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Abstract

a b s t r a c t Waste of electric–electronic equipment (WEEE) with an annual growth rate of about 3–5% is the fastest growing waste stream in municipal wastes. Notwithstanding their environmental pollution potential, waste of electrical and electronic equipment (WEEE) with their high content of base and precious metals, in particular, are regarded as a potential secondary resource when compared with ores. For the recovery of metals from WEEE, various treatment options based on conventional physical, hydrometallurgical and pyrometallurgical processes are available. These process options with particular reference to hydromet-allurgical processes were reviewed in this study. With their relatively low capital cost, reduced environ-mental impact (e.g. no hazardous gases/dusts), potential for high metal recoveries and suitability for small scale applications, hydrometallurgical processes are promising options for the treatment of WEEE. Since the metals are present in native form and/or as alloys, an oxidative leaching process is required for the effective extraction of base and precious metals of interest. A two-stage process based on oxidative acid leaching of base metals (Cu in particular) followed by leaching of precious metals using cyanide, thiosulfate, thiourea or halide as lixiviant(s) can be suitably developed for the hydrometallurgical treat-ment of WEEE. However, further research is required to develop new, cost effective and environmentally friendly processes and/or refine existing ones for leaching and, in particular, downstream processes.

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... Even though a great deal of effort has been directed toward the promotion of harmless recycling of E-waste [6][7][8], recycling E-waste without harming the environment and human health is still a problem. E-waste generated by developed countries is usually exported to developing countries, where recycling techniques include burning and dissolution in strong acids with few measures to protect human health and the environment [9,10]. ...
... The following E-waste treatment options can be used for reference. Common E-waste treatment options are burning [17,18], chemical treatment [7,19,20], and mechanical separation [6,8,21,22]. Burning is the most common method to recycle E-waste. ...
... Chemical treatment is efficient and relatively clean. However, a large amount of waste residue and liquid that are difficult to handle are caused by chemical treatment [7]. Lastly, mechanical separation is a good method in theory, but in fact, mechanical separation can only be used for the primary separation of the metal fraction and non-metal fraction from E-waste. ...
... Studies in [12] have shown that waste electrical and electronic equipment is very complex and varied. The composition of the waste varies according to the type of waste and its life span. ...
... Indeed, the metal contents of printed circuit boards are generally higher than those of primary raw material deposits, which shows the need to upgrade them. They can contain 20 to 40 times more copper and 20 to 250 times more gold than ores [12]. Furthermore, many metals or metalloids contained in printed circuit boards, such as antimony, tungsten, cobalt, germanium, gallium, indium or tantalum, are classified as critical substances by the European Union. ...
... Generally, the oxidative leaching process is required for efficient extraction of base and precious metals of interest. The dissolution step in the hydrometallurgical process, goes through the acid-base reaction, redox reaction or by redox reaction coupled with complexation reactions as well as on more or less complex purification steps so that the product, then shaped in a final step, finds its place in a specific market [12,29]. Various leaching media have been studied such as nitric acid, hydrochloric acid, thiourea, cyanide, etc. [12, 18,]. ...
Article
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Natural minerals are a powerful tool in politics when some have a major role in production. Its depletion is now a hot topic worldwide. Thus, the safety of the environment, natural surface water, groundwater and the protection of soils from chronic contamination by metallic and inorganic elements is a global concern. Indeed, industrialization and development have led to the generation of huge and varied amounts of waste, including electronic waste (e-waste), which is released into the environment. Although e-waste is classified as hazardous, most of it is not recycled and developed countries with strict environmental protection legislation send most of their e-waste to developing countries where regulations are lax. These electronic devices and components after being used are simply dumped into the environment due to lack of treatment and recycling strategy. As a result, they become a threat to the environment, ecosystems and humans. African countries are among the most vulnerable nations. But they are unfortunately ignored and underestimated. To date, there is no e-waste recycling unit (factory) in most African countries and mainly in the Republic of Benin. In response to this challenge, this study explored the different techniques used for the recycling of waste electrical/electronic equipment in order to develop a new environmentally friendly approach in future work, for the extraction and recycling of the usual and valuable metallic elements contained in electronic waste (printed circuit boards) released into the environment. For this purpose, a bibliographic research was carried out from 20 April to 16 October 2021. The results obtained allowed us to identify the advantages and disadvantages of existing recycling methods.
... Platinum is largely used because of its catalytic capacity to oxidize CO and unburnt hydrocarbons into CO 2 and to promote the reduction of NO x in the typical conditions of gas exhausted from light and heavy duties engines of road vehicles [13,14]. The production of platinum from primary extraction processes is characterized by a long sequence of mechanical operations, primary separation, and purification steps [15][16][17] with a relevant environmental impact [18,19]. The need to comply profitability with environmental safety has progressively discouraged mining activities in the European Union and the United States of America. ...
... Free oxygen can enter our system either from the reactions Eq.(18) and Eq. (19) or from the solubilization of the oxygen in the surrounding air. If oxygen is available in solution, the following reactions may take place only at higher temperatures: ...
Article
Spent automotive catalysts are industrial non-hazardous wastes of high added values because of the presence of platinum group metals, whose recovery is gaining increasing attention in European countries. This paper proposes a hydrometallurgical process to recover platinum from diesel catalysts, based on a first leaching step with aqueous solutions of H2O2 (up to 0.2 M) and mild HCl concentrations (0.4 M), followed by a refining step in which platinum is deposited over a granular activated carbon. Tests were carried out at different H2O2 content, temperatures, and sizes of granulated catalyst. The use of H2O2 and low HCl content allows higher sustainability than conventional hydrometallurgical processes by reducing safety risks associated with the use of concentrated HCl and the emissions of NOx deriving from the use of nitrogen species in conventional leaching. Besides, the use of an adsorbent avoids the utilization of cyanides or other toxic organic solvents for the refining of the leaching solution. Experiments revealed that the low HCl concentration results in longer leaching times; however, process conditions can be tuned to completely recover platinum with negligible extraction of other metals on the catalyst, minimizing on the subsequent adsorption process. Optimal conditions appear as leaching at 20°C with a 0.13 M H2O2 0.4 M HCl solution followed by an adsorption step at 20°C using an activated carbon with high BET surface area and high content of reducing surface groups. These findings suggest that the proposed recovery process can be a suitable candidate for future technology implementations.
... In recent years, several techniques have been employed for recycling activities, such as pyro-metallurgy [4], hydrometallurgy [5], bio-hydrometallurgy [6], etc. Various hydrometallurgical methods for the recovery of metals from printed circuit boards (PCBs) have been developed using leaching reagents such as acids, bases, and salts. Meanwhile, hydrometallurgical techniques [7], leaching [8], kinetic studies [9], and bioleaching of precious metals from waste electrical and electronic equipment (WEEE) using bacteria [6,10,11] have been attempted and reported in the literature. ...
... Fe + H2O = Fe (OH)ads + H + (4) Fe + Cl − = Fe (Cl − ) ads (5) Fe (OH)ads + Fe (Cl − ) ads = Fe + FeOH + (Cl − ) + 2e − ...
Article
The recovery of valuable metals from waste printed circuit boards (WPCBs) is crucial in order to harness their economic resources, and prevents potential environmental contamination. However, selective extraction of Cu and Zn, and the co-extraction of other metals as impurities at ambient temperature using selected lixiviants such as HCl, H2SO4, HNO3, trifluoromethanesulfonic acid (TFMS), NaOH, and mixtures of NaCl and CuCl2 was studied. It is shown that the extraction efficiencies of all the metals increased with increases in lixiviant concentrations. High selectivity of Cu and Zn toward Fe were achieved in dilute H2SO4, HNO3, TFMS, and 0.5 M NaCl + 0.1 M CuCl2, and low dissolution of Pb (<5%) was observed in all H2SO4 lixiviants. Almost 100% Zn extraction using NaOH lixiviants without trace of other metals was achieved. Therefore, 0.5 M NaCl + 0.5 M CuCl2, 1.0 M HNO3, 0.5 M H2SO4, and 1.0 M TFMS showed high extraction selectivity toward Cu and Zn with low chemical consumption, and produced pregnant leach solution rich in Cu and Zn, as well as residue containing Fe, Ni, and other metals.
... Treatment processes for metals recovery from them are generally given in three groups as pyrometallurgy (roasting, smelting), hydrometallurgy (leaching, separation), and biohydrometallurgy (leaching, adsorption). Recycling of precious metals from WEEE (Waste Electrical & Electronic Equipment) typically combined with mechanical pretreatment (manually dismantling, separation and shredding) to segregate the valuable components followed by hydrometallurgical treatments through leaching [1][2][3][4]. Aqua regia and mineral acids such as hydrochloric acid (HCl), nitric acid (HNO 3 ), and sulfuric acid (H 2 SO 4 ) are used for the dissolution of PMs (Precious Metals) from WEEE components [2]. Acidic leachates produced are further treated for the recovery of PMs using conventional separation techniques, solvent extraction, membrane filtration, cementation, ion exchange, adsorption, and so forth [3,5]. ...
... Recycling of precious metals from WEEE (Waste Electrical & Electronic Equipment) typically combined with mechanical pretreatment (manually dismantling, separation and shredding) to segregate the valuable components followed by hydrometallurgical treatments through leaching [1][2][3][4]. Aqua regia and mineral acids such as hydrochloric acid (HCl), nitric acid (HNO 3 ), and sulfuric acid (H 2 SO 4 ) are used for the dissolution of PMs (Precious Metals) from WEEE components [2]. Acidic leachates produced are further treated for the recovery of PMs using conventional separation techniques, solvent extraction, membrane filtration, cementation, ion exchange, adsorption, and so forth [3,5]. ...
... The recovery of base and precious metals from waste PCBs can be carried out by using hydrometallurgical, pyrometallurgical and electrometallurgical methods. In comparison with pyrometallurgical methods, hydrometallurgical treatments possess several advantages, such as lower capital cost, lower environmental impact, higher metal recovery and easier management [12,13]. Hydrometallurgical processes include three major steps: leaching to dissolve metals, purification to separate metals via selective chemical reactions, and metal recovery as a solid product [14]. ...
... A number of methods have been studied, such as solvent extraction, precipitation, cementation, ion exchange, adsorption and electrowinning [16,17]. To select suitable purification and recovery processes, it is necessary to consider several factors such as the concentrations of target metals and impurities in the leachate, the property of lixiviant, and the reaction condition in leaching process [5,12]. ...
Article
Full-text available
Recycling of waste printed circuit boards (PCBs) has attracted increasing attention because of its high annually produced amount and high content of gold. In this study, gold recovery from waste PCBs was carried out by using the processes including microwave pyrolysis, acid leaching, solvent extraction and oxidative precipitation. The leaching efficiency of copper was approximately 95% when using a lixiviant composed of sulfuric acid and hydrogen peroxide, and the leaching efficiencies of gold were approximately 59, 95 and 95% by using thiourea, thiosulfate and aqua regia, respectively. The gold ions contained in the leachate previously produced by the leaching processes were not satisfactorily extracted by using organic solvents including di-(2-ethylhexyl)phosphoric acid, tributyl phosphate, dibutyl carbitol and trioctylamine, so the leachate was decided to bypass solvent extraction and directly apply to the oxidative precipitation process. By using the oxidants of hydrogen peroxide and perchloric acid, the precipitation efficiencies of gold were approximately 95 and 99%, and the final recovery rates were approximately 90 and 93%, respectively. The high recovery rates of gold can be attributable to the use of microwave pyrolysis that prevents the loss of gold caused by shredding and grinding processes. In addition, perchloric acid can provide higher selectivity for gold recovery than hydrogen peroxide. The maximum processing capacity of microwave pyrolysis of waste PCBs would be approximately 1.23 kg. The gold recovered from 1 t of waste PCBs can be sold for approximately USD 10,000, and thus the return on investment can be as high as approximately 1400%.
