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Chemical and biological extraction of metals present in E waste: A hybrid technology
Abstract
Management of metal pollution associated with E-waste is widespread across the globe. Currently used techniques for the extraction of metals from E-waste by using either chemical or biological leaching have their own limitations. Chemical leaching is much rapid and efficient but has its own environmental consequences, even the future prospects of associated nanoremediation are also uncertain. Biological leaching on the other hand is comparatively a cost effective technique but at the same moment it is time consuming and the complete recovery of the metal, alone by biological leaching is not possible in most of the cases. The current review addresses the individual issues related to chemical and biological extraction techniques and proposes a hybrid-methodology which incorporates both, along with safer chemicals and compatible microbes for better and efficient extraction of metals from the E-waste.
... Traditional metallurgical processes, i.e., pyro-and hydro-metallurgy are energy extensive, expensive, and release secondary contaminants (Arya and Kumar, 2020;Dutta et al., 2023;Pant et al., 2012). Therefore, in recent years, more research has been reported on the biometallurgy, and application of biocatalysts, such as microbes and enzymes to bioleach metals from WPCBs to address the shortcomings of the traditional techniques (Priya and Hait, 2017;Hait, 2021a, 2021b). ...
... Therefore, in recent years, more research has been reported on the biometallurgy, and application of biocatalysts, such as microbes and enzymes to bioleach metals from WPCBs to address the shortcomings of the traditional techniques (Priya and Hait, 2017;Hait, 2021a, 2021b). Mainly three microbial groups comprising both autotrophic and heterotrophic bacteria and fungi have shown efficient metal bioleaching from WPCBs (Pant et al., 2012;Priya and Hait, 2017, 2018b, 2020. Metabolites secreted by these microorganisms have been widely used for metal leaching from solid substrates (Santhiya and Ting, 2005). ...
... and Penicillium spp. are employed to solubilize metals from solid matrices like WPCBs through contact and noncontact bioleaching mechanisms by using thiosulphate and polysulfide pathways (Pant et al., 2012;Priya and Hait, 2017, 2018b, 2020Trivedi et al., 2022). Though bacteria are able to mobilize metals efficiently, fungi have shown several advantages over other microorganisms, which include a shorter lag phase and a greater tolerance for toxic metals. ...
... Thus, the techniques for separating materials from electrical and electronic waste can be based on an objective or a specific separation. In their study, Pant et al. (2012), reported the extraction of metals from e-waste by physical and biological extraction and proposed a hybrid method that gives higher efficiency to the separation of metals from plastics in ewaste. Hsu et al. (2019) researched and highlighted aspects of the separation and recovery of metals from electronic waste. ...
... The hybrid methodology, which combines many technologies, is a more effective and efficient way to recover metals from e-waste (Pant et al., 2012). This technique offers a higher extraction efficiency and needs less time. ...
... This technique offers a higher extraction efficiency and needs less time. This method may offer a fresh and developing field of metallurgy that could make it easier to remove metals existing in trace amounts from their ores (Pant et al., 2012). Although if biological leaching is a practical way for cost effectiveness, total metal extraction using purely biological methods is occasionally difficult and time-consuming (Ren et al., 2009). ...
The production of electrical and electronic equipment has increased significantly in recent years because of an increase in consumer demand, yet their life expectancies have shortened as a result of the rapid advancement of technology. As a result, a significant amount of electronic waste (or "e-waste") is generated every day. Most of these wastes are made up of materials that, if managed improperly, can affect the habitats in which they are placed as well as implicitly the species that inhabit those environments. These wastes typically include refractory oxides, polymers, and metals. If correctly separated and recovered, these materials can have significant economic value. In this study, the primary methods for separating and extracting valuable elements from electrical and electronic trash were evaluated, and the efficiency of these techniques was evaluated in terms of removing the waste. Processes like pyrometallurgical, hydrometallurgical, pyro-physical, and biological have been analysed.
... Te rapid development of electrical and electronic equipment use and its fast obsolescence due to rapid technical innovation lead to the generation of massive volumes of electronic waste (e-waste) globally [1]. Rapid economic expansion and increased transboundary fows of secondary materials will necessitate 3R (reduce, reuse, and recycle) activities [2]. E-waste is becoming a global concern as a result of informal recycling and reuse activities, particularly in poor nations. ...
... From literature studies, leaching by Acidithiobacillus ferrooxidans [4] and Acidithiobacillus thiooxidans [2,[5][6][7][8][9][10][11][12][13] was found to be extremely successful. A broad range of heterotrophic [14], chemolithotrophic [15], and hemophilic [16] bacteria and fungi [6,17] have been tested for basic metal mobilization, including Cu, Zn, Fe, and Ni [2,18,19]. ...
... From literature studies, leaching by Acidithiobacillus ferrooxidans [4] and Acidithiobacillus thiooxidans [2,[5][6][7][8][9][10][11][12][13] was found to be extremely successful. A broad range of heterotrophic [14], chemolithotrophic [15], and hemophilic [16] bacteria and fungi [6,17] have been tested for basic metal mobilization, including Cu, Zn, Fe, and Ni [2,18,19]. Sulfur-oxidizing bacteria are the most important microorganisms for heavy metal degradation [20,21]. Tis is because iron chemolithotrophy oxidizes iron and sulfur chemolithotrophy oxidizes sulfur. ...
Electronic garbage is one of the fastest-growing waste streams. Its disposal and appropriate management are a worldwide concern. Printed circuit boards (PCBs) are critical components in contemporary electronic gadgets that contain toxic elements. Bioprocessing of PCBs for metal recovery employing microbial methods has evolved as a green solution in metallurgical operations. Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans were used in this study to leach metals from powdered waste PCBs. The RSM is used for optimizing the leaching conditions. The optimal conditions obtained were a bacterial activation period of 28 days, a pulp density of 23 g/L, and a temperature of 31°C. A confirmatory experiment under these optimal circumstances yielded recovery rates of Cu²⁺, Sn²⁺, Pb²⁺, and Zn²⁺ of 95.62%, 96.27%, 95.6%, and 98.25%, respectively.
... The WPCBs used in this study were manually dismantled and cut up into smaller pieces of varying sizes, whereas in most e-waste composition related research the e-waste PCBS would be milled before being assessed for the metal composition leached. This is done to ensure that the surface area of all components can be considered identical, and a more accurate depiction of metals leached can be seen (Pant et al. 2012;Petter et al. 2014;Zhou et al. 2019). ...
... The metals highest in bioavailability, namely: Ni, Ba, Zn, Li, Fe, Al and Cu are all classified as common base metals elements that oxidise and corrode easily (Pant et al. 2012). According to Torres et al. (2018), effective metal leaching is dependent on several factors, such as the concentration of the leaching medium (pH), the temperature, and the solubility of the reaction productsin this case, the e-waste WPCBs. ...
... The WPCBs used in this study were manually dismantled and cut up into smaller pieces of varying sizes, whereas in most e-waste composition related research the e-waste PCBS would be milled before being assessed for the metal composition leached. This is done to ensure that the surface area of all components can be considered identical, and a more accurate depiction of metals leached can be seen (Pant et al. 2012;Petter et al. 2014;Zhou et al. 2019). ...
... The metals highest in bioavailability, namely: Ni, Ba, Zn, Li, Fe, Al and Cu are all classified as common base metals elements that oxidise and corrode easily (Pant et al. 2012). According to Torres et al. (2018), effective metal leaching is dependent on several factors, such as the concentration of the leaching medium (pH), the temperature, and the solubility of the reaction productsin this case, the e-waste WPCBs. ...
Electronic waste (e-waste) has been identified as an emerging pollutant and is the fastest growing waste stream at the present time. Significant technological development and modernization within the last decade has led to the rapid accumulation of outdated, broken and unwanted electrical and electronic equipment (EEE). Electronic products mainly consist of a range of metal containing components that, when disposed of improperly, could result in metal constituents leached into the environment and posing a health risk to humans and animals alike. Metal exposure can induce oxidative stress in organisms, which could lead to synergistic, antagonistic and additive effects. The metals found highest in abundance in the simulated e-waste leachate, were nickel (Ni), barium (Ba), zinc (Zn), lithium (Li), iron (Fe), aluminium (Al) and copper (Cu). An acute exposure study was conducted over a 96 h period to determine the potential toxicity of e-waste on the test organism Danio rerio. Biomarker analysis results to assess the biochemical and physiological effects induced by e-waste leachate, showed a statistically significant effect induced on acetylcholinesterase activity, superoxide dismutase, catalase activity, reduced glutathione content, glutathione s-transferase, malondialdehyde and glucose energy available. The Integrated Biomarker Response (IBRv2) analysis revealed a greater biomarker response induced as the exposure concentration of e-waste leachate increased.
... Patil and Ramakrishna (2020) provided a comprehensive analysis of global e-waste legislation, assessing the strengths and weaknesses of various legislation worldwide. Furthermore, researchers such as Pant et al. (2012), Jujun et al. (2014), and Sanito et al. (2021) conducted experimental analyses of specific e-waste recycling technologies. In the field of business management, increased research has been conducted on how companies view and implement reverse logistics for e-waste products (e.g., Ding & Lee, 2022;Kumar Singh et al., 2022;Truc Doan et al., 2018). ...
