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Precious Metal Recovery from Waste Printed Circuit Boards using Cyanide and Non-Cyanide Lixiviants - A Review
Abstract
Waste generated by the electrical and electronic devices is huge concern worldwide. With decreasing life cycle of most electronic devices and unavailability of the suitable recycling technologies it is expected to have huge electronic and electrical wastes to be generated in the coming years. The environmental threats caused by the disposal and incineration of electronic waste starting from the atmosphere to the aquatic and terrestrial living system have raised high alerts and concerns on the gases produced (dioxins, furans, polybrominated organic pollutants, and polycyclic aromatic hydrocarbons) by thermal treatments and can cause serious health problems if the flue gas cleaning systems are not developed and implemented. Apart from that there can be also dissolution of heavy metals released to the ground water from the landfill sites. As all these electronic and electrical waste do posses richness in the metal values it would be worth recovering the metal content and protect the environmental from the pollution. Cyanide leaching has been a successful technology worldwide for the recovery of precious metals (especially Au and Ag) from ores/concentrates/waste materials. Nevertheless, cyanide is always preferred over others because of its potential to deliver high recovery with a cheaper cost. Cyanidation process also increases the additional work of effluent treatment prior to disposal. Several non-cyanide leaching processes have been developed considering toxic nature and handling problems of cyanide with non-toxic lixiviants such as thiourea, thiosulphate, aqua regia and iodine. Therefore, several recycling technologies have been developed using cyanide or non-cyanide leaching methods to recover precious and valuable metals.
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... On the other hand, these will become an important source of metals, especially when the primary sources are running out. [3]. ...
... MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions, or products referred to in the content. 2 Nowadays, industrial waste is generally incinerated, which is detrimental to the environment due to the large number of metals it contains [7]. As reported by Akcil et al., the incineration and thermal treatment of e-waste have raised concerns because organic pollutants are emitted during these processes, which can cause serious problems due to their toxicity [3]. However, some researchers have found that recovering metals from these wastes could be more economical than extracting them from their primary sources [8]. ...
... In other works where ionic liquids of hydrogen sulphate and hydrogen peroxide were used, they found that the particle size had a great influence on the process [25]. 3 Other researchers, such as Kavousi et al., used hydrogen peroxide in a HBF4 leaching medium to extract copper at the same time as the solder alloy, managing to extract 99.99% of copper [26]. On the other hand, Segura & Lapidus used hydrogen peroxide in combination with an environmentally friendly leacher, in this case sodium citrate, additionally added ammonium phosphate as a chemical inhibitor to avoid the co-dissolution of base metals, achieving leaching with high copper concentrations (greater than 30 g/L) [27]. ...
Currently, with the rapid growth of the population, the demand for metals has increased, especially for the manufacture of electronic devices such as cell phones, computer equipment, among others. Once these devices stop working, most are sent to landfills, which represents a danger since these wastes contain metals and other materials that must be properly managed to prevent them from having a negative effect on the environment and the human being. On the other hand, e-waste contains valuable metals such as copper, gold, and silver, the concentration of which in these materials makes it cost-effective to recover. This paper presents a review of the extraction and recovery of valuable metals from electronic waste by hydrometallurgical methods, as well as patents and industrial processes related to the management and treatment of this waste.
... 1,2 The ubiquity of metal ions and their fundamental role in biology, industry, food, and environment sciences have stimulated research advances in the design of chemical hosts capable of monitoring target metal-ions in complex systems, recovering precious metal ions from secondary resources, and balancing the concentration of metal ions in biological processes. [3][4][5][6] The design of specific hosts for metal-ion recognition originally stemmed from Pedersen's discovery that crown-ethers could selectively form stable complexes with a range of alkali metal ions. 7,8 These early studies showed that subtle structural modifications in the shape, cavity size, types of donor atoms, and total charge of the host influence the binding affinity and sensing selectivity towards target metal-ion guests. ...
... Other selected aromatic guests, including 1,4diisocyanobenzene (dic) and 4,4-bipyridine (bpy) showed negligible chemical shift changes in the proton signals of all hosts despite large excesses of the guests (5 equivalents), emphasizing the importance of guests' electronic properties and host-guest size complementarity towards effective binding (Figure S18-S23, ESI). Having sulfur functional groups at the terminal end of the pillar [5]arene tends to attenuate binding affinities of difunctionalised organic guests despite there being no significant reduction in Ka values as in the case of pillar [4]arene [1]thioarene, where there is incorporation of a single thioarene panel into the macrocyclic scaffold. 35 Complexation with difunctionalised guest molecule having a suitable length can lead to complex host-guest supramolecular assemblies in solution ( Figure 6). ...
Nucleophilic substitution of pertosylated pillar[5]arene (P‐OTs) with commercially available sulfur containing nucleophiles (KSCN, KSAc, and thiophenol), yields a series of sulfur‐functionalised pillar[5]arenes. DLS results and SEM images imply that these pillararene macrocycles self‐assemble in acetonitrile solution, while X‐ray crystallographic evidence suggests solvent‐dependent assembly in the solid state. The nature of the sulfur substituents decorating the rim of the pillararene controls binding affinities towards organic guest encapsulations within the cavity and dictates metal‐ion binding properties through the formation of favorable S–M2+ coordination bonds outside the cavity, as determined by 1H NMR and fluorescence spectroscopic experiments. Addition of a dinitrile guest containing a bis‐triazole benzene spacer (btn) induced formation of pseudorotaxane host‐guest complexes. Fluorescence emission signals from these discrete macrocycles were significantly attenuated in the presence of either Hg2+ or Cu2+ in solution. Analogous titrations utilizing the corresponding pseudorotaxanes alter the binding selectivity and improve fluorescence sensing sensitivity. In addition, preliminary liquid‐liquid extraction studies indicate that the macrocycles facilitate the transfer of Cu2+ from the aqueous to the organic phase in comparison to extraction without pillar[5]arene ligands.
... The growing volume of waste electrical and electronic equipment (WEEE) is a major challenge for waste management worldwide. In addition to having some potentially hazardous substances in their constitution, there is a lot of interest in recovering the valuable elements present in WEEE (Akcil et al. 2015;Istrate et al. 2018;Schluep et al. 2009). For this reason and in compliance with legal requirements, some countries have developed and implemented WEEE reverse logistics (RL) systems. ...
... When EEE reaches the end of its lifespan, it becomes waste electrical and electronic equipment (WEEE) (ABDI 2013;Forti 2019). Some WEEE components have considerable economic value due to resources content, like Au, Ag, Cu, plastics and ferrous scrap (Akcil et al. 2015;Istrate et al. 2018;Schluep et al. 2009). Some components also have substances that pose a high hazard to human health, such as heavy metals and persistent organic pollutants (POPs), which can cause brain damage, allergic reactions, genotoxicity, cancer, lung problems, bioaccumulation and other diseases depending on the substance to which the person is exposed (Moi et al. 2012). ...
Waste electrical and electronic equipment (WEEE) has been largely generated in Brazil and worldwide. Besides the interest in recovering their valuable materials, some contain potentially hazardous components that must be removed and destined for treatment. WEEE pre-treatment is a critical step to efficiently sort and recover such components, but data availability is scarce in Brazil and developing countries, what may hinder feasibility analyses for its wider implementation. There is an increasing demand for studies that analyse the feasibility of WEEE reverse logistics systems, supporting their optimization. The present study analysed the feasibility of implementing WEEE pre-treatment units in a Brazilian municipality based on different levels of WEEE disassembly (A—basic; B—intermediate; and C—advanced) and implementation scenarios. Using the StEP tool and the multicriteria method ELECTRE TRI, the study classified implementation alternatives into three categories: more feasible; intermediate; and less feasible. The most feasible scenarios were related to an intermediate disassembly level (B). Alternatives with at least two pre-treatment units within the city were more feasible, even after some sensitivity analyses, indicating the advantages of smaller units and lower transport distances. The methodology and results may be applicable to other cities, both in Brazil and in other countries.
... CN has long been a popular lixiviant in gold mining, because of its low cost and additional benefits. The foundation of this procedure is the CN solution-based dissolution of gold and silver from the circuit boards [70]. Montero et al. (2012) used a leaching column technique with a sodium CN solution to recover gold, silver, copper, and niobium from the PCBs in discarded computers. ...
... mg/L with a maximum removal efficiency of 75%. Under the same operating conditions, the maximum Cu, Cr, Pb, Mn, Ni, Fe, and Zn removal efficiencies are 90,78,70,85,82,74, and 82%, respectively. Overall, the authors reported that treated gold mining wastewater can be recycled or utilized for purposes such as agricultural irrigation. ...
