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Biohydrometallurgy of Secondary Metal Resources: A Potential Alternative Approach for Metal Recovery
Journal of Chemical Technology and Biotechnology
Abstract
Research on biohydrometallurgy of secondary metal resources is primarily focussed on the leaching of valuable metals. For secondary metal resources biological processing can be an economically more effective and environmentally friendlier alternative to traditional hydrometallurgical and pyrometallurgical processes. Therefore, Bioydrometallurgy is a rapidly evolving biotechnology that has already provided revolutionary solutions to old problems associated with recovery of metals by conventional pyrometallurgy and chemical metallurgy. This review evaluates various pr
ocesses of recovery of metals from waste materials and commercial applications are di
scussed. Case studies and future technology directions are reviewed.
Keywords: Biohydrometallurgy; Metal recovery; Recycling; Secondary metal resources
... Bioleaching is an economical, efficient technique and an environmentally friendly alternative, used for the extraction of valuable minerals from low-grade ores (Gahan et al., 2012;Erüst et al., 2013), which involves a biphasic suspension of solid particles in a liquid medium (Srichandan et al, 2019), where chemolithotrophic bacteria are indirectly involved in the oxidation of ferrous ion (Fe2+) to ferric ion (Fe3+). An example of this group are bacteria of the genus Acidithiobacillus that are present in ore deposits (Fowler et al, 1999). ...
... Looking for carbon removal, the material may undergo combustion and the consequent formation of CO2, SO2 and As2O3, causing environmental pollution. Therefore, biohydrometallurgy is a rapidly evolving biotechnology that has already provided entrenched solutions to old problems associated with metal recovery by conventional pyrometallurgy or chemical metallurgy (Gahan et al., 2012;Erüst et al., 2013). Its application to low-grade gold-bearing sulfide ores allows for a reduction in cyanide consumption (Rodrigues et al, 2021). ...
The worldwide demand for silver is increasing due to the technological development in different areas, especially for the requirements in the production of renewable energies; therefore, for the treatment of refractory minerals by conventional processes, it is necessary to study mechanisms to identify the viability of their processing and the feasibility of their recovery, ensuring profitability. Gold and silver present in the matrix of sulfide-based ores are not affordably recovered by the conventional method involving leaching in sodium cyanide solution. Therefore, it must be subjected to oxidation pretreatment or conversion of the sulfides to simple compounds that allow recovery of the precious metals. The methods of oxidation of minerals considered refractory are carried out by hydro and pyrometallurgical methods, seeking the dissolution of sulfur, iron, arsenic and other elements present. It is important to identify and consider the mineralogical structure, microbiological variety, physicochemical characteristics, types of reactors, bacterial interactions, among other factors. The choice of biooxidation as the preferred process in projects for the recovery of gold, silver, copper or other metals, in most cases is based on the economic advantage, compared to the conventional processes of roasting, chemical leaching and pressurized leaching. The biooxidation of refractory argentiferous ores has been extensively studied in recent years, concluding that its application is feasible, mainly because it is environmentally friendly.
... [813] Notably, the success of recycling highly depends on the source material of the TCEs and many other factors; for further details, the interested reader is referred to the review article by Zheng et al. [808] Recycling remains challenging for gallium and indium due to difficulties in separating them from other metals. For instance, in the leaching processes, this would involve the separation from iron, [814] but also other metals need to be removed prior to selective recovery. ...
This review offers an illuminating journey through the historical evolution and modern‐day applications of liquid metals, presenting a comprehensive view of their significance in diverse fields. Tracing the trajectory from mercury applications to contemporary innovations, the paper explores their pivotal role in industry and research. The analysis spans electrical switches, mechanical applications, electrodes, chemical synthesis, energy storage, thermal transport, electronics, and biomedicine. Each section examines the intricacies of liquid metal integration, elucidating their contributions to technological advancements and societal progress. Moreover, the review critically appraises the challenges and prospects inherent in liquid metal applications, addressing issues of recycling, corrosion management, device stability, economic feasibility, translational hurdles, and market dynamics. By delving into these complexities, the paper advances scholarly understanding and offers actionable insights for researchers, engineers, and policymakers. It aims to catalyze innovation, foster interdisciplinary collaboration, and promote liquid metal‐enabled solutions for societal needs. Through its comprehensive analysis and forward‐looking perspective, this review serves as a guide for navigating the landscape of liquid metal applications, bridging historical legacies with contemporary challenges, and highlighting the transformative potential of liquid metals in shaping future technologies.
... As one of the hydrometallurgical methods for extracting critical and strategic elements from copper slag, bioleaching has been studied for the past decades. Bioleaching is considered an environmentally friendly and sustainable process and is a gradually evolving technology [114]. In bioleaching, microorganisms play a key role as extractants [115]. ...
The technosphere consists of material stocks accumulated by human activities, which can include processing residue, such as slag. Various smelting processes generate slag, and some valuable elements are concentrated in this by-product. In this review, the extraction of critical and strategic metals from non-ferrous slags is discussed. Critical and strategic metals are materials that are vital for the nation’s economy and defence, as well as its industries, and have common features, such as expected shortfalls, increasing demand, and few substitutions. There are several definitions, methods, and classifications of critical and strategic elements by different organisations. In this study, reports from seven institutions around the world are summarised, and a list of recommended critical and strategic metals is presented. Non-ferrous slags contain a considerable amount of critical and strategic elements, and research on technology and process development using both pyro- and hydrometallurgical methods is very attractive. When it comes to the extraction of values from slag and the development of technology, it is not only important to consider the economic aspect but also to ensure the processes are low in emissions and energy consumption but high in efficiency and recycling.
... Most researchers have recognized the indirect bio-oxidation mechanism. Some researcher shows that the physicochemical procedure which fall in a branch of hydrometallurgy that entails using bacteria to create chemical oxidants to carry out this procedure, we make use of in the recovery of metals from such waste, Microorganisms for example Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, Acidithiobacillus thiooxidans [46]. It has been a recognized procedure for the removal of metals consisting of different material [47] (Fig. 5). ...
In spite of the initial e-waste regulations entering into force in India in
2011 and also being modified in 2016, it is approximated that some 90–95% of e-
waste is handled in the casual market in and unorganized manner. The current medal
fabrication for different event in Tokyo Olympics also changed the vision of the
people about e-waste. The present manuscript provides an overview of the awareness
and management of e-waste in the capital of Rajasthan as a part of study. Different
articles have been reviewed and analysed in the domain of e-waste management and a
detailed insight about the current scenario, effects and possible solution are provided
in terms of better management of e-waste.
... Although an extensive number of investigations focused on recycling spent LiBs using different methods documented in recent years, there are only limited discussions about the challenges and advancements of applying flotation process for such purpose. Most of the review studies have been reported on hydrometallurgical processes [27,53,69], and some studies reviewed in particular bio-hydrometallurgical advancements on metal recoveries from different e-waste groups [70][71][72]. Therefore, the present paper for the first time scans the fundamental and applied challenges and opportunities of using froth flotation as a practical solution for recycling batteries not only targeting graphite but also selectively separation critical elements. ...
Lithium-ion batteries (LiBs) have been consumed exponentially due to the rapid growth of electric vehicles and electronics. Efficient recycling of spent LiBs is crucial for sustainability; however, major current technologies have disregarded froth flotation which has been recently introduced as an effective separation method and drawn extensive attention in the literature. The present review summarizes recent fundamental and applied progress on recycling spent LiBs using pretreatment methods followed by froth flotation. Flotation can potentially separate anode and cathode materials based on their surface wettability differences. However, the presence of organic binders reduces this wettability contrast. Thus, pretreatment methods like thermal processes, grinding, and chemical modification were critically reviewed from different perspectives to remove organic binders and enhance flotation efficiency. The article further discusses flotation reagents, physical and chemical pretreatment options, and environmental considerations for the LiBs recycling. Challenges regarding efficiency, scalability, and sustainability are highlighted. It was revealed that future research works should mainly focus on cleaner pretreatment methods, flotation optimization, and minimization of environmental impacts to advance battery recycling.
... The accuracy of these methods often depends on the pro ciency of the operators. Bio-detection methods have been applied to achieve more accurate steel classi cation, utilizing the different elemental properties of various scrap steel types [8,9] . However, the surfaces of automotive scrap steel are often coated with materials for corrosion resistance and oxidation prevention. ...
In the recycling of scrap metal, the establishment of the classification database of recyclables has the advantages of fast classification speed and high analysis accuracy. However, the classification and recycling of unknown samples become highly significant due to the extensive variety of standard metal samples and the challenges in obtaining them. In this study, a method for multi-element classification of automotive scrap metals in general environmental conditions was achieved by utilizing Laser-Induced Breakdown Spectroscopy (LIBS) and Two-Step Clustering Algorithm (K-means, Hierarchical Clustering). The two unsupervised learning algorithms were employed to cluster the LIBS spectral data of 60 automotive scrap metal samples rapidly and hierarchically. Three rare metal elements and three elements for distinguishing metal categories were selected to meet the recycling requirements. After applying the MSC (Multiplicative Scatter Correction) to the spectral data for calibration, the initial clustering clusters were determined using the DB index, CH index, and silhouette coefficient. Then, the Kruskal-Wallis test was conducted on each cluster to check the significance. And the clusters that failed the test were split and reclustered until all clusters met the significance criterion ( α =0.05). The accuracy of the proposed method for classifying the collected automotive scrap metals reached 97.6%. This indicates the great potential of this method in the field of automotive scrap metal classification.
... Most researchers have recognized the indirect bio-oxidation mechanism. Some researcher shows that the physicochemical procedure which fall in a branch of hydrometallurgy that entails using bacteria to create chemical oxidants to carry out this procedure, we make use of in the recovery of metals from such waste, Microorganisms for example Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, Acidithiobacillus thiooxidans [46]. It has been a recognized procedure for the removal of metals consisting of different material [47] (Fig. 5). ...
