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Copper extraction from coarsely ground printed circuit boards using moderate thermophilic bacteria in a rotating-drum reactor
Abstract
The current work reports on a new approach for copper bioleaching from Printed Circuit Board (PCB) by moderate thermophiles in a rotating-drum reactor. Initially leaching of PCB was carried out in shake flasks to assess the effects of particle size (-208μm+147μm), ferrous iron concentration (1.25-10.0g/L) and pH (1.5-2.5) on copper leaching using mesophile and moderate thermophile microorganisms. Only at a relatively low solid content (10.0g/L) complete copper extraction was achieved from the particle size investigated. Conversely, high copper extractions were possible from coarse-ground PCB (20mm-long) working with increased solids concentration (up to 25.0g/L). Because there was as the faster leaching kinetics at 50°C Sulfobacillus thermosulfidooxidans was selected for experiments in a rotating-drum reactor with the coarser-sized PCB sheets. Under optimal conditions, copper extraction reached 85%, in 8days and microscopic observations by SEM-EDS of the on non-leached and leached material suggested that metal dissolution from the internal layers was restricted by the fact that metal surface was not entirely available and accessible for the solution in the case of the 20mm-size sheets.
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... This implies the urgent requirement for organised and sustainable e-waste management (i.e., employ extended producer responsibility or EPR schemes to collect e-waste) and value recovery operations, especially in developing countries [11]. [12] with permission from Waste Management, (b) grain structure of electro-deposited (ED) copper foils and rolled annealed (RA) copper foils [13], (c) hetero-component interfaces: (I) copper foil-epoxy resin (II) epoxy resin-glass fibre cloth interface (epoxy-GFC) (III) copper foil-glass fibre cloth interface (copper foil-GFC)-Reproduced from [14] with permission from Journal of the Air and Waste Management Association. ...
... It is presumed that the shear forces induced by a universal crusher in the longitudinal direction surpass the pre-weakening bonding force at the PCB interface after the heat treatment, which causes the de-bonding of PCBs [53]. Rodrigues et al. [12] also employed pre-weakening effects of 2 cm PCB fragments by generating cracks with a jaw crusher to enhance metal leaching. The internal cracks introduced within the internal structure of PCBs facilitated the accessibility of lixiviant to the internal copper layers. ...
... This chemical coating or the lacquer layer must be removed from the coarse particles prior to metal extraction processes using coarse PCB pieces (Figure 7). Rodrigues et al. [12] reported the concomitant increase in copper extraction efficiency (about 40%) with the lacquer layer removed WPCBs, as compared to the original WPCBs, and the exposed external copper layers resulted in improved leaching efficiency. However, the solder mask removal method depends on the type of PCB. ...
Waste electrical and electronic equipment or e-waste generation has been skyrocketing over the last decades. This poses waste management and value recovery challenges, especially in developing countries. Printed circuit boards (PCBs) are mainly employed in value recovery operations. Despite the high energy costs of generating crushed and milled particles of the order of several microns, those are employed in conventional hydrometallurgical techniques. Coarse PCB pieces (of order a few centimetres) based value recovery operations are not reported at the industrial scale as the complexities of the internal structure of PCBs limit efficient metal and non-metal separation. Since coarse PCB particles’ pre-treatment is of paramount importance to enhance metal and non-metal separations, thermal, mechanical, chemical and electrical pre-treatment techniques were extensively studied. It is quite evident that a single pre-treatment technique does not result in complete metal liberation and therefore several pre-treatment flowsheets were formulated for coarse PCB particles. Thermal, mechanical and chemical pre-treatments integrated flowsheets were derived and such flowsheets are seldom reported in the e-waste literature. The potential flowsheets need to be assessed considering socio-techno-economic considerations to yield the best available technologies (BAT). In the wider context, the results of this work could be useful for achieving the United Nations sustainable development goals.
... The utilised microorganisms have the natural ability to transform and convert metals to a soluble form. Generally, three microbial groups are involved in bioleaching as follows: Autotrophic bacteria, heterotrophic bacteria, and heterotrophic fungi (Arshadi and Mousavi, 2014;Pant et al., 2012;Rodrigues et al., 2015;Zhu et al., 2011). Most autotrophic leaching is performed by chemolithotrophic and acidophilic bacteria, which can fix CO 2 and obtain energy from ferrous iron or reduced sulphur compounds oxidation. ...
... Also, experimental observations indicated that the rate of copper dissolution in the bioleaching process was controlled by external diffusion because of the iron hydrolysis and formation of jarosite precipitates on the surface of the material (Chen et al., 2005;Shamshiri Kourdestani et al., 2017). The formation of jarosite precipitate can be prevented by maintaining acidic conditions of the leaching medium at ambient temperature, however at high temperature jarosite precipitation is encouraged even at a pH lower than 2 (Rodrigues et al., 2015). ...
... The effect of ferrous iron concentrations ranging 0-10 g L -1 on bioleaching of copper from E-waste with pure cultures of A. ferrooxidans and S. thermosulfidooxidans were determined by Rodrigues et al. (2015). They claimed that an increase of Fe (II) concentration was initially enhancing copper leaching in both cultures but then it decreased with further increase of Fe (II) concentrations (Rodrigues et al., 2015). ...
Nowadays, large amount of municipal solid waste is because of electrical scraps (i.e. waste electrical and electronic equipment) that
contain large quantities of electrical conductive metals like copper and gold. Recovery of these metals decreases the environmental
effects of waste electrical and electronic equipment (also called E-waste) disposal, and as a result, the extracted metals can be used
for future industrial purposes. Several studies reported in this review, demonstrated that the biohydrometallurgical processes were
successful in efficient extraction of metals from electrical and electronic wastes. The main advantages of biohydrometallurgy are
lower operation cost, less energy input, skilled labour, and also less environmental effect in comparison with pyro-metallurgical and
hydrometallurgical processes. This study concentrated on fundamentals and technical aspects of biohydrometallurgy. Some points of drawbacks and research directions to develop the process in the future are highlighted in brief.
... A newer technique for extracting copper from WPCBs using mesophilic and moderate thermophile cultures in a rotating-drum reactor was developed by Rodrigues et al. [81]. As a pre-treatment step, hammer milling of WPCBs was done to get particles of different size ranges before employing bioleaching. ...
... Rodrigues et al. [81] Crushing Cryogenic grinding was used for further reduction in the size of WPCBs coarse particles. ...
... Multiphase contacting systems like bioreactors have to be chosen precisely based on the process conditions for largescale bioleaching applications to achieve better performance and efficiency [22]. Column, rotating-drum, and stirred-tank bioreactors are to be operated under optimized conditions to enhance the efficiency of bioleaching of metals from PCBs [23][24][25][26]. Most bioleaching studies have been carried out using lithotrophic bacteria in stirred tank bioreactors to recover metals from various metal-containing substrates [25,27]. ...
... At high e-waste loads, the heterogeneous composition of the PCBs could result in inhibitory effects on bacterial growth and metabolism during bioleaching. This effect was indirectly assessed by Rodrigues et al., [26] in verifying the redox potential (Eh) using thermophilic bacteria in a rotating drum reactor for Cu extraction from PCBs. The other possible reasons for a decrease in bioleaching could be attributed to cell toxicity to higher concentrations of leached metals, and inadequate mixing instigating mass transfer limitations in the system thereby minimizing the contact between the cells and substrate. ...
Technological advancements have led to a demand for modern electronic gadgets and outdated ones discarded as electronic waste (e-waste). The printed circuit boards (PCBs) constitute a significant portion of these wastes that contain hazardous substances that mandate e-waste management. The rich source of precious and base metals makes it a resource for urban mining. Bioleaching, a process of biohydrometallurgy, an alternative to conventional heat and chemical-based metal recovery processes, can be efficiently applied for metal recovery from these wastes in an environmentally safe manner. The process parameters like particle size, inoculum size (v/v), and e-waste load (w/v) for bioleaching of Cu from PCBs in a Fluidized-Bed bioreactor (FBR) and shake flask using Alcaligenes aquatilis as bioleaching agent were optimized. The bioleaching of 47.99% and 37.54% of Cu from PCBs were achieved in shake flask and FBR, respectively. The optimal conditions of Cu bioleaching were 0.175 mm particle size, 5% (v/v) inoculum, and 2% (w/v) e-waste load with 169.45 mg/g and 132.55 mg/g of Cu recovery in shake flask and FBR at 84 and 96 h, respectively. Further, the Cu bioleaching was carried out in sequential batches to improve the recovery with the optimized conditions. There was a prominent increase in the cumulative %Cu bioleaching of about 80.02% after three sequential batch experiments from PCBs with an initial Cu concentration of 353.09 mg/g. The present study proves that sustainable heterotrophic bioleaching of Cu can be efficiently achieved in a Fluidized-bed bioreactor operated in sequential batch mode by Alcaligenes aquatilis.
Graphical Abstract
... Besides, brown precipitates were also observed in the medium containing the isolated bacteria, which was not seen in control sample. This observation could be due to the initial oxidation of Fe (II) to Fe (III), which was present inside the medium [24]. Similar to the proposed ionic exchange in the bioleaching mechanism, these changes were reported in a previous study [13], [25]. ...
... From the 1g copper strip used, 0.80 mg/g (±0.02) was solubilized, as analyzed using AAS compared to the set control with only 0.03 mg/g (±0.08) solubilized in the absence of strain SC. By comparison, a previous study reported the total amount of copper extracted through bioleaching to be approximately 80-90% within a similar timeframe used in the current study [24]. This result indicates that strain SC can solubilize copper, thus confirming the strain shown during the bioleaching process with wPCB. ...
Electronic waste has been the fastest increasing waste generated globally and is predicted to surpass 111 million tons per year by 2050. This trend is concerning, not just due to the growing volume but also due to its high composition of heavy metal elements, leading to potential environmental pollution if not managed properly. However, this issue opens a new prospect in material acquisition through the concept of urban mining via the metal extraction from electronic waste. A conventional method of extraction, i.e., chemical leaching, possesses harmful environmental impact with the production of its residual leachate. Thus, an alternative extraction technique is proposed, known as bioleaching, in which the microbial activity from bacteria mobilized metal into a more soluble form. In this study, bacterial strains were isolated from Malaysia sanitary landfill for bioleaching of copper from waste printed circuit boards (wPCB) with minimal mechanical pre-processing procedure. They were grown in low pH medium to utilize their activity for copper bioleaching from the wPCB. Four bacterial strains were successfully isolated. Using 16S rRNA gene sequencing, the isolates were identified as Bacillus sp. strain SE, Bacillus sp. strain SC, Lysinibacillus sp. strain SE2, and Oryzobacter terrae strain S1A. All the isolates showed appropriate bioleaching ability, with strain SC demonstrated the highest copper extraction with up to 23.36 ppm through the two-step bioleaching process. This strain was further evaluated using a copper strip to observe the actual copper extraction and demonstrated a total of 0.80 ±0.02 mg/g copper recovery. These results suggest that copper bioleaching of wPCB is viable as a standalone process.
... In previous years, the cross-border transportation of electronic waste has occurred frequently, with waste amassed in developed nations being exported to less affluent Asian regions, where disposal facilities are less expensive and environmental regulations and laws are less stringent or poorly enforced. However, the Basel Convention, an international [59][60][61] treaty aimed at regulating the transboundary movement of hazardous waste, has been implemented to curtail such transfers of waste from developed to less developed countries [63]. ...
