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Potential bioleaching developments towards commercial reality: Turkish metal mining’s future

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Abstract

Bioleaching/biooxidation processes have been commercially applied for the recovery of copper, gold and uranium for two decades. Concerning these processes by mesophiles and thermophiles, academic and commercial applications have been extensively increasing in laboratory, pilot, full scale operations. Several bacterial species are used in many commercial operations in South America, Australia, South Africa, India, China. In near future Turkish copper and gold mines will probably use these processes as commercial applications due to the economical and environmental reasons. Therefore, the close relationship between biooxidation and cyanidation with mineralogical composition is important for the commercial selection of these processes. In addition to lab tests, full-scale feasibility studies being performed to determine the impacts of climate and environmental factors for potential mining areas will also be completed in the near future. This paper presents an investigation of the potential bioleaching developments in Turkey.

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... The biooxidation of sulfide minerals in continuous stirred tank reactors (CSTR) has become an important method for the pretreatment of refractory gold ore (Chandraprabha et al., 2002;Akcil, 2004;Watling, 2008). Industrial-scale biooxidation was first carried out in South Africa (Fairview) in 1986 as pretreatment for refractory gold concentrates. ...
... Industrial-scale biooxidation was first carried out in South Africa (Fairview) in 1986 as pretreatment for refractory gold concentrates. Currently, CSTR biooxidation is being used successfully in commercial operation in countries such Brazil, Peru, Australia, Ghana, South Africa, India and China (Gonzalez et al., 2003;Akcil, 2004;Sand and Gehrke, 2006;Watling, 2008). The growth of this technology is promising, and new projects are currently in the research and engineering stages (Van Niekerk, 2009). ...
... Biooxidation is catalyzed by bacteria that oxidize reduced iron and sulfur compounds. In industrial applications of mining and metallurgy, cultures of mesophiles or moderate thermophiles are widely used for the oxidation of sulfide ores (Rossi, 1990;Rawlings et al., 2003;Akcil, 2004;Sand and Gehrke, 2006). Such microorganisms include the iron-and sulfur-oxidizing Acidithiobacillus ferrooxidans, the sulfur-oxidizing Acidithiobacillus thiooxidans and Acidithiobacillus caldus, and the iron-oxidizing Leptospirillum ferrooxidans and Leptospirillum ferriphilum. ...
... Bu da kontrolü oldukça hassas ve maliyetli bir sistem zorunluluğu gerektirmektedir. Nikel gibi değerli fakat cevherleşme açısından düşük tenörlü yataklar için, son 50 yıl içerisinde biyoteknolojik gelişmelere paralel olarak madencilik endüstrisinde biyolojik kazanım teknikleri büyük oranda önem kazanmış ve endüstride gittikçe gelişen bir uygulama alanı bulmuştur [38][39][40] ...
... Nikel gibi değerli fakat cevherleşme açısından düşük tenörlü yataklar için, son 50 yıl içerisinde biyoteknolojik gelişmelere paralel olarak madencilik endüstrisinde biyolojik kazanım teknikleri büyük oranda önem kazanmış ve endüstride gittikçe gelişen bir uygulama alanı bulmuştur [38]. Nikel içeren cevher ve artıkların biyoliçi üzerine yapılmış bilimsel çalışmalar Tablo 3'de gösterilmiştir. ...
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ÖZET Uzun zamandır bir ihtiyaç kaynağı olan nikel, teknolojinin gelişmesi ile yeni ürünlerin önemli bir hammaddesi olmuştur. Cevherleşme bakımından sadece %1-3 oranında Ni içeriğine sahip yataklar üretilebilir konumundadır. Dünya nikel kaynaklarının %28'i sülfürlü ve %72'si lateritik yataklardan oluşmaktadır. Ancak, birincil nikel üretimi söz konusu olduğunda sülfürlü kaynakların kullanımı %58 olup, lateritik kaynaklar ise %42 gibi düşük bir değerde kalmaktadır. Bunun yanı sıra, sülfürlü yataklardaki rezervlerin azalmış olması da lateritik yatakların önemini artırmaktadır. Lateritik nikel cevherlerinden nikel kazanımında en basit geleneksel madencilik, cevher yatağından cevherin çıkarılarak kırma ve öğütme gibi ufalama işleminden geçirilmesi ve daha sonra cevherden metalleri kazanmak için pirometalurjik ve/veya hidrometalurjik yöntemlerin kullanılmasını kapsamaktadır. Cevherden metallerin geleneksel kazanımında yüksek sıcaklıklar (pirometalurji) ve kimyasallar (hidrometalurji) kullanılmakta olup, bu tekniklerin çevresel ve sağlık yönünden zararları bulunmaktadır. Bu nedenle, son 50 yıl içerisinde biyoteknolojik gelişmelerden dolayı madencilik endüstrisinde biyolojik kazanım teknikleri büyük oranda önem kazanmış ve endüstride giderek artan bir uygulama alanı bulmuştur. Biyoliç, düşük tenörlü cevherlerden metallerin kazanılmasında basit, ekonomik ve çevreye dost bir yöntemdir. Lateritik nikel cevherleri oldukça yüksek oranda demir içermesinden dolayı, hidrometalurjik proseslerde H 2 SO 4 tüketimi önemli şekilde artmaktadır. Lateritik nikel cevherinden nikelin kazanımında biyoliç yönteminin uygulanması bu asit tüketiminin ekonomik olarak olumsuz etkilerini azaltması ve ayrıca çevresel açıdan daha kontrollü hale getirmesini sağlayabilir. Bu yazıda, lateritik cevherlerden nikel kazanımında biyoliç uygulamaları ve son gelişmeler incelenmiştir. ABSTRACT Upon progress of technology, nickel has been considered as an important raw material for development of new products. Ore deposits with only 1-3% Ni content are suitable for production. About 72% of the world's nickel resources are laterites. The remaining 28% are sulphides. However, about 58% of the world's primary nickel production comes from nickel sulphide and about 42% of mined nickel comes from nickel laterite deposits. Moreover decrease in sulphide nickel reserves makes lateritic deposits come to the forefront in nickel production. The most common technique in processing of lateritic nickel ores involves traditional mining of the ore, crushing and grinding of the ore after its removal from the ore deposit and the use of pyrometallurgical and/or hydrometallurgical techniques to extract metals from the ore. In traditional extraction of metals from ores, high temperatures (pyrometallurgy) and chemicals (hydrometallurgy) are used which have detrimental effects on environment and human health. Consequently, biological extraction methods gained significant importance due to increase in biotechnological developments and found a growing application area in the mining industry for the last 50 years. Bioleaching is a simple, economical and environmentally friendly technique in leaching of metals from low grade ores. As lateritic nickel ores possess very high amounts of iron, H 2 SO 4 consumption in hydrometallurgical processes increases significantly. The use of bioleaching technique for the extraction of nickel from lateritic nickel ores could reduce the inferior economical effects of acid usage and make the process to be performed in a more controlled way. In this paper, recent developments and bioleaching applications in the nickel recovery from lateritic ores were investigated.
... Even in the 21st century, research has dealt with other possibilities of applying bioleaching in practice using various bacterial cultures [1]. Ore deposits with high concentrations of metals are becoming smaller and in the future rocks with a lower percentage of metals or waste will be used more and more often [2,3]. Globally, up to 10% of copper is obtained by leaching with the help of microorganisms. ...
... Before starting the experiments, the bioleaching parameters were selected on the basis of research [42,47,48]. The advantage of the bioreactor was maintaining constant values throughout the leaching process: temperature (30 • C), pH (2), and agitation (150 rpm). Steady pH values were achieved with an automatic dispenser of 5M H 2 SO 4 and in the case of exceeding the value with an alkaline solution of 0.4M NaOH. ...
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Globally, the amounts of metal ore deposits have been declining, so the research directions investigating the extraction of metals from materials that are classified as waste are gaining more importance every year. High concentrations of Cu, Pb, Zn, and Fe were analyzed in the sludge sediment (Zlaté Hory, Czech Republic), which is a waste product of the mining industry. In the bioleaching process, bacterial cells have been established as being able to convert metals from solid to liquid phase. However, the most important parameters of bioleaching are particle size, pH, and pulp density, thus our research focused on their optimization. The acidophilic and mesophilic bacteria Acidithiobacillus ferrooxidans were applied due to the high Fe content in the sample. The recovery of metals in the leachate was determined by F-AAS and the residual metal concentrations in the waste fraction were analyzed by XRF. The grain size fractions <40 µm –200 µm were investigated. The atomic absorption spectrometry (AAS) results show that the highest Fe (76.48%), Cu (82.01%), and Pb (88.90%) recoveries were obtained at particle size of 71–100 μm. Zn was dissolved for all fractions above 90%. Experiments with different pH values were performed at a pH of 1.6–2.0. The highest dissolution rates of Zn, Fe, and Cu were achieved with a suspension pH of 1.8, where 98.73% of Zn, 85.42% of Fe, and 96.44% of Cu were recovered. Due to the high percentage dissolution of metals, experiments were performed under pilot conditions in a bioreactor at a pulp density of 2.5% and 4.2% (w/v). From an economic point of view, the leaching time of 28 days was evaluated as sufficient.
