Article

Precious Metal Recovery from Waste Printed Circuit Boards using Cyanide and Non-Cyanide Lixiviants - A Review

Authors:
  • SDU/Beijing University of Chemical Technology/Satbayev University/Nazarbayev University
  • Munzur University Rare Earth Elements Application and Research Center
  • Guru Ghasidas Vishwavidyalaya, Bilaspur Chhattisgarh India
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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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... The overall reaction is described by the Elsner's equation (1846) (Eq. (4)), which is stoichiometrically correct [11,15,16]. ...
... Galvanic interactions between gold particles and sulfide minerals may play a crucial role in the behavior of gold dissolution in cyanide solutions (Eqs. (1)-(4)) [12][13][14][15][16]. ...
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... Slightly alkaline cyanide solutions facilitate the dissolution of gold and silver present in ores. The ionic reaction, commonly known as the Elsner equation, is the primary method used to dissolve gold into a solution using cyanide, as described by the following equation (Akcil et al. 2015;Deschênes 2005;Elomaa et al. 2020;Syed 2012): ...
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... Cyanidation is widely employed for recovering metals such as Ag and Au due to its efficiency and simplicity. 151,152 Table S3 combines the diverse leaching agents utilized in hydrometallurgical methods and their advantages, limitations, and toxicity. ...
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... [10,11] According to the Global E-waste Monitor 2020, the amount of global ewaste is estimated to enhance from 9.2 million tons to 74.7 million tons by 2030. [12][13][14][15][16] Moreover, improper disposal and the dramatic rise of electronic waste (e-waste) have caused unavoidable environmental concerns owing to the toxic effect of gold ions in wastewater. [17,18] Hence, for the sake of resource conservation, environmental protection, and sustainable development, gold recovery and its reusability are earnestly required. ...
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Article
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... Hydrometallurgy is considered a promising alternative to pyrometallurgy for e-waste recycling, especially in low-and middle-income countries. It can be operated on a smaller scale and applied to low-grade waste [41]. In the past, the focus of e-waste hydrometallurgy has been on gold and silver, but there is growing interested in the recovery of other metals such as copper, nickel, and cobalt. ...
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... Leaching experiments were performed by adding the corresponding amount of PCBs to 25 mL of the leaching solutions, which were kept in a water bath orbital shaker (J.P. Selecta Unitronic OR, Spain) at a rate of 100 rpm. The experiments were designed to investigate the impact of six independent variables: leaching agent concentration (X 1 , 10-50 g L −1 ), temperature (X 2 , 20-60 °C), solid/liquid ratio (X 3 , 50-150 g L −1 ), initial pH (X 4 , 8-12 for sodium thiosulfate and 1-5 for thiourea which are stable in basic and acidic environments, respectively (Akcil et al. 2015)), average particle size (X 5 , 0.3-1.5 mm) and leaching time (X 6 , 4-10 h) on Y 1 (Cu leaching, µg g −1 ), Y 2 (Pb leaching, µg g −1 ), Y 3 (Sn leaching, µg g −1 ), Y 4 (Au leaching, µg g −1 ), Y 5 (Ag leaching, µg g −1 ), and Y 6 (Pd leaching, µg g −1 ), in order to analyze the applicability and ability of these agents in a single-stage leaching process. ...
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The presence of valuable and hazardous metals in waste printed circuit boards, especially, motherboards, makes their recovery necessary as implies great economic and environmental advantages and develops urban mining processes. Hence, this research is focused on the selective leaching of Cu, Pb, and Sn as base metals using nitric acid and hydrochloric acid and Au, Ag, and Pd as precious metals using thiourea and sodium thiosulfate from waste motherboards’ PCBs in a sequential eco-friendly two-stage process. Previously, thiourea and sodium thiosulfate were used as leaching agents to investigate their applicability for the leaching of metals from PCBs in a single-stage process. Screening experimental design was applied to screen the variables affecting the leaching process in order to evaluate their impact on the recovery of metals and select the significant factors. The results demonstrated that base and precious metals can be leached appropriately in two consecutive stages compared to a single-stage process. Nitric acid was found to be a much more efficient agent to leach Cu and Pb in comparison with hydrochloric acid which was more suitable for the leaching of Sn. In the case of precious metals, higher amounts of Au were leached using thiourea, whereas sodium thiosulfate was able to leach more Pd. Roughly similar results were obtained for the leaching of Ag using these leaching agents. Nitric acid concentration, average particle size, temperature, and leaching time were found to be significant to maximize the leaching of Cu and Pb and minimize that for Au, Ag, and Pd in the first stage. Initial pH was the only variable influencing the second stage, in particular, Au leaching by thiourea.
