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Abstract

Waste generated by the electrical and electronic devices is huge concern worldwide. With decreasing life cycle of most electronic devices and unavailability of the suitable recycling technologies it is expected to have huge electronic and electrical wastes to be generated in the coming years. The environmental threats caused by the disposal and incineration of electronic waste starting from the atmosphere to the aquatic and terrestrial living system have raised high alerts and concerns on the gases produced (dioxins, furans, polybrominated organic pollutants, and polycyclic aromatic hydrocarbons) by thermal treatments and can cause serious health problems if the flue gas cleaning systems are not developed and implemented. Apart from that there can be also dissolution of heavy metals released to the ground water from the landfill sites. As all these electronic and electrical waste do posses richness in the metal values it would be worth recovering the metal content and protect the environmental from the pollution. Cyanide leaching has been a successful technology worldwide for the recovery of precious metals (especially Au and Ag) from ores/concentrates/waste materials. Nevertheless, cyanide is always preferred over others because of its potential to deliver high recovery with a cheaper cost. Cyanidation process also increases the additional work of effluent treatment prior to disposal. Several non-cyanide leaching processes have been developed considering toxic nature and handling problems of cyanide with non-toxic lixiviants such as thiourea, thiosulphate, aqua regia and iodine. Therefore, several recycling technologies have been developed using cyanide or non-cyanide leaching methods to recover precious and valuable metals. Copyright © 2015 Elsevier Ltd. All rights reserved.

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... In particular, gold plays an invaluable role in modern microelectronics, including ubiquitous cell phones and computers. [1][2][3][4][5][6][7][8] Demand for gold and other precious metals is expected to grow continuously in these and many other applications, including medicine, [9] the chemical industry, [10,11] and the space industry, [12] among others. Due to the limited resources of noble metals in Earth's crust, recycling [2][3][4][5][6][7][8][13][14][15] will have to accompany the traditional mineral extractions. ...
... [1][2][3][4][5][6][7][8] Demand for gold and other precious metals is expected to grow continuously in these and many other applications, including medicine, [9] the chemical industry, [10,11] and the space industry, [12] among others. Due to the limited resources of noble metals in Earth's crust, recycling [2][3][4][5][6][7][8][13][14][15] will have to accompany the traditional mineral extractions. [16,17] Circular economy is imperative for their sustainable use. ...
... Main established Au recovery processes include environmentally challenging and toxic methods, such as cyanidation [4,6,[16][17][18][19] (Figure 1, a), and in less developed regions, even the amalgam process. [20] Other dissolution procedures, [4][5][6][16][17][18][19] including aqueous iodine-iodide leaching [5-8, 16-19, 21-31] (Figure 1, b), come with marked improvements in safety and environment issues. ...
Article
Gold is a scarce element in the Earth’s crust but indispensable in modern electronic devices. New, sustainable methods of gold recycling are essential to meet the growing eco‐social demand of gold. Here, we describe a simple, inexpensive, and environmentally benign dissolution of gold under mild conditions. Gold dissolves quantitatively in ethanol using 2‐mercaptobenzimidazole as a ligand in the presence of a catalytic amount of iodine. Mechanistically, the dissolution of gold begins when I 2 oxidizes Au 0 and forms [Au I I 2 ] ‐ species, which undergoes subsequent ligand‐exchange reactions and forms a stable bis‐ligand Au(I) complex. H 2 O 2 oxidizes free iodide and regenerated I 2 returns back to the catalytic cycle. Addition of a reductant to the reaction mixture precipitates gold quantitatively and partially regenerates the ligand. We anticipate our work will open new pathway to more sustainable metal recycling with utilization of just catalytic amounts of reagents and green solvents.
... E-waste contains both base as well as precious metals (Cu, Al, Pb, Ni, Sn, Au, Ag, Pt, Pd, etc.) [5]. High metal content makes e-waste a potential source for metal recovery. ...
... helps in gold leaching [147]. Gold cyanidation is an electrochemical process where the formation of Au(CN) 2 is an anodic reaction while the reduction of oxygen is a cathodic reaction [5]. The overall reaction is shown in equations (4) and (5) 4Au ...
... Equation (7) shows the reaction that consumes thiosulfate to tetrathionate [155]. Hence, it is Overall approach for recovery of metals from e-waste using chemical recycling [5,125,126,127,128,129] important to maintain the proper concentration of leaching reagent for achieving maximum gold recovery. ...
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.
... According to United Nations (UN) data (Hao et al., 2020), an estimated 14 million tons of these wastes were generated in 1992. Between 1994 and 2003, important amounts of WEEE were generated due to the discarding of 500 million personal computers, which were estimated to contain 2.8 million tons of plastics, 0.7 million tons of lead, 1339 tons of cadmium, 848 tons of chromium, and 282 tons of mercury (Akcil et al., 2015). According to Zhang & Xu statistics in 2016, China was one of the largest generators of WEEE with approximately 1.1 million tons/year (Zhang and Xu, 2016). ...
... The high content of base metals (Fe, Al, Cu, Pb, and Ni) and precious metals (Au, Ag, Pd, and Pt) in WEEE makes it a potential source of secondary resources for metal recovery. Primary metal resources can have grades between 0.5% and 1% Cu and between 1 and 10 g Au/ton, while the case of secondary metal resources such as WEEE contains an average of 20% Cu and 250 g Au/ton (Akcil et al., 2015). Performing metal extraction from this type of waste, in addition to having a positive impact on the environment and the economy, involves cost, energy, and natural resource saving compared to direct extraction (Chaverra, 2014;Işıldar et al., 2018). ...
Article
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Currently, the generation of electrical and electronic wastes is growing fast, thereby the reduction of the environmental impacts generated by its inadequate disposal is an ongoing challenge. In this study, a research on the use of monosodium glutamate for copper leaching, with emphasis on the thermodynamics and oxidant characteristics, is presented. Copper dissolution was conducted following a hydrometallurgical route, using monosodium glutamate in alkaline solutions. The effect of oxidizing agents such as hydrogen peroxide (H2O2) and potassium permanganate (KMnO4), and the efficiency of copper leaching with glutamate compared with glycine have been studied. Results, obtained at room temperature, showed 92% recovery of copper using 0.03 M hydrogen peroxide, 0.5 M monosodium glutamate at a pH of 9.44. This novel method would allow the extraction of copper from WEEE at low temperature, using an environmentally friendly leaching amino acid for the recovery of copper from electronic waste.
... Process flow of recovery of silver from WPCBs ( Akcil et al., 2015 ;Zhang et al., 2012 ). ...
... of cyanide and diminish silver recovery ( Akcil et al., 2015 ;Li et al., 2018 ). Montero et al. (2012) worked on the direct cyanide leaching of precious metals in a glass column. ...
Article
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The modernization of technologies has led to the escalation of the demand for silver in the electrical and electronics manufacturing sectors. Conventional lean grade ores of silver are insufficient to account for silver consumption. This deficit compels the extraction engineers to broaden the scope and delve into secondary silver recovery and recycling. The key purpose of current work is to draw attention to the modern hydrometallurgical technologies in silver recovery from waste printed circuit boards (WPCBs). Abundant with the base and precious metals, WPCBs form a plethora of important materials and the efficient recycling of WPCBs is essential for economic and environmental reasons. Low capital cost, high selectivity, no dust generation and reduced environmental effect advocate the versatility of hydrometallurgical route. Silver leaching from WPCBs through cyanide, thiourea and thiosulfate have been investigated. Cementation, ion exchange, solvent extraction, and membrane processes employed for recovery of silver have been studied. This review provides a holistic view of the significant technological advances throughout the world to recover silver from the WPCBs by hydrometallurgical route.
