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Bio hydrometallurgical recovery of metals from Fine Shredder Residues
Abstract
The leaching step of an integrated hydrometallurgical process for the selective recovery of metals from polymetallic concentrates has been investigated. This concentrate has been produced by physical treatment of Fine Shredder Residues derived from a shredding plant processing a mixed feed of metallic scraps, waste electric equipments and end-of-life vehicles. Bacterially assisted leaching experiments have been carried out using a copper-adapted consortium of mesophilic bacterial strains. The influence of various operating conditions such as stirring speed, temperature (25–50 °C), pulp solids density (5–20%) and initial iron concentration (0–15 g/L) has been studied. Temperature and stirring speed have proved to be the most influential parameter regarding copper dissolution kinetics, while pulp solids density and initial iron concentration have been found to have a subordinate importance. In optimum conditions, 95% extractions of zinc and copper were achieved within 48 h. Bacterial presence has been found beneficial in terms of catalysing copper dissolution.Highlights► Bio hydrometallurgy should be regarded as a way to recycle polymetallic wastes. ► Very high copper recoveries have been achieved. ► Strong influence of temperature and agitation speed. ► Significant upgrading of precious metals, tin and lead in the leach residue.
... This is reflected in the lack of systems-oriented approaches in the previous research concerning process development for recovering fines. Generally, these studies are confined to either the recovery of one or few targeted specific valuable materials such as base metals (Allen and Fisher, 2007;Furuyama and Bissombolo, 2005;Konetschnik and Schneeberger, 2009;Lewis et al., 2011;Mallampati et al., 2018;Singh et al., 2016) or utilisation as bulk materials in applications such as construction (Péra et al., 2004;Rossetti et al., 2006) and plastics moulding (Cain et al., 2000;Robson and Goodhead, 2003). A large share of the material is left for disposal in the case of the former, whereas the opportunity to recycle valuable resources is lost in the latter. ...
... Knowledge is also required on the over-time variation of the different constituents, which is an important design parameter ( As far as the reutilisation applications are concerned, the full resource recovery of fines should be the overall focus. However, previous fines studies are confined to either the recovery of specific materials (Lewis et al., 2011;Santini et al., 2012) or bulk materials that are down-cycled in applications such as ground construction (Péra et al., 2004;Rossetti et al., 2006). A large share of the material is left for disposal in the case of the former, whereas the opportunity to recycle valuable resources is lost in the latter. ...
... The assessed resource potential of fines in Article II is used as the basis for the selection of the targeted resources in the different process schemes. Previous fines research is mostly confined to the investigation of either the recovery of specific valuable materials such as metals (Allen and Fisher, 2007;Lewis et al., 2011) or the utilisation of the residue as a substitute bulk material in applications such as ground construction (Péra et al., 2004;Rossetti et al., 2006). Additionally, such research is only focused on the recovery of a single targeted resource, whereas integrated processes for the recovery of several resources while maximising the recovery of a targeted resource, which is the approach in Article III, have been overlooked. ...
In the context of the circular economy in the European region, the role of the recycling
industry has become ever important. Shredder fines (or fines) is a heterogeneous residue
of the shredding industry, which presents a disposal problem and incurs handling costs
to the shredding industry. More importantly, its current handling reduces the resources
efficiency of our society. This thesis aims to contribute systems-oriented knowledge to
facilitate the valorisation of shredder fines in the Swedish context. In doing so, it
contributes to two complementary knowledge areas: Knowledge Area 1 portrays the
current picture concerning fines management, whereas Knowledge Area 2 showcases a
potential approach to initiate process development for fines valorisation.
The findings of Knowledge Area 1 show that the studied shredding company is more
inclined towards continuing the current disposal-oriented management of fines due to
incentives for utilising fines as landfill cover materials as well as disincentives for
valorising fines, created by various policy, market, and organisational factors. On the
other hand, there is a significant need to improve the market prospects for recycling,
especially when it comes to using fines as a secondary aggregate in the construction
sector. The market is chiefly characterised by processes and underlying institutions that
sustain dominant and systematic primary aggregates utilisation, whereas secondary
aggregates utilisation is ad-hoc and only driven by situational benefits to different supply
chain actors due to different individual reasons.
The findings of Knowledge Area 2 show that process development for fines valorisation
has several technical and environmental challenges. The resource potential assessment
of fines shows that the initial technical feasibility of fines valorisation is considerable.
However, the realisation of this potential necessitates integrated and like costly
processes to upgrade the material quality recover resources. The life cycle assessment of
prospective fines valorisation shows that fines valorisation is generally more
environmentally promising compared to landfill-related disposal; still, different resource
recovery strategies would create different levels of environmental impacts and present
different needs for improvements.
Generally, this thesis demonstrates the use of portraying the current picture concerning
the present management and market prospects of a given heterogeneous industrial
residue to elicit the challenges of and necessary measures for initiating changed practices. It also showcases a potential approach in terms of assessing the resource potential, formulating alternative process schemes for material upgrading and resource recovery, and assessing their environmental potential to guide sustainable investment decisions for and governance of the valorisation of a given heterogeneous industrial residue. Overall, this thesis demonstrates how systems-oriented interdisciplinary knowledge could be generated to facilitate the valorisation of heterogeneous industrial residues towards a circular economy.
... It should be stressed that there is no defined protocol for the bacterial adaptation process, which hinders the debate of information and the comparison of data, given that the bio hydrometallurgical studies report the use of different microorganisms, methods, pulp densities and substrates [14][15][16][17][18][19][20] for example, Chiang et al. [16], used fungi to extract metals from a different substrate, while Faramarzi et al. [19] used a cyanogenic bacteria to mobilize gold. The use of different microorganisms may imply different morphological and biochemical modifications, as well as the different methods adopted [20][21][22][23]. ...
... This method did not evaluate the joint influence of the concentration of metals with the boards' other components, such as glass fiber and resin. Since there is no defined method, there are also no restrictions in relation to exploring the capacity of some microorganisms to change the substrate, one example of this is that Haghshenas et al. [3] studied bacterial adaptation using different concentrations of ores, while Lewis et al. [23] did this by means of gradually increasing vehicle scrap. ...
... Precipitation in hydrometallurgical processing could be promoted by saturation of dissolved metals in solution (Park & Fray, 2009) and the presence of precipitating agents such as hydroxides, sulfides, sulfate and oxalates and exopolymeric substances (EPS) secreted by microbes (Li & Yu, 2014). Precipitation in bioleaching of ewastes that have been reported have focused principally in hydrolysed ferric precipitates (Lewis et al., 2011;Wang et al., 2009;Xiang et al., 2010;Zhu et al., 2011). Precipitation in lithotrophic leaching of e-wastes appears to be predominated by the formation of hydrolysed iron precipitates (Lewis et al., 2011;Wang et al., 2009;Xiang et al., 2010;Zhu et al., 2011). ...