... Their study, which conf ir med the effectiveness of reverse e-waste logistics, focused primarily on the business perspective and overlooked the crucial role of consumers. Many studies have focused on the development of improved recycling technologies (e.g., Jujun et al., 2014;Pant et al., 2012;Sanito et al., 2021) or from a governmental point of view on the relevant legal system (e.g., Lepawsky, 2012;Patil & Ramakrishna, 2020). The implementation ...
Purpose - This study extends the theory of planned behavior from a consumer perspective to investigate consumer willingness and behavior in electronic waste products reverse logistics, along with the underlying influencing factors. Design/Methodology/Approach - Based on existing research, this paper has developed a model and hypotheses regarding consumer intentions to participate in electronic waste products reverse logistics and the influencing factors. Subsequently, this study conducted a survey of 355 Chinese consumers aged 20-50 years and used SmartPLS to analyze the relevant data for hypothesis validation. Findings - Results show that consumers’ green attitudes and green subjective norms have a positive impact on their willingness to participate in electronic waste products reverse logistics. And perceived behavioral control only exerts a positive influence on their participatory behavior. On the other hand, concerns about privacy breaches often hinder their willingness and behavior to participate. Moreover, the findings also indicate that consumers’ willingness to participate positively influences their actual participation behavior. Research Implications - This study predominantly examines the positive and negative subjective factors influencing consumers’ intentions and behaviors in participating in reverse logistics for electronic waste products. Based on the findings, we suggest fostering consumer awareness of electronic waste through various channels, including social media, and maintaining ongoing promotional campaigns to enhance environmental awareness and consumer engagement. Additionally, relevant firms should bolster consumer privacy protection, while the government should enhance regulatory oversight and introduce incentive policies to encourage businesses to increase investments in information security, thereby boosting consumer confidence in participation.
... Ewaste involves about half of iron and steel followed by plastics (21%), non-ferrous metals (13%) and different constituents. Non-ferrous metals comprise of exact metals like copper (Cu), aluminum (Al) and valuable metals, for example silver (Ag), gold (Au), platinum, palladium, and so on [10]. Past skirt amounts of components like lead, mercury, arsenic, cadmium, selenium and hexavalent chromium and fire retardants of e-waste groups as perilous waste [11]. ...
... As a result, a more environmentally friendly process for recovering valuable metals from e-waste is required. In the upgrading and refining stages of the recycling process, hydrometallurgical processes are applied [10][11][12]. ...
As we are well acquainted with the world continue to sprint down the path of digital marketing which consists of business processes, exchange of information, and consumer interaction. Similarly, in the name of prison reforms almost all the prisons of India had persisted in earlier traditional means and methods for reformation and rehabilitation of prisoners behind the bar, whereas in the 20 th century, digital marketing drastically came to the pinnacle as a matter of irrefutable empirical evidence, specifically in the era of globalization, industrialization, and privatization. Now we have various resources which underpin advertisements of the product manufactured by the prison manufacturing units through the help of digital marketing, wherein the various skilled prisoners had been working continuously to produce multipronged goods which have great economic significance in the market.
... Unlike the pyrometallurgical method, leaching is the first step in the recovery of metals in the traditional hydrometallurgical process, and it is carried out using appropriate chemical lixiviants to dissolve the metallic fractions in E-waste [9,35,36]. Acid or alkaline solutions such as sulfuric acid, nitric acid, and aqua regia are commonly used as lixiviants or leaching reagents [37][38][39]. These solutions can solubilise the solid matrix of E-waste and liberate the metals in the solution phase. ...
... It is to ensure a better leaching process. Besides that, ligands such as ethylene diaminetetramaide (EDTA), diethylenetriaminepenta acetate (DTPA), and other chelators such as oxalate and citric acid also usually employed in the hydrometallurgical processes for efficient metal recovery [39]. ...
With rapid technological advancement, the life span of electronic devices has become increasingly short, contributing to massive electronic waste (E-waste) and demanding sustainable management. E-waste contains precious metals like gold (Au) many fold higher than natural mining ores. However, the current techniques of recycling are not efficient. Methods like pyrometallurgy and hydrometallurgy not only require higher energy expenditure but also lead to environmental pollution, hence necessitating an alternative greener technology. In line with that, metal leaching using microorganisms is gaining popularity, and Chromobacterium violaceum has been considered a promising candidate. However, the heterogeneity of culture technique and abiotic condition variations have been a perceived challenge in priming C. violaceum as an Au bioleacher for upscaled industrial
applications. Thus, the current review discusses what makes C. violaceum an excellent candidate for Au bioleaching and how to overcome the challenges associated with the application. This review will significantly enhance the current understanding of C. violaceum as an Au bioleaching agent, hence addressing the existing knowledge gaps.
... As a result, the development of a new technology for the recovery of metals from e-waste is urgently needed to improve the added value of the waste materials. Various methods, including mechanical separation, pyrometallurgical, and hydrometallurgical processes, are employed for the removal of metals from ewaste [16][17][18]. However, these techniques are characterized by environmental hazards, high operational costs, high metals loss, and the release of secondary by-products, as well as the consumption of huge amounts of energy and chemicals [19][20][21]. ...
... As a result, the development of a new technology for the recovery of metals from e-waste is urgently needed to improve the added value of the waste materials. Various methods, including mechanical separation, pyrometallurgical, and hydrometallurgical processes, are employed for the removal of metals from e-waste [16][17][18]. However, these techniques are characterized by environmental hazards, high operational costs, high metals loss, and the release of secondary by-products, as well as the consumption of huge amounts of energy and chemicals [19][20][21]. ...
The rapid and improper disposal of electronic waste (e-waste) has become an issue of great concern, resulting in serious threats to the environment and public health. In addition, e-waste is heterogenous in nature, consisting of a variety of valuable metals in large quantities, hence the need for the development of a promising technology to ameliorate environmental hazards associated with the indiscriminate dumping of e-waste, and for the recovery of metal components present in waste materials, thus promoting e-waste management and reuse. Various physico-chemical techniques including hydrometallurgy and pyrometallurgy have been employed in the past for the mobilization of metals from e-waste. However, these approaches have proven to be inept due to high operational costs linked to the consumption of huge amounts of chemicals and energy, together with high metal loss and the release of secondary byproducts. An alternative method to avert the above-mentioned limitations is the adoption of microorganisms (bioleaching) as an efficient, cost-effective, eco-friendly, and sustainable technology for the solubilization of metals from e-waste. Metal recovery from e-waste is influenced by microbiological, physico-chemical, and mineralogical parameters. This review, therefore, provides insights into strategies or pathways used by microorganisms for the recovery of metals from e-waste.
... Hybrid processes as shown in Fig. 6 combine multiple environmentally friendly techniques to optimize metal extraction [25]- [28]. For example, integrating bioleaching with ion exchange or coupling ionic liquids with supercritical fluid extraction can enhance metal recovery rates and reduce the overall environmental impact. ...
The realm of extractive metallurgy, a cornerstone for diverse industrial applications, has traditionally grappled with environmental challenges stemming from conventional extraction methods. This thorough literature review delves into the realm of innovative green approaches within extractive metallurgy, with the overarching goal of synthesizing sustainable practices. The introduction casts a spotlight on the environmental quandaries associated with traditional metallurgical practices, underscoring the imperative for ecologically friendly alternatives. The research methodology meticulously entails a comprehensive review of peer-reviewed literature, applying stringent criteria to handpick studies that delve into sustainable metallurgical practices. The results and discussion section intricately categorizes and dissects an array of green approaches in metal extraction, including bioleaching, ionic liquids, supercritical fluid extraction, green hydrometallurgy, electrochemical methods, and hybrid processes, providing nuanced insights into their efficacy and sustainability. Through the lens of case studies, the study sheds light on recent strides made by industries that have wholeheartedly embraced these sustainable practices, with a keen focus on unraveling their consequential environmental and economic impacts. Moreover, the study conscientiously addresses the challenges encountered in the adoption of green metallurgy and adeptly identifies latent opportunities for further development in this transformative field. The findings resonate with a resounding call for the widespread adoption of sustainable practices within extractive metallurgy, emphasizing their profound implications for both industrial application and the trajectory of future research endeavors. This expanded exploration underscores the pivotal role of environmentally conscious approaches in reshaping the landscape of extractive metallurgy, paving the way for a more sustainable and responsible future.
... Metals are frequently extracted by microorganisms from the sulfide-and/ or iron-containing ores and mineral concentrate. The insoluble metal sulfides of copper, nickel and zinc are converted by microbial oxidation of iron and sulphur to ferric ions and sulphuric acid, which then make the soluble metal sulfates that are easily recoverable from the solution (Pant et al., 2012). Acidolysis, complexolysis, redoxolysis and bioaccumulation are the common mechanisms involved in bioleaching (Bosshard et al., 1996). ...
... En la última década la atención se ha centrado en los procesos acuosos, los cuales representan una opción prometedora debido a los relativos bajos costos de capital, reducidos impactos ambientales, potencial para recuperaciones altas de metales, y son métodos adecuados para su aplicación a pequeña escala [1]. Las principales propuestas consisten en lixiviaciones usando agua regia, cianuro, tiosulfato, tiourea o haluros [4], [10], [11]. Para la extracción de cobre se han estudiado diferentes procesos en solución acuosa empleando ácido sulfúrico [12], cloro [11], [13], [14], ácido nítrico y extracción por solventes [9], [15], soluciones de amonio-sulfato [16], [17], con recuperaciones de cobre superiores al 71 % . ...