... Increasing attention is currently devoted towards effective and sustainable agents for noble metal (NM) recovery from secondary sources, due to the scarcity of accessible natural reserves of these metals which represent crucial elements for a great number of industrial applications (high-tech equipment, jewelry, catalysis, etc.) [1][2][3]. In this context, stimulated by world-wide regulations aiming for a more respectful approach towards the environment and natural resources, several classes of organic ligands have been investigated in the last three decades as potential alternatives to the harmful and polluting cyanides and aquaregia lixiviants conventionally employed at industrial level for the hydrometallurgical reclamation of NMs [4][5][6][7][8][9]. Among them, thiourea and thiourea derivatives have long been recognized as versatile and effective complexing agents, finding application in a variety of fields. ...
Article
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In the context of new efficient and safe leaching agents for noble metals, this paper describes the capability of the Me2pipdt/I2 mixture (where Me2pipdt = N,N′-dimethyl-piperazine-2,3-dithione) in organic solutions to quantitatively dissolve Au, Pd, and Cu metal powders in mild conditions (room temperature and pressure) and short times (within 1 h in the reported conditions). A focus on the structural insights of the obtained coordination compounds is shown, namely [AuI2(Me2pipdt)]I3 (1), [Pd(Me2pipdt)2]I2 (2a) and [Cu(Me2pipdt)2]I3 (3), where the metals are found, respectively, in 3+, 2+ and 1+ oxidation states, and of [Cu(Me2pipdt)2]BF4 (4) and [Cu(Me2dazdt)2]I3 (5) (Me2dazdt = N,N′-dimethyl-perhydrodizepine-2,3-dithione) compared with 3. Au(III) and Pd(II) (d8 configuration) form square–planar complexes, whereas Cu(I) (d10) forms tetrahedral complexes. Density functional theory calculations performed on the cationic species of 1–5 help to highlight the nature of the bonding in the different complexes. Finally, the valorization of the noble metals-rich leachates is assessed. Specifically, gold metal is quantitatively recovered from the solution besides the ligands, showing the potential of these systems to promote metal recycling processes.
... Generally, pyrometallurgical and electrochemical treatments [13,14] are used to recover base metals (Cu, Sn, Pb…) from secondary resources. PM sludges produced by this "primary" treatment is then treated using a multi-step complex hydrometallurgical process, composed of a leaching step -cyanide (Mc-Arthur Forest process [15]) or aqua regia leaching [16,17] and followed by numerous separation steps using volatile solvents -liquid/liquid extraction, fractional distillationbefore a final recovery of each PM by electrolysis, cementation or crystallization. These multi-step processes, set up at the end of the 20th century, have some important limitations for workers or installation safety and remain far from sustainable development considerations. ...
Article
Precious metal refining from ore or electronic devices includes hydrometallurgical processes with major concern about toxicity or wastewater production. As an alternative, one-step electroleaching-electrochemical deposition process (EL-ECD) using ionic liquid mixtures was evaluated for palladium and gold recovery. A halide based ionic liquid combined with a diluting ionic liquid was chosen among ten electrolytes after cyclic voltammetry and potentiostatic experiments. These low viscous electrolytes allow complexing Au and Pd, leading to metal leaching at low anodic potential. Moreover, the complexes formed could be simultaneously deposited at the cathode. Metal behaviour is similar for all halide anions tested (chloride, bromide and iodide). Results show that chloride based mixtures are the more suitable electrolyte providing the highest leaching faradic yield. This process appears more sustainable than conventional processes (chlorination, cyanide leaching) thanks to the electrolyte stability limiting solvent losses but also workers exposition.
... The main steps of hydrometallurgical methods are the rinsing operations of solid electronic waste with acids or lyes [17]. The resulting solutions are then subjected to separation and purification (extraction, adsorption, or ion exchange) [18,19]. ...
Article
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This study indicates that a new amine derivative of β-diketone (EDAB-acac) can be successfully used in an acidic medium (HCl) to separate a mixture containing Au(III), Pd(II), and Pt(IV) ions using solvent extraction. The study was conducted in single and ternary model solutions. The impact of acid concentration and the type of solvent (toluene, chloroform, methylene chloride, 2-ethylhexanol) on separation efficiency was discussed. It has been shown that increasing the HCl concentration in the aqueous phase does not favor extraction. In contrast, solvents with high donor numbers (methylene chloride, 2-ethylhexanol) increase both the extraction percentage of Pd and Au as well as the separation coefficients of Pd in relation to Au and Pt. The palladium(II) and gold(III) (which form 4-coordinated planar [MCl4]2− complexes) are extracted most efficiently, Pd(II) (87–93%) and Au(III) (56–62%). The stripping of Au(III), Pd(II), and Pt(IV) ions from the EDAB-acac-methylene chloride phase was also investigated using 0.5 M ammonia aq., mineral acid (5 M HCl, 5 M HNO3), 0.1 M thiourea in HCl and 0.5 M ammonium thiocyanate. A 3-step stripping process was proposed for the recovery of Pd(II), Au(III), and Pt(IV) from the Pd-Au-Pt mixture in the EDAB-acac-methylene chloride system. In the first stage, the aqueous phase is treated with 5 M HNO3 (Pt separation), followed by the application of 0.5 M ammonia (Pd separation) and, finally, 0.1 M thiourea in HCl (Au separation). The solvent extraction with EDAB-acac in acidic medium (HCl) can be used for separation of Pd(II) and Au(III) ions from e-waste leach solutions.
... The non-metallic fraction has traditionally been considered a low-value product and heat-treated in an uncontrolled way (Kim et al., 2015) or simply landfilled (Ning et al., 2017). During thermal treatments, toxic compounds such as polybrominated dibenzo-p-dioxins/furans (PBDD/Fs) can be emitted (Altarawneh and Dlugogorski, 2015;Sakai et al., 2001) while landfilling can lead to the soil and groundwater being contaminated by the leachate, which contains brominated toxic compounds (Zhou et al., 2013) as well as heavy metals (Akcil et al., 2015;Hadi et al., 2015); it can also pollute the atmosphere through the evaporation of hazardous substances (Guo et al., 2012). Controlled thermal treatments could be useful to obtain fuels or recover valuable materials, but brominated toxic compounds can be still emitted. ...
Article
Waste printed circuit boards (WCBs) were debrominated under hydrothermal treatment, using potassium carbonate as an alkaline additive to improve debromination efficiency (DE). Two different high-pressure reactors were used: a 1-L stirred reactor, where the evolution of the DE was followed over time at a low CO3²⁻/Br⁻ ratio (1:25), and an elementary 0.1-L non-stirred reactor, used to find the optimal parameters and to simplify the hydrothermal debromination (HTD) process. Considering both reactors, experiments were conducted changing the temperature (200 °C, 225 °C, 250 °C, 275 °C), and also the CO3²⁻/Br⁻ anionic ratio (1:50, 1:25, 1:10, 1:5, 1:2.5, 1:1, 2:1, 4:1) and the solid/liquid ratio (1:10, 1:5, 1:2) in the case of the 0.1-L reactor. No metallic catalyst was required. A maximum DE of about 98.9 wt % was reached in the agitated vessel at 275 °C after 4 h, with an additive/bromine ratio of 1:25. Similar DE (99.6 wt %) was also achieved in the non-stirred reactor at only 225 °C and after 2 h, using an additive/bromine ratio of 4:1 and a solid/liquid ratio of only 1:2. Concerning the solid phase behaviour during debromination, only 5 % of the net calorific value (NCV) was lost after a complete HTD treatment of WCB.