In spite of the initial e-waste regulations entering into force in India in 2011 and also being modified in 2016, it is approximated that some 90–95% of e-waste is handled in the casual market in and unorganized manner. The current medal fabrication for different event in Tokyo Olympics also changed the vision of the people about e-waste. The present manuscript provides an overview of the awareness and management of e-waste in the capital of Rajasthan as a part of study. Different articles have been reviewed and analysed in the domain of e-waste management and a detailed insight about the current scenario, effects and possible solution are provided in terms of better management of e-waste.
... Currently, hydrometallurgical methods account for most of the global gold production from primary and secondary sources [5]. A bio-hydrometallurgical process, a branch of hydrometallurgy, includes related microbial processes, such as bioleaching, biooxidation, and biosorption that are useful for the recovery of metals from ores, concentrates, and recycled or residual materials [6,7]. Recently, bioleaching has become a popular green technology for recovering gold from the waste of electronic and electrical equipment. ...
Cyanide usage in gold processing techniques has become increasingly challenging due to its toxicity and environmental impact. It is possible to develop environmentally friendly technology using thiosulfate because of its nontoxic characteristics. Thiosulfate production requires high temperatures, resulting in high greenhouse gas emissions and energy consumption. The biogenesized thiosulfate is an unstable intermediate product of Acidithiobacillus thiooxidans sulfur oxidation pathway to sulfate. A novel eco-friendly method was presented in this study to treat spent printed circuit boards (STPCBs) using biogenesized thiosulfate (Bio-Thio) obtained from Acidithiobacillus thiooxidans cultured medium. To obtain a preferable concentration of thiosulfate among other metabolites by limiting thiosulfate oxidation, optimal concentrations of inhibitor (NaN3: 3.25 mg/L) and pH adjustments (pH= 6-7) were found to be effective. Selection of the optimal conditions has led to the highest bio-production of thiosulfate (500 mg/L). The impact of STPCBs content, ammonia, ethylenediaminetetraacetic acid (EDTA), and leaching time on Cu bio-dissolution and gold bio-extraction were investigated using enriched-thiosulfate spent medium. The suitable conditions were a pulp density of 5 g/L, an ammonia concentration of 1 M, and a leaching time of 36 h, which led to the highest selective extraction of gold (65 ± 0.78%).
... Also, Sadia et al. [30], Erüst et al. [49] showed that metal leaching efficiencies decrease significantly with increasing pulp density. This can be due to the alkaline nature of the e-waste material and is therefore acid-consuming. ...
The recycling of printed circuit boards (PCBs) causes environmental problems by releasing dioxins and furans. The objective of this study is the recovery of copper from PCBs through the bioleaching process using Aspergillus niger which was isolated from the surface of Abu Tartur phosphate. In the bioleaching process, the optimum conditions were used to modify ammonium medium with inoculum spore size are 2Χ10⁶ SFU/50 ml for 5 days at 30ͦ C in a pulp of 0.5% solid 150 mesh particle size and aeration at 200 rpm. Different carbon and nitrogen sources were used. Glucose (1.5%) and ammonium chloride (0.2%) were the best source of carbon and nitrogen, respectively. Also, the optimum initial medium’s pH was 7. At these conditions, about 100% of Cu was extracted. The mechanism of bioleaching was studied by detecting the production of organic acid through using brome cresol green as an indicator and HPLC analysis. The color change of agar medium of the incubated plate with A. niger from blue to yellow, and HPLC analysis showed detection malic and citric acids in the sample in presence e-waste higher than the sample without e-waste. E-waste before and after the bioleaching process was investigated using SEM. The surface of e-waste becomes more smooth and porous due to the bioleaching process.
... In biomining, microorganisms are at the core of the process; therefore, their efficacy depends on the suitability of the selected biominer or its consortium. For instance, copper extraction from chalcocite and chalcopyrite ore using different species of Acidithiobacillus, Leptospirillum, and Sulfolobus spp has been well studied (Okibe et al. 2003;Erüst et al. 2013;Zhao et al. 2013). However, due to the recalcitrant nature of chalcopyrite ore most commonly high-temperature processing has been adopted to increase the kinetics of the process (Norris et al. 2017;Hedrich et al. 2018). ...
The mining industry has powered the human endeavor to make life more innovative, flexible, and comfortable. However, it has also led to concerns due to the increasing amount of mining and associated industrial waste. Special attention is highly desired for its proper management and safe disposal in the environment. The problem has only augmented with the increase in the mining costs because of the investments needed for ecological remediation after the mining operation. It is pertinent that the targeted technologies need to be developed to utilize mining and associated industrial waste as a secondary resource to ensure sustainable mining operations. Every perceived waste is a valuable resource that is needed to be utilized to create additional value. In this review, the case of alkaline bauxite residue (red mud)—alumina refinery waste has been discussed at length. The highlight of the proposed work is to understand the importance of alkaliphile-assisted biomining—a sustainable alternative to conventional metal recovery processes. Along with the recovery of metals, pH reduction of red mud is possible through biomining, which ultimately paves the way for its complete utilization. The unique adaptation strategies of alkaliphiles make them more suitable for biomining of red mud through bioleaching, biosorption, and bioaccumulation, which have been discussed here. Furthermore, we have focused on the potential of the indigenous microflora of red mud for metal recovery in addition to its neutralization. The study of indigenous alkaliphiles from red mud, including its isolation and propagation, is crucial for the industrial-scale application of alkaliphile-based technology and has been emphasized.
... As far as precious metals are concerned, E-waste contains around 0.02 %, 0.1 %, and 0.005 % of Ag, Au, and Pt respectively (Desmarais et al., 2020). Erüst et al., 2013, have reported that the precious metal content of E-waste (ATMs, computer monitors, television sets, etc.) is 25-250 folds higher than their respective ores. To leach base (1)-(4) (Habibi et al., 2020). ...
E-waste management has become a global concern because of the enormous rise in the rate of end-of-life electrical and electronic equipment's (EEEs). Disposal of waste EEE directly into the environment leads to adverse effects on the environment as well as on human health. For the management of E-waste, numerous studies have been carried out for extracting metals (base, precious, and rare earth) following pyrometallurgy, hydrometallurgy, and biometallurgy. Irrespective of the advantages of these processes, certain limitations still exist with each of these options in terms of their adoption as treatment techniques. Several journal publications regarding the different processes have been made which aids in future research in the field of E-waste management. This review provides a comprehensive summary of the various metal recovery processes (pyrometallurgy, hydrometallurgy, and biometallurgy) from E-waste, along with their advantages and limitations. A bibliometric study based on the published articles using different keywords in Scopus has been provided for a complete idea about E-waste with green technology perspective like bioleaching, biosorption, etc. The present study also focussed on the circular economic approach towards sustainable E-waste management along with its socio-economic aspects and the economic growth of the country. The present study would provide valuable knowledge in understanding E-waste and its different treatment processes to the students, researchers, industrialists, and policymakers of the country.
... 4 Factors That Influence the Extraction of Precious Metals from E-wastes(Erüst et al., 2013;Ilyas et al., 2021) ...
... Distribution of electrical and electronic waste was determined in EU Directive 2002/96. Spent lamps were calculated 1.7% of total electrical and electronic wastes as the 5B lighting equipment e-waste group by European Union in 2005 (Erust et al., 2013;EU Directive 2002/96). E-waste stream is very fast growing in the modern world (Huang et al., 2009;Behnamfard et al., 2013) and these wastes should to be designed considering their recycle and reuse potential (Petter et al., 2014;Sahin et al., 2015). ...
In this paper, oxidative leaching and electrowinnig processes were performed to recovery of mercury from spent tubular fluorescent lamps. Hypochlorite was found to be effectively used for the leaching of mercury to the solution. Mercury could be leached with an efficiency of 96% using 0.5 M/0.2 M NaOCl/NaCl reagents at 50°C and pH 7.5 for 2-h. Electrowinning process was conducted on the filtered leaching solutions and over the 81% of mercury was recovered at the graphite electrode using citric acid as a reducing agent. The optimal process conditions were observed as a 6 A current intensity, 30 g/L of reducing agent concentration, 120 min. electrolysis time and pH of 7 at the room temperature. It was found that current intensity and citric acid amount had positive effect for mercury reduction. Recovery of mercury in its elemental form was confirmed by SEM/EDX. Oxidative leaching with NaOCl/NaCl reagent was followed by electrowinning process can be effectively used for the recovery of mercury from spent fluorescent lamps.
... Bioremediation is described as the utilization of microorganisms to eradicate or change pollutants into non-hazardous or less-hazardous forms by utilizing their metabolic processes [83]. Microbial technologies operate at certain specific temperatures and in moderate environments, making them easier to control and maintain compared to other methods [84]. The use of biological technologies for the removal of heavy metals has received high attention as they are environmentally friendly, have less cost, and require less energy [85]. ...
Around 50 million tonnes of electronic waste has been generated globally per year, causing an environmental hazard and negative effects on human health, such as infertility and thyroid disorders in adults, endocrine and neurological damage in both animals and humans, and impaired mental and physical development in children. Out of that, only 15% is recycled each year and the remaining is disposed of in a landfill, illegally traded or burned, and treated in a sub-standard way. The processes of recycling are challenged by the presence of brominated flame retardants. The different recycling technologies such as the chemical and mechanical methods have been well studied, while the most promising approach is the biological method. The process of utilizing microbes to decontaminate and degrade a wide range of pollutants into harmless products is known as bioremediation and it is an eco-friendly, cost-effective, and sustainable method. The bioremediation process is significantly aided by biofilm communities attached to electronic waste because they promote substrate bioavailability, metabolite transfer, and cell viability, all of which accelerate bioleaching and biodegradation. Microbes existing in biofilm mode relatable to free-floating planktonic cells are advantageous of bioremediation due to their tolerant ability to environmental stress and pollutants through diverse catabolic pathways. This article discusses the harmful effects of electronic waste and its management using biological strategies especially biofilm-forming communities for resource recovery.
... This is mainly due to the difficulty in recovering Co from lowgrade sources using conventional pyrogenic method where co-occurs with other metal minerals such as chalcopyrite, pyrite, carrollite, pentlandite [124], and associated environmental concerns. In contrast to conventional methods, the biohydrometallurgy method of bioleaching offers a range of economic and environmental benefits [125,126]. Recognizing these benefits, Co was extracted using bioleaching methods from tailings of a former copper mine site located in Kasese, Uganda. It was the first commercial application (began operation in 1998) to bioleach Co from mine tailings containing Coiferous pyrite. ...