Se propone una metodología de recuperación de cobre a partir residuos de tarjetas de circuitos impresos (TCI), como un primer aporte a un proceso de reciclaje completo de los residuos electrónicos. El proceso consistió en una reducción de tamaño y clasificación, separación magnética y electrostática, lixiviación con ácido sulfúrico y electroobtención de cobre. La metodología se desarrolló a nivel de laboratorio, obteniendo concentrados con 63 % y 58 % de cobre para las fracciones de tamaño 0.3 mm < T2 < 0.8 mm y 0.8 mm < T3 < 2.0 mm respectivamente, con una recuperación promedio del 79 %. Se recuperó cobre con una pureza superior al 99 %.
... La implementación de métodos no convencionales de bajo impacto ambiental, para la recuperación de metales preciosos provenientes de residuos eléctricos y electrónicos, es un tema importante a considerar, debido al aumento desmedido en la generación de estos residuos y a la carencia de métodos ecológicamente seguros que permitan la recuperación y aprovechamiento de metales preciosos como el oro, ampliamente utilizado para la fabricación de aparatos eléctricos y electrónicos [1]. En la actualidad, los métodos pirometalúrgicos [2] e hidrometalúrgicos [3] tienen una gran demanda y aplicabilidad para la recuperación de estos metales, sin embargo su implementación está asociada con severos daños ambientales [4] ocasionados por la formación de dioxinas y furanos en el proceso de fundición de los residuos y por el uso indiscriminado de agentes de lixiviación de alto impacto ambiental, como el ácido sulfúrico [5], ácido clorhídrico [6], agua regia [7], peróxido de hidrógeno [8], cloruro férrico [9], cianuros, haluros, tiourea y tiosulfatos [10]. En consecuencia, es vital conocer los procesos de bajo impacto ambiental existentes, como alternativas para la recuperación de metales preciosos no lixiviados a partir de residuos eléctricos y electrónicos, con el objetivo de desarrollar nuevos métodos de recuperación viables que puedan ser implementados en la industria colombiana. ...
Este trabajo presenta la revisión de dos métodos no convencionales que utilizan técnicas de oxidación selectiva con persulfato de potasio (K2S2O8) y cloruro cúprico (CuCl2) como reactivos de bajo impacto ambiental, para la recuperación de oro no lixiviado a partir de residuos eléctricos y electrónicos. Los métodos son comparados en términos de eficiencia y disminución de impacto ambiental, y se selecciona el persulfato de potasio para evaluar su comportamiento sobre puntos metálicos de inserción provenientes de residuos eléctricos y electrónicos del sector telecomunicaciones, desarrollando un nuevo procedimiento experimental cuyos resultados son presentados en este trabajo.
... Approximately 40 million metric tons of E-waste are generated worldwide, which constitutes 5% of the total solid waste all over the world (Islam et al., 2020). Moreover, almost 50%À80% of this global E-waste is exported to developing countries wherein improper management and disposal techniques are a threat to public health (Pant et al., 2012). The composition of E-waste has a wide presence of metals, plastics, concrete, ceramic, and rubber along with a multitude of other materials. ...
Large scale technoindustrial development has transformed the entire world with extensive application of electronic appliances on a daily basis. However, the increase in general use of electronic devices has also led to an inevitable rise in electronic waste (E-waste) generation that is primarily composed of high amounts of toxic and valuable metals such as copper (Cu), gold (Au), silver (Ag), aluminum (Al), iron (Fe), zinc (Zn), and nickel (Ni). Several potential risks of E-waste have been reported that can adversely affect human health and environment. With such a rapid rise in global E-waste production, it is imperative to investigate metal recovery methods from E-waste that are innovative, cost-effective, environmentally friendly, and rapid. Microbe-assisted metal recovery is a promising method that is discussed in detail in this chapter. Biohydrometallurgy primarily involves the utilization of microorganisms in the effective dissolution of metals from waste materials. Several bacterial strains such as Acidithiobacillus ferrooxidans, Acinetobacter sp., Chromobacterium violaceum, Magnetospirillum sp., Pseudomonas fluorescens, Sulfobacillus thermosulfidooxidans, and others can effectively recover metals such as Cu, Au, Ni, Zn, Al, and Fe. Additionally, certain cyanogenic bacteria are also explored for enhanced dissolution and extraction of heavy metals from electronic scraps. Hence, bioleaching of industrially important metals from E-waste using bacteria is a sustainable approach for bioremediation as well as for effective metal recovery at an industrial scale.
... More literatures related to HDS technique were studied by authors (Hensen et al., 2003;Hussain et al., 2013;Sadare et al., 2017;Bose, 2015). To overcome on these obstacles, Non-HDS techniques can be used such as Adsorptive (Miao et al., 2015;Zhou et al., 2009;Yang et al., 2003;Jiang et al., 2003;Ahmed and Ahmaruzzaman, 2015), extraction (Pant et al., 2012;Shiraishi et al., 2002), Biological (Dinamarca et al., 2010;Davoodi-Dehaghani et al., 2010;Bhasarkar et al., 2015;Borzenkova et al., 2013) and oxidative (Dai et al., 2008;Figueras, 2004;Hiba Ramadam Mohammed, 2021;Ghazwan et al., 2018;Amer, 2015;Kareem, 2021;Bakar et al., 2012;Wadood et al., 2015), and electrochemical desulfurization (Tavan et al., 2020) have been suggested using various catalysts such as zeolite (Hmood et al., 2024), activated carbon (Mohammed et al., 2023b;Abdulqader et al., 2023, June;Ahmed Alwaise et al., 2023;Gheni et al., 2024). Among these techniques electrochemical-oxidation or reduction have been attracted more attention due to more advantages than others such as low temperature and pressure which make the process friendly and less energy consumption . ...
... Ghosh et al., 2015;Nshizirungu et al., 2020;Roy et al., 2021). Furthermore, exposure to such metals through food and water beyond their permissible limit may cause several health issues, such as cancer, acute kidney failure, and respiratory diseases (Needhidasan et al., 2014;Pant et al., 2012). Therefore, an ecofriendly and economical metal removal recycling and recovery approach is needed to extract valuable metals from spent batteries. ...
This study presents the bio-extraction and mineralization properties of 5 different Magnetotactic bacteria (MTB) to extract valuable metals from spent Li-ion and Ni-Cd batteries. The powdered spent batteries were incorporated for particle size, FTIR, XRD, and XRF analysis. Further, MTB (1 × 10⁷CFUs/ml) was treated individually with the powdered battery sample, and the bioabsorption results showcased the successful removal of lead (98%), nickel (90%), cadmium (97%), zinc (100%), and lead/cadmium (33%) from MSR1, RJS2, RJS5, RJS6, and RJS7, respectively. In addition, the MAG1 consortium treatment effectively removed cadmium (98.5%) and lead (60%). Also, the MAG2 consortium treatment removed cadmium (100%), followed by copper (67%). Similarly, MTB treated with Ni-Cd battery showed the strains RJS5 and MSR1 removed 60% and 66% of cadmium; furthermore, RJS2 and RJS6 removed 72% and 71.4% nickel, respectively. Finally, the RJS7 strain removed 100% lead and 75% cadmium. However, the Ni-Cd battery treated with MAG1 showed effective removal of 67.07% copper and 65% cadmium. Similarly, the MAG2 consortium removed 87% lead and 71% cadmium. The final SEM-EDX and XRF analysis on the Li-ion batteries showed that the RJS2 and RJS5 strains removed zinc and lead effectively. Also, the RJS5 and RJS7 strains treated with the Ni-Cd battery showed better removal of lead and manganese, respectively. This is the first report on the Magnetotactic bacteria to be used for the bio-extraction of valuable metals from spent battery waste.
... Lead in CRTs is found in the funnel and neck components, and concentrated in the neck glass (Pant and Singh, 2013). The role of lead is absorbing UV and X-ray radiation produced by the CRT (Pant et al. 2012). ...
The use of Cathode Ray Tube (CRT) glass as an aggregate in concrete is a promising approach for sustainable construction. The CRT technology, once innovative, is now obsolete, leading to the accumulation of millions of CR tubes globally, posing disposal challenges due to their toxic composition. The CRT glass, consisting mainly of silica along with various oxides and heavy metals, holds potential for recycling and reuse applications. Recycling methods for CRT glass, including closed-loop and open-loop recycling, offer avenues to mitigate waste and conserve resources. Integrating CRT glass into concrete improves mechanical properties and durability. Although replacing natural sand with CRT glass may slightly reduce compressive strength, innovative mix designs offset this effect. Concrete with CRT glass exhibits resistance to environmental factors, making it suitable for diverse construction applications. Addressing environmental concerns related to CRT glass disposal requires efficient recycling technologies and stringent regulations. Overall, integrating CRT glass into concrete presents a sustainable solution to mitigate environmental impacts while enhancing concrete performance.