Cyanide (CN) is a serious concern in industrial and goldmine wastewater. Strict regulatory standards have been established by various agencies due to the detrimental effects that CN has on human health. Therefore, before discharge to water bodies or land, it is essential to create a sustainable model for the safe removal of CN. Carbon-based materials are well known for their adsorption and oxidation features, which can be conducive to CN removal. This paper reviews the relevant literature on the application of modified and unmodified carbon-based materials to CN removal in water; these materials include activated carbon (AC), graphene, graphene oxide (GO), and carbon nanotubes (CNTs). Moreover, CN removal mechanisms and photocatalytic removal of CN are comprehensively discussed, with a particular emphasis on modifying carbon-based materials. It has been observed that adding various elements to carbon-based materials improves their surface area, functional groups, CN adsorption capacity, and pore volume. Impacts of operational parameters, isotherm models, kinetics, and types of carbon-based materials are also outlined. This study provides insight into the real-scale applicability of carbon-based materials for CN removal from waters. Moreover, this review indicates that essential work on CN removal using carbon-based materials is still needed. Future research should focus on developing modified carbon-based materials to encourage multidisciplinary research. The most crucial gap in the literature is that the studies have been performed on a lab scale. Therefore, further pilot and real-scale applications should be conducted. Overall, the cost assessment, environmental effects, and human health risks of carbon-based materials should be studied in future research to achieve a realistic perspective on applicability on an industrial scale.
... Akcil et al. present a flow chart for metal recovery from E-waste ( Figure 5). The presented schema is divided into pre-processing and end-processing [18]). Pre-processing refers to separating and sorting parts and materials for safe disposal and recovery processes. ...
... Scheme for recovery of precious metals (adapted from[18]). ...
With the continuous growth of electric and electronic appliances’ usage, the waste produced with obsolete material (e-waste) has an increasing environmental impact. Also, the production of such appliances bears to increased consumption of natural resources and produces a multitude of toxic and hazardous substances, which typically are not properly treated. One of the approaches that may be adopted to reduce such problems relies on the circularization of the current linear model, commonly adopted in the EEE value chain. This includes recovering eol products and reintroducing its parts, components, or raw materials into the value chain (e.g. semiconductors, circuit boards, raw metals, etc.), thus contributing to a more sustainable value chain. In this article, we present a state-of-art review that focuses on approaches and solutions for the EEE value chain traceability, and analyses the technologies that may be beneficial for promoting and implementing the CE model in this value chain.
... Akcil et al. presented a flowchart for the recovery of metal from e-waste ( Figure 5). The presented scheme is divided into pre-processing and end processing [19]). Pre-processing refers to separating and sorting of parts and materials for safe disposal and recovery. ...
... Scheme for recovery of precious metals (adapted from[19]). ...
With the continuous growth in the use of home appliances and electronics, waste produced with obsolete material (e-waste) has an increasing environmental impact. Furthermore, the production of such devices leads to increased consumption of natural resources and produces a multitude of toxic and hazardous substances, which are normally not treated properly. One of the approaches that may be adopted to reduce such problems relies on the circularization of the current linear model, commonly adopted in the Electric and Electronic Equipment (EEE) value chain. This includes recovering End-of-Life products and reintroducing their parts, components, or raw materials into the value chain (e.g., semiconductors, circuit boards, raw metals, etc.), contributing to a more sustainable value chain. In this article, we present a state-of-the-art review that focuses on approaches and solutions for EEE value chain traceability and analyze the technologies that may be beneficial for promoting and implementing the Circular Economy model in this value chain.
... As compared to cyanides, halogens provide environmentally friendly bioleaching mechanisms. They are relatively safe with higher level of chemical stability (Akcil et al. 2015). ...
... Alkaline cyanide solution dissolves the gold and results in the formation of cyanide complexes. Here, oxygen concentration affects the gold solubility in cyanide solution (Akcil et al. 2015). 208 V. Dhiman ...
For the past few years, the e-waste problem has taken over on a larger scale, so we are now forced to rethink how to tackle this e-waste problem. So, people start thinking about the e-waste management concept and trying to develop new methods by which we can reduce e-waste. The present chapter highlights the scenario of e-waste in India and other parts of the globe. It also exhibits the trends of e-waste in India through a comparison with other countries. The study reveals that electronic equipment such as computers, mobile, and telephones are identified as the principal e-waste generators in India. A report suggests that computers contributed to 70% of the total e-waste generated in India, while telecommunication equipment accounted for 12%. Among cities, Mumbai is one of the biggest hubs and ranked number one on the list as it generates an estimated 120,000 tons of e-waste annually. Approximately 70% of heavy metals found in landfills are accounted for by e-waste. In light of this, this chapter also offers suggestions to deal with the challenges, conventional e-waste management methods, eco-friendly e-waste management methods, and problems of e-waste.
... However, there is the loss of precious metals and the recovered metals need to be purified through a hydrometallurgical or pyrometallurgical process [30]. Waste treatment and metals recovery using hydrometallurgical techniques are based on acid leaching [31], cyanide lixiviation [32] and a combination of supercritical water (SCW) pre-treatment and acid leaching [33]. Hydrometallurgical techniques allow segregation, refining and recovery of metals from waste. ...
... This process comprises many operations, such as high-temperature roasting, smelting, and calcination. The proposed methodology involves incineration of electronic waste in a controlled furnace environment, separating polychlorinated biphenyl (PCB) pollutants as residual byproducts (Akcil et al., 2015). Pyrometallurgical processes are often conducted without air or inside an inert atmosphere. ...
Electronic waste is one of the most concerns of human in the current century. Inappropriate disposal of this type of waste and informal management, such as landfilling and incineration, can lead to severe risks to human health and ecosystems. Nevertheless, electronic waste can be recycled to valuable materials by various formal technologies and protects energy and resources. This chapter addresses concerns related to electronic waste and its inappropriate management. Subsequently, the chapter focuses on various technologies and approaches for electronic waste recycling and finally discusses existing challenges as well as opportunities and limitations in electronic waste recycling.
... This presents a financial advantage to mining E-waste instead of ores from virgin sources. Ironically, only 20% of the metals in E-waste were being collected back, and due to a lack of selectivity for highyield non-cyanide recycling practices, 80% were being dumped back into landfills [6][7][8]. The currently employed recycling methods are the pyrometallurgy and hydrometallurgy processes, both of which were shown to have considerable With rapid technological advancement, the life span of electronic devices has become increasingly short, contributing to massive electronic waste (E-waste) and demanding sustainable management. ...
With rapid technological advancement, the life span of electronic devices has become increasingly short, contributing to massive electronic waste (E-waste) and demanding sustainable management. E-waste contains precious metals like gold (Au) many fold higher than natural mining ores. However, the current techniques of recycling are not efficient. Methods like pyrometallurgy and hydrometallurgy not only require higher energy expenditure but also lead to environmental pollution, hence necessitating an alternative greener technology. In line with that, metal leaching using microorganisms is gaining popularity, and Chromobacterium violaceum has been considered a promising candidate. However, the heterogeneity of culture technique and abiotic condition variations have been a perceived challenge in priming C. violaceum as an Au bioleacher for upscaled industrial
applications. Thus, the current review discusses what makes C. violaceum an excellent candidate for Au bioleaching and how to overcome the challenges associated with the application. This review will significantly enhance the current understanding of C. violaceum as an Au bioleaching agent, hence addressing the existing knowledge gaps.
... Typical metal contents are 10-27% copper (Cu), 2-8% aluminium (Al), 1-4% lead (Pb), 1-8% iron (Fe), 1-6% tin (Sn) and <0.1% precious metals (Au; 10-1600 ppm, Ag: 20-200x103 ppm, Pd: 5-970 ppm). 3 There are i) mechanical/physical [4][5][6][7] , ii) thermal 8,9 , and iii) chemical [10][11][12][13][14] , iv) physicochemical techniques 15 and their combinations [16][17][18] applied to recover the targeted metallic fraction from PCBs. Physical methods include dismantling; screening; shape separation; flotation; jigging; air, electrostatic, magnetic, eddy-current and density-based separation. ...
In recent years, there has been a growing focus on the reuse of metallic components from waste electrical and electronic equipment (WEEE) which refers to electrical and electronic equipment that has become obsolete, stopped working, or developed defects during production. In this research, shaking table was selected as a gravity concentration tool for the recovery of copper from the light components. The flowsheet included comminution, gravimetric concentration and physical/chemical characterization of feed material and products. The process parameters were deck angle (degrees), motion frequency (Hz), wash water rate (Lpm), and particle size diameter. The Box Behnken Design (BBD) was used to optimize the performance of the wet shaking table and to identify the ideal combination of its operating parameters. By analysing the experimental design, it was found that the optimal settings for deck angle, motion frequency, wash water rate, and particle size diameter were 2 degrees, 50 Hz, 12 Lpm, and -500+300 mm, respectively. These optimal settings were located near the central points of the experimental design, suggesting that the actual optimal point could be within the design space.