Tailings storage facilities (TSFs) are the main source of pollution from mining operations. However, TSFs are increasingly being considered as the potential secondary sources of some critical minerals. Recovering the critical minerals from TSFs is important due to both environmental and economic implications. Yet, identification of the potential TSFs is the major challenge in this venture due to the lack of publicly available database of TSFs. The objective of this study was to identify the TSFs and document their status in the form of a database for Australia. Visual inspection and interpretation of satellite images in Google Earth were used to identify the TSFs in 6 states and the publicly available database of TSFs for Western Australia (WA) was validated in this study to incorporate into a national-level database. This study has identified 331 active and 759 inactive TSFs in Australia. Among the sites, 42 active and 56 inactive mine sites with TSFs were found within 2 km of urban centres in the studied states. Coal and gold were the major commodities of 27% of active mine sites with the TSFs and 38% of inactive mine sites with TSFs, respectively. Approximately 16% of active mine sites with TSFs and 28% of inactive mine sites with TSFs were found to process copper as a major commodity. Considering the companionability matrix, many of these TSFs could be explored for the possible recovery of critical minerals (e.g. rare earth elements, cobalt). This study has developed a national-level database of TSFs for Australia for the first time, and it could be used for a number of applications.
... Bioleaching is a promising technology for extracting valuable metals from electronic waste (e-waste); because it has relatively low capital and operating costs and low energy consumption (Erüst et al. 2013;Sa et al. 2015;Fang et al. 2022). Currently, bioleaching is known as one of the main methods of biohydrometallurgy and plays an essential role in recycling various metals (Ferraro et al. 2019;Pourhossein et al. 2022). ...
Manganese is extensively used in various advanced technologies. Due to high manganese demand and scarcity of primary manganese resources, extracting the metal from spent batteries is gaining increasing interest. The recycling of spent batteries for their critical metal content, is therefore environmentally and economically feasible. The conventional pyro- and hydrometallurgical extraction methods are energy-intensive or use hazardous chemicals. Bioleaching of manganese from spent batteries as secondary resource has been suggested to meet two objectives: reduce environmental footprint and turn waste into wealth. A bioleaching process can operate with less operating costs and consumption of energy and water, along with a simple process, which produces a reduced amount of hazardous by-products. Hence, this review discusses various approaches for bioleaching manganese from secondary resources using redoxolysis, acidolysis, and complexolysis. Candidate microbes for producing inorganic and organic biolixiviants are reviewed, along with the role of siderophores and extracellular polymeric substances as other effective agents in manganese extraction. The three main types of bioleaching are discussed, incorporating effective parameters with regard to temperature, pH, and pulp density, and future perspectives for manganese bioleaching and provided.
Graphical abstract
... Bioleaching depends on the metabolic process of microorganisms, and the leaching mechanism depends on the type of microorganisms (Kaksonen et al., 2017). For example, acidophilic bacteria can convert sulfide in minerals into sulfate and oxidize Fe 2+ into Fe 3+ (Sethurajan et al., 2013). Kaksonen et al. (2016) dissolved about 80% of copper and 25% of zinc in copper slag (from Finland) by providing H 2 SO 4 continuously to acidophilic bacteria at a temperature of 27 • C and pH of 2.5 (Kaksonen et al., 2016). ...
Copper slags can hardly be utilized because the fayalite in it produces silica gel during the dissolution process. This work proposes a new process on sulfuric acid treatment of copper slag (Jinchuan Group, Gansu Province, China.). The results show that over 98% of recovery efficiency of Cu²⁺, Co²⁺, Ni²⁺ and Zn²⁺ was achieved through the whole process cycle. Ammonia was used to control the pH of the solution in order to completely precipitate Fe²⁺, and then produce hematite powder. More than 85% of the non-ferrous metal ions were left in the solution, and the utilization method of stepwise extraction was evaluated. The generation of silica gel during the acid digestion of copper slag was not restricted, and the silica gel in the acid-leach residue was subsequently dissolved with NaOH solution to obtain sodium metasilicate solution. Acidification and other steps were carried out to produce high-purity silica with a purity of 99.9%. Magnetite and pyroxene were obtained by using a simple magnetic separation process to segregate the remaining slag phase. The whole process achieves the full resource utilization of copper slag, and exhibits great potential for the future industrial utilization of copper slag in an economically and environmentally friendly way.
... This is mainly due to the difficulty in recovering Co from lowgrade sources using conventional pyrogenic method where co-occurs with other metal minerals such as chalcopyrite, pyrite, carrollite, pentlandite [124], and associated environmental concerns. In contrast to conventional methods, the biohydrometallurgy method of bioleaching offers a range of economic and environmental benefits [125,126]. Recognizing these benefits, Co was extracted using bioleaching methods from tailings of a former copper mine site located in Kasese, Uganda. It was the first commercial application (began operation in 1998) to bioleach Co from mine tailings containing Coiferous pyrite. ...
Society’s hunger for commodities is leading to an increased consumption of minerals considered critical or strategic. A range of minerals containing elements such as lithium (Li), cobalt (Co), rare earth elements (REEs) are considered critical and more important for strategic uses than others. In this paper we describe these as strategically important critical minerals (SICMs). However, their continuous depletion from primary sources coupled with supply risks due to geopolitical issues and geographical segregation is a major concern. As a consequence, recovering these valuable elements from non-conventional sources such as abandoned mine tailings has recently gained increased worldwide attention. In some part this is due to the fact that the potentially recoverable amount of these elements in abandoned mine tailings is often higher than the concentration in some primary ores. A review of the scientific literature reveals the use of modern recovery techniques such as tailored made hydrometallurgical and bio-hydrometallurgical processes can lead to effective recovery of these elements from low grade sources such as mine tailings. However, there remain some technical, economic and environmental challenges associated with recovering SICMs from mine tailings. This review critically analyzes these challenges and discusses the opportunities available for recovering SICMs from abandoned mine tailings using conventional hydrometallurgical techniques as well as bioleaching methods, which can offer significant advantages in reprocessing. This paper also concludes by providing an outlook of an integrated approach to the reprocessing of mine tailings where the recovery of SICMs as well as clean water production should be the combined overall reprocessing and recovery goal, helping to realize the full economic potential of the tailings.
... Currently, hydrometallurgical (Tuncuk et al., 2012) and pyrometallurgical (Xiu et al., 2013) methods are used to recover metals from e-waste. However, bioleaching is a costeffective and environmentally friendly biochemical method for recycling metals (Erust et al., 2013;Gu et al., 2018;Huang et al., 2019). Bioleaching works at ambient temperature and pressure (Khatri et al., 2018). ...
Recently electronic waste (e-waste) includes the fastest growing waste stream in the world. Nevertheless, it also
contains about 40 different elements of the periodic table; hence it is a significant metal source. Generally,
e-waste recycling is done by the pyrometallurgy and/or hydrometallurgy method. However, the use of microorganisms in hydrometallurgy called bioleaching is a good alternative for eco-friendly and cost-effective
recycling of e-waste and recover metals. Leptospirillum-dominated consortium was used to generate ferric iron lixiviant by oxidizing ferrous iron. The resulting lixiviant was used for bioleaching of metals from waste cell
phone printed circuit boards (WPCBs). The pretreatment of pulverized WPCB (p-WPCB) and unpulverized
WPCB (up-WPCB) was done using 2 M NaOH to see the effect of pretreatment on metal extraction. Moreover,
the effect of maintenance of pH of the system was also checked. The controlling of pH of the system to 2.0 – 0.1
showed enhancement of Cu, Zn, and Ni solubilization. The highest solubilization of copper was 96.86%, which
was achieved with pretreated up-WPCB; zinc was 90.69% with pretreated p-WPCB, whereas nickel was
93.65% with untreated up-WPCB. Ours is the first report for extraction of copper, zinc, and nickel from
unpulverized mobile phone WPCBs at high pulp density. The solubilization of metals achieved with 100 g/L
pulp density provides a promising indication to scale up the process.
... Considering the priority of metal recycling, ecological factors, and economic prospective, it is crucial to choose an optimal metal recycling approach from WEEE (Priya and Hait 2018;Joshi et al. 2017). Compared with pyrometallurgical process and hydrometallurgical process, biometallurgical process avoids the risk of generating secondary pollution such as air pollution or water pollution Erüst et al. 2013). Meanwhile, in terms of economy, this technology can also extract metals from WEEE under the condition of low energy consumption and low cost. ...
In the twenty-first century, the increasing demand for electrical and electronic equipment (EEE) has caused its quick update and the shortening of its service life span. As a consequence, a large number of waste electrical and electronic equipment (WEEE) needs to be processed and recycled. As an environmentally friendly method, biometallurgy has received extensive attention in the disposal of WEEE in recent years. Aspergillus niger is an acid-producing fungus with a potential applicability to improve metals’ recycling efficiency. This review article describes the latest statistical status of WEEE and presents the latest progress of various metallurgical methods involved in WEEE recycling for metal recovery. Moreover, based on the summary and comparison towards studies have been reported for bioleaching metals from WEEE by A. niger, the bioleaching mechanisms and the bioleaching methods are explained, as well as the effects of process parameters on the performance of the bioleaching process are also discussed. Some insights and perspectives are provided for A. niger to be applied to industrial processing scale.
... In the process of bioleaching of base and precious metals, the acidophilic group of bacteria plays a vital role in the recovery of valuable metals [36]. These sundry acidophiles like Acidithiobacillus ferrooxidans, Acidithiobacillusthiooxidans, Leptospirilliumferriphilum, Sulfolobusthermosulfidooxidans, etc. are being used in metal extraction from e-waste and also gave efficient results [37].Numerous types of microorganisms, used in the bioleaching process are shown in Table 3. ...