... However, interest in PCB´s waste is focused on the large number of metals that it could be a rich source of exploitation (Li et al., 2007) turning this process in part of urban mining. The recovered amount of gold per Tm of PCB´s (depending on generation) is ≈ 250 g, while gold ores yield of 1 to 10 g per Tm (Tuncuk et al., 2012); so the gains reflected per Tm of gold present in the PCB´s are $15200 USD, which is a strong economic incentive (Wang and Gaustad, 2012), (Cho et al., 2018). Furthermore, huge amounts of gold have been used on WEEE during decades due to its low electric resistance, excellent corrosion resistance and exceptional electric conductivity (Syed, 2012). ...
... After physicochemical characterization of collected pins, experiments of dynamic acid leaching at 288, 298, 303, 308, 313, 318, 323, 333 and 343 K were carried out as it was described in section 2.2. In this sense, recent studies have confirmed temperature is one of the most important factors influencing metal leaching/extracting from electronic waste (Tuncuk et al., 2012), (Mooiman et al., 2005). As known, the kinetic parameter for determining the type of control of a chemical reaction in the activation energy (Ea), which is related to the temperature and reaction rate constant according to Arrhenius equation. ...
Article
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This lab-scale experimental study presents a novel combined hydrometallurgical and electrochemical process for gold and non-precious metals (Cu, Ni, Pb and Zn) recovery, from waste printed circuit boards (PCB´s). First, a leaching of non-precious metals from pins (contained in the PCB´s) has been carried out and then a complete gold extraction was obtained using H2SO4 0.5 M (pH ≈ 1.5)/O2 (1 atm) in the temperature range from 288 to 343 K. The activation energies found showed values of 97.2 kJ•mol-1 , 86 kJ•mol-1 and 93.6 kJ•mol-1 for Cu, Ni and Zn respectively and were obtained in the temperature range mentioned above. Afterwards, leaching liquor was treated electrochemically in several conditions: selective Cu and Pb removal was performed at pH 1.5 and Ni and Zn removal was also obtained when pH increased to 5. All processes involved here are friendly, and even, final liquor could be reutilized for leaching and electro wining processes. Resumen Este estudio experimental a escala laboratorio, presenta un novedoso proceso combinado hidrometalúrgico y electrometalúrgico para la recuperación de oro y metales no preciosos (Cu, Ni, Pb y Zn), a partir de desechos de placas de circuitos impresos (DPCI). Primero, se llevo a cabo una lixiviación de los metales no preciosos de los pines (contenidos en los DPCI y entonces se obtuvo una completa extracción de oro usando H2SO4 0.5 M (pH ≈ 1.5)/O2 (1 atm) en el rango de temperatura de 288 a 343 K. Las energías de activación encontradas muestran valores de 97.2 kJ•mol-1 , 86 kJ•mol-1 y 93.6 kJ•mol-1 para Cu, Ni y Zn, respectivamente y fueron obtenidas en el rango de temperaturas mencionado anteriormente. Posteriormente, el licor de lixiviación fue tratado electroquímicamente en varias condiciones: la remoción selectiva de Cu y Pb se realizó a PH 1.5, y la remoción de Ni y Zn también se obtuvo cuando el pH aumentó a 5. Todos los procesos involucrados aquí son amigables con el medio ambiente e, incluso el licor final podría ser reutilizado para los procesos de lixiviación y electro recuperación. Palabras Clave: Recuperación de oro, Proceso de lixiviación, Recuperación selectiva electroquímica, Desechos electrónicos, Placas de circuitos impresos.
... For metal waste, there are more alternatives with different associated costs. For instance, hydrometallurgy is relatively cheap in terms of investment and has a low environmental impact since it does not generate dangerous gases or dust, which makes it ideal for small and mediumscale applications, in addition to having a high percentage of metal recovery, using a two-stage process based on metal leaching [30]. On the other hand, pyrometallurgy has a great disadvantage, since, due to the high temperatures that are handled in this process, secondary materials such as plastic can be lost. ...
Article
There have been many problems generated by the COVID-19 pandemic. One of them is the worrying increase in the generation of medical waste due to the great risk they represent for health. Therefore, this work proposes a mathematical model for optimal solid waste management, proposing a circular value chain where all types of waste are treated in an intensified industrial park. The model selects the processing technologies and their production capacity. The problem was formulated as a mixed-integer linear programming problem to maximize profits and the waste processed, minimizing environmental impact. The proposed strategy is applied to the case study of the city of New York, where the increase in the generation of medical waste has been very significant. To promote recycling, different tax rates are proposed, depending on the amount of waste sent to the landfill. The results are presented on a Pareto curve showing the trade-off between profits and processed waste. We observed that the taxes promote recycling, even of those wastes that are not very convenient to recycle (from an economic point of view), favoring profits, reducing the environmental impact, and the risk to health inherent to the medical waste.
... Especially in the lower micrometer and nanometer particle range, classical separation methods are limited as they are often driven by inertia or gravity. Some separation problems in this size range are the recycling of valuable components from waste such as the dust fraction of electronic scrap [1,2], cell separation for analytics and diagnostics [3,4], or the generation of highly specific particle systems, e.g. for solar cells [5]. A separation technique suitable for use in this size range is dielectrophoresis. ...
Preprint
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In numerous of studies, dielectrophoresis (DEP) has proven that its high selectivity and versatility make it a promising separation technique in a variety of fields. So far, however, only a few processes in the bioanalytics have made it to commercial use. One of the main challenges is to achieve a technically relevant throughput while maintaining a high selectivity. We present a novel approach of a mesh-based DEP filter with ordered field disturbing structures that has a high potential for upscaling because low-cost and commercially available materials are used. In this filter, we firstly trap a mixture of particles and then selectively remobilize them via a frequency shift, which allows for multidimensional separation. Shape-selective separation is demonstrated using ellipsoidal and spherical polystyrene particles, first in established microchannels and subsequently in the mesh-based filter. Hence, particles were trapped at flow rates up to 120 mLh ⁻¹ and then selectively remobilized according to their shape. These results pave the way for high-throughput multitarget separations in a single and scalable device.
... On PCBs, the majority of Pd is used in multilayer ceramic chip capacitors (MLCC), while smaller portions can be found in conductive tracks in hybrid integrated circuits (HIC) and for plating printed circuits. It is calculated that Pd makes up to nearly half of the economic value derived from computers or laptops after the ECs have been disassembled and sorted [167]. However, little research has been conducted on Pd recovery in WPCBs [168][169][170][171]. ...
Article
Full-text available
This critical review focuses on advanced recycling strategies to enable or increase recovery of chemical elements present in waste printed circuit boards (WPCBs). Conventional recycling involves manual removal of high value electronic components (ECs), followed by raw crushing of WPCBs, to recover main elements (by weight or value). All other elements remain unrecovered and end up highly diluted in post-processing wastes or ashes. To retrieve these elements, it is necessary to enrich the waste streams, which requires a change of paradigm in WPCB treatment: the disassembly of WPCBs combined with the sorting of ECs. This allows ECs to be separated by composition and to drastically increase chemical element concentration, thus making their recovery economically viable. In this report, we critically review state-of-the-art processes that dismantle and sort ECs, including some unpublished foresight from our laboratory work, which could be implemented in a recycling plant. We then identify research, business opportunities and associated advanced retrieval methods for those elements that can therefore be recovered, such as refractory metals (Ta, Nb, W, Mo), gallium, or lanthanides, or those, such as the platinum group elements, that can be recovered in a more environmentally friendly way than pyrometallurgy. The recovery methods can be directly tuned and adapted to the corresponding stream.
... Throughout the world, rigorous researches on efficient and cost effective methods for handling e-waste and recovery of valuable metals from it are ongoing; with governments, private and individual sectors investing billions of dollars on the recycling process. In recent years, several techniques have been employed for recycling activities, such as pyro-metallurgy (Kingzett, 2010), hydrometallurgy (Tuncuk et al., 2012), bio-hydrometallurgy (Bryan et al., 2015), etc. But most of these techniques were experimented for recovery of valuable metals from WEEEs with major emphasis on Printed Circuit Boards (PCBs). ...
... In view of this, more priorities have been given to recovery of metal values from only waste printed circuit boards (Ajiboye et al. 2019). To mention a few: hydrometallurgical techniques (Tuncuk et al. 2012), leaching (Kumar et al. 2014), and pyrolysis of polymer part (Jakab et al. 2003). Kinetic studies (Grause et al. 2010) and bioleaching of precious metals from e-waste using bacteria (Arshadi and Mousavi 2014;Bryan et al. 2015;Natarajan and Ting 2014;Saidan et al. 2012) among others have been attempted and reported in the literature. ...
Article
High-tech electrical and electronic equipment contain large numbers of silica-rich integrated circuits (SRICs) which after its end of life generate huge amount of waste; however, its valuable metal contents can be properly recycled. Extraction of Cu, Ni, and Zn from pulverized SRIC obtained from discarded waste electrical and electronic equipments (WEEE) by sulfation roasting followed by water leaching was studied. Co-extraction of other metals such as Fe, Al, and Pb present in the sample was also explored. Effects of H2SO4/SRIC ratio, roasting temperature, time, and varying water leaching conditions on the extraction efficiencies were evaluated. The optimum conditions for Cu, Zn, and Ni extractions were determined as H2SO4/SRIC ratio 0.5, roasting temperature 300 °C, roasting time 60 min, leaching temperature 50 °C, leaching time 60 min, and liquid–solid ratio = 10:1 (i.e., 100 mL/10 g) with extraction efficiencies of 61.9, 84.9, and 93.6% for Cu, Ni, Zn, and co-extractions of Fe and Al were 71.1 and 55.6, respectively. Under the optimum conditions, approximate 20% Fe3+ was naturally precipitated which is advantageous for the subsequent step. Comparatively, higher extraction efficiencies of Cu, Zn, and Ni were observed in water leaching of H2SO4-roasted sample than direct H2SO4 leaching of raw sample keeping other leaching conditions constant. Lead retained in the roasted–leached residue was extracted with dilute HCl leaving silica and Al in the final leached residue. Process flow sheet for the extraction of Cu, Ni, Zn, and Pb and reuse of silicon from waste SRICs was proposed.
... However, it has some disadvantages like lower efficacy to recover some metals, the necessity of a high demand of C and metal sulfuring agents, and high energy demand to execute procedures like smelting, generally above 1000ºC. The hydrometallurgical process is more promising to recover valuable and rare metals from e-wastes than pyrometallurgy (Tuncuk et al., 2012), since it is more predictable, accurate, and controlable, besides consuming less energy since is a wet treatment technique that uses acid and basic solutions to promote metal recovery from WEEE. Nevertheless, the use of strong acids and alkaline solutions is detrimental for the environment, since a large amount of liquid effluent with heavy metals and unstable solid wastes are generated (Jorge and Soares, 2011;Kim et al., 2016;Xie et al., 2009;Kaya, , 2019. ...