... The disassembly of waste smartphones reveals that their main constituent parts can be categorized into various models of batteries, multimaterial cases (e.g., ceramic and plastic), microphones, printed circuit boards (PCBs), and LCD screens (Fontana et al., 2019;Sandmann et al., 2019;Sawanishi et al., 2014). Waste smartphones contain large amounts of toxic and hazardous substances (i.e., lead, chromium, and polybrominated biphenyls), which can damage the soil and water bodies if disposed of in an unregulated manner (Akcil et al., 2015;Mama et al., 2021;Singh et al., 2020). By contrast, proper recycling of e-waste can not only achieve greater environmental benefits, but also extract various CRMs, including copper, cobalt, vanadium, tungsten, antimony, and lithium (Mejame et al., 2018;Panchal et al., 2021;Singh et al., 2019). ...
... Currently, driven by the economic interests, the recovery of metallic components from WPCBs has attracted extensive attention by using various extraction processes, including leaching, mechanical and hydrometallurgical processing techniques [35][36][37]. For comprehensive reviews of metal recovery from WPCB, readers can refer to the reviews written by Hao et al. [38], Qiu et al. [39], Lu et al. [40], and Akcil et al. [41]. While this review will focus on the recovery techniques used for non-metallic components, which account for about 70 wt% of waste PCBs and still face serious environmental and economic challenges [24]. ...
The reutilization non-metallic components from a waste-printed circuit board (WPCB) has become one of the most significant bottlenecks in the comprehensive reuse of electronic wastes due to its low value and complex compositions, and it has received great attention from scientific and industrial researchers. To effectively address the environmental pollution caused by inappropriate recycling methods, such as incineration and landfill, extensive efforts have been dedicated to achieving the high value-added reutilization of WPCB non-metals in sustainable polymer composites. In this review, recent progress in developing sustainable polymer composites based on WPCB non-metallic components was systematically summarized. It has been demonstrated that the WPCB non-metals can serve as a promising reinforcing and functional fillers to significantly ameliorate some of the physical and chemical properties of polymer composites, such as excellent mechanical properties, enhanced thermal stability, and flame retardancy. The recovery strategies and composition of WPCB non-metals were also briefly discussed. Finally, the future potentials and remaining challenges regarding the reutilization of WPCB non-metallic components are outlined. This work provides readers with a comprehensive understanding of the preparation, structure, and properties of the polymer composites based on WPCB non-metals, providing significant insights regarding the high value-added reutilization of WPCB non-metals of electronic wastes.
... Reviews on PCB recycling have primarily focused on hydrometallurgical processes (Akcil et al., 2015;Cui and Anderson, 2016;Sethurajan et al., 2019;Tabelin et al., 2021;Tuncuk et al., 2012), pyrometallurgical processes (Tabelin et al., 2021;Wang et al., 2017b), pre-treatment approaches (Kang et al., 2021;Kaya, 2016;Moyo et al., 2020;Qiu et al., 2020), and gold recovery (Rao et al., 2020;Syed, 2012). However, very few focused on comprehensive metal recycling processes (Hao et al., 2020), and to our best knowledge none of them deals with the recycling of electronic components (an integral component) of PCBs or the generation of value-added end-products. ...
Among the different types of secondary post-consumption wastes, E-wastes or waste electrical and electronic equipment represent the fastest growing and most problematic waste stream with printed circuit boards (PCBs) constituting its major ingredient. Results from the extraction of Cu and Ni from PCBs using biogenic Fe2(SO4)3 obtained from the original isolate Acidithiobacillus ferrooxidans 61 (KM819692) are presented. At. ferrooxidans 61 was grown at a temperature of 30 °C in a modified 9 K medium supplemented with ferrous iron. Two-stage bioleaching was carried out at 600 rpm and 40 °C. Experiments were performed at 10% of pulp density (PD) with 48-h duration (each stage of 24 h), under pH 1 and 20 g/L Fe³⁺. Under these conditions, overall recovery of Cu and Ni of 95% and 87% respectively was achieved. The obtained results indicate that non-ferrous metals in PCBs may be efficiently leached within two-stage bioleaching coupling bio-oxidation to subsequent redoxolysis. Scanning electron microscope (SEM) images acquisition and elemental mapping were performed to assess the liberation degree of essential phases after size-reduction steps and their implication on bioleaching efficiency.
... Although these techniques are relatively inexpensive and quick for gold recovery, they exhibit low efficiency and low selectivity, and there are health risks associated with these conventional methods [8]. Currently, 50% of e-waste ends up in landfills due to a lack of recycling programs with high selectivity and productivity [9,10]. 2 of 11 It is compelling to develop sustainable and eco-friendly technologies with higher selectivity and extraction capacity for gold extraction from the leachate of waste PCBs [4,6]. Various novel gold extraction methods have been explored recently [11][12][13][14][15]. Xue et al. reported a record-breaking extraction rate, with high Au 3+ removal efficiency (>99%) within seconds (less than 45 s), a competitive capacity (1.6 g/g) with a highly porous metalorganic framework (MOF)-polymer composite and BUT-33-poly(para-phenylenediamine) for gold extraction from e-waste [12]. ...
The recovery of gold from water is an important research area. Recent reports have highlighted the ultrahigh capacity and selective extraction of gold from electronic waste using reduced graphene oxide (rGO). Here, we made a further attempt with the thermal rGO membranes and found that the thermal rGO membranes also had a similarly high adsorption efficiency (1.79 g gold per gram of rGO membranes at 1000 ppm). Furthermore, we paid special attention to the detailed selectivity between Au3+ and other ions by rGO membranes. The maximum adsorption capacity for Au3+ ions was about 16 times that of Cu2+ ions and 10 times that of Fe3+ ions in a mixture solution with equal proportions of Au3+/Cu2+ and Au3+/Fe3+. In a mixed-ion solution containing Au3+:Cu2+:Na+:Fe3+:Mg2+ of printed circuit board (PCB), the mass of Au3+:Cu2+:Na+:Fe3+:Mg2+ in rGO membranes is four orders of magnitude higher than the initial mass ratio. A theoretical analysis indicates that this selectivity may be attributed to the difference in the adsorption energy between the metal ions and the rGO membrane. The results are conducive to the usage of rGO membranes as adsorbents for Au capture from secondary metal resources in the industrial sector.
... Genetic information is contained in DNA, a polyanion. Anionic cofactors are common in enzymes; one example is carboxypeptidase A. In metallurgical processes, cyanide is used to extract valuable metals like gold and silver [3,4]. Goiter can be prevented by using iodide. ...
Iodine is an essential ingredient in thyroid hormones of which both low and high intakes may cause thyroid disease. This study develops a Pyrrole-2-Carboxaldehyde functionalized chitosan-Cu(II) Complex [PCAFC-Cu(II)] chemosensor, for quick and easy detection of iodide ions from its aqueous solutions. PCAFC-Cu(II) complex was synthesized from a simple condensation reaction of chitosan (CS) and pyrrole-2-carboxaldehyde (PCA) along with an aqueous solution of copper(II) salt. The starting materials and the products were characterized by spectroscopic (FT-IR and UV-Visible), X-ray powder diffraction, and microscopic methods (Scanning Electron Microscopy). The PCAFC-Cu(II) colorimetric sensing of I- revealed a color change adduced to the formation of a hydrogen bond or deprotonation of the complex matrix. Colorimetric detection for I- ions was obtained with a detection limit (LoD) of 0.005 M and the complex has high specificity for I- ions detection from a solution consisting of several anions. The synthesized complex [PCAFC-Cu(II)] could serve as an on-site reagent for the qualitative detection of iodide ions.
... The scheme was designed with minimum number of reagents (i.e., hydrochloric acid, nitric acid, hydrazine hydrate) rendering successful the downstream wastewater treatment in a novel denitrifying biological system (Mendrinou et al., 2021). Gold extraction from primary ores has been dominated by cyanide (Medina and Anderson, 2020) which has been successfully applied to Au extraction from PCBs (Akcil et al., 2015;Rao et al., 2020). However, due to the toxicity of cyanide, research has focused on other lixiviants, such as halogens, thiosulphate and thiourea, for precious metal leaching (Au, Ag and Pt) from PCBs (Mir and Dhawan, 2022). ...
A hydrometallurgical process for the recovery of gold and silver from waste printed circuit boards (PCBs) was experimentally verified and tested at pilot scale. The process comprises four sequential leaching stages; the first two based on HCl, correspond to base metals (e.g. Sn, Cu) removal, while the third is based on HNO3 for Ag leaching and the final on aqua regia for Au leaching. After base metals leaching, the solid residue, enriched in silver and gold about 5 times, contained silver almost quantitively as insoluble AgCl and significant losses (Ag loss <8%) were avoided. The necessary reduction of Ag in the solid phase was achieved with a solution of 0.5 M N2H4 and 3 M NaOH, at 80 °C and S/L ratio 10%. Leaching of silver by 4 M HNO3 was followed by its recovery from nitrate solution by 0.08 Μ N2H4 at ambient temperature with an efficiency of 83%. Gold was leached by aqua regia and quantitively recovered by 0.13 M N2H4 at ambient temperature. Wastewater resulting from the process, rich in nitrate (5 g/L) and chloride (50 g/L), was treated by an effective and novel biological denitrification system tolerating metals at ppm level, to comply with zero nitrate and residual metals discharge guidelines. The overall process requires low reagents and energy input and has zero discharge for liquid effluents. The scheme is appropriate to be applied at local small to medium industrial units, complying with decentralized circular economy principles for metal recovery from electronic waste.