Solar energy has emerged as a prominent contender in this arena, attracting significant attention across the globe. Governments worldwide have undertaken extensive efforts to encourage the adoption of renewable energy, increasing the usage of solar panels. Despite its benefits, the deployment of photovoltaic (PV) modules generates significant waste, thereby posing a major environmental challenge. This study explores several recycling techniques, including physical, thermal, and chemical methods, that could be employed to manage solar panel waste. An in-depth analysis of separation techniques presently employed and underdevelopment was studied and compared to determine the physical treatment necessary for the separation of glass and aluminium. Extraction of rare earth metals cadmium, copper and tellurium requires chemical treatments using organic and inorganic solvents along with thermal treatment at 500–600°C to remove the EVA polymer. Recovery of silicon wafers and rare metals through various metal extraction processes is further examined. Europe was concluded as a frontrunner in solar waste management policies after analysis of the governmental policies of developed and developing nations of the world. The circular economy model developed portrayed a systematic approach for the removal of different components of a solar panel and reintegration into the manufacturing process. The implementation of a robust circular economy for renewable energy systems is conditional upon the optimization of resource recovery while minimizing energy consumption and this serves as the governing framework of this review.
... E-wastes are mostly composed of heavy metals (e.g., Ni, Cd, Al, Cu, Mn, Zn, Au, Zn, Fe, Ag, Pb, Hg, Cr, and Sn), polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons (PAHs). Certain microbes have a diverse catabolic capacity that allows them to degrade, transform, or accumulate a wide range of compounds, including hydrocarbons such as oil, polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceuticals, pesticides, and metals ( [11,36,44,94,98,145,147,154,182]. Although heavy metals are not biodegradable, they could potentially be converted from one chemical state to another, making them less hazardous to the environment [63]. ...
Electronic waste, also known as e-waste, is the discarded or by-products of electronic appliances, constituting a major percentage of the total solid waste produced globally. Such e-waste is mostly composed of plastics, various heavy metals, azo dyes, and xenobiotic components, which are mostly non-biodegradable or less degradable in nature. As a result, they increase environmental toxicity, preventing the growth of crops and causing health issues for humans and other animals. On the other hand, recycling e-waste may also lead to the consumption of heavy metals through water or the inhalation of polluted air after combustion, which may cause various health issues such as asthma, nerve, respiratory, kidney, liver disease, and even cancer. Hence, microbial degradation of e-waste has become a new trend in managing such solid wastes. However, their mode of action is somewhat less explored. Microbes degrade various components of e-waste through a number of mechanisms such as bioleaching, biosorp-tion, biotransformation, bioaccumulation, and biomineralization. Some microorganisms release enzymes such as reductases, laccases, esterases, carboxylesterases, catalases, and dioxygenases for the bioconversion of various components of e-waste into their less toxic forms. This review provides insight into the role of microbes in the conversion of various components of e-wastes such as polyaromatic hydrocarbons (PAHs), azo dyes, and heavy metals and their mode of action.
... Os resultados obtidos na análise química apresentaram um teor médio de cobre de 21,40 ± 2,64%, sendo o elemento majoritário presente na fração cominuída. Tal valor condiz com os teores observados na literatura, conforme descrito por Yamane et al., 13 Veit et al., 16 26 as PCI são constituídas por quatro camadas de cobre (duas internas e duas externas), as quais encontram-se intercaladas entre estruturas de fibra de vidro e de polímero. Além disso, alguns CE apresentam indutores de cobre, bem como a presença de algumas ligas metálicas de cobre, corroborando para o alto teor desse elemento obtido na análise química. ...
PRE-TREATMENT AND CHARACTERIZATION OF PRINTED CIRCUIT BOARDS OF COMPUTERS WITH EMPHASIS IN METAL CONTENT. The recycling of waste electrical and electronic equipment (WEEE) is a worldwide challenge and this is one of the biggest issues debated on 21st century, motivating the participation of governments research institutions and also the private sector in order to develop technologies based on the cleaner production (C + P) concept so that the eco-efficiency of the electronics industry is improved. In this work, the manual dismantling and mechanical processing steps, including grinding, magnetic and electrostatic separations were the procedures employed for this. Subsequently, the physical and chemical printed circuit board (PCB) characterizations was carried out by particle size classification and inductively coupled plasma optical emission spectroscopy/scanning electron microscopy-energy dispersive spectroscopy (ICP OES/SEM-EDS) analyses, respectively in order to confirm the release, separation and concentration of metal content. After magnetic separation, the percentages of the magnetic and non-magnetic fractions were 15.18 and 56.70%, respectively. In the magnetic fraction, the concentration of iron, nickel, silver and gold reached 1.26 ± 0.33%, 1.24 ± 0.27%, 650.03 ± 77.60 mg kg-1 and 504.88 ± 18.53 mg kg-1, respectively. In the case of copper, the magnetic fraction had a content of 11.27 ± 1.41%, corresponding to about 50% of the value obtained in the non-magnetic fraction. Hence, iron, nickel, silver and gold were concentrated in the magnetic fraction, while copper was concentrated in the non-magnetic fraction.
... A number of studies have been published on the selective recovery of base and precious metals from other types of ewaste, such as PCBs, using direct bioleaching to solubilize base metals. Generally, relatively high to high base metal recovery rates (75 to >99%) have been achieved in the laboratory using Fe 2+ -and/or S-oxidizing prokaryotes [40][41][42][43][44][45][46][47][48][49][50][51][52][53]. However, particularly when multiple base metals were targeted for extraction, the metal recovery rates could be significantly lower (mostly 50-60%) [51,53,54]. ...
Industrial waste is accumulating, while primary metal resources are depleting. Bioleaching has been shown to be a cost-effective and environmentally friendly approach to metal recovery from waste, but improved designs are needed for large-scale recycling. Metal components that are manufactured by electrodeposition over a mandrel can be difficult to recycle using conventional techniques due to their complex geometry and inner Ag coating. A sustainable biotechnology for separating Cu and Ag from waste electrodeposited components is presented. Two-step bioleaching experiments were performed, during which Cu was solubilized by Fe³⁺ regenerated by Acidithiobacillus (At.) ferrooxidans CF3 and a consortium of ten acidophilic Fe²⁺-oxidizers. High Cu recovery rates were achieved in agitated flasks (22 °C, pH 1.9), with At. ferrooxidans solubilizing 94.7% Cu in 78 days and the consortium 99.2% Cu in 59 days. Copper bio-solubilization was significantly accelerated in a laboratory-scale bioreactor (32 °C, 1 L air min⁻¹) using the bacterial consortium adapted to elevated Cu concentrations, reaching >99.6% Cu extraction in only 12 days. The bioreactor was dominated by Leptospirillum and Acidithiobacillus, with their proportions changing (from 83.2 to 59% of total reads and from 3.6 to 29.4%, respectively) during the leaching process. Dissolved Cu was recovered from the bioleachates (containing 14 to 22 g Cu L⁻¹) using electrowinning; >99% of the Cu was deposited (with Cu purity of 98.5 to 99.9%) in 3.33 h (at current efficiency between 80 and 92%). The findings emphasize the importance of a bioleaching system design to achieve economical separation of base and precious metals from industrial wastes. The presented technology minimizes waste generation and energy consumption. On a larger scale, it has the potential to contribute to the development of industrial recycling processes that will protect natural resources and contribute to the Net Zero target.
... Mäkinen et al. (2015) obtained 99% copper leaching in a 3 L bioreactor with 5% low grade PCBs in 72 h with C in (Fe 2+ ), 7.8 g L − 1 . Rodrigues et al. (2015) adapted the concept by using a 12 L aerated rotating-drum reactor. Yields reached 76% in 8 days (pulp density: 2.5% and C in (Fe 2+ ): 5 g L − 1 ). ...
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... Maximum leaching efficiencies of 80% (zinc), 64% (aluminum), 86% (copper), and 74% (nickel) were obtained. A higher copper extraction of 85% at 50 • C in 8 d by Sulfobacillus thermosulfidooxidans was reported by Rodrigues et al. [144] using a rotating drum bioreactor. Hubau et al. [140] recorded peak recovery efficiencies of 96% (copper), 73% (nickel), 85% (zinc), and 93% (cobalt) during the bioleaching of metals from PCBs in a double-stage continuous bioreactor for 2 d in the presence of Leptospirillum ferriphilum and Sulfobacillus benefaciens. ...
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.
... This group takes into account how the leaching technique used has affected the environment, for instance, whether the process is completed in one or two steps [85][86], the quantity of treated solid [87][88][89][90], or the way it operates (column, heap, or bioreactor activities) [91][92][93][94][95][96][97][98][99][100][101][102] All of these elements that could potentially have an impact on the process are being optimized in an effort to enhance metal recovery. However, because the experimental parameters will vary depending on the metalcontrolling substance and the bioleaching system [103][104][105][106][107][108], optimization must be done for each system and waste. ...
Aims: This study aims to present a comprehensive analysis of bioleaching, the fundamental idea behind it, the emergence of microbes and the bioleaching approaches. Study Design: To do this, this research has been developed on a foundation of significant topics. The researcher used a quantitative approach in this particular investigation. The quantitative study is presented in tables that list the bioleaching processes and efficient microorganisms. Place and Duration of Study: This study was carried out in Chemical Engineering department, Delta State University of Science and Technology, Ozoro, Nigeria. Methodology: The researcher decided on a combination methodology because of the context of the present investigation. The approach of data collection and analysis employing qualitative as well as quantitative methodologies is known as combined research design. Results: The lengthy training period of microorganisms at the laboratory scale, which is significantly impacted by other experimental variables, is one of the key difficulties faced by the bioleaching process. Therefore, the key to increasing the simplicity of bioleaching technologies in large-scale industrial production is to enhance the bioleaching microorganism’s currently in use so that they can continue to be highly active under more complicated reaction conditions. Regarding the microbial problem, biological leaching piles of just a few genes in the offspring of acidophilic microorganisms have been documented. Although some bacterial genomes from acid mine drainage and acidic environments have been used to create replacements, these models cannot fully depict the potential for leaching; in addition, it can be difficult for researchers to obtain samples of microbes from actual production, making further research challenging. Conclusion: In the years to come, microbial use for waste treatment and mineral processing will continue to gain importance on a global scale. The need to process ores with trace amounts of copper and gold, the potential for recycling waste spoils and tailings, financial limitations, and potential legislative changes on the environmental impact of more conventional approaches like hydrometallurgy will all contribute to this. The employment of chemolithotrophic and heterotrophic bacteria will be a significant addition, boosting the leaching rates and metal recoveries and enabling the treatment of resistant ores like chalcopyrite.
... In packed bed bioreactors several operational challenges such as clogging, channelling [13] and mass transfer limitations are encountered. In view of treating high e-waste load, a rotating-drum reactor was suggested by Rodrigues et al., which used coarsely ground PCBs for Cu bioleaching [14]. A choice of a bioreactor that does not involve mechanical moving parts and which can overcome the limitations and challenges of a packed bed bioreactor is desired. ...
