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Aqueous Metal Recovery Techniques from E-Scrap: Hydrometallurgy in Recycling
Abstract
a b s t r a c t Waste of electric–electronic equipment (WEEE) with an annual growth rate of about 3–5% is the fastest growing waste stream in municipal wastes. Notwithstanding their environmental pollution potential, waste of electrical and electronic equipment (WEEE) with their high content of base and precious metals, in particular, are regarded as a potential secondary resource when compared with ores. For the recovery of metals from WEEE, various treatment options based on conventional physical, hydrometallurgical and pyrometallurgical processes are available. These process options with particular reference to hydromet-allurgical processes were reviewed in this study. With their relatively low capital cost, reduced environ-mental impact (e.g. no hazardous gases/dusts), potential for high metal recoveries and suitability for small scale applications, hydrometallurgical processes are promising options for the treatment of WEEE. Since the metals are present in native form and/or as alloys, an oxidative leaching process is required for the effective extraction of base and precious metals of interest. A two-stage process based on oxidative acid leaching of base metals (Cu in particular) followed by leaching of precious metals using cyanide, thiosulfate, thiourea or halide as lixiviant(s) can be suitably developed for the hydrometallurgical treat-ment of WEEE. However, further research is required to develop new, cost effective and environmentally friendly processes and/or refine existing ones for leaching and, in particular, downstream processes.
... Pyrometallurgy and hydrometallurgy are widely used technologies for the extraction of metals from ores and wastes such as spent catalysts and electronic wastes [11][12][13]. Pyrometallurgy is an intensive process that involves releasing harmful chemicals such as furan and dioxins [11]. Material loss occurs during the energy-intensive pyrometallurgical process [10]. ...
... Hydrometallurgy involves the leaching of metals into a highly acidic or basic medium. However, hydrometallurgical processes discharge a colossal volume of aqueous waste into the environment during metal extraction, which should be further treated and purified before disposal [13,14] Another drawback is the occurrence of multi-metal pregnant solutions during the hydrometallurgical process due to the poor selectivity of metals. Additionally, individual pure metal is recovered using various other solvents and through a multi-step process. ...
... In hydrometallurgy, metal extraction was conventionally done by halide leaching, acid leaching, cyanide leaching, etc., which affects the aquatic and soil ecosystem adversely [12][13][14][15]. Strong mineral acids such as HCl and H 2 SO 4 were used in metal dissolution, with hydrogen evolution [16]. ...
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.
... Datos recientes informan que anualmente en el mundo se generan de 20 a 50 millones de toneladas aproximadamente de estos residuos (Tuncuk et al., 2012). Tan solo en el 2016 se generaron 44.7 millones de toneladas métricas (Mt) de desechos, que significa 6.1 kilogramos por habitante en el planeta (kg/hab), lo cual equivale al peso de 9 pirámides de Giza o 4,500 torres Eiffel; y se estima que esta cifra pueda incrementar a 52.2 Mt para el 2021 (Baldé et al., 2017); esta estimación se puede observar en la Figura 1. ENERLAC • Volumen IV. ...
... Este gran problema del manejo de RAEE puede tener diversas razones, una de ellas es que los países desarrollados poseen un costo de jornada laboral alta y varias regulaciones para disposición final de estos residuos, por lo cual se exportan a países subdesarrollados. Estos a su vez, poseen herramientas y tecnologías más rudimentarias para la extracción/reciclaje de los RAEE (Perkins et al., 2014) y es de esperarse que estos sean recibidos en casi cualquier vertedero por su alto valor comercial (Tuncuk et al., 2012). Por otra parte, se estima que el 40% de la composición de los RAEE son metales de interés comercial, tales como cobre, plomo, estaño, mercurio, plata, oro, platino y paladio. ...
... Aunque su extracción está limitada debido a la compleja composición de metales en los desechos electrónicos, más del 80% del valor total de recuperación comprende metales preciosos (Ag, Au y Pt) y más del 95% del total de metales son básicos (Cu, Sn, Hg, Pb) (Diaz et al., 2017). Aunado a esto, los RAEE pueden contener de 25 a 250 veces más oro comparado con la cantidad encontrada en los minerales de los que se extraen estos metales en la actividad minera (Tuncuk et al., 2012). Además, el costo de extraer estos metales a partir de minerales es 13 veces más alto en yacimientos naturales que en RAEE (Zeng et al., 2018). ...
En este artículo se presenta una revisión sistemática de la literatura publicada sobre los RAEE, incluyendo información sobre su generación, destino y metodologías ambientalmente amigables que se han propuesto para su gestión-reciclaje, así como sobre impactos ambientales y en la salud derivados de los RAEE y su manejo. Esta revisión tiene el propósito de sensibilizar a la población sobre el peligro de un tratamiento inadecuado de los RAEE, y a su vez considerar la implementación de estrategias de gestión y acciones a tomar, a través de procesos de reciclaje amigables con el medio ambiente. Las primeras menciones de los RAEE en la producción científica datan de 1996, evidenciándose que el tópico ha seguido en constante crecimiento hasta el 2019, cuando se publicaron 735 documentos. Las categorías con mayor número de documentos donde se ha generado mayor conocimiento y aportaciones científicas de alto impacto destacan las enfocadas al medio ambiente o a la sustentabilidad energética, así como las áreas de metalurgia, química, eléctrica y de combustibles fósiles. Además, se presenta el mapeo de los desechos electrónicos en millones de toneladas que se produce mundialmente y se muestran las regiones que envían RAEE a otros países en su mayoría en forma ilegal. Por otra parte, el reciclaje de RAEE es un proceso complicado, pero con un alto potencial para generar una economía circular verde.
Recuperado a partir de https://enerlac.olade.org/index.php/ENERLAC/article/view/127
... Aqua regia (AR), a well-known solvent for gold, has been widely used to extract Au and other precious metals from e-waste, jewelry, and industrial waste [15,16]. The AR-based process has several advantages, including low costs, high leaching rates, and ease of operation, making it the most efficient method for dissolving Au from solid electronic components, such as PCBs, when compared to other leaching reagents [17][18][19][20]. Although various leaching agents such as cyanide, halide, thiourea, and thiosulfate have been investigated for metal recovery, they frequently pose significant environmental risks, are inefficient, or are expensive. ...
... Ag contamination, while initial leaching with HNO 3 reduces the hindrance caused by metastannic acid from solder [41]. Thus, before leaching PMs from PCBs, base metals such as Cu, Fe, Zn, Al, Sn, and others must be removed through physical separation and chemical treatment [18,50,51]. ...
Electronic waste (e-waste) has emerged as a valuable secondary source of metals, including precious metals (PMs), surpassing those found in natural ores. The objective of this study is to explore the use of cellulose-based adsorbents, specifically dithiocarbamate-modified cellulose (DMC) and proline-incorporated DMC with epoxy-cross-linkage (DMC-Pro-Epo6), in the recovery of Au from e-waste, particularly under harsh aqua regia (AR) conditions. DMC adsorption behavior in AR is influenced by several factors, such as AR dilution, pre-adsorption phenomena, contact time, and Au III concentration. DMCs displayed competitive adsorption across varied AR dilutions, benefiting from diluted AR due to hindered adsorption in undiluted AR. Contact time analysis demonstrated rapid Au(III) adsorption, with equilibrium achieved in approximately 30 min. Four anion exchange-type commercial resins (Lewatit MonoPlus TP 214, Diaion WA30, Dowex 1X8, and AmberChrom 1X8) and one chelating CR (Q-10R) were tested for comparison, and their adsorption capacities were evaluated. Both the DMC and DMC-Pro-Epo6 have higher adsorption capacities for Au(III) than commercial resins, which can be attributed to their sorption-active dithiocarbamate functional groups. The study also outlined a step-by-step Au extraction from printed circuit boards (PCBs), and the effective recovery of metallic Au from PCBs using DMCs was demonstrated.
... The remaining consists of ceramics, refractory oxides, and plastics along with several hazardous substances, such as chlorofluorocarbons (CFCs), polycyclic hydrocarbons, poly-brominated biphenyls, dioxins, epoxy resins, polychlorinated biphenyls, fiberglass, and polyvinyl chlorides [8]. E-wastes are among the fastest growing wastes, with an annual growth rate of 3-5% [9]. Only about 17% of the e-waste is collected and recycled, and the rest ends up in landfills and waste dumps [10]. ...
... In view of this, there has been a surge in review articles on e-wastes in recent past (for example, between 2020 and present), research and review articles on various topics of e-waste generation and precious metal recovery are presented in Fig. 1. In contrast, reviews on recovery of precious metals involving biological, chemical and physical processes are relatively few, and furthermore articles on phytoremediation are minuscule [9]. Hence, the present review accounts for the prevalent e-waste management practices for the recovery for precious metals, the extraction efficiencies through conventional physico-chemical and bio-metallurgical procedures, uptake efficiencies of precious metals by different tolerant plants, and the estimated projection of the phytominable Au and Ag from PCB wastes, till 2050. ...