... Enquanto que, nas técnicas mais verde, estão a lixiviação com ligantes, utilizando EDTA (ácido etilenodiaminotetra-acético), sais de DTPA (dietilenotriaminopenta-acetato de pentassódio, complexante alcalino), sais de oxalato e citrato; gravação com FeCl 2 , CuCl 2 , HCl e solventes orgânicos; e a biolixiviação, com utilização de micro-organismos. 10,30,32 A Figura 10 destaca os vários ramos da hidrometalurgia e os principais agentes de lixiviação utilizados para extração de metais de resíduos de PCI. ...
... Metal separation is one necessary step. The separation technology is mainly divided into solvent extraction, chemical precipitation, ion exchange, electrodeposition etc [21][22][23][24]. Solvent extraction method mainly uses extractant to selectively leach certain metal in leaching solution. ...
The recycling of key components in waste lithium-ion batteries (LIBs) is an important route to make up for the shortage of battery materials. Metal separation and purification is an important step. It is of great significance to propose an efficient and green separation technology. In this paper, an electrochemical precipitation method was applied to metal separation from spent LiNi0.5Mn1.5O4 cathode material. The Li and metal elements were effective separated and the precipitates were then used as precursor to synthesize high-performance R–O3-NaNFM cathode material for sodium-ion batteries. The R–O3-NaNFM exhibits excellent electrochemical cycling stability. The capacity retains 71.3 mAh g⁻¹ after a long-term cycling of 200 times at 1 C. This method offers a referable strategy of the recycling for the waste cathode material in spent LIBs.
... The HDS technique is costly and an efficient method for some of the sulfur compounds such as thiophenes and their derivatives. However, looking for alternatives techniques are needed such as adsorptive desulfurization (ADS) [9][10][11][12][13], biological desulfurization (BDS) [14][15][16][17], extraction desulfurization (EDS), [18,19], oxidative desulfurization (ODS) [20][21][22][23][24][25][26] chemical desulfurization (CDS), [27][28][29]. The ODS technique has recently attracted significant interest as a promising technology for the deep desulfurization of refinery products [30,31]. ...
... Therefore, other methods to reduce costs, save energy and reach a sulfur content of fewer than 50 ppm, such as extractive desulfurization (EDS) [12], bio desulfurization (BDS) [13], absorptive desulfurization (ADS) [14] and oxidative desulfurization (ODS) [15][16][17] were developed. ODS has been considered amongst these methods due to its moderate operating conditions, lack of hydrogen consumption, cost-effectiveness, and high efficiency [18]. ...
... BES system includes microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) which are highly efficient for metals recovery and removal, respectively [128]. In BES, bacteria transport electrons through extracellular electron transport (EET) mechanisms viz., direct contact, electron-shuttle, and conductive pili mediated [129]. There are several applications of improved BES like removal and recovery of metals, production of value-added chemicals, desalination, biosensors, sediment bioremediation, and degradation of persistent pollutants [130,131]. ...
... Moreover, the current gaps in e-waste legislation have enabled many developing nations i.e., Bangladesh, Bhutan, Indonesia, Kenya, Malaysia, Nigeria, Philippines, Sri Lanka and South Africa to import e-waste without any proper policy for its management [35,46]. About 50-80% of the global e-waste is being exported to developing countries, especially Asian and African nations for recycling [48], in contrast to their individual low e-waste collection rates of 15% and 0%, respectively [49]. ...
E-waste, also known as waste from electrical and electronic equipment, is a solid waste that accumulates quickly due to high demand driven by the market for replacing newer electrical and electronic products. The global e-waste generation is estimated to be between 53.6 million tons, and it is increasing by 3–5% per year. Metals make-up approximately 30% of e-waste, which contains precious elements Au, Ag, Cu, Pt, and other high-value elements, valued at USD 57 billion, which is driving the e-waste recycling industry. It is noteworthy that the recycling of precious elements from e-waste has emerged as a profitable enterprise in several parts of developing nations. E-waste contains 50–100 times higher levels of precious metals compared to natural ores, making it suitable for mining. E-waste recycling in developing nations, mostly occurs through the informal sector comprising manual collection, crushing, segregation and selling of precious elements, such as Au, Ag, Cu, Pb, Pt, and other rare elements (Nd, In, and Ga). The organized sector, on the other hand, mostly employs mechano-chemical methods, such as pyrometallurgy, hydrometallurgy, and bio-hydrometallurgy, which have serious environmental consequences. Both the informal and formal sectors of e-waste processing lead to the leaching of toxic elements into groundwater and soils. Owing to the lesser efficiency of greener technologies, such as phytoremediation and bioremediation, their use in precious metal extraction is very limited. However, this review explores several hyper-accumulating and tolerant plants viz. Brassica juncea and Berkheya coddii, which holds great potential in phytomining of precious metal from e-waste. Thus, the state of the art in precious metal extraction from e-waste as well as the advantages and disadvantages of different metal extraction technologies has been reviewed.
... Exposure to these e-wastes could cause health hazards such as changes in functioning of thyroid , neonatal complications such as sudden abortions, still births and preterm births, etc. (Grant et al., 2013). Electric and electronic waste can be treacherous if the elements like Pb, Hg, As, Cd, Se, Cr(VI) and flame retardants are present beyond allowable quantities (Pant et al., 2012). ...
After the computer and mobile revolution, electric and electronic waste had become a serious threat to urban and rural communities equally. Prevention of the hazardous exposure and proper management are challenging in developing nations. One way to turn the crisis to opportunity is to extract metals from this Waste Electronic and Electric Equipment (WEEE) is making waste into a source of metal ores. The involvement of microbes in this technology could increase the boons by being an eco-friendly technique for reducing the hazardous nature. This article reviews the mechanisms involved in the process of bioleaching, the microorganisms employed, methods used and various developments as well as limitations along with recent advances and future prospects of the process of bioleaching of metals from WEEE.
The world stands on the brink of an electronics waste (e-waste) revolution, fueled by a drive for sustainability
and technological advancement. In 2022, an astonishing 62 billion kilograms of e-waste were generated globally,
averaging 7.8 kg per person. Yet, only 22.3 % of this massive amount was responsibly recycled. Since 2010, ewaste
production has surged at nearly five times the rate of collection and recycling efforts. With more electronic
devices being discarded, it’s crucial to harness this vast resource effectively. The article dives deep into the core
of this revolution and lays out a roadmap for future progress. It tracks the evolution of e-waste recycling from its
infancy to today’s sophisticated methods. Numerous challenges, like identifying toxic chemicals and dwindling
resources, highlight the pressing need for action. This article provides a review on the development of e-waste
recycling technologies with special emphasis on the nature of mechatronic system and sensor-based automation
in improving the efficiency of the recycling technology. Some of the strategies that have been discussed include
the employ of cyber physical system (CPS) for real-time monitoring, robotic sorting that provides accurate
sorting of materials, and sensor network for detecting risky components. Special attention is paid to such aspects
as scalability and sustainability and how mechatronics can create value in accordance with circular economy and
contribute to the reduction of e-waste while aiming at net-zero emissions.
With rapid population growth, as well as, technological advancement, the generation of e-wastes is increasing day by day and has become a fact of emergent concern for scientific and research communities worldwide. Though the most developed territories generate the highest amount of e-wastes, little efforts has been put towards managing them. European countries, including United Kingdom, Germany, and France are managing significant amount of e-wastes responsibly. The informal and unscientific management of e-wastes led to severe health and environmental hazards. The traditional waste management methods, such as, landfilling, and incineration expels significant amount of heavy and toxic chemicals to the environment, leading to severe air, water, and soil pollution. However, proper management strategies for e-wastes not only inhibit the associated harmful effect towards the lives on earth, but also favor circular economy. The sustainability of the strategies for managing e-wastes lie in the responsibility of all stakeholders associated with it. In this review, we have discussed the statistics of global of e-wastes generation and recycling, effect of e-wastes towards lives and the environment, different methodologies of managing e-wastes, and strategies for sustainable e-waste management.
One of the major negative environmental implications of economic growth and the advancement of information technology is the large quantity of electronic waste dumped in landfills. Cathode ray tubes (CRTs) from outdated televisions and computer monitors are a significant source of electrical waste. The CRT funnel primarily consists of silica, significant alkalis (Na 2 O‐K 2 O), and heavy metals like barium‐strontium, along with a substantial lead (Pb) content that may contaminate the soil. Owing to its heavy metal content, CRT is considered hazardous waste, and regulations require its glass to be recycled or repurposed instead of landfill disposal. The low pozzolanic activity of CRT silica suggests that its high content, when paired with an optimized particle size and specific curing conditions, can enhance the mechanical properties of cement‐based products. Hydrothermal treatment has been found to speed up both the hydration of ordinary Portland cement (OPC) and the pozzolanic reactions. Since the main objective was to safely recycle large amounts of CRT, three mixes were proposed with 10%, 20%, and 30% OPC + 90%, 80%, and 70% CRT, respectively, and the effect of hydrothermal curing conditions on mechanical properties and durability of these blends was investigated. CRT‐70, a blend containing 70% CRT glass waste, showed enhanced strength due to the formation of zeolitic phases and calcium silicate hydrate (CSH). These phases also provided CRT‐70 with notable fire resistance, ensuring its structural stability under elevated temperatures. These results demonstrate the possibility of production of precast building products via high‐volume recycling of hazardous CRT waste.