... Introduction 7 It is widely accepted that, in many cases, the heavy metals 8 wrapped in complex sulphide ores are difficult, not-environment- 9 friendly and costly to be leached with conventional mineral 10 processing methods [1]. With the depletion of the easy-to-process 11 ores, the energy costs and the growing movement toward 12 sustainable mining are increasing. ...
... The 17 technology and technique of the bioleaching, oxidation and 18 complexation processes, which are supported and promoted by 19 the developments in the fields of hydrometallurgy, geology, 20 microbiology, chemical analysis, mineralogy, surface science and 21 molecular biology. These have been applied and employed widely 22 for the recovery of the heavy metals from sulfuric minerals and 23 ores, such as copper, nickel, zinc, cobalt and uranium [4][5][6][7]. 24 Operation and applications of biohydrometallurgy in industries 25 are artificially divided into two terms, bioleaching and bioox- 26 idation. The first term is related to the solubilization of base metals 27 such as copper, nickel, and zinc from the ores, whereas 28 biooxidation is used for the bioleached solubilized metals which 29 are wrapped, or locked, in sulfide minerals, in most cases, iron and 30 arsenic, and some precious metal, typically gold and silver [8]. ...
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This review outlines classic and current research, scientific documents and research achievements in bioleaching, particularly in respect of the bioleaching of chalcopyrite and pyrite. The diversity and commonality of the microbial leaching process can be easily studied through comparing the bioleaching mechanism and the application of these two metal sulfides. The crystal, electronic and surface structures of chalcopyrite and pyrite are summarized in detail in this paper. It determines the specific and complicated interaction pathways, kinetics of the atmospheric/aqueous oxidation, and the control process of bioleaching of the minerals as the precondition. Bioleaching of metal sulfides is performed by a diverse group of microorganisms and microbial communities. The species of the bacteria which have a significant effect on leaching ores are miraculously diverse. The newly identified acidophilic microorganisms with unique characteristics for efficient bioleaching of sulfidic minerals are increasing sharply. The cell-to-cell communication mechanisms, which are still implicit, elusive and intangible at present day, have gradually become a research hotspot. The different mineralogy characteristics and the acid solubility of the metal sulfides (e.g., chalcopyrite and pyrite) cause two different dissolution pathways, the thiosulfate and the polysulfide pathways. The bioleaching mechanisms are categorized by contact (an electrostatic attachment) and noncontact (planktonic) process, with emphasis on the produce of extracellular polymeric substances and formation of biofilm on the surface of the metal sulfides in this paper. The division of the direct and indirect effect are not adopted due to the redox chain, the reduction of the ferric iron and oxidation of the ferrous iron. The molecular oxygen is reduced by the electrons extracted from the specific metal sulfide, via a redox chain forming a supercomplex spanning the periplasmic space and connecting both outer and inner membrane. The passivation of the mineral surface can obviously hinder the dissolution of metal sulfides during the bioleaching process, which is significantly affected by the kinetic model, microenvironment on the surface of ore and the leach conditions, such as temperature, pH and Eh. The new development of mechanism research, enhanced and intensified technologies on the bioleaching of chalcopyrite and pyrite, are conducted and summarized from the different branches of natural science. Some are depicted and explained based on molecular level in this paper. Catalyst and catalytic mechanisms in bioleaching and biooxidation for this two sulfide minerals have been concluded and applied for several decades, the continuous emergence of the new material and technology are also gradually applied into the biohydrometallurgy. The industrial applications of the bioleaching on chalcopyrite and pyrite are totally based on the understanding of the interaction mechanism between microbes and minerals, the optimization of ore leaching conditions and the development of new material and the leaching equipment. It is not incredible and unimaginable to take a different bioleaching process and diagram to deal with the two sulfuric metals, which is vital to succeed in elevating the leaching rate of copper.
... En Ecuador no se realiza pretratamiento a estas menas refractarias de manera comercial, razón por la que se vuelve importante esta investigación a nivel Nacional, debido a que se cree que existen perdidas de oro y la biooxidación es una herramienta biotecnológica importante para mejorar la recuperación de este metal. Esta tecnología se caracteriza principalmente por depender de la actividad de bacterias como: Acidithiobacillus ferrooxidans y Leptospirillum ferroxidans con habilidad para acelerar la disolución oxidativa de minerales sulfurosos presentes en relaves de minas (Argelia, 2004), la presencia de estos microorganismos ayudan a la recuperación del metal de interés, pues son capaces de oxidar o disolver los sulfuros en donde está ocluido el metal de interés (e. g. oro, cobre, zinc, cobalto, etc.) (Akcil, 2004;Donati, 2006;Harneit et. al., 2006). ...
... En el proceso oxidativo se utilizan microorganismos acidófilos que son aislados de drenajes ácido de mina y adaptados a medios de cultivos específicos, estos microorganismos crecen a expensas de la liberación u obtención de electrones a partir de la oxidación del mineral, permitiendo así la liberación de las partículas de oro ocluidas en la matriz sulfurada (González et. al., 2003, Akcil, 2004Ospina et. al., 2012). ...
... Uranium processing involving microbial action has also been demonstrated at a large scale (Munoz et al., 1995;Qiu et al., 2011). It is estimated that bioleaching contributes to the treatment of 25% of the total global production of gold, 15% of copper, and 13% of the produced uranium (Kawatra and Natarajan, 2001;Akcil, 2004). Another recent commercial development includes the use of bioleaching in the extraction of cobalt (Brierley and Brierley, 2001). ...
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This review addresses the detrimental effects of fluoride on the various steps which constitute any hydrometallurgical operation. It focuses on the specific examples of apatite flotation, copper bioleaching, zinc electrowinning and the manufacture of phosphoric acid. The presence of fluoride modifies the surface characteristics of minerals altering their effective flotation. Toxicity of fluoride to bacteria directly affects the mechanisms of bioleaching. Fluoride can interfere with the adhesion of metals to cathodes and effect deposit morphology during electrodeposition. In phosphoric acid synthesis from phosphate ores, fluoride affects production efficiency by altering the crystal morphology of the gypsum by-product.
... Microbial metal solution methods are generally more economical and environmentally friendly compared to physical chemical methods (Rawlings, 2004;Akcil, 2004;Akcil and Deveci, 2010;Gahan et al., 2013;Srichandan et al., 2013). ...
Article
With the increase in environmental awareness, the disposal of any form of hazardous waste has become a great concern for the industrial sector. Spent catalysts contribute to a significant amount of the solid waste generated by the petrochemical and petroleum refining industry. Hydro-cracking and hydrodesulfurization (HDS) catalysts are extensively used in the petroleum refining and petrochemical industries. The catalysts used in the refining processes lose their effectiveness over time. When the activity of catalysts decline below the acceptable level, they are usually regenerated and reused but regeneration is not possible every time. Recycling of some industrial waste containing base metals (such as V, Ni, Co, Mo) is estimated as an economical opportunity in the exploitation of these wastes. Alkali roasted catalysts can be leached in water to get the Mo and V in solution (in which temperature plays an important role during leaching). Several techniques are possible to separate the different metals, among those selective precipitation and solvent extraction are the most used. Pyrometallurgical treatment and bio-hydrometallurgical leaching were also proposed in the scientific literature but up to now they did not have any industrial application. An overview on patented and commercial processes was also presented. Copyright © 2015 Elsevier Ltd. All rights reserved.
... Considering that the biohydrometallurgical techniques can reduce above-mentioned negative effects, many researches have been conducted on application of biotechnology for extracting metals from low-grade ores and concentrates since 1950s (Ehrlich 2001;Liao and Deng 2003;Ehrlich 2004;Rehman et al. 2009;Baba et al. 2011;Ilyas et al. 2012;Sarirchi et al. 2012;Manafi, Abdollahi, and Tuovinen 2013). Bacterial leaching technology, which is based on the ability of microorganisms to aid transformation of solid compounds into soluble and extractable elements, has been rapidly developed in recent decades for its advantages, which include mild reaction conditions, low energy consumption, simple process, low environmental impacts, and being suitable for low-grade mine tailings and residues (Akcil 2004;Cheng et al. 2009;Akcil and Deveci 2010). ...
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The purpose of this study is to test the feasibility of using mixed culture of iron and sulfur-oxidizing bacteria for the dissolution of metals from high-grade zinc and lead sulfide ore. Considering that the roll crusher could reduce the ore size to less than 2 mm, this size fraction was selected in order to study the possibility of removing mill circuit. Effects of parameters such as pulp density, initial pH, Fe2+, oxidation–reduction potential (ORP), and pH fluctuations were investigated, as well. The maximum Zn dissolution was achieved under the conditions of initial pH 2, initial 75 g/L FeSO4 · 7H2O, and pulp density of 50 g/L. The results indicated that under the optimum conditions, about 68.8% of zinc was leached during 24 days of bacterial leaching treatment. The lead recoveries were low (about 1%), because of precipitation of Pb as lead arsenate chloride. Furthermore, the surface studies by using SEM images showed that during chemical leaching the ore dissolution starts from surface discontinuities, but in bacterial leaching all surface becomes involved. In addition, in another process the ore was leached separately with sulfuric acid and sodium hydroxide, and then final results were compared to the bacterial leaching tests in order to find the optimum hydrometallurgical method to extract zinc and lead from these ores.