Water pollution and contamination is a major environmental issue throughout the world. As the world is urbanizing rapidly at an increasing rate the water bodies are getting toxic. Rivers, canals, and even groundwater are getting contaminated by various manmade activities. One of the major issues of water pollution is disposing and dumping waste into the water bodies. It is considered one of the most polluting anthropogenic activities. Out of all the different types of waste, e-waste is recorded as a rapidly growing waste stream in the world. Many electronic scrap materials that contain potentially harmful materials are dumped into the water bodies. It contains mainly raw materials like iron, copper, steel, etc. Every year electronic waste of 50 million tones is being generated globally. According to the estimate given by EPA, only 20% of the e-waste is recycled and the remaining waste is sent to incinerators or dumped into landfills and water bodies. E-waste is increasing due to the swift changes and high usage of technology, falling prices, and the invention of new devices, and the outdating of old processors. Over 50% of the e-waste consists of ferrous materials and it can be processed and extracted by mechanical shredding, hydrometallurgical methods, and bioleaching, etc. In this study, with the help of these methods, we can extract valuable metals like Cu, Al, Ag, Au, converting e-waste pollution threats into metal resources thereby increasing the revenue and economy of the country. Sustainable e-waste management practices can reduce waste contamination and the health risk from different harmful materials like dioxins, cadmium, chromium, radioactive isotopes, etc.
... Biohydrometallurgy is an effort to develop an environmental process with a high potential to lower energy requirements and operational costs; it is gaining much interest in metal recovery from E-waste [7]. Bioleaching is the main field of biohydrometallurgy, which is defined as the leaching of metals using microorganisms [8]. ...
The high amount of base metals poses an important challenge in gold bioleaching from spent printed circuit boards (PCBs). The best objective in the current study is the bioleaching of important base metals (Cu, Ni, and Fe) from a mixture of spent PCBs (E-waste) using adapted Acidithiobacillus ferrooxidans in the bubble column bioreactors. The adaptation process firstly is done from 1- 15 g/L in Erlenmeyer flasks in 187 days, then the concentration of E-waste increased to 40 g/L in the bubble column bioreactors in 44 days. The concurrent recovery of copper, nickel, and iron using adapted bacterium in a bioreactor was optimized by central composite design. Various effective parameters such as aeration rate, initial ferrous sulfate concentration, and solid waste loading that significantly affected bioleaching yields were studied. 54% of Cu (6% dissolution/d), 75% of Ni (8% dissolution/d), and 55% of Fe (6.1% dissolution/d) were recovered simultaneously under the optimum condition of 20 g/L of solid content, 1.5 vvm of aeration rate, and 40 g/L of the initial concentration of ferrous sulfate after only 9 days. The results proved 100% recovery of each metal is possible separately, 100% of Cu and Fe are extracted maximally on the 4th and 13th day, respectively. Ni is recovered maximally 96% on the 17th day. This is the first report of an ecofriendly method for bioleaching of important base metals from E-waste in bubble column bioreactor. Thus, the obtained results contribute to the knowledge of microbial hydrometallurgy on large scale.
... The results were corrected for the content of sulfate sulfur in the ore dumps, which was determined using a boiling solution of Na2CO3 (the soda-extract method) and subsequent precipitation as BaSO4. 23 The sample of polymetallic ore contained 9.12 % Cu, 2.08 % Zn, 18 ...
The growing issue of electronic waste (E-waste), driven by the exponential growth in electronic device usage, presents significant environmental and economic challenges. E-waste production has surged, increasing by approximately 2 million metric tonnes (Mt) annually, reaching 60 Mt in 2023, with projections suggesting it will exceed 70 Mt by 2030. Despite China, the USA, and India being the top E-waste producers, their recycling rates remain critically low at 16%, 15%, and 1%, respectively. E-waste contains valuable metals, such as gold (Au), silver (Ag), and copper (Cu), which comprise around 60% of its composition. However, only 17.4% of the global E-waste was appropriately recycled in 2023. This review discusses the latest data on E-waste, evaluates current metal recovery methods, and emphasizes the urgency of sustainable solutions to mitigate environmental hazards and promote a circular economy. The paper also covers case studies highlighting challenges and potential strategies to enhance metal recovery efficiency, contributing significantly to global sustainability efforts and waste management
The transition to renewable energies and electric vehicles has triggered an unprecedented demand for metals. Sustainable development of these technologies relies on effectively managing the lifecycle of critical raw materials, including their responsible sourcing, efficient use, and recycling. Metal recycling from electronic waste (e-waste) is of paramount importance owing to ore-exceeding amounts of critical elements and high toxicity of heavy metals and organic pollutants in e-waste to the natural ecosystem and human body. Heterotrophic microbes secrete numerous metal-binding biomolecules such as organic acids, amino acids, cyanide, siderophores, peptides, and biosurfactants which can be utilized for eco-friendly and profitable metal recycling. In this review paper, we presented a critical review of heterotrophic organisms in biomining, and current barriers hampering the industrial application of organic acid bioleaching and biocyanide leaching. We also discussed how these challenges can be surmounted with simple methods (e.g., culture media optimization, separation of microbial growth and metal extraction process) and state-of-the-art biological approaches (e.g., artificial microbial community, synthetic biology, metabolic engineering, advanced fermentation strategies, and biofilm engineering). Lastly, we showcased emerging technologies (e.g., artificially synthesized peptides, siderophores, and biosurfactants) derived from heterotrophs with the potential for inexpensive, low-impact, selective and advanced metal recovery from bioleaching solutions.
The increasing scarcity of precious metals necessitates the development of sustainable recycling strategies to fulfill industrial requirements while mitigating environmental impact. Aqua regia has emerged as a key leaching agent for precious metal recovery from secondary raw materials due to its economic viability, swift leaching kinetics, and straightforward implementation. Due to synergistic benefits such as enhanced recovery rates, improved selectivity, and increased environmental sustainability, aqua regia leaching integrated with sorption, solvent extraction, and biohydrometallurgical techniques. This review article provides a comprehensive overview of aqua regia-based hybrid approaches for recovering Au, Pt, and Pd from diverse secondary sources, including waste electrical and electronic equipment, spent catalysts, industrial effluents, and others. The study evaluates a wide range of functional sorbent and extractant materials for their effectiveness in recovering precious metals from acidic environments, and aqua regia settings. Evaluating various factors that affect precious metal sorption, this study emphasizes the need for acid-resistant and highly selective sorbents. The review also addresses the challenges associated with aqua regia and evaluates potential solutions like selective leaching and diluted aqua regia applications. Finally, the review outlines future directions, focusing on advancements in hybrid methods to achieve superior precious metal recovery with minimal environmental impact.
In the recycling of scrap metal, the establishment of the classification database of recyclables has the advantages of fast classification speed and high analysis accuracy. However, the classification and recycling of unknown samples become highly significant due to the extensive variety of standard metal samples and the challenges in obtaining them. In this study, a method for multi-element classification of automotive scrap metals in general environmental conditions was achieved by utilizing laser-induced breakdown spectroscopy (LIBS) and two-step clustering algorithm (K-means, hierarchical clustering). The two unsupervised learning algorithms were employed to cluster the LIBS spectral data of 60 automotive scrap metal samples rapidly and hierarchically. Three rare metal elements and three elements for distinguishing metal categories were selected to meet the recycling requirements. After applying the multiplicative scatter correction to the spectral data for calibration, the initial clustering clusters were determined using the Davies–Bouldin index, Calinski–Harabasz index, and silhouette coefficient. Then, the Kruskal–Wallis test was conducted on each cluster to check the significance. The clusters that failed the test were split and reclustered until all clusters met the significance criterion (α=0.05). The accuracy of the proposed method for classifying the collected automotive scrap metals reached 97.6%. This indicates the great potential of this method in the field of automotive scrap metal classification.
Metal production is facing new challenges due to climate change and declining primary ore quality; thus, new technologies with sustainable processing routes are needed. One way to address this is to recover metals from secondary resources such as end-of-life batteries using a cleaner reducing agent hydrogen that would reduce direct carbon dioxide emissions during pyrometallurgical processing. Recycling of Li-ion battery cathode materials using hydrogen would result in a more benign metal production process and would simultaneously provide a sustainable solution to treat wastes. This study investigated the kinetics of H2 reduction of LiCoO2 at 600–1000 °C up to 180 min reaction time using an isothermal mass change analysis supported with detailed microstructure evolution observations. The overall reduction mechanism appeared to follow the shrinking-core model with a different rate-limiting step depending on the reduction temperature. The activation energy of reduction at 600–800 °C was calculated to be 37.4 kJ/mol and was controlled by the nucleation step. The information and data obtained are useful when comparing different recycling methods and optimizing the reduction parameters of spent Li-ion battery process.
Recycling critical elements from spent batteries has always been an emphasis of green chemistry. However, the reduction or minimization of the input of chemicals, secondary wastes and energy consumption still...
While e-waste poses significant environmental and health risks, it also harbors valuable metals like gold, ripe for recycling. However, extracting gold from e-waste carries its own ecological footprint. Therefore, employing tools like Life Cycle Assessment (LCA) to evaluate environmental impacts and identify mitigation measures is imperative. This research addresses critical gaps in the literature surrounding gold recovery from e-waste. It covers a range of methods, including hydrometallurgical and pyrometallurgical (well-established) to mechanical and biotechnological (less explored for gold recovery), rectifying the imbalance in methodological attention. This study also prioritizes environmental assessment, elevating LCA to a central investigative focus for understanding the sustainability of gold recovery from e-waste. Notably, there is a paucity of consistent and systematic comparisons between diverse gold recovery methods from e-waste in existing literature. While some publications touch on environmental aspects, comprehensive LCA investigations are lacking. Thus, this research explicitly bridges this gap through a comparative LCA, evaluating mechanical, hydrometallurgical, pyrometallurgical, electrochemical, and biotechnological methods and contrasting them with conventional mining (baseline method). The results highlight significant reductions in damage to human health, with the mechanical and electrochemical methods leading the way with a noteworthy 98% reduction compared to the baseline. The hydrometallurgical and pyrometallurgical methods also demonstrate substantial decreases of 83% and 92%, respectively. Though the biotechnological method exhibits a comparatively lower reduction of 60%, it represents a significant advancement in curbing damage to human health. Regarding ecosystem quality, the mechanical and electrochemical methods excel with exceptional reductions of over 99%, while the biotechnological, hydrometallurgical, and pyrometallurgical methods collectively achieve a decrease of approximately 99% compared to the baseline. Across the board, all evaluated methods manifest substantial reductions in total weighted environmental impacts, amounting to an approximate 99% reduction. The biotechnological method does entail the highest exergy demand, signifying greater energy consumption, while the mechanical method demonstrates the lowest exergy consumption. Considering feasibility and scalability, the electrochemical and mechanical methods emerge as the most favorable options for sustainable gold recovery. These methods demonstrate promising results in reducing environmental impacts and are well-suited for practical implementation.