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.
E-waste, also referred to as electronic waste, is a term used to describe discarded or obsolete electronic devices and equipment. It includes a wide range of electronic items such as computers, laptops, smartphones, televisions, printers, cameras, and other consumer electronics. E-waste also encompasses electronic components, circuit boards, cables, and accessories. The proliferation of technology and rapid advancement in electronic devices has led to a significant surge in global e-waste production. The constant evolution of electronic products, driven by technological progress, results in their frequent replacement, raising valid environmental concerns. The management and disposal of e-waste pose substantial environmental and health hazards. Hazardous elements like lead, mercury, cadmium, brominated flame retardants, and several others are present in various electronic devices. These hazardous components can leach into the soil, water, and air when e-waste is discarded in landfills or incinerated, causing ecological harm and posing risks to public health. In response to these challenges, numerous countries have enacted regulations and initiatives to foster responsible e-waste management. The core pillars of effective e-waste management involve recycling and proper disposal. Recycling processes for electronic devices encompass the recovery of valuable metals (such as gold, silver, and copper), polymers, and glass. These actions are pivotal in ensuring efficient e-waste management, mitigating environmental impact, and promoting sustainable practices. The extraction and processing of raw materials can be minimized by using these resources in the production of new electrical devices.
Additionally, some organizations and manufacturers have established e-waste collection programs and take-back initiatives to ensure the safe disposal of electronic devices. These initiatives strive to avert the deposition of e-waste in landfills and the illicit exportation of such waste to developing nations with lenient environmental standards. Additionally, endeavors are underway to enhance public consciousness regarding the significance of e-waste recycling, alongside advocating for the creation of electronic products characterized by prolonged usability and simplified recyclability. This includes encouraging manufacturers to adopt environmentally friendly practices, such as using fewer hazardous materials, designing products for easy disassembly and recycling, and providing repair options to extend the lifespan of electronic devices. In conclusion, e-waste refers to discarded electronic devices and equipment. Proper management, recycling, and responsible disposal of e-waste are crucial to minimize environmental damage and health risks associated with hazardous materials present in electronic devices. The notion of a circular economy presents a hopeful blueprint for tackling these predicaments and advocating for sustainable methodologies. Within this context, this chapter delves into the interconnection between e-waste and the circular economy, accentuating the conceivable advantages and pivotal factors entailed in executing a circular strategy for the management of electronic waste.
Electrical and electronic components, the silent orchestrators of our technological symphony, have been crucial for enabling societal advances. From the simple beginnings of vacuum tubes to the complex circuitry in today’s smartphones, the role and type of electronic components have continued to evolve. The components of electrical and electronic equipment once it has reached the end of its useful life as a product are called electronic waste (e-waste). The exponential growth of electronic devices has made e-waste management an important environmental issue. Improper disposal of e-waste to landfills has serious environmental consequences for the global ecosystem. The majority of discarded e-waste such as computers, mobile phones, televisions, printers, and so on, are embedded with printed circuit boards (PCBs), which are an essential and basic component. PCBs of e-waste contain many different metals including precious metals (Ag, Au, Pd, Pt, etc.), critical elements (Li, Ni, Ga, graphite, rare earth elements, etc.) and non-critical metals (Al and Fe) in varying percentages depending on the electronics. In the emerging era of circular economy recycling, waste printed circuit boards (wPCBs) of any e-waste are seen as an alternative to processing mining ores to meet future metals demand. Different recycling methods such as mechanical separation, pyrometallurgy, hydrometallurgy, biohydrometallurgy, pyrolysis, electrolysis and supercritical fluid technologies have been explored to extract the valuable metals from e-waste. This article aims to provide a critical review of the different recycling routes for e-waste, with a focus on the emerging supercritical fluid technologies (SFT), and their opportunities and challenges. This review will compare the emerging SFTs for existing processes used in industry and other alternative treatment methods. The specific areas of comparison include technical complexity and environmental impacts.
Graphical abstract
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.
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.
Among the emerging technologies for the decarbonization
of various energy sectors, electrolyzers for fuel production (power-to-X) and fuel cells for power generation (X-to-power) are the most modular, efficient, and low-cost technologies. Electrochemical technologies can be broadly classified into alkaline cells, proton exchange membrane cells, phosphoric acid fuel cell, molten carbonate cells and solid oxide cells, in short SOCs. SOCs offer higher efficiency and lower cost and are available in hundreds of kW scale stacks/modules. However, if commercialized and deployed at a large scale (GW), the quantities of materials required for solid oxide technologies can be a challenge. More importantly, such materials include rare earth elements (REEs) like lanthanum, yttrium, scandium, and other critical metals like cobalt and nickel. Thus, strategies and a long-term vision need to be developed at an early stage to (1) outline and implement recycling technologies to recover these metals from end of life (EOL) SOCs and (2) reduce the quantities used or find alternative materials to avoid usage of metals that are scarce. Although a lot of work has been directed toward synthesizing and testing alternative materials in recent times, the topic of recycling metals from SOCs has been paid little attention. This review discusses the global supply demand of REEs and critical metals used in state-of-the-art SOCs, and their projected demand if SOCs are deployed at GW scale in the next 20 years. This review also briefs the strategies being used for REE and critical metal recovery from other sources like e-waste, optical waste, and coal fly ash, and proposes how these techniques can be used for metal recycling from SOCs.
E-waste includes both base metals and precious metals. Traditional e-waste metal recovery processes, such as hydrometallurgical and pyrometallurgical operations, are rapid and effective, but they harm the environment and are not cost-effective. Due to the limitations of traditional procedures, a transition to bio-metallurgical processes including eco-friendly microbial leaching of metals from e-waste has occurred. Biological heavy metal remediation employs organisms such as diverse microbes, plants, and their derivatives or products as a gentle and ecologically acceptable approach of decontaminating the environment. Bioleaching is the process of extracting metals using either metabolic chemicals (indirect bioleaching) or microorganisms (direct bioleaching). This chapter discusses microorganism-based e-waste remediation, as well as processes and chembio engineering techniques that have previously been used in waste remediation and may be used in bioremediation. A discussion of technological breakthroughs that have permitted this study path, and how these technologies could be applied in future research, will also be included.
A method of recovering a precious metal from a sulphide mineral slurry which contains the precious metal which includes the steps of subjecting the slurry to a bioleaching process, supplying a feed gas which contains in excess of 21% oxygen by volume to the slurry, and recovering precious metal from a bioleach residue of the bioleaching process.
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.
The concept of microbiological leaching have played a greater role to recover valuable metals from various sulfide minerals or low grade ores during the middle era of twentieth century and that continued till the end of the century. Slowly, due to depletion of ore/minerals, and implementation of stricter environmental rules, microbiological leaching process has been shifted for its application to recover valuable metals from the different industrial wastes. Although there are conventional processes, physical and chemical methods, for treatment of industrial wastes, these technologies have certain limitation in practical applications. The microbial method is an efficient and cost-effective alternative to chemical and physical methods because of its low demand for energy, material and less generation of waste byproduct. There are several industrial wastes that possess toxic elements and thus when leached into atmosphere cause serious environmental problem. Among the wastes, spent petroleum catalysts, electronic scraps, lithium battery wastes, sewage sludge, fly ash etc. are some of the major industrially produced wastes. These solid wastes mostly contain Ni, V, Mo, Co, Cu, Pb, Zn, and Cr like heavy metals in it. The major microorganisms those play the significant role in recovery of heavy metals from such wastes belong to acidophilic group. These acidophilic groups thrive in acidic pH ranges (pH 2.0 – 4.0) and help in dissolving the metals from solid phase of wastes into the aqueous phase. Among the bacteria Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans, and Sulfolobus sp., are well known consortia for the bioleaching activity while Penicillium, and Aspergillus niger are some fungi those help in metal leaching process. The current chapter will be thoroughly studied about the application of these acidophilic microorganisms for the metal recovery from different industrial wastes. The key microorganisms and their bioleaching mechanism have been focused here.
This work constitutes the first part of activities being carried out within the context of beneficiation of valuable metals from a brand of spent mobile phones by leaching process in laboratory scale. The printed circuit board of the mobile phone was employed in this study. The effects of parameters such as acid concentration, particle size and temperature on the leaching efficiency at different time intervals were investigated. With 4M HCl solution about 87.4% was dissolved within 120 minutes at a temperature of 80 o C using 300rpm and a particle size of about 0.1mm. Finally, the results of this investigation showed that the rate of dissolution of the spent powdered cell phone was found to depend on the hydrogen ion concentration, the system temperature and particle diameter.
The production of EDDS (ethylene-diamine-disuccinic acid), a potential substitute for EDTA, has been optimized up to a product
concentration of 20 grams per litre in fermentations of Amycolatopsis orientalis. Decisive steps for the increase in productivity were variation of the synthetic medium composition, investigation of the
influence of metal ions on product formation, controlled feeding of carbon and nitrogen sources in fed-batch fermentations
and improvement of the downstream processing steps.