... are the well-known hydrometallurgical and pyrometallurgical processes [12][13][14]. Many reviews have been published in the literature on the current status of extraction methods and perspectives [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. These have been presented as physical, mechanical, and thermal pre-treatment steps, followed by physical, pyrolysis, supercritical fluid, pyrometallurgical (smelting-refining), and hydrometallurgical processes with chemical leaching. ...
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... This acknowledgement stems from the fact that the metal content in such wastes is comparable to that found in natural ores [9,14,15]. For instance, e-waste can contain Cu levels up to 26.0 times higher and Au content up to 50.0 times higher compared to ores and concentrates [16]. Most of the available base, precious and hazardous metals in e-waste are landfilled in the printed circuit boards (PCBs). ...
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... It has been reported that in PCB, Au and Ag concentrations can be as high as 700 g/t and 800 g/t, respectively (Kasper & Veit, 2018;Ribeiro et al., 2019). The concentration of Cu in waste PCBs is 13-26 times higher than in primary ores and that of Au is up to 50 times higher (Akcil et al., 2015;Cui & Zhang, 2008;Zhang & Forssberg, 1998). PCBs are commonly treated with brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBP-A), and hexabromocyclododecane (HBCD) (Alaee & Wenning, 2002). ...
Chapter
Several profound societal changes such as the shift towards renewable energies have created an ever-increasing demand for base and critical metals. Electronic wastes constitute a significant secondary source of such elements and a potential environmental hazard if disposed of improperly. In contrast to traditional methods of recycling e-waste, biohydrometallurgy is an environmentally friendly, low-cost, and energy-efficient alternative. Although processes developed in laboratories display promising yields, it is still premature to implement these biotechnological strategies on a larger scale as the bioleaching and biorefinery mechanisms are still poorly understood. Moreover, very few studies focus on fully biological processes, and most opt for more efficient hybrid approaches. Thus, this book chapter compiles the optimal parameters reported in recent studies, from waste pre-treatment to metal biorecovery, along with insights to complete and close the biohydrometallurgical recycling loop.
... While bioleaching is a promising technology for PCB pre-treatment prior to recover of precious metals, one of the major challenges is the inhibition due to the accumulation of inhibitory levels of metal ions and other constituents of PCBs within the system. These decrease Fe 2+ to Fe 3+ turnover rates, affecting metal extraction rates adversely (Liang et al., 2010;Akcil et al., 2015). Inhibition of microbial growth at PCB concentrations greater than 10 g/L was observed in the study by Brandl et al. (2001) where the authors investigated the bioleaching of PCBs using a mixed mesophilic culture dominated by Acidithiobacillus (At.) thiooxidans and At. ...
... In today's rapidly developing world of technology, electrical and electronic equipment such as TV sets, computers, printers, mobile phones or laptops have a shorter lifespan compared to devices from previous years [1]. The lifetime of electronic components, which at the end of the 20 th century was 4 to 6 years, was shortened to 2 years in the first decade of the 21 st century [2]. ...
... Pb-Sn alloy has the advantages of stable performance, good toughness, low porosity, and superior soldering performance, and it is widely used as solder in electronic industry and electroplating industry. With the technological innovation and consumer expansion, municipal electronic waste is growing rapidly and needs urgent treatment [1,2]. The most economically valuable and intractable part of the electronic waste is printed circuit boards, in which the Pb-Sn alloy as a commonly used metal solder to connect the original circuit board and the substrate. ...