... Na prze³omie XX i XXI w. metody biohydrometalurgiczne zosta³y zastosowane w wielu instalacjach przemys³owych (Brierley, 2008). Proces bio³ugowania jest wykorzystany równie¿ do utylizacji odpadów p³ynnych i gazowych (Akcil, 2004), a tak¿e osadów oeciekowych, odpadów komunalnych (Deng & Liao, 2002) czy ³upków bitumicznych (Xu & Ting, 2004) zawieraj¹cych metale ciê¿kie. ...
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Various bioleaching processes are applied to recover valuable elements from low-grade ores and metallurgical waste. The activity of microorganisms leads to solubilization of metals from solid substrates and, in this way, makes possible recovery of elements from solutions. The study of wastes from the nickel-chromium steelworks in Szklary showed that a mobile fraction of elements remaining in residues from bioleaching process was substantially larger than in raw waste material. The highest mobility was displayed by metals in wastes leached by heterotrophic bacteria prior to autotrophic ones. In that case the mobile fraction makes up 60-80% of the total concentration of Ni, Cr, Cu and Zn. Storage of bioleached mine tailings increases risk of permeation of hazardous matter to aquifers. When this is the case, a careful flushing and use of metal-binding materials such as bentonite, zeolites, cement, and commercial preparations containing these ingredients are recommended. The obtained results showed that concrete, which is the cheapest of the applied materials, bound almost entirely the mobile fractions of Ni, Cr, Co, Pb, Cu and Zn.
... La necesidad de procesar minerales refractarios cada vez más complejos ha generado el desarrollo y la aplicación de nuevas tecnologías que permitan mejorar la extracción de metales localizados en este tipo de depósitos [1]. La biooxidación de menas refractarias de oro en reactores de tanque agitado usando bacterias mesófilas como pretratamiento al proceso de extracción de oro por cianuración, ha demostrado ser económicamente factible y una alternativa competitiva a los procesos tradicionales de tostación y oxidación a presión [2,3]. Actualmente, este proceso biotecnológico es aplicado para la recuperación de oro en varias plantas a nivel comercial, entre las que se encuentran las establecidas en Australia, Sudáfrica, Ghana, Perú y Brasil [2,4,5]. ...
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The bioxidation of refractory gold mineral of the "El Zancudo" mine (Titiribi-Antioquia) was carried out in a continuous stirred tank reactor using an acidofile microorganisms compatible with Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The reactor was operated initially in batch to achieve the ferric iron maximum concentration in solution, before beginning the continuos process. The mineralogical characterization was performed to samples gathered in batch, transitory and steady state in continuous using Scanning Electron Microscopy (SEM) and XRay Diffraction (DRX). The mineralogical characterization showed an advanced oxidation of the pyrite and arsenopyrite in batch and partial in continuous operation. Additionally, it was found the formation of silicates, jarosite and brushita. The results indicate that the system reached the steadystate after 8 days of operation in continuous, achieving a ferric iron concentration in solution of 8.3 g/l corresponding to a gold and silver extraction percentage of 78 and 80%, respectively.
... i o le ac hing is the so lu bi li za ti on of me tals from me tal lic ores and con cen tra tes of compo unds by using ca talysts of bac te ri a un der nor mal pres su re and in the tem pe ra tu re ran ge of 5-90 o C. Bi op ro ces ses-using mic ro or ga nisms ha ve beco me well-es tab lis hed tech no logy over the ye ars and ha ve fo und app li ca ti ons for the ex trac ti on of cop per and ura ni um from me tal-be a ring ores and scrap ma te ri als. [1][2][3][4][5][6] Li ke wi se, bi o-oxi da ti ve pre-treat ment of ref rac tory gold ores and con cen tra tes is now com mer ci ally prac ti ced as an al ter na ti ve to tra di ti o nal pro ces ses. 4,[7][8][9] In re cent ye ars, bi o le aching tech no logy has be en ex ten ded to ex trac ting ot her me tals, inc lu ding zinc, nic kel, co balt and man ga ne se from sul fi de ores and con cen trates. ...
... Biohydrometallurgy has been employed to economically extract metal from certain sulfide minerals over half a century (Brierley and Brierley, 2013). In the recent two decades, biohydrometallurgy developed rapidly and achieved in industrial applications for extraction of copper, gold, nickel, zinc, cobalt, uranium, etc., the production of copper by bioleaching technology accounted for 15% of world production (Akcil, 2004). ...
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The distribution and diversity of microbial community in Zijinshan commercial non-aerated copper heap-bioleaching system operated at pH 0.8 for three years were investigated. In this research, 12 ore residue samples and 3 liquid samples were collected, the microbial community structure of heap was investigated by clone libraries, key acidophiles were assayed by real-time PCR, and physicochemical characteristics of the samples were also analyzed. 27 OTUs were obtained from 16S rRNA libraries, among them, bioleaching microorganism accounted for 40.7% of OTUs and 95.6% of clones. The species which had the ability to oxidize reduced inorganic sulfur compound accounted for 52.9% of clones and to oxidize Fe2+ accounted for 42.7% of clones. The other remaining OTUs accounted for 59.3% of OTUs and 4.4% of clones, most of which belong to heterotrophic and facultative bacteria. These bacteria could use organic compounds of the heap system and decrease the inhibition of organic compounds to autotrophic bacteria. In the heap, Acidithiobacillus mainly located in the inner and higher sites of ore heap, Leptospirillum mainly located in the outer and lower sites of ore heap, and heterotrophic and facultative microbes mainly located in the middle of the ore heap. There was higher leaching efficiency in the core of the heap, this might be related with the higher temperature of the heap core and higher diversity of microorganism community.
... Bacterial leaching can be an economical alternative in metal recovery from ores in place of conventional treatments used by the mining industry. Microorganisms can also be exploited in the recovery of metals from mine drainage, industrial effluents, solid waste incineration (MSWI) fly ash, spent catalysts, waste sludge, contaminated sediments, medical waste and electronic scrap, etc. 30,93 ...
Article
Waste generated by the electrical and electronic devices is huge concern worldwide. With decreasing life cycle of most electronic devices and unavailability of the suitable recycling technologies it is expected to have huge electronic and electrical wastes to be generated in the coming years. The environmental threats caused by the disposal and incineration of electronic waste starting from the atmosphere to the aquatic and terrestrial living system have raised high alerts and concerns on the gases produced (dioxins, furans, polybrominated organic pollutants, and polycyclic aromatic hydrocarbons) by thermal treatments and can cause serious health problems if the flue gas cleaning systems are not developed and implemented. Apart from that there can be also dissolution of heavy metals released to the ground water from the landfill sites. As all these electronic and electrical waste do posses richness in the metal values it would be worth recovering the metal content and protect the environmental from the pollution. Cyanide leaching has been a successful technology worldwide for the recovery of precious metals (especially Au and Ag) from ores/concentrates/waste materials. Nevertheless, cyanide is always preferred over others because of its potential to deliver high recovery with a cheaper cost. Cyanidation process also increases the additional work of effluent treatment prior to disposal. Several non-cyanide leaching processes have been developed considering toxic nature and handling problems of cyanide with non-toxic lixiviants such as thiourea, thiosulphate, aqua regia and iodine. Therefore, several recycling technologies have been developed using cyanide or non-cyanide leaching methods to recover precious and valuable metals. Copyright © 2015 Elsevier Ltd. All rights reserved.
... Biohydrometallurgical methods for processing and remediation consume less energy and are eco-friendly and emit no harmful gases in the environment [1][2][3][4][5][6]. These processes are based on the ability of specific bacteria and fungi to dissolve refractory minerals in form of extractable elements which can be recovered. ...
Article
In this research, the bioleaching mechanism of zinc and lead from high-grade Zn–Pb ore has been investigated. It is done by using mixed culture of iron and sulfur oxidizing moderate thermophilic bacteria at 45 C. Pulp density, initial pH and ferrous concentration were studied as influential parameters in bioleaching experiments. The optimum conditions were achieved at pulp density = 50 (g/L), initial pH = 1 and FeSO4.7H2O concentration = 75 (g/L) with 98.5% zinc recovery after 25 days treatment. Generally, an increase in ferrous concentration caused an improve zinc recovery, and an increase in initial pH and pulp density caused reduction in zinc recovery. However, in the test with optimum condition the lead dissolution was just 0.027% due to the lower Pb solubility. Furthermore, cadmium dissolution was 98% under optimum condition and results showed the cadmium dissolution was in direct proportion with zinc dissolution. Finally, 7.82% of arsenic and 8.52% of antimony dissolved during zinc bioleaching after 25 days treatment, both under above mentioned optimum condition.
... It has many advantages such as formation of a micro-climate around particles with elevated concentrations of leaching agents, low energy demand, no emission of gaseous pollutants, increase in leaching competence, and production of leaching agents in situ. The process has also certain limitations such as longer reaction times, dependence on climate, toxicity of heavy metals, flotation and SX reagents to microorganisms activity, and potential for acid leaks (Tuovinen 1978;Okibe and Johnson 2002;Akcil 2004;Rawlings 2004;Chen and Lin 2009;Escobar et al. 2009;Anjum et al. 2010;Brierley 2010;Amiri et al. 2011;Gholami et al. 2012). ...