... Precipitation in bioleaching of ewastes that have been reported have focused principally in hydrolysed ferric precipitates (Lewis et al., 2011;Wang et al., 2009;Xiang et al., 2010;Zhu et al., 2011). Precipitation in lithotrophic leaching of e-wastes appears to be predominated by the formation of hydrolysed iron precipitates (Lewis et al., 2011;Wang et al., 2009;Xiang et al., 2010;Zhu et al., 2011). This is largely because ferric ions are present in substantial quantities in bacterial leaching because it is present in the waste and as it is often used as Fe 2+ /Fe 3+ redox couple to support the biooxidation and dissolution of copper. ...
The aim of this study was to examine the role of epoxy in the bioleaching of copper from electronic wastes. Metal dissolution tests were performed by chemical leaching using fungi generated citric acid mimicking the spent medium based leaching. Copper dissolution from electronic waste was found to be inhibited by the decomposition of its epoxy component during the leaching process. Citric acid attack and partial depolymerisation of epoxy resulted in amine group cleavage and release raising the solution pH from an initial of 1.8 up to 6.1 and with resulting epoxy surface modification promoted the removal of dissolved copper by adsorption and precipitation as di-copper citrate. Independent measurement of epoxy induced copper loss was used to reconcile the true copper recovery from citric acid at pH from 1.8-3.0, temperatures from
30-90°C, pulp densities of 5-100 g/L and 24 hours. Copper loss of up to 30%
of the total copper in the waste or 83% of the dissolved metal was observed.
Inhibition of copper dissolution with increasing waste pulp density was largely
attributed to the epoxy induced copper removal. In addition these secondary
reactions masked the self catalysis of copper dissolution by Cu
2+
. Minimal
effect of epoxy induced copper removal and optimal copper recoveries were
observed at the lowest pH of 1.8, lowest pulp density 5 g/L and highest
temperature 90°C. These results demonstrated the importance of overcoming
the effects of epoxy depolymerisation and the potential merit of applying spent
medium leaching in overcoming these effects and in optimising the recovery of
copper from e-wastes.
... The process involving Roast-Leach-Electrowin (RLE) has been used to treat this kind of ores (Peters, 1992). With the depletion of zinc sulphide ores, zinc recovery from other type of ores and secondary resources attracts much attention (Rashchi et al., 2005;Gouvea and Morais, 2007;Vahidi et al., 2009;Lewis et al., 2011). However the process of RLE is not suitable for the treatment of zinc ores in oxide, silicate and carbonate-based forms (Cole and Sole, 2003;Qin et al., 2007) and also for the secondary zinc resources (Vahidi et al., 2009;Gouvea and Morai, 2010;Lewis et al., 2011). ...
... With the depletion of zinc sulphide ores, zinc recovery from other type of ores and secondary resources attracts much attention (Rashchi et al., 2005;Gouvea and Morais, 2007;Vahidi et al., 2009;Lewis et al., 2011). However the process of RLE is not suitable for the treatment of zinc ores in oxide, silicate and carbonate-based forms (Cole and Sole, 2003;Qin et al., 2007) and also for the secondary zinc resources (Vahidi et al., 2009;Gouvea and Morai, 2010;Lewis et al., 2011). A hydrometallurgical process consisting of leach-solvent extraction-electrowinning was developed and used in Skorpion zinc process, Namibia (Cole and Sole, 2003;Musadaidzwa and Tshiningayamwe, 2009). ...
Zinc recovery by solvent extraction with D2EHPA from its leach solutions has been successfully commercialised. As Fe(III) is strongly extracted by D2EHPA, 6 M HCl is employed in the process to remove it in the organic bleed solution. The use of HCl complicates the process because extra process must be conducted to regenerate the HCl. In order to possibly avoid the use of HCl, zinc extraction and separation from impurities using Ionquest 801 and its mixtures with D2EHPA were studied. Zinc extraction with Ionquest 801 is lower than that with D2EHPA. However, the stripping of Fe(III) from the Ionquest 801 system using 4 M H2SO4 is more effective than that from the D2EHPA system with 6 M HCl. Therefore the use of HCl could be avoided leading to a simplified process. The application of the mixture of Ionquest 801 and D2EHPA for zinc recovery from its leach solution was also discussed.
... Thermoplasma acidophilum) would offer greater bioleaching potential, although to gain high metal bioleaching efficiencies (about 70%-80% for Ni, Al and Zn, 90% for Cu, with 150 g/L pulp density; Ilyas et al. 2014) a preadaptation step for the microorganisms involved is needed. Mesophilic Fe/S-oxidising strains have been tested at 50°C and an increase in the Cu solubilisation rate was observed, but it was confirmed to be due to abiotic processes (Lewis et al. 2011). Ilyas and co-authors have also demonstrated that sources of biogenic S 0 from desulphurisation refinery plants can be a suitable growth substrate (greater sulphur oxidation in a shorter time period). ...
... 150 g/L of powdered PCBs (pre-treated by acid leaching to stabilise pH and reduce toxic effects) can be processed in a 2.5 L stirred-tank reactor (STR) with biogenic S 0 as a sole energy source for bacteria, while 10 kg can be treated by column bioleaching (about 1.2 L volume) in the presence of both Fe(II) and S 0 powder, after removing non-metallic components by a high-density saturated solution of NaCl (Ilyas et al. 2010;Ilyas et al. 2014). The recovery of more than 95% of Cu and Zn is possible in 50 h with 100 g/L pulp density and in the presence of Fe(II) 3 g/L as the sole energy source, by a two-step bioleaching strategy in a batch-mode reactor with ceramic rings as biofilm carriers (Lewis et al. 2011): in these conditions, mesophilic bacteria have been demonstrated to favour the solubilisation of Cu (Zn solubilisation was probably abiotic) and regenerate ferric ions. ...
The production of end-of-life equipment, known as waste of electrical and electronic equipment (WEEE) or e-waste, is a direct consequence of the modern revolution of the electronic industry and of the constant evolution of technology. According to the United Nations Environment Programme (UNEP), a dramatic increase in the illegal import of e-waste, 200%-400% in South Africa and 500% in India, can be estimated for the period between 2017 and 2020 (Schluep et al. 2009). Organic and inorganic components in WEEE can cause environmental problems if not properly managed. Today, in the United States and Europe, the main WEEE management strategies are incinerators and landfills and these can represent a serious threat to the environment and human health, due to contaminant leaching in soils and ground waters, and to a release of potentially hazardous by-products in the atmosphere (Robinson 2009; Tsydenova and Bengtsson 2011). On the other hand, base (e.g. Cu) and precious metals (e.g. Au, Ag and Pd) in WEEE could be employed as raw materials, making WEEE an attractive secondary resource of valuable elements (Oguchi 2013). In the last decade, the scientific community and industrial research have made a significant effort in developing techniques for the recovery of metal components from WEEE, especially by pyrometallurgical and hydrometallurgical approaches. Nevertheless, such techniques may be extremely polluting and not environmentally sustainable (Korte et al. 2000; Mecucci and Scott 2002; Cui and Zhang 2008; Tsydenova and Bengtsson 2011). Biohydrometallurgical strategies, based mainly on the ability of microorganisms to produce leaching agents, are gaining increasing prominence in this field. For instance, the technique known in mining activities as bioleaching (i.e. biological leaching) is considered a novel approach for metal mobilisation from various types of solids (Beolchini et al. 2012). The main advantages of biohydrometallurgical methods would be low operating costs (due to a low energy input), reduced environmental impact and a general minimisation of the end product (Ehrlich 2001; C. L. Brierley 2010).