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Critical minerals (CMs) are essential for the development and function of renewable energy technologies, such as solar panels, wind turbines, and batteries, and for utilization in other industrial sectors, such as high-tech., automotive, information technology, aerospace, and defense. Recycling these minerals from electronic waste (e-waste) offers a sustainable solution to meet the growing industrial demand, if done technically effectively and with appropriate process inputs and rewards. This study proposes a holistic approach in addressing CMs recovery from e-waste. In doing so, seven connecting factors (nexuses) were identified and discussed. These nexuses are as follows: (i) the technical dimension that addresses the limitations of the current technologies used for e-waste recycling and recovering; (ii) the energy dimension addressing the level of consumed energy in the recycling and recovery processes; (iii) the economic dimension that addresses the economy of scale; (iv) the consumer dimension in view of consumer and manufacturer attitudes toward recycling; (v) the circularity dimension that deals with the circular design principles aiming to promote the recyclability and sustainability; (vi) the technical innovation dimension, particularly through the integration of digital technologies; and (vii) the research and development effort dimension aiming at advancing recycling technologies and recovery processes. Overcoming these limitations is crucial for maximizing resource recovery rates, reducing environmental impacts, and promoting the transition toward a more sustainable and circular economy.
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The coal gasification (CG) process, while beneficial for producing syngas, poses environmental risks due to the production of highly toxic wastewater containing high concentrations of polycyclic aromatic hydrocarbons (PAHs), phenolics, and cyanides. This study examines the oxidation of pollutants in wastewater from a simulated underground coal gasification (UCG) process, with initial pollutant levels of pH 1.8, total cyanides 21.00 mg/L, total phenols 61.95 mg/L, heavy metals 7.68 mg/L, PAHs 2459 μg/L, and dissolved organic carbon (DOC) 148.0 mg/L. Three oxidation systems (Ce(SO4)2·4H2O, Ce(SO4)2·4H2O + H2O2, and Fenton process with FeSO4 + H2O2) were used to remove pollutants from wastewater from the coal gasification process. In the first system, the oxidising agent was Ce4+ ions, while in the second and third systems, where hydrogen peroxide was added, the oxidising agents were hydroxyl radicals. Using central composite design and response surface methodology (CCD/RSM), the most favourable oxidation conditions were identified for Ce(SO4)2·4H2O (35 min, Ce4+:C molar ratio of 5:1, pH 2.5, temp. 40 °C). For the Ce(SO4)2·4H2O + H2O2 system DOC:Ce4+:H2O2 molar ratio of 1:2:10. Results showed significant reduction in pollutants: Ce(SO4)2·4H2O reduced PAHs, phenols, cyanides, DOC, and heavy metals by 99.40 %, 99.97 %, 97.67 %, 65.34 %, and 90.01 %, respectively; Ce(SO4)2·4H2O + H2O2 achieved reductions of 99.91 %, 99.66 %, 98.14 %, 76.35 %, and 81.45 %; and the Fenton process achieved reductions of 99.91 %, 99.95 %, 95.07 %, 56.49 %, and 89.33 %. An application of alternative oxidation processes (Ce(SO4)2·4H2O and Ce(SO4)2·4H2O + H2O2) is a viable option in removing toxic pollutants with simultaneously cerium recovery.
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In this work, an industrial hazardous jarosite residue produced in the zinc hydrometallurgical process containing silver was used to evaluate the feasibility of using thiourea (Tu) for silver leaching under acidic conditions in the presence of oxalate (C2O42− ion denoted as Ox2−). The shrinking core kinetic model (SCKM) was applied to evaluate the effect of variables on the reaction rate. The chemical reaction of H3O+ with the jarosite surface was the controlling stage. The results of batch experiments revealed that silver extraction is influenced by various factors in the descending order: pH > T (temperature) > [Tu] (thiourea concentration) > [Ox2−] (oxalate concentration). The extraction efficiency of Ag was 98 % at high levels of both T and [H2SO4], although a higher [Tu] was required. High Tu consumption was associated with the stability of Tu due to the presence of Fe3+ and Cu2+ ions leached along with Ag+, which affect the redox potential catalyzing Tu oxidation. Temperature is the most effective variable with a reaction rate constant of kexp = 1.1 min−1 at 60 °C, but it causes a decrease in silver extraction to 92.5 %. The kinetic parameters were obtained using the SCKM; furthermore, the experimental results were statistically validated through a surface response experimental design.