... Summary of the different lixiviant systems for gold extraction from WEEE[33,44]. ...
Article
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The direct use in catalysis of precious metal recovery products from industrial and consumer waste is a very promising recent area of investigation. It represents a more sustainable, environmentally benign, and profitable way of managing the low abundance of precious metals, as well as encouraging new ways of exploiting their catalytic properties. This review demonstrates the feasibility and sustainability of this innovative approach, inspired by circular economy models, and aims to stimulate further research and industrial processes based on the valorisation of secondary resources of these raw materials. The overview of the use of recovered gold and palladium in catalytic processes will be complemented by critical appraisal of the recovery and reuse approaches that have been proposed.
... While progress has been made in WEEE disassembly, metal-nonmetal separation, and base metal recovery in the past few years (Xue et al., 2012;Sun et al., 2015), precious metal (PM) recycling is severely blocked by the lack of facile dissolution strategy especially for Au. Due to the corrosion resistance feature of PM, corrosive oxidant (aqua regia or chlorate), toxic/unstable ligand (CN -/thiosulfate/thiourea), or high acidity is still indispensable for PM dissolution (Syed, 2012;Akcil et al., 2015). This fact leads to hazardous material (Cl 2 /NO x ) generation, tremendous reagent consumption, and health damage for workers. ...
Article
Precious metal (PM) retrievement from e-waste is of great significance for reducing virgin mining activity and promoting rare resource sustainability. However, current PM recycling methods rely mainly on caustic aqua regia or unstable sulfur-based ligand, which cause severe environmental damage and process inefficiency. Here, we propose an environmentally friendly halide-regulated strategy, utilizing milder and renewable oxidant cupric/ferric ion for facile PM dissolution. This is realized by the synergistic effect of enhanced oxidizing ability of Cu(II) and reduced oxidation potential of PM with halide addition. Electrochemical tests and leaching experiments results show that Cu(II)/Cu(I) redox potential experiences great change with halide, increasing from 0.4 to 0.75 V under bromide. Fast corrosion feature was observed for Au in Cu(II)/Fe(III)-Br⁻ and Pd in Cu(II)/Fe(III)-Cl⁻, and can be accelerated by increasing oxidant and halide concentration. Our proposed strategy outperforms traditional methods on stable and fast dissolution, where 2.5 mol/L Br⁻ is appropriate for Au dissolution. Moreover, selective dissolution of base metal, Pd/Ag, and Au can be achieved via ligand alteration and be further combined with electrodeposition technique for multi metal recovery and oxidant regeneration. This halide-regulated strategy can lead PM recycling from pollutive status towards environmentally friendly road.
... Electrical and electronic equipment (EEE) is usually defined as items or wares which are made with electrical or electronic parts. E-waste is defined as the EEEs which have been abandoned as waste or rubbish without reusing (Wath Responsible Editor: Philippe Garrigues Researchers from different regions and countries have implemented a variety of studies, in the progress of researching e-waste, such as environment conditions at e-waste recycling site (Wang et al. 2012;Zhang et al. 2014;Huang et al. 2011;Ha et al. 2009), the influences on of e-waste human (Zheng et al. 2015;Zheng et al. 2008;Zheng et al. 2013;Chen et al. 2011), the public management on e-waste (Yin et al. 2014;Tanskanen 2013;Afroz et al. 2013;Yu et al. 2010), and the processing and recycling technique of e-waste (Akcil et al. 2015;Zhang and Xu 2016;Cui and Zhang 2008;Mishra et al. 2019;Pant et al. 2012). However, as so far there were just a few studies ( Filippo Corsini et al. 2012;Liming Zhang et al. 2019;Gao et al. 2019aGao et al. , 2019b to study the present situation and demonstrate the direction and way forward of researching e-waste using bibliometric analysis method. ...
Article
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With rapid development of energy, information, and communication technology, e-waste problem has become one of the global issues to be settled urgently. The main features on publication years, journals, countries and institutions, authors, keywords, and content types of the 100 most-cited articles on e-waste had been unfolded in this research. The direction and way forward were illustrated, the trends to date were demonstrated, and the terrain and pathways were evaluated on the research of e-waste. Bibliometric analysis method was applied to analyze various attributes on the 100 most-cited articles which were retrieved from WoSCC on May 25, 2021, by utilizing the software tools Microsoft Excel 2016 and VOS viewer 1.6.9. The publication year and citation number of the 100 articles ranged between 2003 and 2017 and from 83 to 925, respectively. Environmental Science & Technology (n=17) published the maximum articles. Waste Management, Journal of Hazardous Materials, and Environmental Science & Technology were the core journals on e-waste. One hundred twenty-three institutions and 25 countries were involved in publishing the 100 articles. Three hundred seventy authors contributed to the 100 articles in total. A total of 267 keywords occurred in the 100 articles. The keywords “e-waste” and “recycling” held the highest occurrences. The study content of the 100 articles could be classified into four types including the characteristic-and-property type, the environment-and-health type, the management-and-economic type, and the technique-and-processing type. Overall completeness and applicability of the evidence found in this study were verified sufficiently; the potential biases in the review process were also considered. The innovations of the research from the past bibliometric analysis work on e-waste were stated, and the implication for practice and research of this study were explained as well. 2007, 2008, and 2009 were a peak of the researches on e-waste, while the recent years were experiencing a valley. China and its institutions were most influential in this field on e-waste. India was becoming more and more influential on e-waste research in the world. Nigeria was the research center in Africa, and Brazil was the research center in Latin America. Wong Minghung was the most important expert on e-waste. The impact on environment and human being’s health was the hot topic of researches on e-waste; the characteristic and property of e-waste were studied not enough. The researches of technique and processing would be the direction and way forward in the study field on e-waste. The characteristic and property on e-waste would need more attention to be researched. The researchers could develop new pathways based on and beyond the four types of content evaluated in this research.
... This report was motivated by the environmentally friendly method of thiourea against the conventional methods and the selectivity for gold [72]. Due to the disadvantage of utilizing extensive leaching reagents with high waste, Wu et al. reported on the use of polyaniline films and polyaniline-coated cotton to recover gold from an acid/halide solution during e-waste treatment in a hydrometallurgical process [75]. Akcil et al. proposed a soft leaching process to extract gold from e-waste utilizing chlorine leaching [76]. ...
Article
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The need to drive towards sustainable metal resource recovery from end-of-cycle products cannot be overstated. This review attempts to investigate progress in the development of recycling strategies for the recovery of strategic metals, such as precious metals and base metals, from catalytic converters, e-waste, and batteries. Several methods for the recovery of metal resources have been explored for these waste streams, such as pyrometallurgy, hydrometallurgy, and biohydrometallurgy. The results are discussed, and the efficiency of the processes and the chemistry involved are detailed. The conversion of metal waste to high-value nanomaterials is also presented. Process flow diagrams are also presented, where possible, to represent simplified process steps. Despite concerns about environmental effects from processing the metal waste streams, the gains for driving towards a circular economy of these waste streams are enormous. Therefore, the development of greener processes is recommended. In addition, countries need to manage their metal waste streams appropriately and ensure that this becomes part of the formal economic activity and, therefore, becomes regulated.