... Bioleaching is a bio-hydrometallurgical process that utilizes microorganisms to leach out metals. This process is simple because of lower operating costs and energy consumption, easier management, operating conditions at atmospheric pressure and room temperature, ecofriendliness.Bacteria such as Thiobacillus ferrooxidans, Thiobacillus thiooxidans, and Leptospirillum ferrooxidans were used to recover Cu from ASR (Lewis et al., 2011). The only disadvantage of this process is the processing time of 50 h. ...
Following treatment in a shredding facility and metals removal, Automotive Shredder Residue (ASR) is generated as a waste. This paper reviewed the state-of-the-art of research and development of thermochemical conversion and metal recovery from ASR. The characteristics of ASR are discussed in terms of compositions, and then the emphasis is given to different thermochemical conversion methods - incineration, pyrolysis, and gasification. In addition, the characterization of products obtained from these processes is then critically reviewed. The latter part deals with metal recovery focussed on conventional metallurgical processes - pyrometallurgy and hydrometallurgy of ASR. The limitations of the conventional metal recovery process are discussed, followed by recommendations for technology development on energy and metal recovery options from ASR, in particular solvometallurgy, an emerging trend for efficient metal recovery. A clear conclusion is that ASR is a valuable feedstock for energy production and metal recovery as it comprises mainly plastics and metals.
... The current copper output fraction from automobile shredders is used for copper production and residues of automobile shredders have been considered for the recovery of geochemical scarce elements (e. g. Andersson, Söderman and Sandén 2019; Gunaratne et al. 2020a;Jordao, Sousa and Cavalho 2016;Kodier, Williams and Dallison 2018;Lewis et al. 2011;Restrepo et al. 2017;Singh and Lee 2016). There are major geographical differences in the amount of Cu that is recovered after shredding. ...
Copper ores, end-of-life electric and electronic equipment and car electronics can contain, besides Cu, substantial amounts of geochemically scarce companion elements. Geochemically scarce elements have an upper crustal abundance of <0.025 (weight)%. In view of resource conservation and reduction of pollution there is a case for near-zero waste processing. Improving the generation of ore concentrates and use of kinetic and thermodynamic data regarding smelting and converting can increase the production of geochemically scarce elements in the pyrometallurgical processing of copper ores. Reprocessing of copper ore processing residues can serve the generation of geochemically scare elements and the clean-up of matrix materials. Modularization of products, closed-loop take-back, including deposit-refund, systems for end-of -life products, and changes in the pre-processing thereof can be conducive to improved recovery of geochemically scarce elements from end-of-life electric and electronic equipment and car electronics. A comparatively large variety of geochemically scarce elements originating in end-of-life products can be recovered when in smelting lead and copper serve as collectors. Substantial research and development work is needed to optimize the co-production of geochemically scarce elements by hydrotechnology from copper ores and (mined) end-of-life products and to assess the potential of solvochemistry. There is technical scope for significant progress in the direction of near-zero waste processing in processing copper ores and (mined) end-of-life products, but for the realization of near-zero waste processing there are hurdles to be overcome related to marketability of outputs, safe handling of hazardous elements and company behavior. Also, the techno-economic potential of hydrotechnology and solvochemistry in extracting copper ores, copper ore processing residues and end-of-life products is uncertain. In view thereof, the feasibility near-zero waste production of copper and its geochemically scarce companion elements from copper ores and end-of-life electric and electronic equipment and car electronics is uncertain.
... The availability of oxygen is fundamental, given that the bacteria A. ferrooxidans is aerobic and consumes the O 2 in the oxidization of the ferrous ion [21,22]. According to Lewis et al. [38], the temperature and the shaking speed have proven to be the factors that have the greatest impact on the kinetics of the copper's dissolution. ...
... Material characterisation studies have assessed potential resources such as metals, plastics, and minerals, and contaminants such as heavy metals and organic pollutants [15][16][17][18]. The process development studies have investigated either the retrieval of specific resources contained in the material [19,20] or the reutilisation of fines as a substitute bulk material [21,22], for instance, in ground construction applications such as road base layer, noise barriers, parking lots, and play areas. While these two types of studies provide valuable contributions regarding assessing the resource potential of fines and developing upgrading (i.e., addressing material constraints) and resource recovery processes, they also carry substantial knowledge limitations [9]. ...
The recycling-industry residue called shredder fines (fines) presents a disposal problem, incurs handling costs, and reduces resource efficiency in general. This study aims to identify the challenges of facilitating fines valorisation in the Swedish context. Hence, the shredding company perspective of the underlying factors that sustain the current practice of fines management is established by studying the case of a specific shredding company using semi-structured interviews. Utilisation in landfill covering offers the company a secure outlet and a legislatively-compliant low-cost disposal option for fines. Additionally, lack of specific regulatory standards, unfavourable regulation of waste reutilisation, and lack of market demand for secondary raw materials (SRMs) create disincentives to develop valorisation options. Also, the lack of corporate-level focus on the issue has resulted in a lack of organising for and capacities to improve the handling of the material. Initiating fines valorisation needs to challenge these prevailing circumstances and thus necessitates governmental interventions. Simultaneously, favourable conditions for SRM utilisation are needed; that is, established outlets for fines-derived SRMs and clear regulatory and market playing rules that reduce uncertainty and investment risk of developing tailored processes for upgrading and resource recovery need to be available.
... Bryan et al., 2015;Guezennec et al., 2015) and other forms of post-consumer, metallic waste 308(Lewis et al., 2011). The use of biohydrometallurgy to generate the lixiviant from mine wastes is 309 preferable to chemical oxidation options as it can be done at standard temperature and pressure, 310 does not require expensive or environmentally damaging reagents and traditionally offers lower 311 12 operating expenditures as a result. ...
Most coal mines produce waste which has the potential to generate acid mine drainage (AMD). If not properly managed, this can cause environmental damage through contamination of ground and surface waters and soils for hundreds of years. At the same time, the pace of technological development means that most electrical and electronic equipment becomes obsolete within a matter of years, resulting in the generation of vast quantities of electronic waste (e-waste). Where this cannot be recycled, it must be discarded. The CEReS concept is a co-processing approach for both waste streams to produce metals and other valuable products, and to reduce or eliminate the their environmental impact. This brings together two waste streams from opposite ends of the supply chain; turning each into a novel resource in a single, coherent ‘grave-to-cradle’ process. This industrial ecology approach is key to supporting a circular economy whilst securing the sustainable supply of critical raw materials. The project successfully elaborated a novel co-processing flow-sheet comprising: (i) the accelerated bioweathering of AMD-generating coal production wastes to generate a biolixiviant; (ii) the pyrolysis and catalytic cracking of low-grade PCBs to produce hydrocarbon fuel, a halogen brine and a Cu-rich char; (iii) the leaching of base metals from the char using the biolixiviant; (iv) the reuse of stabilised coal wastes; and (v) the full or partial (as enriched substrates) recovery of valuable metals. These process units were demonstrated individually at lab-pilot scale. The data were then used to validate the entire flow-sheet in an integrated process simulator and determine the economic balance. Finally, an LCA approach was used to demonstrate the environmental benefits of the CEReS process over the status quo.