With the ever-increasing population, industrialization, and urbanization there has been rapid rise in the demand of water resources. This has resulted in issues like inadequate supply of water, degradation in the quality of water. Contamination of water resources with metals has become a serious concern these days. Metals, themselves being non-renewable resource are discarded in the aqueous environment, thus are not only wasted but also impose serious health issues to every form of life. Besides the inherent concern of water contamination through metals, it is also seen as an opportunity to regain and recover the metal resource from wastewater. The current emphasis to achieve sustainable development goals, which includes circular economy i.e., circular utilization of resources, has opened up challenges and opportunities where wastewater is considered as a resource and its treatment is done for removing pollutants as well as recovering valuable resources from it. The current chapter elaborates the conventional, as well as novel and emerging chemical, physical and biological techniques used for the recovery of heavy metal resources from wastewater.
Advanced high-tech applications for communication, renewable energy, and display, heavily rely on technology critical elements (TCEs) such as indium, gallium, and germanium. Ensuring their sustainable supply is a pressing concern due to their high economic value and supply risks in the European Union. Recovering these elements from end-of-life (EoL) products (electronic waste: e-waste) offers a potential solution to address TCEs shortages. The review highlights recent advances in pre-treatment and hydrometallurgical and biohydrometallurgical methods for indium, gallium, and germanium recovery from EoL products, including spent liquid crystal displays (LCDs), light emitting diodes (LEDs), photovoltaics (PVs), and optical fibers (OFs). Leaching methods, including strong mineral and organic acids, and bioleaching, achieve over 95% indium recovery from spent LCDs. Recovery methods emphasize solvent extraction, chemical precipitation, and cementation. However, challenges persist in separating indium from other non-target elements like Al, Fe, Zn, and Sn. Promising purification involves solid-phase extraction, electrochemical separation, and supercritical fluid extraction. Gallium recovery from spent GaN and GaAs LEDs achieves 99% yield via leaching with HCl after annealing and HNO 3 , respectively. Sustainable gallium purification techniques include solvent extraction, ionic liquid extraction, and nanofiltration. Indium and gallium recovery from spent CIGS PVs achieves over 90% extraction yields via H 2 SO 4 with citric acid-H 2 O 2 and alkali. Although bioleaching is slower than chemical leaching (several days versus several hours), indirect bioleaching shows potential, achieving 70% gallium extraction yield. Solvent extraction and electrolysis exhibit promise for pure gallium recovery. HF or alkali roasting leaches germanium with a high yield of 98% from spent OFs. Solvent extraction achieves over 90% germanium recovery with minimal silicon co-extraction. Solid-phase extraction offers selective germanium recovery. Advancements in optimizing and implementing these e-waste recovery protocols will enhance the circularity of these TCEs.
Nupur Srivastava and Ajeet K. Srivastav from Visvesvaraya National Institute of Technology in India discuss how a sustainable metal supply chain could be derived from metal e-waste.
Copper slag, a waste solid produced in the copper smelting process, is a high-quality secondary resource with huge output. The recycling and utilization of copper slag is of great interest because it avoids the loss of valuable metals and the threat of harmful metals, and saves a lot of natural resources and energy. This paper firstly reviews the main methods for the recovery of valuable metals from copper slag, such as beneficiation method, pyrometallurgical approach, and hydrometallurgical process. Then, based on the physical and chemical properties of copper slag, the applications of copper slag in the field of building materials like concrete, cement, inorganic polymers, etc., and functional materials such as catalyst, glass–ceramic, slag wool, thermal energy storage material, etc., were summarized. Finally, the scientific treatment method of copper slag in future is prospected that green, economic, and environmentally friendly sustainable disposal process is the main theme.
The interfacial heat transfer coefficient (IHTC) formed at the casting-mould interface is an important parameter to affect the quality of cast product. Hence, the present study aims to perform the heat transfer analysis on the interface of mould and casting. The effect of pouring temperature and the properties of the cast metal were investigated by evaluating interfacial heat flux and interfacial heat transfer coefficient (IHTC) using transient temperatures inside the mould and casting. During the experiments, transient temperatures inside the mould and casting are recorded. Effects of pouring temperature, casting material and mould material on the transient heat flux and IHTC are also studied. From the results, both interfacial heat flux and interfacial heat transfer coefficient are found to be increasing with increase in pouring temperature keeping all other parameters constant. At same pouring temperature, interfacial heat flux is found to be independent of casting material, whilst IHTC is found to be dependent on the properties of casting material. Peak value of IHTC is found to be much higher in case of zinc metal casting as compared to aluminium metal casting. Novel and physically based analytical interpretation of the results is provided. The results will be useful for metal forming industries to develop better castings at lower costs.
A hydrometallurgy is one of the most important techniques for recycling waste LIBs, where identifying the exact composition of the metal-leached solution is critical in controlling the metal extraction efficiency and the stoichiometry of the regenerated product. In this study, we report a simple and selective optical detection of high-concentrated Co2+ using a graphitic carbon nitride (g-CN)-based fluorescent chemosensor. g-CN is prepared by molten salt synthesis using dicyandiamide (DCDA) and LiI/KI. The mass ratio of LiI/KI to DCDA modifies the resulting g-CN (CNI) in terms of in-plane molecular distances of base sites including cyano functional groups (─CN) and fluorescent emission wavelength via nucleophilic substitution. The fluorescent sensing performance of CNIs is evaluated through photoluminescence (PL) emission spectroscopy in a broad Co2+ concentration range (10-4-10° M). The correlation between the surface exposure of hidden nitrogen pots (base sites) and PL intensity change is achieved where the linear relationship between the PL quenching and the logarithm of Co2+ concentration in the analyte solution is well established with the regression of 0.9959. This study will provide the design principle of the chemosensor suitable for the fast and accurate optical detection of Co2+ present in a broad concentration range for hydrometallurgy for the recycling of waste LIBs.
In this study for the first time, microbe-produced thiosulfate is considered as a new lixiviant in bioleaching of precious metals from discarded TPCBs. The effects of significant parameters for the selective over bio-production of thiosulfate (S2O32−) and sulfate (SO42−) were investigated. The cultivation of Acidithiobacillus thiooxidans in the 9K medium with inhibitor (3.2 mg/L KCN) by pH adjustment, led to the overproduction of thiosulfate up to 350 mg/L and significantly decreased sulfur oxidation rate to sulfate to 6%. In contrast, without inhibitor and pH adjustment considerably increased amounts of sulfate to 26000 mg/L by 83% of sulfur oxidation rate to sulfate. A 100% copper dissolution was obtained at optimum condition (Sulfate: 26000 mg/L; pH 0.5;H2O2: 5% (v/v); 20 g/L TPCBs; 24 h) prior thiosulfate bioleaching. In the next stage, at 10 g/L TPCBs, 31% (0.11 mg/gTPCB) gold and 40% (1.23 mg/gTPCB) silver after 48 h were successfully recovered by thiosulfate bioleaching.
This review discusses physical, chemical and direct lithium-ion battery recycling methods in order to have an outlook on future recovery routes. Physical and chemical processes are employed to treat cathode active materials which are the greatest cost contributor in the production of lithium batteries. Direct recycling processes maintain the original chemical structure and process value of battery materials by recovering and reusing them directly. Mechanical separation is essential to liberate cathode materials that are concentrated in the finer size region. However, currently, the cathode active materials are being concentrated at a cut point that is considerably greater than the actual size found in spent batteries. Effective physical methods reduce the cost of subsequent chemical treatment and thereafter re-lithiation successfully reintroduces lithium into spent cathodes. Some of the current challenges are the difficulty in controlling impurities in recovered products and ensuring that the entire recycling process more sustainable.
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.
Ultrasonication has been mechanically applied widely in the recycling of spent lithium-ion (SLI) batteries while its influence on chemical pathways has barely been reported. In this study, ultrasonication and sulfate radicals were used in a coupling system to obtain efficient recoveries of Co and Li from SLI batteries. The synergistic effect of ultrasonication and sulfate radicals on recycling was quantitatively analysed by significance analysis and surface responses in a central composite design. The employment of persulfate significantly affected the whole recycling process during the sonication. Factors including acoustic time, operating powers, and temperature all had a significant effect on the recoveries of Co and Li. The maximum recovery efficiencies of Co and Li of 97.33% and 99.25%, respectively, and the minimum loss rate of Al of 4.13% were simultaneously obtained by the fitting predictor. The optimal combination of factors for the sonication system included an acoustic time (min) of 5.5, an operating power (W) of 168, a temperature (°C) of 86, and a ratio of cathode foil to S-solution (mg/mL) of 1:60. A moiety of cathode active material was directly separated from the aluminium collector by sulfate radical-related reactions. Co and Li cations dissolved from LiCoO2 by carbon dioxide radicals were reprecipitated by excess oxalate. The research demonstrated the positively synergistic influence caused by ultrasonication and sulfate radicals on achieving efficient recoveries of Co and Li from SLI batteries, explicitly expanding the technical choices for the recycling procedure.
Inefficient waste management has led to the contamination degradation of various ecological resources. Several physicochemical techniques are already in place to remediate this issue. However, remediation through adsorption presents several advantages over existing physicochemical techniques in terms of cost‐effectiveness. Furthermore, biosorbents present the additional advantage of sustainability and offer remediation of affected natural resources. This chapter presents an overview of the deployment of biosorbents and their potential in conserving natural resources. This chapter also highlights the recovery of metals through used biosorbents. Finally, the chapter discusses current challenges in the implementation of biosorbents.