Article
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Bio-hydrometallurgical applications have been receiving more attention globally for processing of several metal bearing wastes. Compared to the conventional methods, bioleaching has proved to be a more effective way in treating low-grade ores, due to its economic and ecofriendly advantages. Developments in bioleaching enables this technique to be utilized as an alternative process for extraction of base metals from complex ores (copper, gold etc.) or even concentrates, consequently solving several environmental issues. A variety of parameters can influence the bioleaching efficiency such as physicochemical and microbiological factors, properties of the minerals and processing conditions. Certain organic and inorganic reagents or additives used during the process such as flotation and SX reagents, Ag+, Fe2+, Fe3+, Cu2+, Mg2+, Ni2+, silica, pyrite, activated carbon etc., affect the microorganisms activity and their efficiency for metal leaching. More precise investigation on the effect such materials can provide insights and hence studies have been directed to understand such aspects. Owing to their importance, the present review discusses the influence of certain organic-inorganic reagents and other materials or additives on the growth, oxidation activity and bioleaching efficiency of acidophiles on metal dissolution.
... Nutrient deficiencies can be overcome by adding them and creating suitable growth conditions but finding microbes resistant to high levels of Cd remains the greatest challenge. Although some researchers consider domestication of microbes is a time-consuming process (Wang et al., 2014), the use of indigenous microbes in harsh environments may be the appropriate solution to avoiding the use of engineered microorganisms and mutants (Akcil, 2004). ...
Article
The present study aimed at assessment of different application methods of Bacillus subtilis MF497446 to induce development of cowpea ensuring food safety under cadmium (Cd) stress. Also, isolation, plant growth promoting (PGP) traits and 16 S rRNA-based identification of Bacillus subtilis MF497446 is documented. Out of 24 Bacillus isolates (AS1-AS24), only four isolates (AS4, AS12, AS14 and AS22) showed greater Cd tolerance up to 18 mg L −1. The greatest PGP traits under Cd stress were displayed by Bacillus isolate (AS12); which, also, enhanced seedling elongation and vigor index of cowpea under Cd stress. Phylogenetic analysis, based on 16 S rRNA, confirmed that this promising Bacillus isolate (AS12) belongs to Bacillus subtilis and is referred to as B. subtilis MF497446. Treatment of inoculation+soaking for 90 min of cowpea seeds by B. subtilis MF497446 resulted in the best development of cowpea plants under Cd stress (up to 9 mg kg −1); as fresh and dry masses of cowpea increased from 6.80 to 1.54 to 12.35 and 2.59 g plant −1 , respectively. Moreover, shoot and root lengths were 19.66 and 28.33 cm when cowpea seeds were treated by B. subtilis MF497446 (inoculation+soaking for 90 min) compared to 11.33 and 10.66 cm, respectively, for control (Cd stress only). Application of B. subtilis MF497446 (as inoculation+soaking for 90 min) reduced Cd accumulation and bioconcentration factor in cowpea plants by 29.2 and 28.9%, respectively, compared to control (Cd stress only). These results clearly reveal that applying of B. subtilis MF497446 to crops grown on Cd-contaminated soil enhances plant growth and eliminates (or at least diminishes) the risks to human health ensuring food safety.
... Variations in the metal price have caused very intense competition among the high prestigious mining companies (Anglo American, BHP, Rio Tinto, Glencore, etc.) to revise their feasibility studies where the feasibility of mining projects has significantly depended on the project costs. Moreover, the problem of global warming and environmental pollution has led the mineral processing industry to focus on the use of low-cost, low-energy, and environmentally friendly methods [4,[6][7][8][9][10]. Thus, several investigations have been focused on the operation and optimization of the bioleaching processes for the extraction of metals from Processes 2019, 7, 653 2 of 17 low-grade deposits (by heap bioleaching [11,12]), waste (by columns [13,14]), and concentrates (by bioleaching tanks [13,15,16]) which considerably have lower costs and environment effects [11,[16][17][18][19][20][21][22][23][24]. ...
Article
Bioleaching is an environment-friendly and low-investment process for the extraction of metals from flotation concentrate. Surfactants such as collectors and frothers are widely used in the flotation process. These chemical reagents may have inhibitory effects on the activity of microorganisms through a bioleaching process; however, there is no report indicating influences of reagents on the activity of microorganisms in the mixed culture which is mostly used in the industry. In this investigation, influences of typical flotation frothers (methyl isobutyl carbinol and pine oil) in different concentrations (0.01, 0.10, and 1.00 g/L) were examined on activates of bacteria in the mesophilic mixed culture (Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, and Acidithiobacillus thiooxidans). For comparison purposes, experiments were repeated by pure cultures of Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans in the same conditions. Results indicated that increasing the dosage of frothers has a negative correlation with bacteria activities while the mixed culture showed a lower sensitivity to the toxicity of these frothers in comparison with examined pure cultures. Outcomes showed the toxicity of Pine oil is lower than methyl isobutyl carbinol (MIBC). These results can be used for designing flotation separation procedures and to produce cleaner products for bio extraction of metals.
... Biohydrometallurgy or bioleaching is the interaction between metals and microbes with the specific aim of converting insoluble metal sulfides to soluble metal sulfates. Bioleaching has been defined as the dissolution of metals from their mineral sources by certain naturally occurring microorganisms or the use of collection microorganisms to transform solid compounds to soluble and extractable elements through the production of organic acids, further recovered by water filtration [2,11]. ...
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The strategic situation of Sinai made it an urgent national target for the sustainable development. One of the important factors in such development is the exploration and the processing of uraniferous rock materials. Consequently, the Lower Carboniferous sedimentary rocks were chosen for the present study to test the uranium bioleaching capacity of fungal strains isolated from exposed sedimentary rocks in southwestern Sinai. Eight fungal species were isolated from three grades of uraniferous sedimentary rock samples in southwestern Sinai, Egypt and tested for their bioleaching activity. Aspergillus niger (A. niger) and Aspergillus terreus (A. terreus) were the only isolates which gave a high grade leaching efficiency of uranium from the studied uraniferous rocks. The most favorable factors for solubilization of uranium were 7 days incubation time, 3% ore concentration, solid/liquid ratio 1/3 and 30 °C incubation temperature. Both fungi produced organic acids (oxalic, citric, formic and ascorbic) in the culture filtrate which are the key compounds of bioleaching processes. Applying these conditions on one kilogram of Ag-3 sample (the lowest U grade), the A. niger strain gave high uranium leaching efficiency of 71.4%. The recovery test of U has been performed by proper precipitation to obtain a high quality uranium concentrate.
... Microbial metal-extraction processes are usually more economical and eco-friendly than physicochemical processes (Rawlings, 2004;Akcil, 2004). They do not use large amounts of energy as compared to roasting and smelting and do not produce sulphur dioxide, another harmful gas (Mishra et al., 2004). ...
Article
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The main objective of this study was to find a more feasible and economical method to extract metal ions from laterite ore by Penicillium chrysogenum. The effect of different substrates on microbial recovery of metal ions from laterite ore using indigenous strain of P. chrysogenum was observed. Maximum recovery of aluminum (86.78%), iron (97.78%), manganese (77.61%), nickel (57.31%) and chromium (34.32%) was recorded in case of shaking flasks experiments up to 24 days of incubation. Metal ions solubilization was also compared with the samples, which were not shaken and maximum recovery of Al (83.54 %), Fe (96.12 %), Mn (88.56 %), Ni (46.53 %) and Cr (37.82 %), were attained up to 24 days of incubation period. Enhanced recovery of Fe and Al may be due to the result of the acidic effect of the environment and the chelating capacity of organic acids.
... It is, therefore, based on the exploitation of the economic potential of the interactions between microorganisms and metals/ minerals in aqueous environments. In this context, mineral biotechnology embraces a diverse range of disciplines, mainly hydrometallurgy, geomicrobiology, microbial ecology and microbial biochemistry (Cupp 1985, Rossi 1990 of copper and uranium from low grade ores or old tailings at industrial scale in heap, dump and in-situ operations (Campell et al. 1985, Tuovinen and Bhatti 1999, Brierley and Brierley 2001, Olson et al. 2003, Akcil 2004, Watling 2006. Likewise, biooxidative pre-treatment of refractory gold ores and concentrates is now commercially practised as an alternative to the traditional processes such as oxidative roasting (Miller 1997, van Aswegen and Marais 1999, Olson et al. 2003, Rawlings et al. 2003. ...
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Geomicrobiology is a combination of geology and microbiology, which includes the study of interaction of microorganisms with their environment, such as in sedimentary rocks. This is a new and rapidlydeveloping field that has led in the past decade to a radically-revised view of the diversity and activity of microbial life on Earth. Geomicrobiology examines the role that microbes have played in the past and are currently playing in a number of fundamental geological processes. Microorganisms are very important for the environment. Biogeochemical cycles performed by these organisms are necessary to maintain normal life on Earth. These microorganisms are very important in the petroleum and pharmaceutical industries from the economic point of view. Beside which, increased agricultural productivity through soil microorganisms, natural products and a wide range of industrially important substances isolated from these microorganisms, have popularized this field as a thrust area for present and future researchers. The curiosity to know about life on other planets is also evident in present-day researchers. The Earth’s earliest biological sediments can solve the enigma about the origin of life on Earth and give an indication about the presence of life on other planets. The future of this field is definitely bright, people are dependent on these microorganisms not only for their food but also for maintaining a proper healthy environment. Inspite of the bright future of this field, quality literature related to geomicrobiology is not sufficient to fulfil the requirements of students and researchers. There is an immense need to gather quality literature for scientists working in this thrust area.