... The composition of the fractions strongly depends on the shredded material, usually it contains > 10% metals (iron, copper and aluminum) (Evangelopoulos et al., 2018;LUA NRW, 2003;Ni and Chen, 2015). In one specific study, different microorganisms were investigated for the recovery of metals from a milled shredder sample (Lewis et al., 2011). Temperature and stirring rate were identified as main influencing parameters. ...
Competitive sustainable production in industry demands new and better biocatalysts, optimized bioprocesses and cost-effective product recovery. Our review sheds light on the progress made for the individual steps towards these goals, starting with the discovery of new enzymes and their corresponding genes. The enzymes are subsequently engineered to improve their performance, combined in reaction cascades to expand the reaction scope and integrated in whole cells to provide an optimal environment for the bioconversion. Strain engineering using synthetic biology methods tunes the host for production, reaction design optimizes the reaction conditions and downstream processing ensures the efficient recovery of commercially viable products. Selected examples illustrate how modified enzymes can revolutionize future-oriented applications ranging from the bioproduction of bulk-, specialty- and fine chemicals, active pharmaceutical ingredients and carbohydrates, over the conversion of the greenhouse-gas CO2 into valuable products and biocontrol in agriculture, to recycling of synthetic polymers and recovery of precious metals.
... Sularda bulunan metallerin arıtılarak izin verilebilir sınır değerler seviyesine düşürülmesi çevre sağlığı bakımından büyük önem taşımaktadır [3]. Metallerin elde edilmesinde kullanılan proseslerin çevre kirliliğine neden olması nedeniyle son yıllarda Biyoliç (Biyohidrometalurjik) yöntemi kullanılmaya başlanmıştır [5,6]. Biyo-hidrometalurjik proseslerin daha az enerjiye ihtiyaç duyması, ayrılma seviyesinin iyi olması, geri kazanılan ürünlerin saflık derecesi yüksek olması gibi avantajları bulunmaktadır [7]. ...
... exploitation of both the recovery of valuable resources and minimising the disposable quantity via utilisation as bulk-material in certain applications) shredder fines has often been overlooked. For instance, there are several studies focusing only on the recovery of metals such as copper and zinc from fines (Lewis et al., 2011;Reuter et al., 1999;Singh et al., 2017Singh et al., , 2016aSingh and Lee, 2016), while others instead target the bulk utilisation of fines as a substitute material in applications such as construction applications and plastics moulding (Cain et al., 2000;Péra et al., 2004;Robson and Goodhead, 2003;Rossetti et al., 2006). In regard to the former, once metals are recovered there will still be a large quantity of fines left un-valorised. ...
The lack of process development based on a comprehensive understanding of the material characteristics and the marketability of recoverables is the primary reason why the valorisation of shredder fines has not been realised in practice. In response, a systematic approach was undertaken consisting of 1) strategic sampling and material
characterisation, 2) establishing gate and regulatory requirements of potential valorisation applications, and 3) initial feasibility assessment of the selected applications, to guide future research.
The material was sampled over ten weeks in order to obtain both average values and variations of the physical and chemical composition. Thus weekly, primary fractions and sieved fractions ZA (7.10–5.00 mm), ZB (5.00–3.35 mm), ZC (3.35–2.00 mm), ZD (2.00–0.25 mm), and ZE (0.25–0.063 mm) were prepared, and analysed, and benchmarked against the requirements pertaining to five potential applications. The mercury and aluminium concentrations are the biggest challenge in copper smelting and only ZA and ZB show significant potential. Energy recovery is limited to ZA, ZB, and ZC, provided the chlorine and metals concentrations are decreased. Regarding the recovery as bulk-material in construction, the reduction of the metal content would likely be a pre-requisite.
The utilisation of fines in the individual applications would either leave a significant amount of fines unvalorised or overlook the recovery of valuable resources. The upgrading of the material to suit the different applications would also require addressing multiple material constraints simultaneously. Therefore, realising the full resource potential of shredder fines would require the integration of different upgrading and recovery processes.
... Howev-er, the research maturity and knowledge about the process attributes are substantially higher in the bottom ash literature. The different process attributes investigated in the fines literature are pre-treatment, recovery efficiencies, the Smelting (2) Base metals (2) Pre-treatment requirements (1) Operating parameters (1) Recovery efficiency (1) Output characteristics (1) Solvent extraction (4) Base metals (4) Heavy metals (3) Operating parameters (4) Recovery efficiency (4) Output characteristics (3) Pyrolysis (1) Fuels (1) Operating parameters (1) Recovery efficiency (1) Utilisation as substitute raw material (9) Construction applications b (5) Shredder fines (5) Pre-treatment requirements (2) Extent of utilisation (4) Operating parameters (2) Output characteristics (4) Economic feasibility (1) Italy Studies focusing on the recovery of specific materials from fines: (Jody et al., 1996), (Reuter et al., 1999), (Izumikawa, 1999), (Furuyama and Bissombolo, 2005), (Bonifazi and Serranti, 2006), (Allen and Fisher, 2007), (Allen and Kolb, 2009), (Konetschnik and Schneeberger, 2009), (Lewis et al., 2011), (Santini et al., 2012), (Gent et al., 2015), (Singh et al., 2017), (Huang et al., 2017), and (Mallampati et al., 2018). Studies focusing on the utilisation of fines as a substitute raw material: (Jody et al., 1996), (Cain et al., 2000), (Robson and Goodhead, 2003), (Péra et al., 2004), (Rossetti et al., 2006), (Konetschnik and Schneeberger, 2009), and . ...
Millions of tonnes of shredder fines are generated and disposed of globally, despite compelling reasons for its recovery. The absence of a review of previous literature, however, makes it difficult to understand the underlying reasons for this. Thus, this study attempts to investigate and assess what, to what extent, and in what ways shredder fines have been addressed in previous research. In doing so, guidelines are drawn for future research to facilitate the valorisation (upgrading and recovery) of shredder fines.
Previous research concerning shredder fines was identified with respect to three main research topics. The material characterisation studies are predominantly confined to the occurrence of metals due to their recovery and contamination potential. The process development studies have often undertaken narrowly conceived objectives of addressing one resource opportunity or contamination problem at a time. Consequently, the full recovery (the retrieval of valuable resources and the bulk-utilisation as substitute material) potential of shredder fines has been largely overlooked. The main limitation of policy and regulation studies is the absence of in-depth knowledge on the implications of governmental waste- and resource-policies (macro-level) on actors’ incentives and capacities (micro-level) for
fines valorisation, which is necessary to understand the marketability of fines-derived resources.