Bioleaching is an eco-friendly and cost-effective technology for processing low-grade and complex ores and may also be an important bioremediation technology for processing solid waste and secondary resources such as tailings, electronic waste, spent catalyst, sludge, sediment, fly ash, and smelter waste. However, large-scale commercial applications of chalcopyrite bioleaching, especially heap bioleaching of chalcopyrite, are still developing slowly owing to the refractory nature of chalcopyrite. Some industrial practice cases of chalcopyrite bioleaching are summarized in this chapter, which provides a reference for its future industrial application. Key parameters and controlling techniques for chalcopyrite bioleaching, mainly including redox potential/oxidation-reduction potential, pH, temperature, and additives, are summarized and discussed.
Recycling of spent lithium-ion batteries (LIBs) has become a global issue because of the potential environment risks raised by spent LIBs as well as high valuable metal content remaining in them. Although bioleaching is an environmentally friendly method to recover metals from spent LIBs, the commonly utilized bioleaching bacterial consortia or strains enriched/isolated from acidic environments cannot be applied at large scales owing to their long leaching cycle and poor tolerance to organic compounds. Here, two bioleaching consortia were enriched in 60 days from neutral activated sludge and were identified phylogenetically divergent from the documented bioleaching bacteria. The results showed that the novel consortia shortened the leaching cycle almost by half when compared to the previous reported consortia or strains, of which one consortium dominated by Acidithiobacillus ferrooxidans displayed high bioleaching efficiency on LiMn2O4, as 69.46% lithium (Li) and 67.60% manganese (Mn) were leached out in seven days. This consortium was further domesticated using cathodic materials for 100 days and proved consisted of three mixotrophs and two chemoautotrophs, three of which were novel species from the genera Sulfobacillus and Leptospirillum. More genes coding for proteins that utilize organic compounds were annotated in the metagenomic assembled genomes (MAGs) than previously reported. A mutualistic relationship between mixotrophs and chemoautotrophs was suggested to help the consortium surviving under either organic- rich or shortage environments. The results discovered that novel bioleaching bacteria with shorter leaching cycle and higher tolerance to organics could be enriched from non-acidic environments, which showed high potential for the metal recovering from spent LIBs or other organic-rich environments.
Circular economy, acknowledged as “an opportunity to rethink our economic future”, is considered a new chance to build a more sustainable world from both the social and the economic point of view. In this Essay, the perspective contribution of inorganic chemistry towards a smooth transition to circularity in inorganic materials design and production, to enable them to enter into the circular loop, is outlined by adopting a truly interdisciplinary approach, encompassing expertise in inorganic materials chemistry, modelling, materials engineering, circular waste management, metallurgy, and mineralogy. image
A bioelectrochemical system (BES) can produce energy in the form of electricity in microbial fuel cells or hydrogen in microbial electrolysis cells while treating wastewater or sequester carbon by reducing CO2 to long-chain organic products of high calorific or market value via a microbial electrosynthesis pathway. Augmenting the circular bioeconomy (CBE) models with BES can aid in bridging the gap between reality and the concepts. This chapter discusses the different variants of BESs and their constraints for understanding the feasibility of incorporating BES in the future CBE models. Suggestive measures such as minimized primary material consumption, utilization of waste-based materials for electrode and proton-exchange membrane synthesis, CO2 emission reduction, regeneration of spent electrodes and membranes, and bioelectrochemical mining of metals from waste stream for on-site reutilization and recovery have been discussed. A detailed scope for the future is also outlined for designing BES variants to fit in the futuristic circular bioeconomy models.
The origin of a rational (scientific) approach to extraction of metal values from ores with the aid of microorganisms (bioleaching) is traced. The removal by microbiological means of ore constituents that interfere with metal extraction (biobeneficiation), an outgrowth from bioleaching, is also traced. © 2004 SDU. All rights reserved.
This paper presents the experimental results for the leaching of printed circuit boards (PCB) from obsolete computers for extracting and recovering tin and copper by means of leaching followed by precipitation. Printed circuit boards were dismantled, cut into small pieces, and fed into a cylinder mill. The powder obtained was leached by using the aqueous solutions 2.18N H2SO4, 2.18N H2SO4 + 3.0N HCl, 3.0N HCl, and 3.0N HCl + 1.0N HNO3. The lowest values for the percentage of metal extraction were obtained with 2.18N H2SO4 (2.7% for Sn and lower than 0.01% for Cu), while the 3.0N HCl + 1.0N HNO3 leach system exhibited an extraction of 98% for Sn and 93% for Cu. Precipitates were obtained at different pH values by neutralizing the leach liquors using NaOH. The 3.0N HCl + 1.0N HNO3 leach system presented the highest recovery values from the powder feed (84.1% for Sn and 31.9% for Cu), as well as from the leach liquor (85.8% for Sn and 34.3% for Cu).
Previous studies have shown that various microorganisms can enhance the dissolution of silicate minerals at low (<5) or high (>8) pH. However, it was not known if they can have an effect at near-neutral pH. Almost half of 17 isolates examined in this study stimulated bytownite dissolution at near-neutral pH while in a resting state in buffered glucose. Most of the isolates found to stimulate dissolution also oxidized glucose to gluconic acid. More detailed analysis with one of these isolates suggested that this partial oxidation was the predominant, if not sole, mechanism of enhanced dissolution. Enhanced dissolution did not require direct contact between the dissolving mineral and the bacteria. Gluconate-promoted dissolution was also observed with other silicate minerals such as albite, quartz, and kaolinite.
This paper deals with bioleaching of metals from hazardous spent hydro-processing catalyst by means of iron/sulphur oxidizing bacteria. The exhaust catalyst was rich in nickel (45 mg/g), vanadium (44 mg/g) and molybdenum (94 mg/g). Before bioleaching, the solid was washed by means of a mixture of Tween 80 and ethyl alcohol, for hydrocarbons removal. The effects of elemental sulphur, ferrous iron and actions contrasting a possible metal toxicity (either the presence of powdered activated charcoal or the simulation of a cross current process by means of filtration stages in series) was investigated. Ferrous iron resulted to be essential for metals extraction and for bacteria adaptation. Nickel and vanadium were successfully bioleached in the presence of iron, reaching extraction yields of 83% and 90%, respectively; on the other hand extractions around 50% for nickel and vanadium were observed both in biological systems in the absence of iron and in the chemical controls with iron. As concerns molybdenum, the highest extraction yields experimentally observed for molybdenum was about 50%, after 21 days bioleaching in the presence of iron, while a maximum extraction of 25 was observed in the other treatments. In conclusion, a bio-oxidative attack with iron could successfully extract nickel, vanadium and partially molybdenum. Further actions aimed at contrasting a possible metal toxicity resulted not to be effective and partially inhibited the metal extraction processes.
A 3-phase computational ∞uid dynamics (CFD) model for heap bioleaching of chalcocite is investigated to identify and understand the efiect of oxygen ∞ow during air sparging. The study uses an existing one-dimensional model of liquid ∞ow, bacterial transport (including attachment/detachment of bacteria to ore particles), and the depletion of a copper-sulphide, coupled with a two-dimensional (2D) model of gas ∞ow in the heap. The CFD model includes the efiects of oxygen and ferrous ion consumption, coupled with leaching of copper-sulphide via a shrinking core model. The model is used to investigate the 2D efiects of air ∞ow in heap bioleaching with regard to oxygen limitation.
According to the properties of bioleaching solutions of printed circuit boards (PCBs), copper in the leaching solution were recovery by ion exchange with macroporous styrene iminodiacetic acid chelating resin D401. The bed height of resin, flow rate, pH value on copper adsorption had been studied. Work Exchange Capacity (WEC) of copper increased with increasing bed height of resin and flow rate. The copper WEC of 7.88 mg/mL can be obtained with pH 2.5 and 200 mm bed height at flow rate of 2 mL/min. More than 99.5% of copper could be eluted from loaded resin to get the copper enriched solution by 1.0 M sulphuric acid at A/R ratio 20 in at flow rate of 2 mL/min. Results of the present investigation indicated that D401 resin can efficiently recovery copper from bioleaching solution of PCBs.
Bioleaching studies of metals from a spent catalyst were conducted using both adapted and unadapted bacterial cultures. The bacterium used in this experiment was Acidithiobacillus ferrooxidans. A comparison of the kinetics of leaching was made between the two cultures by varying the leaching parameters, including the pulp density, particle size and temperature. Both cultures showed similar effects with respect to the above parameters, but the leaching rates of all metals were higher with the adapted compared to the unadapted bacterial cultures. The leaching reactions were continued for 240 h in the case of the unadapted bacterial culture, but only for 40 h in the case of the adapted bacterial culture. The leaching reactions followed first order kinetics. In addition, the kinetics of leaching was concluded to be a diffusion control model; therefore, the product layers were impervious.
Bioleaching of spent catalyst were carried out using Acidithiobacillus type of microorganisms. Various leaching parameters like contact time, Fe(II) concentration, particle size, pulp densities, pH and temperature were studied in details. All the four metal ions like Ni, V, Mo and Al followed dual kinetics, i.e., initial faster followed by slower rate. The leaching kinetics of Ni and V observed to be higher compared to that of Mo and Al. The thermodynamic parameters like ΔG, ΔH and ΔS for all metals were calculated. The leaching kinetics followed first order rate. Rates of dissolution of Al, V and Ni increased, and Mo decreased with increase of Fe(II) addition whereas that of all metals decreased with increase of pulp density and particle size. Leaching kinetics of Al, Mo, V increased with decrease of pH. Variation of initial pH of the leaching medium showed an inadequate effect on Ni dissolution. The rate determining step found to be pore diffusion controlled. The correlation between observed and theoretical values of leaching efficiency for different parameters was evaluated using Multi-Linear Regression Analyses which showed the significance of the leaching. A total of 5 factors were evaluated by data reduction technique using Principal Component Analysis.