E-waste, also known as waste from electrical and electronic equipment, is a solid waste that accumulates quickly due to high demand driven by the market for replacing newer electrical and electronic products. The global e-waste generation is estimated to be between 53.6 million tons, and it is increasing by 3–5% per year. Metals make-up approximately 30% of e-waste, which contains precious elements Au, Ag, Cu, Pt, and other high-value elements, valued at USD 57 billion, which is driving the e-waste recycling industry. It is noteworthy that the recycling of precious elements from e-waste has emerged as a profitable enterprise in several parts of developing nations. E-waste contains 50–100 times higher levels of precious metals compared to natural ores, making it suitable for mining. E-waste recycling in developing nations, mostly occurs through the informal sector comprising manual collection, crushing, segregation and selling of precious elements, such as Au, Ag, Cu, Pb, Pt, and other rare elements (Nd, In, and Ga). The organized sector, on the other hand, mostly employs mechano-chemical methods, such as pyrometallurgy, hydrometallurgy, and bio-hydrometallurgy, which have serious environmental consequences. Both the informal and formal sectors of e-waste processing lead to the leaching of toxic elements into groundwater and soils. Owing to the lesser efficiency of greener technologies, such as phytoremediation and bioremediation, their use in precious metal extraction is very limited. However, this review explores several hyper-accumulating and tolerant plants viz. Brassica juncea and Berkheya coddii, which holds great potential in phytomining of precious metal from e-waste. Thus, the state of the art in precious metal extraction from e-waste as well as the advantages and disadvantages of different metal extraction technologies has been reviewed.
... Os REEE contêm uma vasta gama de substâncias orgânicas e inorgânicas (> 1000) com conteúdos que dependem em grande medida do tipo, fabricação e idade do equipamento (Tuncuk et al., 2012) A figura 4 sintetiza o conteúdo de elementos metálicos e não metálicos em placas de circuito impresso típicos. (Huang et al., 2009;Kumar et al., 2015). ...
... Tendo em vista que existe a presença destes elementos potencialmente poluidores (por exemplo, metais tóxicos e retardadores de chama) nas placas de circuito impresso dos aparelhos eletrônicos, dificulta-se a reciclagem pirometalúrgica nas pequenas e médias indústrias, devido ao elevado custo envolvido na implantação de filtros e equipamentos para evitar a poluição do ar (Hall et al., 2007;Sepúlveda, 2010). O processamento hidrometalúrgico por sua vez, sendo mais viável, geralmente envolve um pré-tratamento mecânico dos resíduos, a lixiviação dos metais, purificação da solução e a recuperação dos metais (Tuncuk, 2012 ...
Os resíduos de equipamentos eletroeletrônicos (REEE) estão cada vez mais presentes no cotidiano. Algumas empresas brasileiras realizam apenas o pré-tratamento de REEE: triagem e desmantelamento, desconsiderando o processo de refino, que apresentaria benefícios econômicos. O artigo apresenta, através da revisão de literatura, a situação atual da reciclagem brasileira e destaca alguns metais desperdiçados das PCI e indica o processo hidrometalúrgico para recuperar estes materiais. Palavras-chave: Lixo eletrônico; Gestão de resíduos; Reciclagem de metais. INTRODUÇÃO Os resíduos de equipamento eletroeletrônicos (REEE) estão entre os fluxos de crescimento mais rápido do mundo (Li, 2017). Um relatório lançado pelas Nações Unidas em 2019 mostrou que o ritmo da taxa de crescimento anual de resíduos eletroeletrônicos subiu para 50 milhões de toneladas, com uma tendência crescente ano após ano (Bel et al., 2019). A gestão correta destes resíduos em simbiose com a reciclagem adequada pode gerar resultados significativos no âmbito econômico, uma vez que apresentam substâncias de alto valor em sua composição, como o cobre e metais nobres como a prata, ouro e paládio, sendo esse último encontrado em concentrações dez vezes maiores em PCIs (Placas de circuito impresso) do que no minério comercialmente extraído (Santos, 2012). Há uma preocupação também com os riscos à saúde e ao meio ambiente, quando associados a uma possível disposição incorreta dos REEE. Os mesmos apresentam um elevado potencial poluidor, já que cada aparelho pode conter até 12 elementos considerados altamente prejudiciais a saúde e ao meio ambiente, dentre eles cádmio, chumbo e arsênio (Wu et. al., 2008). A Política Nacional de Resíduos Sólidos (Brasil, 2010), prevê a prevenção e a redução na geração de resíduos. Podem ser realizadas alterações impostas pela política, incluindo a proibição de importação de resíduos perigosos, que podem causar danos ao ambiente ou à saúde humana, incentivos financeiros de âmbito federal a conselhos locais para a elaboração de planos de gestão de resíduos, o fim das chamadas "lixeiras" (locais impróprios onde a população se desfazia dos seus resíduos) e a implementação da logística reversa. A logística reversa (Lei 12.305/2010) pretende dar continuidade ao ciclo de vida de um material, fazendo com que os fabricantes, importadores, distribuidores e comerciantes dos produtos sejam envolvidos em um ciclo responsável. Assim, as empresas que fabricam produtos são responsáveis por encontrar alternativas para o fim da sua vida útil, e são responsáveis por desenvolver estratégias de retorno, tanto de embalagens, quanto dos eletrônicos, além de descartar corretamente os seus resíduos (Brasil, 2010; Nelen et al., 2014). A presença de metais preciosos proporciona um forte incentivo à reciclagem de resíduos de equipamentos eletroeletrônicos (REEE) (Wang e Xu, 2014). Todos REEE contêm placa de circuito impresso (PCI: peça base na qual são montados os circuitos eletrônicos) e, com os avanços tecnológicos, a concentração de metais nestas placas tem se tornado cada vez mais heterogênea, e seus componentes, compactos, dificultando os processos de reciclagem. Tais peças contém a maior quantidade de metais, cerca de 40% do total, sendo a principal parte de interesse para a recuperação (Ladou, 2006; Cucchiella et al., 2015; Gosh et al., 2015; Kumar, Holuszko, Espinosa, 2017). No entanto, infelizmente, no Brasil, mesmo com a recente implementação de políticas nacionais de gestão de resíduos, os governos federais e locais não controlam o número de REEE gerados pela sociedade. A maioria dos aparelhos eletrônicos não chegam no processo de refino e são encaminhados para empresas
... These solutions can solubilise the solid matrix of E-waste and liberate the metals in the solution phase. Besides that, leaching reagents such as cyanide, thiourea, thiosulfate, and halides have also been widely utilised [40]. Thiosulfate and thiourea have been proposed as alternatives to cyanidation because of their rapid leaching rates. ...
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.
... Conventional leaching of the platinum group metals has been through use of chlorides (Tuncuk et. al., 2012) or cyanide (Hourn and Turner, 2012). Thus, if a bioprocessing route would be developed, it follows then that chlorine or cyanide-producing microorganisms might be a good option. However, whereas cyanogenic microorganisms have been identified and isolated, chlorine-producing microorganisms have not yet been identified. Therefore, the use ...
This paper explores bioleaching as a viable method for extracting precious group metals (PGMs) with potential advantages over the traditional energy-intensive extraction processes that cannot cope with the depletion of high-grade ores. The proposed bioleaching process consists of three main steps: base metal removal, bio-decomposition of silicates and PGM extraction using biogenic cyanide. Base metals form stable complexes with cyanide under similar oxidative conditions required for PGM leaching. Such that efficient removal of base metals minimizes biogenic cyanide consumption, while the subsequent decomposition of silicates prevents PGM loss. The use of mixed thermophilic microorganisms enhances kinetics during base metal removal, resulting in a base metal-free residue for PGM bioleaching. For PGM bioleaching, a decoupled approach was proposed, involving biogenic cyanide production, followed by its utilization for PGM leaching. This accommodates the different conditions required by cyanide-producing microorganisms and those for PGM leaching. A conceptual flowsheet was drawn to illustrate the bioleaching of PGMs. The challenges related to the influence of PGM mineralogy on the flowsheet were brought to attention, along with their respective solutions.
... 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.
... According to studies by Danthinne et al. (2022), Kumar et al. (2017) and Flávia et al. (2015), "electronic and electrical equipment that has stopped working or has defects during production" is referred to as waste of electrical and electronic equipment (WEEE). Various items, including mobile phones, printers, microwaves and scientific equipment, are included in the category of "e-waste," according to research like Tuncuk et al. (2012) and Afroz et al. (2013). ...