Undertaking a systems perspective is the key to recognising not only the different aspects within the individual research topics but also the inter-relations between them. It also facilitates the internalisation of the inter-relations into topical research.
... However, they achieved a lower recovery rate, 13.79% of copper, 2.55% of silver, and 0.44% of gold of untreated SIM waste, while about 72% of copper mobilized from SIM e-waste, by using acidic pretreatment of SIM e-waste in two-step bioleaching (Sheel and Pant, 2018;Xia et al., 2018aXia et al., , 2018b. So, these are the perfect examples that indicate that a biohydrometallurgical method is one of the promising biotechnological approaches for metal extraction from e-waste Lewis et al., 2011). In this context, in recent years, a number of scientific studies define the potential of bioleaching methods for the extraction of valuable metals from e-waste (Arshadi and Mousavi, 2015;Arshadi et al., 2016;Chi et al., 2011;Xin et al., 2012;Heydarian et al., 2018;Horeh et al., 2018;Kim et al., 2016;Niu et al., 2015;Sun et al., 2016). ...
The rapid e-waste volume is generating globally. At the same time, different recycling technologies, mainly the mechanical and chemical methods well studied, while the biological method is the most promising approach. Therefore, this article provides a comprehensive information about extracting valuable metals from e-waste. In addition, this article outlines the process and key opportunity for extraction of metals, identifies some of the most critical challenges for e-waste environmentally sound management practices, and opinions on possible solutions for exiting challenges, and emphasis on importance of advanced recycling technologies that can be utilized, in order to minimize the environmental impact causes due to improper recycling of e-waste.
... Despite this, Kumada et al. [11] correctly predicted that the machining rate could be controlled by adjusting the Fe 3+ concentration in the liquid medium. Moreover, although the microbial consortium has proven to be very efficient at regenerating Fe 3+ , the chemical mechanism of copper dissolution is too fast when compared with the bio-oxidation of Fe 2+ [12,13]. Given this assumption, a rest period to allow the complete bio-regeneration of Fe 3+ after each biomachining testing time was included in our previous work (4 or 8 h of rest after 1 or 4 h of biomachining, respectively) using the autotrophic, acidophilic and mesophilic bacterium Acidithiobacillus ferrooxidans [14]. ...
The machining of copper contained in oxygen-free copper workpieces by extremophile bacteria has been studied. The effect of the main parameters affecting the continuity of the process and which decrease the removal rate were analysed during the incubation, biomachining and regeneration phases. The presence of copper affected the bacterial culture, while the enhancement of process performance due to the simultaneous presence of A. ferrooxidans and L. ferrooxidans was relatively limited. pH was maintained below 1.80 to avoid Fe3+ losses in the form of jarosite precipitates. Measurement of the redox potential allowed a rapid monitoring of the process status.
... A washing procedure of ASR fly ash using HCl leaching solution, investigated by Shibayama et al. (2006), resulted in a high recovery of Cu and Zn (97%). Lewis et al. (2011) obtained a similar recovery rate (95%) using an integrated hydrometallurgical process for the selective recovery of metals, specifically Cu and Zn. ...
On the basis of statistical data, approximately 6.5milliontons of ELVs were produced in Europe in 2011. ELVs are processed according to a treatment scheme comprising three main phases: depollution, dismantling and shredding. The ferrous fraction represents about 70-75% of the total shredded output, while nonferrous metals represent about 5%. The remaining 20-25% is referred to as automotive shredder residue (ASR). ASR is largely landfilled due to its heterogeneous and complex matrix. With a start date of January 1st 2015, the European Directive 2000/53/EC establishes the reuse and recovery of a minimum of 95% ELV total weight. To reach these targets various post-shredder technologies have been developed with the aim of improving recovery of materials and energy from ASR. In order to evaluate the environmental impacts of different management options of ELVs, the life cycle assessment (LCA) methodology has been applied taking into account the potential implication of sustainable design of vehicles and treatment of residues after shredding of ELVs. Findings obtained reveal that a combination of recycling and energy recovery is required to achieve European targets, with landfilling being viewed as the least preferred option. The aim of this work is to provide a general overview of the recent development of management of ELVs and treatment of ASR with a view to minimizing the amount of residues disposed of in landfill.
Copyright © 2015 Elsevier Ltd. All rights reserved.
... A disponibilidade de oxigênio é fundamental, visto que a bactéria Acidithiobacillus ferrooxidans é aeróbica e consome o O 2 na oxidação do íon ferroso. (25) Segundo Lewis et al., (26) a temperatura e a velocidade de agitação têm provado serem os parâmetros que mais influenciam a cinética de dissolução do cobre. ...
... The rate of bioleaching of copper from e-waste is apparently controlled intimately by the availability (i.e. initial concentration) and the rate of biooxidation of ferrous iron (i.e. the rate of generation of ferric iron) in the bioleaching environment. Many studies have already demonstrated the beneficial effect of external addition of Fe(II)/Fe(III) on the rate and extent of copper extraction (Choi et al., 2004;Lewis et al., 2011;Xiang et al., 2010;Yang et al., 2009;Zhu et al., 2011). Others have reported remarkably slow rate of metal extraction apparently due to the limited availability of soluble iron at the onset of bioleaching and/or low iron content of the e-waste sample used (Brandl et al., 2001;Ilyas et al., 2007Ilyas et al., , 2010Willscher et al., 2007). ...
Given the current highest demand in history for raw materials, there is a growing demand for the recovery of key metals from secondary sources, in order to prevent metal depletion and to reduce the risk of toxic discharges into the environment. This paper focuses on the current nature-based solutions (i.e., biomining and bioleaching) applied to resource recovery (metals) from solid matrices. Biomining exploits the potential of microorganisms to facilitate the extraction and recovery of metals from a wide range of waste materials as an interesting alternative, replacing primary raw materials with secondary material resources (thus improving metal recycling rates in the context of the circular economy). Special attention was paid to the analysis of metal biomining from a process sustainability perspective. In this regard, several supporting tools (e.g., life cycle assessment, LCA), developed to assist decision-makers in the complex process of assessing and scaling-up remediation projects (including biomining), were discussed. The application of LCA in biomining is still evolving, and requires comprehensive case studies to improve the methodological approach. This review outlines the fact that few studies have focused on demonstrating the environmental performance of the biomining process. Also, further studies should be performed to promote the commercial opportunities of biomining, which can be used to recover and recycle metals from solid matrices and for site remediation. Despite some important disadvantages (poor process kinetics; metal toxicity), biomining is considered to be a cleaner approach than conventional mining processes. However, implementing it on a large scale requires improvements in regulatory issues and public acceptance.
In concomitance with the growing developments around the circular economy concept
in the region, the resource recovery and recycling of industrial production residues is
increasingly being envisaged in the European Union and its member states. The role of
the recycling industry has become ever important in this context. The shredding
industry is based on shredding discarded products such as end-of-life vehicles, and
municipal white goods, and subsequent retrieval of (primarily) metals. Shredder fines
(or fines) is a heterogeneous fine-granular production residue of this industry, which is
currently disposed of. Shredder fines presents, and will continue to do so in the
foreseeable future, several challenges that need to be addressed. It creates a disposal
problem given the shrinking landfill availability and incurs handling costs to the
shredding industry. Furthermore, it reduces our resources efficiency in general.