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The transition to renewable energies and electric vehicles has triggered an unprecedented demand for metals. Sustainable development of these technologies relies on effectively managing the lifecycle of critical raw materials, including their responsible sourcing, efficient use, and recycling. Metal recycling from electronic waste (e-waste) is of paramount importance owing to ore-exceeding amounts of critical elements and high toxicity of heavy metals and organic pollutants in e-waste to the natural ecosystem and human body. Heterotrophic microbes secrete numerous metal-binding biomolecules such as organic acids, amino acids, cyanide, siderophores, peptides, and biosurfactants which can be utilized for eco-friendly and profitable metal recycling. In this review paper, we presented a critical review of heterotrophic organisms in biomining, and current barriers hampering the industrial application of organic acid bioleaching and biocyanide leaching. We also discussed how these challenges can be surmounted with simple methods (e.g., culture media optimization, separation of microbial growth and metal extraction process) and state-of-the-art biological approaches (e.g., artificial microbial community, synthetic biology, metabolic engineering, advanced fermentation strategies, and biofilm engineering). Lastly, we showcased emerging technologies (e.g., artificially synthesized peptides, siderophores, and biosurfactants) derived from heterotrophs with the potential for inexpensive, low-impact, selective and advanced metal recovery from bioleaching solutions.
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Відпрацьовані друковані плати (WPCB) є невід'ємними компонентами практично всього електричного та електронного обладнання (ЕЕО), формуючи структурну основу електронної промисловості. Класифікуються на односторонні, двосторонні, багатошарові, жорсткі та гнучкі плати, друковані плати складаються з різних електронних компонентів, включаючи напівпровідники, транзистори та конденсатори, що ускладнює їхню переробку через різноманітний склад матеріалів. Приблизно 40% маси друкованих плат складають метали, 30% - пластик і 30% - органічні матеріали, причому серед металів переважає мідь. Процес переробки включає кілька етапів, зокрема подрібнення та розділення для вилучення цінних металів та електронних компонентів. Подрібнення із застосуванням таких технологій, як молоткові млини, має вирішальне значення для ефективного вилучення металів. Для ефективного відокремлення електронних компонентів були розроблені передові методи, такі як автоматичні системи видалення на основі інфрачервоного нагрівача, що забезпечують мінімальний вплив на навколишнє середовище. Механічні та фізичні методи переробки зосереджені на вилученні цінних металів, таких як золото, срібло, паладій і мідь, визнаючи при цьому потенціал неметалевої фракції. Хімічна обробка з використанням неорганічних кислот, таких як азотна та сірчана, разом з окислювальними вилуговувачами довела свою ефективність для вилучення металів. Інноваційні методи, зокрема використання акварелі для вилуговування золота, продемонстрували високі показники вилучення. Такий комплексний підхід до переробки WPCB підкреслює важливість інтеграції механічних, фізичних і хімічних процесів для досягнення стійких, ефективних і екологічно чистих результатів переробки.
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There are enormous economic benefits to conveniently increasing the selective recovery capacity of gold. Fe/Co‐MOF@PDA/NdFeB double‐network organogel (Fe/Co‐MOF@PDA NH) is synthesized by aggregation assembly strategy. The package of PDA provides a large number of nitrogen‐containing functional groups that can serve as adsorption sites for gold ions, resulting in a 21.8% increase in the ability of the material to recover gold. Fe/Co‐MOF@PDA NH possesses high gold recovery capacity (1478.87 mg g⁻¹) and excellent gold selectivity (Kd = 5.71 mL g⁻¹). With the assistance of an in situ magnetic field, the gold recovery capacity of Fe/Co‐MOF@PDA NH is increased from 1217.93 to 1478.87 mg g⁻¹, and the recovery rate increased by 24.7%. The above excellent performance is attributed to the efficient reduction of gold by FDC/FC⁺, Co²⁺/Co³⁺ double reducing couple, and the optimization of the reduction reaction by the magnetic field. After the samples are calcined, high‐purity gold (95.6%, 22K gold) is recovered by magnetic separation. This study proposes a forward‐looking in situ energy field‐assisted strategy to enhance precious metal recovery, which has a guiding role in the development of low‐carbon industries.