Today, use of electronic devices has increased in exponential manner. The rapid technological advancements have led to the usage of updated products and an increase in demand for electronics, resulting in a surge of electronic waste production. Major objectives of this study are (a) reviewing previous research on electronic waste production and management practices, (b) identifying the recycling challenges and (c) suggesting potential future research directions. The waste stream is the growing globally. With the lowest recycling rates, its mismanagement can negatively impact the environment and human health. On the other hand, proper management of electronic waste can yield various benefits such as the extraction of valuable metals, a market for secondhand electronics equipment and the supply of raw materials to enhance environmental competitiveness of other industries. Despite these advantages, there are numerous challenges in recycling electronic waste, leading to low recycling rates in both developed and developing nations. The study is based on a review of papers published between 2012 and 2022 as found in the Scopus database. Based on this review, all critical issues on recycling of electronic waste are explored and future research directions are also proposed.
... Hydrometallurgical processes are promising options for the treatment of EEE. Hydrometallurgy is a process in which the e-waste metals are leached using acid or caustic to dissolve the required metals into the solution (Fleming 1992, Tuncuk, Stazi et al. 2012). This is then followed by refining of the concentrate further through process such as solvent extraction, adsorption, or ion exchange to isolate the target metal. ...
Electronic waste (e-waste is one of the fastest growing waste streams which contains valuable materials such as plastic, glass, and precious metals. This study investigates different recycling methods such as pyrometallurgy, hydrometallurgy, and bio-metallurgy process used to recover precious metals such as Au and Ag from e-waste based on the information available in the literature. Mechanisms, improvements, and suitability of each method were critically analysed and corelated to have a complete understanding in this area. It was found that recovered materials can be reused as a secondary input material source. e-waste also contains hazardous materials and chemicals which requires proper care during recycling to prevent contamination. Besides the development of proper experimental techniques, it also required to raise the awareness among the people to deal with this issue sustainably.
... PCBs treatment involves size reduction (dismantling, shredding, grinding) and magnetic separation (Rocchetti et al., 2018); followed by metals recovery via pyrometallurgical, hydrometallurgical, electrometallurgical or biohydrometallurgical processes Vegliò, 2018a, 2018b;Hubau and Bryan, 2023;Kaya, 2016). Hydrometallurgical processing Vegliò, 2016, 2022) can be established in local WEEE recycling industries permitting the decentralized "green" production of pure metals (Tuncuk et al., 2012;Tunsu and Retegan, 2016) compared to pyrometallurgy which is by far more energy intensive requiring expensive and complicated facilities (Copani et al., 2019). Hydrometallurgy involves essentially two steps: (a) leaching of metals; and (b) separation/selective extraction of the metals of interest from the pregnant leaching solution (PLS). ...
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.
... Therefore, the recovery of metals from WEEE is of economic and environmental interest. Various metal recovery options based on conventional physical and metallurgical (bio/hydro-, pyro-and electro-metallurgical) processes appear to be available ( Cui and Zhang, 2008;Tuncuk et al., 2012;Kaya, 2016;Chauhan et al., 2018;Deveci et al., 2019, Işıldar et al., 2019Sethurajan et al., 2019). WEEE that is rich in gold (i.e., >400 g/t Au) is considered as "high-value" WEEE with a high economic incentive for recycling (Hagelüken, 2006). ...
Waste of Electrical and Electronic Equipments (WEEE) is one of the fastest growing waste streams in the world. The treatment of WEEE with high content of precious metals (Au in particular) has received the most attention due to their high economic potential. The development of simple, environmentally friendly and cost-effective methods for the recovery of metals from “low-value” WEEE (e.g., <100 g/t Au) is important from the circular economy perspective. In this study, the separation of base (Cu) and precious (Ag) metals from scrap TV boards (STVBs) by using a zig-zag air separator was investigated. Size-reduced scrap STVBs (-1 mm) were subjected to separation tests after the removal of the fine fraction (-0.1 mm). The sized scrap material (-1 +0.1 mm) was determined to have a metal content of 15.4% Cu, 47 g/t Ag and 0.05% Fe, with no gold. In the air separation tests, the effect of air flow rate (4-16 m/s) on the recovery of metals was studied. Increasing the air flow rate resulted in low metal recoveries with concurrent high metal grades in the concentrate. Separation efficiency (%) calculations showed that the most efficient separation is obtained at the highest air flow rate of 16 m/s. At this flow rate, 15.4% of the material was recovered in the concentrate which contains 62.3% Cu and 198 g/t Ag with recoveries of 63.3% Cu and 73.9% Ag. The findings indicated that zig-zag air separators can be used to obtain a metal-rich fraction under suitable conditions of the flow regime.
... All these processes are well developed when treating natural sources. However, the valuable metals listed above can also be obtained from secondary sources (e-waste, sludge, ash, tailing, etc.) [4][5][6]. The problem is acute when using, for example, lithium-ion batteries (LIBs). ...
New processes for recycling valuable materials from used lithium-ion batteries (LIBs) need to be developed. This is critical to both meeting growing global demand and mitigating the electronic waste crisis. In contrast to the use of reagent-based processes, this work shows the results of testing a hybrid electrobaromembrane (EBM) method for the selective separation of Li+ and Co2+ ions. Separation is carried out using a track-etched membrane with a pore diameter of 35 nm, which can create conditions for separation if an electric field and an oppositely directed pressure field are applied simultaneously. It is shown that the efficiency of ion separation for a lithium/cobalt pair can be very high due to the possibility of directing the fluxes of separated ions to opposite sides. The flux of lithium through the membrane is about 0.3 mol/(m2 × h). The presence of coexisting nickel ions in the feed solution does not affect the flux of lithium. It is shown that the EBM separation conditions can be chosen so that only lithium is extracted from the feed solution, while cobalt and nickel remain in it.
... Hydrometallurgy systems are relatively small in capacities coupled with a controlled recovery process when compared to pyrometallurgy (Ranjbar et al. 2014). Hydrometallurgy is concerned with the use of aqueous solutions known as leaching reagents (cyanide, thiourea, thiosulphate, acids) to isolate, purify, and recover precious metals from its attendant effluents (Tuncuk et al. 2012). There is a wide spectrum of leaching reagents used for this process as described in Table 3. Table 4 describes the chemistry involved vis-a-vis the leaching solvent selected for the leaching process. ...
The loss of highly sought-after metals such as gold, silver, and platinum during extraction processes not only constitutes a significant waste of valuable resources but also contributes to alarming environmental pollution. The ever-growing adverse impacts of these highly valued metals significantly increase the contamination of water bodies on discharge, while reducing the reusability potential of their corresponding processed wastewater. It is, therefore, of great interest to identify pragmatic solutions for the recovery of precious materials from processed water. In this review, pollution from targeted precious metals such as gold, silver, platinum, palladium, iridium, ruthenium, and rhodium was reviewed and analyzed. Also, the hazardous effects are elicited, and detection techniques are enumerated. An insightful approach to more recent treatment techniques was also discussed. The study reveals nano- and bio-sorption techniques as adoptable pragmatic alternatives, among other techniques, especially for industrial applications with merits of cost, time, waste management, and eco-friendliness. The results indicate that gold (46.2%), palladium (23.1%), platinum (19.2%), and silver (11.5%) are of utmost interest when considering recent recovery techniques. High yield and cost analysis reduction are reasons for the observed preference of this recovery process when considering groups of precious metals. The challenges and prospects of nanomaterials are highlighted.
HIGHLIGHTS
Precious metals are present in processed wastewater as pollutants.;
Conventional recovery methods are associated with limitations.;
Bio- and nano-sorption provide pragmatic alternatives to other existing techniques with cost-effectiveness, simplicity of design, and eco-friendly disposal methods.;
The technological approach via trapping and impregnation of precious metals in sorbents is effective in the recovery of precious metals.;
... Studies into the characterization and physical processing of E-Waste is not new with numerous studies performed to recover valuable metals from WPCBs using a variety of processing techniques [17,18]. These techniques can be categorized into mechanical/physical separation [19][20][21][22][23][24] and chemical separation [25][26][27][28]. Mechanical/physical separation usually starts with size reduction, with further separation utilizing physical properties, such as density, electrostatic, and conductivity [1]. ...
Due to the rapid development of electronic devices and their shortened lifespans, waste electrical and electronic equipment (WEEE), or E-waste, is regarded as one of the most fast-growing wastes. Among the categories of E-waste, waste printed circuit boards (WPCBs) are considered the most complex waste materials, owing to their various constitutes, such as plastics, capacitors, wiring, and metal plating. To date, a variety of processing technologies have been developed and studied. However, due to the heterogeneous nature of WPCBs, a thorough study on both material characterization and physical separation was needed to provide a better understanding in material handling, as well as to prepare a suitable feedstock prior to the downstream chemical process. In the present study, integrated size and density separations were performed to understand the liberation of contained metals, particularly Cu and Au, from the plastic substrates. The separation performance was evaluated by the elemental concentration, distribution, and enrichment ratio of valuable metals in different size and density fractions. Further, SEM-EDS on the density separation products was carried out to characterize the surface morphology, elemental mapping, and quantified elemental contents. Moreover, thermo-gravimetric properties of waste PCBs were investigated by TGA, in order to understand the effect of temperature on volatile and combustible fractions during the thermal processing.