Leaching studies of Ni, V, Mo and Al from spent refinery catalysts were conducted using both adapted and unadapted bacterial cultures. The effects of variations in leaching parameters such as pH and Fe(II) concentration on the leaching rate of both bacterial cultures were evaluated. The leaching kinetics was characterized by an initial faster rate followed by a slower rate, which corresponded to surface and pore diffusion model, respectively. Additionally, the leaching efficiencies of Ni and V were found to be ~ 95% and ~ 85% in the case of adapted and unadapted bacteria cultures, respectively. The lower leaching rate of Mo than Ni and V was due to the mutual effects of the hydrophobic sulfur layer over the molybdenum matrix and refractory nature. The leaching rates increased as the pH increased from 1.5 to 2.0, then decreased at pH 3.0 for all metals. The variation in the concentration of Fe(II) supplement also had a substantial effect on the leaching rates.The dissolution of all metals followed first order reaction kinetics; therefore, unified dissolution rate equations were developed using the first order rate equation for different parameters. The pore diffusion mechanism was found to be the rate determining step.
Bioleaching studies of spent petroleum catalyst containing Ni, V and Mo were carried out using iron oxidizing bacteria. Various leaching parameters such as Fe(II) concentration, pulp density, pH, temperature and particle size were studied to evaluate their effects on the leaching efficiency as well as the kinetics of dissolution. The percentage of leaching of Ni and V were higher than Mo. The leaching process followed a diffusion controlled model and the product layer was observed to be impervious due to formation of ammonium jarosite (NH(4))Fe(3)(SO(4))(2)(OH)(6). Apart from this, the lower leaching efficiency of Mo was due to a hydrophobic coating of elemental sulfur over Mo matrix in the spent catalyst. The diffusivities of the attacking species for Ni, V and Mo were also calculated.
The ferrous oxidation ability of Acidithiobacillus ferrooxidans was studied in the presence of Ni2+, V4+ and Mo6+ in 9 K media in order to implement the culture in the bioleaching of spent catalyst. The rate of iron oxidation decreased with increasing concentration of metal ions, but the rate of inhibition was metal-ion dependent. The tolerance limit was critical at a concentration of 25 g/L Ni2+, 5 g/L V4+ and 0.03 g/L Mo6+. The growth rate of microorganisms was negligible at concentrations of 6 g/L V4+ and 0.04 g/L Mo6+. Levels and degree of toxicity of these ions have been quantified in terms of a toxicity index (TI). The toxicity order of metal ions was found to be Mo6+>V4+>Ni2+. The significance and relevance of multi-metal ion tolerance in Acidithiobacillus ferrooxidans has been highlighted with respect to bioleaching of spent refinery catalyst.
Our goal was to recreate a passive hemagglutination inhibition (PHAI) test to diagnose brown recluse spider (BRS; Loxosceles reclusa) bite envenomation for treatment trials. Guinea pigs received intradermal injections of concentrated spider venom from the following species: Loxosceles reclusa, Argiope aurantia, Argiope trifasciata, Phidippus audax, and Lycosa frondicola. Skin lesion exudate was collected and tested with the BRS venom PHAI assay. From 51 separate collections of exudate, test sensitivity was 90% as long as 3 days after venom injection. Specificity was 100% with venom from the other spider species listed above in vivo (7 test samples) and in vitro (5 test samples), as well as with random bacterial exudate with and without added serial dilutions of BRS venom (10 test samples). The test was reproducible over repetitive assays to within one 10-fold dilution. A positive PHAI test result could function as an entry criterion for BRS bite victims in human treatment trials.
The way municipal solid waste is handled greatly determines its impact on the local as well as the global environment. New technologies have emerged for the treatment of waste, for the recovery of raw materials and energy, and for safe final disposal. The environmental performance of technologies, their social acceptance and their economic viability are key issues to be considered in sustainable waste management. This book provides an overview of current practices in waste management and a synthesis of new developments achieved through interdisciplinary discussions of recent research results.
Nowadays bioleaching occupies an increasingly important place among the available mining technologies. Today bioleaching is no longer a promising technology but an actual economical alternative for treating specific mineral ores. An important number of the current large-scale bioleaching operations are located in developing countries. This situation is determined by the fact that several developing countries have significant mineral reserves and by the characteristics of bioleaching that makes this technique especially suitable for developing countries because of its simplicity and low capital cost requirement. The current situation of commercial-size bioleaching operations and ongoing projects in developing countries is presented and discussed with especial reference to copper and gold mining. It is concluded that this technology can significantly contribute to the economic and social development of these countries.
This chapter describes the cultural characteristics, the iron oxidation reaction, and heterotrophic metabolism action of the iron-oxidizing bacteria. The iron-oxidizing thiobacilli are chemolithotrophic organisms—bacteria able to produce metabollically useful energy by biological reactions dependent upon the oxidation of inorganic matter. The bacteria have an essentially heterotrophic metabolism, but somewhere in their evolutionary development, they have acquired this additional lithotrophic capacity for obtaining energy and for using CO2. The ability of T. ferrooxidans to grow on glucose, in conjunction with the repression of CO2 fixation and iron oxidation, would suggest a drastic alteration in the organism's metabolic profile. The products of the Entner–Doudoroff pathway, pyruvate and 3-phosphoglyceraldehye, must be channeled through the tricarboxylic acid cycle for energy to be obtained. Under conditions of autotrophy, relatively large amounts of ATP and NADH are needed for the endergonic fixation of CO2, both of which inhibit the T. ferrooxidans glucose-6-phosphate dehydrogenase. Conceivably, the regulation of glucose-6-phosphate dehydrogenase may be a determining factor in the ability of T. ferrooxidans to exist as both autotroph and heterotroph.
The mixed culture of acidophilic bacteria was used as the inoculant to bioleach waste printed wire boards. Meanwhile, bacteria in different leaching phases (0, 5, 24 and 60 h) were sampled, and denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction (PCR)-amplified 16Sr RNA genes was used to evaluate the change of microbial community structure during the bioleaching process. The results showed that the mixed culture of acidophilic bacteria could bioleach 96.36% copper from the boards in 48 h. The analysis of the bands selected from the DGGE gel revealed that the sequences of seven bands (Z1~Z7) had over 99% sequence similarity with Acidithiobacillus ferrooxidans. It meant that the seven strains were all clustered to Acidithiobacillus ferrooxidans genus. The relative abundance of Z1 to Z7 in the four samples was not changed significantly. Meanwhile, Z3 showed the highest relative abundance during the whole bioleaching process, which was 72.70%, 82.90%, 79.00% and 85.80%, respectively. Therefore, the microbial community structure changed a little bit during the bioleaching, which always consisted of Acidithiobacillus ferrooxidans strains and was dominated by strain Z3.
The efforts made by several countries to resolve the environmental impact and health hazards produced by the electronic waste are discussed. Approximately 20 to 50 million tons of electronic waste are discarded annually worldwide where as 2 million tons of e-waste-laden with lead and other heavy metals go to the US landfills. State legislatures throughout the country have introduced several e-waste bills, and passed some of substantive laws. European Union (EU) has enacted legislation that makes electronics recycling mandatory and restrict use of certain hazardous substance. A e-waste bills has been passed by Washington, where the EU's recycling law requires manufacturers to participate finally in the recycling process.
The most familiar and well-studied microorganisms indigenous to acidic mineral leaching environments are autotrophic sulfur- and iron-oxidizing bacteria such as Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillum ferrooxidans. Some photoautotrophs, such as the thermophilic rhodophyte Cyanidium caldarium, may also be present in extremely acidic environments that receive light. Other microorganisms which require pre-fixed (organic) carbon have been isolated from mineral leach dumps and acid mine drainage (AMD) waters. These heterotrophic microorganisms include eukaryotes, such as some fungi and yeasts1 and protozoa,2 as well as prokaryotic bacteria and archaea. It is somewhat paradoxical, given that heterotrophy is the most widespread form of metabolism among bacteria, that the first acidophilic heterotrophic bacterium which is indigenous and active in mineral leaching environments was isolated and characterized some 40 years after the iron/sulfur-oxidizing chemolithotroph T. ferrooxidans and 70 years after the sulfur-oxidizing acidophile T. thiooxidans.
Tests of heavy metal extraction from municipal solid waste incineration fly ashes (MSWFAs) were conducted using Thiobacillus spp. strain TM-32. Six types of MSWFAs were collected from actual incineration plants. Despite different ash sources, the samples showed approximately the same percentages by heavy metal extraction. The percentages were 55.3-68.5%, 57.4-84.6%, 2.2-19.6%, and 38.8%-56.4% for Cd, Cu, Pb, and Zn, respectively. To treat large amount of ash, large sulfate accumulation was essential. Sulfur free culture was employed for the tests and showed approximately the same extraction percentage as original ONM media culture.
The Acidithiobacillus ferrooxidans (At. f) and Acidithiobacillus thiooxidans (At. t) were used in bio-dissolution experiments of heavy metals in spent MH/Ni batteries. The influences of the initial pH value, the concentration of electrode materials, the temperature and substrate concentration on the leaching rate of heavy metal Ni, Co have been investigated. The obtained results indicate that the efficiency of nickel extraction and cobalt extraction is dependent on all of the mentioned factors. Especially, the initial pH value and the temperature have more effect than other factors for these microorganisms. In addition, the results show that the optimal leaching rate of Ni and Co in the spent MH/Ni batteries reaches to 95.7% and 72.4% respectively after 20 days under the conditions of the initial pH value 1.0, concentration of electrode materials 1.0%, temperature 30 °C and substrate (sulfur) concentration 4.0 g·L-1.
In this study experimental conditions were expressed for a new process of recycling lead paste at relatively lower temperatures. Lead acid battery paste was reacted with the mixture of citric acid, sodium citrate and hydrogen peroxide solution in this process. The solution mixture provided the removal of sulphur content of the paste as well as the decomposition of lead dioxide. Complete transformation to lead citrate was achieved by experimenting hydrometallurgical conditions of leaching-crystallisation step. Then thermal behaviour of lead citrate was investigated accordingly. Lead citrate crystals were decomposed to lead oxide at around 300°C without any addition. Direct reduction of lead from lead citrate was also possible under specific conditions. Experimental results reflected the efficient recovery of spent lead acid battery pastes without the use of high temperature pyrometallurgy or energy intensive electrolysis techniques.
