsequently, the ever-increasing quantity of waste electrical and electronic equipment (WEEE) has become a serious social problem and threat to the environment. Therefore, the gradual increase in the generation of WEEE intensifies the interest for recycling to conserve the resources and protect the environment. In view of the above, a review has been made related to the present status of the recycling of waste electrical and electronic equipment in Korea. This paper describes the present status of generation and recycling of waste electrical and electronic equipment, namely TVs, refrigerators, washing machines, air conditioners, personal computers and mobile phones in Korea. The commercial processes and the status of developing new technologies for the recycling of metallic values from waste printed circuit boards (PCBs) is also described briefly. Since 1998, three recycling centers are in full operation to recycle WEEE such as refrigerators, washing machines and air conditioners, having the total capacity of 880,000 units/year. All waste TVs are recently recycled on commission basis by several private recycling plants. The recycling of waste personal computers and mobile phones is insignificant in comparison with the amount of estimated obsolete those. Korea has adopted and enforced the extended producer responsibility (EPR) system. Korea is making consistent efforts to improve the recycling rate to the standards indicated in the EU directives for WEEE. Especially environmentally friendly and energy-saving technologies are being developed to recycle metal values from PCBs of WEEE.
The constant growth in generation of waste printed circuit boards (WPCB) poses a huge disposal problem because they consist of a heterogeneous mixture of organic and metallic chemicals as well as glass fiber. Also the presence of heavy metals, such as Pb and Cd turns this scrap into hazardous waste. Therefore, recycling of WPCB is an important subject not only from the recovery of valuable materials but also from the treatment of waste. The aim of this study was to present a recycling process without negative impact to the environment as an alternative for recycling WPCB. In this work, a process technology containing vacuum pyrolysis and mechanical processing was employed to recycle WPCB. At the first stage of this work, the WPCB was pyrolyzed under vacuum in a self-made batch pilot-scale fixed bed reactor to recycle organic resins contained in the WPCB. By vacuum pyrolysis the organic matter was decomposed to gases and liquids which could be used as fuels or chemical material resources, however, the inorganic WPCB matter was left unaltered as solid residues. At the second stage, the residues obtained at the first stage were investigated to separate and recover the copper through mechanical processing such as crushing, screening, and gravity separation. The copper grade of 99.50% with recovery of 99.86% based on the whole WPCB was obtained. And the glass fiber could be obtained by calcinations in a muffle furnace at 600 degrees C for 10 min. This study had demonstrated the feasibility of vacuum pyrolysis and mechanical processing for recycling WPCB.
Waste printed circuit boards (WPCBs) contain lots of valuable resources together with plenty of hazardous materials, which are considered both an attractive secondary resource and an environmental contaminant. In this research, a new process of "centrifugal separation+vacuum pyrolysis" for the combined recovery of solder and organic materials from WPCBs was investigated. The results of centrifugal separation indicated that the separation of solder from WPCBs was complete when WPCBs were heated at 240 degrees C, and the rotating drum was rotated at 1400 rpm for 6 min intermittently. The results of vacuum pyrolysis showed that the type-A of WPCBs without solder pyrolysed to form an average of 69.5 wt% residue, 27.8 wt% oil, and 2.7 wt% gas; and pyrolysis of the type-B of WPCBs without solder led to an average mass balance of 75.7 wt% residue, 20.0 wt% oil, and 4.3 wt% gas. The pyrolysis residues contain various metals, glass fibers and other inorganic materials, which could be recycled for further processing. The pyrolysis oils can be used for fuel or chemical feedstock and the pyrolysis gases can be collected and combusted for the pyrolysis self-sustain. This clean and non-polluting technology offers a new way to recycle valuable materials from WPCBs and prevent the environmental pollution of WPCBs effectively.
From the use of renewable resources and environmental protection viewpoints, recycling of waste printed circuit boards (PCBs) receives wide concerns as the amounts of scrap PCBs increases dramatically. However, treatment for waste PCBs is a challenge due to the fact that PCBs are diverse and complex in terms of materials and components makeup as well as the original equipment's manufacturing processes. Recycle technology for waste PCBs in China is still immature. Previous studies focused on metals recovery, but resource utilization for nonmetals and further separation of the mixed metals are relatively fewer. Therefore, it is urgent to develop a proper recycle technology for waste PCBs. In this paper, current status of waste PCBs treatment in China was introduced, and several recycle technologies were analyzed. Some advices against the existing problems during recycling process were presented. Based on circular economy concept in China and complete recycling and resource utilization for all materials, a new environmental-friendly integrated recycling process with no pollution and high efficiency for waste PCBs was provided and discussed in detail.
Waste electric and electronic equipment, or electronic waste, has been taken into consideration not only by the government but also by the public due to their hazardous material contents. In the detailed literature survey, value distributions for different electronic waste samples were calculated. It is showed that the major economic driver for recycling of electronic waste is from the recovery of precious metals. The state of the art in recovery of precious metals from electronic waste by pyrometallurgical processing, hydrometallurgical processing, and biometallurgical processing are highlighted in the paper.
Introduction to Copper and Copper Alloy
- H C Kwon
H.C. Kwon, Introduction to Copper and Copper Alloy, Korea Institute of Industrial
Technology, 2008, pp. 196-216.
Electrolytic refining
- M E Schlesinger
- M J King
- K C Sole
- W G Davenport
M.E. Schlesinger, M.J. King, K.C. Sole, W.G. Davenport, Electrolytic refining,
Chapter 14, in: M.E. Schlesinger, M.J. King, K.C. Sole, W.G. Davenport (Eds.),
Extractive Metallurgy of Copper, fifth ed., Elsevier, Oxford, 2011, pp. 251-280.
Hydrometallurgical copper extraction: introduction and leaching
- M E Schlesinger
- M J King
- K C Sole
- W G Davenport
M.E. Schlesinger, M.J. King, K.C. Sole, W.G. Davenport, Hydrometallurgical copper
extraction: introduction and leaching, Chapter 15, in: M.E. Schlesinger, M.J. King,
K.C. Sole, W.G. Davenport (Eds.), Extractive Metallurgy of Copper, fifth ed.,
Elsevier, Oxford, 2011, pp. 281-322.