... Pyrometallurgical recycling facilitates scalability and uses few chemicals (Assefi et al. 2020) but releases harmful and toxic gases such as dioxins and carbon dioxide, and volatile metals like Hg (Lu and Xu 2016). Currently, hydrometallurgical processes are preferred over pyrometallurgy for the recovery of precious metals from E-waste (Akcil et al. 2015;Rodríguez-Padrón et al. 2020). Aside from low emissions, hydrometallurgical recycling yields high recovery rates, minimal slag generation, consumes less energy and offers easier working conditions (Lu and Xu 2016). ...
Efficient and sustainable secondary sourcing of Rare-Earth Elements (REE) is essential to counter supply bottlenecks and the impacts associated with primary mining. Recycled electronic waste (E-waste) is considered a promising REE source and hydrometallurgical methods followed by chemical separation techniques (usually solvent extraction) have been successfully applied to these wastes with high REE yields. However, the generation of acidic and organic waste streams is considered unsustainable and has led to the search for “greener” approaches. Sorption-based technologies using biomass such as bacteria, fungi and algae have been developed to sustainably recover REE from e-waste. Algae sorbents in particular have experienced growing research interest in recent years. Despite its high potential, sorption efficiency is strongly influenced by sorbent-specific parameters such as biomass type and state (fresh/dried, pre-treatment, functionalization) as well as solution parameters such as pH, REE concentration, and matrix complexity (ionic strength and competing ions). This review highlights differences in experimental conditions among published algal-based REE sorption studies and their impact on sorption efficiency. Since research into algal sorbents for REE recovery from real wastes is still in its infancy, aspects such as the economic viability of a realistic application are still unexplored. However, it has been proposed to integrate REE recovery into an algal biorefinery concept to increase the economics of the process (by providing a range of additional products), but also in the prospect of achieving carbon neutrality (as large-scale algae cultivation can act as a CO2 sink).
Graphical abstract
... Moreover, it is suggested that cyanidation should be carried out above the pH of 10 because toxic HCN is predominantly formed at pH < 8.5. Theoverall reaction is given in Eq. (5) (Akcil et al., 2015): ...
The growing development of technology has increased the amount of waste generated by electrical and electronic equipment (WEEE) every year. WEEE contains valuable metals and hazardous materials which, if not properly recovered, may drastically contribute to the depletion of natural resources while posing threat to the environment. The recent escalation of geopolitical tensions has fueled a growing spike in commodity and energy prices. In today's world, the recycling technologies have already evolved from primitive methods to more sophisticated techniques such as automatic disassembly, chemical leaching, electrolysis and so on. It is mandatory that researchers will develop novel technologies to tackle the complexity of WEEE treatment and material recovery. This analysis critically reviews the accomplishments in the field of e-waste recycling and further assesses the principles of recycling, separation, and optimized parameters of different technologies. The application of conventional techniques like pyrometallurgy and chemical leaching (non-cyanide, reduced wastewater) results in an active recovery of various materials. Compared to cyanide and strong acid leading, thiourea and thiosulphate have achieved significant advancements in environmental protection. Additionally, novel technologies like bio-metallurgy cryo-milling, siderophores and supercritical extraction technology also resulted in enhanced recovery efficiencies for base and precious metals, along with metal recovery techniques using recyclable lixiviates. However, the application of these technologies is restricted due to the heterogeneous nature of WEEE. Therefore, this review focuses on the deficiencies of each of them and further discusses the interpretation of future urgent developments in the WEEE recycling sector.
... Last decade, the end-of-life metal-bearing materials, can be also called as metal bearing wastes, has been widely accepted as secondary resource of critical raw materials due to metal content of metal-bearing wastes is comparable with natural ores Lee et al. 2022a;Sarker et al. 2022). For example, electronic wastes contain up to 26 times higher Cu and 50 times higher Au content compared to ores/concentrates (Akcil et al. 2015). Another example is that some tailings can have higher Co content (0.02-1.38%) than a natural ore (0.05-0.3%) (Gutiérrez-Gutiérrez et al. 2015;Sarker et al. 2022). ...
The global transition to a circular economy calls for research and development on technologies facilitating sustainable resource recovery from wastes and by-products. Metal-bearing materials, including electronic wastes, tailings, and metallurgical by-products, are increasingly viewed as valuable resources, with some possessing comparable or superior quality to natural ores. Bioleaching, an eco-friendly and cost-effective alternative to conventional hydrometallurgical and pyrometallurgical methods, uses microorganisms and their metabolites to extract metals from unwanted metal-bearing materials. The performance of bioleaching is influenced by pH, solid concentration, energy source, agitation rate, irrigation rate, aeration rate, and inoculum concentration. Optimizing these parameters improves yields and encourages the wider application of bioleaching. Here, we review the microbial diversity and specific mechanisms of bioleaching for metal recovery. We describe the current operations and approaches of bioleaching at various scales and summarise the influence of a broad range of operational parameters. Finally, we address the primary challenges in scaling up bioleaching applications and propose an optimisation strategy for future bioleaching research.
... Strong mineral acids such as HCl and H 2 SO 4 were used in metal dissolution, with hydrogen evolution [16]. Currently, highly toxic aqua regia and cyanide solutions have been used at the industrial level, which is harmful to the environment [17]. Conventional mineral acids such as HCl, H 2 SO 4, and HNO 3 are low-cost but hold a high environmental impact after usage. ...
Deep eutectic solvents (DESs) are green alternatives to highly acidic solvents or ionic liquids (ILs). The flexible complexation properties of eutectic solvents open their scope as a prospective dissolution medium for metal extraction. The present study investigates the range of monocarboxylic acids-choline chloride (Monocarboxy A-ChCl) and dicarboxylic acid-choline chloride (Dicarboxy A-ChCl) DESs as solvent media for copper oxide dissolution with a discussion on physical properties and their effect on dissolution. Thermal stability, freezing point, Kamlet Taft parameter, density, and viscosity of Carboxy A-ChCl DESs were experimentally determined.
The density of Carboxy A-ChCl DESs follows the trend: FA-ChCl < Acetic A-ChCl < OA-ChCl < MA-ChCl < CA-ChCl. The viscosity of Monocarboxy A-ChCl was observed to be lesser than Dicaboxy A-ChCl DESs. The polarity of Monocarboxy A-ChCl was observed to be in the range of 1.2-0.8, while Dicarboxy A-ChCl, polarity was greater than 1. Further, the effect of hydrogen bond donors (HBD), hydrogen bond acceptors (HBA), KFT parameters, viscosity, fukui function of HBD, reaction time and temperature affecting the dissolution of Cu are elaborated in detail. Most dependant to least dependent parameters with respect to dissolution is recognized and some crucial conclusions were put together. Formic acid: Choline chloride (FA-ChCl) DES indicated the highest copper dissolution in the range >106 ppm. Copper dissolution from ionic CuO to low polar Monocarboxy A-ChCl DESs was higher than in high polar Dicarboxy A-ChCl DESs. DFT calculation reveals that Formic Acid (FA) has the highest fukui functions compared to other carboxylic acids, which is directly reflected in the higher solubility of copper oxides. Additionally, the effect of reaction time and temperature on CuO dissolution in best-performing FA-ChCl DES was studied, 75 °C, 27 h, 100 °C, 18 h were chosen as the optimum time and temperature for maximum dissolution of Cu. The results cover important parameters of Carboxy A-ChCl DES, which could be helpful in metal extraction applications.
... This process causes high energy consumption and CO 2 emission and requires long process times. As an alternative method, hydrometallurgy has gained attention due to its effectiveness, low energy consumption, and low emissions during processing [7][8][9]. The hydrometallurgical ...
The importance of gold recovery from waste printed circuit boards is continuously increasing due to raising gold prices and demand as well as the need for innovative and flexible recycling methods for this complex waste stream. The state-of-the-art recycling process aims at the pyrometallurgical recovery of noble metals, mainly using a copper collector. Different technical limitations justify the application of a hydrometallurgical process alternative for recovering gold. The direct application of gold lixiviants on comminuted PCBs is hardly possible due to the high concentration of metal impurities. As a solution, most researchers propose hydrometallurgical separation of disturbing base metals prior to gold extraction. For this, different leaching systems with aggressive chemicals can be applied, often leaving residual base metal concentrations behind. Within this study, two different leaching parameter sets were investigated to separate base metals and determine the impact of residual base metals on subsequent gold recovery. The gold lixiviants that were applied for comparison were thiosulfate, thiourea, iodine-iodide, NBS, and cyanide. It was found that thiosulfate and thiourea are less sensitive than other lixiviants to metal impurities. When base metals are separated completely, gold recovery is strongly improved, and cyanide also achieves a good gold recovery.