For the practical application of a three-phase bubble column as a reactor in the dehydration of ortho-boric acid, we investigated
the bubble distribution and its effects on the reaction in a three-phase bubble column reactor (0.102 m IDx2.0 m in height)
operating at relatively low pressure (below the atmospheric pressure). Effects of reaction time, temperature, gas velocity,
particle size and gas injection mode (even, wall-side, central and asymmetric distribution) on the fractional conversion of
the reaction were determined. The complicated bubble distribution as well as bubbling phenomena in the reactor were diagnosed
and interpreted by means of the attractor trajectories and correlation dimension which were obtained from the resultant pressure
fluctuations. The fractional conversion was closely related to the attractor shape or correlation dimension of the pressure
fluctuations in the reactor. The fractional conversion in the case of even distribution of gas injection exhibited the highest
value in all cases studied, at which the attractor of pressure fluctuations was less scattered in the phase space, while their
correlation dimension had the lowest value. When the gas was injected by means of wall-side distribution, the conversion level
was higher than that in case of central or asymmetric distribution mode. Although a fluid-solid heterogeneous reaction model
can be applicable to the reaction, deviations from the model become considerable when the gas injection mode changes from
even to wall-side, central or asymmetric mode, orderly.
Rapid economic growth in Asia and the increasing transboundary movement of secondary resources will increasingly require both
3R endeavors (reduce, reuse, recycle) in each country and appropriate control of international material cycles. Recently,
managing electrical and electronic waste (E-waste) has become an important target for domestic and international material
cycles from the viewpoints of environmental preservation and resource utilization efficiency. To understand the current status
of E-waste issues in the context of international material cycles and to discuss the future tasks related to achieving 3R
in the region, we organized the National Institute for Environmental Studies (NIES) E-waste Workshop in December 2004. This
article reviews past studies on E-waste and briefly describes the topics presented and discussions held at the workshop. The
topics at the workshop included E-waste generation, recycling systems, international trade, and environmental impacts. In
addition, we discussed various issues such as terminology, current environmental concerns, and possible solutions. Transboundary
shipments of E-waste should be conducted taking into consideration the concept of sustainable development. The direction of
future research and possible collaborations are also discussed.
Sensitive detection and efficient removal of an increasing number of persistent and emerging environmental pollutants are major challenges in our industrialized world. Now these challenges can be better answered by utilizing the advantages of nanotechnology in addition to traditional methods. Due to unique features of nanomaterials, such as size, surface area, adsorptivity, photoelectronic, and photocatalytic properties, they have emerged to be important materials in the analytical detection and remediation of environmental pollutants.
Much recent work in the field of biohydrometallurgy has been directed to the study of bio-oxidation of gold ores by acidophilic iron and sulfur oxidizing microorganisms. This work has been done worldwide and has resulted in several pilot plant and commercial scale operations for gold ore bio-oxidation. Bioleaching of gold by metabolic products of microorganisms has received less attention, but also offers opportunities for industrial application, especially if future regulations restrict the use of cyanide. This paper reviews recent progress in the use of microorganisms to oxidize the sulfidic matrix in refractory gold ores (bio-oxidation) and to solubilize elemental gold (bioleaching).
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
In Virtual Reality Interactive Systems, texture is one of the most important factors which affects the scene fidelity and the entire system resources. In this article, we talk about the texture making methods in constructing virtual reality interactive scene. We discuss the bake mapping technique, and make the comparison and analysis among different mapping methods to find the method that can get the best effect with limited resources. According to our study method, users can choose the most appropriate methods based on their needs to construct the virtual reality scenes effectively, and make more realistic effects with limited hardware and software resources.
The collection and management of waste electrical and electronic appliances around the world, and the possible negative environmental consequences have been an issue of current debate. Cathode ray tubes (CRTs) used as display screen for computer monitors and televisions contains large quantities of lead, estimated at between 0.5 and 4kg, depending on the size of the CRT and has been identified as the most polluting of all electronic waste components. Having failed the tests used in the toxicity characterization of solid wastes, CRTs have been declared ‘hazardous’ and subsequently banned from landfills and incinerators in most developed countries. Presently, large quantities of CRTs are generated globally with only few developed countries having effective take back and sound management program. Meanwhile, large quantities of CRT-containing devices are being moved across frontiers into developing countries in the name of ‘reuse’ and ‘bridging the digital divide’. With near absence of recycling infrastructure for electronic wastes in most developing countries, waste CRTs are disposed of with MSW at open dumps and unsanitary landfills. This paper reviews the current practices in the management of CRTs around the world, with emphasis on the role of regulations, availability of recycling infrastructure, recycling/reuse routes, and export into developing countries. Inappropriate disposal of waste CRTs creates the opportunity for large-scale environmental contamination with heavy metals, especially lead. Appropriate disposal routes are required globally in the management of CRTs in order to mitigate environmental contamination and human exposure to toxins.
This study assessed the capability of the fungus, Phanerochaete chrysosporium, to decompose pyrite, arsenopyrite and a sulfide-containing flotation concentrate in an effort to develop a microbial process for pretreating refractory gold ores. The extent of biotransformation was monitored by analyzing for iron, sulfur and arsenic in incubation solutions, and for sulfide sulfur in the residual solids. The results were then expressed as percentages of the initial weights. For arsenopyrite, 1.5wt.%, 7.2wt.% and 10.3wt.% of iron, arsenic and sulfur respectively were present as soluble constituents in the incubation solution within 21days of fungal treatment, whereas for pyrite, there was 1.2wt.% iron and 6.0wt.% sulfur. For the same processing period in the case of the flotation concentrate, 1.8wt.%, 6.1wt.% and 10.7wt.% respectively of iron, arsenic and sulfur remained in solution. Overall, the decomposition of sulfide sulfur in the samples was 15wt.%, 35wt.% and 57wt.% respectively for pyrite, arsenopyrite and the flotation concentrate. Changes in sulfide sulfur concentration and the formation of oxide phases during fungal treatment were confirmed using Raman spectroscopy and X-ray diffraction analysis. These results suggest that P. chrysosporium is a potential microorganism for oxidative decomposition of metal sulfides associated with refractory gold ores.
Nutrients in leaching solution play an important role in removal of iron impurities from kaolin when using dissimilatory Fe(III)-reducing bacteria (DIRB). However, the effect of organic acids, complexing agents and heavy metals on Fe leaching from kaolin when added to the leaching solution was not well understood and was investigated in this study. The results showed that the removal of iron impurities increased in the presence of oxalic acid in the leaching solution where the removal of iron reached 3.76mgFegclay−1. In contrast, acetic and salicylic acids inhibited or ceased microbial growth. Furthermore, iron dissolution was enhanced by nitrilotriacetic acid (NTA), while the addition of EDTA to the solution medium had little impact on iron reduction. The reduction of Fe(III) was completely inhibited by the addition of 0.08gL−1 Cu(II) to the solution, while dissolved iron was enhanced by the addition of Mn(II) and Fe(II). Low concentrations of Fe(III) caused a slight decline in iron reduction, but reduction of Fe(III) was significantly inhibited at an initial Fe(III) concentration of 0.08gL−1. Fourier transform infrared analysis (FTIR) and differential thermal analysis–thermogravimetry (DTA–TG) techniques were used to characterize kaolin before and after bioleaching demonstrating that there was no major change in structural composition or physicochemical properties.
This work compares gold bioleaching from e-waste containing gold and copper by Chromobacterium violaceum and Pseudomonas fluorescens. The effect of pulp density (ranging from 0.5 to 8%w/v) was examined. Although C. violaceum produced more cyanide than P. fluorescens in the absence of e-waste, P. fluorescens showed higher growth rate, cyanide production and gold leaching efficiency at all pulp densities. Pretreatment with biooxidation of the e-waste using Acidithiobacillus ferrooxidans resulted in the removal in excess of 80% of the copper present in the waste, and increased the gold/copper ratio in the residual solid. Bioleaching the biooxidised e-waste significantly improved gold recovery, especially by C. violaceum, particularly at high pulp density. For example, at pulp densities of 2 and 4% w/v, gold recovery from non-biooxidzed e-waste was 0.22 and 0.14% respectively. Higher gold recovery, at 8%, was obtained for bioleaching of the biooxidised e-waste at both these pulp densities. The ratio of gold/copper in leachates after bioleaching of the biooxidized e-waste was also found to be increased.
Various weak organic acids and/or their salts were tested for the remediation of a loam and a sandy clay loam naturally polluted by heavy metals for over three years against two strong synthetic chelating agents (EDTA and DTPA). Among 7 weak organic acids and/or their salts, citrate, tartarate and oxalate were found to effectively remove Cd, Cu, Pb and Zn from the two soils in double extractions, at a wide range of pH. Citrate removed 80 to 99.9% of all four metals within 24 h at pH from 2.3 to 7.5. Tartarate removed 84 to 99.9% of all metals from both soils within 24 h at pH from 2.1 to 6.7. Oxalate alone is not effective in removing metals particularly Pb but with ammonium citrate (1:1 ratio) removed effectively 82, 70, 99.9, and 99.9% for Cd, Pb, Cu and Zn, respectively at pH from 2.6 to 5.8. Zinc met the Quebec A level soil clean-up criteria after two extractions whereas Cu and Pb reached the B level. Probably, two more extractions with these weak organic acids and/or their salts are required to meet the A level for the soil clean-up criteria for Cd, Cu and Pb. EDTA and DTPA removed 75 to 99.9% of the heavy metals within 24 h at pH from 3.5 to 9.0 for both soils. Citrate and tartarate were found to remove heavy metals from two contaminated soils, as effectively as EDTA and DTPA. But compared to EDTA and DTPA they removed 80% less macronutrients from the soil and improve its structure. Weak organic acids and/or their salts therefore can be used as an environmentally friendly remediation technique.