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Ecosystems and human health are being negatively impacted by the growing problem of electrical waste, especially in developing countries. E-waste poses a significant risk to ecological systems because it can release a variety of hazardous substances into the environment, containing polybrominated diphenyl ethers and heavy metals, brominated flame retardants, polychlorinated dibenzofurans and polycyclic aromatic hydrocarbons, and dioxins. This review article provides a critical assessment of the toxicological consequences of e-waste on ecosystems and human health and data analyses from scientific journals and grey literature on metals, BFRs, PBDEs, PCDFs, and PAHs in several environmental compartments of commercial significance in informal electronic trash recycling. The currently available techniques and tools employed for treating e-waste are sustainable techniques such as bioremediation, chemical leaching, biological leaching, and pyrometallurgy have been also discussed along with the necessity of implementing strong legislation to address the issue of unregulated exports of electronic trash in recycling practices. Despite the ongoing hurdles, implementing environmentally sustainable recycling methods have the potential to address the detrimental impacts of e-waste and foster positive economic development.
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The increasing scarcity of precious metals necessitates the development of sustainable recycling strategies to fulfill industrial requirements while mitigating environmental impact. Aqua regia has emerged as a key leaching agent for precious metal recovery from secondary raw materials due to its economic viability, swift leaching kinetics, and straightforward implementation. Due to synergistic benefits such as enhanced recovery rates, improved selectivity, and increased environmental sustainability, aqua regia leaching integrated with sorption, solvent extraction, and biohydrometallurgical techniques. This review article provides a comprehensive overview of aqua regia-based hybrid approaches for recovering Au, Pt, and Pd from diverse secondary sources, including waste electrical and electronic equipment, spent catalysts, industrial effluents, and others. The study evaluates a wide range of functional sorbent and extractant materials for their effectiveness in recovering precious metals from acidic environments, and aqua regia settings. Evaluating various factors that affect precious metal sorption, this study emphasizes the need for acid-resistant and highly selective sorbents. The review also addresses the challenges associated with aqua regia and evaluates potential solutions like selective leaching and diluted aqua regia applications. Finally, the review outlines future directions, focusing on advancements in hybrid methods to achieve superior precious metal recovery with minimal environmental impact.
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As technology advances and auxiliary electrical and electronic equipment expands, waste printed circuit boards are among the quickest growing sources of waste. Throughout the world, the exploitation of waste printed circuit boards has become one of the lucrative commercial enterprises in the recycling production company. Additionally, it can also cause a variety of effects on humans and the environment in terms of metal ions. In order to facilitate the recovery and recycling of printed circuit board, several innovative techniques have been developed, including pyrometallurgy, hydrometallurgy, and biometallurgy. It is possible to recover and recycle precious metals through the hydrometallurgy process simply and conveniently. Economic efficiency, environmental friendliness, and durability make this technology auspicious. On the other hand, there are few comprehensive studies on the hydrometallurgy and chemical processing of waste printed circuit board. As a result, in this work, a mini-review was performed in order to assess different chemical leaching methods, optimize parameters, and examine future investigation pathways.
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The ever‐increasing importance of critical metals (CMs) in modern society underscores their resource security and circularity. Waste‐printed circuit boards (WPCBs) are particularly attractive reservoirs of CMs due to their gamut CM embedding and ubiquitous presence. However, the recovery of most CMs is out of reach from current metal‐centric recycling industries, resulting in a flood loss of refined CMs. Here, 41 types of such spent CMs are identified. To deliver a higher level of CM sustainability, this work provides an insightful overview of paradigm‐shifting pathways for CM recovery from WPCBs that have been developed in recent years. As a crucial starting entropy‐decreasing step, various strategies of metal enrichment are compared, and the deployment of artificial intelligence (AI) and hyperspectral sensing is highlighted. Then, tailored metal recycling schemes are presented for the platinum group, rare earth, and refractory metals, with emphasis on greener metallurgical methods contributing to transforming CMs into marketable products. In addition, due to the vital nexus of CMs between the environment and energy sectors, the upcycling of CMs into electro‐/photo‐chemical catalysts for green fuel synthesis is proposed to extend the recycling chain. Finally, the challenges and outlook on this all‐round upgrading of WPCB recycling are outlined.