... Pd is generally applied in many domains, such as electronic products, catalysts, fuel cells and medicine, because of its different physical and chemical properties. [1] In some cases, Pd may cause cell death by disrupting the mitochondrial respiratory chain. [2] So, their separation from industrial wastewater is essential because of these metals' high toxicity and impact on human health. ...
In this study, chitin was extracted from shrimp shells (SS) and characterized by scanning electron microscopy, X-ray diffraction, and Fourier transforms infrared spectroscopy. And investigate the adsorption of vanadium (V) and palladium (Pd) toxic metals onto the chitin. The effect of parameters such as the concentration of V and Pd, contact time, solution pH, adsorbent dose, cations, and anions were studied on the adsorption process. Kinetic, isotherm, and thermodynamic models
were investigated. Genetic programming (GP) is used to obtain an appropriate equation showing the relationship between the variables. Experimental optimum conditions were found in the V and Pd concentrations of 25mg/L, pH of 9, an adsorbent dose of 0.8 g/L and a contact time of 15 minutes. The maximum adsorption capacities (qm) of 13.15 and 12.65mg/g were obtained for V and Pd, respectively. Among the anions and cations examined in this study, Ca2þ and SO4
2- had the greatest effect on the absorption of V and Pd on chitin. The adsorption kinetics followed a pseudo-second-order kinetic model and the equilibrium data showed a good fit of the Langmuir model and demonstrated a monolayer and favorable physisorption process. The thermodynamic analysis depicted that the process of adsorbing V and Pd using chitin was endothermic and spontaneous.
Findings also presented GP as a potential tool for identifying the behavior of V and Pd adsorption. It can be concluded that chitin extracted from SS wastes, as a nontoxic and cheap adsorbent, could efficiently remove V and Pd from aqueous solutions.
... Green techniques for metal extraction from industrial effluent include membrane filtration, green adsorption, and photocatalysis. Green adsorption is frequently used to remove metals from contaminated locations, which comprises low-cost materials derived from agricultural sources, agricultural by-products, agricultural residues, and agricultural wastes (Akcil et al. 2015;Sahni et al. 2016). For the first time, dyes (MB, MG, and CR) were extracted from aqueous solutions using CLP and ZMC, demonstrating the potential for adsorption of green adsorbents. ...
The electrical and electronic waste is expected to increase up to 74.7 million metric tons by 2030 due to the unparalleled replacement rate of electronic devices, depleting the conventional sources of valuable metals such as rare earth elements, platinum group metals, Co, Sb, Mo, Li, Ni, Cu, Ag, Sn, Au, and Cr. Most of the current techniques for recycling, recovering, and disposing of e-waste are inappropriate and therefore contaminate the land, air, and water due to the release of hazardous compounds into the environment. Hydrometallurgy and pyrometallurgy are two such conventional methods used extensively for metal recovery from waste electrical and electronic equipment (WEEE). However, environmental repercussions and higher energy requirements are the key drawbacks that prevent their widespread application. Thus, to ensure the environment and elemental sustainability, novel processes and technologies must be developed for e-waste management with enhanced recovery and reuse of the valued elements. Therefore, the goal of the current work is to examine the batch and continuous processes of metal extraction from e-waste. In addition to the conventional devices, microfluidic devices have been also analyzed for microflow metal extraction. In microfluidic devices, it has been observed that the large specific surface area and short diffusion distance of microfluidic devices are advantageous for the efficient extraction of metals. Additionally, cutting-edge technologies have been proposed to enhance the recovery, reusability, and recycling of e-waste. The current study may support decision-making by researchers in deciding the direction of future research and moving toward sustainable development.
... Currently, active scientific research on the recycling of waste PCBs is ongoing within the framework of hydrometallurgical technologies. Moreover, a significant part of these studies is related to extracting the most valuable components of PCBs-noble metals (mainly gold) and copper [1][2][3][4][5][6]. ...
This paper presents the results of the leaching of metals from computer PCBs by electrochemical hydrochlorination using alternating current (AC) with an industrial frequency (50 Hz). Leaching was carried out with a disintegrator-crushed computer motherboard with a particle size (d) of <90 μm. In the course of the research, the leaching efficiency of metals including Fe, Sn, Mn, Al, Cu, Zn, Pb, Ni, Ti, Sb, Cr, Co and V was evaluated depending on process parameters, such as AC density, experiment duration, hydrochloric acid concentration in the electrolyte solution, solid/liquid ratio, electrolyte temperature, and the loading option of raw material (loading option 1 involving loading into the electrolyte solution, and loading option 2 involving loading into the filter containers attached to electrodes). The research results showed that AC superimposition significantly intensifies the leaching of metals. It was established that the complete leaching of metals including Al, Mn, Sn, Ti and Zn, under experimental conditions (loading option 2, CHCl = 6 mol·L−1, i = 0.80 A·cm−2, S/L = 8.6 g·L−1), is reached after 1.5 h, and that of Cu and Ni is reached after 2 h from the beginning of the experiment. At the same time, the degree of leaching of other metals after 2 h is Co-78.8%, Cr-84.4%, Sb-91.7%, Fe-98.9%, V-98.1% and Pb-5.1%. The paper also reports the results on the leaching of all abovementioned metals, as well as Ag and Pd, with disintegrator-crushed mixed computer PCBs with d < 90 μm and loading option 1.
Background
Etching solutions of spent printed circuit boards (PCBs) contain precious metal ions like Au(III) and Pd(II) together with Cu(II). Therefore, it is crucial to recover Au(III) and Pd(II) from these solutions. To investigate the possibility of separating Au(III) from the etching solutions, solvent extraction experiments were conducted using synthetic hydrochloric acid solutions containing Au(III), Pd(II), Cu(II), and Ni(II). The solvent extraction behavior of these four metal ions was investigated by using cationic (Cyanex 301, LIX 63), neutral (Cyanex 923 and TBP), and basic (Alamine 336 and Aliquat 336) extractants in the HCl concentration range from 1 to 9 M.
Results
TBP and Cyanex 923 were successful in separating Au(III) from other metal ions when the HCl concentration was higher than 7 M. When the concentrations of Au(III) and Pd(II) changed from 0.1 to 5 g/L, TBP was able to selectively extract Au(III) from 7 M HCl solution, while Cyanex 923 was effective in separating Au(III) from 9 M HCl solution. However, Au(III) and Pd(II) were co‐extracted by Alamine 336 and Aliquat 336 from 1 M HCl solution. Thiourea or a mixture of thiourea and HCl solution effectively stripped Au(III) from the loaded organic phases of TBP, Cyanex 923, and amines.
Conclusions
Among the six kinds of the extractants employed in this work, TBP was recommended as an extractant for the selective extraction of Au(III) from the HCl solutions containing Cu(II), Ni(II) and Pd(II) on the basis of high separation degree.
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The extraction processes of gold, silver, and various metals from ores consume
of million metric tons of hydrogen cyanide produced worldwide annually. Therefore, developing efficient processes to treat the issuing effluents before releasing them into the environment is imperative. In this context, the present study aims to evaluate the effect of three factors: inter-electrodes distance, current density and electrolysis time on the cyanide removal efficiency by a combination between Electro-Coagulation process and Internal Loop Airlift Reactor. Employing an airlift reactor enables an effective dispersion of the coagulant without the need for additional stirring. The optimization of the process was conducted using Response Surface Methodology in conjunction with Box–Behnken Design. The statistical analysis results reveal that electrolysis time and current density have significant effects on reactor performance to reduce cyanide with a confidence level of and, respectively. The multiple regression analysis method demonstrates the model's overall predictability as the coefficient of determination was 98 % for the cyanide removal efficiency. The investigation inside the RSM 2 and 3-dimensional graphs allowed us to define the optimal domains of the variables to reduce cyanide. At a current density of 68 and an interelectrodes distance of during of electrolysis time, of cyanide removal is achieved. The knowledge obtained through this study using the airlift reactor operating in batch mode and the EC process for the treatment of cyanide effluent confirms EC's ability to successfully remove cyanide and might be useful for the transposition from batch to continuous mode.