... In a very short period, the most innovative of modern devices become obsolete at a faster rate than in the past. Therefore, the increase in waste originating from electrical and electronic equipment (WEEE) traces back to both private homes and professional users [1,2]. These materials are not properly treated when they reach the end of their useful life because they are sent untreated to landfills. ...
Article
Full-text available
Reclamation of printed circuit boards (PCBs) to recover metals is gaining growing attention due to minerals being non-renewable resources. Currently, metals extraction from PCBs through an efficient and green method is still under investigation. The present investigation concerns the recycling of printed circuit boards using hydrometallurgical processes. First, the basic metals (Cu, Ni, Zn and Fe) were separated using a sulfuric acid solution at moderate temperatures. The remaining solids were characterized by SEM-EDS, whereby a high content of precious metals (Au, Ag and Pt) was observed. In the second stage, solids were leached with a solution of HCl and NaClO in a 1-L titanium reactor with varied oxygen pressure (0.2, 0.34 and 0.55 MPa), temperature (40, 50 and 80 °C) and concentration of HCl (2 and 4 M), obtaining extractions above 95% at [HCl] = 4 M, P = 0.34 MPa and T = 40 °C. The extraction increased depending on the concentration of HCl. Eh–pH diagrams for Ag–Cl–H2O, Au–Cl–H2O and Pt–Cl–H2O were constructed to know the possible species in the solution.
... Pyrometallurgical, hydrometallurgical and integrated pyro-hydrometallurgical techniques are employed in formal and semi-formal value recovery operations, though hydrometallurgy based operations are the norm in developing countries [3,[15][16][17]. Metal extraction through various hydrometallurgical routes has been extensively investigated, and PCB pre-treatment operations (i.e., dismantling, size reduction, metal separation) are invariably performed prior to the hydrometallurgical methods. ...
Article
Full-text available
Waste electrical and electronic equipment or e-waste generation has been skyrocketing over the last decades. This poses waste management and value recovery challenges, especially in developing countries. Printed circuit boards (PCBs) are mainly employed in value recovery operations. Despite the high energy costs of generating crushed and milled particles of the order of several microns, those are employed in conventional hydrometallurgical techniques. Coarse PCB pieces (of order a few centimetres) based value recovery operations are not reported at the industrial scale as the complexities of the internal structure of PCBs limit efficient metal and non-metal separation. Since coarse PCB particles’ pre-treatment is of paramount importance to enhance metal and non-metal separations, thermal, mechanical, chemical and electrical pre-treatment techniques were extensively studied. It is quite evident that a single pre-treatment technique does not result in complete metal liberation and therefore several pre-treatment flowsheets were formulated for coarse PCB particles. Thermal, mechanical and chemical pre-treatments integrated flowsheets were derived and such flowsheets are seldom reported in the e-waste literature. The potential flowsheets need to be assessed considering socio-techno-economic considerations to yield the best available technologies (BAT). In the wider context, the results of this work could be useful for achieving the United Nations sustainable development goals.
... Due to the presence of heavy metals with hazardous effects on humans and the environment in E-wastes, several analytical techniques have been developed for the monitoring, sensing, and capture of heavy ions such as Cu(II) and Pd(II). Those techniques include atomic absorption techniques, inductively coupled plasma, electrochemical methods, X-ray and atomic fluorescence [28][29][30][31][32][33][34][35][36][37]. Those techniques have been restricted by pre-concentration procedures and the generation of organic wastes. ...
Article
The current study created an optical, chemical sensor that uses a mesoporous silica surface for the colorimetric recognition and capture of Cu(II) and Pd(II) ions with great sensitivity. The optical nanosensor was fabricated by direct immobilization of a synthesized 2,2’-((1E,1’E)-((6-hydroxy-2-mercaptopyrimidine-4,5-diyl) bis(azaneylylidene))bis(methaneylylidene)) bis(4-bromophenol) (HMPAMB) chromophore onto the porous of mesoporous silica nanoparticeles carriers. The HMPAMB sensor was characterized by XRD, TEM, SEM-EDX, and BET. The fabricated chemical sensor has the ability to sense Cu(II) and Pd(II) ions colorimetry with detection limits of 0.34, and 0.28 ppb, respectively, in quick, straightforward steps with high sensitivity. Three isotherm models were used to study the mechanism of Cu(II) and Pd(II) adsorption on the surface of HMPAMB. The results show that the modeling isotherm followed the Langmuir isotherm. The sensing efficiency of the HMPAMB sensor within the recycle numbers was calculated by three replicates (n = 3). Our outcomes reveal that the developed HMPAMB sensor offers an effective and reliable colorimetric procedure for detecting and extracting the target ions from E-wastes.
... The Cu and FR-4 liberated for large particle sizes had the maximum ductility difference, showing a large gap in each substance grade according to particle size. Given that it is difficult to physically separate the effective components from the ineffective ones in smaller particle groups [40,41], it is necessary to liberate the target component, Cu, from a large particle size range. In addition, for a particle size of 4000 µm or larger, a considerable amount of glass fibers remained tangled. ...
Article
Full-text available
Printed circuit boards (PCBs) are difficult to recycle because of the layered structure of non-metal (i.e., epoxy resin, glass fiber) and copper. In this work, we conducted a systematic investigation to effectively recover copper from PCB. A thermal treatment was employed for improving the crushing performance of PCB and conducted by varying the temperature and the gas. Then, the mechanical strength, degree of liberation (DL), and copper separation efficiency of the heat-treated and untreated PCBs were investigated. After heat treatment under a 300 °C air atmosphere, the mechanical strength of PCB decreased from 386.36 to 24.26 MPa, and copper liberation improved from 9.3% to 100% in the size range of a coarser size fraction (>1400 μm). Accordingly, when electrostatic separations were performed under these conditions, a high-Cu-grade concentrate and high recovery could be obtained. The results show that the change in the physical properties of the PCBs leads to an improvement in the DL following thermal decomposition at 300 °C in air. Our study elucidates the physical properties of PCBs and the DL under various heat treatment conditions. Furthermore, it shows that the heat treatment condition of 300 °C in air is ideal for recovering copper from the PCB.
... Global e-waste generation from 2014 to 2019 and projection from 2020 to 2030 (modified from Forti et al., 2020;Panda et al., 2021) (Effect of COVID 19 is not included in the projected data). extracted by electrolytic refining technique (Tuncuk et al., 2012). In this process, only a partial separation of metals is achieved, so other processes such as hydrometallurgy and electrochemistry are required (Cui and Zhang, 2008). ...
Article
Due to the rapid development in electronic industries and high consumer demand, electrical and electronic equipment have a shorter lifetime in developed and developing countries markets, leading to tons of electronic waste. The waste Printed circuit board (PCBs) contain many valuable metals like gold and copper and hazardous materials like lead. Therefore, recycling the metallic and non-metallic fractions from waste PCBs using environmentally friendly and suitable sustainable resource utilization techniques is in high demand. In this direction, nanotechnology has also been recently used to recover base metals, toxic metals, and precious metals in different sizes and morphologies. This study provides an up-to-date review of research on recovering high added value (HAV) materials from various electronic waste components. These include high purity metals, nanoparticles, nanostructured alloys, nanocomposites, high purity ultrafine particles, and microfibers. It also includes the properties investigated and the potential applications of the obtained HAV products in fields such as wastewater treatment, detection of incessant pollutants, biomedicine, and catalysis. Current challenges faced in scaling up the e-waste derived nanoproducts manufacturing are also discussed in the concluding remarks.
... Secondary copper materials are added to existing copper smelters, but processing challenges arise as the tonnage of recycled WEEE increases (Reuters et al., 2013;Forsén et al., 2017;Wan et al., 2021). To treat the black copper (or dirty blister) produced by smelting high WEEE content feeds, pyrometallurgical converting and electrorefining (Forsén et al., 2017;Chen et al., 2012;Montenegro et al., 2013;Zhang et al., 2021) or pressurized sulfuric acid leaching and electrowinning (Tuncuk et al., 2012;Khaliq et al., 2014;Tesfaye et al., 2017) are being used. ...
Article
Copper producers face increased demand associated with increasing complexity in feedstock composition, including high amounts of impurity metals. In this work, linear sweep voltammetry was used to study the electrodeposition behavior of copper and arsenic, define strategies for the production of grade A copper, and the removal of arsenic from complex electrolytes. Our results show that the copper concentration is a key parameter to control in the electrodeposition process. The continuous deposition of arsenic from the electrolyte requires copper in solution (≤10 g L⁻¹ Cu(II) for 2 g L⁻¹ As(III)) to form copper arsenides. The deposition of metallic arsenic does not occur readily. Conversely, the use of a concentrated Cu(II) solution (e.g. 40 g L⁻¹) resulted in grade A copper from an electrolyte with a maximum of 2 g L⁻¹ As(III) under galvanostatic control at a current density of – 42 mA cm⁻². Time-of-Flight Secondary Ion Mass Spectrometry depth profile measurements on copper deposits revealed that arsenic contamination was entirely concentrated near the substrate side of the deposit and progressively decreased further into the deposit. The codeposition of arsenic occurred along with the initial copper nucleation, when the electrochemical potential for electrodepostion under galvanostatic control is temporarily lower. These findings provide important insights for future sustainable copper electrodeposition technologies from complex feedstocks.
... The hydrometallurgical process had a great advantage in the recovery of rare earth metals from discarded NdFeB magnets due to the availability of a single REO with a wider range of applications (Tuncuk et al. 2012). In addition, the mixed REOs obtained by pyrometallurgical process would eventually have to be separated by hydrometallurgical process to obtain a single REO. ...
Article
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Due to the increasing demands and supply shortages for rare earth elements (REEs), the recovery of REEs from discarded NdFeB with high REE content has become extremely important. In this paper, a hydrometallurgical coupling process involving mechanical activation and selective acid leaching was proposed for the recovery of REEs from discarded NdFeB magnets. The effects of ball milling activation speed, hydrochloric acid concentration, and solid–liquid ratio on the leaching efficiencies of REEs in NdFeB magnets were studied. The results indicated that the ball milling activation method could enhance the reactivity of the samples through the action of mechanical force, which promoted the leaching efficiency and leaching speed of REEs. Under the optimum conditions (650-rpm activation speed, 0.4 M hydrochloric acid, 100 g/L solid–liquid ratio), the leaching efficiency of REEs increased up to 99% with low hydrochloric acid consumption and the leaching speed of REEs was triple than that of without activation. The final purity of recovered rare earth oxides reached up to 99.9%. All results demonstrated that ball milling activation coupled with selective leaching of hydrochloric acid could be an effective and environment-friendly strategy to achieve the recovery of REEs.
... However, it has some disadvantages like lower efficacy to recover some metals, the necessity of a high demand of C and metal sulfuring agents, and high energy demand to execute procedures like smelting, generally above 1000ºC. The hydrometallurgical process is more promising to recover valuable and rare metals from e-wastes than pyrometallurgy (Tuncuk et al., 2012), since it is more predictable, accurate, and controlable, besides consuming less energy since is a wet treatment technique that uses acid and basic solutions to promote metal recovery from WEEE. Nevertheless, the use of strong acids and alkaline solutions is detrimental for the environment, since a large amount of liquid effluent with heavy metals and unstable solid wastes are generated (Jorge and Soares, 2011;Kim et al., 2016;Xie et al., 2009;Kaya, , 2019. ...