Technological advancements with the use of new-generation electronic devices and accumulated electronic wastes (e-wastes) raise environmental concerns. E-waste, especially mobile phone Printed Circuit Boards (PCBs) is a rich source of metals. Bioleaching, a microbe-mediated metal dissolution process is employed for the recovery of metals. The operational parameters like particle size, inoculum percentage (v/v) and e-waste load (w/v) were optimised for Zn bioleaching by Alcaligenes aquatilis in shake flasks and fluidised bed bioreactor (FBR). The e-waste feed particle size of 0.175 mm and 5% inoculum was found to be the optimum for Zn bioleaching in both the shake flask and FBR. The optimum e-waste load was 5% in the shake flask and 2% in FBR. The maximum recovery of Zn was 0.6 mg/g (13.73%) in the shake flask and 0.57 mg/g (13%) in FBR, implying that FBR exhibits similar efficiency of Zn bioleaching as in the shake flask. Further three sequential batch runs increased the recovery to a maximum of 1.66 mg/g from 4.37 mg/g Zn present in the PCBs ie., 38% Zn recovery. This shows that efficient bioleaching of Zn on a larger scale can be achieved with sequential batches and applied for the simultaneous recovery of metals from PCBs.
... Recently, studies done at the University of Liege, Belgium [34,35] have revealed that leaching of WEEE materials is inhibited by the presence of toxic elements in the substrate itself. In such a way, the toxicity is considered as a key factor which limits pulp density and leaching efficiency [36,37]. ...
The increased production and use of electrical and electronic equipment leads to obsolescence and disposal problems, necessitating materials recovery and recycling. This paper reports results on metal bioleaching from printed circuit boards (PCBs) using chemolithotrophic bacteria isolated at different sulphide ore biotopes in Armenia. Different ways of generating lixiviants were investigated, namely using combination of Acidithiobacillus ferrooxidans 61 and Acidithiobacillus thiooxidans SO-1 bacteria generating biogenic Fe2(SO4)3 and biogenic H2SO4. The sequence between these leaching agents permitted design of a 2-step process based on acidolysis and redoxolysis to leach non-ferrous metals from PCBs. To compare the efficiency of the sequential bioleaching of PCBs, several experimental runs were realised under the six modes at 10% pulp density. The flasks-based tests have witnessed almost complete recovery of Cu with the rest of the metals reaching extraction degree above 80%.
... Biomining, or biohydrometallurgy, is a strand of hydrometallurgy that utilizes a biotechnological approach using microorganisms to solubilize metals (Da Silva, 2015). Therefore, it is gaining acceptance as an ecofriendly and economic alternative to traditional methods to recover metals from WEEE, although limited research in this field has been performed (Priya and Hait, 2018;Rodrigues et al., 2015;Sodha et al., 2020). Biomining can be classified into two separate processes: bioleaching and bio-oxidation. ...
Agriculture plays a vital role in every national economy. It represents a substantial trading industry for an economically strong country. Remote sensing and geographical information system used to analyze and visualize agriculture environmentals have proved to be very beneficial to the farming community as well as inudstry. In this chapter, I tried to overview the application of remote sensing and geographical information system in agriculture and natural resource management. Application of different remote sensing technique are important for crop monitoring, crop condition assessment, and yield estimation for the sustainability of agriculture and natural resources. The spectral information is the important aspect of remote sensing data for crop modeling and it is strongly related to canopy parameters which are representative of crop health and crop growth stage. Remote sensing and GIS can also be used very effectively in land use, land cover analysis as well as damage assessment because of drought, floods, and other exteme weather events information on meteorology and vegetation are the two major important inputs into agriculture meteorology application of remote sensing technologies are an important and effective method to identify pests and disease. It is one of the effective tools for assesing and monitoring water resources.
... Biomining, or biohydrometallurgy, is a strand of hydrometallurgy that utilizes a biotechnological approach using microorganisms to solubilize metals (Da Silva, 2015). Therefore, it is gaining acceptance as an ecofriendly and economic alternative to traditional methods to recover metals from WEEE, although limited research in this field has been performed (Priya and Hait, 2018;Rodrigues et al., 2015;Sodha et al., 2020). Biomining can be classified into two separate processes: bioleaching and bio-oxidation. ...
... From the 1g copper strip used, 0.80 mg/g (± 0.02) was solubilized, as analyzed using AAS in comparison to the set control with only 0.03 mg/g (± 0.08) solubilized in the absence of strain SC. By comparison, a previous study reported, the total amount of copper extracted through bioleaching to be approximately 80-90% within a similar timeframe used in the current study (Rodrigues et al. 2015). This result indicates that strain SC has the ability to solubilize copper, thus con rming the activity of the strain shown during the bioleaching process with wPCB. ...
Electronic waste has been the fastest increasing waste generated globally and predicted to surpass 111 million tons per year by the end of 2050. The amount of e-waste is a concern not just due to its volume, but also due to its high composition of heavy metal elements, which has leads to increased development of urban mining in terms of heavy metal extraction. One common method of extraction, i.e., acid leaching, is known for its harmful residual leachate, in which can have a high impact on the environment. This focuses on the alternative leaching techniques known as bioleaching, which take advantages of microbial activity in mobilization of metal into a more soluble form. Strains from sanitary landfill soil were isolated in acidic media and identified as Bacillus sp. strain SE, Lysinibacillus sp. strain SE2, Bacillus sp. strain S1A, and Oryzobacter sp. strain SC. Among the isolated stains, the identified strain Oryzobacter sp. strain SC was able to extract up to 23.36 ppm copper from waste printed circuit boards using a two-step bioleaching process, confirming the ability of the strain to perform bioleaching of copper from e-waste.
... It is an efficient alternative to stirred tank reactors with the advantages of using high solid loading, higher particle size, lower energy requirement and reduced physical stress on the microbial cells. In view of eliminating the crushing step to achieve size reduction, coarsely ground e-waste can be used in this type of bioreactor [65]. ...
Obsolete electronic devices and their components majorly contributed by the computer and mobile phone printed circuit boards (PCBs) constitute the electronic waste (e-waste). The e-wastes pose an environmental threat due to their eco-toxicological characteristics, thus making its management a mandate through an ecologically sustainable process. Further, the high concentration of metals in the e-waste makes it a secondary ore for metal recovery. Bioleaching is a bio-hydrometallurgical process, which is microbe-mediated dissolution of metals. Different nutritional classes of microorganisms like autotrophs and heterotrophs are active bioleaching agents of e-wastes. The mode of action of microbes for bioleaching of metals is obscure and is believed to ensue through redox reactions, protonic attack, or chelation. The process of bioleaching is influenced by biotic factors like the group and class of microorganism, growth rate, metabolic activity, etc. However, there are several abiotic factors that strongly affect the bioleaching efficiency.
... Presently, many technologies were suggested for recovering copper from WPCBs. The suggested technologies include primarily pyro metallurgy [10,11], hydrometallurgy [7,8,12], bio-technology [13][14][15] and mechanical methods [16,17]. Amongst these technologies, hydrometallurgical processes are fairly low expenses, producing no fumes or dusts, selective and appropriate for traditional applications, are considered promising choices for the handling of WPCBs [18,19]. ...
... The percentage of Cu dissolution from the respective tests was compared, because Cu forms the major element in terms of composition (% w/w) amongst other metals in WPCB and has been considered as a standard metal for recovery from PCBs. 50 The dissolution of Cu, pH, ORP variations and Fe (II) concentration with time are shown in Fig. 4. ...
BACKGROUND
Waste printed circuit boards (WPCBs) are a resource containing a wide array of metals and are of great importance because their metal concentration is much greater than that in the ores. Previous studies have been devoted mostly to copper (Cu) bioleaching from WPCBs because it has the highest proportion ( ∼ 10–30%) of all their component metallic elements. The present study focused on an intensified mixed meso‐acidophilic bacterial leaching of multi‐metals from WPCBs of spent mobile phones, with the system operating under high oxido‐reductive potentials (HORPs). Inductively coupled plasma‐optical emission spectrometry (ICP‐OES), X‐ray diffraction (XRD) and scanning electron microscopy‐energy dispersive X‐ray (SEM‐EDX) characterization indicated the WCPB sample had recoverable contents of Cu, aluminium (Al), nickel (Ni) and zinc (Zn) which were targeted for bioleaching.
RESULTS
Shake flask optimization studies, under HORP >750 mV indicated dissolutions of 98.1% Cu, 55.9% Al, 79.5% Ni and 66.9% Zn under optimized conditions of 9 g L–1 iron [Fe (II)], 10% pulp density, initial pH 1.8 and 10% (v/v) as initial inoculum. Under these conditions, at ORP >650 mV, 97.3% Cu, 55.8% Al, 79.3% Ni and 66.8% Zn were achieved in bench‐scale (1 L) bioreactor systems without any significant reduction in efficiency (compared to shake flasks) after 8 days of operation.
CONCLUSION
Variations in co‐relatable parameters, such as pH, ORP and Fe (II) concentrations, indicated that these parameters significantly contributed to metal leaching. Operating the system under high and controlled ORPs is a faster and more efficient way to leach multi‐metals from WPCBs. © 2020 Society of Chemical Industry
... Many researchers have studied the recycling of WPCBs, including the mechanical--physical process [8,9], pyrometallurgy [10], hydrometallurgy [11,12] and biometallurgy [13,14]. The mechanical-physical process is the most widely used for the industrial treatment but it is usually as the preparation due to the limitation of metal alloy separation. ...
... However, most reported literatures focused on high-grade waste PCBs and cleaning of resin powder are ignored (Isildar et al., 2019). These may due to the fact that the traditional bioleaching technology that bioleaching in pH 1.5 to 2.0 easily produced Fe(III)-precipitates would lead to Fe loss, the generation of new impurities, halfway extraction of metals and the formation of kinetics barrier (Riley et al., 2018), Furthermore, the high toxicity of solid waste on cells make bioleaching must be performed at pulp density below 10% (Rodrigues et al., 2015;Xia et al., 2018). All these increased the requirement of cost and resulted in low economic returns. ...
Metals removal from industrial process residues is essential to alleviate the potential threat to environment and avoid the resource waste. Because of very low concentration of metals and complexity of residues, conventional pyrometallurgical and hydrometallurgical routes suffer high cost and uncompleted removal. Here acid catalysis coupling bioleaching strategy was proposed for cost-efficient cleaning of metals from waste resin powder by applying double stress adapted consortium. The results showed that low pH bioleaching significantly improved the metals release, near 100% metals was leached out and no impurities of Fe(III)-precipitates was present in bioleached residue at pulp density of 10% and pH 0.7, which indicated the positive effects of acid in bioleaching of waste resin powder. Economic analysis exhibited that more profits of 33.7 /t residue were obtained respectively from metals recovery in case of pH 0.7 bioleaching compared with bioleaching at pH 1.5 and acid leaching at pH 0.7. Further stirring bioleaching and static leaching showed similar metals extraction rate under high pulp density conditions and TCLP tests indicated all bioleached residues could be reused as nonhazardous materials safely. However, static bioleaching showed higher ferric iron regeneration capacity and more stable community composition. These findings demonstrated that static low pH bioleaching might be more feasible for treatment of solid waste in full-scale applications from a technological and economical perspective.
... So there is no need to use 10 M NaOH for the treatment of WPCB. Rodrigues et al. (2015) have described the treatment of 50 g WPCB sheets with the mixture of 500 mL of diethylene glycol and potassium hydroxide at 90°C for 60 min to remove the lacquer coating. This comes out to be about 20 L diethylene glycol and potassium hydroxide used if 2 kg of WPCBs is to be treated. ...