Physical separation is the most widely used technology concerning waste printed circuit board (WPCB) recycling in practical terms. The dust generated from the process poses a significant environmental and human health risk. Amounts of heavy metals in dust present in each processing zone of the workshop showed differences. However, to date, few studies have reported this. The mean metal concentrations in workshop dust from different processing zones were investigated in this study and it was found that Zn, Pb, and Sn appeared in higher levels than other metals, followed by Mn > Cr > Ni > V > As > Cd. The enrichment factors (EFs) ranged from 1.15 to 207.4, and decreased in the order of Cu > Sn > Pb > Zn > Cd > Cr > Ni > V > As, which was exactly consistent with the geo-accumulation index values. The comparison of the EF values of workshop dust in and outside showed that the EFs in workshop dust were mostly smaller. Metals in the dust of the crushing zone (CrZ) showed significant and strong enrichment. The non-carcinogenic risk for different processing zones was all less than 1, which is recognized safety for people's health. The total carcinogenic risk from Cr, and Ni in all zones and As in the CrZ exposure was not negligible. The carcinogenic and non-carcinogenic risks in the CrZ were significantly higher than in the other zones. Masks to filter dust, a ventilation system, daily work hours reduction, and automation improvement was proposed for reducing workers' exposure to heavy metal.
In recent years, electronic waste (E-waste) has emerged as a severe risk to worldwide environmental security and human health because it contains many hazardous chemicals of heavy metals, plastics, flame retardants, etc. Notably, gold – one of the noblest metals – consisted of E-waste that can be reused not only to save natural resources but also to curtail the harsh effect on the environment of mineral exploitation and engineering new products in the future. Highly porous material platforms made up of either metal ions or organic ligand-linked clusters have gained attention owing to specific properties including high surface area, tunable pore sizes, and the ability to selectively adsorb gold ions. This review discusses the recent advances and progress of porous structure-based materials for the recent application in recycling gold from E-waste. Moreover, the current difficulties and future advancements of novel and unique porous structure-introduced platforms in recycling gold derived from E-waste are also discussed by exhibiting reusability, high selectivity, stability, and easiness in handling.
The physical and chemical properties of gold promote its application, such as in the high-tech, electronic products, and aerospace industries. The easily leachable ore is gradually depleted. Thus, it becomes necessary to extract gold from other resources such as refractory ore and electrical and electronic equipment. The normal method of leaching for gold is cyanide leaching, but it is very dangerous for both environment and operator. Non-cyanide leaching methods, including thiourea leaching, halide leaching, and sulfate leaching have been developed to substitute cyanide leaching. A variety of methods to enrich gold from leaching solutions are described in this paper, including solvent extraction, electrowinning, activated carbon adsorption, and ion exchange resins. Among those methods, ion exchange resins can adsorb gold with high adsorption efficiency and regenerate easily as well. This paper focuses on the research progress of the recovery of gold from non-cyanide leachates by ion exchange resins, summarizes the existing resin types and elution processes, points out the limitations in the application of current ion exchange resins, and discusses possible solutions.
The work presented here focused on the extraction of gold (Au), silver (Ag) and palladium (Pd) from
electronic waste using a solution of ammonium thiosulfate. Thiosulfate was used as a valid alternative
to cyanide for precious metal extractions, due to its non-toxicity and high selectivity. The interactions
between sodium thiosulfate, total ammonia/ammonium, precious metal concentrations and the particle
size of the waste printed circuit boards (WPCBs) were studied by the response surface methodology
(RSM) and the principal component analysis (PCA) to maximize precious metal mobilization. Au
extraction reached a high efficiency with a granulometry of less than 0.25 mm, but the consumption of
reagents was high. On the other hand, Ag extraction depended neither on thiosulfate/ammonia
concentration nor granulometry of WPCBs and it showed efficiency of 90% also with the biggest
particle size (0.50 < Ø < 1.00 mm). Pd extraction, similarly to Au, showed the best efficiency with the
smallest and the medium WPCB sizes, but required less reagents compared to Au. The results showed
that precious metal leaching is a complex process (mainly for Au, which requires more severe
conditions in order to achieve high extraction efficiencies) correlated with reagent concentrations,
precious metal concentrations and WPCB particle sizes. These results have great potentiality,
suggesting the possibility of a more selective recovery of precious metals based on the different
granulometry of the WPCBs. Furthermore, the high extraction efficiencies obtained for all the metals
bode well in the perspective of large-scale applications.
Current hydrometallurgical processing routes for copper recovery from waste printed circuit boards (PCBs) utilise strong mineral acids, which pose environmental hazards. Glycine has been proposed as an alternate lixiviant with a lower environmental impact. This study aimed to investigate the effectiveness of glycine as lixiviant for copper dissolution from waste PCBs. Bench scale laboratory leaching tests were performed to investigate the effect of key process variables such as temperature, oxidant type and lixiviant concentration on the rate, extent and selectivity of copper leaching. In the presence of oxygen as oxidant, the glycine concentration did not have a significant effect on the rate or extent of copper leaching in the range 1 M to 2 M. Increasing the temperature from 25 °C to 60 °C increased copper dissolution after 22 h from 29.6% to 81.2% when using a glycine concentration of 1 M. When air instead of oxygen was used as oxidant, the copper dissolution achieved with 1 M glycine after 22 h at 60 °C decreased by 43.9 percentage points to 37.3%, due to the lower concentration of dissolved oxygen in the system. Using hydrogen peroxide instead of oxygen as oxidant, did not improve the overall extent of copper leaching achieved. Leaching with 1 M glycine and oxygen as oxidant at 60 °C is proposed as the most feasible operating conditions within the ranges investigated, because these conditions yielded the highest copper dissolution (81.2%) with relatively low (1.3%) gold co-extraction.
Iron content in printed circuit board (PCB) dust consumes complexing agents, compromises recovery and contaminates leach solution during precious metals recovery from this waste stream. This study evaluated the prospects of iron removal from PCB dust via wet magnetic separation (WMS) versus sulphuric acid leaching. Chemical conditioning of the PCB pulp is required to make WMS effective in this case; this is a factor still new to magnetic separation technology. This was studied as a function of surface tension variation to optimize magnetic separation. For selective leaching route, the PCB dust was first treated with ammonia to selectively pre-remove copper, followed by sulphuric acid treatment of the residue for iron removal. After these investigations, the best performance from WMS gave a separation efficiency of 87%, whilst selective leaching efficiency for iron removal was 98%. Both routes compromise zinc and nickel into their ferrous streams, but the WMS route also compromised gold and silver. Though wet magnetic separation efficiency was greatly enhanced by pulp surfactant conditioning investigated herein, the selective leaching route is still more effective for iron removal from the PCB dust for this assorted material fraction, considering the risk of compromising gold loss to the ferrous fraction.
High doses of silver compounds in water have been found to be extremely toxic to the cells of plants and animals. Removal then reutilization of silver ions as antibacterial materials in one step from wastewater is an urgent but challenging issue from the views of environment and economy. In this research, we reported a planar benzothiazole Schiff base derivative BTS1 that can selectively precipitate silver ions from wastewater over other metal ions through chemical precipitation. The precipitation reaction showed promising activity in the pH range of 6 to11, realizing a high silver ions precipitation ratio of 95.4%, and low LOD of 0.059 mg/L. More importantly, the filtrated precipitate BTS1-Ag can be directly used as an antibacterial material. The test papers coated with BTS1-Ag exhibited antibacterial activity against both gram-positive and gram-negative bacteria. This research provides a promising strategy for simultaneous removal and conversion of silver ions from wastewater into functional materials.
Designing adsorption materials with high adsorption capacities and selectivities is highly desirable for precious metal recovery. Desorption performance is also particularly crucial for subsequent precious metal recovery and adsorbent regeneration. Herein, a metal‐organic framework (MOF) material (NH2‐UiO‐66) with an asymmetric electronic structure of the central zirconium oxygen cluster has an exceptional gold extraction capacity of 2.04 g/g under light irradiation. The selectivity of NH2‐UiO‐66 for gold ions is up to 98.8% in the presence of interfering ions. Interestingly, the gold ions adsorbed on the surface of NH2‐UiO‐66 spontaneously reduce in situ, undergo nucleation and growth and finally achieve the phase separation of high‐purity gold particles from NH2‐UiO‐66. The desorption and separation efficiency of gold particles from the adsorbent surface reaches 89%. Theoretical calculations indicate that ‐NH2 functions as a dual donor of electrons and protons, and the asymmetric structure of NH2‐UiO‐66 leads to energetically advantageous multinuclear gold capture and desorption. This adsorption material can greatly facilitate the recovery of gold from wastewater and can easily realize the recycling of the adsorbent.
Designing adsorption materials with high adsorption capacities and selectivities is highly desirable for precious metal recovery. Desorption performance is also particularly crucial for subsequent precious metal recovery and adsorbent regeneration. Herein, a metal-organic framework (MOF) material (NH2-UiO-66) with an asymmetric electronic structure of the central zirconium oxygen cluster has an exceptional gold extraction capacity of 2.04 g/g under light irradiation. The selectivity of NH2-UiO-66 for gold ions is up to 98.8% in the presence of interfering ions. Interestingly, the gold ions adsorbed on the surface of NH2-UiO-66 spontaneously reduce in situ, undergo nucleation and growth and finally achieve the phase separation of high-purity gold particles from NH2-UiO-66. The desorption and separation efficiency of gold particles from the adsorbent surface reaches 89%. Theoretical calculations indicate that -NH2 functions as a dual donor of electrons and protons, and the asymmetric structure of NH2-UiO-66 leads to energetically advantageous multinuclear gold capture and desorption. This adsorption material can greatly facilitate the recovery of gold from wastewater and can easily realize the recycling of the adsorbent.