... Copper is the important metal in the waste printed circuit boards substrate, and copper contributes 10-20% of the total weight of waste printed circuit boards. Apart from copper, other metals in waste printed circuit boards include aluminium, iron, zinc, lead, arsenic, gold, silver, lead, etc. Akcil et al., 2015). WEEE contains different materials, and most of them are associated with the property of toxicity to human health and potential to cause environmental damage. ...
... Different groups of lixiviants such as inorganic acid [30,31,33,38], organic acid [27,36] and alkaline reagents [36,[39][40][41], are used for metal leaching from e-waste. Recently, several reports were made with respect to REE and precious metals [26,37,[42][43][44]. Table 1 shows a list of chemical leaching approaches that were carried out for various e-waste samples along with their experimental conditions and metal recovery. ...
Article
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There is a growing interest in electronic wastes (e-wastes) recycling for metal recovery because the fast depletion of worldwide reserves for primary resources is gradually becoming a matter of concern. E-wastes contain metals with a concentration higher than that present in the primary ores, which renders them as an apt resource for metal recovery. Owing to such aspects, research is progressing well to address several issues related to e-waste recycling for metal recovery through both chemical and biological routes. Base metals, for example, Cu, Ni, Zn, Al, etc., can be easily leached out through the typical chemical (with higher kinetics) and microbial (with eco-friendly benefits) routes under ambient temperature conditions in contrast to other metals. This feature makes them the most suitable candidates to be targeted primarily for metal leaching from these waste streams. Hence, the current piece of review aims at providing updated information pertinent to e-waste recycling through chemical and microbial treatment methods. Individual process routes are compared and reviewed with focus on non-ferrous metal leaching (with particular emphasis on base metals dissolution) from some selected e-waste streams. Future outlooks are discussed on the suitability of these two important extractive metallurgical routes for e-waste recycling at a scale-up level along with concluding remarks.
... PCBs contain less than 1 wt% of precious metals, but they account for nearly 80% of their total intrinsic value, making precious metal recovery from electronic waste essential. Gold is widely used in electrical and electronic devices components because of its ductility, high electrical conductivity, and resistance to oxidative corrosion (Akcil et al., 2015;Vats and Singh, 2015). The sustainability of gold is of great concern as the grade of gold ore is declining (Mudd, 2007). ...
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.
... Hydrometallurgy is a promising alternative to pyrometallurgy for E-waste recycling especially in low-and middle-income countries because it can be operated on smaller scales and applied to low-grade wastes (Akcil et al., 2015). There are two essential steps in hydrometallurgy: (i) extraction using suitable lixiviants, and (ii) recovery via adsorption, cementation or electrowinning. ...
Article
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Porphyry ores and E-wastes/WEEE are two of the most important copper-bearing materials on the planet. Over 60% of world copper output comes from porphyry copper ores while E-waste(s) is globally the largest copper-bearing waste category since the 1980s. They also contain critical elements for low-carbon technologies essential in the clean energy transition's success. In this review, a critical analysis of ore distribution/processing, metal extraction, E-waste generation and E-waste recycling is presented, focusing on identifying challenges and how to address them with emerging technologies and sustainable socio-environmental strategies. Access to ore deposits is a major hurdle for mine development while the absence of a consistent E-waste classification and legislation, including poor collection rates, remains serious problems in E-waste recycling. As lower grade porphyry ores are exploited, difficulties in processing/extraction due to mineralogical complexities, very fine particles and the generation of “dirty” concentrates will become more prevalent. For E-wastes recycling, current trends are to develop smaller, more mobile, and eco-friendly hydrometallurgical alternatives to pyrometallurgy that can handle localised compositional and feed variabilities. Finally, more sustainable mine waste management strategies, including better LCIA tools with spatial and temporal dimensions, are needed to limit socio-environmental impacts of resources exploitation and maintain the sector's SLO.
... This review aims to assess the current status of thioureagold leaching from e-waste combined with the potential methods for recovering gold from a thiourea gold complex. While previous works have reviewed gold-thiourea leaching from primary ores [52], and others have discussed the status of precious metal recovery from PCB and compared thiourea leaching with thiosulfate and cyanide leaching [53], this review will provide an insight into thiourea-gold chemistry and give an update on the status and challenges of leaching gold from e-waste using acid thiourea solutions. It will focus on researcher endeavor to limit the consumption of thiourea while achieving maximal gold recovery. ...
Article
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Electronic waste is a dominant global issue with over 50 million tons generated annually. Still, as an amalgamation of precious and rare raw materials, electronic waste is a considerable economic resource with the most valuable components located on the printed circuit boards. Gold is widely used in electronics in numerous applications, although principally for contact points and external connectors. The recovery of gold, due to its high value, is one of the main motivations for recycling e-waste. Although pyrometallurgy and hydrometallurgy processing are still the preferred modes of recovery for gold, the use of high-energy consuming pyro-methods, and the use of gold cyanidation that uses harmful lixiviants are increasingly discouraged. Thiourea has received attention as an alternative lixiviant for gold leaching due to its fast reaction kinetics and less harmful nature. This review aims to provide an up-to-date evaluation of thiourea-gold leaching studies from electronic waste, with emphasis on the recent progression from the classic chemical method to a more sustainable hybrid bioleaching-based system, while its challenges are highlighted. The complementary methods applied for gold retrieval from the pregnant solution are also described with a focus on sustainable methods that have the potential to provide a closed-loop system, the key objective for material recovery in a circular economy. Graphical Abstract
... Time-series data on domestic production and imports/exports of EEE were collected for the period 2007-2018 from the China Statistical Yearbook (China NBS 2007-2018. Data on the composition and market prices of specific resources contained in e-waste were obtained from related literature and websites (Akcil et al. 2015, Li et al. 2008, Parajuly and Wenzel 2017, U.S. Geological Survey 2010-2019, Zeng et al. 2016. Accordingly, the fund policy model is redesigned, specifically including an EEE sales model, an obsolete quantity estimation model, a resource supply model, and a fund supply model. ...
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... It is worth mentioning that only one fraction of the sample evaluated corresponded to the metallic part and the other, non-metallic fraction, was composed by fiberglass [2]. It is important to point out that the company previously recovered precious metals such as Au and Ag by leaching the WPCBs using cyanide, remaining only the base metals in the residues to be further processed [49], as was done in this work. In Figure 1A, an image of the material is shown. ...
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Chapter
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Electronic waste (e-waste) has a complex composition and contains numerous pollutants. Noticeable pollutant is lead, which can affect environment and human health, and has been the focus of increasing attention. It is an essential component of electronic products, and inappropriate disposal of e-waste can result in severe lead pollution. At present, recycling of lead from urban mineral resources, such as spent lead-acid batteries, cathode-ray tube glass, and waste printed circuit boards, has been the major form of lead recovery rather than smelting from the primary ore. Lead is a heavy metal element and can be harmful. Despite measures taken for many years to prevent and control lead poisoning, lead is a hazard that remains an unresolved problem of various e-waste recycling processes. This study presents the current status of lead recovery from e-wastes and electronic equipment and reviews related technological progress. The current status of lead recovery using various types of e-waste treatment technology is discussed, and a range of technological principles, advantages, and disadvantages are analyzed to provide references and new ideas for lead recycling from e-waste.