... The production of electrical and electronic equipment (EEE) is increasing rapidly due to the revolution of information technology; accordingly, the waste deriving from electrical and electronic equipment (WEEE) has also increased [1]. WEEE comes from private homes and as a result of professional use. ...
Printed circuit boards (PCBs) are a valuable source of raw materials for metal recycling considering that base metal concentration analyses have confirmed that PCB powders are multimetallic in nature and contain high concentrations of Cu, Zn, Ni, and Fe. Given that minerals are not renewable resources, these metals can be recycled through hydrometallurgical processes. In this study, we determined that 2 M sulfuric acid, 0.55 MPa oxygen pressure, and a temperature of 90 °C represent the optimal conditions for leaching of Cu, Zn, and Ni of PCBs, obtaining the highest observed values of recovery of greater than 90% for Zn and 98% for Cu and Ni. The characterization of PCBs by SEM–EDS analyses showed that plates mainly consist of Cu, Ni, and Zn. PCBs can be seen as a potential secondary resource for the recovery of copper, nickel, and zinc. The best potential and pH conditions for the extraction of Cu, Zn, and Ni were also determined on the basis of thermodynamic diagrams.
... This work demonstrates a high-capacity packed-bed sulphate-reducing bioreactor for treating (i) acid mine drainage (AMD), a typical wastewater found at mining sites and (ii) wastewater generated upon the hydrometallurgical treatment of waste printed circuit boards (PCBs) with sulphuric acid for copper recovery. The latter was selected as PCBs are considered excellent secondary raw materials for metal extraction and hydrometallurgical PCB processing has recently proven efficient for the decentralized "green" production of pure metals (Tuncuk et al., 2012;Tunsu et al., 2016). ...
Contains abstracts from the G16 Conference organised in Galway, Ireland (November 17-18, 2022).
... Según las últimas estadísticas, la generación anual de RAEE superó los 53 millones de toneladas, en el 2025 se espera que alcance los 95 millones de toneladas en la próxima década (Forti et al., 2020). La generación de RAEE está creciendo aproximadamente entre un 3% y un 5%, tres veces (Burke, 2007) más que el crecimiento de los residuos municipales (Tuncuk et al., 2012). ...
La investigación tuvo como objetivo diagnosticar el nivel cognitivo, procedimental y actitudinal de los estudiantes universitarios frente a los desechos eléctricos y electrónicos. Para poder concretizar la investigación se aplicó un cuestionario de 24 preguntas relacionadas a las tres dimensiones bajo un enfoque por competencias, a 235 estudiantes todos cursando el segundo ciclo académico realizado de una manera aleatoria simple no estratificada. Dando como resultados que se encuentra un bajo nivel de conocimientos, procedimientos y actitudes sobre los residuos eléctricos y electrónicos, convirtiéndose en la actualidad en un peligro muy latente para la salud y la vida de las personas; sino se realiza una adecuada gestión debido al crecimiento exponencial que se está evidenciando a nivel mundial fruto del desarrollo tecnológico y el fácil acceso y tiempo de vida de dichos objetos. Donde se llega a la conclusión que se debe mejorar dichas competencias en los estudiantes universitarios para hacer frente a este problema desde los espacios familiares y educativos.
Metal production is facing new challenges due to climate change and declining primary ore quality; thus, new technologies with sustainable processing routes are needed. One way to address this is to recover metals from secondary resources such as end-of-life batteries using a cleaner reducing agent hydrogen that would reduce direct carbon dioxide emissions during pyrometallurgical processing. Recycling of Li-ion battery cathode materials using hydrogen would result in a more benign metal production process and would simultaneously provide a sustainable solution to treat wastes. This study investigated the kinetics of H2 reduction of LiCoO2 at 600–1000 °C up to 180 min reaction time using an isothermal mass change analysis supported with detailed microstructure evolution observations. The overall reduction mechanism appeared to follow the shrinking-core model with a different rate-limiting step depending on the reduction temperature. The activation energy of reduction at 600–800 °C was calculated to be 37.4 kJ/mol and was controlled by the nucleation step. The information and data obtained are useful when comparing different recycling methods and optimizing the reduction parameters of spent Li-ion battery process.
The environment is considered the most significant component for man and other biotic units for their survival. The level of environmental sustainability reflects the fundamental value of both biotic and abiotic components. To achieve the goal of sustainability, the best comprehensive technique is recycling the waste and other by-products to make the waste more beneficial. It will also help the relationship between biotic and abiotic components to preserve a visual and vigorous equilibrium that distinguishes a perfect environment. Biotechnology is considered an evolving science for the sustainability of the environment. The conventional treatment methods required a high amount of cost and energy in most cases to remove the pollutants from the contaminated area. However, most of these processes only change the state of pollutants rather than eliminate them. On the other hand, biological methods include the degradation of the contaminants. In biological treatment methods, pollutants can be fixed, purified, and detached by using mainly microorganisms. Due to the comparatively low cost and the dissimilarity of work development, the bioremediation procedure has been most extensively used all over the world. Environmental biotechnology has been in existence for a while, but with the emergence of new methods such as contemporary microbiology and molecular genetics, researchers can now address the more pressing environmental issues such as detoxifying hazardous waste over the use of microbes. Exponential population growth has resulted in a decrease in the natural ecosystem, and disruptions to the stability of natural cycles have a detrimental effect on both humans and other living systems. Biotechnology seems to be the most sustainable method of nourishing the environment, despite the obstacles posed by the increase in population and the ensuing problems with pollution.
Recovering gold from unconventional sources, such as electronic waste, offers significant environmental and economic benefits. Exploiting materials and methods with high efficiency and selectivity is demanding. Herein, we reported a novel light-enhanced Au(III) recovery process using a porphyrin-based metal-organic framework (PCN-224). Our results showed that PCN-224 exhibited a remarkable Au(III) recovery capacity of up to 2613 mg/g when exposed to visible light irradiation, which was 3 times higher than that in the dark. Furthermore, light irradiation also improved the Au selectivity of PCN-224 against coexisting ions, including Zn²⁺, Mg²⁺, Cd²⁺, Ni²⁺, Hg²⁺, Cu²⁺, Pb²⁺, Al³⁺, and Fe³⁺. Based on characterization and kinetic analysis, an adsorption-reduction mechanism was proposed for the light-enhanced Au recovery, and porphyrin linkers played an essential role as active sites for both adsorption and reduction. To further protect the porphyrin linkers in PCN-224, acetic acid was introduced as a representative electron donor molecule in electronic waste, which could further enhance the Au(III) recovery capacity to 4946 mg/g. In addition, we demonstrated that PCN-224 and its light-enhanced feature also performed effectively in the actual leaching solution of waste electrical and electronic equipment, and the framework was successfully reused for at least six cycles. Overall, our discoveries could inspire the design of more outstanding materials and the artful use of clean energy to recover precious metals while minimizing the environmental impact.
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.
Innovations in the field of science and technology transferred to engineering applications led to the rapid pace of urbanisation across the globe. The impact of urbanisation and change in lifestyle of the society is producing thumping municipal solid wastes of 62 million tonnes per year in our ecosystem and its concomitant environmental issues, which need to be addressed critically. Processing of the waste collected can be conducted only on 34.14% of the collected wastes remaining are dumped openly. This paper critically reviews different techniques to convert municipal waste to useful products with specific emphasis on municipalities of India because of its diversified terrain and culture. It is observed that 0.44 kg/capita/day, per capita waste, is generated in metro cities of India. The management and processing of these wastes are analysed. Reprocessing of non-renewable wastes for structural applications from this municipal waste into novel composites is discussed here. Cost and energy-efficient composite materials can be fabricated using biodegradable waste materials, detailed fabrication methods and mechanisms are discussed in this review. Carbonised biodegradable waste is used as reinforcement with an aluminium matrix, exposing the opportunities to use it in composite applications. The challenges and research scopes are briefly discussed in this paper.
The transformation towards a circular economy based on sustainable technologies requires future-oriented materials development, which considers materials recycling with a minimum environmental impact (EI). This demands a holistic approach towards...