This article is intent on the bioleaching of metals from e-waste using fungal communities. These communities are employed to retrieve valuable HMs present in the e-waste. The key components of e-waste cause an enormous level of environmental pollution. The toxic metals impose serious health concerns on the residing flora and fauna of the earth. The conventional bioleaching methods such as chemical bioleaching using solvents and different chemicals result in the generation of secondary waste. However, microbial bioleaching is an alternative to chemical bioleaching. But, the use of bacteria for bioleaching purposes has its limitations too in their reaction cycle and leaching efficiency. The literature on the use of fungal species for e-waste bioleaching purposes is very limited. Therefore, the present article provides an overview of the fungal bioleaching mechanism from e-waste.
The aim of the present study is to produce flexible, flame-retardant, water-resistant and biodegradable composite materials. The ultimate goal of this research is to develop simple processes for the production of bio-based materials capable of replacing non-degradable substrates in printed circuit board. Cellulose was chosen as a renewable resource, and dissolved in 1-ethyl-3-methylimidazolium acetate ionic liquid to prepare a cellulosic continuous film. Since flame retardancy is an important criterion for electronic device applications and cellulose is naturally flammable, we incorporated ammonium polyphosphate (APP) as a flame-retardant filler to increase the flame retardancy of the produced materials. The developed material achieved a UL-94 HB rating in the flammability test, while the cellulose sample without APP failed the test. Two hydrophobic agents, ethyl 2-cyanoacrylate and trichloro(octadecyl)silane were applied by a simple dip-coating technique to impart hydrophobicity to the cellulose-APP composites. Dynamic mechanical analysis indicated that the mechanical properties of the cellulosic materials were not significantly affected by the addition of APP or the hydrophobic agents. Moreover, the biodegradability of the cellulosic materials containing APP increased owing to the presence of the cellulase enzyme. The hydrophobic coating slightly decreased the biodegradability of cellulose-APP, but it was still higher than that of pure cellulose film.
Rational design of functional material interfaces with well-defined physico-chemical-driven forces is crucial for achieving highly efficient interfacial chemical reaction dynamics for resource recovery. Herein, via an interfacial structure engineering strategy, precious metal (PM) coordination-active pyridine groups have been successfully covalently integrated into ultrathin 1T-MoS2 (Py-MoS2). The constructed Py-MoS2 shows highly selective interfacial coordination bonding-assisted redox (ICBAR) functionality toward PM recycling. Py-MoS2 shows state-of-the-art high recovery selectivity toward Au3+ and Pd4+ within 13 metal cation mixture solutions. The related recycling capacity reaches up to 3343.00 and 2330.74 mg/g for Au3+ and Pd4+, respectively. More importantly, above 90% recovery efficiencies have been achieved in representative PMs containing electronic solid waste leachate, such as computer processing units (CPU) and spent catalysts. The ICBAR mechanism developed here paves the way for interface engineering of the well-documented functional materials toward highly efficient PM recovery.
Modular connectors are applied by computer users, and they can be metallic secondary sources containing metals such as gold and copper. Because gold is a micro-component, the solution obtained after the pin digestion contains a low concentration of gold(III) ions, and efficient and selective sorbent should be used for gold(III) ion recovery. The selective removal of small amounts of gold(III) from 0.001–6 M hydrochloric acid solutions using pure and solvent-impregnated macroporous polystyrene crosslinked with divinylbenzene sorbents (Purolite MN 202 and Cyanex 272) is presented. Gold(III) ions were recovered effectively from the chloride solution after the digestion of the modular connector RJ 45 (8P8C) using Purolite MN 202 after the impregnation process. The dependence of the recovery percentage (R%) of gold(III) on the contact time was determined. The highest value of gold(III) ion sorption capacity (259.45 mg·g−1) was obtained in 0.001 M HCl for Purolite MN202 after the Cyanex 272 impregnation. The results can be applied to gold recovery from e-waste. The presented method of gold recovery does not generate nitrogen oxides and does not require the use of cyanides.
The article presents the results of a study on metallurgical sludge reduction using electronic waste such as Printed Circuit Boards (PCBs). Two aspects were taken into account when selecting such a reducer, namely the environmental aspect and the technological aspect. The research was an attempt to use waste metal-bearing material of which the effective management causes many problems from an environmental point of view. In the technological aspect, the specific chemical composition of this waste was taken into account. Its gasification yields significant amounts of hydrocarbons, which are excellent reducing agents in such process. The separation of these compounds may additionally cause the mixing of the molten slag, which should result in faster separation of the formed metal droplets and the molten slag. In the case of the fragmented PCB (Printed Circuit Board) reducer used in this study, a significant degree of copper removal was achieved, as much as 92%. As the reduction-process time increased, the degree of copper removal also increased. For the 1 h process, the average value of copper removal was 60%, and for the 4.5 h process it was over 70%. The case was the same with the addition of reductant: as the amount of reductant added to the process increased, an increase in copper removal was observed. With the addition of 30 g of the reducing agent (per 65 g of slag), the degree of copper removal was over 90%.
With the new legislation for Waste Electrical and Electronic Equipment (WEEE) coming up in Europe a substantial increase of end-of-life electronic equipment to be treated will take place. In this context, often much attention is placed on logistical issues, dismantling and shredding/pre-processing of electronic-scrap, whereas the final, physical metals recovery step in a smelter is often just taken for granted. However, a state-of-the-art smelter and refinery process has a major impact on recycling efficiency, in terms of elements and value that are recovered as well as in terms of toxic control and overall environmental performance. Umicore has recently completed major investments at its Hoboken plant, where besides precious metals and copper a large variety of base and special metals are recovered. Equipped with state-of the art off-gas and waste water purification installations, the plant has been developed to the globally most advanced full-scale processor of various precious metals containing secondary materials such as automotive catalysts and electronic-scrap, generating optimum metal yields at increased productivity. To utilise this potential to its full extend for WEEE fractions like circuit boards or mobile phones, especially the interface between pre-processing (shredding/sorting) and smelting/refining is of importance. Here, a mutual optimization of sorting depth as well as of destination of the various fractions produced can lead to a substantial increase
in overall yields, especially for precious and special metals.
End-of-life printed circuit boards (PCB) and waste in electrical and electronics equipment (WEEE) in general, are a high value materials resource. Physical processing is accepted most environmentally friendly for value recovery from this polymetallic resource stream. Currently, commodity streams from physical processing are still largely a mix, making pyrometallurgical follow-up indispensable. While the pyrometallurgical route is still being tolerated, the smelting chemistry can be much more simplified if physical processing produces cleaner fractions at equivalent recoveries. Approaching this as an applied mineral processing problem, a kind of occurrence, reserve and representative compositions of the PCB stream is first presented like a characterization of a new type of ore. The trend in almost three decades of PCB physical processing is discussed, identifying issues for improving the value recovery. The -75μm fines sizes generated during comminution contributes an overall drop in grade and recovery of values when using the electrostatic separation, which is presently almost the industry standard for treating the submillimeter sizes. It may be necessary to reconsider wet processes to attend to fines problem, opposed to the general preference for dry operations. Composition determination is critical to recovery analysis, and a means of obtaining initial estimates which can aid analysis of such complex stream, as well as serve as pointer for effective treatment approach, is proposed. PCB is a complex resource stock; the beneficiation flowsheets still seem too simple.
The rapid growth in the use of electronic equipments, combined with early obsolescence has contributed enormously to the generation of large quantity of electronic (e) waste. One such e-waste, the mobile phone printed circuit boards (PCBs) contain various precious metals which can be extracted by different hydrometallurgical routes. The present work deals with the recovery of gold using ammonium thiosulfate as a leaching agent from waste mobile PCBs containing 0.021% Au, 0.1% Ag, 56.68% Cu, 1.61% Ca, 1.42% Al, 1.40% Sn, 0.24% Fe, 0.22% Zn, 0.01% Pd etc.. The cutting granules of 0.5-3.0 mm PCBs were used for leaching in a 500 mL glass beaker in open atmosphere. The effect of various parameters viz. ammonium thiosulfate concentration, copper sulfate concentration, pH and pulp density was studied. A leaching of 56.7% gold was obtained under the optimum condition of 0.1M ammonium thiosulfate, 40 mM copper sulfate, pH: 10-10.5, pulp density: 10 g/L at room temperature and stirring speed of 250 rpm in 8h duration. The maximum leaching of gold in the pH range 10-10.5 may be attributed to the higher stability of the ammonium thiosulfate. The decomposition of ammonium thiosulfate in the different pH ranges was chemically analysed by iodometric method. The ammonium thiosulfate contents in the leach liquors were in agreement with the quantity of gold leached in the respective pH ranges. In this process the copper sulfate worked as a catalyst. The experiment conducted with complete PCBs scrap exhibited a maximum leaching of 78.8% gold at the above optimised condition.