Chapter
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Agriculture plays a vital role in every national economy. It represents a substantial trading industry for an economically strong country. Remote sensing and geographical information system used to analyze and visualize agriculture environmentals have proved to be very beneficial to the farming community as well as inudstry. In this chapter, I tried to overview the application of remote sensing and geographical information system in agriculture and natural resource management. Application of different remote sensing technique are important for crop monitoring, crop condition assessment, and yield estimation for the sustainability of agriculture and natural resources. The spectral information is the important aspect of remote sensing data for crop modeling and it is strongly related to canopy parameters which are representative of crop health and crop growth stage. Remote sensing and GIS can also be used very effectively in land use, land cover analysis as well as damage assessment because of drought, floods, and other exteme weather events information on meteorology and vegetation are the two major important inputs into agriculture meteorology application of remote sensing technologies are an important and effective method to identify pests and disease. It is one of the effective tools for assesing and monitoring water resources.
... In this work, we studied the solvometallurgical extraction of metals from printed circuits boards (PCBs). Due to the high association of metals with plastics, metal liberation processes often lead to fine particles, which may, in turn, result in inefficient metal recovery [10]. To reduce such metal losses, we used large pieces of PCBs instead of pulverized PCB powder [11,12]. ...
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The development of a truly circular economy necessitates the recovery and recycling of resources from secondary streams. In this work, we studied the extraction of metals from printed circuit boards (PCBs) using choline chloride: ethylene glycol deep eutectic solvents: Cu, Ni, Zn, and Sn were selectively extracted from the PCBs, with >75% extraction after 72 h for Cu, Ni, and Sn, and circa. 45% extraction for Zn. This solvometallurgical approach promises to minimize the use of water and acid/base reagents in processing. The results show a considerable ability to compete with current methods of metal extraction and therefore generate a strong potential to attain the goal of a sustainable circular economy via zero-waste green urban mining.
... Milling process with the use of a combination of knife (with grid of 6 mm) and hammer mill (with grid of 1 mm) loosed lower than 6% by weight (Silvas et al., 2015). The reduction in the particle size of less than 2 mm promotes complete release of copper, which is due to encapsulation of copper in connectors and pins of higher particles size than 2 mm (Tuncuk et al., 2012). Hammer mill operation carried on 2 × 2 cm 2 samples of PCBs, (PCBA printed circuit boards assembly; ECs electronic components) (Reproduced with permission (Park et al., 2015). ...
Article
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Decrease in life span of electronic devices and consumer’s urge to use advanced technology leads to obsolescence of such devices, resulting in electronic waste generation. The technology for e-waste components recycling has made great progress. However, due to growing environmental concern, there is a need to find alternatives for conventional e-waste recycling methods to achieve a safer environment. Rapid surge in e-waste generation is a matter of concern due to elevated levels of heavy metals and persistent organic pollutants (POPs) in air, soil and water caused by informal recycling practices. Moreover, recycling of printed circuit board (PCB), a major part of electronic waste, in order to recover metals, results in release of waste acid leach water, if untreated, which contain heavy metals like Pb, Cr, Ni, etc. This has given rise to the development of several remediation techniques for soil- and water-like phytoremediation, soil washing, bioremediation, and application of nanoparticles, which have been compared and reviewed in this paper along with their limitations for application at larger scale for real-contaminated soil. This review focuses on the existing remediation techniques and their limitations to decrease environmental hazards caused by the release of various pollutants through e-waste recycling. Graphic abstract
... Due to the rapid advancement of technology, the global production of electrical and electronic equipment is increasing rapidly (Tuncuk et al. 2012). Along with technological innovations, economic growth and market expansion, a significant increase is observed in waste electrical and electronic equipment (wEEE) and this increase generates environmental problems (He et al. 2006;Khetriwal et al. 2009). ...
Article
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The paper presents an assessment of flotation efficiency in the separation of plastics from metals derived from printed circuit boards (PCBs). The PCBs were ground in a knife mill prior to flotation. The contact angles of various materials corresponding to the grains from ground PCBs were measured, and a series of flotation tests was carried out to obtain the best product. The impact of the following parameters were investigated: the reagent and its dose, the airflow rate through the flotation tank and the feed concentration. The highest efficiency of metal recovery from PCBs was achieved for Dimethoxy dipropyleneglycol at a concentration of 157 mg/dm3 and with an airflow of 200 dm3/h and a feed concentration of <50 g/dm3. In the hydrophilic product (concentrate), it was mainly Cu (40%) and Sn (7.8%) that were identified by means of XRF, but there were also trace amounts of precious metals such as Au (0.024%), Ag (0.5797%) and Pd (149 ppm). Impurities in the form of Si (5%), Ca (3.2) and Br (2.1) were also identified in this product. Small amounts of metals in their metallic form were identified in the hydrophobic product (waste), mainly Cu (2.3), Al (1.7) and Sn (1.1). As a result of the research, high recovery ratios were obtained for Cu (93%), Sn (84), Ag (83) and Au (69). The purity of obtained metal concentrate with this method was lower in comparison with the other methods of the recovery of metals from ground PCBs for the same feed, i.e. electrostatic or gravity separation. Also considering other factors such as the environmental impact of the flotation process, the number of facilities and their energy consumption, this process should not be used in the developed metal recovery technology. Using electrostatic separation for the same feed obtained much better results.
... On the other hand, hydrometallurgy has shown better performance in recovering metals from PCBs, as it allows much more flexibility during upscaling and better process control than high-temperature processing routes. [17][18][19] Different leaching agents have already been investigated for the dissolution of metals from PCBs, such as sulphuric acid (H 2 SO 4 ), hydrochloric acid (HCl), nitric acid (HNO 3 ), acetic acid (C 2 H 4 O 2 ) and citric acid (C 6 H 8 O 7 ), once the solder mask has been separated. 20 Meanwhile, aqua regia and iodine/iodide leaching systems allow the recovery of gold from waste PCBs. ...
Article
Due to their high metal content, printed circuit board (PCBs) are an attractive resource for metal recovery. Until now, the dissolution and subsequent recovery of metals from PCBs considers either...
... 15 Therefore, it is also largely applied to the recycling of waste fluorescent lamps. 16,17 In order to resource the recovery of REMs, their dissolution in suitable lixiviants that carry out impurity (base metals) removal followed by the mutual separation of the REMs, using solvent extraction, 18 precipitation, 19 supercritical fluid extraction, 20 ion exchange, 21 and ionic liquid, 22 are practiced. The products can also be deoxidized to the metallic state instead of using the usual molten salt electrolysis and metallothermic reduction. ...
Article
Waste fluorescent lamps containing a significantly high quantity of rare earth metals have great potential to be an unconventional source of critical metals if exploited efficiently for resource recovery. Therefore, the present study dealt with the selective leaching of red phosphor rare earths from waste fluorescent lamps. The parametric effects of the acid media and their concentrations, addition of H2O2, pulp density, temperature, and time were studied. The results revealed that 2.0 M HCl with 5 vol.% H2O2 yielded 100% yttrium and more than 95% europium compared to only 92% and 96% yttrium and 89% and 91% europium while using H2SO4 and HNO3, respectively. The green phosphor compounds Ce0.67Tb0.33MgAl11O19 and (La0.65Ce0.15Tb0.2)PO4 were undissolved in a residual mass that can be handled separately. Kinetics data followed logarithmic rate law, and the chemically-controlled mechanism was indicated by the values of apparent activation energy (i.e., Ea(Y), 87.8 kJ/mol and Ea(Eu), 54.1 kJ/mol).
... Therefore, it is important to recover metals from e-waste to prevent the depletion of the primary metal resources and maintain the demand-supply chain. It is worth mentioning that the concentration of metals in e-waste is quite high as compared to the ores, for example, Cu and Au ores contain 0.5-1 wt% Cu and 1-10 g/ton Au, while the Printed Circuit Board (PCB) of the computer contains 20 wt% Cu and 250 g/ton Au which is significantly higher compared to ores [7]. The value of materials present in e-waste was around 60 billion USD in 2016 [8]. ...
Article
The technological advancement in the field of electrical and electronic equipment leads to the rapid increase in the obsolescence rate of these devices and the generation of electronic waste (e-waste). The problem is further exacerbated due to the limited awareness about disposal methods of e-waste coupled with limited viable recycling avenues. Rising demand and limited recycling capacity further lead to increased resource extraction and mining activities having a degenerative impact on biota. The improper recycling and unregulated accumulation of e-waste too has its ramifications on human health, economy, and environment at large. However, e-waste is also an asset as metals and plastics account for around 75 wt.% of e-waste and provide an opportunity for resource recovery. Therefore, there is a need to find a sustainable solution for resource recovery and the sound management of e-waste. Hence, this review focuses on the current technologies from the aspect of e-waste management and resource recovery i.e. chemical conversion of e-waste plastic to valuable products as well as energy generation and metal recovery from e-waste using hydrometallurgical and pyrometallurgical approaches. This review covers various technologies such as pyrolysis, catalytic pyrolysis, gasification, and supercritical fluids to recycle e-waste plastic. In addition, the recovery of metals using hydrometallurgical technologies such as cyanide, thiosulfate, thiourea, halide, and acid leaching has also been critically discussed. The pyrometallurgical approach for the recovery of metals has been also discussed. This review considers the environment-friendly approach, economic value, and recycling efficiency of the process as important parameters for e-waste recycling. Novel and greener technologies for metal recovery are suggested for the future. The review recommends an integrated sustainable solution for e-waste recycling which includes e-waste plastic recycling and metal recovery which is expected to provide guidance for future research and technology development for industrial practice.
... The found weight loss during all the processes was about 15% of the initial weight. During physical separation processes, losses can reach amounts of 10-35% [34]. To increase the efficiency of the mechanical pre-treatment plants, a material loss evaluation during the shredding and separation steps would be necessary to analyze in further works. ...
Article
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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.
... From a sustainable chemistry perspective, hydrometallurgy is often favoured as it can lead to excellent material and energy balances, as reagents can be recycled through multi-step processes, and the emission of toxic substances is limited (Cui and Anderson, 2016;Li et al., 2018;Tuncuk et al., 2012). The metallic and non-metallic J o u r n a l P r e -p r o o f components of the PCB can be separated by a delamination step (Verma et al., 2017;Wath et al., 2015;Zhu et al., 2013), and the enriched metallic fraction leached in acidic or alkaline solution to dissolve the desired metals, leaving a residual gangue (Jha et al., 2014). ...