... There has been much interest in the development of bio-hydrometallurgical methods for the extraction of copper and other elements from sulfide minerals because they have many advantages over the more traditional pyrometallurgical techniques, which include reduced emissions to air, simplicity of operation, low cost and applicability to low-value ores or mineral resources that cannot be treated by conventional mining techniques (Brierley and Brierley, 2001;Akcil, 2004;D'Hugues and Spolaore, 2008;Anjum et al., 2010;Brierley, 2010;Castro et al., 2013). Bioleaching is an economical method for the recovery of metals which involves low investment and operation costs. ...
Article
This paper presents the application of an artificial neural network (ANN) in order to predict the effects of operational parameters on the dissolution of Cu, Mo and Re from molybdenite concentrate through meso-acidophilic bioleaching. The initial pH, solid concentration, inoculum percent and time (days) were used as inputs to the network. The outputs of the models included the percent of Cu, Mo and Re recovered. The development and training of a feed-forward back-propagation artificial neural network (BPNN) was used to model and predict their recoveries. 105 sets of data were used to develop the neural network architecture and train it. To reach the network with highest generalizability, the space of neural networks with different hidden layers (one up to three hidden layers) and with the varying number of neurons each layer were searched. As a result, it was found that (4-5-5-2-1); (4-7-5-2-1) and (4-7-1-1-1) arrangements could give the most accurate prediction for Cu, Mo and Re extraction respectively. The regression analysis of the models tested gave a good correlation coefficient of 0.99968, 0.99617 and 0.99768 respectively for Cu, Mo and Re recoveries. The results demonstrated that ANN has a good potential to predict Cu, Mo and Re recoveries. Also, genetic algorithm (GA) was used to find out the optimum levels of parameters in the best models defined by ANN. The maximum recovery of Cu, Mo and Re on the 30th day were nearly 73%, 2.8% and 27.17% respectively.
... It is a challenge to achieve an improved and sustainable method of zinc extraction from sulfide minerals while zinc (Zn)-lead (Pb) deposits in the form of oxide minerals are becoming increasingly depleted. Among all suggested methods, bioleaching has been accepted as an environmentally friendly process, with minimum carbon foot print [2,3,27,34,46]. In fact, the most important advantages of bioleaching are avoiding the emission of huge amount of SO 2 and reducing the dependence on fossil fuels as required during the conventional roasting stage of the RLE process. ...
Article
The present study investigates the influence of ferrous iron (as FeSO4) and ferric iron (as Fe2 (SO4)3), and pyrite (FeS2) on the ability of bacterial leaching of a high-grade sulfide Zn–Pb ore. In this regard, shake flask experiments were carried out at 5% (w/v) pulp density of the ore sample (having 40.7% Zn and 12.4% Pb initial metal content) using a consortium of mesophilic iron and sulfur-oxidizing acidophiles. A concentration of 0.04 mol/L of ferric iron in the leaching media was found to be optimum for zinc extraction without affecting growth of the microorganisms. Under this concentration, the dissolution of Zn, Pb, Cd, and As was found to be 57%, 0.2%, 0.03%, and 9.9% in 25 days. Using ferrous iron in the media, 0.16 mol/L of Fe²⁺ was found to be the optimum concentration for efficient bacterial growth and metal dissolution (54.6% Zn, 0.08% Pb, 0.03% Cd, and 10.2% As) from the sample in 25 days. On the other hand, using pyrite as the source of energy for bacterial growth, an initial 12-day lag period was observed when compared to the effect of ferrous iron in the media. Under the optimum concentration (test with 0.24 mol/L iron in the form of pyrite), the dissolution of Zn, Pb, Cd, and As was found to be 39.8%, 0.1%, 0.03%, and 10% in 25 days. The surface chemistry analysis indicated formation of a sulfur layer over the particle surface that hindered reagent diffusion and affected metal recovery through bioleaching.
Article
Environmental laws concerning spent catalysts disposal have become increasingly more severe in recent years. Due to the toxic nature of spent catalysts, their disposal can pollute the environment. The recovery of heavy metals decreases the environmental impact of the waste catalysts and the recycled product can be further used for industrial purposes. Bio-hydrometallurgical approaches, such as bioleaching, appear to offer good prospects for recovering valuable metals from spent refinery catalysts. Currently, identifying and modifying the parameters that influenced the efficiency of bioleaching is important for industrial sector. The biological system can be further improved through optimizing the bioleaching parameters, such as the nutrient culture media, amount of oxygen and carbon dioxide, pH, temperature, inoculum, metal resistance of microorganisms, chemistry of solid waste, particle size of solid waste, solid liquid ratio, bioleaching period, size of substrate, shaking speed, and also the development of more effective bioleaching microorganisms. In our previous review (Asghari et al. in J Ind Eng Chem 19:1069–1081, 2013), information available in the literature on the bioleaching fundamentals of spent catalysts with a focus on recent developments was reviewed in detail. In this study, the effects of most important factors that influence an efficient bioleaching process of spent refinery catalysts with the hope that these valuable and useful data can help determine the most efficient process will be discussed. The details of metals recovery with a focus on the effects of different variables in the bioleaching such as reaction time, pulp density, initial pH, particle size, nutrient concentration, temperature and buffer will also be presented.
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Bacillus subtilis 38 (B38) is a mutant species of Bacillus subtilis acquired by UV irradiation with high cadmium tolerance. This study revealed that B38 was a good biosorbent for the adsorption of multiple heavy metals (cadmium, chromium, mercury, and lead). Simultaneous application of B38 and NovoGro (SNB) exhibited a synergetic effect on the immobilization of heavy metals in soil. The heavy metal concentrations in the edible part of the tested plants (lettuce, radish, and soybean) under SNB treatment decreased by 55.4-97.9% compared to the control. Three single extraction methods, diethylenetriaminepentaacetic acid (DTPA), Mehlich 3 (M3), and the first step of the Community Bureau of Reference method (BCR1), showed good predictive capacities for metal bioavailability to leafy, rhizome, and leguminous plant, respectively. The polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) profiles revealed that NovoGro could enhance the proliferation of both exotic B38 and native microbes. Finally, the technology was checked in the field, the reduction in heavy metal concentrations in the edible part of radish was in the range between 30.8% and 96.0% after bioremediation by SNB treatment. This study provides a practical strategy for the remediation of farmland contaminated by multiple heavy metals.
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In this research, the bioleaching mechanism of zinc and lead from high-grade Zn-Pb ore has been investigated. It is done by using mixed culture of iron and sulfur oxidizing moderate thermophilic bacteria at 45°C. Pulp density, initial pH and ferrous concentration were studied as influential parameters in bioleaching experiments. The optimum conditions were achieved at pulp density=50 (g/L), initial pH=1 and FeSO4.7H2O concentration= 75 (g/L) with 98.5% zinc recovery after 25 days treatment. Generally, an increase in ferrous concentration caused an improve zinc recovery, and an increase in initial pH and pulp density caused reduction in zinc recovery. However, in the test with optimum condition the lead dissolution was just 0.027% due to the lower Pb solubility. Furthermore, cadmium dissolution was 98% under optimum condition and results showed the cadmium dissolution was in direct proportion with zinc dissolution. Finally, 7.82% of arsenic and 8.52% of antimony dissolved during zinc bioleaching after 25 days treatment, both under above mentioned optimum condition.
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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 environmental 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 treatment 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.
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Bioleaching studies were carried out in percolation columns using low-grade copper containing rock (granite). The lixiviant consisted of acidified ferric sulfate containing acidophilic microorganisms. The iron oxidizing strain was isolated from Malanjkhand mine water and after adaptation the iron oxidation observed to be 500 mg/L/h. Leaching parameters studied were lixiviant flow rate, particle size and bed height. It was observed that leaching efficiency increased with decrease of particle size and lixiviant flow rate. The precipitation of iron during leaching observed to be low as pH was maintained at 2. Based on the leaching kinetics, a unified rate equation was developed and shown as rά(d p )−0.61 (F)−0.76 (H b )0.97.
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Biohydrometallurgy is no longer a promising technology but is now an established economical alternative for treating specific mineral ores. It occupies an increasingly important place among the available mining technologies. A significant number of the current large-scale bioprocessing operations are located in developing countries. The popularity of this technology in most developing countries is largely due to low capital cost requirements and its simplicity in operation. The African continent, with South Africa in particular, pioneered and currently houses institutes that count among the top researchers in further development of the biohydrometallurgical technology. However, despite its abundant mineral reserves and deposits, Africa is still much behind in the commercialization process. This paper looks at possible reasons behind the lag in adoption of this technology in the African continent. It further considers the influencing factors for the adoption and effective application of biohydrometallurgy for the sustainable development of the African minerals industry.