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This article examines the opportunity that the Smart City Mission (SCM) provides for the e-waste recycling sector in India. The SCM is aimed at improving the quality of life in 100 cities across the country, but is it in line with responsible consumption and production? A larger reliance on technology and rudimentary methods of e-waste recycling would give rise to more toxins polluting land, water and air. We posit that the SCM provides some leeway to formalise the informal sector, where most of India’s e-waste recycling takes place. The E-Waste Management Rules of 2016 mandate all recycling units to register with the Central Pollution Control Board (CPCB). Formal recycling capacity is lagging behind the domestic generation of e-waste, let alone dealing with imports. An augmentation of recycling capacity is required. Based on interviews with informal and formal e-waste recyclers, we set forth the e-waste recycling of both and suggest alternatives to the malpractices in the informal sector recycling to make it sustainable and safe. We propose a segmented flow of bulk and retail consumer e-waste into large-scale and small-scale e-waste enterprises, respectively. Measures to trace the e-waste flow properly are recommended, and Producer Responsibility Organisations are identified as key facilitators and capacity builders to spearhead the process. The increase in volume of e-waste flow due to SCM will reduce the competitive antagonism between the formal and informal sectors over e-waste flow, making it an opportune moment to strike a separate flow between the formal and formalised small-scale units.
Chapter
The use of Rare earth element(s) (REE) in high technology in the world is becoming more and more important day by day. This importance has caused REEs used in high technology to be declared in the critical raw material lists of many countries or country groups, especially the European Union (EU), and their criticality and strategic level have increased. The EU is dependent on many countries around the world for REE supplies. Due to their use of high technology, this dependence will continue for decades. Taking this into consideration, the EU has given great importance to the recovery of these REEs in recent years. However, the recovery of these REEs from mining and industrial tailings/wastes is not sufficient for the annual REE needs of these countries. At this point, the recovery of REEs in abandoned mine deposits, which contain high amounts of REEs in many mine residues, attracts the attention of countries using high technology in terms of REE supply. In this regard, studies that determine the amounts and grade characteristics and feasible methods of REEs that can be recovered from mine tailings can contribute to reducing the REE supply risk. Thus, these new findings will be able to contribute to the REE supply of many countries, especially EU countries that produce high technology. In this study, recovery opportunities of REEs from mining residues and urban wastes were evaluated. An attempt has been made to clarify the issue of REE recovery from urban waste in the world and to find an answer to the question of whether REE can be supplied without opening a mining operation. In addition, this study reviewed the literature on the environmentally responsible management of WEEE for recycling.
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Waste PCBs the core of e‐waste is rich in copper, tin, zinc, iron, and nickel. Leaching base metals from PCB used to be done in toxic, corrosive acidic/alkali mediums. In this work, an environmentally friendly method for leaching metals from thermally treated PCBs (TPCBs) of mobile phones was proposed using choline chloride based deep eutectic solvents (DES). DES selectivity and solubility of metals from metal oxides were the main screening criteria. FA−ChCl had the maximum solubility of Cu, Fe, and Ni, while Urea−ChCl had high Zn selectivity and solubility. Oxalic acid has high selectivity for Sn. FA−ChCl extracted Cu and Fe best at 16 h, 100 °C, and 1/30 g/mL. Urea−ChCl extracted Zn (90.4±2.9 %) from TPCBs at 100 °C, 21 h, 1/20 g/mL, and 400 rpm. Oxalic acid (1 M) removed 92.3±2.1 % Sn from TPCBs in 1 h at 80 °C and 1/20 g/mL. The shrinking core model‐based kinetic investigation of FA−ChCl for Cu extraction showed a diffusion‐controlled process. The proposed method is greener than mineral acids utilized for metal extraction.
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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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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.
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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.
Article
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.
Article
In this study experimental conditions were expressed for a new process of recycling lead paste at relatively lower temperatures. Lead acid battery paste was reacted with the mixture of citric acid, sodium citrate and hydrogen peroxide solution in this process. The solution mixture provided the removal of sulphur content of the paste as well as the decomposition of lead dioxide. Complete transformation to lead citrate was achieved by experimenting hydrometallurgical conditions of leaching-crystallisation step. Then thermal behaviour of lead citrate was investigated accordingly. Lead citrate crystals were decomposed to lead oxide at around 300°C without any addition. Direct reduction of lead from lead citrate was also possible under specific conditions. Experimental results reflected the efficient recovery of spent lead acid battery pastes without the use of high temperature pyrometallurgy or energy intensive electrolysis techniques.