The electronic waste is the fastest-growing solid waste all over the world. The printed circuit board (PCB), an
essential part of all the electronic waste is a potential source of various metals thus known as “Urban-mine”. In
this paper, a novel approach to enhance the extraction of copper from non-pulverized waste printed circuit
boards (WPCBs) was carried out. WPCBs pre-treatment with NaOH for removal of the epoxy coating was optimized
before the bioleaching process. The pretreatment resulted in the exposure of the metal present on
WPCBs. Copper was extracted by two-step bioleaching process. In the first step ferric sulphate was biogenerated
by Leptospirillum ferriphilum dominating iron oxidizing consortium with 1196.0 mg/L/h of average ferrous sulphate
oxidation rate. In the second step, the biogenerated ferric iron was used for copper extraction from a single
plate as well as from multiple plates in scale-up studies. In the scale-up study, 3 batches of eleven WPCB plates at
a time were studied and an average 168 ± 1.3 g copper was recovered at the end of the process, which corresponds
to 99% leaching. The recovered copper was precipitated from the leachate by the cementation process
using iron scrap and almost 99% copper was recovered after the process. The developed process shows the
potential to be applied at commercial scale for recovery of metals and the management of electronic waste which
leads to conservation of resources and environment.
... Nevertheless, the waste from electric and electronic equipment (WEEE) could be a secondary metal resource, especially from printed circuit boards (PCBs) that are the brain of electronic products (Xiang et al., 2010). The attention for the metal recovery from end-oflife PCBs is due to the high metal content, mainly Cu, which makes them a potential source of secondary raw materials in the perspective of the circular economy implementation (Rocchetti, Amato & Beolchini, 2018;Rodrigues et al., 2015). The positive effect could be further enhanced by the avoided disposal of these components, classified as hazardous waste (Leung et al., 2008;Musson et al., 2006;Shen et al., 2008). ...
A kinetic study of the process for the copper leaching from printed circuit board, by Fe3+, was reported. A mathematical model, supported by experimental data, considered the mechanisms that control the reaction (chemical reaction, particle or liquid film diffusion). The kinetic of the chemical reaction was studied by two models (pseudo-first and pseudo-second order), with a calculated activation energy of 18-25 kJ/mol. Nevertheless, both the models showed two criticalities: the Cu concentration dependence from the 〖Fe〗_0^(3+) and the 〖Fe〗^(3+) reducing rate. Therefore, a new mathematical model was proposed to predict the recoverable Cu from PCB, by three parameters: the Cu content, the Fe3+ concentration and the temperature. The high reliability of the model makes it an essential tool for the urban mining process optimization.
Rapid elevation of global population along with increased urbanization and industrialization afflict the water resources leading to the blooming of wastewater. Two or more aromatic rings fused with organic compound Polycyclic Aromatic Hydrocarbons (PAHs) emerged worldwide through anthropogenic processes, mainly due to the incomplete combustion of organic fuels. In accordance with the United States Environmental Protection Agency (USEPA), there are 16 PAHs that are deemed as primary pollutants. These are toxic to the living organisms due to their pervasive existence, rebelliousness, potential for bioaccumulation and carcinogenic venture. Several methods including fixation, incineration and oxidation are put forward to remove PAHs. Occasionally some fictional toxic products are produced by the incomplete removal of PAHs. Bioremediation is one of the ecological techniques to remove the PAHs. Microbial biodegradation is considered as an effective and inexpensive technique to remove PAHs along with other hydrocarbons and xenobiotic compounds and are accomplished by few PAHs degrading bacteria including Haemophilus spp., Mycobacterium spp., Paenibacillus spp., Pseudomonas aeruginosa, P. fluorescens, Rhodococcus spp. along with few biosurfactant-producing microbes. The novel biochemical events involved in hydrocarbon catabolism are microbial physical adaptation, their acquisition and uptake. The bioremediation efficacy can be further ameliorated through genetic modification of the microbes. This chapter will focus on the eco-friendly treatment for the PAHs remediation in in situ and ex situ. This chapter will explore the remediation of the PAH by-products through the multi-process conjunctional treatment processes under the green therapy.
The rapid consumption and disposal of electronic waste due to technological innovations and changes in living commodities are causing the development of a significant environmental challenge. Among the components of these wastes, spent printed circuit boards are particularly considered to be among the most valuable owing to their content of precious metals, such as gold first and potentially platinum, which may be available in a lower proportion. Effective methods as part of gold recovery strategies by industries and policymakers are developed and envisioned from economic and environmental perspectives. Currently, cyanidation dominates global gold production from e-waste due to its selectivity for gold. The high toxicity of cyanide, however, poses serious environmental issues, leading thiosulphate leaching to emerge as a non-toxic and promising alternative for gold extraction. Its industrial viability has been demonstrated by Barrick Gold Corporation at the Goldstrike site with the pretreatment of acidic or alkaline pressure oxidation. This review introduces bioleaching as a promising economic and environmentally friendly process for gold extraction. This review explores thiosulphate leaching of gold as an alternative to conventional cyanidation, with a particular focus on biothiosulphate production by adapted microorganisms. The factors that affect the pretreatment, chemical reaction mechanism, and design engineering are discussed. The consumption of thiosulphate was identified as one of the main challenges, restricting the reliability of the process. Various solutions for the reduction of its consumption and relevant process costs were discussed, with a particular examination from the engineering aspect of the process design and scalability to industrially relevant operating conditions by using bioreactors adapted to large pulp density loads of electrical waste.
The increasing amount of electronic waste (e-waste) has placed significant burdens on society and the environment, particularly with regards to waste printed circuit boards (WPCBs), which are essential in electronics manufacturing. As natural resources become scarce, it is crucial to effectively recycle and reclaim WPCBs due to their high value and large output. Comminuting printed circuit boards is a crucial step in enabling the recovery of valuable materials, and this review provides an in-depth analysis of WPCB comminution. It explores the structure, types, and composition of the WPCBs, including their mechanical properties. The review thoroughly surveys conventional mechanical comminution machinery and also discusses emerging technologies such as innovative pretreatment approaches, electrodynamic disintegration, high voltage electrical pulses, and abrasive waterjet cutting. The literature has been critically examined to identify research gaps and inconsistencies , and future directions for increased efficiency and sustainability are proposed.
The end-of-life (EoL) c-Si photovoltaic (PV) solar cell contains valuable silver, and chemical leaching can extract silver from the cell. However, limited works have been reported on the leaching kinetics and hydrodynamic behaviour of silver leaching process. In this work, an integrated experiment and numerical study are conducted to understand and optimise the silver leaching process in rotating systems. First, the lab-scale physical experiments are conducted to obtain a reaction kinetics model of silver leaching from PV cells. Then, a CFD-DEM model is developed to describe the reacting flow details related to solar cell particles' leaching process including this kinetic model. The model is validated against the lab measurement in terms of flow pattern and leaching performance. Then the CFD-DEM model is applied to a larger rotating system and studies the effects of rotator speed, rotator length, and rotator shape on leaching efficiency. The simulation results indicate that the particles inside the reactor experience mixing, transition, and suspension states with increased rotator length and rotator speed. In the transition state, the particles accumulate near the wall and form a packed bed, leading to the lowest leaching efficiency. In the suspension state, the particles are well fluidized and form a loose, ring-like particle wall. The leaching efficiency has a positive relationship with the fluidization level of the solid phase. The results also show that the leaching efficiency drops when linearly scaling up the reactor size while fixing other operating conditions. This work lays a foundation for process scale-up and optimization of EoL PV panel recycling.
In this work, the recovery of Cu from large waste printed circuit board (PCB) pieces by biogenic ferric sulphate at high solid to liquid ratio was studied. PCB parts were packed in a column and biogenic ferric was constantly recirculated. A high oxidation reduction potential (ORP) decrease was observed in ferric leaching due to ferric ion consumption; this drop caused a slower copper dissolution kinetics. After 25 days, 62.2% of copper was leached from PCBs column. PCBs column was connected to a flooded packed-bed (FPB) bioreactor to study the biological regeneration of ferric ion consumed in chemical reaction. The bioreactor connection enabled working at a constant ORP (700 mV vs. Ag/AgCl) during the whole test time. The improvement of oxidising conditions hugely increased copper dissolution rate, reaching 90% of copper recovery after 25 days. The FPB bioreactor operated continuously without showing inhibition problems and generating a leaching liquor with a high and constant ORP. The novel proposed configuration consists of a chemical reactor, where large PCBs pieces are piled at a high solid load, connected to a FPB bioreactor that regenerates the spent ferric ion enabling the leaching without reagents consumption, is a simple, inexpensive, low energy consumption, eco-friendly and effective system to recover copper from PCBs.
E-waste is considered to be an emerging global issue, the bulk of which is generated in Asia and then followed by the other continents. Inappropriate handling and recycling of e-wastes containing heavy metals, halogenated compounds, and radioactive substances can affect the environment. E-wastes when burnt in an open environment produce dioxins and polycyclic aromatics that are highly harmful and toxic in comparison to compounds produced during the burning of domestic waste. Bioleaching is the most effective and sustainable approach to meet the needs of future with respect to e-waste treatment and management. Bioleaching refers to the usage of naturally occurring microorganisms for the solubilization of metals from insoluble secondary wastes for its subsequent extraction. The development of molecular biology techniques has enabled the identification of microbes and deepened our knowledge about the role of microbes and its interaction in extraction of metal. This in turn has opened up new possibilities and in the application of biomining of e-waste.
Electronic waste is a growing waste stream globally. With 54.6 million tons generated in 2019 worldwide and with an estimated value of USD 57 billion, it is often referred to as an urban mine. Printed circuit boards (PCBs) are a major component of electronic waste and are increasingly considered as a secondary resource for value recovery due to their high precious and base metals content. PCBs are highly heterogeneous and can vary significantly in composition depending on the original function. Currently, there are no standard methods for the characterisation of PCBs that could provide information relevant to value recovery operations. In this study, two pre-treatments, smelting and ashing of PCB samples, were investigated to determine the effect on PCB characterisation. In addition, to determine the effect of particle size and element-specific effects on the characterisation of PCBs, samples were processed using four different analytical methods. These included multi-acid digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) analysis, nitric acid digestion followed by X-ray fluorescence (XRF) analysis, multi-acid digestion followed by fusion digestion and analysis using ICP-OES, and microwave-assisted multi-acid digestion followed by ICP-OES analysis. In addition, a mixed-metal standard was created to serve as a reference material to determine the accuracy of the various analytical methods. Smelting and ashing were examined as potential pre-treatments before analytical characterisation. Smelting was found to reduce the accuracy of further analysis due to the volatilisation of some metal species at high temperatures. Ashing was found to be a viable pre-treatment. Of the four analytical methods, microwave-assisted multi-acid digestion offered the most precision and accuracy. It was found that the selection of analytical methods can significantly affect the accuracy of the observed metal content of PCBs, highlighting the need for a standardised method and the use of certified reference material.
There is a growing interest in electronic wastes (e-wastes) recycling for metal recovery because the fast depletion of worldwide reserves for primary resources is gradually becoming a matter of concern. E-wastes contain metals with a concentration higher than that present in the primary ores, which renders them as an apt resource for metal recovery. Owing to such aspects, research is progressing well to address several issues related to e-waste recycling for metal recovery through both chemical and biological routes. Base metals, for example, Cu, Ni, Zn, Al, etc., can be easily leached out through the typical chemical (with higher kinetics) and microbial (with eco-friendly benefits) routes under ambient temperature conditions in contrast to other metals. This feature makes them the most suitable candidates to be targeted primarily for metal leaching from these waste streams. Hence, the current piece of review aims at providing updated information pertinent to e-waste recycling through chemical and microbial treatment methods. Individual process routes are compared and reviewed with focus on non-ferrous metal leaching (with particular emphasis on base metals dissolution) from some selected e-waste streams. Future outlooks are discussed on the suitability of these two important extractive metallurgical routes for e-waste recycling at a scale-up level along with concluding remarks.