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This study investigates the biooxidation of a refractory gold concentrate using a mixed culture of acidophilic mesophiles, moderate thermophiles and extreme thermophiles and their effect on the subsequent cyanidation and gold recovery. The experiments with high % solids using mixed mesophiles showed better oxidation potential compared to moderate thermophiles and extreme thermophiles. However, the extreme thermophiles performed better than mesophiles and moderate thermophiles during the biooxidation with
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The microbes are generally responsible for the exploitation of ores which cannot be otherwise processed economically , and are sometimes the only option to handle the complexities associated with vast un-exploited mineral treasures including secondary resources. In the Indian context, bio-processing of copper and uranium based resources, and bio-beneficiation of off-grade ores are considered to be of sufficient interest. Metal bio-remediation is a potential tool to treat wastewaters from mining and metallurgical operations with high level of cations, anions and excess acids , which are hazardous to ecosystem. National Metallurgical Laboratory (CSIR), Jamshedpur has made use of such bio-technological tools in metal solubilization from ores/ concentrates/wastes and metal bio-remediation. The notable amongst these includes the bio-processing of ocean nodules , copper converter slag and concentrate, and other low grade ores of copper and uranium. The achievements in some of these activities and the possibilities of extraction of a few such non-ferrous metals focusing the country 's requirements by applying the biohydrometallurgy are presented in this paper.
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This paper studies the effects of ultraviolet irradiation on the mutation of bacteria (i.e., Acidithiobacillus ferrooxidans LD-1) and on the bioleaching system for low-grade copper tailings. It is shown that ultraviolet irradiation can lead to an obvious LD-1 mutation, can improve bio-activity and bioleaching capability. The mutant LD-1 bacteria, after ultraviolet irradiation for 30min, had the best oxidation activity, the oxidation rate of ferrous ion (Fe2+) in mutant bacteria culturing medium can reach 100% after 24h (18h less than that of the original bacteria under the same leaching conditions). After 30days, copper extraction with mutant bacteria is increased by about 17%, compared with original bacteria, and by 70% compared to chemical leaching. These results show that the effects of mutant bacteria after ultraviolet irradiation are better than those of the original bacteria and much better than those of chemical leaching. The improved bioleaching rate of the mutant bacteria is attributed to the faster propagation rate and capabilities for stronger sulfuric acid generation. This study shows that mutant bacteria from ultraviolet irradiation have great potential for improving copper recovery from low-grade copper tailings.
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Society’s hunger for commodities is leading to an increased consumption of minerals considered critical or strategic. A range of minerals containing elements such as lithium (Li), cobalt (Co), rare earth elements (REEs) are considered critical and more important for strategic uses than others. In this paper we describe these as strategically important critical minerals (SICMs). However, their continuous depletion from primary sources coupled with supply risks due to geopolitical issues and geographical segregation is a major concern. As a consequence, recovering these valuable elements from non-conventional sources such as abandoned mine tailings has recently gained increased worldwide attention. In some part this is due to the fact that the potentially recoverable amount of these elements in abandoned mine tailings is often higher than the concentration in some primary ores. A review of the scientific literature reveals the use of modern recovery techniques such as tailored made hydrometallurgical and bio-hydrometallurgical processes can lead to effective recovery of these elements from low grade sources such as mine tailings. However, there remain some technical, economic and environmental challenges associated with recovering SICMs from mine tailings. This review critically analyzes these challenges and discusses the opportunities available for recovering SICMs from abandoned mine tailings using conventional hydrometallurgical techniques as well as bioleaching methods, which can offer significant advantages in reprocessing. This paper also concludes by providing an outlook of an integrated approach to the reprocessing of mine tailings where the recovery of SICMs as well as clean water production should be the combined overall reprocessing and recovery goal, helping to realize the full economic potential of the tailings.
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Malolactic fermentation (MLF), mainly carried out by lactic acid bacterium, is of immense importance in winemaking allowing for improvement of microbiological stability and organoleptic characteristics of wine. However, it is difficult to address the problems of decoloration and loss of taste along with MLF induced by traditional starter culture. To further the aim at realizing a controlled and efficient MLF process, mutant of Oenococcus oeni strains after ultraviolet irradiation was selected to enhance quality of MLF. The treated strains with a lethality rate of 80–90 % were preliminarily screened, and then were secondly screened by evaluating their sensory and fermentation properties, by which O. oeni C10-1 were successfully screened. The malolactic conversion rate of O. oeni C10-1 is up to 38.81 %, which is remarkably increased when compared to original strains. Pivotally, wine fermented by O. oeni C10-1 demonstrated the highest color density of 9.240 and got the score of 5.95 in softness index, suggesting a remission of decoloration phenomenon and improved mouth feeling of wine. In all, these make it highly valuable for industrial application. Graphical Abstract
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Two kinds of biochars, one derived from corn straw and one from pig manure, were studied as carriers of a mutant genotype from Bacillus subtilis (B38) for heavy metal contaminated soil remediation. After amendment with biochar, the heavy metal bioavailability decreased. Moreover, the heavy metal immobilization ability of the biochar was enhanced by combining it with B38. The simultaneous application of B38 and pig manure-derived biochar exhibited a superior effect on the promotion of plant growth and the immobilization of heavy metals in soil. The plant biomass increased by 37.9% and heavy metal concentrations in the edible part of lettuce decreased by 69.9-96.1%. The polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) profiles revealed that pig manure-derived biochar could enhance the proliferation of both exotic B38 and native microbes. These results suggest that B38 carried by pig manure-derived biochar may be a promising candidate for the remediation of soils contaminated by multiple heavy metals.
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The aim of this paper is to provide geologists, metallurgical engineers, or mineral resource strategists with a first overview of the currently available state-of-the-art knowledge of the extraction of key metallic values from black shales. The key metallic values considered were vanadium (V), molybdenum (Mo), uranium (U), nickel (Ni), zinc (Zn), as well as platinum group elements and gold. First, a global geological and mineralogical overview is given. Following this, each technological approach is explained and, finally, a summary is provided. Each topic also includes brief overview of the possible environmental impacts. All information was sourced from academic papers, patents, and technological reports. The main conclusions are: (i) black shales are enriched in different sets of metals, yet the V-Mo-U-Ni-Zn association is relatively universal, (ii) mineralization is mostly disseminated and rocks are very fine grained, (iii) hosts of key metals are either sulfides of organometallic complexes, V is often associated with silicates, (iv) the latter 3 along with additional factors result in poor opportunities for beneficiation (flotation, etc.), (v) extraction methods range from conventional hydrometallurgy, bio-leaching, and in-situ leaching in many combinations with roasting, microwave, autoclave or other aiding steps. The final choice of technology is site-specific and there are no rule-of-thumb solutions. There is only one fully operational production unit that exploits black shale as a raw material – Talvivaara/Terrafame in central Finland.
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Chapter
With the pursuit of high energy-density and low cost lithium-ion batteries (LIBs), cobalt content in the cathode materials decreases gradually. In addition, the limited nature of lithium mineral reserves is a prominent issue as the demand for LIBs is expanding fast. Hence, traditional pyrometallurgical methods is not competent to recycle spent LIBs, because not only their economic efficiency strongly depends on the cobalt content, but also they cannot recover lithium from spent LIBs. Bio-hydrometallurgical methods for recycling spent LIBs have been proposed and attracted increasing attentions in the past decades. These methods involve biological processes in which some metabolites excreted by microorganisms are used for extraction of metals from spent LIBs. Bio-hydrometallurgy, which is a special kind of hydrometallurgy, has its unique advantages and disadvantages due to the use of living biomass. This chapter gives an overview of this method in terms of leaching mechanisms, impacts on leaching efficiency and pros and cons of it.
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Artificial fracture stimulation in host rock formations is a potential technique to improve the recovery efficiency of in-situ leaching mining applications, which is gradually creeping in as an alternative mining method for mineral extraction in low-grade ore deposits. In this study, we report two new methods of fracture stimulation by injecting a modified Soundless Cracking Demolition Agent (SCDA) into a target rock through an injection well as opposed to completely filling the injection well once with SCDA to produce a fracture. The first method, intermittent charging (where the injection well is charged intermittently with SCDA), was found to minimize the amount of SCDA used to fracture a finite rock mass. Experimental results suggest a 22.4% improvement in the efficiency (measured by the area of fracture produced per unit mass of SCDA) of fracturing for intermittent charging compared to continuous charging. Numerical simulations were carried out in conjunction using Particle Flow Code 3D (PFC3D) to understand the underlying mechanics of rock fragmentation during intermittent charging. The simulations reveal that during intermittent charging, an additional bending force is applied to the uncharged regions resulting in a supplementary fracture propagation, which improves fracturing efficiency. The second method, multi-stage charging (where SCDA is injected in two consecutive stages using the same injection well) increases the fracture density of a finite rock mass without the need for multiple injection wells. During stage two injection, the fracture density was increased, first by extending the fractures created during the first stage of injection, and second by creating micro hairline fractures around the first stage fractures. The laboratory experiments suggest that the methods introduced in this study can be used to optimize the fracture network generated in a host rock formation.
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Today's mining activities are facing deposits of decreasing metal content and an increase of complexity. Biohydrometallurgy is an industrial application that uses microorganisms to facilitate the release of metals from mineral ores, especially sulfide ores. A testing site for in situ bioleaching was established in an underground mine to recover indium and germanium from a zinc sulfide ore vein. The downstream processing of the pregnant leaching solution is also realized as in situ application by means of a membrane pilot plant, which was exclusively designed for this special application. An in situ bioleaching site is installed in the underground mine “Reiche Zeche” at the Technical University Bergakademie Freiberg to recover indium and germanium from a zinc sulfide ore vein. The in situ downstream processing of the bioleaching solution is realized by a membrane pilot plant which was exclusively designed for this special application.