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Thioureas and their derivatives are organosulfur compounds having excellent biological and non-biological applications. These compounds contain S- and N-, which are nucleophilic and allow for establishing inter-and intramolecular hydrogen bonding. These characteristics make thiourea moiety a very important chemosensor to detect various environmental pollutants. This article covers a broad range of thioureas and their derivatives that are used for highly sensitive, selective, and simple fluorimetric (turn-off and turn-on), and colorimetric chemosensors for the detection and determination of different types of anions, such as CN-, AcO-, F-, ClO- and citrate ions, etc., and neutral analytes such as ATP, DCP, and Amlodipine, etc., in biological, environmental, and agriculture samples. Further, the sensing performances of thioureas-based chemosensors have been compared and discussed, which could help the readers for the future design of organic fluorescent and colorimetric sensors to detect anions and neutral analytes. We hope this study will support the new thoughts to design highly efficient, selective, and sensitive chemosensors to detect different analytes in biological, environmental, and agricultural samples.
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Waste printed circuit boards represent one of the most challenging parts of e-waste recycling. The extraction of precious metals (gold, silver, palladium and platinum) from waste printed circuit boards has commonly been done using highly toxic, corrosive, or expensive lixiviants, such as sodium cyanide, aqua regia and iodine/iodide. The present study provides a greener approach to extract precious metals from waste printed circuit boards using alkaline glycine solution in the presence of an oxidant. The common strong oxidant of potassium permanganate and the non-hazardous potassium ferricyanide were investigated and compared in alkaline media. Decrease of the particle size of sample, and the rise of oxidant concentration (0.04–0.16 M) enhanced gold extraction significantly. However, the increase of temperature (∼55 °C) and glycine concentration (0.5–1 M), and the staged addition of oxidant did not significantly improve gold extraction. Control of solution Eh could not reduce permanganate consumption whereas the ferricyanide consumption could be reduced by>50% in 72 h. Under the recommended conditions, 86.8% gold, 70.2% silver, 89.3% palladium and 87.9% copper could be extracted using glycine-permanganate leaching system. In comparison, 79.3% gold, 69.0% silver, 68.5% palladium and 83.1% copper could be extracted using glycine-ferricyanide leaching system. These extractions are comparable with what is achievable from cyanide (NaCN)-based leaching systems. Both of the leaching systems showed fairly good selectivity to copper and precious metals. The present study paves a way for the further development of non-NaCN glycine process for e-waste recycling.
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Copper powder of waste printed circuit boards (WPCBs), an important secondary metal resource, is usually processed by copper concentrate pyrometallurgy system to recover valuable metals. However, metals such as Pb, Sn, Zn and Al in copper powder of WPCBs are harmful to copper smelting system. Therefore, a two-stage leaching process was proposed to remove impurity metals from copper powder, and different routes were screened. Copper powder was firstly leached in the hydrochloric acid to remove Al, and then the Al-removed residue was treated to recover Sn and Pb by two routes, i.e., acid oxidation leaching or alkaline pressure oxidation leaching, respectively. The results showed that more than 97.15% of Al in copper powder was removed by the hydrochloric acid leaching. In HCl system adding H2O2, the leaching ratios of Pb and Sn reached 91.07% and 94.67%, respectively. In the alkaline pressure oxidation leaching system, the leaching ratios of Pb and Sn were 86.63% and 93.80%, respectively. In general, the separation and recovery of valuable metal resources in the WPCB copper powder were realized, and Cu was further enriched, providing high-quality raw materials for copper pyrometallurgy.
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Gold is a scarce element in the Earth’s crust but indispensable in modern electronic devices. New, sustainable methods of gold recycling are essential to meet the growing eco‐social demand of gold. Here, we describe a simple, inexpensive, and environmentally benign dissolution of gold under mild conditions. Gold dissolves quantitatively in ethanol using 2‐mercaptobenzimidazole as a ligand in the presence of a catalytic amount of iodine. Mechanistically, the dissolution of gold begins when I 2 oxidizes Au 0 and forms [Au I I 2 ] ‐ species, which undergoes subsequent ligand‐exchange reactions and forms a stable bis‐ligand Au(I) complex. H 2 O 2 oxidizes free iodide and regenerated I 2 returns back to the catalytic cycle. Addition of a reductant to the reaction mixture precipitates gold quantitatively and partially regenerates the ligand. We anticipate our work will open new pathway to more sustainable metal recycling with utilization of just catalytic amounts of reagents and green solvents.
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In this study, the extraction of metal-cyanide complex ions in gold-leaching, cyanide-containing wastewater by a trioctylmethylammonium chloride (N263)-tributyl phosphate (TBP)-n-octanol-sulfonated kerosene system was investigated. The effects of N263 and TBP concentrations, the aqueous phase pH, and phase ratio (O/A) on the extraction were investigated by adopting the response surface methodology, and the operating parameters were optimized. The optimal solution was obtained by solving the model optimally. A Cu ion concentration of 3,000 mg/L, an N263 concentration of 0.459 mol/L, a TBP concentration of 0.214 mol/L, an initial pH of the aqueous phase of 10.064, and O/A of 0.900 were determined to be optimal for realizing an extraction yield of 99%. The effects of column height, oil droplet volume, metal ion concentration, N263 and TBP concentrations, and temperature on the mass transfer rate were investigated using the single droplet method. Kinetic studies showed that the kinetic equation for the extraction system was Rf (Mass transfer rate) = 1.57×10⁻⁴·CCu·CTBP·CN263. The apparent activation energy of Cu(I) was 15.186 kJ/mol. The extraction process was controlled by the diffusion process. Furthermore, the chemical reaction occurred at the two-phase interface, where the copper cyanide complex ions preferentially bound to TBP at the interface between the two phases, and the bound anion cluster then reacted with the N263 cation to form the extractive complex, which then entered the organic phase from the interface.
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This review is intent on the environmental pollution generated from printed circuit boards and the methods employed to retrieve valuable and hazardous metals present in the e-wastes. Printed circuit boards are the key components in the electronic devices and considered as huge e-pollutants in polluting our surroundings and the environment as a whole. Composing of toxic heavy metals, it causes serious health effects to the plants, animals and humans in the environment. A number of chemical, biological and physical approaches were carried out to recover the precious metals and to remove the hazardous metals from the environment. Chemical leaching is one of the conventional PCBs recycling methods which was carried out by using different organic solvents and chemicals. Need of high cost for execution, generation of secondary wastes in the conventional methods, forces to discover the advanced recycling methods such as hydrometallurgical, bio-metallurgical and bioleaching processes to retrieve the valuable metals generate through e-wastes. Among them, bioleaching process gain extra priority due to its higher efficiency of metal recovery from printed circuit boards. There are different classes of microorganisms have been utilized for precious metal recovery from the PCBs through bioleaching process such as chemolithoautotrophy, heterotrophy and different fungal species including Aspergillus sp. and Penicillium sp. The current status and scope for further studies in printed circuit boards recycling are discussed in this review.