Article
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 company and do not occur more frequently with a specific type of mining activity. The main aspects of cyanide management that should be addressed at mining operations include transportation of cyanide to site, process solution conveyance, worker health and safety training, water management and treatment, emergency response and preparedness, workplace and environmental monitoring, and community relations. If these aspects of cyanide management are integrated into an overall cyanide management plan, dramatic reductions in risk and potential incidents at mine sites will be realized.
Article
This study refers to two chemical leaching systems for the base and precious metals extraction from waste printed circuit boards (WPCBs); sulfuric acid with hydrogen peroxide have been used for the first group of metals, meantime thiourea with the ferric ion in sulfuric acid medium were employed for the second one. The cementation process with zinc, copper and iron metal powders was attempted for solutions purification. The effects of hydrogen peroxide volume in rapport with sulfuric acid concentration and temperature were evaluated for oxidative leaching process. 2 M H2SO4 (98% w/v), 5% H2O2, 25 °C, 1/10 S/L ratio and 200 rpm were founded as optimal conditions for Cu extraction. Thiourea acid leaching process, performed on the solid filtrate obtained after three oxidative leaching steps, was carried out with 20 g/L of CS(NH2)2, 6 g/L of Fe3+, 0.5 M H2SO4, The cross-leaching method was applied by reusing of thiourea liquid suspension and immersing 5 g/L of this reagent for each other experiment material of leaching. This procedure has lead to the doubling and, respectively, tripling, of gold and silver concentrations into solution. These results reveal a very efficient, promising and environmental friendly method for WPCBs processing.
Article
An environmentally benign process involving thiosulphate leaching was developed in order to recover gold from the printed circuit boards (PCBs) of discarded mobile phone. The effect of concentration of the reagents such as thiosulphate, copper(II) and ammonia on the leaching of gold was investigated in the temperature range 20–50 °C. Parameters were optimized through modeling of the leaching process using response surface methodology (RSM) based on central composite design (CCD). The optimum conditions for leaching of gold from PCBs were identified to be 72.71 mM thiosulphate, 10.0 mM copper(II) and 0.266 M ammonia. The initial rate of gold leaching was found to be 2.395 × 10− 5 mol∙m− 2∙ s− 1 under the optimum conditions. As regards the kinetics of gold leaching, the pseudo-second order kinetic model with chemical control was found to be applicable in the low concentration range (40–60 mM thiosulphate, 5–7 mM copper(II) and 0.22 − 0.247 M ammonia), compared to that of pseudo-first order kinetic model at mid concentration range of the reactants viz., 60–70 mM thiosulphate, 7–9 mM copper(II) and 0.247 − 0.263 M ammonia. The apparent activation energy of the reaction in the temperature range 20–50 °C was found to be 78.6 kJ∙mol− 1. The samples were characterized before and after leaching using scanning electron microscopy (SEM) which corroborated the chemical controlled leaching mechanism.
Data
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
Article
Electronic waste has been increasing proportionally with the technology. So, nowadays, it is necessary to consider the useful life, recycling, and final disposal of these equipment. Metals, such as Au, Ag, Cu, Sn and Ni can be found in the printed circuit boards (PCB). According to this, the aims of this work is to characterize the PCBs of mobile phones with aqua regia; obtaining "reference" values of leaching, to gold and silver, with cyanide and nitric acid, respectively; and study the process of leaching of these metals in alternative leaching with sodium thiosulfate and ammonium thiosulfate. The metals were characterized by digesting the sample with aqua regia for 1 and 2h at 60°C and 80°C. The leaching of Au with a commercial reagent (cyanide) and the Ag with HNO3were made. The leaching of Au and Ag with alternative reagents: Na2S2O3, and (NH4)2S2O3 in 0.1M concentration with the addition of CuSO4, NH4OH, and H2O2, was also studied. The results show that the digestion with aqua regia was efficient to characterize the metals present in the PCBs of mobile phones. However, the best method to solubilize silver was by digesting the sample with nitric acid. The leaching process using sodium thiosulfate was more efficient when an additional concentration of 0.015 and 0.030M of the CuSO4 was added.