This thesis aims to contribute knowledge on the challenges of facilitating the
valorisation of shredder fines in the context of Sweden. In doing so, the current
situation concerning fines and its management was investigated by addressing the
research questions; 1) What is the resource potential of fines generated at the studied
shredding plant, and 2) Why is the current disposal-oriented management of shredder
fines sustained in Sweden. There, a systems perspective was employed, where the
research questions were addressed on the material, actor, and institution levels, based
on three scientific articles, which are appended.
The studied material carries a certain amount of potentially recoverable resources,
nevertheless shows a significant need for upgrading pertaining to the user requirements
and regulatory standards of different recovery applications. The full recovery of fines
requires integrated processes that could simultaneously harness these resource
opportunities and resolve the material constraints. When it comes to the current
practice of managing fines in Sweden, the utilisation in landfill covering offers the
shredding companies a secure outlet for the material, given it is a well-established
practice that has evolved over decades of operations and there is still a significant
demand for landfill cover materials. Additionally, it provides shredding companies with
a legislatively-compliant low-cost disposal option for managing fines. On the other
hand, the complex materiality, lack of marketability of secondary raw materials (SRMs),
and unfavourable governmental regulation of waste recovery create strategic
disincentives for shredding companies in opting for fines valorisation.
Fines valorisation calls for change in the well-established current practice of utilising
the material in landfill covering. Thus, drastic policy measures such as phasing out
landfilling and mandating resource recovery and recycling of fines are required to
remove the incentives for fines disposal and compel the shredding industry to seek
valorisation alternatives for its management. In order to ensure long-term sustenance,
applications based on fines valorisation need favourable and more predictable
circumstances and settings on different societal levels. There, secure outlets for potential fines-derived SRMs is one of the essential elements. Governmental
interventions to create demand and alleviate valorisation investments via market and
financial instruments play a significant role in that regard. The other primary
requirement to facilitate fines valorisation in the long term is to set clear market and
regulatory playing rules. Established supply and demand structures would enable clear
pricing mechanisms for fines-derived SRMs and accurate economic assessments of
fines valorisation, thus reducing the investment risk for shredding companies. On the
other hand, clear regulatory standards and favourable regulatory practices would reduce
the uncertainty of the realisation of valorisation applications and gain trust among
actors.
Nowadays, regarding the increasing development of electronic devices and their expanded wastes, concerns about running out of non-renewable resources have increased the interest in recycling metal pieces of these wastes. On the other hand, compared to pyrometallurgical methods, biological destruction of wastes possess a higher potential to reduce the operational costs and energy consumption and it is the most desirable method from an environmental perspective. However, one major challenge on the way of recycling these electronic wastes is their toxic contents. Hence, the current study is aimed to investigate the application of bioleaching technology in reproducing metal compounds (cu) from electronic wastes. Furthermore, different categories of microorganisms are studied from different perspectives including type, supply, ratio of extracted metal, effect of binding type of microorganism (bacterial or non-bacterial), and being single or consortium (group) to obtain the best result over the electronic wastes. Therefore, the consortium of microorganisms offers a higher advantage for practical applications since organisms can directly harvest from their resource without any need for single organisms. On the other hand, results of a temperature comparison between microorganisms reveal that the extent of metals bioleaching from ores by absolute thermophiles is higher than that by medium thermophiles and mesophiles.
Nowadays, regarding the increasing development of electronic devices and their expanded wastes, concerns about running out of non-renewable resources have increased the interest in recycling metal pieces of these wastes. On the other hand, compared to pyrometallurgical methods, biological destruction of wastes possess a higher potential to reduce the operational costs and energy consumption and it is the most desirable method from an environmental perspective. However, one major challenge on the way of recycling these electronic wastes is their toxic contents. Hence, the current study is aimed to investigate the application of bioleaching technology in reproducing metal compounds (cu) from electronic wastes. Furthermore, different categories of microorganisms are studied from different perspectives including type, supply, ratio of extracted metal, effect of binding type of microorganism (bacterial or non-bacterial), and being single or consortium (group) to obtain the best result over the electronic wastes. Therefore, the consortium of microorganisms offers a higher advantage for practical applications since organisms can directly harvest from their resource without any need for single organisms. On the other hand, results of a temperature comparison between microorganisms reveal that the extent of metals bioleaching from ores by absolute thermophiles is higher than that by medium thermophiles and mesophiles.
End-of-life printed circuit boards have been subjected to proprietary pyrolysis resulting in a copper-rich char containing liberated metals. For downstream processing and copper recovery, the char was exposed to two different leaching solutions: one containing mixed microbial consortia originating from bioleaching of coal spoils and a cell-free chemical solution for comparative purpose. The influence of char pre-treatment, reactor type, temperature and type of leaching solution on the dissolution of the zero-valent copper was studied. It was found out, that for bringing copper in solution, the type of leaching solution had less pronounced effect than the type of reactor. Other than ferric iron concentration and temperature, the bacterial presence has shown effect on copper leaching kinetics and process efficiency. The fact that copper was continuously dissolved by ferric iron at initial concentrations well below the stoichiometric required ratio, demonstrated microbial regeneration of ferric iron and its back-cycling in the system. In case of the absence of microbe, the regeneration of ferric iron is driven by oxidation in the presence of O2 and H⁺. A simplified kinetic model of copper dissolution suggested that the reaction order depends upon the initial concentration of ferric iron.
This study examined the role of epoxy, present in glass fibre reinforced laminate (FR-4), in inhibiting the leaching of copper from electronic wastes (e-wastes). FR-4 makes up the majority of the base materials used in printed circuit boards and would be a prevalent polymeric constituent of e-wastes. To mimic the spent medium based leaching of fungi, leaching of e-waste was performed using citric acid. Metal dissolution tests with citric acid revealed epoxy decomposition during the leaching process and this in turn inhibited copper dissolution by two routes. The first route is by raising the solution pH from 1.8 up to 4.88 through the cleavage and release of amine group in solution and through the transformation of the epoxy surface sites. Both promoted the removal of copper from solution by adsorption of copper on the epoxy followed by its precipitation as di-copper citrate. Tests over various leaching conditions specifically at pH 1.8–3.0, temperatures from 30 to 90 °C, pulp densities of 5–100 g/dm³ and periods of up to 24 h revealed various aspects of the process. These included epoxy decomposition induced copper loss of up to 40.3% and the masking of copper dissolution self-catalysis by Cu2 + ion. This study showed that inhibition of copper leaching can be minimised. This required spent medium leaching at low pH (1.8), low pulp density (5 g/dm³) and high temperature (90 °C). These results demonstrated the impact of epoxy depolymerisation in e-wastes leaching and the potential merit of spent medium leaching in overcoming these effects and in optimising the recovery of copper from e-wastes.