Much recent work in the field of biohydrometallurgy has been directed to the study of bio-oxidation of gold ores by acidophilic iron and sulfur oxidizing microorganisms. This work has been done worldwide and has resulted in several pilot plant and commercial scale operations for gold ore bio-oxidation. Bioleaching of gold by metabolic products of microorganisms has received less attention, but also offers opportunities for industrial application, especially if future regulations restrict the use of cyanide. This paper reviews recent progress in the use of microorganisms tooxidize the sulfidic matrix in refractory gold ores (bio-oxidation) and to solubilize elemental gold (bioleaching).
A method of recovering precious metal values from refractory sulfide ores is provided. The method includes the steps of separating clays and fines from a crushed refractory sulfide ore, forming a heap from the refractory sulfide ore, bioleaching the heap to thereby oxidize iron sulfides contained therein, and hydrometullurgically treating the bioleached ore to recover the precious metal values. If sufficient quantity of precious metal values are contained in the separated clays and fines, these materials can be further processed to recover the precious metal values contained therein.
A new species of ferrous-iron-oxidizing, moderately thermophilic, acidophilic bacteria, Acidimicrobium ferrooxidans, has been described. Two isolates of the species differed only in the tendency of one, previously known as strain TH3, to grow in filaments. The chromosomal DNA base composition is between 67 and 69 mol0/o G +C. The capacity of this species to fix CO, from air was greater than that of iron-oxidizing thermoacidophiles of the genus Sulfobacillus, which required an enhanced CO, concentration for optimum autotrophic growth. Under air, ferrous iron oxidation in mixed cultures of A. ferrooxidans with either Sulfobacillus thermosulfidooxidans or Sulfobacillus acidophilus was more extensive than in pure cultures of these three strains. The greater part of ferrous iron oxidation in mixed cultures probably resulted from activity of the Sulfobacillus species, which possess a greater tolerance of ferric iron, and which presumably grew mixotrophically utilizing organic compounds from A. ferrooxidans .
Alumina nanoparticles were developed by the sol−gel method and were used for the removal of Ni(II) ions from aqueous solutions. The nanoparticles were characterized by TEM and XRD. Nanoparticles of alumina were then used for removal of Ni(II) ions from aqueous solutions of nickel. The nanosize of the adsorbent was confirmed by TEM and XRD. Removal (%) was found to be dependent on the initial concentration of nickel, and maximum removal was found to be 96.6% at 25 mg/L Ni(II). The removal increased from 99 to 99.6% by decreasing the initial concentration from 75 to 25 mg/L. Equilibrium time was found to be 120 min. As expected, higher removal was obtained at higher adsorbent dose. The removal was governed by first-order kinetics, and the value of the rate constant of adsorption was found to be 1.83 × 10−2 min−1 at 25 mg/L and 25 °C. The removal was found to be pH dependent, and maximum removal was found to be at pH 8.0. The adsorption process was endothermic in nature. The experimental data fit well the Langmuir and Freundlich isotherms. Constants of the two isotherm equations were determined. Thermodynamic studies for the present process were performed by determining the values of ΔG°, ΔH°, and ΔS° at different temperatures.
Borohydride reduction of an aqueous iron salt in the presence of a support material gives supported zero-valent iron nanoparticles that are 10−30 nm in diameter. The material is stable in air once it has dried and contains 22.6% iron by weight. The supported zero-valent iron nanoparticles (“Ferragels”) rapidly separate and immobilize Cr(VI) and Pb(II) from aqueous solution, reducing the chromium to Cr(III) and the Pb to Pb(0) while oxidizing the Fe to goethite (α-FeOOH). The kinetics of the reduction reactions are complex and include an adsorption phase. About 10% of the iron in the material appears to be located at active surface sites. Once these sites have been saturated, the reduction process continues but at a much lower rate, which is likely limited by mass transfer. Rates of remediation of Cr(VI) and Pb(II) are up to 30 times higher for Ferragels than for iron filings or iron powder on a (Fe) molar basis. Over 2 months, reduction of Cr(VI) was 4.8 times greater for Ferragels than for an equal weight of commercial iron filings (21 times greater on the basis of moles of iron present). The higher rates of reaction, and greater number of moles of contaminant reduced overall, suggest that Ferragels may be a suitable material for in situ remediation.
Ethylenediaminetetraacetate (EDTA), an industrially important chelating agent, forms very stable complexes with di- and trivalent metal ions, and in both wastewater and natural waters it is normally present in the metal-associated form. Therefore, the influence of EDTA speciation on its utilization by the EDTA-degrading bacterial strain DSM 9103 was investigated. EDTA-grown cells harvested from the exponential phase of a batch culture were incubated with 1 mM of various EDTA species and the EDTA concentration in the assay was monitored as a function of time. Uncomplexed EDTA as well as complexes with low stability constants (MgEDTA2-, CaEDTA2-, and MnEDTA2-, stability constant < 1016) were found to be readily degraded to completion at a constant rate. For more stable EDTA chelates (i.e. chelates of Co2+, Cu2+, Zn2+, and Pb2+) the data suggest that these complexes were not used directly by the cells but that they had to dissociate prior to degradation. The rate of this dissociation step possibly determined the microbial degradation of these complexes. CdEDTA2- and Fe(III)EDTA- were not degraded within 48 h. In case of CdEDTA2- the toxicity of freed Cd2+ ions most likely prevented a significant degradation of the complex, whereas in case of Fe(III)EDTA- a combination of metal or complex toxicity and the very slow dissociation of the complex might explain the absence of degradation.
Microbiological processes were applied to mobilize metals from electronic waste materials. Bacteria Thiobacillus . . thiooxidans, T. ferrooxidans and fungi Aspergillus niger, Penicillium simplicissimum were grown in the presence of electronic scrap. The formation of inorganic and organic acids caused the mobilization of metals. Initial experiments showed that microbial growth was inhibited when the concentration of scrap in the medium exceeded 10 g Ly1. However, after a prolonged adaptation time, fungi as well as bacteria grew also at concentrations of 100 g L y1. Both fungal strains were able to mobilize Cu and Sn by 65%, and Al, Ni, Pb, and Zn by more than 95%. At scrap concentrations of 5-10 g L y1, Thiobacilli were able to leach more than 90% of the available Cu, Zn, Ni, and Al. Pb precipitated as PbSO while Sn 4
A study was initiated to determine the feasibility of using the fungus Aspergillus niger for bioleaching metals from oxide low-grade ore. Large quantities of the metals are embodied in the low-grade ores and mining residues that can be recovered. Presently available techniques (pyrometallurgical and hydrometallurgical) are expensive or may have a negative impact on the environment. An oxidized mining ore containing mainly copper (7245 mg kg−1 residue) was studied. In this study, the fungus A niger produced a variety of organic acids. Addition of small quantities of sulfuric acid enhanced the organic acids, efficiency. Various agricultural wastes were evaluated as substrates and a maximum solubilization of 68% for copper for a medium containing potato peels was achieved. In conclusion, leaching of copper from a mining ore is technically feasible using A niger. Further research must be performed to increase the rate of copper removal. Copyright © 2003 Society of Chemical Industry
A process for biological removal of iron from quartz sands, kaolins and clays was developed in which these industrial minerals were leached at 90°C with lixiviant produced as a result of the cultivation of acid‐producing heterotrophic microorganisms, mainly strains of Aspergillus niger , at 30°C in a nutrient medium containing molasses as a source of carbon and energy. The lixiviant, i.e. the fermentation fluid, contained oxalic and citric acids as main components and after the cultivation was acidified to a pH of 0.5 by means of hydrochloric acid. The leaching was carried out in mechanically stirred acid‐resistant vats for a period of from 1 to 5 hours. The iron content of some sands treated by this method was lowered from 0.035–0.088 to below 0.012% Fe 2 O 3 making them suitable for the preparation of high quality glass. The iron content of different kaolins was lowered from 0.65–1.49 to 0.44–0.75% Fe 2 O 3 and as a result of this their whiteness was increased from 55–87 to 86–92%. The iron content of a clay was lowered from 6.25 to 1.85% Fe 2 O 3 and this increased the fireproofness of the clay from 1 670 to 1 750°C. Similar process was used for leaching of aluminium from aluminosilicates, mainly clays and kaolins. However, after the cultivation the fermentation fluid was acidified either by means of sulfuric or hydrochloric acid or by means of different mixtures of inorganic acids. For enhancing aluminium solubilization the aluminosilicates were heated before leaching at 600–650°C for 1–2 hours. Over 90% of the aluminium present in different clays and kaolins was leached within 3–6 hours in this way.
“Silicate” bacteria related to the species Bacillus circulans and B. mucilaginosus were used to leach silicon from low‐grade bauxite ores containing aluminosilicates as impurities. The bacterial action was connected with the formation of mucilaginous capsules consisting of expolysaccharides. The solid residues after leaching were characterized by higher values of alumina content and were suitable for processing by means of the B AYER process for recovering aluminium.