Article
In the present investigation, the selective recovery of nickel from a leach solution of delaminated metal clads from obsolete mobile phone PCBs using the industrial reagent ACORGA M5640 has been studied. As a first step, copper is selectively separated from the mixed metal leach liquor by solvent extraction at pH 2, to leave a nickel-rich raffinate solution. A second stage solvent extraction process conducted at pH 8 then permits recovery of the nickel. Small quantities of zinc and cadmium are also co-extracted. In this study, the conditions for most suitable nickel extraction and stripping have been explored. Results indicate that quantitative extraction of nickel (99.7%) can be achieved using a 1:5 organic (10 vol% extractant in kerosene) to aqueous (pH 8) phase ratio in 60 min. The nickel in organic phase is readily stripped from the extractant, with more than 95% recovered, along with low levels of zinc (1.7 mg/L) and cadmium (0.6 mg/L), following a 0.5 M hydrochloric acid or 1 M nitric acid strip step. Cyclic usage of the extractant organic layer revealed that its effectiveness to extraction has remained equivalent to the first cycle. Finally, the separation of trace elements such as lead, tin and cadmium from the raffinate of stage 2 solvent extraction is also studied by cementation with zinc powder. The study reveals that the removal of these elements and the generation of pure zinc solution can be obtained by adding 300% excess zinc powder (74 μm) at 50 °C with 500 rpm stirring speed in 60 min. The separation of copper in stage 1, nickel from copper-free aqueous solution in stage 2 and other minor elements from the raffinate of stage 2 solvent extraction ensures the proposed process is sustainable and avoids complexity in the sequential metal recovery processes.
Article
Supercritical water (SCW) technology can be applied as an efficient and environment-friendly method to recover toxic or complex chemical wastes. Separation and chemical reactions under supercritical conditions may be realized by changing the temperature, pressure, and other operating parameters to adjust the physical and chemical properties of water. However, salt deposition and corrosion are often encountered during the treatment of inorganic substances, which will hinder the commercial applications of SCW technology. The solubility of salt in high pressure/temperature water forms the theoretical basis for studying the recovery of metal salts in supercritical water and understanding salt deposition. Therefore, this work systematically and objectively reviews different research methods used to analyze salt solubility in high pressure/temperature water, including the experimental method, prediction theoretical modeling, and computer simulation method; the research status and existing data of this parameter are also analyzed. The purpose of this review is to provide ideas and references for follow-up research by providing a comprehensive overview of salt solubility research methods and the current situation. Suggestions for more efficient metal recovery through technology integration are also provided.
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Waste of electrical and electronic equipment (WEEE, also known as E-Waste) has emerged as a serious issue for the whole world along with the evolution of modern industry. WEEE plastic contains heavy metals (arsenic, mercury, chromium, cadmium, lead, etc.) and halogen materials (bromine, chlorine, etc.), which are toxic and harmful to the environment, therefore the recycling of WEEE plastic is necessary and critical. Not only the various additives in the polymer but also the contaminations from polychlorinated biphenyl (PCB), batteries, etc, make the recycling process challenging. In this review, the functional application of plastic in electrical and electronic equipment (EEE) including electrical insulation, heat insulation, etc, is firstly introduced. The various components and additives of plastic in EEE are provided. Moreover, the state-of-the-art treatment and recycle methods of the WEEE plastic are summarized and discussed. This review can provide a comprehensive reference for investigation of plastic in e-waste.
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Ionic imprinted membrane (IIM) was successfully synthesized using sulfonated polyeugenol, a derivative of eugenol as a functional polymer, with PVA as a base membrane and PEGDE as a crosslinker. IIM Au(III) is a membrane with an Au(III) ion template. This study aimed to determine the pH effect of a feed phase for selective transport of IIM Au(III), comparing it with a non-imprinted membrane (NIM) against Au3+ metal ions from motherboard waste. It also aimed to compare the membrane selectivity of Au3+ metal ions to Cu2+ metal ions, which are also found in motherboard waste. Gold samples were prepared using H(AuCl4) standard and leaching solutions from motherboard waste. The leaching of the motherboard used aqua regia and the assistance of a microwave to accelerate the leaching process. The optimum transport of Au3+ metal ions was when using IIM Au(III) at pH 3. This proved that the presence of a template affected IIM Au(III) to recognize Au(III) ions. IIM Au(III) showed higher selectivity than NIM, as evidenced by the percentage in the receiving phase of the Au3+ metal ions, which was more significant than the Cu2+ metal ions from the motherboard leaching solution.
Chapter
Inefficient waste management has led to the contamination degradation of various ecological resources. Several physicochemical techniques are already in place to remediate this issue. However, remediation through adsorption presents several advantages over existing physicochemical techniques in terms of cost‐effectiveness. Furthermore, biosorbents present the additional advantage of sustainability and offer remediation of affected natural resources. This chapter presents an overview of the deployment of biosorbents and their potential in conserving natural resources. This chapter also highlights the recovery of metals through used biosorbents. Finally, the chapter discusses current challenges in the implementation of biosorbents.
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Halogen-containing organic components in waste electrical and electronic equipment have an obvious influence on the distribution behaviors of valuable metals during the smelting processes. However, the mechanism is still incomplete in the literature. The equilibration-quenching-(ICP+EPMA) experimental technique has been applied in studying the partitioning behaviors of Au, Ag, and Sn in the Cu-FeOx-SiO2-CaO-Al2O3 smelting system in the presence of halogen elements (F, Cl, Br). The obtained results showed that: (1) 93% Au terminated into the alloy phase in CaF2 adding experiments, and a maximum of 32% Au reported to the gas phase in CaCl2 or CaBr2 adding experiments; (2) 22–49% Ag entered the gas phase when adding CaF2 into the system, and 3–34% Ag entered into the gas phase when adding CaCl2 or CaBr2; and (3) halogen elements influenced Sn dramatically, and portions of Sn in the gas phase and slag phase increased along with increasing temperature or halides dosage.
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The study of copper (Cu) recovery is crucial for the entire recovery process of waste printed circuit boards (WPCBs), and Cu can be leached efficiently via a sulfuric acid–hydrogen peroxide (H2SO4–H2O2) system. To achieve high Cu recovery, it is important to evaluate the parameters of the leaching process and understand the Cu leaching kinetics. Applying statistical and mathematical techniques to the leaching process will further benefit the optimization of the Cu leaching parameters. Moreover, the leaching kinetics of Cu in the H2SO4–H2O2 solution is yet to be fully understood. Hence, in the present work, process parameters, such as temperature, H2SO4 and H2O2 concentrations, solid–liquid ratio, particle size, and stirring speed, were optimized statistically by the response surface methodology (RSM). The results showed that the leaching kinetics conformed to the Avrami model. The maximum Cu leaching efficiency was 99.47%, and it was obtained based on the following optimal conditions: 30.98 °C, 2.6 mol/L H2SO4, 1.87 mol/L H2O2, a solid–liquid ratio of 0.05 g/mL, 135 mesh, and 378 rpm. RSM was used for the optimization of the process parameters, and the leaching kinetics in this system was clarified. This study provides an important pathway for the investigation of other metal recoveries from WPCBs.
Article
Limited natural resources and a continuous increase in the demand for modern technological products, is creating a demand and supply gap for rare earth elements (REEs) and Sc. There is therefore a need to adopt the sustainable approach of the circular economy system (CE). In this review, we defined six steps required to close the loop and recover REEs, using a holistic approach. Recent statistics on REEs and Sc demand and the number of waste generations are reported and studies on more environmentally friendly, economic, and/or efficient recovery processes are summarized. Pilot-scale recovery facilities are described for several types of secondary sources. Finally, we identify obstacles to closing the REE loop in a circular economy and the reasons why secondary sources are not preferred over primary sources. Briefly, recovery from secondary sources should be environmentally and economically friendly and of an acceptable standard concerning final product quality. However, current technologies for recovery from for secondary sources are limiting and technology needs will vary depending on the source type. The quality/purity of the recovered metals should be proven so that they do not result in any adverse effects on the product quality, when they are being used as secondary raw material. In addition, for industrial-scale facilities, process improvements are required that consider environmental conditions.
Article
Printed circuit boards (PCBs) are an essential and central component of electronic waste. The rapid depletion of natural resources, massive generation of end-of-life PCBs and inherently metal-loaded values inevitably call for recycling and recovery. This review critically discusses the systematic and sequential processes adopted for PCB metallic recoveries via physical, pyrometallurgical, hydrometallurgical, and combined technologies. Pre-treatments play a decisive and significant role in upgradation and efficient metal extraction. A novel combination of different pre-treatments and hybrid thermal-chemical routes are often reported for improved separation efficiency and performance. Selective recovery (using solvent extraction, precipitation, polymer inclusion membrane, adsorption, ion exchange) of high purity product from multi-elemental leach solution has recently gained interest and is reviewed. Current recycling techniques at a commercial scale are preferably based on pyrometallurgy (smelting-refining), where electronic waste is only a fraction of the total feed stream. Electronic components such as monolithic ceramic capacitors, tantalum capacitors, integrated circuits, and central processing units mounted on the PCBs are important due to precious metals' presence. The futuristic recycling perspective should treat base and precious metal-rich components separately with minimal environmental effect, end product usage, and maximum economic benefit. Sustainable processing routes for converting discarded PCBs into value-added products should also be attempted, as amplified in this review. An integrated, definite framework for full resource recovery from waste PCBs was proposed.
Article
Electrical and electronic waste is a significant problem threatening countries’ economic, social, and environmental aspects. Electrical waste is toxic but contains valuable substances. With the increasing consumption of electronic devices, large amounts of this waste are generated worldwide. Due to the appearance of poisonous and precious metals in electronic waste, the management policy is different from traditional waste management. Therefore, knowing more about new methods and combining them is necessary. Various methods have been developed to extract these metals, but extraction with carbon dioxide has received particular attention due to its environmental friendliness. This study aimed to increase the extraction efficiency of silver using supercritical carbon dioxide from computer printed circuit boards waste. The use of supercritical water pretreatment was applied to such wastes to enhance the concentration of silver and remove organic matter. Six experiments at the pressure of 250 bar), the temperature of 350–450 °C, and the residence time of 15–45 min were conducted. The pressure of 230 bar, the temperature of 400 °C, and the retention time of 45 min were selected as the optimal point for supercritical water oxidation conditions. Pretreated solids were used as feed for the supercritical carbon dioxide extraction process. Optimal test conditions include the pressure of 217 bar, the temperature of 51 °C, and the residence time of 40 min. The extraction of silver from the residues of printed circuit boards in optimal situations reached 98% without solvents and ligands, which is selected as the best extraction point.
Article
The amount of waste from electrical and electronic equipment has been growing every year. The printed circuit boards contained in this waste include metals that can be recovered through urban mining, adding value to this waste and minimizing environmental impacts with its incorrect disposal or treatment. In this work, memory boards obsolete with 0.053 wt.% Ag were used. The extraction of all metals studied (Ag, Al, Cu, Fe, Ni, Sn, and Zn) involved the evaluation of the Pourbaix and speciation diagrams to identify the pH and redox potential conditions, considering the possible species formed with leaching agents: sulfuric, nitric, and hydrochloric medium. After the definition of the leaching agent, the extraction routes by hydrometallurgical processing were proposed from the parameters of temperature, s/l ratio, and reaction time previously studied. Route A was composed of sequential stages (the first leaching in a sulfuric medium and the second in an oxidizing sulfuric medium) and obtained 100% of Ag recovery. Route B consisted only of leaching in an oxidizing sulfuric medium, obtained about 94% of the Ag recovery, and could not contribute to the subsequent purification steps (if necessary) of this solution, as all metals would also be in the solution. These two routes showed that Ag can only be recovered in an oxidizing sulfuric acid medium, according to the conditions studied. Ag recovered in the leach liquor of the second stage of Route A was purified by chemical precipitation with NaCl, and the AgCl was solubilized in an NH4OH solution. This solution was used to synthesize silver nanoparticles by the Turkevich method in 25 minutes. The spherical nanoparticles synthesized an average size distribution of 67 nm.