The current study aimed to determine the characteristics and kinetic parameters for the pyrolysis of printed circuit board (PCB) wastes including the analysis of evolved gases during the processes at different particle sizes. First, PCB wastes were examined using SEM–EDS, SEM-Mapping and FTIR to gain a better understanding of their structures. Then, non-isothermal TG-FTIR analyses of PCB wastes were conducted from ambient temperature to 800 °C under N2 atmosphere. The thermal decomposition of PCB wastes occurred in four stages. The second stage was determined as the main pyrolysis stage. The average apparent activation energies (Ea) of main pyrolysis stage calculated using the isoconversional methods (Friedman, Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Starink) were in the ranges of 205–240, 144–158 and 147–161 kJ mol−1 ranges for the studied particle sizes of PCB-2 (180 μm–1.18 mm), PCB-3 (90–180 μm) and PCB-4 (63–90 μm), respectively, which pointed out an effect of particle size on Ea value conversely to a previously reported literature study. Moreover, Coats-Redfern and Criado methods confirmed each other and revealed the reaction mechanism of main pyrolysis stage as F2-2.5. Based on the evolved gas analyses, the most common emission of PCB wastes was CO2 associated with plastic, brominated compounds, polycarbonate, and epoxy resins decomposition.
Pyrogallol molecules were successfully immobilized onto aminopropyl molecule functionalized MCM41 nanoparticles to obtain a fast and high gold adsorption capacity. The Taguchi statistical method was used to determine the factors affecting the gold(III) adsorption efficiency. The effect of six factors, pH, rate, adsorbent mass, temperature, initial Au(III) concentration and time, each with 5 levels, on the adsorption capacity was investigated by forming an L25 orthogonal. The analysis of variance (ANOVA) of each factor showed that all factors had significant effects on adsorption. pH 5, 250 rpm stirring speed, 0.025 g adsorbent mass, 40 °C temperature, 600 mg L-1 Au(III) concentration and 15 min time were determined to be the optimum adsorption conditions. The maximum Langmuir monolayer adsorption capacity of APMCM1-Py for Au(III) was calculated to be 168.54 mg g-1 at 303 K. The adsorption mechanism fits the pseudo-second-order kinetic model assuming the formation of a single chemical adsorption layer on the adsorbent surface. The adsorption isotherms are best represented using the Langmuir isotherm model. It exhibits a spontaneous endothermic behavior. FTIR, SEM, EDX and XRD analyses showed that mostly phenolic -OH functional groups adsorb Au(III) ions on the APMCMC41-Py surface with their reducing character. These results enable the rapid recovery of gold ions from weakly acidic aqueous solutions by reduction of APMCM41-Py NPs.
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.
Artan dünya nüfusu ile gelişen teknolojik yenilikler sonucunda hızla artan hammadde tüketimi ve bunun sonucunda oluşan atık ürünlerinden hammadde geri dönüşümü önem kazanmıştır. Özelliklede değerli metaller açısından geri kazanım çok büyük öneme sahiptir. Bu çalışmada, bilgisayarlarda bulunan seramik işlemci (CPU) ve cep telefonu kartlarından değerli metallerin geri kazanımı amaçlanmıştır. Çalışmada ömürlerinin sonuna gelmiş elektrikli ve elektronik ekipmanlarından (EEE) olan seramik CPU ve telefon kartlarında bulunan değerli metaller fiziksel, hidrometalurji ve pirometalurjik yöntemler kullanılarak elde edilmiştir. Bu değerli metalleri içeren minerallerin yüksek değeri ve sınırlı rezervleri, değerli metallerin kentsel madenciliğini çok çekici kılmaktadır. Uygulanan yöntemler sürecinde değerli metal miktarları ICP-OES ile ölçülmüştür. Çalışmada diğer değerli metallerin yanı sıra seramik CPU’da Altın(Au) oranı yaklaşık olarak 1119 mg/kg olarak bulunmuştur. Atık cep telefon kartlarında ise yaklaşık 54,40 mg/kg Altın(Au) tespit edilmiştir.
Electrical and electronic wastes are one of the biggest solid waste problems today and contain many recyclable materials such as gold. In this study, an adsorbent was synthesized by modifying the valonia tannin polymer with ethylenediamine to increase the electrostatic interaction. The obtained ethylenediamine-modified tannin polymer (ATAR) was characterized by Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and thermogravimetric analysis (TGA), and it was confirmed that the amine group was successfully attached to the main structure within the scope of the synthesis. Under optimum conditions for gold(iii) ion adsorption at varying pH, adsorbent mass, initial concentration, time, and temperature values, the adsorption performance of gold ion-containing solutions was investigated. Adsorption isotherm, kinetic and thermodynamic calculations were made from the data obtained from these experiments, and it was seen that the kinetic equation that best fits the experimental data is intraparticle diffusion and the best-fit isotherm equation is Langmuir's equation. According to the Langmuir isotherm, the monolayer saturation capacity of Au(iii) ions on the ethylenediamine-modified tannin polymer was determined to be 1488.4 mg g⁻¹ at a temperature of 328 K. In the FTIR analysis performed after adsorption, it was determined that the ethylenediamine functional groups actively participated in the adsorption of Au(iii) species and had an effect increasing the adsorption performance besides the polyphenolic groups. In X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS) analyses, it was determined that almost all of the Au(iii) ions were reduced to metallic gold after adsorption. It was observed that the adsorbent showed high performance for the adsorption of Au(iii) from the real leaching solution obtained from electronic wastes.
Waste Electrical and Electronic Equipment (WEEE) are electrical and electronic gadgets known to have reached their end-of-life. They are made of printed circuit boards (PCBs) containing valuable metals like copper, gold, iron, lead nickel, silver, tin and zinc which can leach into the environment when landfilled. Current extraction methods for the recovery and recycling of metals from WEEE uses various solvents which are not selective, releases toxic gases and recover metals in a mixed form which requires further purification steps to recover individual metals. This paper has reviewed the use of inorganic acids, organic acids and designer solvents which do not release toxic gases when used for extraction of metals from WEEE. The results reveal that ionic liquids ae promising solvents for extracting metals.
Platinum (Pt) catalysts are the most practical electrocatalysts; however, their low abundance and high cost severely limit their large-scale applications. Efficient recovery is a key issue to be resolved before the use of Pt-based electrocatalysts can be broadly extended. Herein, the newly designed polyoxometalate [PtII(NH3)4]2[Mo8O26] (Mo8Pt) acts as an ideal recycling medium for renewable and highly effective Pt electrocatalysts. Starting from Mo8Pt, by a facile reduction reaction, the formed Pt/Mo2C/Mo2N@C-N electrocatalyst shows superior electrocatalytic activity as compared to commercial Pt/C (20%) under both acidic and alkaline conditions. Notably, the reaction of Pt/Mo2C/Mo2N@C-N in H2O2 solution can regenerate Mo8Pt for Pt renew-ability. It is also demonstrated that the Pt electrocatalyst can be used for at least five rounds of recycling and regeneration, showing its efficiency and stability as well as its effectiveness. This work highlights a recycling medium strategy to the new generation of renewable Pt-based catalysts.
The aim of this study was to develop cellulose-based, fibrous adsorbents for the selective recovery of gold (Au) and to reveal the adsorption–reduction–attachment–aggregation mechanism. Polyethylenimine (PEI)-functionalized cellulose fibers (PCFs) were fabricated by extruding a mixture of PEI and cellulose into a sulfuric acid solution. To maximize the performance of the PCFs, the amounts of PEI and ethylene glycol diglycidyl ether, a crosslinking agent, were optimized. The maximum uptake of Au(III) by PCFs was 1108.2 ± 58.8 mg/g obtained based on adsorption isotherm experiments. PCFs characterization and mechanistic investigations were carried out using FT-IR, XPS, XRD, FE-SEM, EDX, and HR-TEM. After 0.5 h of Au(III) adsorption on the PCFs, Au(III) was reduced to Au(I) owing to electron transfer when –NH3⁺/−NH2⁺‒, functional groups of PCFs, were oxidized to = NH⁺‒ and = N‒. After 12 h, –NH3⁺/−NH2⁺‒ were oxidized to = N‒, and C–N was oxidized to C[dbnd]O; therefore, Au(I) present on the fibers was reduced to Au(0) owing to the oxidation–reduction reaction. The released nitrogen was detected as NO2⁻ and NO3⁻ in the solution. Subsequently, the Au particles detached from the PCFs, and the aggregated Au particles on the vessel wall were recovered. In addition, the prepared PCFs showed outstanding selectivity for Au(III) in a solution containing the main metals found in electronic waste. PCFs maintain the Au(III) adsorption performance even in the 10 times adsorption-desorption cycles. These results indicated the application potential of PCFs as efficient adsorbents for Au recovery.
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.