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The recovery of strategic elements from secondary mineral sources and low-grade ores is of increasing relevance due to a changing global market as well as for reasons of sustainability. The present article shows the potential of biohydrometallurgy as an effective technology for mobilization of metals from secondary sources. Furthermore, the application of membrane separation as a successful technique to recover metals from bioleaching solutions is presented. These issues are discussed within the scope of recent research projects.
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de Die Gewinnung sekundärer Rohstoffe ist nicht allein aus Gründen der Weltmarktsituation relevant, auch die Ressourceneffizienz gebietet die Nutzung von Deponien, Altablagerungen und Armerzlagerstätten als Rohstoffquellen im Sinne der Nachhaltigkeit. Der vorliegende Artikel zeigt die Einsatzpotenziale der Biohydrometallurgie als effizientes Verfahren der Wertstoffmobilisierung im Rahmen der Nutzung derartiger Rohstoffpotenziale auf und widmet sich weiterhin der Membrantrenntechnik zur Separation gelöster Wertstoffe aus Laugungslösungen an ausgesuchten Fallbeispielen aktueller Forschungsprojekte. Abstract en The recovery of strategic elements from secondary mineral resources and low grade ores is of increasing relevance, due to a changing global market as well as for reasons of sustainability. The present article shows the potential of biohydrometallurgy as an efficient technology for mobilization of metals from secondary mineral resources. Furthermore, the application of membrane separation as a successful technique for the recovery of metals from bioleaching solutions is presented. These issues are discussed within the scope of recent research projects.
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This paper aims to investigate the mass and characteristics of colloid in leaching process to provide useful information for assessing the effects of colloid on leach at vertical and safety assessment of the disposal of (ultra-) low uraniferous radioactive waste. The variation of pH, colloid mass and effects on leach were studied at ambient conditions. The experimental results showed that the formation of colloid was strongly influenced by the pH value, it increased with time from 24 h to 96 h, and mass of colloid showed the opposite trend. The mass of colloid increased by the thick of uranium residual ores from 0.2 m to 0.8 m, but the pH showed opposite trend. The colloid morphology was identified using S-4800 scanning electron microscopy (SEM/EDS), and confirmed Al, Fe, Mg, Cs, U, Pr, O, and C as main composition. It implies that the existence of colloids would retard uranium leaching process. The residue grade of different thick nicely verified this point.
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In this twenty-first Century, Africa is still lagging behind both in the development and utilization of new cost-effective and high-productive technologies. This is expected to remain so for a long time to come. The lack of technological innovations and monetary investments are some of the key factors that are viewed as contributing to Africa's perpetual underdevelopment and economic instability. In this context, sound technology transfer and acquisition can play an active role in African development and economic sustainability. This chapter looks at how appropriate technology transfer can enhance economic development in Africa, with particular focus on two specific areas, namely Biotechnology and Nanotechnology. Concurrently, this chapter also reviews and discusses some of the key factors that generally impede technology transfer in Africa. Equally, this chapter also addresses some of the merits and demerits of technology transfer, in particular as related to the African continent and its quest for sustainable development and economic growth. Both Biotechnology and Nanotechnology are relatively new, but these are hot technologies that have great potential in many industrial sectors where they can serve to cost-effectively optimize operational processes, increase efficiency, and maximize productivity. © 2013 Springer-Verlag Berlin Heidelberg. All rights are reserved.
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The effect of Ag+ on bioleaching of As-bearing gold concentrate was studied. The concentrations of Fe3+, Ag+ and As in the bioleaching solution were monitored during the leaching process. The effect of Ag+ on the bacterial density was investigated and the leaching residue was characterized by XRD and SEM. The experimental results show that Ag+ can enhance the bioleaching rate especially at the high concentration of Fe3+, but the growth of bacteria was restrained under at higher concentration of Ag+, leading to the decrease of leaching rate. Based on the leaching results and leaching residue analysis, the catalytic mechanism of Ag+ was that the arsenic on the surface of concentrate was displaced by Ag+, and Ag2S formed, which could be dissolved by Fe3+, releasing Ag+ again.
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The rapid growth demand for power follows that nuclear power industry has led to progressive exhaustion of high grade reserves of uranium ore and new extraction techniques should be developed to use along with low grade ore. On the other hand, the uranium recovery from low grade and refractory ores with conventional techniques of processing is very expensive and tough because these methods require high level of energy and capital costs. Therefore, making use of low cost and influential method is too significant for this issue. One proposed method is microbial leaching. Microbial leaching is regarded as one of the most promising and certainly the most revolutionary solution to these problems in comparison with pyrometallurgy or chemical metallurgy. Microbial leaching is the extraction of metals from their ores using microorganisms. Microbial technology offers an economic alternative to the mining industry. This paper intends to render a general overview of the microbial leaching research activities all over the world. © 2009 by Mrs. Pushpa Agarwal, Managing Editor, Asian Journal of Chemistry, Sahibabad, India.
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Surface pretreatment on minerals prior to flotation was proved to increase the selectivity of separation process. Organic acid pretreatment of low-grade diasporic-bauxite was conducted, and the effects of oxalic acid on bauxite flotation were investigated in this work. The oxalic acid pretreatment mechanisms were studied by adsorption measurements, zeta potential testing, XPS analysis, and ICP analysis. The flotation results showed that the oxalic acid treatment could significantly improve Al2O3 recovery from 75.39% to 81.88% and decrease SiO2 recovery from 53.26% to 47.30%. The adsorption capacity of diaspore for sodium oleate (NaOL) increased by 8.50%, while that of kaolinite decreased by 11.72%. XPS analysis revealed that oxalic acid treatment improved the relative contents of unsaturated Al at diaspore surface beneficial to the adsorption of NaOL. While the relative contents of Al at kaolinite surface was decreased due to the Al dissolution revealed by ICP results. Zeta potential analysis indicated that oxalic acid changed the surface property of minerals favorable for the selective adsorption of NaOL on diaspore surface rather than kaolinite surface. These findings provided a promising direction for surface pretreatment of low-grade bauxite using oxalic acid for the improvement of the flotation desilication.
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For the low-grade copper sulfide ores with 0.99% of copper, of which 41.5% was primary copper sulfide, and 54.5% was secondary copper sulfide, well-controlled column bioleaching on a novel equipment was carried out to investigate the optimal conditions of pre-leaching, particle sizes of ores, temperature, spray intensity and strain consortium. Results show that copper extraction of 91.11% can be obtained after 90 d with the optimal pH value of pre-leaching of 0.8; the pH values of pre-leaching significantly affect the final copper extractions. Copper extractions of 93.11%, 91.04% and 80.45% can be obtained for the bioleaching of ores with particles size of 5–8 mm, 5–15 mm and 5–20 mm, respectively. Copper extractions are 83.77% and 91.02% for bioleaching under the conditions of room temperature and 35 ºC. Copper extractions are 77.25%, 85.45% and 91.12% for the bioleaching when flow rate of spray was 5 L/(h·m2), 10 L/(h·m2) and 15 L/(h·m2), respectively. Additionally, the strain consortium C3 is the best among the four strain consortia in bioleaching. By considering the energy consumption, the optimal conditions of bioleaching in this work are determined as pH of pre-leaching of 0.8, particles size of 5–15 mm, temperature of 35 °C, spray intensity of 15 L/(h·m2), and strain consortium C3. © 2015, Central South University Press and Springer-Verlag Berlin Heidelberg.
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Applicability of bioleaching of Cu, Pb, and As from paddy soil in the vicinity of a refinery site was experimentally examined using a sulfur-oxidizing bacterium, Acidithiobacillus thiooxidans. As a result of aqua regia digestion, the concentrations of Cu (187 mg/kg), Pb (380 mg/kg), and As (107 mg/kg) in the studied soil exceeded the environmental criteria regulated by the Korean government. Batch experiments were performed to investigate the removal efficiency of the heavy metals according to various sulfur supply (0%, 0.1%, 0.5%, and 1%). All microbial experimental sets amended with sulfur showed the enhanced amount of heavy metals extracted, which showed the extraction processes require sulfur addition for proper metabolism of the bacterium. Among various amounts of sulfur addition, 1% (w/v) sulfur addition to the soil inoculated with bacterium led to the removal efficiencies of 67.6%, 25.8%, and 53.3% for Cu, Pb, and As, respectively. The relatively low removal efficiency of Pb resulted from formation of insoluble PbSO4 precipitate. As a result of sequential extraction for the treated soil, most metals were found to exist as a highly stable fraction which is recalcitrant against change of the surrounding environment.