Waste electrical and electronic equipment (WEEE), also known as electronic waste (e-waste), is considered as a secondary reservoir of metals because of their tremendous metal content. Conventional approaches for the extraction of metals from WEEE are basically pyrometallurgy and hydrometallurgy. However, both of these techniques have their own limitations, which have led to a shift toward biometallurgical technique. Biometallurgy or bioleaching technique, involving mostly acidophilic microorganisms, is an eco-friendly, cost-effective technique but is inherently time-consuming. This necessitated the need for the application of bioprocess engineering for the development of suitable bioreactors as mechanized systems for fast, efficient, and improved metal extraction from WEEE. The bioleaching process operated in batch or continuous mode in specialized bioreactors is reported to be promising on the quantitative extraction of various metals from WEEE. Metal extraction is further reported to improve by implementing the optimized process parameters. In these contexts, process engineering aspects, including the applicability of bioreactors and bioprocess engineering for bioleaching of metals employing chemolithotrophic and organotrophic microbes from WEEE are comprehensively presented. Mechanism of bioleaching, potential microbes, metal extraction ability, operational strategies, and process development with future research perspectives are outlined.
Two of the main challenges presented by the implementation of nickel laterites atmospheric acid leaching are: (i) high acid consumption and (ii) high final iron concentrations in the PLS. In the current work, a novel process was devised by applying pyrometallurgical and bio-hydrometallurgical operations. The experimental set-up comprised the reduction of a nickel limonitic ore with hydrogen gas in a rotary kiln, at 900 °C, until all the goethite was converted to metallic iron. Subsequently, the reduced sample was bioleached by mesophilic microorganisms grown on Fe²⁺ (Acidithiobacillus ferrooxidans) at 5% solids, 32 °C, and pH < 3. The results showed that an increase in the Eh values, promoted by the bacteria, resulted in the leaching Fe, Ni and Co, therefore a dissolution of 92% of the nickel and 35% of the cobalt was observed in experiments carried out with 35 Kg H2SO4/(ton of the reduced ore). The iron concentration in the liquor generated under these experimental conditions was below 5 mg/L owing to the fact that Fe³⁺ precipitated as jarosite. The experimental conditions applied also resulted in low acid consumption and the final total iron concentration was also reduced in the leach liquor (< 200 mg/L), which were considerably lower than the values reported for the HPAL process.
This study has attempted to ascertain the linkages between circular bio-economy (CirBioeco) and recycling of electronic (e-)waste by applying microbial activities instead of the smelter and chemical technologies. To build the research hypothesis, the advances on biotechnology-driven recycling processes for metals extraction from e-waste has been analyzed briefly. Thereafter, based on the potential of microbial techniques and research hypothesis, the structural model has been tested for a significance level of 99%, which is supported by the corresponding standardization co-efficient values. A prediction model applied to determine the recycling impact on CirBioeco indicates to re-circulate 51,833 tons of copper and 58 tons of gold by 2030 for the production of virgin metals/raw-materials, while recycling rate of the accumulated e-waste remains to be 20%. This restoration volume of copper and gold through the microbial activities corresponds to mitigate 174 million kg CO2 emissions and 24 million m3 water consumption if compared with the primary production activities. The study potentially opens a new window for environmentally-friendly biotechnological recycling of e-waste under the umbrella concept of CirBioeco.
The rapidly expanding use of electronic products has led to the generation of very large quantities of waste electrical and electronic equipment (WEEE). This waste essentially consists of polymeric, ceramic, and metallic materials, with the metal fraction including noble and base metals, which may be toxic. It is therefore important to recycle printed circuit boards (PCBs) for both economic and environmental reasons, especially since this solid waste contains noble metals (gold and silver). Given this background, the aim of the present work was to develop a hydrometallurgical route for leaching of the silver present in computer PCBs, using a combination of sodium chloride and calcium hypochlorite as the lixiviants. Optimization was performed of the following independent variables: (i) pulp density, (ii) calcium hypochlorite concentration, (iii) sodium chloride concentration, and (iv) leaching time. Multivariate experimental designs were employed, consisting of a 2⁴ full factorial design and response surface methodology with a spherical central composite design (CCD). The operational conditions were varied according to the mathematical equation obtained from the CCD, in order to find their best values which resulted in the maximum Ag extraction. The optimal conditions for the leaching of silver were a pulp density of 48 g.L⁻¹, calcium hypochlorite concentration of 165 g.L⁻¹, sodium chloride concentration of 65 g.L⁻¹, and extraction time of 200 min, resulting in 95.29 ± 0.72% extraction of silver. Silver was dissolved by forming complexes with chloride, being AgCl4aq3− the predominant specie. In summary, the hydrometallurgical route employed in this work enabled satisfactory and environmentally favorable extraction of silver.
The growing production and use of electric and electronic components has led to higher rates of metal consumption and waste generation. To solve this double criticality, the old linear management method (in which a product becomes waste to dispose), has evolved towards a circular approach. Printed circuit boards (PCBs) are the brains of many electronic devices. At the end of their life, this equipment represents a valuable scrap for the content of base metals such as Cu and Zn (25 and 2 wt %, respectively) and precious metals such as Au, Ag, and Pd (250, 1000, and 110 ppm, respectively). Recently, biotechnological approaches have gained increasing prominence in PCB exploitation since they can be more cost-efficient and environmentally friendly than the chemical techniques. In this context, the present paper describes a sustainable process which uses the fungal strain Aspergillus niger for Cu and Zn extraction from PCBs. The best conditions identified were PCB addition after 14 days, Fe³⁺ as oxidant agent, and a pulp density of 2.5% (w/v). Extraction efficiencies of 60% and 40% for Cu and Zn, respectively, were achieved after 21 days of fermentation. The ecodesign of the process was further enhanced by using milk whey as substrate for the fungal growth and the consequent citric acid production, which was selected as a bioleaching agent.
Parmi les différents types de déchets secondaires, les déchets électroniques représentent le flux de déchets dont la croissance au niveau mondiale est la plus forte. La récupération des métaux dans ces déchets est théoriquement plus efficace d’un point de vue énergétique que l’exploitation de gisements primaires. Cependant, la complexité de ces produits est telle qu’il n’est pas toujours possible de les insérer dans les chaînes de recyclage conventionnelles. La pyrométallurgie est le procédé le plus utilisé pour le raffinage des métaux contenus dans les circuits imprimés mais ce procédé de recyclage est très consommateur d’énergie et est réservé aux déchets à haute teneur en métaux précieux. Les procédés hydrométallurgiques sont moins coûteux et particulièrement flexibles. En particulier, l’utilisation de microorganismes permettant de catalyser les processus d’oxydation des métaux représente une alternative intéressante tant d’un point de vue économique qu’environnemental. Des études ont été menées sur la biolixiviation des circuits imprimés: d’un côté l’utilisation d’acides organiques et cyanure produits par des champignons ; de l’autre, l’utilisation de fer ferrique produit par des bactéries acidophiles, qui ne nécessitent pas de conditions stériles. L’étude de la biolixiviation des déchets de circuits imprimés par des bactéries acidophiles est l’objectif de la thèse. Pour ce faire, un procédé en 2 étapes en continu est mis au point. Différentes problématiques sont prises en compte : caractérisation et préparation des circuits imprimés ; influence du type de broyage ; adaptation des bactéries aux conditions spécifiques de la lixiviation ; rôle du fer ferrique, du pH et de la température ; besoins en O2 et CO2; mécanismes qui contrôlent la cinétique de mise en solution des métaux ; détermination des conditions physico-chimiques et biologiques. Cette thèse est réalisée à l’IRCP et au BRGM, en partenariat avec GeoRessources et est financée par la Chaire ParisTech Mines Urbaines soutenue par Eco-systèmes.
Critical metals are key raw materials for new generation clean energy production. The extraction of critical metals often follows the difficult processing of primary ores and they are many times recovered as the companion metals. With the depletion of primary reserves, the focus has now shifted to processing the urban mines, like electronic (e‐)waste. Among the different types of e‐waste, the waste printed circuit boards (WPCBs) are the major reservoir of high‐value critical metals and are usually treated by the traditional pyro‐ and/or hydro‐metallurgical techniques. However, the application of microbial activities in metals recycling is rapidly emerging as a green technology in comparison to smelter or chemical processing. The application of microorganisms (bacteria/fungi) in WPCBs’ recycling is being increasingly explored in order to meet the parallel objectives of resource recovery and pollution mitigation. Therefore, the present article assesses the current frontiers in bioleaching of critical metals from WPCBs and contains discussions on process fundamentals, challenges, and perspectives. The applicability of microbial recycling of WPCBs at a higher scale in terms of a circular economy and urban mining notion, the techno‐economic analysis, and environmental sustainability in comparison to the chemical processing route are also discussed. © 2020 Society of Chemical Industry
Adsorption is a surface phenomenon based on scientific and engineering principles and is widely explored for water treatment and purification. The low cost and eco‐friendly nature of the process makes it suitable to treat various kinds of waste for the extraction and recovery of precious metals from it. Factors governing the adsorption and kinetics of the process are elucidated in this chapter using adsorption kinetics models. Researchers are exploring new and green adsorbents specifically for metal recovery from waste streams. Clay, biopolymers, zeolites, and agricultural and industrial sludge have the advantage of low economics and high adsorption capacity. The chapter explores the potential of green adsorbents for the extraction of metals from industrial waste and waste electrical and electronic equipment (WEEE). In addition, a brief review on the scope of the adsorption process in other research areas is included at the end of the chapter. A case study is provided to understand the reaction conditions and efficiency of the process. Technical feasibility and challenges to the industrial scale application of the process are discussed, which may provide further research goals in this emerging field for solid waste management.
This chapter presents a range of conventional technologies for metal extraction from contaminated sites. The positive and negative aspects of each process have been reviewed in order to understand the applicability of each process for metal recovery from industrial/electronic waste in a sustainable way. A detailed literature survey on various mineral processing methods indicates that pyrometallurgical operations, despite showing significant extraction of metals, are not preferred due to the high energy requirement and release of toxic gases into the ecosystem. Hydrometallurgical processes are easy to implement in the laboratory and offer better reaction control and high extraction efficiency. However, the reagents are, in general, hazardous to handle; therefore, some of them such as cyanide leaching have already been phased out. In addition, the secondary pollution possibility, the need for pretreatment, and electrochemical method based post processing increase the process cost and limit the applicability of hydrometallurgical processes at large scales. An urgent need is felt to work on a sustainable framework to develop an eco‐efficient process for metal recovery.
Large amounts of waste electric and electronic equipment (WEEE) has been produced due to continuous technological innovation and the improvement of living standards. Based on the rich metal compositions, waste printed circuit boards (WPCBs) are considered as the most valuable component among WEEE. The recycling of metals from WPCBs with inappropriate methods or in informal sectors has been a profitable business, which, however, wastes resources and is harmful to environment and human health. Proper methods that are eco-friendly to recover metals from WPCBs are therefore urgent and essential for both industries and policy makers. In this article, the technology details of metal recycling processes are reviewed based on past research efforts to provide a complete image of the current status. The advantages and problems of several conventional methods are summarized and compared according to cost, environmental impact, and recovery efficiency. Possible approaches for improving mechanical treatment and bioleaching methods, are accordingly analyzed. Novel hybrid processes, such as chelation technology & bioleaching process, green adsorption & chemical leaching process, etc., are put forward to open up possibilities of multi-technology coupling processes for metal recycling from WPCBs.