Heterotrophic bacteria were used to leach manganese from oxide ores using different organic compounds as reducing agents.
This paper attempts to make an assessment and policy recommendation for the Indian perspective through a cross-national review of current practice and policy. It also addresses in a transition economy with some reference to policies and practices in other transition economies. It has been shown that existing Hazardous Waste Rules could overturn the necessity of a separate national legislation dealing with e-waste alone after it is being configured to accommodate e-waste for its management in India. The regulatory approach proposed could serve as a model or at least a starting point for other transition countries that may not be so far along as India with respect to management of e-waste. Reference to this paper should be made as follows: Bandyopadhyay, A. (2008) 'A regulatory approach for e-waste management: a cross-national review of current practice and policy with an assessment and policy recommendation for the Indian perspective', Int. J. Environment and Waste Management, Vol. 2, Nos. 1/2, pp.139–186. Biographical notes: Amitava Bandyopadhyay is an Environmental Engineer of the West Bengal Pollution Control Board that implements various Environmental Rules and Regulations. He did his BTech from the Calcutta University, MTech and PhD in Chemical Engineering from the Indian Institute of Technology, Kharagpur. Initially, he worked in a trans-national organisation in carrying out EIA and Hazop Studies, Risk Analysis, conceptual designing of ETP and Air Pollution Control systems. Besides his active background in teching, his major research areas include waste minimisation, advanced separation methods and emission control. Incidentally, he has gained experiences in almost all fields of Environmental Science and Engineering.
The kinetics of the bioleaching of ZnS concentrate by Thiobacillus ferrooxidans was studied in a well-mixed batch reactor. Experimental studies were made at 30°C and pH 2.2 on adsorption of the bacteria to the mineral, ferric iron leaching, and bacterial leaching. The adsorption rate of the bacteria was fairly rapid in comparison with the bioleaching rate, indicating that the bacterial adsorption is at equilibrium during the leaching process. The adsorption equilibrium data were correlated by the Langmuir isotherm, which is a useful means for predicting the number of bacteria adsorbed on the mineral surface. The rate of chemical leaching varied with the concentration of ferric iron, and the first-order reaction rate constant was determined. Bioleaching in an iron-containing medium was found to take place by both direct bacterial attack on the sulfide mineral and indirect attack via ferric iron. In this case, the ferric iron was formed from the reaction product (ferrous iron) through the biological oxidation reaction. To develop rate expressions for the kinetics of bacterial growth and zinc leaching, the two bacterial actions were considered. The key parameters appearing in the rate equations, the growth yield and specific growth rate of adsorbed bacteria, were evaluated by curve fitting using the experimental data. This kinetic model allowed us to predict the liquid-phase concentrations of the leached zinc and free cells during the batch bioleaching process.
Bioleaching is a simple and effective technology for metal extraction from low-grade ores and mineral concentrates. Metal recovery from sulfide minerals is based on the activity of chemolithotrophic bacteria, mainly Thiobacillus ferrooxidans and T. thiooxidans, which convert insoluble metal sulfides into soluble metal sulfates. Non-sulfide ores and minerals can be treated by heterotrophic bacteria and by fungi. In these cases metal extraction is due to the production of organic acids and chelating and complexing compounds excreted into the environment. At present bioleaching is used essentially for the recovery of copper, uranium and gold, and the main techniques employed are heap, dump and in situ leaching. Tank leaching is practised for the treatment of refractory gold ores. Bioleaching has also some potential for metal recovery and detoxification of industrial waste products, sewage sludge and soil contaminated with heavy metals.
Nanoscale iron particles represent a new generation of environmental remediation technologies that could provide cost-effective solutions to some of the most challenging environmental cleanup problems. Nanoscale iron particles have large surface areas and high surface reactivity. Equally important, they provide enormous flexibility for in situ applications. Research has shown that nanoscale iron particles are very effective for the transformation and detoxification of a wide variety of common environmental contaminants, such as chlorinated organic solvents, organochlorine pesticides, and PCBs. Modified iron nanoparticles, such as catalyzed and supported nanoparticles have been synthesized to further enhance the speed and efficiency of remediation. In this paper, recent developments in both laboratory and pilot studies are assessed, including: (1) synthesis of nanoscale iron particles (10–100nm, >99.5% Fe) from common precursors such as Fe(II) and Fe(III); (2) reactivity of the nanoparticles towards contaminants in soil and water over extended periods of time (e.g., weeks); (3) field tests validating the injection of nanoparticles into aquifer, and (4) in situ reactions of the nanoparticles in the subsurface.
Oxalate (Ox) was investigated as an extractant for decontaminating two metal-polluted soils, one with elevated total zinc (ZnT = 2700 mg kg-1) from the Palmerton, Pennsylvania smelter site and the other from a grossly contaminated (PbT = 210 000 mg kg-1) automobile battery recycling facility in Indiana. Metal retention within the soils was substantially different as shown by sequential fractionation experiments. High Zn removal (>80%) was achieved with 1.0 M Ox when Zn existed predominantly in non-detrital metal fractions. However, Ox was an unsuitable Pb extractant due to the sparing solubility of PbOx(s). Despite the dramatically higher stability of ZnEDTA2- (log K = 16.5) compared to ZnOx (log K = 3.4), Ox released more Zn than EDTA from the Palmerton soil because 40% of ZnT was associated with the oxide fraction. Extract analysis indicated that Ox, but nor EDTA, dissolved soil Fe oxides in the 24 hr extraction period. When contaminating metals are associated with soil oxides, Ox may be a superior extractant to powerful chelants like EDTA. It is essential to establish thoroughly metal solution chemistry and fixation behavior within the soil when extractive decontamination is proposed for site remediation.
A mixed culture of moderately thermophilie microorganisms was enriched from acid mine drainages(AMDs) samples collected from
several sulphide mines in China, and the bioleaching of chalcopyrite was conducted both in shake flask and bioreactor. The
results show that in the shake flask, the mixture can tolerate 50 g/L chalcopyrite after being acclimated to gradually increased
concentrations of chalcopyrite. The copper extraction increases obviously in bioleaching of chalcopyrite with moderately thermophilic
microorganisms supplemented with 0.4 g/L yeast extract at 180 r/min, 74% copper can be extracted in the pulp of 50 g/L chalcopyrite
after 20 d. Compared with copper extractions of mesophilic culture, unacclimated culture and acclimated culture without addition
of yeast extract, that of accliniated culture with addition of yeast extract is increased by 53%, 44% and 16%, respectively.
In a completely stirred tank reactor, the mass fraction of copper and total iron extraction reach up to 81% and 56%, respectively.
The results also indicate that it is necessary to add a large amount of acid to the pulp to extract copper from chalcopyrite
effectively.
In a resin-in-pulp process for the recovery of gold cyanide from a very dilute solution it is desirable that the resin should exhibit the ability to load gold at the natural pH of the leach liquor and be stripped by an aqueous alkali. The present work describes the results of gold cyanide adsorption by new ion-exchange hollow fibers prepared by the amination of sulfochlorinated polyethylene. The fibers, chopped into suitably sized pieces, showed very fast adsorption and desorption of gold from mixed cyanide solutions.
A new method for the recovery of precious metals, in particular gold, from electronic waste is proposed. This work focused
on the research of an easily renewable etching agent, in order to make an environmentally friendly process possible. Two well
known hydrometallurgical etching agents, FeCl3 and CuCl2, were evaluated in terms of efficiency and kinetics, testing solutions with different concentration of etchant and hydrochloric
acid. The recovery of spent etching solutions was evaluated: promising results were found in the case of CuCl2, which can be completely restored by oxidation of the cuprous chloride formed during the etching using atmospheric oxygen.
KeywordsCupric chloride-Ferric chloride-Chemical etching-Precious metals recovery-Electronic waste
Exudation of low molecular weight organic acids by fungi was studied in a project focusing on bioremediation of metal-contaminated
soils. The production of acids (mainly oxalic and citric acid) as a response to nutrient variations and presence of metals
has recently been reported (Arwidsson et al. 2009). A significant release of metals was observed and was related not only to the production of organic acids but also to the
resulting pH decrease in the systems. The processes governing the release and redistribution of metals in the soil–water fungus
system were the focus of the present continuation of the project, based on observations of Aspergillus niger, Penicillium bilaiae, and a Penicillium sp. The release of lead was 12% from the soil with the second highest initial load (1,600mgkg−1), while the release of copper was 90% from the same soil (140mgkg−1). The dominating mechanism behind the release and subsequent redistribution was the change in pH, going from near neutral
to values in the range 2.1–5.9, reflecting the production of organic acids. For some of the systems, the formation of soluble
complexes is indicated (copper, at intermediate pH) which favors the metal release. Iron is assumed to play a key role since
the amount of secondary iron in the soils is higher than the total load of secondary heavy metals. It can be assumed that
most of the heavy metals are initially associated with iron-rich phases through adsorption or coprecipitation. These phases
can be dissolved, or associated metals can be desorbed, by a decrease in pH. It would be feasible to further develop a process
in technical scale for remediation of metal-contaminated soil, based on microbial metabolite production leading to formation
of soluble metal complexes, notably with copper.