This paper presents the experimental results for the leaching of printed circuit boards (PCB) from obsolete computers for extracting and recovering tin and copper by means of leaching followed by precipitation. Printed circuit boards were dismantled, cut into small pieces, and fed into a cylinder mill. The powder obtained was leached by using the aqueous solutions 2.18N H2SO4, 2.18N H2SO4 + 3.0N HCl, 3.0N HCl, and 3.0N HCl + 1.0N HNO3. The lowest values for the percentage of metal extraction were obtained with 2.18N H2SO4 (2.7% for Sn and lower than 0.01% for Cu), while the 3.0N HCl + 1.0N HNO3 leach system exhibited an extraction of 98% for Sn and 93% for Cu. Precipitates were obtained at different pH values by neutralizing the leach liquors using NaOH. The 3.0N HCl + 1.0N HNO3 leach system presented the highest recovery values from the powder feed (84.1% for Sn and 31.9% for Cu), as well as from the leach liquor (85.8% for Sn and 34.3% for Cu).
Previous studies have shown that various microorganisms can enhance the dissolution of silicate minerals at low (<5) or high (>8) pH. However, it was not known if they can have an effect at near-neutral pH. Almost half of 17 isolates examined in this study stimulated bytownite dissolution at near-neutral pH while in a resting state in buffered glucose. Most of the isolates found to stimulate dissolution also oxidized glucose to gluconic acid. More detailed analysis with one of these isolates suggested that this partial oxidation was the predominant, if not sole, mechanism of enhanced dissolution. Enhanced dissolution did not require direct contact between the dissolving mineral and the bacteria. Gluconate-promoted dissolution was also observed with other silicate minerals such as albite, quartz, and kaolinite.
A 3-phase computational ∞uid dynamics (CFD) model for heap bioleaching of chalcocite is investigated to identify and understand the efiect of oxygen ∞ow during air sparging. The study uses an existing one-dimensional model of liquid ∞ow, bacterial transport (including attachment/detachment of bacteria to ore particles), and the depletion of a copper-sulphide, coupled with a two-dimensional (2D) model of gas ∞ow in the heap. The CFD model includes the efiects of oxygen and ferrous ion consumption, coupled with leaching of copper-sulphide via a shrinking core model. The model is used to investigate the 2D efiects of air ∞ow in heap bioleaching with regard to oxygen limitation.
According to the properties of bioleaching solutions of printed circuit boards (PCBs), copper in the leaching solution were recovery by ion exchange with macroporous styrene iminodiacetic acid chelating resin D401. The bed height of resin, flow rate, pH value on copper adsorption had been studied. Work Exchange Capacity (WEC) of copper increased with increasing bed height of resin and flow rate. The copper WEC of 7.88 mg/mL can be obtained with pH 2.5 and 200 mm bed height at flow rate of 2 mL/min. More than 99.5% of copper could be eluted from loaded resin to get the copper enriched solution by 1.0 M sulphuric acid at A/R ratio 20 in at flow rate of 2 mL/min. Results of the present investigation indicated that D401 resin can efficiently recovery copper from bioleaching solution of PCBs.
Bioleaching of spent catalyst were carried out using Acidithiobacillus type of microorganisms. Various leaching parameters like contact time, Fe(II) concentration, particle size, pulp densities, pH and temperature were studied in details. All the four metal ions like Ni, V, Mo and Al followed dual kinetics, i.e., initial faster followed by slower rate. The leaching kinetics of Ni and V observed to be higher compared to that of Mo and Al. The thermodynamic parameters like ΔG, ΔH and ΔS for all metals were calculated. The leaching kinetics followed first order rate. Rates of dissolution of Al, V and Ni increased, and Mo decreased with increase of Fe(II) addition whereas that of all metals decreased with increase of pulp density and particle size. Leaching kinetics of Al, Mo, V increased with decrease of pH. Variation of initial pH of the leaching medium showed an inadequate effect on Ni dissolution. The rate determining step found to be pore diffusion controlled. The correlation between observed and theoretical values of leaching efficiency for different parameters was evaluated using Multi-Linear Regression Analyses which showed the significance of the leaching. A total of 5 factors were evaluated by data reduction technique using Principal Component Analysis.
Cyanide has been recognized for a long time as a powerful lixiviant for gold and silver, forming very stable cyano complexes with both metals. While cyanide is very effective in leaching free milling ores, there are certain classes of gold and silver ores (i.e., carbonaceous, pyritic. arsenical, manganiferous, cuperferous) that are considered refractory to conventional cyanidation dissolution. Recently there has been considerable effort directed towards new and improved reagents for leaching these difficult-to-treat ores and concentrates. A large portion of this effort has been devoted to finding alternative lixiviants that might compete with conventional cyanidation. Furthermore, there is a general interest in developing non-toxic environmentally safe substitutes for cyanide.There are a number of reagents that form stable complexes with gold and silver e.g., thiourea, thiosulfate, halides, malononitrile, acetonitrile and polysulfides. The chemistry of gold and silver dissolution using alternative lixiviants is discussed in this paper. Special emphasis is given to the application of Eh-pH diagrams to interpret the dissolution behavior.
Biomining is currently used successfully for the commercial-scale recovery of met- als such as copper, cobalt, and gold from their ores. The mechanism of metal extraction is mainly chemistry-driven and is due to the action of a combination of ferric and hydrogen ions, depending on the type of mineral. These ions are produced by the activity of chemolithotrophic microorganisms that use either iron or sulfur as their energy source and grow in highly acidic conditions. Therefore, metal extraction is a combination of chemistry and microbiology. The mixture of organisms present may vary between processes and is highly dependent on the temperature at which mineral oxidation takes place. In general, rel- atively low-efficiency dump and heap irrigation processes are used for base metal recovery, while the biooxidation of difficult-to-treat gold-bearing arsenopyrite concentrates is carried out in highly aerated stirred-tank reactors. Bioleaching reactions, the debate as to whether the reactions are direct or indirect, the role of microorganisms, and the types of processes by which metals are extracted from their ores are described. In addition, some new processes under development and the challenges that they present are discussed.
The rapidly increasing consumption of electric-electronic equipments leads to the increase in their quantity in municipal wastes. Notwithstanding the environmental pollution potential of e-wastes, e-wastes with their high content of base and precious metals in particular are regarded as a potential secondary resource when compared with ores. For the recovery of metals from e-wastes, various treatment options based on conventional pyhsical, hydrometallurgical, biohydrometallurgical and pyrometallurgical processes are proposed. Electronic wastes are composed inherently of non-homogenous and complex set of materials and components, which presents difficulties for their recycling. Furthermore, the decrease in the precious metal content of e-wastes adversely affects the economics of recovery/recycling processes. Research and development of environmentally acceptable and low cost processes are, therefore, required for the extraction of metals from e-wastes. Treatment of e- wastes for metal recovery is also of importance for the preservation and effective exploitation of our natural/primary metal resources.
In this study, physical, chemical and hazardous characteristics of computer printed circuit boards (PCBs) were studied. PCBs manually obtained from end-of-life computers of various brands were subjected to size reduction down to -3.35 mm in two stages of crushing. Size fractions were obtained by dry-sieving and used to determine the liberation size of metals. Furthermore, hazardous characteristics of PCBs were investigated using standard protocols including TCLP (Toxicity Characteristic Leaching Procedure) and SPLP (Synthetic Precipitation Leaching Procedure) tests of US Environmental Agency (USEPA), ASTM D-3987 and EN 12457-2 tests to simulate different environmental scenario. The tests have shown that printed circuit boards can be classified as hazardous wastes. Copper content of PCBs was found to be 15.5 per cent. © (2010) by the Australasian Institute for Mining and Metallurgy (AusIMM).
Bioleaching/biooxidation is essentially a dissolution process with the involvement of acidophilic bacteria acting as the "catalyst" to accelerate the dissolution of metals from sulfide minerals. The contribution of bacteria to the metal dissolution is closely controlled by the growth of bacteria, which is itself affected by the physico-chemical conditions within the bioleaching environment. There are a number of operating parameters controlling bioleaching processes, which are required to be maintained within a certain range in the leaching environment whereby the activity of bacteria with the resultant oxidation of sulfide minerals can be optimized. In this regard temperature, acidity, oxidizing conditions, availability of nutrients, oxygen and carbon dioxide, surface area and presence of toxic ions are of prime importance for control and optimization of bioleaching of sulfide ores/concentrates. Bioleaching processes are temperature and pH dependent with optimum metal dissolution occurring in a particular range where the bacterial strain is most active e.g. mesophiles at 35-40°C and pH 1.6-2.0. Provision of nutrient salts is required to maintain the optimum growth and hence metal dissolution with the quantity of nutrients apparently being dependent on the availability of substrate i.e. head grade/pulp density of an ore/concentrate. Oxygen transfer is one of the most critical factors since the oxygen levels below 1-2 mg/l may adversely affect the oxidizing activity of bacteria. Bioleaching rate tends to improve with increasing the surface area at low pulp densities but, in practice, the pulp density is limited to ~20% w/v. Increasing concentrations of ions such as Cl -may also adversely affect the oxidative activity of bacteria.