The increase of waste from electric and electronic equipment has pushed the research towards the development of high sustainability treatments for their exploitation. The end-of-life printed circuit boards (PCBs) represent one of the most significant waste in this class. The interest for these scraps is due to the high Cu and Zn content, with concentrations around 25% and 2% respectively, combined with further precious metals (e.g. Au, Ag, Pd). Currently, the most common approaches developed for PCBs recycling include pyrometallurgical and hydrometallurgical treatments. On the other hand, biohydrometallurgical strategies are gaining increasing prominence, for the possibility to decrease both the environmental and the economic costs. Nevertheless, these techniques show the main limit due to the possibility to treat low quantities of waste, which makes unsustainable the further scale-up. To overcome this criticality, the present paper introduces an innovative bioleaching process carried out by Acidithiobacillus ferrooxidans (At. ferrooxidans) and Leptospirillum ferrooxidans (L. ferrooxidans). The developed technology allows to reach high PCB concentration, up to 5% (w/v), thanks to a high efficiency two-step design, able to reduce the metal toxicity on the bacteria metabolism. The treatment uses the ferric iron generated by bacterial oxidation, as oxidant, to leach Cu and Zn from PCBs. The possibility to overcome the solid concentration criticality is combined with high yield of 94% and 70% for Cu and Zn, respectively. The best selected conditions involve the At. ferrooxidans bacteria use at: 30 °C, solid concentration of 5% (w/v), 10 g/L of Fe²⁺, time of treatment 9 days. The experimental results are further enhanced by the carbon footprint assessment which proved the environmental advantage, compared to both the reference chemical treatment through ferric iron and literature processes (hydrometallurgical and bioleaching approaches). The analysis explained as the PCBs concentration in the solution allows to decrease the bioreactor size with the consequent reduction of energy and raw material demand. This benefit can be translated into a 4 times reduction of the CO2-eq./kg treated PCB emissions, compared to the best bioleaching processes, reported in the literature.
Many studies are now focusing on bioleaching methods to recover metals from WEEE. The efficiency of this process is highly dependent on microorganisms but also on the solid-liquid-gas mass transfer, which is controlled by the reactor design. In this study, bioleaching of comminuted spent printed circuit boards (PCBs) was performed in a stirred tank reactor operated in batch mode and in a double-stage continuous bioreactor. The metal dissolution kinetics were compared. The first stage of the continuous bioreactor was a bubble column in which a BRGM-KCC acidophilic consortium comprising Leptospirillum ferriphilum and Sulfobacillus benefaciens was used to oxidise Fe(II) into Fe(III). The resulting liquor was used to leach out metals contained in PCBs in the second stage of the bioreactor with mechanical stirring. The use of two distinct stages allowed the bacteria to adapt gradually to the PCBs and reach high dissolution yields, i.e. 96% Cu, 73% Ni, 85% Zn and 93% Co when 1% (w/v) PCB scraps were added into the bioleaching reactor, with a hydraulic residence time of 48 h. By using the double-stage bioreactor, the concentration of PCB scraps could be increased up to 1.8% (w/v) without reducing bioleaching performance. Biomass concentration in the second stage and adaptation of the microorganisms to the toxicity of the metals were sufficient for only the second stage to be used. Under these conditions, the dissolution kinetics were stable, even when iron was provided only by the comminuted PCBs.
Background
E-waste management is extremely difficult to exercise owing to its complexity and hazardous nature. Printed circuit boards (PCBs) are the core components of electrical and electronic equipment, which generally consist of polymers, ceramics, and heavy metals.
Results
The present study has been attempted for removal of heavy metals from printed circuit board by metal-resistant actinobacterium Streptomyces albidoflavus TN10 isolated from the termite nest. This bacterium was found to recover different heavy metals (Al 66%, Ca 74%, Cu 68%, Cd 65%, Fe 42%, Ni 81%, Zn 82%, Ag 56%, Pb 46%) within 72 h under laboratory conditions. The metal content of PCB after bioleaching was analyzed by ICP-MS. The crude PCB and bioleaching residue were characterized by FT-IR, XRD, SEM for the determination of structural and functional group changes for confirmation of bioleaching.
Conclusion
The findings of the present study concluded that Streptomyces albidoflavus TN10 is a promising candidate for bioleaching of heavy metals from the printed circuit board as an eco-friendly and cost-effective process.
Fe2+ oxidation by Acidithiobacillus ferrooxidans (At. ferrooxidans) under different solid contents by adding inert Al2O3 powder was examined in rotating-drum and stirred-tank reactors. The results show that the bioactivity of At. ferrooxidans in the stirred-tank is higher than that in the rotating-drum in the absence of Al2O3 powder, but the biooxidation rate of Fe2+ decreases markedly from 0.23 g/(L·h) to 0.025 g/(L·h) with increasing the content of Al2O3 powder from 0 to 50% (mass fraction) in the stirred- tank probably due to the deactivation of At. ferrooxidans resulting from the collision and friction of solid particles. The increase in Al2O3 content has a little adverse effect on the bioactivity of At. ferrooxidans in the rotating-drum due to different mixing mechanisms of the two reactors. The biooxidation rate of Fe2+ in the rotating-drum is higher than that in the stirred-tank at the same content of Al2O3 powder, especially at high solid content. The higher bioactivity of At. ferrooxidans can be maintained for allowing high solid content in the rotating-drum reactor, but its application potential still needs to be verified further by the sulfide bioleaching for the property differences of Al2O3 powder and sulfide minerals.
Heap leaching is a well established mining technology that involves stacking crushed ore into piles constructed on an impermeable layer fitted with a solution drainage system, or arranged on a slope to facilitate drainage. In many cases the ore is agglomerated through tumbling with acid and/or irrigation solution prior to stacking. Solution is irrigated (continuously or intermittently) over the top surface of the heap andleft to seep through the orebedwhereit can react with the target minerals. Dissolved metals are then transported with the flowing solution to the bottom of the heap from where they are removed via the drainage system into a collection pond as the pregnant leach solution (PLS). The target metal is removed from the PLS through a suitable technology (by solvent extraction, cementation or adsorption), and the barren solution (usually referred to as the raffinate) returned to the top surface of the heap. The technology has been in use since the 1960's for the acid leaching of copper oxide minerals, and since the 1970's for the cyanide leaching of gold and silver. A related technology, dump leaching, is based on the same principles as heap leaching, but usually uses uncrushed run-of-mine (ROM) material, usually containing sulfide minerals, or spent residue from leached heaps with a mineral grade too low to warrant further processing. Any additional metal liberated in a dump contributes to additional revenue of the mining operation, but dump leaching is rarely the primary method of metal extraction. It was in copper sulfide dump leach operations that the potential for bioleaching micro-organisms was first realized (Brierley, 1997; Olson et al., 2003). As the organisms involved occur naturally, no external intervention is needed to sustain their growth. Subsequently, heap bioleaching of copper sulfide minerals as a primary method for metal extraction was introduced first at Lo Aguirre in Chile in 1980 and then in numerous other operations from the early 1990's (Brierley, 1997). In the same vein as conventional oxide heap leaching, crushed and agglomerated ore is stacked into piles and irrigated with recycled acid solution. In addition, air is blown through pipes placed underneath the heap to ensure ready supply of oxygen and CO2 throughout. In some cases inoculation is practiced and the microbial environment is enhanced by addition of nutrient material to the feed solution, but in general microbial growth in bio heaps proceeds naturally with little external intervention (Schnell, 1997). Heap bioleaching results in the oxidative dissolution of sulfide minerals. Industrially this is practiced in two main applications, the dissolution of pyrite and arsenopyrite in refractory gold ores to liberate cyanide leachable gold, and the dissolution of copper from sulfide minerals. Biological dissolution of copper sulfide minerals occurs also in dumps, although the lack of artificial aeration tends to limit the extent of this. Furthermore, acid rock drainage (ARD) can, in a sense, be seen as a natural dump bioleaching process.
Iron is a key element influencing bacterial growth, oxidation efficiency and precipitate formation for most industrial applications using bioleaching and biooxidation processes. In this study, iron oxidation by an enrichment culture dominated by Leptospirillum ferriphilum was studied in a simulated heap leaching solution containing (g/L); Fe2+ (20); Mn2+ (3); Mg2+ (4); Al3+ (0.1); Na+ (3.6); Ca2+ (0.6). Initially, studies were conducted in batch bottles at 25 °C in order to determine possible toxicity effect and settling properties of precipitates produced at different pHs. Settling characteristics including interface height, zone settling velocity and sludge volume index were determined. The precipitates had good settling ability. Thereafter, a continuous-flow fluidized-bed reactor (FBR) was operated at 37 °C. The percent iron oxidation in the FBR decreased gradually from 98.5% to around 60% within 20 d due to precipitate formation. After installing a gravity settler to the recycle line of the FBR, the iron oxidation rate increased from 2 to 4 g Fe2+/L·h within 15 d. The maximum Fe2+ oxidation rate was 10 g Fe2+/L·h at a HRT of 2 h and optimum oxidation performance was achieved at a loading rate of 10.7 g Fe2+/L·h. The oxygen mass transfer limited the Fe2+ oxidation corresponding to an oxygen transfer rate of 35 kg O2/m3·d. This study reveals that a FBR combined with a gravity settler in the recycle line has potential for Fe3+ regeneration in heap leaching of sulfidic minerals.
The present work was aimed at studying the bioleachability of metals from electronic scrap by the selected moderately thermophilic strains of acidophilic chemolithotrophic and acidophilic heterotrophic bacteria. These included Sulfobacillus thermosulfidooxidans and an unidentified acidophilic heterotroph (code A1TSB) isolated from local environments. Among the strategies adapted to obtain enhanced metal leaching rates from electronic scrap, a mixed consortium of the metal adapted cultures of the above-mentioned bacteria was found to exhibit the maximum metal leaching efficiency. In all the flasks where high metal leaching rates were observed, concomitantly biomass production rates were also high indicating high growth rates. It showed that the metal bioleaching capability of the bacteria was associated with their growth. At scrap concentration of 10 g/L, a mixed consortium of the metal adapted cultures was able to leach more than 81% of Ni, 89% of Cu, 79% of Al and 83% of Zn. Although Pb and Sn were also leached out, they were detected in the precipitates formed during bioleaching.
The present work was aimed at studying the column bioleaching feasibility of metals from electronic scrap by the selected moderately thermophilic strains of mixed adapted consortium of acidophilic chemolothotrophic and acidophilic heterotrophic bacteria. These included Sulfobacilllus thermosulfidooxidans and Thermoplasma acidophilum. The tolerance of bacterial cultures to mixed metal ions (Ag+, Al3+, Cu2+, Fe3+, Ni2+, Pb2+, Sn2+and Zn2+) could be improved markedly after nearly two year adaptation from 12 g/L to 20 g/L. During whole leaching process included acid pre-leaching operation of 27 days and bioleaching operation of 280 days about 80% Zn, 64% Al, 86% Cu and 74% Ni was leached out.