Bioleaching of copper from pure granular shots and from a “pre-consumer” secondary resource from automotive industry (Brake Pads Powder, “BPP”) was carried out in a comparative study with conventional planktonic and PVA-encapsulated micro-organisms using a mixed culture of iron oxidizing bacteria: A. ferrooxidans, L. ferrooxidans and L. ferriphilum. The global process is characterized as “sequential” since a preliminary acid leaching is performed for ferrous iron extraction from the BPP material before the copper bioleaching itself.
Prior to bioleaching experiments, resistance to dissolved copper has been quantified at various concentrations to assess a potential protective effect of the biomass by the PVA-matrix. PVA-encapsulated bacteria showed a better resistance to dissolved copper with a linear progression in the ferrous iron oxidation kinetic up to 40 gCu²⁺/L concentrations while planktonic cells presented a drastic decrease in this kinetic between 10 and 40 gCu²⁺/l, resulting in a 2 to 3-fold kinetic increase for the encapsulated bacteria depending on the strain. Bioleaching of elemental granular copper in 9 K medium (Fe²⁺: 10 g/L) showed significant enhancement of copper leaching kinetic with encapsulated biomass (1.9 · 10⁻¹ gCu²⁺/L h) in comparison with the planktonic mode (8.2 · 10⁻² gCu²⁺/L h). These tests demonstrated thereby the role of ferrous iron bio-oxidation and acid consumption values close to the stoichiometric ratio. Finally, the bioleaching with encapsulated bacteria was applied to copper extraction from BPP and showed a 150% enhanced kinetic in comparison with equivalent planktonic system and a 300% increase vs abiotic mode with respective leaching rates of 4.43 · 10⁻²; 2.9 · 10⁻² and 1.48 · 10⁻² gCu²⁺/L h.
Cell immobilization offers complementary benefits as continuous process and permanent bacteria acclimation. This technology presents an interesting alternative to conventional planktonic and “two-step” processes.
This chapter reviews the use of biohydrometallurgical technology in the recovery of metals from electronic wastes (e-wastes), specifically focusing on copper extraction. This discussion includes an analysis of bioleaching of copper from printed circuit boards with particular emphasis on the use of chemolithoautotrophic bacteria and heterotrophic fungi, the leaching chemistry, and the secondary reactions and kinetics of the chemical and bioleaching processes. The biggest challenge in reclaiming e-waste is developing a process that can adapt to the complexity, changing compositions, toxicity, and volume of e-waste. Biomining offers a viable option for processing waste electrical and electronic equipment (WEEE) with potential benefits including lower cost and lower-energy options over conventional approaches. Optimizing the recovery of metallic fractions from e-waste requires confirmation that these reactions occur and identification of conditions under which these reactions could be minimized or avoided.
IntroductionMaterials and methodsResults and DiscussionConclusions
Acknowledgements
When solid materials areexposed to a liquid, some constituents will dissolve to a greater or lesserextent. The degree of dissolution of individual constituents by the contacting liquid leads to a leachate/percolate orextract composition that can be of interest for different purposes [1], such as theextraction of metals from solid waste through a suitable leachant. Leaching is a step in hydro-andelectrometallurgical processes and has been alsoemployed for the recovery of metals from waste ofelectrical andelectronicequipment (WEEE). The process may be preceded by a mechanical pretreatment of the waste see Chap.and followed by purification and metal recovery from the solution see Chaps. This chapter will discuss the different leaching solutions and conditions for WEEE processing.
This study examines the leaching of copper from waste electric cables by chemical leaching and leaching catalysed by Acidithiobacillus ferrooxidans in terms of leaching kinetics and reagents consumption. Operational parameters such as the nature of the oxidant (Fe3+, O2), the initial ferric iron concentration (0–10 g/L) and the temperature (21–50 °C) were identified to have an important influence on the degree of copper solubilisation. At optimal process conditions, copper extraction above 90% was achieved in both leaching systems, with a leaching duration of 1 day. The bacterial leaching system slightly outperformed the chemical one but the positive effect of regeneration of Fe3+ was limited. It appears that the Fe2+ bio-oxidation is not sufficiently optimised. Best results in terms of copper solubilisation kinetics were obtained for the abiotic test at 50 °C and for the biotic test at 35 °C. Moreover, the study showed that in same operating conditions, a lower acid consumption was recorded for the biotic test than for the abiotic test.
Two independent technical developments have transformed the metal mining industry in considerable ways: the increasing share of waste materials in the feedstock of metallurgical operations has partially transformed metal extraction into a recycling industry, and the employment of microorganisms in the extraction of metals from mineral ores has rendered metals mining a biologically based industry. Increasing industrial interest and research activity in the application of biotechnologies to the extraction of metals from waste, particularly electronic waste, intimate a potential intersection of those two processes, destabilizing further the analytical distinctions between extraction and manufacturing, biologically based and nonbiologically based production, waste and resources. This combined deterritorialization of metal extraction requires a theoretical deterritorialization: rethinking extraction beyond extractive industry narrowly defined and the role that nonhuman forms of life play in the production of value in nonbiologically based (extractive) industries. This article is a first step toward outlining the effects of such developments on understanding extraction. It begins by reflecting on the effects of recycling on the spatiality and materiality of the mine and then it proceeds to examine the productive role of microorganisms in mining, the limits of biomining, and the biotechnologies that have developed to transcend those limits. The conclusion draws out theoretical implications of those ongoing lines of deterritorialization and their combination on understanding the spatiotemporality of extraction and the active involvement of nonhuman nature in the production of value.
Physical process represents an important step for treatment of waste printed circuit boards (WPCBs), this being necessary for metals classification and their recovery. This work reports a review analysis coupled with lab-scale tests in WPCB treatment. The operations consisted in comminuting (shredding by a hand cutter and crushing with a mill having multi-use rotational knives equipped with a bottom sieve) and size separation (sieve shaker with a set of four sieves). Four various PCBs samples were used, differenced by provenience, on which chemical characterization was performed in order to observe metals distribution at different particle size after physical process. Due high content in all samples, copper was noticed as main element, followed by iron, tin, lead and zinc, their concentrations ranged from a sample to another one. Presence of precious metals in a large amount represents an important factor by economic point of view for waste PCBs treatment. By size distribution was noticed that more than 45% of metallic part was concentrated in the coarse fraction (2>1nun), which mean that the metals are not completely liberated by plastic materials. This will be a determinant factor for a further hydrometallurgical process.
A review of the literature published in 2011 on topics relating to automotive wastes is presented. This includes solid wastes from automotive bodies, tires, vehicular emissions and their influence to air and soil contamination, as well as the impact of alternative fuels. Potential toxicological and health risks associated with automotive wastes are also reviewed.