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Palladium, as a member of platinum group metals, has very little reserve in nature. It usually plays a role in corrosion resistance in the electroplating industry, and is easily discharged into electroplating wastewater during processing. Therefore, it is of great significance to develop efficient functional materials which can rapidly and selectively capture Pd(II). Herein, a mesoporous ion exchange resin (SiAaC) based on a silica framework was designed and synthesized by in situ polymerization method to efficiently remove Pd(II) from simulated electroplating wastewater. SiAaC exhibited unique advantages over traditional commercial resins, such as high adsorption capacity (121.8 mg/g), high selectivity (SFPd/M>230 in 0.01 M HNO3 solution) and excellent reusability (n>5). The adsorption results of SiAaC resin on Pd(II) are consistent with Langmuir isotherm and pseudo-second-order kinetic models. In addition, the column experiment can efficiently separate Pd(II) from simulated electroplating wastewater. Furthermore, FT-IR and XPS spectra proved an ion exchange mechanism between SiAaC and Pd(II). In general, this research not only demonstrated an excellent material which can effectively and efficiently remove low-level palladium from simulated electroplating wastewater, but also provided a new perspective for the synthesis or improvement of ion exchange resins.
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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.
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In this study, the synergistic extraction system of trioctylmethyl ammonium chloride (N263)-tributyl phosphate (TBP)-n-octanol-sulfonated kerosene was used to enrich and recover valuable metals from cyanide gold extraction of wastewater. The effects of the proportion of N263 and TBP, contact time, initial pH of water phase, temperature, and phase ratio (O/A) on the extraction percentage of metal cyanide complex ions and the synergistic extraction reaction mechanism were mainly investigated. Results showed that the single-stage extraction percentages of Cu, Zn, and Fe ions in wastewater were 99.87%, 99.8%, and 96.2%, respectively, and the saturated extraction capacity was 4356.4 mg/L under the conditions of N263 (20 vol.%)-TBP (20 vol.%)-n-octanol (10 vol.%)-sulfonated kerosene system at 25 °C, O/A of 1:1, pH of 10, and contact time of 5 min. Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS) analyses showed that metals entered the organic phase in the form of metal cyanide complex ions during extraction. Metal cyanide complex ions preferentially combined with TBP to lose hydrophilicity and then reacted with N263 cations to enter the organic phase. The saturated organic phase was stripped by NaOH and NaSCN mixed solution, and the total concentration of metal ions in the stripping solution reached 11996.6 mg/L.
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The leaching of silver sulfide was performed for the first time from a novel copper-thiosulfate-metabisulfite solution. The effects of all leaching conditions, e.g., the concentrations of copper cations, thiosulfate, and metabisulfite, as well as temperature, pH, and leaching time on silver extraction from this novel leaching system were systematically investigated. Liquid samples were analyzed by atomic absorption spectrophotometry (AAS) to determine their silver content, and the remaining solid powder was then characterized by field-emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). Based on the results of leaching experiments, it was found that silver sulfide extraction efficiency could be enhanced to 97% with the addition of metabisulfite to the thiosulfate-copper leaching medium. It was revealed that silver extraction is kinetically controlled by diffusion from the product layer. The activation energies (Ea) of silver sulfide leaching and Cu²⁺ reactions were calculated to be 22.2 and 41.2 kJ/mol, respectively. Thus, the thiosulfate-copper-metabisulfite medium is introduced as an efficient leaching system for silver extraction.
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In this paper, PEI-Alginate fibers were prepared using a more environmentally friendly method for the recovery of gold (Au (III)) from acidic wastewater. Adsorption results show that PEI plays a major role in the recovery of Au (III), and the maximum adsorption capacity of Au (III) was 644.92 ± 43.06 mg/g calculated by Langmuir model at pH 1, 25 °C. In addition, the constants k1 and k2 was 0.7044 ± 0.1038 L/min and 0.0025 ± 0.0002 g/mg min were calculated by pseudo-first-order and pseudo-second-order, which was outstanding compared to the most of the adsorbents reported in the literature. The mechanism of adsorbent preparation, characterization of adsorbents and adsorption-reduction mechanism of Au (III) were analyzed by Field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results showed that Au (III) was adsorbed by electrostatic attraction between protonated nitrogen-containing functional groups (=NH+-, and –NH2+-/-NH3+) and AuCl 4−. Furthermore, Au (III) was reduced to Au(I) and Au (0) during the adsorption process, and -NH-/-NH2, –NH2+-/-NH3+, and C-O provided electrons for Au (III) reduction and then they were oxidized to =N-, =NH+-, and C=O, respectively.
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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
Article
Waste printed circuit boards (WPCBs) constitute a hazardous material with up to 40 different metals, including numerous many heavy metals and environmentally harmful metals. Most hydrometallurgical processing approaches use high concentrations of toxic reagents and generate significant amounts of harmful effluents. This research investigates the use of cyanide-starved glycine solution containing no free cyanide in the leachate to extract precious metals from WPCBs, with most of copper and base metals pre-removed by upstream glycine-only leaching. Under the optimised conditions, 90.1% Au, 89.4% Ag and 70.1% Pd were extracted together with 81.0% Cu and 15.0% Zn. The extraction of other base metals remained low at 8.3% for Al and <5% for Pb, Ni, Co, Fe and Sn, indicating a fairly good selectivity of the leaching system. By comparing with stoichiometric and intensive cyanidation, the cyanide-starved glycine system showed comparable or better performance on precious metals extraction, but cyanide use was reduced by >70% whereas the glycine can be reused. Analysis indicates that with an initial cyanide dose of 250 ppm, the leaching solution was starved of cyanide after 4 h with no free cyanide, which minimises safety and health risks significantly compared with traditional intensive cyanidation ([CN] > 3500 ppm). Glycine and cyanide dose, pH, and particle size dominated leaching kinetics, while staged addition of cyanide did not enhance the extractions. A significant (70–90%) reduction in required cyanide use and cyanide-bearing effluents can be achieved while performing polymetallic metal removal and allowing reagent recycling.
Conference Paper
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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.
Conference Paper
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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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The rapid growth in the use of electronic equipments, combined with early obsolescence has contributed enormously to the generation of large quantity of electronic (e) waste. One such e-waste, the mobile phone printed circuit boards (PCBs) contain various precious metals which can be extracted by different hydrometallurgical routes. The present work deals with the recovery of gold using ammonium thiosulfate as a leaching agent from waste mobile PCBs containing 0.021% Au, 0.1% Ag, 56.68% Cu, 1.61% Ca, 1.42% Al, 1.40% Sn, 0.24% Fe, 0.22% Zn, 0.01% Pd etc.. The cutting granules of 0.5-3.0 mm PCBs were used for leaching in a 500 mL glass beaker in open atmosphere. The effect of various parameters viz. ammonium thiosulfate concentration, copper sulfate concentration, pH and pulp density was studied. A leaching of 56.7% gold was obtained under the optimum condition of 0.1M ammonium thiosulfate, 40 mM copper sulfate, pH: 10-10.5, pulp density: 10 g/L at room temperature and stirring speed of 250 rpm in 8h duration. The maximum leaching of gold in the pH range 10-10.5 may be attributed to the higher stability of the ammonium thiosulfate. The decomposition of ammonium thiosulfate in the different pH ranges was chemically analysed by iodometric method. The ammonium thiosulfate contents in the leach liquors were in agreement with the quantity of gold leached in the respective pH ranges. In this process the copper sulfate worked as a catalyst. The experiment conducted with complete PCBs scrap exhibited a maximum leaching of 78.8% gold at the above optimised condition.