Metal containing wastes/byproducts of various industries, used consumer goods, and municipal waste are potential pollutants, if not treated properly. They may also be important secondary resources if processed in eco-friendly manner for secured supply of contained metals/materials. Bio-extraction of metals from such resources with microbes such as bacteria, fungi and archaea is being increasingly explored to meet the twin objectives of resource recycling and pollution mitigation. This review focuses on the bio-processing of solid wastes/byproducts of metallurgical and manufacturing industries, chemical/petrochemical plants, electroplating and tanning units, besides sewage sludge and fly ash of municipal incinerators, electronic wastes (e-wastes/PCBs), used batteries, etc. An assessment has been made to quantify the wastes generated and its compositions, microbes used, metal leaching efficiency etc. Processing of certain effluents and wastewaters comprising of metals is also included in brief. Future directions of research are highlighted.
The aim of the current work is to develop an environmentally friendly process for the removal of heavy metals (Cu, Zn, Ni, Cd, Al, Cr, Pb) from recycling industry electronic waste with a consortium of Sulfobacillus thermosulfidooxidans and Thermoplasma acidophilum. The performances of commercial S0 powder and biogenic S0 sludge as substrates for the bio-removal of heavy metals were compared. Empirical models for the bioleaching process based on a statistical analysis were developed to evaluate the individual and combined effects of critical variables including S0 dosage, particle size, pulp density and bacterial feed formulation (inoculum size and inoculation style) in shaken flasks while specifying the effective variable ranges. Upscale feasibility experiments in a stirred tank reactor demonstrated a maximum metal bio-removal efficiency (92%) at a 1% dosage of biogenic S0 sludge and 2% dosage of commercial S0 powder (82%), given a 15% pulp density and 150 μm particle size with an intermittent low-concentration addition of inoculum (1ｘ106 cells/mL). Biogenic S0 sludge showed a higher degree of S0 oxidation (95%) in a shorter time period (12 days) compared to commercial S0 powder (82% in 24 days), thereby reducing the process cost. Risk assessments of discarded electronic wastes before and after bioremediation by the toxicity characteristic leaching procedure (TCLP), waste extraction test (WET), synthetic precipitation test (SPLP) and total threshold limit concentration (TTLC) indicated that the leaching/toxicity of bio-remediated residue was well within the regulatory limits.
In this study, ability of moderately thermophilic bacterial consortium to extract metals from electronic scrap was evaluated using shake flasks and lab-scale column reactor. We investigated the effects of having additional energy source (FeS2, S0, FeS2 + S0), using different consortia of moderately thermophilic bacteria and washing charge material as a pretreatment. At scrap concentrations of 10%, an adapted consortium of Sulfobacillus thermosulfidooxidans and Thermoplasma acidophilum extracted approximately 85% of Cu, 75% of Al, 80% of Ni and 80% of Zn from pretreated electronic scrap with FeS2 + S0 (1%). However, a consortium of S. thermosulfidooxidans and Sulfobacilllus acidophilus, containing FeS2 + S0, extracted 90% of Cu, 80% of Al, 82% of Ni and 85% of Zn.During column bioleaching studies of 165 days, approximately 74% Zn, 68% Al, 85% Cu, 78% Ni was leached out. The results of the leaching process are significant for understanding how to implement these processes on an industrial scale.
A comprehensive modelling study of the HydroZinc™ heap bioleach process, using the HeapSim modelling tool, is described. The model was calibrated on the basis of a small number of column leach experiments and compared against pilot heap test results. The model calibration thus confirmed, a detailed sensitivity study was conducted in order to establish the key parameters that determine the overall rate of Zn extraction. In the present case these were found to be oxygen gas–liquid mass transfer, various factors affecting the delivery of acid into the heap, and factors affecting the temperature distribution within the heap. A set of improved design parameters are proposed that would almost double the zinc conversion rate measured in the pilot plant – from 83% in 740 days to 78% in 383 days – and increase zinc production rate from 1.77 to 4.35 kg/m2/day. However, this improvement must be evaluated in the context of various implications for the downstream process.
Separation of waste printed circuit boards (WPCBs) has been a bottleneck in WPCBs resource processing. In this study, the separation of WPCBs was performed using dimethyl sulfoxide (DMSO) as a solvent. Various parameters, which included solid to liquid ratio, temperature, WPCB sizes, and time, were studied to understand the separation of WPCBs by dissolving bromine epoxy resin using DMSO. Experimental results showed that the concentration of dissolving the bromine epoxy resin increased with increasing various parameters. The optimum condition of complete separation of WPCBs was solid to liquid ratio of 1:7 and WPCB sizes of 16mm(2) at 145°C for 60min. The used DMSO was vapored under the decompression, which obtained the regenerated DMSO and dissolved bromine epoxy resin. This clean and non-polluting technology offers a new way to separate valuable materials from WPCBs and prevent the environmental pollution of waste printed circuit boards effectively.
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
The purpose of this study was to assess the solubilization of silicates during the chemical and bacterial leach-ing of finely ground black schist in shake flasks. The main sulfide minerals were pyrrhotite (Fe 1 − x S) and py-rite (FeS 2) with lesser amounts of sphalerite (ZnS), pentlandite (Ni,Fe,Co) 9 O 8), violarite (FeNi 2 S 4), and chalcopyrite (CuFeS 2). Quartz, micas, and feldspars were the main Si-containing phases. Dissolution of the non-sulfidic minerals was monitored by analysis of Si, Al, Ca, Mg, and K solubilized from the black schist in 30 day leaching experiments at 22 ± 2 °C. The dissolution of main constituent elements from silicate minerals was a function of the pH of the leach solution and no direct role of bacterial action on the solubilization of silicates was evident. Ferrous or ferric iron addition did not affect the concentrations of elements dissolved from silicates except for mica interlayer K + , which was incorporated into the jarosite fraction.
High dielectric permittivity barium titanate/epoxy resin (BaTiO3/EPR) composites with different size BaTiO3 particles were prepared and their dielectric properties were studied via a wide range of temperature and frequency. The results show that an appropriate silane coupling agent can be used in order to improve the interaction between BaTiO3 and EPR, and subsequently induces a high dielectric permittivity and a low loss tangent. The size and concentration of BaTiO3 particles also have an effect on the microstructure and dielectric property of composites. Additionally, the dielectric properties of the composites with different size of BaTiO3 particles give different temperature dependence because of the existence of phase transition of large size BaTiO3 particles at its Curie temperature.
a b s t r a c t Waste of electric–electronic equipment (WEEE) with an annual growth rate of about 3–5% is the fastest growing waste stream in municipal wastes. Notwithstanding their environmental pollution potential, waste of electrical and electronic equipment (WEEE) with their high content of base and precious metals, in particular, are regarded as a potential secondary resource when compared with ores. For the recovery of metals from WEEE, various treatment options based on conventional physical, hydrometallurgical and pyrometallurgical processes are available. These process options with particular reference to hydromet-allurgical processes were reviewed in this study. With their relatively low capital cost, reduced environ-mental impact (e.g. no hazardous gases/dusts), potential for high metal recoveries and suitability for small scale applications, hydrometallurgical processes are promising options for the treatment of WEEE. Since the metals are present in native form and/or as alloys, an oxidative leaching process is required for the effective extraction of base and precious metals of interest. A two-stage process based on oxidative acid leaching of base metals (Cu in particular) followed by leaching of precious metals using cyanide, thiosulfate, thiourea or halide as lixiviant(s) can be suitably developed for the hydrometallurgical treat-ment of WEEE. However, further research is required to develop new, cost effective and environmentally friendly processes and/or refine existing ones for leaching and, in particular, downstream processes.
Bioleaching is the biological conversion of an insoluble metal compound into a water soluble form. In case of metal sulfide bioleaching, metal sulfides are oxidized to metal ions and sulfate by aerobic, acidophilic Fe(II) and/or sulfurcompound oxidizing Bacteria or Archaea. Bioleaching involves chemical and biological reactions. Despite molecular oxygen being the final electron acceptor for the overall metal sulfide bioleaching process, Fe(III) ions are the relevant oxidizing agent for the metal sulfides. The metal sulfide oxidation itself is a chemical process in which Fe(III) ions are reduced to Fe(II) ions and the sulfur moiety of the metal sulfide is oxidized to sulfate, and various intermediate sulfur compounds, e.g. elemental sulfur, polysulfide, thiosulfate, and polythionates. For example the oxidation of sphalerite (ZnS) to elemental sulfur is given in the following equation: (1) ZnS+2Fe3+→Zn 2++0.125S8+2Fe2+ Because of two different groups of metal sulfides exist, two different metal sulfide oxidation mechanisms have been proposed, namely the thiosulfate mechanism (for acid-insoluble metal sulfides, such as pyrite) and the polysulfide mechanism (for acid-soluble metal sulfides, e.g. sphalerite or chalcopyrite, CuFeS2). These mechanisms explain the occurrence of all inorganic sulfur compounds which have been detected in the course of metal sulfide oxidation (for review see: Sand et al., 2001; Rohwerder et al., 2003; Schippers, 2004; Chapter 2). The role of the microorganisms in the bioleaching process is to oxidize the products of the chemical metal sulfide oxidation (Fe(II) ions and sulfur-compounds) in order to provide Fe(III) and protons, the metal sulfide attacking agents. In addition, proton production keeps the pH low and thus, the Fe ions in solution. Aerobic, acidophilic Fe(II) oxidizing Bacteria or Archaea provide Fe(III) by the following equation: (2) 2Fe2++0.5O2+2H+→ 2Fe3++H2O Aerobic, acidophilic sulfur-compound oxidizing Bacteria or Archaea oxidize intermediate sulfur compounds to sulfate and protons (sulfuric acid). Most relevant is the oxidation of elemental sulfur to sulfuric acid since elemental sulfur can only be biologically oxidized under bioleaching conditions: (3) 0.125S8+1.5O2+H2O→SO 24 +2H+ The sulfur-compound oxidizing Bacteria or Archaea produce protons which dissolve metal sulfides besides pyrite which is not acid-soluble. Pyrite is only attacked by Fe(III) ions (not by protons) and therefore only dissolved by Fe(II) oxidizing Bacteria or Archaea. This book chapter gives an update of previous excellent reviews on microorganisms involved in bioleaching (e.g. Harrison, 1984; Rossi, 1990; Rawlings, 1997, 2002; Johnson, 1998; Hallberg &Johnson, 2001). In the first part of this chapter, the metal sulfide oxidizing microorganisms are described. In the second part, acidophilic microorganisms which do not oxidize metal sulfides and their importance for bioleaching are reviewed. In the third part, nucleic-acid based methods for the identification and quantification of these microorganisms are introduced.
Collation of published data for the four described Sulfobacillus species failed to generate a clear account of their relative bioleaching capabilities. The two main goals of this work were therefore to generate comparable data for the four described species and to incorporate the data into an evaluation of their contribution to metals extraction in bioleaching environments, summarised as follows: The sulfobacilli are moderately thermophilic acidophiles that grow in sulfurous and sulfidic environments with broad geographical distribution, across a range of temperatures and solution pH relevant to bioleaching. They attach to mineral sulfide surfaces, which may promote faster sulfide oxidation and they enhance to different degrees the leaching of mineral sulfides. In general, their tolerances to soluble metals tend to be low in comparison with the concentrations they may experience in leaching reactors. However, their presence in both heaps (low grade sulfide ores) and agitated tanks (high grade sulfide concentrates) demonstrates a strong ability to adapt to high metal ion concentrations in leachates. Their ability to form spores confers the ability to survive hostile environments and resume active growth when favourable conditions are restored. This last characteristic may counter their sensitivity to soluble base metals.