Chapter
The rapid growth of information technology and industrialization are the key components for the development of electronic equipment, and their inevitable role in human day-to-day life has an important stint in the generation of electronic waste (e-waste). This waste has far-reaching environmental and health consequences. One such e-waste printed circuit board (PCB) contains significant amounts of valuable heavy metals such as copper (Cu), lead (Pb), zinc (Zn), nickel (Ni), and others that can be extracted through various metallurgical routes. Recovery and recycle of heavy metal ions is a major challenge to prevent environmental contamination. The present study discusses the current e-waste scenario, health impacts and treatment methods in detail, and also presents experimental results of recovery of heavy metals from printed circuit boards (PCBs) by leaching using aqua regia (HCI + HNO3 and HCI + H2SO4). Under varying conditions such as specified conditions of 80°C, 0.05 mm of thickness, 3 hrs of contacttime, 80rpm shaking speed, and concentration of PCB sample of 0.5 g ml−1, it results in the composition of extracted heavy metal ions in such a way that 97.59% of copper, 96.59% of lead, 94.66% of tin, and 96.64% of zinc, respectively. The recovery of heavy metal ions from PCBs has an important leading contribution in electronic waste management and the result shows a higher rate.
Chapter
Pyrometallurgy is one of the most viable extractive metallurgy techniques for recycling high volumes of waste electrical and electronic equipment (WEEE). Pyrometallurgical processes often involve the simultaneous presence of multiple liquid solutions such as slag, matte, metallic melt, and molten salt in which valuable metals and impurities can be partitioned and eventually discarded (in the case of impurities). Pyrometallurgy includes many extractive metallurgical operations such as smelting (performed in high‐temperature furnaces) and refining (which includes chemical and electrochemical processes). This chapter describes pyrometallurgical processes to recover metals from WEEE, such as waste printed circuit boards. Furthermore, it discusses their advantages, limitations, and associated challenges. Further details on the copper‐ and lead‐smelting strategies used to recycle e‐wastes are also presented.
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A bootstrap to build a novel solid chemical sensor was used functionalized by silica nanotubes (F-SNTs). This novel nanosized sensor has been developed to be immobilized directly on the F-SNTs with the new azo-chromophorous (z)-2-(2,4-dihydroxyphenyl)-terephthalic acid (HPDTP) using the two carboxylic acid groups. In the fluorescent technique detection range 5-825 ppb was achieved for Pd(II) ions, with linear correlation values of 0.9969. The new nanosized sensor has a high sensitivity for Pd(II) ions up to 28.8 ppb at extremely low concentration. This nanosized sensor was evaluated for its use as an adsorber. The sensor (HPDTP) has a fast detection feature for the removal without preconcentration of Pd(II) ions. This nanosized sensor also exhibits an effective Pd(II) identification in e-residues and preferential recovery.
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This review discusses physical, chemical and direct lithium-ion battery recycling methods in order to have an outlook on future recovery routes. Physical and chemical processes are employed to treat cathode active materials which are the greatest cost contributor in the production of lithium batteries. Direct recycling processes maintain the original chemical structure and process value of battery materials by recovering and reusing them directly. Mechanical separation is essential to liberate cathode materials that are concentrated in the finer size region. However, currently, the cathode active materials are being concentrated at a cut point that is considerably greater than the actual size found in spent batteries. Effective physical methods reduce the cost of subsequent chemical treatment and thereafter re-lithiation successfully reintroduces lithium into spent cathodes. Some of the current challenges are the difficulty in controlling impurities in recovered products and ensuring that the entire recycling process more sustainable.
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Ionic polymers have been proven to be promising adsorbents in recovering Au(III) due to their advantages of simple synthesis and high adsorption efficiency. However, the unclarity of the relationship between the adsorption ability of ionic polymers and their cationic structures hinders further optimization of their adsorption performance. This study synthesized a series of ionic polymers with pyridinium, imidazolium, piperidinium, pyrrolidinium, and triethylammonium cations to discover the effects of the cationic structure on their adsorption properties. Experimental results show that the existence of anion-π interaction between aromatic cations and [AuCl4]- makes the aromatic cations-anion interaction stronger, which does not enhance the adsorption performance of the aromatic-based ionic polymer. This is due to the charge delocalization in the aromatic ring, resulting in a lower electrostatic potential (ESP) of aromatic cations than that of aliphatic cations with a localized charge. The higher the ESP of cations, the better the adsorption performance of the corresponding ionic polymer. This study serves as a deep understanding of the cationic structure-adsorptive performance relationship of the ionic polymer at the molecular level and further provides a theoretical guidance to optimize the adsorption performance of ionic polymers.
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Electronic waste (e-waste) is one of the major pollutants accumulated due to its huge demand and short lifespan. Hence, it is essential to reuse and extract the value added components from e-waste. In this context, firstly, a printed circuit board (PCB) is used to produce calorific valuable gases by pyrolysis and gasification reactions. Secondly, the resultant residue of PCB is combusted to extract metals such as iron, copper, nickel etc. as oxygen carriers for the chemical looping combustion (CLC) process. CLC is an emerging and appealing technology for producing rich CO2 that can be directly sent for sequestration. In the present study, a detailed investigation is performed to ensure the reactivity of the e-waste based metal oxide with high ash coal, rice straw and their blends in the CLC process. CO2 yield, gas conversion, and char conversion are evaluated to assess the performance of the co-combustion based CLC process. It is found that 90.9% CO2 yield, 94.1% gas conversion and 93.2% char conversion can be obtained using the blends of coal and rice straw in the first cycle of the CLC operation. Further, a reduction of 5% to 7% of these parameters is evaluated at the end of the third consecutive cycle of CLC operations. The interaction between coal and rice straw is further studied by evaluating their synergistic effects, char-oxygen carrier interaction and kinetic parameters using a thermogravimetric analyzer under N2 and CO2 atmosphere. The co-combustion process has reduced the activation energy by 13.4% at 800–1000 °C under CO2 atmosphere.
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Excessive waste is continually accumulating owing to increased consumption, and an excellent example is the consumption of electrical and electronic equipment (EEE), which are eventually transformed into waste from electrical and electronic equipment (WEEE). WEEE is an interesting material stream because it includes various valuable materials that have great potential for recycling and reutilization. To maximize recycling and utilization potential, all fractions in WEEE must be reviewed from a sustainable perspective. Several WEEE contain plastic, which comprises approximately one-third of the total WEEE composition; thus, this plastic content is a good target for recycling purposes. However, the recycling of WEEE plastics might include some challenges, such as the treatment of harmful substances in the material, which can prevent effective and high-quality material recycling. This study investigates the polymer composition and critical elements of the material stream of WEEE polymer. These polymers were identified using portable near-infrared (NIR) spectroscopy and energy-dispersive X-ray spectroscopy (EDS) at an elemental level. The results showed that among various other polymers, acrylonitrile butadiene styrene (ABS) was the main polymer identified in WEEE. The proportion of unidentified polymers was alarmingly large; specifically, when the presence of bromine was positively correlated with the presence of an unidentified WEEE polymer. This study also corroborated that bromine is actually not present in bromine-free plastics, demonstrating that industrial classification works with WEEE polymers.
Chapter
The effective dissolution of metals is widely known with the help of microorganisms called bioleaching or biomining used for the extraction of metals from their ores. Usually the microorganisms involved in biomining are chemolithoautotrophic and extremophilic in nature, since they are living in highly acidic environments (pH 1-3.0) containing heavy concentrations of metals. The commonly found genera of archea are Sulfolobus, Acidianus, Metallosphaera, and Sulfurisphaera. Throughput microbial genomics and proteomics analysis provides novel insights of metabolism mechanisms of bioleaching microbes. These microbes are having significant impact on the bioremediation of acid mine drainage (AMD) resulted from many industrial operations. Using these microbes, various metals including Ni, Cd, Cu, Fe, As, Pb, Hg, Cr, Mn, Zn, etc. are removed from the environment. Biomining microorganisms are having significant applications in the biotechnological processes including extraction of gold from ores, extraction of nickel from low-grade sulfide ores, extraction of copper from chalcopyrite, etc.
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Printed circuit boards represent a source of urban mining for the reuse of resources in a circular economy. The number of metals in these boards can vary according to the model, year of manufacture, and function, making these scraps a complex residue for the application of recovery routes. In the present study, the leaching process was evaluated as an alternative to the magnetic separation step of the current hydrometallurgical routes for the recovery of iron and copper in these waste in which recovery of the metals present was carried out. The first stage of the hydrometallurgical route was leaching in sulfuric acid, for the recovery of iron. Subsequently, the copper recovery study was carried out, through the second stage of acid leaching in an oxidizing medium. The third stage was carried out in a nitric medium for the solubilization of the remaining metals. After using the same solid/liquid ratio for the solubilization of the metals present in the two types of boards, it was found that for the board with the highest concentration of metals that this ratio should be changed for greater extraction results. The percentage of leaching for the motherboard samples increased (to about 98 wt%) together with the residue/acid ratio, and this showed that for each type of waste, according to its composition, the metal/acid ratio must be established for complete solubilization of the metals of interest. The recovery of this waste, depending on the type of scrap, can reach at least US$ 1,230,000.00 /t waste.
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With the new legislation for Waste Electrical and Electronic Equipment (WEEE) coming up in Europe a substantial increase of end-of-life electronic equipment to be treated will take place. In this context, often much attention is placed on logistical issues, dismantling and shredding/pre-processing of electronic-scrap, whereas 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 toxic control and overall environmental performance. Umicore has recently completed major investments at its Hoboken plant, where besides precious metals and copper a large variety of base and special metals are recovered. Equipped with state-of the art off-gas and waste water purification installations, the plant has been developed to the globally most advanced full-scale processor of various precious metals containing secondary materials such as automotive catalysts and electronic-scrap, generating optimum metal yields at increased productivity. To utilise this potential to its full extend for WEEE fractions like circuit boards or mobile phones, especially the interface between pre-processing (shredding/sorting) and smelting/refining is of importance. Here, a mutual optimization of sorting depth as well as of destination of the various fractions produced can lead to a substantial increase in overall yields, especially for precious and special metals.
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End-of-life printed circuit boards (PCB) and waste in electrical and electronics equipment (WEEE) in general, are a high value materials resource. Physical processing is accepted most environmentally friendly for value recovery from this polymetallic resource stream. Currently, commodity streams from physical processing are still largely a mix, making pyrometallurgical follow-up indispensable. While the pyrometallurgical route is still being tolerated, the smelting chemistry can be much more simplified if physical processing produces cleaner fractions at equivalent recoveries. Approaching this as an applied mineral processing problem, a kind of occurrence, reserve and representative compositions of the PCB stream is first presented like a characterization of a new type of ore. The trend in almost three decades of PCB physical processing is discussed, identifying issues for improving the value recovery. The -75μm fines sizes generated during comminution contributes an overall drop in grade and recovery of values when using the electrostatic separation, which is presently almost the industry standard for treating the submillimeter sizes. It may be necessary to reconsider wet processes to attend to fines problem, opposed to the general preference for dry operations. Composition determination is critical to recovery analysis, and a means of obtaining initial estimates which can aid analysis of such complex stream, as well as serve as pointer for effective treatment approach, is proposed. PCB is a complex resource stock; the beneficiation flowsheets still seem too simple.