With the new legislation for Waste Electrical and Electronic Equipment (WEEE) coming up in Europe and similar developments in other parts of the world, a substantial increase of end-of-life electronic equipment to be treated will take place on a global scale. In this context, often much attention is placed on logistical issues, dismantling and shredding/pre-processing of electronic-scrap, while 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 overall environmental performance. Besides copper and precious metals, modern integrated smelters recover a large variety of other elements, and can make use of organics such as plastics to substitute coke as a reducing agent and fuel as an energy source. Umicore has recently completed major investments at its Hoboken Works, completely shifting the plants focus from mining concentrates to recyclable materials and industrial by-products. Based on complex Cu/Pb/Ni metallurgy, the plant has been developed to the globally most advanced full-scale processor of various precious metals containing fractions from electronic scrap, generating optimum metal yields for precious and special metals at increased productivity and minimised environmental impact. Especially the interface between pre-processing (shredding/sorting) and integrated smelting offers additional optimisation potential, which can lead to a substantial increase in overall (precious) metals yields.
The present work was aimed at studying the bioleachability of metals from electronic scrap by the selected moderately thermophilic strains of acidophilic chemolithotrophic and acidophilic heterotrophic bacteria. These included Sulfobacillus thermosulfidooxidans and an unidentified acidophilic heterotroph (code A1TSB) isolated from local environments. Among the strategies adapted to obtain enhanced metal leaching rates from electronic scrap, a mixed consortium of the metal adapted cultures of the above-mentioned bacteria was found to exhibit the maximum metal leaching efficiency. In all the flasks where high metal leaching rates were observed, concomitantly biomass production rates were also high indicating high growth rates. It showed that the metal bioleaching capability of the bacteria was associated with their growth. At scrap concentration of 10 g/L, a mixed consortium of the metal adapted cultures was able to leach more than 81% of Ni, 89% of Cu, 79% of Al and 83% of Zn. Although Pb and Sn were also leached out, they were detected in the precipitates formed during bioleaching.
The effects of pH, ferrous and ferric ion concentrations on iron oxidation by Thiobacillus ferrooxidans were examined. The initial temperature and bacterial concentration were maintained at 37°C and 2±1×104cells/ml, respectively. The iron oxidation rate increased with increased initial ferrous iron concentration to 4g/l and thereafter decreased. The presence of iron(III) showed a negative effect on the bacterial iron oxidation rate. The increase of pH also showed an increase in the oxidation rate up to pH 1.75. The oxidation rate followed first order kinetics for the parameters studied. A rate equation has been developed.
Microbiological processes were applied to mobilize metals from electronic waste materials. Bacteria Thiobacillus . . thiooxidans, T. ferrooxidans and fungi Aspergillus niger, Penicillium simplicissimum were grown in the presence of electronic scrap. The formation of inorganic and organic acids caused the mobilization of metals. Initial experiments showed that microbial growth was inhibited when the concentration of scrap in the medium exceeded 10 g Ly1. However, after a prolonged adaptation time, fungi as well as bacteria grew also at concentrations of 100 g L y1. Both fungal strains were able to mobilize Cu and Sn by 65%, and Al, Ni, Pb, and Zn by more than 95%. At scrap concentrations of 5-10 g L y1, Thiobacilli were able to leach more than 90% of the available Cu, Zn, Ni, and Al. Pb precipitated as PbSO while Sn 4
Manganese is often associated with zinc and copper minerals, and can build up in the processing circuits. Part III of the review outlines the current practice and new developments to get a better understanding of manganese behaviour and control in electrowinning of zinc and copper, and identifies suitable methods and processes to control manganese.In zinc electrowinning, the presence of small amounts of manganese (1–5 g/L) can minimise the corrosion rate of the anodes and reduce the contamination of the cathodic zinc with lead, but excess manganese results in significant decreases in the current efficiency. The neutralized zinc feed solution that contains little acid is considered to be the best place to implement manganese control. Various methods and processes for manganese control in zinc electrowinning have been developed. Oxidative precipitation and solvent extraction are the most important methods. For the neutralized zinc solution at pH 5, oxidative precipitation using a strong oxidant such as Caro's acid and SO2/O2 can selectively precipitate manganese as insoluble MnO2 or Mn(OOH), leaving other impurities, e.g., Mg, Cl−, F−, etc. in the circuit. Solvent extraction of zinc using D2EHPA (di-2-ethylhexyl phosphoric acid) can selectively recover zinc from the solution and leave other impurities including manganese in the raffinate.In copper solvent and electrowinning circuits, the problem of manganese is mainly associated with the decrease in the current efficiency and degradation of the solvent caused by the higher valent manganese species generated on the anode. The prevention or minimisation of Mn(II) oxidation during the electrowinning is critical. This can be achieved by adding ferrous ions or sulfur dioxide to control the cell potential.
The bioleaching of copper contained in the printed circuit boards (PCB) of waste computers by A. ferrooxidans was studied. The Fe oxidation rates by A. ferrooxidans in the 9K medium supplemented with the leachate of PCB (0.15-0.13 g L(-1) d(-1)) were similar to that in the 9K medium without the leachate (0.15 g L(-1) d(-1)). This finding suggests that the leachate of PCB did not seriously affect the bioleaching process by this bacterium. The amount of copper leached from PCB shreds increased with the addition of ferrous ion and reached up to 5190 mg L(-1) when the initial concentration of Fe2+ ion was 7 g L(-1). As the microbial leaching progressed, pale brown precipitate was observed to form in the solution. Based on the total amount of copper, both in solution and precipitate, the optimal addition of ferrous ion for the leaching of copper was around 7 g L(-1). When citric acid was not added, only about 37 wt% of the total leached copper remained dissolved; however, the amount of dissolved copper increased to greater than 80 wt% in the presence of citric acid. This fact indicates that the addition of a complexing agent (citric acid) to the bioleaching solution can raise the solubility of the leached metal ions.
Bioleaching of spent lithium ion secondary batteries, containing LiCoO2, was attempted in this investigation. The present study was carried out using chemolithotrophic and acidophilic bacteria Acidithiobacillus ferrooxidans, which utilized elemental sulfur and ferrous ion as the energy source to produce metabolites like sulfuric acids and ferric ion in the leaching medium. These metabolites helped dissolve metals from spent batteries. Bio-dissolution of cobalt was found to be faster than lithium. The effect of initial Fe(II) concentration, initial pH and solid/liquid (w/v) ratio during bioleaching of spent battery wastes were studied in detail. Higher Fe(II) concentration showed a decrease in dissolution due co-precipitation of Fe(III) with the metals in the residues. The higher solid/liquid ratio (w/v) also affected the metal dissolution by arresting the cell growth due to increased metal concentration in the waste sample. An EDXA mapping was carried out to compare the solubility of both cobalt and lithium, and the slow dissolution rate was clearly found from the figures.
Waste electric and electronic equipment, or electronic waste, has been taken into consideration not only by the government but also by the public due to their hazardous material contents. In the detailed literature survey, value distributions for different electronic waste samples were calculated. It is showed that the major economic driver for recycling of electronic waste is from the recovery of precious metals. The state of the art in recovery of precious metals from electronic waste by pyrometallurgical processing, hydrometallurgical processing, and biometallurgical processing are highlighted in the paper.
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An eco-efficient solution for metals–plastics-mixtures from electronic waste: the integrated metals smelter
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