Over the last 35 years, there has been a debate concerning the interaction of iron- and sulfur-oxidizing bacteria and sulfide minerals. Two basic positions are held. The proponents of the direct mechanism argue that the bacteria possess a specific biological mechanism to degrade the mineral and thereby gain energy directly from the sulfide mineral. On the other hand, the proponents of the indirect mechanism argue that it is the ferric ions in solution that dissolve the mineral, and the bacteria gain their energy requirements from regenerating the ferric ions. The indirect mechanism undoubtedly occurs, but proponents of the direct mechanism argue that it is not the dominant route. In other words, the debate hinges on the kinetics of each of these possible paths. The evidence presented in the published literature both for and against each of these mechanisms has been critically examined. Arguments based on stoichiometry, bacterial attachment or observations of the mineral surface cannot resolve this debate. Since the critical factor is the kinetics of each proposed path, only kinetic studies can resolve the debate. Based on the evidence of the kinetic studies that were performed, a resolution to the debate is suggested.
In this paper, the experiments were conducted in a concentric cylinder shear device. The effect on oxidation activity of ferrous iron by Acidithiobacillus ferrooxidans was tested under different shear conditions achieved through regulating the rotating speed of the inner cylinder. The results suggested that the fluid shear rate had little adverse effect on the oxidation activity of At. ferrooxidans. In this study, silicon dioxide powder was added to the medium to investigate the effect of particles collision on the oxidation activity of bacterial cells, and it was found that the oxidation rate of ferrous iron by At. ferrooxidans was greatly decreased with the increase of silicon dioxide concentration.
Numerous processes co-exist for metal extraction and for metal removal from effluents of mining operations. Each process enjoys an economic advantage, including environmental cost and benefit, if utilized in a specific situation. This applies equally to biohydrometallurgical processes. This paper will analyze four types of biohydrometallurgical processes for their economic and environmental attributes: biooxidation of refractory gold, extraction of copper from sulfide, metal removal from effluents by active sulfate reduction, and metal removal by the use of wetlands. By examining the economic and environmental advantages of these processes, generalizations can formalized and it becomes possible to define niches of application where biohydrometallurgy can be considered. Our analysis shows that biohydrometallurgy can be efficient at small scale, be more environmentally friendly than conventional technologies and is relatively easier to operate. The higher financial risk associated with unproven technologies at the commercial scale is being eliminated as biotechnology-based plants are put into production.
The aim of this paper is to understand the factors that influence copper leaching from electronic scrap. It is revealed that the bioleaching is greatly influenced by process variables such as Fe3+ concentration, quantity of stock culture added, and pH. Before starting the leaching process, A. ferrooxidans was cultivated for 3–4 days as stock culture, until the concentration of Fe3+ ions had reached about 7.00 g/L, which was considered strong enough to dissolve metallic copper. The results show that high leaching rates of copper could be achieved in the presence of 6.66 g/L of Fe3+, 100% addition quantities of stock culture, and pH 1.5. It is concluded that bioleaching copper from printed circuit boards (PCB) using Acidithiobacillus ferrooxidans (A. f.) is feasible.
This review outlines current research in heap bioleaching, particularly in respect of the bioleaching of chalcopyrite, assesses the status of the bioprocessing of copper sulphides and evaluates promising developments.The bioleaching of sulphide minerals is reviewed with emphasis on the contribution from the microbial community, especially attachment and biofilm formation, bioleaching mechanisms and the potential benefits to be gained by a greater understanding of the molecular genetics of the relevant microbial strains.The leaching and bioleaching of copper sulphides is examined. The main focus is on heap bioleaching of whole ores, and the development of models to describe heap and dump processes that can be applied in the design phase as well as to optimise metal extraction. The characteristics of chalcopyrite leaching are discussed in respect of those conditions and controls that might be needed to make a heap bioleach commercially productive.
Jarosite precipitation is a very important phenomenon that is observed in many bacterial cultures. In many applications involving Acidithiobacillus ferrooxidans, like coal desulphurization and bioleaching, it is crucial to minimize jarosite formation in order to increase efficiency. The formation of jarosite during the oxidation of ferrous iron by free suspended cells of A. ferrooxidans was studied. The process was studied as a function of time, pH and temperature. The main parameter affecting the jarosite formation was pH. Several experiments yielded results showing oxidation rates as high as 0.181–0.194 g/L h, with low jarosite precipitation of 0.0125–0.0209 g at conditions of pH 1.6–1.7 with an operating temperature of 35 °C.
Silicate minerals are found with sulfide minerals and therefore, can be present during heap bioleaching for metal extraction. The weathering of silicate minerals by chemical and biological means is variable depending on the conditions and microorganisms tested. In low pH metal rich environments their dissolution can influence the solution chemistry by increasing pH, releasing toxic trace elements, and thickening of the leach liquor. The amenity of five silicate minerals to chemical and biological dissolution was tested in the presence of either ‘Ferroplasma acidarmanus’ Fer1 or Acidithiobacillus ferrooxidans with olivine and hornblende being the most and least amenable, respectively. A number of the silicates caused the pH of the leach liquor to increase including augite, biotite, hornblende, and olivine. For the silicate mineral olivine, the factors affecting magnesium dissolution included addition of microorganisms and Fe2+. XRD analysis identified secondary minerals in several of the experiments including jarosite from augite and hornblende when the medium contained Fe2+. Despite acidophiles preferentially attaching to sulfide minerals, the increase in iron coupled with very low Fe2+ concentrations present at the end of leaching during dissolution of biotite, olivine, hornblende, and microcline suggested that these minerals supported growth. Weathering of the tested silicates would affect heap bioleaching by increasing the pH with olivine, fluoride release from biotite, and production of jarosite during augite and hornblende dissolution that may have caused passivation. These data have increased knowledge of silicate weathering under bioleaching conditions and provided insights into the effects on solution chemistry during heap bioleaching.
This paper describes an investigation into the effect of iron concentration in the leach solution on the bioleaching of a low grade copper ore, where chalcopyrite was the dominant copper sulphide. The concentration of dissolved iron is primarily controlled by pH and the relative proportion of ferric to ferrous iron, with significant jarosite precipitation occurring above pH ≈ 1.8 in a highly oxidised system. The solution pH may be increased by the dissolution of acid soluble gangue and when iron oxidation is significantly higher than sulphur oxidation. The study was approached using two experimental systems. In the former, the leach solution was recycled through an ore bed of low aspect (reactor height divided by diameter) ratio for a portion of the experiment. During the recycle phase, no acid was added to the system and acid consumption by gangue material led to a pH increase (1.6–2.2). The resulting jarosite precipitation reduced soluble iron from 2.5 g/l to less than 250 mg/l. Copper recovery decreased, but not in proportion to the decrease in iron. This was partly attributed to adsorption on, or entrainment within, the jarosites. To study the effect of reduced iron concentration on leach performance under more controlled conditions, bioleaching was performed in packed bed column reactors with feed iron concentrations ranging from 5 g/l to 200 mg/l. Observations indicated an initial decreased rate of copper liberation with reduced iron concentration in the feed. The relationship between available Fe3+ concentration and copper liberation was not proportional. However, with time, the liberation of copper became independent of iron concentration in the percolation liquor. Further, the specific rate of copper liberation was consistently below the theoretical value on a basis of ferric iron concentration. The highest values of copper liberation were reported at the lowest iron concentrations. In summary, while increased iron concentration in solution may enhance the initial rate of leaching, mineral availability appears to dominate CuFeS2 leach kinetics through the majority of the leach. Furthermore, high iron concentrations in solution aggravate jarosite formation with concomitant retention of copper in the ore bed.
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.
Metal concentrates of printed circuit boards (PCBs) are the residue valuable metals from which non-metallic components are removed. The non-metallic components show bacterial toxicity in bioleaching process and can be recycled as well. In this study, the effects of initial pH, initial Fe(II) concentration, metal concentrate dosage, particle size, and inoculation quantity on the bioleaching were investigated so as to determine the optimum conditions and evaluate the feasibility of bioleaching of metal concentrates of PCBs by mixed culture of acidophilic bacteria (MCAB). The results showed that the initial pH and Fe(II) concentration played an important role in copper extraction and precipitate formation. Under the optimized conditions of initial pH 2.00, 12g/L initial Fe(II), 12g/L metal concentrate dosage, 10% inoculation quantity, and 60-80 mesh particle size, 96.8% the copper leaching efficiency was achieved in 45h, and aluminum and zinc 88.2% and 91.6% in 98h, respectively. All findings demonstrated that metals could be efficiently leached from metal concentrates of waste PCBs by using the MCAB, and the leaching period was shorten from about 8 days to 45h.
The objectives of this study were to evaluate the solubility of copper in waste printed circuit boards (PCBs) by bacterial consortium enriched from natural acid mine drainage, and to determine optimum conditions of bioleaching copper from PCBs. The results indicated that the extraction of copper was mainly accomplished indirectly through oxidation by ferric ions generated from ferrous ion oxidation bacteria. The initial pH and Fe(2+) concentration played an important role in copper extraction and precipitate formation. The leaching rate of copper was generally higher at lower PCB powder dosage. Moreover, a two-step process was extremely necessary for bacterial growth and obtaining an appropriate Fe(2+) oxidation rate; a suitable time when 6.25 g/L of Fe(2+) remained in the solution was suggested for adding PCB powder. The maximum leaching rate of copper was achieved 95% after 5 days under the conditions of initial pH 1.5, 9 g/L of initial Fe(2+), and 20 g/L of PCB powder. All findings demonstrated that copper could be efficiently solubilized from waste PCBs by using bacterial consortium, and the leaching period was shortened remarkably from about 12 days to 5 days.
Silicate minerals are present in association with metal sulfides in ores and their dissolution occurs when the sulfide minerals are bioleached in heaps for metal recovery. It has previously been suggested that silicate mineral dissolution can affect mineral bioleaching by acid consumption, release of trace elements, and increasing the viscosity of the leach solution. In this study, the effect of silicates present in three separate samples in conjunction with chalcopyrite and a complex multi-metal sulfide ore on heap bioleaching was evaluated in column bioreactors. Fe(2+) oxidation was inhibited in columns containing chalcopyrite samples A and C that leached 1.79 and 1.11 mM fluoride, respectively but not in sample B that contained 0.14 mM fluoride. Microbial Fe(2+) oxidation inhibition experiments containing elevated fluoride concentrations and measurements of fluoride release from the chalcopyrite ores supported that inhibition of Fe(2+) oxidation during column leaching of two of the chalcopyrite ores was due to fluoride toxicity. Column bioleaching of the complex sulfide ore was carried out at various temperatures (7-50 degrees C) and pH values (1.5-3.0). Column leaching at pH 1.5 and 2.0 resulted in increased acid consumption rates and silicate dissolution such that it became difficult to filter the leach solutions and for the leach liquor to percolate through the column. However, column temperature (at pH 2.5) only had a minor effect on the acid consumption and silicate dissolution rates. This study demonstrates the potential negative impact of silicate mineral dissolution on heap bioleaching by microbial inhibition and liquid flow.
Waste electric and electronic equipment, or electronic waste, has been taken into consideration not only by the government but also by the public due to their hazardous material contents. In the detailed literature survey, value distributions for different electronic waste samples were calculated. It is showed that the major economic driver for recycling of electronic waste is from the recovery of precious metals. The state of the art in recovery of precious metals from electronic waste by pyrometallurgical processing, hydrometallurgical processing, and biometallurgical processing are highlighted in the paper.
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Estudo da biolixiviação e a da lixiviação química de um concentrado sulfetado de zinco Thesis
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