The present work investigated the influence of Fe+2 initial concentrations in the bioleaching of copper from printed circuit board using Acidithiobacillus ferrooxidans-LR. Printed circuit boards were collected from obsolete computers and mechanically processed through size reduction followed by magnetic separation. The bacteria Acidithiobacillus ferrooxidans-LR were grown and adapted in presence of printed circuit boards. A shake flask study was carried out on the printed circuit boards samples (non-magnetic fraction) using a rotary shaker under the following fixed conditions (185 rpm, 30°C). The bioleaching efficiency was evaluated by comparison between the concentration in the initial sample and in the leached liquor, pH of the medium and concentration of ferrous iron produced. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the metals concentration. The results showed that Acidithiobacillus ferrooxidans-LR leached 63% copper from printed circuit boards using supplemented medium with Fe+2.
Bioleaching of metal sulfides isdis effected by bacteria like Thiobacillus ferrooxidans, Leptospirillum ferrooxidans, Sulfolobus/Acidianus etc. via the (re)generation of iron(III) ions and sulfuric acid. According to the new integral model for bioleaching presented here, metal sulfides are degraded by a chemical attack of iron(III) ions and/or protons on the crystal lattice. The primary iron(III) ions are supplied by the EPS, where they are complexed to glucuronic acid residues. The mechanism of degradation is determined by the mineral structure. The disulfides pyrite (FeS2), molybdenite (MoS2), and tungstenite (WS2) are degraded via the main intermediate thiosulfate. Iron(III) ions are exclusively the oxidizing agents for dissolution. Thiosulfate is consequently degraded in a cyclic process to sulfate, with elemental sulfur being a side product. This explains, why only iron(II) ion-oxidizing bacteria are able to oxidize these metal sulfides. The metal sulfides galena (PbS), sphalerite (ZnS), chalcopyrite (CuFeS2), hauerite (MnS2), orpiment (As2S3), and realgar (As4S4) are degradable by iron(III) ion and proton attack. Consequently, the main intermediates are polysulfides and elemental sulfur (thiosulfate is only a by-product of further degradation steps). The dissolution proceeds via a H2S*+-radical and polysulfides to elemental sulfur. Thus, these metal sulfides are degradable by all bacteria able to oxidize sulfur compotmds (like Thiobacillus thiooxidans etc.). The two mechanisms, based on the mineral structure of a metal sulfide, are summarized in the following Figure 1.
Hydrotreating heavy oils produces catalysts that are contaminated with coke and with nickel, vanadium and iron. Regeneration may be possible but sooner or later irreversible deactivation occurs. Means of regenerating or disposing of spent catalysts are reviewed. Regeneration may or may not involve decoking, with selective removal of Ni, V and Fe being achieved by leaching with different reagents. Leaching of all metals from the spent catalyst may be achieved if disposal is required and the economic justification exists. The solid wastes must be encapsulated or stabilized before final disposal in order to meet environmental standards.
The recent U.S. Environmental Protection Agency's (EPA's) memorandum clarified that spent catalysts resulting from 'dual purpose' hydroprocessing reactors are hazardous waste. This article provides insight into the definitions in the EPA regulations that refiners must follow when determining how spent hydroprocessing catalysts should be classified.
Billiton Process Research has carried out extensive research over the past four years to develop new process technology using bioleaching for extraction of copper and nickel from their sulphide concentrates. Continuous pilot scale and laboratory batch testwork has been carried out with adapted mesophile bacterial cultures at 40°C-45°C, moderate thermophile cultures at 50°C-55°C and thermophile cultures at 65°C-85°C. Pilot scale work has demonstrated the commercial viability of mesophile cultures for bioleaching of secondary copper sulPhide and nickel sulphide concentrates. Moderate thermophiles offer benefits in terms of reduced cooling requirements for commercial reactors and, in the case of bioleaching of nickel concentrates, some selectivity over bioleaching of pyrite. Continuous pilot scale testwork has shown that thermophiles achieve efficient bioleaching of primary copper sulphide and nickel sulphide concentrates, giving much higher recoveries than achieved by bioleaching with a mesophile or moderate thermophile culture.
Microorganisms are intimately involved in metal biogeochemistry with a variety of processes determining mobility, and therefore, bioavailability. The balance between mobilization and immobilization varies depending on the organisms involved, their environment and physicochemical conditions. Metal mobilization can arise from a variety of leaching mechanisms, complexation by metabolites and siderophores, and methylation, where this results in volatilization. Immobilization can result from sorption to biomass or exopolymers, transport and intracellular sequestration or precipitation as organic and inorganic compounds, e.g., oxalates (fungi) and sulfides. In addition, reduction of higher valency species may effect mobilization, e.g,, Mn(IV) to Mn(II), or immobilization, e.g., Cr(VI) to Cr(III). In the context of bioremediation, solubilization of metal contaminants provides a means of removal from solid matrices, such as soils, sediments, dumps and other solid industrial wastes. Alternatively, immobilization processes may enable metals to be transformed in situ and are particularly applicable to removing metals from aqueous solution. This contribution will outline selected microbiological processes which are of significance in determining metal mobility and which have actual and potential application in bioremediation of metal pollution. These include autotrophic and heterotrophic leaching mechanisms, reductive precipitation, sulfate reduction and metal sulfide precipitation.
As an alternative using cyanide chemicals for gold extraction, the application of a cyanogenic bacterium viz. Chromobacterium violaceum (C. violaceum) in YP medium has been investigated. The catalytic roles of metal ions such as Na+, Mg2+, Fe2+, and Pb2+, as well as the effect of Na2HPO4 nutrient addition on the cyanide generation efficiency of the bacterium in this medium have been elucidated. While MgSO4 and FeSO4 added to the medium were equally effective for cyanide generation, improved efficiency was obtained in the presence of Na2HPO4 and Pb(NO3)(2). In order to examine the effectiveness of C. violaceum cultured in YP medium for the generation of cyanide ions, the dissolution of gold and copper from waste mobile phone printed circuit boards (PCBs), a good source of gold and copper in alkaline conditions, was tested at 30 degrees C, for various pH values and metal ion contents. Gold leaching was found to be 11% in 8 d at pH 11.0 in presence of 4.0 x 10(-3) mol/L MgSO4, whereas; copper recovery was high (11.4%) at pH 10.0. Addition of 1.0 x 10(-2) mol/L Na2HPO4 and 3.0 x 10(-6) mol/L Pb(NO3)(2) to the YP medium increased copper leaching to 30.3% and 38.1%, respectively, at pH 10.0 in 8 d. However, this effect was not observed for gold leaching.
In previous studies it has been showed that bacterially produced sulphuric acid is a good leaching agent for laterite tailings. In this work we evaluated heavy metals leaching from low grade laterite ore for cobalt and nickel extraction using sulphuric acid produced in situ by Acidithiobacillus thiooxidans under different culture conditions. In studies where that material was initially added to the cultures, considerable percentages of metals were leached (100 % Mn, 70 % Co, 7.5 % Ni, less than 5 % of Cr and Fe) after 18 days of incubation at low pulp densities (1 % and 2.5 %) of overburden. The maximum percentages were reached when cultures pH was approximately or below than 1.5. At higher pulp densities material was added to the cultures after different pre-cultivating times; also higher sulphur amounts were assayed; in such way about 100 % Mn, 60 % Co, 9 % Ni and Fe and 2.5 % Cr were leached. Although toxic metals were not completely leached, sequential extractions results indicate that these metals are not readily available. All studies finally suggest that bioleaching is a suitable technology for recovery of valuable metals as Co and remediation of mining residues by extraction of heavy metals.
Material and energy resource consumption is on the rise in both the industrialized and developing world (e.g., countries like India and China). In order to sustain this growth and provide resources for future generations, there is a need to design products that are easy to recover and recondition, thus enabling multiple use cycles. Processes are needed that can achieve this multi-use while producing zero (or very near zero) waste. There exist a number of barriers and challenges to achieving this vision of multi-use with zero waste; one such challenge is the development of a product recovery infrastructure that will minimize short-term impacts due to existing products and will be robust enough to recover products of the future. This paper identifies the barriers to developing such a recovery and reuse infrastructure. The aim is to achieve product multi-use and zero waste.
Spent petroleum catalyst from Korean petrochemical industry contains trace amount of metals such as Ni, V and Mo. Therefore an attempt was made to recover those trace metal using bioleaching process. Different leaching parameters such as Fe(II) concentration, pulp density, pH, temperature and particle size of spent catalyst particle were studied to evaluate their effects on the leaching efficiency. All the three metal ions like Ni, V and Mo followed dual kinetics, i.e., initial faster followed by slower rate. The percentage of leaching efficiency of Ni and V were higher than Mo. The leaching process followed a diffusion controlled model and the product layer was observed to be impervious due to formation of ammonium jarosite (NH4)Fe3(SO4)2(OH)6. In addition, the lower leaching efficiency of Mo was observed due to a hydrophobic coating of elemental sulfur over Mo matrix in the spent catalyst.
The kinetics of bioleaching of Mo, Ni, and Al from spent hydrocracking catalyst, using Aspergillus niger was studied. The four most effective bioleaching variables were selected in accordance with the Plackett–Burman design and were further optimized via central composite design (CCD). The optimal values of the variables for maximum multi-metal bioleaching were as follows: particle size 150–212 μm, sucrose 93.8 g/L, pulp density 3% w/v, and pH 7. The maximum metal recoveries corresponding to these conditions were 99.5 ± 0.4% Mo, 45.8 ± 1.2% Ni, and 13.9 ± 0.1% Al. The relatively low Ni extraction was attributed to the precipitation of Ni in the presence of oxalic acid. Under the optimal conditions, the fungus growth was found to be higher in the presence of spent catalyst than that in the catalyst-free medium. Determinations of the organic acid concentration showed noticeable variation during bioleaching, particularly for gluconic acid. Accordingly, a modified form of shrinking core model was used to take these variations into account. The predictions by the model showed good consistency with the experimental results, suggesting that diffusion of bioleaching agent through the solid matrix was the rate-controlling step.