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Rapid technological development induces increase of generation of used electric and electronic equipment waste, causing a serious threat to the environment. Waste printed circuit boards (WPCBs), as the main component of the waste, are significant source of base and precious metals, especially copper and gold. In recent years, most of the activities on the recovery of base and precious metals from waste PCBs are focused on hydrometallurgical techniques as more exact, predictable and easily controlled compared to conventional pyrometallurgical processes. In this research essential aspects of the hydrometallurgical processing of waste of electronic and electrical equipment (WEEE) using sulfuric acid and thiourea leaching are presented. Based on the developed flow-sheet, both economic feasibility and return on investment for obtained processing conditions were analyzed. Furthermore, according to this analysis, SuperPro Designer software was used to develop a preliminary techno-economical assessment of presented hydrometallurgical process, suggested for application in small mobile plant addressed to small and medium sized enterprises (SMEs). Following of this paper, the described process is techno-economically feasible for amount of gold exceeding the limit value of 500ppm. Payback time is expected in time period from up to 7 years, depending on two deferent amounts of input waste material, 50kg and 100kg of WEEE per batch.
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Used electronic equipment became one of the fastest growing waste streams in the world. In the past two decades recycling of printed circuit boards (PCBs) has been based on pyrometallurgy, higly polluting recycling technology whic causes a variety of environmental problems. The most of the contemporary research activities on recovery of base and precious metals from waste PCBs are focused on hydrometallurgical techniques as more exact, predictable and easily controlled. In this paper mechanically pretrated PCBs are leached with nitric acid. Pouring density, percentage of magnetic fraction, particle size distribution, metal content and leachability are determined using optical microscopy, atomic absorption spectrometry (AAS), X-ray fluorescent spectrometry (XRF) and volumetric analysis. Three hydrometallurgical process options for recycling of copper and precious metals from waste PCBs are proposed and optimized: the use of selective leachants for recovery of high purity metals (fluoroboric acid, ammonia-ammonium salt solution), conventional leachants (sulphuric acid, chloride, cyanide) and eco-friendly leachants (formic acid, potassium persulphate). Results presented in this paper showed that size reduction process should include cutting instead of hammer shredding for obtaining suitable shape & granulation and that for further testing usage of particle size -3 +0.1mm is recommended. Also, Fe magnetic phase content could be reduced before hydro treatment.
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The origin of a rational (scientific) approach to extraction of metal values from ores with the aid of microorganisms (bioleaching) is traced. The removal by microbiological means of ore constituents that interfere with metal extraction (biobeneficiation), an outgrowth from bioleaching, is also traced. © 2004 SDU. All rights reserved.
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Au-Ag noble metal wastes represent a wide range of waste types and forms, with various accompanying metallic elements. The presented leaching strategy for Au-Ag contained in circuit boards (PCBs) aims at gaining gold and silver in the metallic form. Application of the proposed ammonium thiosulphate leaching process for the treatment of the above mentioned Au-Ag containing wastes represents a practical, economic and at the same time an ecological solution. The ammonium thiosulphate based leaching of gold and silver from PCBs waste, using crushing as a pretreatment, was investigated. It was possible to achieve 98 % gold and 93 % silver recovery within 48 hours of ammonium thiosulphate leaching. This type of leaching is a better leaching procedure for recovery of gold and silver from PCB waste than the classical toxic cyanide leaching. 84 % Cu, 82 % Fe, 77 % Al, 76 % Zn, 70 % Ni, 90 % Pd, 88 % Pb and 83 % Sn recovery of the accompanying metals was achieved, using sulphuric acid with hydrogen peroxide, sodium chloride and aqua regia. A four steps leaching process gave a very satisfactory yield and a more rapid kinetics for all observed metals solubilization than other technologies.
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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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This paper deals with bioleaching of metals from hazardous spent hydro-processing catalyst by means of iron/sulphur oxidizing bacteria. The exhaust catalyst was rich in nickel (45 mg/g), vanadium (44 mg/g) and molybdenum (94 mg/g). Before bioleaching, the solid was washed by means of a mixture of Tween 80 and ethyl alcohol, for hydrocarbons removal. The effects of elemental sulphur, ferrous iron and actions contrasting a possible metal toxicity (either the presence of powdered activated charcoal or the simulation of a cross current process by means of filtration stages in series) was investigated. Ferrous iron resulted to be essential for metals extraction and for bacteria adaptation. Nickel and vanadium were successfully bioleached in the presence of iron, reaching extraction yields of 83% and 90%, respectively; on the other hand extractions around 50% for nickel and vanadium were observed both in biological systems in the absence of iron and in the chemical controls with iron. As concerns molybdenum, the highest extraction yields experimentally observed for molybdenum was about 50%, after 21 days bioleaching in the presence of iron, while a maximum extraction of 25 was observed in the other treatments. In conclusion, a bio-oxidative attack with iron could successfully extract nickel, vanadium and partially molybdenum. Further actions aimed at contrasting a possible metal toxicity resulted not to be effective and partially inhibited the metal extraction processes.
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Current research on leaching precious metals from waste printed circuit boards (PCBs) in the world is introduced. In the paper, hydrometallurgical processing techniques including cyanide leaching, thiourea leaching, thiosulfate leaching, and halide leaching of precious metals are addressed in detail. In order to develop an environmentally friendly technique for recovery of precious metals from Waste PCBs, a critical comparison of main leaching methods is analyzed based on three-scale analytic hierarchy process (AHP). The results suggest that thiourea leaching and iodide leaching make more possible to replace cyanide leaching.
Book
The way municipal solid waste is handled greatly determines its impact on the local as well as the global environment. New technologies have emerged for the treatment of waste, for the recovery of raw materials and energy, and for safe final disposal. The environmental performance of technologies, their social acceptance and their economic viability are key issues to be considered in sustainable waste management. This book provides an overview of current practices in waste management and a synthesis of new developments achieved through interdisciplinary discussions of recent research results.
Article
Nowadays bioleaching occupies an increasingly important place among the available mining technologies. Today bioleaching is no longer a promising technology but an actual economical alternative for treating specific mineral ores. An important number of the current large-scale bioleaching operations are located in developing countries. This situation is determined by the fact that several developing countries have significant mineral reserves and by the characteristics of bioleaching that makes this technique especially suitable for developing countries because of its simplicity and low capital cost requirement. The current situation of commercial-size bioleaching operations and ongoing projects in developing countries is presented and discussed with especial reference to copper and gold mining. It is concluded that this technology can significantly contribute to the economic and social development of these countries.
Article
The mixed culture of acidophilic bacteria was used as the inoculant to bioleach waste printed wire boards. Meanwhile, bacteria in different leaching phases (0, 5, 24 and 60 h) were sampled, and denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction (PCR)-amplified 16Sr RNA genes was used to evaluate the change of microbial community structure during the bioleaching process. The results showed that the mixed culture of acidophilic bacteria could bioleach 96.36% copper from the boards in 48 h. The analysis of the bands selected from the DGGE gel revealed that the sequences of seven bands (Z1~Z7) had over 99% sequence similarity with Acidithiobacillus ferrooxidans. It meant that the seven strains were all clustered to Acidithiobacillus ferrooxidans genus. The relative abundance of Z1 to Z7 in the four samples was not changed significantly. Meanwhile, Z3 showed the highest relative abundance during the whole bioleaching process, which was 72.70%, 82.90%, 79.00% and 85.80%, respectively. Therefore, the microbial community structure changed a little bit during the bioleaching, which always consisted of Acidithiobacillus ferrooxidans strains and was dominated by strain Z3.