Rapid technological development induces increase of generation of used electric and electronic equipment waste, causing a serious threat to the environment. Waste printed circuit boards (WPCBs), as the main component of the waste, are significant source of base and precious metals, especially copper and gold. In recent years, most of the activities on the recovery of base and precious metals from waste PCBs are focused on hydrometallurgical techniques as more exact, predictable and easily controlled compared to conventional pyrometallurgical processes. In this research essential aspects of the hydrometallurgical processing of waste of electronic and electrical equipment (WEEE) using sulfuric acid and thiourea leaching are presented. Based on the developed flow-sheet, both economic feasibility and return on investment for obtained processing conditions were analyzed. Furthermore, according to this analysis, SuperPro Designer software was used to develop a preliminary techno-economical assessment of presented hydrometallurgical process, suggested for application in small mobile plant addressed to small and medium sized enterprises (SMEs). Following of this paper, the described process is techno-economically feasible for amount of gold exceeding the limit value of 500ppm. Payback time is expected in time period from up to 7 years, depending on two deferent amounts of input waste material, 50kg and 100kg of WEEE per batch.
Used electronic equipment became one of the fastest growing waste streams in the world. In the past two decades recycling of printed circuit boards (PCBs) has been based on pyrometallurgy, higly polluting recycling technology whic causes a variety of environmental problems. The most of the contemporary research activities on recovery of base and precious metals from waste PCBs are focused on hydrometallurgical techniques as more exact, predictable and easily controlled. In this paper mechanically pretrated PCBs are leached with nitric acid. Pouring density, percentage of magnetic fraction, particle size distribution, metal content and leachability are determined using optical microscopy, atomic absorption spectrometry (AAS), X-ray fluorescent spectrometry (XRF) and volumetric analysis. Three hydrometallurgical process options for recycling of copper and precious metals from waste PCBs are proposed and optimized: the use of selective leachants for recovery of high purity metals (fluoroboric acid, ammonia-ammonium salt solution), conventional leachants (sulphuric acid, chloride, cyanide) and eco-friendly leachants (formic acid, potassium persulphate). Results presented in this paper showed that size reduction process should include cutting instead of hammer shredding for obtaining suitable shape & granulation and that for further testing usage of particle size -3 +0.1mm is recommended. Also, Fe magnetic phase content could be reduced before hydro treatment.
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.
Au-Ag noble metal wastes represent a wide range of waste types and forms, with various accompanying metallic elements. The presented leaching strategy for Au-Ag contained in circuit boards (PCBs) aims at gaining gold and silver in the metallic form. Application of the proposed ammonium thiosulphate leaching process for the treatment of the above mentioned Au-Ag containing wastes represents a practical, economic and at the same time an ecological solution. The ammonium thiosulphate based leaching of gold and silver from PCBs waste, using crushing as a pretreatment, was investigated. It was possible to achieve 98 % gold and 93 % silver recovery within 48 hours of ammonium thiosulphate leaching. This type of leaching is a better leaching procedure for recovery of gold and silver from PCB waste than the classical toxic cyanide leaching. 84 % Cu, 82 % Fe, 77 % Al, 76 % Zn, 70 % Ni, 90 % Pd, 88 % Pb and 83 % Sn recovery of the accompanying metals was achieved, using sulphuric acid with hydrogen peroxide, sodium chloride and aqua regia. A four steps leaching process gave a very satisfactory yield and a more rapid kinetics for all observed metals solubilization than other technologies.
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.
Current research on leaching precious metals from waste printed circuit boards (PCBs) in the world is introduced. In the paper, hydrometallurgical processing techniques including cyanide leaching, thiourea leaching, thiosulfate leaching, and halide leaching of precious metals are addressed in detail. In order to develop an environmentally friendly technique for recovery of precious metals from Waste PCBs, a critical comparison of main leaching methods is analyzed based on three-scale analytic hierarchy process (AHP). The results suggest that thiourea leaching and iodide leaching make more possible to replace cyanide leaching.
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.
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 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.
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.
A highly effective process based on a hammer mill, a pneumatic column separator and an electrostatic separator was developed for recovering copper from waste printed circuit boards. The factors influencing the degree of copper liberation are discussed. Two physical separation methods were compared and discussed. Experimental results show that a well-controlled impact crusher can produce satisfactory copper liberation at a relatively coarse particle size. Around 90% copper recovery from waste printed circuit boards can be achieved using a combination of electrostatic separation and pneumatic separation.
This study was carried out to recover valuable metals from the printed circuit boards (PCBs) of waste computers. PCB samples were crushed to smaller than 1 mm by a shredder and initially separated into 30% conducting and 70% nonconducting materials by an electrostatic separator. The conducting materials, which contained the valuable metals, were then used as the feed material for magnetic separation, where it was found that 42% of the conducting materials were magnetic and 58% were nonmagnetic. Leaching of the nonmagnetic component using 2 M H2SO4 and 0.2 M H2O2 at 85 °C for 12 hr resulted in greater than 95% extraction of Cu, Fe, Zn, Ni, and Al. Au and Ag were extracted at 40 °C with a leaching solution of 0.2 M (NH4)2S2O3, 0.02 M CuSO4, and 0.4 M NH4OH, which resulted in recovery of more than 95% of the Au within 48 hr and 100% of the Ag within 24 hr. The residues were next reacted with a 2 M NaCl solution to leach out Pb, which took place within 2 hr at room temperature.
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.
Although copper is the principal metal in most electronic scrap, printed circuit boards in mobile phones also contain a significant amount of silver, gold and palladium. A bench-scale extraction study was carried out on the applicability of economically feasible hydrometallurgical processing routes to recover these precious metals. The starting material contained 27.37% copper, 0.52% silver, 0.06% gold and 0.04% palladium. In a first step, the following leaching solutions were applied: An oxidative sulfuric acid leach to dissolve copper and part of the silver; an oxidative chloride leach to dissolve palladium and copper; and cyanidation to recover the gold, silver, palladium and a small amount of the copper. A thiourea leach, as an alternative to cyanidation, was also investigated but did not give a sufficiently high yield. To recover the metals from each leaching solution, the following methods were evaluated: cementation, precipitation, liquid/solid ion exchange and adsorption on activated carbon. Precipitation with NaCl was preferred to recuperate silver from the sulfate medium; palladium was extracted from the chloride solution by cementation on aluminum; and gold, silver and palladium were recovered from the cyanide solution by adsorption on activated carbon. The optimized flowsheet permited the recovery of 93% of the silver, 95% of the gold and 99% of the palladium.
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.
Chemical replacements for cyanide have been investigated for decades; however cyanide remains the exclusive lixiviant of choice in the mining industry due to a combination of its availability, effectiveness, economics and ability to use it with acceptable risk to humans and the environment. About 90% of the significant gold producing operations worldwide currently utilize cyanide for gold and silver extraction. Despite the number of cyanide-related mining operations, there have been no documented accounts during the previous three decades of the death of humans due to cyanide as a direct consequence of major mining-related environmental incidents. Major mining-related environmental incidents have not been concentrated in any geographic location, may occur regardless of the size of the company and do not occur more frequently with a specific type of mining activity. The main aspects of cyanide management that should be addressed at mining operations include transportation of cyanide to site, process solution conveyance, worker health and safety training, water management and treatment, emergency response and preparedness, workplace and environmental monitoring, and community relations. If these aspects of cyanide management are integrated into an overall cyanide management plan, dramatic reductions in risk and potential incidents at mine sites will be realized.
This study refers to two chemical leaching systems for the base and precious metals extraction from waste printed circuit boards (WPCBs); sulfuric acid with hydrogen peroxide have been used for the first group of metals, meantime thiourea with the ferric ion in sulfuric acid medium were employed for the second one. The cementation process with zinc, copper and iron metal powders was attempted for solutions purification. The effects of hydrogen peroxide volume in rapport with sulfuric acid concentration and temperature were evaluated for oxidative leaching process. 2 M H2SO4 (98% w/v), 5% H2O2, 25 °C, 1/10 S/L ratio and 200 rpm were founded as optimal conditions for Cu extraction. Thiourea acid leaching process, performed on the solid filtrate obtained after three oxidative leaching steps, was carried out with 20 g/L of CS(NH2)2, 6 g/L of Fe3+, 0.5 M H2SO4, The cross-leaching method was applied by reusing of thiourea liquid suspension and immersing 5 g/L of this reagent for each other experiment material of leaching. This procedure has lead to the doubling and, respectively, tripling, of gold and silver concentrations into solution. These results reveal a very efficient, promising and environmental friendly method for WPCBs processing.