Leaching studies using spent petroleum catalyst containing Ni, V and Mo were carried out using two different acidophiles, iron oxidizing (IOB) and sulfur oxidizing (SOB) bacteria. XRD analysis proved the existence of V in oxide form, Ni in sulfide form, Mo both in oxide and sulfide forms, and sulfur in elemental state. Both bacteria showed similar leaching kinetics at the same leaching parameters, such as pH, nutrient concentration, pulp density, particle size and temperature. The dissolution kinetics for Ni and V was much higher than Mo. Bioleaching kinetics was observed to follow dual rates, initially faster followed by a slower rate. So, dissolution mechanism was based on surface- and pore-diffusion rate. The dissolution process was found to follow 1st order kinetics. Unified dissolution rate kinetics equations were developed using 1st order rate kinetics. Various thermodynamic parameters were also calculated. Rate determining step for both the bacteria were evaluated and the average D1 (surface) and D2 (pore) values were found to be around 7 × 10− 9 and 1 × 10− 10 cm2 respectively. The lower value of D2 suggested that the pore diffusion is the rate determining step during bioleaching process.
In plants for the recycling of waste electric and electronic equipment (WEEE) as well as for conventional mineral processing, the comminution equipment dictates whether and how the specifications for the separation and sorting of the feed material are achieved. For the comminution of WEEE, the machines must meet specific requirements in respect of size reduction, insensitivity to solid components and flexibility for adapting to different feed materials. To liberate single components, composites must be broken up, but harmful components that are contaminated with pollutants should not, however, be destroyed completely. With the Rotorshredder RS and Rotor Impact Mill RPMV presented here, BHS Sonthofen supplies two machines to achieve the main objectives of WEEE processing - i.e. effective size reduction and gentle desintegration of composites to liberate the individual components. The achievement of these aims in combination with an extremely flexible and at the same time cost-efficient operation represents a leap in technology compared to conventional systems.
Nowadays, the pyrometallurgical treatment in copper smelters is the common process for the recycling of metals from the electronic scrap. Furthermore the European Directive on the Waste from Electrical and Electronic Equipment (WEEE) and the Directive on the Restriction of Hazardous Substances (RoHS), increase the importance of electronic scrap recycling. Besides these a high amount of plastic and inert components in these materials leads to problems at the processing. An optimisation concerning the internal recovery and the high amount of plastic is necessary to reach the recycling quota of the European directive. The majority of the scrap is treated mechanically in order to separate in a first step plastics from metals, iron from nonferrous metals and harmful substances from valuable materials. But the quality of the different fraction often rather low and further treatment leads to higher costs. Therefore an interaction between mechanical treatment and metallurgical processing should be realised. The Christian Doppler Laboratory for Secondary Metallurgy of Nonferrous Metals at the Institute of Nonferrous Metallurgy at the University of Leoben carried out investigations concerning the optimisation of the metallurgical recycling and the treatment of the input materials especially of printed circuit boards.
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.
Sustainability and the environment are important and topical themes currently. There is a generally growing awareness of resource consumption, possible resource depletion, and the polluting effects of indiscriminate dumping at the end of the useful life of an item, as well as of the pollution caused by producing items and making them available to the end user. The issues are complex and interlinked. In order to improve understanding, it is important to obtain holistic and quantitative perspectives. To help in quantification, concepts such as the ecological and carbon footprints have been defined and are in common use. This paper introduces the concept of a material footprint to help quantify the material resource usage in an item, in terms of globally available resources. It allows comparison of various items to one another in terms of their use of material resources. Thus the types of items available for recycling can be ranked to determine recycling priorities. The material footprint can also help in determining recycling priorities for the various materials in the items. Several examples are used as illustration. It is shown that recycling of printed circuit boards is especially worthwhile. Printed circuit boards are complex and heterogeneous from a materials recycling perspective. The paper describes the complexities of recycling these boards, but also points out the benefits. An overview is given of currently available metallurgical technologies for such recycling. It is shown that in these processes there are many factors that affect the environment It thus remains difficult to determine the total impact of recycling on the environment holistically. Possibly some benefits are to be gained in the Southern African context by better integration between secondary material processors and primary metal producers. © The Southern African Institute of Mining and Metallurgy, 2008.
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.
Material and energy resource consumption is on the rise in both the industrialized and developing world (e.g., countries like India and China). In order to sustain this growth and provide resources for future generations, there is a need to design products that are easy to recover and recondition, thus enabling multiple use cycles. Processes are needed that can achieve this multi-use while producing zero (or very near zero) waste. There exist a number of barriers and challenges to achieving this vision of multi-use with zero waste; one such challenge is the development of a product recovery infrastructure that will minimize short-term impacts due to existing products and will be robust enough to recover products of the future. This paper identifies the barriers to developing such a recovery and reuse infrastructure. The aim is to achieve product multi-use and zero waste.
Electronic waste, or e-waste, is an emerging problem as well as a business opportunity of increasing significance, given the volumes of e-waste being generated and the content of both toxic and valuable materials in them. The fraction including iron, copper, aluminium, gold and other metals in e-waste is over 60%, while pollutants comprise 2.70%. Given the high toxicity of these pollutants especially when burned or recycled in uncontrolled environments, the Basel Convention has identified e-waste as hazardous, and developed a framework for controls on transboundary movement of such waste. The Basel Ban, an amendment to the Basel Convention that has not yet come into force, would go one step further by prohibiting the export of e-waste from developed to industrializing countries. Section 1 of this paper gives readers an overview on the e-waste topic—how e-waste is defined, what it is composed of and which methods can be applied to estimate the quantity of e-waste generated. Considering only PCs in use, by one estimate, at least 100 million PCs became obsolete in 2004. Not surprisingly, waste electrical and electronic equipment (WEEE) today already constitutes 8% of municipal waste and is one of the fastest growing waste fractions. Section 2 provides insight into the legislation and initiatives intended to help manage these growing quantities of e-waste. Extended Producer Responsibility (EPR) is being propagated as a new
A novel energy-saving hydrometallurgical recovery process for copper from electronic scrap employing the Cu(I)-ammine complex has been presented on the basis of a thermodynamic consideration. In order to experimentally explore the feasibility of the leaching stage in this process, the copper leaching behavior from a printed circuit board (PCB) in ammoniacal alkaline solutions has been investigated under a nitrogen atmosphere. Copper in PCB was oxidized by Cu(II) to form Cu(I)-ammine complex ions. The leaching reaction can be expressed as: Cu + Cu(NH3)(4)(2+) = 2Cu(NH3)(2+). The Cu(II)-ammine complex significantly enhanced the leaching rate, while the Cu(I)-ammine complex slightly depressed it. Crushing of the PCB effectively enhanced the leaching rate, because the exposed metallic copper area is increased by the crushing. The effect of temperature on the leaching rate was insignificant. Consequently, the feasibility of the leaching stage in the proposed copper recovery process has been experimentally confirmed.
A suitable method has been proposed to purify a copper electrolyte within the framework of an energy-saving cuprous electrowinning process. In this method, the impurities are selectively removed from the electrolyte that contains a large amount of cuprous ion in an ammoniacal alkaline solution at pH 9–11. Among these impurities, precious metals such as silver are removed by cementation with copper powder. Other metals such as cobalt, nickel, zinc, aluminum, manganese, lead etc. are removed selectively by solvent extraction using an oxine-type chelating extractant (LIX 26). Equilibrium and kinetic studies for the extraction of cobalt, nickel, and zinc were performed under different experimental conditions with or without synergistic agents. Loading tests of LIX 26 were carried out, and McCabe–Thiele diagrams were constructed for stage calculations for these metals. The metals are extracted with LIX 26 via a cation exchange mechanism, and slope analysis suggested that the nickel and zinc chelates, extracted by LIX 26, were 1:2 metal:reagent species. The loaded organic is regenerated by stripping the metals completely using dilute sulfuric acid. Copper loss in the purification stages is about 10% because monovalent copper is not extracted with LIX 26 from the ammoniacal alkaline solution.
Of the various mechanical metal recycling techniques employed in electronic scrap processing, air table separation, magnetic separation and eddy current separation technolo gies have proved to be the most commercially successful. In addition, it is very important, even indispensable, that, prior to the physical processing of electronic scrap, selective dis mantling and identification (if necessary) be employed. It is, however, recognized that problems such as process optimiza tion and organics handling remain and that in-depth charac terization of electronic scrap will be essential in this context.
Purpose
This paper aims to present a review carried out under DEFRA‐funded project WRT208, describing: the composition of WEEE, current treatment technologies, emerging technologies and research.