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This paper presents the experimental results for the leaching of printed circuit boards (PCB) from obsolete computers for extracting and recovering tin and copper by means of leaching followed by precipitation. Printed circuit boards were dismantled, cut into small pieces, and fed into a cylinder mill. The powder obtained was leached by using the aqueous solutions 2.18N H2SO4, 2.18N H2SO4 + 3.0N HCl, 3.0N HCl, and 3.0N HCl + 1.0N HNO3. The lowest values for the percentage of metal extraction were obtained with 2.18N H2SO4 (2.7% for Sn and lower than 0.01% for Cu), while the 3.0N HCl + 1.0N HNO3 leach system exhibited an extraction of 98% for Sn and 93% for Cu. Precipitates were obtained at different pH values by neutralizing the leach liquors using NaOH. The 3.0N HCl + 1.0N HNO3 leach system presented the highest recovery values from the powder feed (84.1% for Sn and 31.9% for Cu), as well as from the leach liquor (85.8% for Sn and 34.3% for Cu).
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Previous studies have shown that various microorganisms can enhance the dissolution of silicate minerals at low (<5) or high (>8) pH. However, it was not known if they can have an effect at near-neutral pH. Almost half of 17 isolates examined in this study stimulated bytownite dissolution at near-neutral pH while in a resting state in buffered glucose. Most of the isolates found to stimulate dissolution also oxidized glucose to gluconic acid. More detailed analysis with one of these isolates suggested that this partial oxidation was the predominant, if not sole, mechanism of enhanced dissolution. Enhanced dissolution did not require direct contact between the dissolving mineral and the bacteria. Gluconate-promoted dissolution was also observed with other silicate minerals such as albite, quartz, and kaolinite.
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A 3-phase computational ∞uid dynamics (CFD) model for heap bioleaching of chalcocite is investigated to identify and understand the efiect of oxygen ∞ow during air sparging. The study uses an existing one-dimensional model of liquid ∞ow, bacterial transport (including attachment/detachment of bacteria to ore particles), and the depletion of a copper-sulphide, coupled with a two-dimensional (2D) model of gas ∞ow in the heap. The CFD model includes the efiects of oxygen and ferrous ion consumption, coupled with leaching of copper-sulphide via a shrinking core model. The model is used to investigate the 2D efiects of air ∞ow in heap bioleaching with regard to oxygen limitation.
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According to the properties of bioleaching solutions of printed circuit boards (PCBs), copper in the leaching solution were recovery by ion exchange with macroporous styrene iminodiacetic acid chelating resin D401. The bed height of resin, flow rate, pH value on copper adsorption had been studied. Work Exchange Capacity (WEC) of copper increased with increasing bed height of resin and flow rate. The copper WEC of 7.88 mg/mL can be obtained with pH 2.5 and 200 mm bed height at flow rate of 2 mL/min. More than 99.5% of copper could be eluted from loaded resin to get the copper enriched solution by 1.0 M sulphuric acid at A/R ratio 20 in at flow rate of 2 mL/min. Results of the present investigation indicated that D401 resin can efficiently recovery copper from bioleaching solution of PCBs.
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Bioleaching of spent catalyst were carried out using Acidithiobacillus type of microorganisms. Various leaching parameters like contact time, Fe(II) concentration, particle size, pulp densities, pH and temperature were studied in details. All the four metal ions like Ni, V, Mo and Al followed dual kinetics, i.e., initial faster followed by slower rate. The leaching kinetics of Ni and V observed to be higher compared to that of Mo and Al. The thermodynamic parameters like ΔG, ΔH and ΔS for all metals were calculated. The leaching kinetics followed first order rate. Rates of dissolution of Al, V and Ni increased, and Mo decreased with increase of Fe(II) addition whereas that of all metals decreased with increase of pulp density and particle size. Leaching kinetics of Al, Mo, V increased with decrease of pH. Variation of initial pH of the leaching medium showed an inadequate effect on Ni dissolution. The rate determining step found to be pore diffusion controlled. The correlation between observed and theoretical values of leaching efficiency for different parameters was evaluated using Multi-Linear Regression Analyses which showed the significance of the leaching. A total of 5 factors were evaluated by data reduction technique using Principal Component Analysis.
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Cyanide has been recognized for a long time as a powerful lixiviant for gold and silver, forming very stable cyano complexes with both metals. While cyanide is very effective in leaching free milling ores, there are certain classes of gold and silver ores (i.e., carbonaceous, pyritic. arsenical, manganiferous, cuperferous) that are considered refractory to conventional cyanidation dissolution. Recently there has been considerable effort directed towards new and improved reagents for leaching these difficult-to-treat ores and concentrates. A large portion of this effort has been devoted to finding alternative lixiviants that might compete with conventional cyanidation. Furthermore, there is a general interest in developing non-toxic environmentally safe substitutes for cyanide.There are a number of reagents that form stable complexes with gold and silver e.g., thiourea, thiosulfate, halides, malononitrile, acetonitrile and polysulfides. The chemistry of gold and silver dissolution using alternative lixiviants is discussed in this paper. Special emphasis is given to the application of Eh-pH diagrams to interpret the dissolution behavior.
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Biomining is currently used successfully for the commercial-scale recovery of met- als such as copper, cobalt, and gold from their ores. The mechanism of metal extraction is mainly chemistry-driven and is due to the action of a combination of ferric and hydrogen ions, depending on the type of mineral. These ions are produced by the activity of chemolithotrophic microorganisms that use either iron or sulfur as their energy source and grow in highly acidic conditions. Therefore, metal extraction is a combination of chemistry and microbiology. The mixture of organisms present may vary between processes and is highly dependent on the temperature at which mineral oxidation takes place. In general, rel- atively low-efficiency dump and heap irrigation processes are used for base metal recovery, while the biooxidation of difficult-to-treat gold-bearing arsenopyrite concentrates is carried out in highly aerated stirred-tank reactors. Bioleaching reactions, the debate as to whether the reactions are direct or indirect, the role of microorganisms, and the types of processes by which metals are extracted from their ores are described. In addition, some new processes under development and the challenges that they present are discussed.
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The rapidly increasing consumption of electric-electronic equipments leads to the increase in their quantity in municipal wastes. Notwithstanding the environmental pollution potential of e-wastes, e-wastes with their high content of base and precious metals in particular are regarded as a potential secondary resource when compared with ores. For the recovery of metals from e-wastes, various treatment options based on conventional pyhsical, hydrometallurgical, biohydrometallurgical and pyrometallurgical processes are proposed. Electronic wastes are composed inherently of non-homogenous and complex set of materials and components, which presents difficulties for their recycling. Furthermore, the decrease in the precious metal content of e-wastes adversely affects the economics of recovery/recycling processes. Research and development of environmentally acceptable and low cost processes are, therefore, required for the extraction of metals from e-wastes. Treatment of e- wastes for metal recovery is also of importance for the preservation and effective exploitation of our natural/primary metal resources.
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In this study, physical, chemical and hazardous characteristics of computer printed circuit boards (PCBs) were studied. PCBs manually obtained from end-of-life computers of various brands were subjected to size reduction down to -3.35 mm in two stages of crushing. Size fractions were obtained by dry-sieving and used to determine the liberation size of metals. Furthermore, hazardous characteristics of PCBs were investigated using standard protocols including TCLP (Toxicity Characteristic Leaching Procedure) and SPLP (Synthetic Precipitation Leaching Procedure) tests of US Environmental Agency (USEPA), ASTM D-3987 and EN 12457-2 tests to simulate different environmental scenario. The tests have shown that printed circuit boards can be classified as hazardous wastes. Copper content of PCBs was found to be 15.5 per cent. © (2010) by the Australasian Institute for Mining and Metallurgy (AusIMM).
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Bioleaching/biooxidation is essentially a dissolution process with the involvement of acidophilic bacteria acting as the "catalyst" to accelerate the dissolution of metals from sulfide minerals. The contribution of bacteria to the metal dissolution is closely controlled by the growth of bacteria, which is itself affected by the physico-chemical conditions within the bioleaching environment. There are a number of operating parameters controlling bioleaching processes, which are required to be maintained within a certain range in the leaching environment whereby the activity of bacteria with the resultant oxidation of sulfide minerals can be optimized. In this regard temperature, acidity, oxidizing conditions, availability of nutrients, oxygen and carbon dioxide, surface area and presence of toxic ions are of prime importance for control and optimization of bioleaching of sulfide ores/concentrates. Bioleaching processes are temperature and pH dependent with optimum metal dissolution occurring in a particular range where the bacterial strain is most active e.g. mesophiles at 35-40°C and pH 1.6-2.0. Provision of nutrient salts is required to maintain the optimum growth and hence metal dissolution with the quantity of nutrients apparently being dependent on the availability of substrate i.e. head grade/pulp density of an ore/concentrate. Oxygen transfer is one of the most critical factors since the oxygen levels below 1-2 mg/l may adversely affect the oxidizing activity of bacteria. Bioleaching rate tends to improve with increasing the surface area at low pulp densities but, in practice, the pulp density is limited to ~20% w/v. Increasing concentrations of ions such as Cl -may also adversely affect the oxidative activity of bacteria.
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Leaching studies using spent petroleum catalyst containing Ni, V and Mo were carried out using two different acidophiles, iron oxidizing (IOB) and sulfur oxidizing (SOB) bacteria. XRD analysis proved the existence of V in oxide form, Ni in sulfide form, Mo both in oxide and sulfide forms, and sulfur in elemental state. Both bacteria showed similar leaching kinetics at the same leaching parameters, such as pH, nutrient concentration, pulp density, particle size and temperature. The dissolution kinetics for Ni and V was much higher than Mo. Bioleaching kinetics was observed to follow dual rates, initially faster followed by a slower rate. So, dissolution mechanism was based on surface- and pore-diffusion rate. The dissolution process was found to follow 1st order kinetics. Unified dissolution rate kinetics equations were developed using 1st order rate kinetics. Various thermodynamic parameters were also calculated. Rate determining step for both the bacteria were evaluated and the average D1 (surface) and D2 (pore) values were found to be around 7 × 10− 9 and 1 × 10− 10 cm2 respectively. The lower value of D2 suggested that the pore diffusion is the rate determining step during bioleaching process.
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In plants for the recycling of waste electric and electronic equipment (WEEE) as well as for conventional mineral processing, the comminution equipment dictates whether and how the specifications for the separation and sorting of the feed material are achieved. For the comminution of WEEE, the machines must meet specific requirements in respect of size reduction, insensitivity to solid components and flexibility for adapting to different feed materials. To liberate single components, composites must be broken up, but harmful components that are contaminated with pollutants should not, however, be destroyed completely. With the Rotorshredder RS and Rotor Impact Mill RPMV presented here, BHS Sonthofen supplies two machines to achieve the main objectives of WEEE processing - i.e. effective size reduction and gentle desintegration of composites to liberate the individual components. The achievement of these aims in combination with an extremely flexible and at the same time cost-efficient operation represents a leap in technology compared to conventional systems.