Article
An Acidiphilium strain named DX-A was isolated from acid mine drainage of Dexing mine, Jiangxi Province, China. Strain DX-A is rod-shaped in (0.45-0.55) μm×(1.1-2.1) μm and Gram negative. The optimum temperature and pH for cultivation of DX-A are 30°C and 3.5. FeCl3, and other kinds of sulfide ores and organics (such as glucose), except FeSO4, can be utilized to help strain DX-A grow. Strain DX-A has the closest relativity to the Acidiphilium sp. PK46 (AY765995), with 99% sequence similarity based on the phylogenetic tree, which was constructed according to the published 16S rDNA gene sequences of the relative bacteria species. After cultivating strain DX-A in the flask respectively containing pyrite and marmatite for 28 d, the mass concentrations of the Fe2+ and Zn2+ reach to 2.36 g/L and 2.47 g/L, respectively, while those of the controls are only 0.60 g/L and 0.39 g/L. After strain DX-A and A. ferrooxidans ATCC23270 together leached pyrite as well as marmatite, the mass concentrations of Fe2+ and Zn2+ are 2.7% and 10.3% respectively higher than only A. ferrooxidans ATCC23270 did. The results show that the strain can leach pyrite and marmatite and promote the leaching ability of autotrophic bacteria. All of these provide some evidences for further study on the promotion effects of bioleaching, which are caused by heterotrophic bacteria.
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Conference Paper
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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.
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Modern commercial application of biohydrometallurgy for processing ores became reality in the 1950s with the advent of copper bioleaching at the Kennecott Copper Bingham Mine. Early application entailed dump leaching of low-grade, low-value, run-of-mine material. Dump bioleaching has evolved into a commercially accepted option for bioheap copper leaching of higher-grade, higher value ores. This commercial practice is exemplified by at least 11 mining operations. Paradoxically, application of biohydrometallurgy in the pretreatment of refractory gold ores began with processing high value concentrates, using biooxidation-tank processes and was followed by extension to processing low-grade, lower value ores in heaps. Now, bioleaching has been extended to the commercial extraction and recovery of cobalt. Even with the current success of biohydrometallurgical applications in the mining industry, the real potential of biotechnology in mining remains to be realized. As confidence in commercial bioprocessing grows and experience extends the application's knowledge base, innovations and new commercial practices will emerge. Near-term future commercial applications will likely remain focused on recoveries of copper, gold and possibly nickel. Recent technical advances show that very refractory chalcopyrite can be successfully bioleached. Processes for copper recovery from this mineral will include both heap and stirred-tank reactors. Next generation technologies for pretreatment of refractory gold ores will be based on use of thermophilic bacteria for sulfide oxidation. For biohydrometallurgy to commercially advance, the microbiologist must work cooperatively with the practitioners of the technology for mutual understanding of operational limitations and practical constraints affecting the microbiological component. q 2001 Elsevier Science B.V. All rights reserved.
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The presence of some anions and cations at certain levels in the bioleaching environment may exert an inhibitory effect on the growth and hence leaching activity of a bacterial culture. In this respect, the quality of process water available with particular reference to salinity can be of prime importance for the application or development of a bioleaching process for a particular feed at an operation site. The current study investigates the extent to which salinity up to 8% Cl- (~80 g/l) affects the bioleaching activity of mesophilic, moderately and extremely thermophilic strains of bacteria during the bioleaching of a complex Zn/Pb sulphide ore. The results indicated that salinity can adversely influence the “optimum” bioleaching activity of mesophiles and moderate thermophiles; the extent being dependent upon the strain (and type) of bacteria and the concentration of chloride. The mesophilic WJM strain was found to oxidise the complex ore at concentrations of up to 0.8% Cl- (~8 g/l) without any significant effect on the extraction of zinc while the limited extraction of zinc by DSM 583 strain occurred at 0.2% Cl-. It was noted that mesophiles can be adapted to tolerate 0.8-1% Cl- (~8-10 g/l) in solution. The bioleaching ability of the strains of moderate themophiles was adversely influenced even at 0.2% Cl- (~2 g/l). On the other hand, the extreme thermophiles were shown to perform well under saline conditions up to 5% Cl- (~50 g/l). This probably indicates the halophilic peculiarity of the extreme thermophiles compared with the mesophiles and the moderate thermophiles.
Article
The extraction of copper from chalcopyrite has for centuries been limited to pyrometallurgical methods. Smelting of chalcopyrite is an efficient process but costly both in terms of capital investment, operating costs and environmental compliance. Biological extraction appeared as an appealing alternative. Unfortunately, traditional mesophilic biological extraction methods have met with little success. The chalcopyrite quickly becomes passivated and unacceptable copper extractions are achieved. It was not until the adoption of thermophilic systems that the biological leaching of chalcopyrite became a reality. Several questions remain as to the applicability of the thermophilic system for chalcopyrite; can the system operate auto-thermally; can high extraction rates be achieved; is the process sensitive to mineralogy or grade; and can the precious metals be recovered? GeoBiotics, LLC has embarked on an extensive program to develop the GEOCOAT ® bioleaching system to chalcopyrite ores. This program encompasses mathematical heap modeling, laboratory amenability and column tests, and large scale field trials. The GEOCOAT ® process involves the coating of concentrates onto a suitable substrate, usually barren rock, then stacking the coated material in a conventional heap fashion. The heap is irrigated with acidic solutions containing iron and nutrients while low pressure ambient air is applied at the heap base. To-date, copper extractions in excess of 97% have been achieved in approximately 140 days. Excellent gold extractions have been achieved from the biooxidation residue by cyanidation. Modeling indicates that obtaining thermophilic temperatures within the GEOCOAT ® heap is not a problem. Development is continuing, focusing on the heap design parameters and additional copper concentrates including enargite. Plans are now underway for the first large scale field test in the fall of 2002.
Article
Strategies for efficient start-up of a continuous process for biooxidation of refractory gold ore and concentrate obtained from Hutti Gold Mines Limited (HGML), India are discussed in this work. The biooxidation of the concentrate at high pulp density (10%) with wild strain of Thiobacillus ferrooxidans isolated from HGML mines is characterized by significant lag phase (20 days) and incomplete oxidation (35%) even after prolonged operation (60 days). Two strategies, biooxidation with concentrate adapted cells and a step leaching strategy, in which the pulp density is progressively increased from 2% to 10% were considered and the latter resulted in efficient biooxidation of concentrate. Conversion of such a process from batch to continuous operation is shown to result in complete biooxidation of the concentrate and gold extraction efficiency in excess of 90%.
Article
Recently, chemical recovery of metallic values from low-grade sulphur-bearing ores or concentrates has been replaced by biological treatment; an important recovery process from the environmental and economical respects. Bioleaching has been utilized in several countries to recover metals from sulphide ores with commercial success. In Turkey, there are also some copper and gold-bearing sulphides appropriate for bioleaching process. In this study, the copper recovery from pyritic copper ores in Küre copper mine is investigated with acidophilic bacteria (Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans). As a result of laboratory tests, the highest copper recovery was obtained by Leptospirillum ferrooxidans, Approximately 54% copper recovery was determined after 24 days (576 hours) bioleaching tests.
Chapter
The present article illustrates the increased interest which is manifested in the microorganisms, Thiobacillus ferrooxidans, involved in the biohydrometallurgical extraction processes. The wide varieties of problems currently studied are very important in order to gain a better understanding about the factors which are governing the growth of microorganisms, and as a consequence, the metal dissolution phenomena. In several mining sites, the microbiological leaching techniques are currently practiced at industrial-scale, especially for recovery of copper and uranium from low-grade materials. However, an accurate assessment of further potential possibilities for the application of microorganisms in leaching metal sulfides requires a more fundamental knowledge about the interactions of the physical and chemical factors with the growth of T. ferrooxidans in pure and mixed cultures including heterotrophic and thermophilic cohabitants. Altogether, the future industrial exploitation of these microbiological leaching techniques are very attractive in many countries of the world.
Article
In the history of Turkey the first use of cyanide for gold recovery has been at the Ovacik Gold Mine. During one-year test period, this mine has successfully been mining and processing after a complicated and extensive environmental impact procedure. In Turkey about 2500 ton of sodium cyanide are used with about 240 ton of sodium cyanide being used at this mine annually. During the test period, it has been shown that an effluent quality (CNWAD) between 0.06 ppm (min) and 1 ppm (max) was achievable after cyanide destruction with the Inco Process. It was also found that treated effluent values (CNWAD) of process water (decant) were between 0.04 ppm (min) and 0.59 ppm (max). This paper presents a review of the cyanidation and cyanide destruction processes at the Ovacik Gold Mine.
Article
Biomining is the use of microorganisms to extract metals from sulfide and/or iron-containing ores and mineral concentrates. The iron and sulfide is microbially oxidized to produce ferric iron and sulfuric acid, and these chemicals convert the insoluble sulfides of metals such as copper, nickel and zinc to soluble metal sulfates that can be readily recovered from solution. Although gold is inert to microbial action, microbes can be used to recover gold from certain types of minerals because as they oxidize the ore, they open its structure, thereby allowing gold-solubilizing chemicals such as cyanide to penetrate the mineral. Here, we review a strongly growing microbially-based metal extraction industry, which uses either rapid stirred-tank or slower irrigation technology to recover metals from an increasing range of minerals using a diversity of microbes that grow at a variety of temperatures.
Mineral Biotechnology Society for Mining, Metallurgy and Exploration Biomineralization of metal containing ores and concentrates The Role of Thiobacillus ferrooxidans in hydrometallurgical processes
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Recovery of copper from sulphide ores by Acidithiobacillus ferrooxidans. SDU, Research Project Foundation
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