Design/methodology/approach
This paper summarises the output from the first part of the project. It provides information on the composition of WEEE and an extensive survey of technologies relevant to materials recycling from WEEE. A series of further papers will be published from this research project.
Findings
WEEE has been identified as one of the fastest growing sources of waste in the EU, and is estimated to be increasing by 16‐28 per cent every five years. Within each sector a complex set of heterogeneous secondary wastes is created. Although treatment requirements are complicated, the sources from any one sector possess many common characteristics. However, there exist huge variations in the nature of electronic wastes between sectors, and treatment regimes appropriate for one cannot be readily transferred to another.
Research limitations/implications
A very large number of treatment technologies are available, both established and emerging, that singly and in combination could address the specific needs of each sector. However, no single set of treatment methods can be applied universally.
Originality/value
This paper is the first part of work leading to the development of technical strategies and methodologies for reprocessing WEEE into primary and secondary products, and where possible the recovery of higher added‐value components and materials.
The electrochemical reduction of gold thiosulfate has been studied and compared to the reduction of gold cyanide. Gold thiosulfate is a potential replacement for gold cyanide in electro and electroless plating baths. Gold thiosulfate has a more positive reduction potential than gold cyanide and eliminates the use of cyanide. The standard heterogeneous rate constant, transfer coefficient, and diffusion coefficient for gold thiosulfate reduction were found to be 1.58 >< 1O cm/s, 0.23 and 7 x 10 cm2/s, respectively. The effect of sulfite as an additive to gold thiosulfate solutions was examined.
Abstract-A new hydrometallurgical recovery technology of leaching gold and silver from E-waste has been presented by Lime Sulfur Synthetic Solution (LSSS) method. The influences of sodium sulfite concentration, divalent copper ions concentration, aqueous ammonia concentration, reaction temperature and leaching time were investigated experimentally. The results indicated that it was favorable for gold and silver leaching when solid-liquid ratio was 1:3 , leaching time 2.5h, at temperature of 318K, under the condition of Na2SO3 0.1mol/I, Cu2+ 0.03 mol/I, NH4+ 0.5 mol/I solution, pH=10, for 5g e-waste power. The best leaching rate of gold and silver reached about 92% and 90% in this favorably experimental condition, which suggested this technological viability for gold and silver recovery. On the basis of practice, LSSS method has the advantages of non-toxic, low-cost, simple process, easy to operate and was expected to be a great potential method in recycling gold and silver from e-waste.
A culture independent molecular methodology was used to investigate the bacterial and archaeal microbial dynamics of Ieachate collected from a 60°C chalcopyrite bioleaching column inoculated with a known microbial consortium. A 16S rRNA gene clone library was constructed for both the bacterial and archaeal populations in the leachate from the column. PCR-RFLP analysis of these clone libraries indicate species dominance and generally low species diversity.
The chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans has been known as an aerobe that respires on iron and sulfur. Here we show that the bacterium could chemolithoautotrophically
grow not only on H2/O2 under aerobic conditions but also on H2/Fe3+, H2/S0, or S0/Fe3+ under anaerobic conditions. Anaerobic respiration using Fe3+ or S0 as an electron acceptor and H2 or S0 as an electron donor serves as a primary energy source of the bacterium. Anaerobic respiration based on reduction of Fe3+ induced the bacterium to synthesize significant amounts of a c-type cytochrome that was purified as an acid-stable and soluble 28-kDa monomer. The purified cytochrome in the oxidized form
was reduced in the presence of the crude extract, and the reduced cytochrome was reoxidized by Fe3+. Respiration based on reduction of Fe3+ coupled to oxidation of a c-type cytochrome may be involved in the primary mechanism of energy production in the bacterium on anaerobic iron respiration.
The present investigation aimed to study the thermophilic bioleaching of spent catalyst with different size fractions in modified Kelly medium with and without iron supplement using Sulfolobus metallicus. The results obtained showed Ni and Al recovery ranging from 94 to 97% and 54 to 59% respectively, with a lower recovery of Mo and V. The difference in the leaching yield in iron free and iron supplemented growth medium at all size fractions did not show much difference stating iron free modified Kelly medium to be a suitable growth medium for bioleaching of spent catalyst. However, the leaching yield obtained from different size fractions also suggested that the particle size >212 mm could be conducive for leaching of desired metal values without any problem. The redox potential profile during the bioleaching experiments and planktonic cell count ranging from 10(6) to 10(8) cells mL(-1) showed a luxuriant growth performance of the microorganisms in the experiments in iron free modified Kelly medium.
The demand for metals is ever increasing with the advancement of the industrialized world. On the other hand, worldwide reserves of high grade ores are close to depletion. However, there exists a large reserve of metals in low and lean grade ores and other secondary sources. Metal recovery from low and lean grade ores using conventional techniques such as pyrometallurgy, etc. requires high energy and capital inputs which often result in the secondary environmental pollution. Thus, there is a need to utilize more efficient technologies to recover metals. Biohydrometallurgy, which exploits microbiological processes to recover metal ions, is regarded as one of the most promising and revolutionary biotechnologies. The products of such processes are dissolved in aqueous solution, thereby rendering them more amenable to containment, treatment and recovery. On top of this, biohydrometallurgy can be conducted under mild conditions, usually without the use of any toxic chemicals. Consequently, the application of biohydrometallurgy in the recovery of metals from lean grade ores and wastes has made it an eco-friendly technology for enhanced metal production. This paper reviews the current status of biohydrometallurgy of low grade ores around the world. Particular attention is focused on the bioleaching of black shale ore and its metallogenic diversity in the world. The review assesses the status of bioprocesssing of metals to evaluate promising developments. Bioleaching of metals is comprehensively reviewed with the emphasis on the contribution of microbial community, especially fungal bioleaching coupled with ultrasound treatment. In this manuscript, the principles of bioleaching, their mechanisms, and commercial applications are presented. The case studies and future technology directions are also reviewed
Present paper focuses on the selective recovery of copper from the enriched ground printed circuit boards (PCBs) using leaching and solvent extraction. The metal-enriched ground sample obtained from the beneficiation of the sized PCBs in a laboratory scale column type air separator contained mainly 49.3% Cu, 3.83% Fe, 1.51% Ni, 5.45% Sn, 4.71% Pb, and 1.85% Zn. The leaching of the enriched sample with 3.5 mol/L nitric acid dissolved 99% copper along with other metals at 323 K temperature and 120 g/L pulp density in 1 h time. The composition of the leach liquor with wash solution was found to be 42.11 g/L Cu, 2.12 g/L Fe, 4.02 g/L Pb, 1.58 g/L Zn, and 0.4 g/L Ni. The McCabe–Thiele plot indicated the requirements of three counter-current stages for maximum extraction of copper from the leach liquor at pH 1.5 using 30, 40, and 50% (v/v) LIX 984 N at the phase ratios (A/O) of 1:3, 1:2, and 1:1.5, respectively. The counter-current simulation studies show the selective extraction of 99.7% copper from the leach liquor feed of 1.5 pH in three stages with 50% LIX 984 N at A/O phase ratio of 1:1.5. The stripping of copper from the loaded organic with sulfuric acid produced copper sulfate solution from which copper metal/powder could be recovered by electrolysis/ hydrogen reduction.
Penicicllium variabile P16, encapsulated in agar or calcium alginate, produced gluconic acid in repeated batch shake-flask cultures. Agar-encapsulated mycelium produced 21% more gluconic acid than Ca-alginate-encapsulated fungus, and was utilized in experiments for rock phosphate solubilization. The latter was closely related to gluconic acid production, which was affected by the presence of rock phosphate. Maximum amounts of dissolved P (0.226 gl−1 batch−1) were found at 14.0 gl−1 rock phosphate, but the solubilization efficiency was higher at 3.5 gl−1 rock phosphate. Gluconic acid productivity pattern and the degree of phosphate solubilization were not influenced by decreasing the glucose concentration in the cultivation medium from 80 to 25 gl−1. Encapsulated fungal cells systems could substitute for chemical solubilization of rock phosphate and could be applied as soil microbial inoculants.
In the present experimental study, the pressure drop of the two-phase dry-plug flow (dry wall condition at the gas portions) in round mini-channels was investigated. The air–water mixtures were flowed through the round mini-channels made of polyurethane and Teflon, respectively, with their inner diameters ranging from 1.62 to 2.16 mm. In the dry-plug flow regime, the pressure drop measured became larger either by increasing the liquid superficial velocity or by decreasing the gas superficial velocity due to the increase of the number of the moving contact lines in the test section. In such a case, the role of the moving contact lines turned out to be significant. Therefore, a pressure drop model of dry-plug flow was proposed through modification of the dynamic contact angle analysis taking account of the energy dissipation by the moving contact lines, which represents the experimental data within the mean deviation of 4%.