Chapter
The most familiar and well-studied microorganisms indigenous to acidic mineral leaching environments are autotrophic sulfur- and iron-oxidizing bacteria such as Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillum ferrooxidans. Some photoautotrophs, such as the thermophilic rhodophyte Cyanidium caldarium, may also be present in extremely acidic environments that receive light. Other microorganisms which require pre-fixed (organic) carbon have been isolated from mineral leach dumps and acid mine drainage (AMD) waters. These heterotrophic microorganisms include eukaryotes, such as some fungi and yeasts1 and protozoa,2 as well as prokaryotic bacteria and archaea. It is somewhat paradoxical, given that heterotrophy is the most widespread form of metabolism among bacteria, that the first acidophilic heterotrophic bacterium which is indigenous and active in mineral leaching environments was isolated and characterized some 40 years after the iron/sulfur-oxidizing chemolithotroph T. ferrooxidans and 70 years after the sulfur-oxidizing acidophile T. thiooxidans.
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Tests of heavy metal extraction from municipal solid waste incineration fly ashes (MSWFAs) were conducted using Thiobacillus spp. strain TM-32. Six types of MSWFAs were collected from actual incineration plants. Despite different ash sources, the samples showed approximately the same percentages by heavy metal extraction. The percentages were 55.3-68.5%, 57.4-84.6%, 2.2-19.6%, and 38.8%-56.4% for Cd, Cu, Pb, and Zn, respectively. To treat large amount of ash, large sulfate accumulation was essential. Sulfur free culture was employed for the tests and showed approximately the same extraction percentage as original ONM media culture.
Article
The Acidithiobacillus ferrooxidans (At. f) and Acidithiobacillus thiooxidans (At. t) were used in bio-dissolution experiments of heavy metals in spent MH/Ni batteries. The influences of the initial pH value, the concentration of electrode materials, the temperature and substrate concentration on the leaching rate of heavy metal Ni, Co have been investigated. The obtained results indicate that the efficiency of nickel extraction and cobalt extraction is dependent on all of the mentioned factors. Especially, the initial pH value and the temperature have more effect than other factors for these microorganisms. In addition, the results show that the optimal leaching rate of Ni and Co in the spent MH/Ni batteries reaches to 95.7% and 72.4% respectively after 20 days under the conditions of the initial pH value 1.0, concentration of electrode materials 1.0%, temperature 30 °C and substrate (sulfur) concentration 4.0 g·L-1.
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Hydrotreating heavy oils produces catalysts that are contaminated with coke and with nickel, vanadium and iron. Regeneration may be possible but sooner or later irreversible deactivation occurs. Means of regenerating or disposing of spent catalysts are reviewed. Regeneration may or may not involve decoking, with selective removal of Ni, V and Fe being achieved by leaching with different reagents. Leaching of all metals from the spent catalyst may be achieved if disposal is required and the economic justification exists. The solid wastes must be encapsulated or stabilized before final disposal in order to meet environmental standards.
Article
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.
Article
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.
Article
The recent U.S. Environmental Protection Agency's (EPA's) memorandum clarified that spent catalysts resulting from 'dual purpose' hydroprocessing reactors are hazardous waste. This article provides insight into the definitions in the EPA regulations that refiners must follow when determining how spent hydroprocessing catalysts should be classified.
Article
Billiton Process Research has carried out extensive research over the past four years to develop new process technology using bioleaching for extraction of copper and nickel from their sulphide concentrates. Continuous pilot scale and laboratory batch testwork has been carried out with adapted mesophile bacterial cultures at 40°C-45°C, moderate thermophile cultures at 50°C-55°C and thermophile cultures at 65°C-85°C. Pilot scale work has demonstrated the commercial viability of mesophile cultures for bioleaching of secondary copper sulPhide and nickel sulphide concentrates. Moderate thermophiles offer benefits in terms of reduced cooling requirements for commercial reactors and, in the case of bioleaching of nickel concentrates, some selectivity over bioleaching of pyrite. Continuous pilot scale testwork has shown that thermophiles achieve efficient bioleaching of primary copper sulphide and nickel sulphide concentrates, giving much higher recoveries than achieved by bioleaching with a mesophile or moderate thermophile culture.
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.
Article
As an alternative using cyanide chemicals for gold extraction, the application of a cyanogenic bacterium viz. Chromobacterium violaceum (C. violaceum) in YP medium has been investigated. The catalytic roles of metal ions such as Na+, Mg2+, Fe2+, and Pb2+, as well as the effect of Na2HPO4 nutrient addition on the cyanide generation efficiency of the bacterium in this medium have been elucidated. While MgSO4 and FeSO4 added to the medium were equally effective for cyanide generation, improved efficiency was obtained in the presence of Na2HPO4 and Pb(NO3)(2). In order to examine the effectiveness of C. violaceum cultured in YP medium for the generation of cyanide ions, the dissolution of gold and copper from waste mobile phone printed circuit boards (PCBs), a good source of gold and copper in alkaline conditions, was tested at 30 degrees C, for various pH values and metal ion contents. Gold leaching was found to be 11% in 8 d at pH 11.0 in presence of 4.0 x 10(-3) mol/L MgSO4, whereas; copper recovery was high (11.4%) at pH 10.0. Addition of 1.0 x 10(-2) mol/L Na2HPO4 and 3.0 x 10(-6) mol/L Pb(NO3)(2) to the YP medium increased copper leaching to 30.3% and 38.1%, respectively, at pH 10.0 in 8 d. However, this effect was not observed for gold leaching.
Article
In previous studies it has been showed that bacterially produced sulphuric acid is a good leaching agent for laterite tailings. In this work we evaluated heavy metals leaching from low grade laterite ore for cobalt and nickel extraction using sulphuric acid produced in situ by Acidithiobacillus thiooxidans under different culture conditions. In studies where that material was initially added to the cultures, considerable percentages of metals were leached (100 % Mn, 70 % Co, 7.5 % Ni, less than 5 % of Cr and Fe) after 18 days of incubation at low pulp densities (1 % and 2.5 %) of overburden. The maximum percentages were reached when cultures pH was approximately or below than 1.5. At higher pulp densities material was added to the cultures after different pre-cultivating times; also higher sulphur amounts were assayed; in such way about 100 % Mn, 60 % Co, 9 % Ni and Fe and 2.5 % Cr were leached. Although toxic metals were not completely leached, sequential extractions results indicate that these metals are not readily available. All studies finally suggest that bioleaching is a suitable technology for recovery of valuable metals as Co and remediation of mining residues by extraction of heavy metals.
Article
Chemical replacements for cyanide have been investigated for decades; however cyanide remains the exclusive lixiviant of choice in the mining industry due to a combination of its availability, effectiveness, economics and ability to use it with acceptable risk to humans and the environment. About 90% of the significant gold producing operations worldwide currently utilize cyanide for gold and silver extraction. Despite the number of cyanide-related mining operations, there have been no documented accounts during the previous three decades of the death of humans due to cyanide as a direct consequence of major mining-related environmental incidents. Major mining-related environmental incidents have not been concentrated in any geographic location, may occur regardless of the size of the comp