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Nowadays, the pyrometallurgical treatment in copper smelters is the common process for the recycling of metals from the electronic scrap. Furthermore the European Directive on the Waste from Electrical and Electronic Equipment (WEEE) and the Directive on the Restriction of Hazardous Substances (RoHS), increase the importance of electronic scrap recycling. Besides these a high amount of plastic and inert components in these materials leads to problems at the processing. An optimisation concerning the internal recovery and the high amount of plastic is necessary to reach the recycling quota of the European directive. The majority of the scrap is treated mechanically in order to separate in a first step plastics from metals, iron from nonferrous metals and harmful substances from valuable materials. But the quality of the different fraction often rather low and further treatment leads to higher costs. Therefore an interaction between mechanical treatment and metallurgical processing should be realised. The Christian Doppler Laboratory for Secondary Metallurgy of Nonferrous Metals at the Institute of Nonferrous Metallurgy at the University of Leoben carried out investigations concerning the optimisation of the metallurgical recycling and the treatment of the input materials especially of printed circuit boards.
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A highly effective process based on a hammer mill, a pneumatic column separator and an electrostatic separator was developed for recovering copper from waste printed circuit boards. The factors influencing the degree of copper liberation are discussed. Two physical separation methods were compared and discussed. Experimental results show that a well-controlled impact crusher can produce satisfactory copper liberation at a relatively coarse particle size. Around 90% copper recovery from waste printed circuit boards can be achieved using a combination of electrostatic separation and pneumatic separation.
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This study was carried out to recover valuable metals from the printed circuit boards (PCBs) of waste computers. PCB samples were crushed to smaller than 1 mm by a shredder and initially separated into 30% conducting and 70% nonconducting materials by an electrostatic separator. The conducting materials, which contained the valuable metals, were then used as the feed material for magnetic separation, where it was found that 42% of the conducting materials were magnetic and 58% were nonmagnetic. Leaching of the nonmagnetic component using 2 M H2SO4 and 0.2 M H2O2 at 85 °C for 12 hr resulted in greater than 95% extraction of Cu, Fe, Zn, Ni, and Al. Au and Ag were extracted at 40 °C with a leaching solution of 0.2 M (NH4)2S2O3, 0.02 M CuSO4, and 0.4 M NH4OH, which resulted in recovery of more than 95% of the Au within 48 hr and 100% of the Ag within 24 hr. The residues were next reacted with a 2 M NaCl solution to leach out Pb, which took place within 2 hr at room temperature.
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Sustainability and the environment are important and topical themes currently. There is a generally growing awareness of resource consumption, possible resource depletion, and the polluting effects of indiscriminate dumping at the end of the useful life of an item, as well as of the pollution caused by producing items and making them available to the end user. The issues are complex and interlinked. In order to improve understanding, it is important to obtain holistic and quantitative perspectives. To help in quantification, concepts such as the ecological and carbon footprints have been defined and are in common use. This paper introduces the concept of a material footprint to help quantify the material resource usage in an item, in terms of globally available resources. It allows comparison of various items to one another in terms of their use of material resources. Thus the types of items available for recycling can be ranked to determine recycling priorities. The material footprint can also help in determining recycling priorities for the various materials in the items. Several examples are used as illustration. It is shown that recycling of printed circuit boards is especially worthwhile. Printed circuit boards are complex and heterogeneous from a materials recycling perspective. The paper describes the complexities of recycling these boards, but also points out the benefits. An overview is given of currently available metallurgical technologies for such recycling. It is shown that in these processes there are many factors that affect the environment It thus remains difficult to determine the total impact of recycling on the environment holistically. Possibly some benefits are to be gained in the Southern African context by better integration between secondary material processors and primary metal producers. © The Southern African Institute of Mining and Metallurgy, 2008.
Article
Although copper is the principal metal in most electronic scrap, printed circuit boards in mobile phones also contain a significant amount of silver, gold and palladium. A bench-scale extraction study was carried out on the applicability of economically feasible hydrometallurgical processing routes to recover these precious metals. The starting material contained 27.37% copper, 0.52% silver, 0.06% gold and 0.04% palladium. In a first step, the following leaching solutions were applied: An oxidative sulfuric acid leach to dissolve copper and part of the silver; an oxidative chloride leach to dissolve palladium and copper; and cyanidation to recover the gold, silver, palladium and a small amount of the copper. A thiourea leach, as an alternative to cyanidation, was also investigated but did not give a sufficiently high yield. To recover the metals from each leaching solution, the following methods were evaluated: cementation, precipitation, liquid/solid ion exchange and adsorption on activated carbon. Precipitation with NaCl was preferred to recuperate silver from the sulfate medium; palladium was extracted from the chloride solution by cementation on aluminum; and gold, silver and palladium were recovered from the cyanide solution by adsorption on activated carbon. The optimized flowsheet permited the recovery of 93% of the silver, 95% of the gold and 99% of the palladium.
Conference Paper
Material and energy resource consumption is on the rise in both the industrialized and developing world (e.g., countries like India and China). In order to sustain this growth and provide resources for future generations, there is a need to design products that are easy to recover and recondition, thus enabling multiple use cycles. Processes are needed that can achieve this multi-use while producing zero (or very near zero) waste. There exist a number of barriers and challenges to achieving this vision of multi-use with zero waste; one such challenge is the development of a product recovery infrastructure that will minimize short-term impacts due to existing products and will be robust enough to recover products of the future. This paper identifies the barriers to developing such a recovery and reuse infrastructure. The aim is to achieve product multi-use and zero waste.
Electronic waste, or e-waste, is an emerging problem as well as a business opportunity of increasing significance, given the volumes of e-waste being generated and the content of both toxic and valuable materials in them. The fraction including iron, copper, aluminium, gold and other metals in e-waste is over 60%, while pollutants comprise 2.70%. Given the high toxicity of these pollutants especially when burned or recycled in uncontrolled environments, the Basel Convention has identified e-waste as hazardous, and developed a framework for controls on transboundary movement of such waste. The Basel Ban, an amendment to the Basel Convention that has not yet come into force, would go one step further by prohibiting the export of e-waste from developed to industrializing countries. Section 1 of this paper gives readers an overview on the e-waste topic—how e-waste is defined, what it is composed of and which methods can be applied to estimate the quantity of e-waste generated. Considering only PCs in use, by one estimate, at least 100 million PCs became obsolete in 2004. Not surprisingly, waste electrical and electronic equipment (WEEE) today already constitutes 8% of municipal waste and is one of the fastest growing waste fractions. Section 2 provides insight into the legislation and initiatives intended to help manage these growing quantities of e-waste. Extended Producer Responsibility (EPR) is being propagated as a new
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A novel energy-saving hydrometallurgical recovery process for copper from electronic scrap employing the Cu(I)-ammine complex has been presented on the basis of a thermodynamic consideration. In order to experimentally explore the feasibility of the leaching stage in this process, the copper leaching behavior from a printed circuit board (PCB) in ammoniacal alkaline solutions has been investigated under a nitrogen atmosphere. Copper in PCB was oxidized by Cu(II) to form Cu(I)-ammine complex ions. The leaching reaction can be expressed as: Cu + Cu(NH3)(4)(2+) = 2Cu(NH3)(2+). The Cu(II)-ammine complex significantly enhanced the leaching rate, while the Cu(I)-ammine complex slightly depressed it. Crushing of the PCB effectively enhanced the leaching rate, because the exposed metallic copper area is increased by the crushing. The effect of temperature on the leaching rate was insignificant. Consequently, the feasibility of the leaching stage in the proposed copper recovery process has been experimentally confirmed.
Article
A suitable method has been proposed to purify a copper electrolyte within the framework of an energy-saving cuprous electrowinning process. In this method, the impurities are selectively removed from the electrolyte that contains a large amount of cuprous ion in an ammoniacal alkaline solution at pH 9–11. Among these impurities, precious metals such as silver are removed by cementation with copper powder. Other metals such as cobalt, nickel, zinc, aluminum, manganese, lead etc. are removed selectively by solvent extraction using an oxine-type chelating extractant (LIX 26). Equilibrium and kinetic studies for the extraction of cobalt, nickel, and zinc were performed under different experimental conditions with or without synergistic agents. Loading tests of LIX 26 were carried out, and McCabe–Thiele diagrams were constructed for stage calculations for these metals. The metals are extracted with LIX 26 via a cation exchange mechanism, and slope analysis suggested that the nickel and zinc chelates, extracted by LIX 26, were 1:2 metal:reagent species. The loaded organic is regenerated by stripping the metals completely using dilute sulfuric acid. Copper loss in the purification stages is about 10% because monovalent copper is not extracted with LIX 26 from the ammoniacal alkaline solution.
Article
Of the various mechanical metal recycling techniques employed in electronic scrap processing, air table separation, magnetic separation and eddy current separation technolo gies have proved to be the most commercially successful. In addition, it is very important, even indispensable, that, prior to the physical processing of electronic scrap, selective dis mantling and identification (if necessary) be employed. It is, however, recognized that problems such as process optimiza tion and organics handling remain and that in-depth charac terization of electronic scrap will be essential in this context.
Article
Purpose This paper aims to present a review carried out under DEFRA‐funded project WRT208, describing: the composition of WEEE, current treatment technologies, emerging technologies and research. Design/methodology/approach This paper summarises the output from the first part of the project. It provides information on the composition of WEEE and an extensive survey of technologies relevant to materials recycling from WEEE. A series of further papers will be published from this research project. Findings WEEE has been identified as one of the fastest growing sources of waste in the EU, and is estimated to be increasing by 16‐28 per cent every five years. Within each sector a complex set of heterogeneous secondary wastes is created. Although treatment requirements are complicated, the sources from any one sector possess many common characteristics. However, there exist huge variations in the nature of electronic wastes between sectors, and treatment regimes appropriate for one cannot be readily transferred to another. Research limitations/implications A very large number of treatment technologies are available, both established and emerging, that singly and in combination could address the specific needs of each sector. However, no single set of treatment methods can be applied universally. Originality/value This paper is the first part of work leading to the development of technical strategies and methodologies for reprocessing WEEE into primary and secondary products, and where possible the recovery of higher added‐value components and materials.
Article
The electrochemical reduction of gold thiosulfate has been studied and compared to the reduction of gold cyanide. Gold thiosulfate is a potential replacement for gold cyanide in electro and electroless plating baths. Gold thiosulfate has a more positive reduction potential than gold cyanide and eliminates the use of cyanide. The standard heterogeneous rate constant, transfer coefficient, and diffusion coefficient for gold thiosulfate reduction were found to be 1.58 >< 1O cm/s, 0.23 and 7 x 10 cm2/s, respectively. The effect of sulfite as an additive to gold thiosulfate solutions was examined.
Article
Abstract-A new hydrometallurgical recovery technology of leaching gold and silver from E-waste has been presented by Lime Sulfur Synthetic Solution (LSSS) method. The influences of sodium sulfite concentration, divalent copper ions concentration, aqueous ammonia concentration, reaction temperature and leaching time were investigated experimentally. The results indicated that it was favorable for gold and silver leaching when solid-liquid ratio was 1:3 , leaching time 2.5h, at temperature of 318K, under the condition of Na2SO3 0.1mol/I, Cu2+ 0.03 mol/I, NH4+ 0.5 mol/I solution, pH=10, for 5g e-waste power. The best leaching rate of gold and silver reached about 92% and 90% in this favorably experimental condition, which suggested this technological viability for gold and silver recovery. On the basis of practice, LSSS method has the advantages of non-toxic, low-cost, simple process, easy to operate and was expected to be a great potential method in recycling gold and silver from e-waste.