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Role and contribution of pure and mixed cultures of mesophiles in bioleaching of a pyritic chalcopyrite concentrate

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Abstract

This study compares the capacity of pure and mixed cultures of mesophilic bacteria for bioleaching of a low grade, pyritic chalcopyrite concentrate. In pure culture form, Acidithiobacillus ferrooxidans was found to have a higher bioleaching capacity than Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans with the capability of the latter to bioleach copper being very limited. Mixed cultures, MixA (At. ferrooxidans, L. ferrooxidans and At. thiooxidans) and MixB (L. ferrooxidans and At. thiooxidans) were shown to perform better than the pure cultures with the highest extraction of copper (62.1% Cu) being achieved by MixA. Copper bioleaching performances of the cultures were observed to agree with their respective growth pattern. The results also indicated that the increase in the pulp density (1–5% wt/vol) adversely affected bioleaching process regardless of the pure and mixed cultures used having led to the decrease in the extent of final copper extraction i.e. 50.3% Cu recovery at 1% wt/vol for At. ferrooxidans compared with 38.6% Cu at 5% wt/vol. This study underlines the importance of mixed cultures and, iron and sulphur-oxidising activity of a bacterial culture to efficiently oxidise chalcopyrite.

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... Heap bioleaching is used worldwide to extract metals particularly from low-grade sulphide ores (Brierley, 2008). Effective mineral oxidation inside the heaps is dependent on the activity of iron-and sulphuroxidising microorganisms (Akcil et al., 2007). Studies on Talvivaara multimetal black schist ore deposit located in Sotkamo, Finland have demonstrated that the bioheaps have diverse indigenous microbial communities (Halinen et al., 2009a(Halinen et al., , 2009b(Halinen et al., , 2012. ...
... Effective sulphide mineral oxidation requires active sulphur oxidation in addition to iron oxidation (Akcil et al., 2007;Fu et al., 2008). Experiments performed with different process liquors showed that ironand sulphur-oxidising microorganisms were present in all the process waters, and that they could be enriched. ...
... Other process liquors examined in the present study also contained bacteria similar to A. caldus, Acidiferrobacter thiooxydans, Alicyclobacillus pomorum, L. ferriphilum, and Sulfobacillus sp. It has been shown that mixed cultures are more efficient at bioleaching than pure cultures (Akcil et al., 2007;Fu et al., 2008;Xia et al., 2008). As several iron-and sulphur-oxidising microorganisms were indigenously present in the studied process liquors, it can be hypothesised that by improving their growth conditions, the bioleaching process could be significantly improved. ...
Article
In the present study, six process liquors (PL1 - PL6) originating from heap bioleaching of a complex sulphide ore were examined to reveal factors limiting microbial activity in the bioheaps. PL4 had the lowest iron oxidation activity even though its indigenous iron-oxidising community was diverse (Acidithiobacillus, Leptospirillum, Acidiferrobacter, and Sulfobacillus species). Shake flask experiments at 27 °C revealed that ferrous iron (Fe2 +) and aluminium (Al3 +) concentrations up to 16 and 12 g/L, respectively, were not inhibitory for the iron-oxidising microorganisms in PL4. In addition, Al3 + concentrations of ≤ 6 g/L were shown to enhance iron oxidation rates. High correlation between increased concentrations of cadmium (Cd), sulphate (SO42 −), and vanadium (V) and decreased iron oxidation rates was detected when comparing process liquors 1–6. Moreover, possible nutrient limitation in PL4 was delineated by selectively supplementing it with macro- and micronutrients. Supplementation of 320 mg/L of nitrogen (as NH4⁺) to PL4 significantly increased iron oxidation rates from 20 mg/L/h (no nutrient supplementation) to 160 mg/L/h and would likely also enhance the heap bioleaching process. Additionally, microorganisms growing in high inhibitory ion concentrations (e.g. Cd2 +) were shown to be more sensitive to nitrogen deficiency than microorganisms growing in more dilute liquors.
... El Potencial Redox (Eh) al igual que el pH permite determinar el estado fisiológico de las bacterias oxidadoras de Fe +2 en los procesos de biolixiviación. Principalmente se utiliza para determinar la capacidad oxidación del par iónico Fe +3 /Fe +2 , debido a esto es posible determinar indirectamente el estado de los sistemas de biolixiviación (Liang et al., 2010;Akcil et al., 2007). La formación de un ciclo de transformación de Fe +3 a Fe +2 , permite que el proceso siga desarrollándose de manera regular durante la catálisis bacteriana de los minerales sulfurados. ...
... La formación de un ciclo de transformación de Fe +3 a Fe +2 , permite que el proceso siga desarrollándose de manera regular durante la catálisis bacteriana de los minerales sulfurados. En procesos de biolixiviación de calcopirita el Eh alcanza valores entre 600 y 650 mV en condiciones óptimas de solubilización de cobre, pero cuando se logran valores bajos los 400 mV inicia la precipitación del Fe en forma de jarosita, disminuyendo el rendimiento en la extracción de metales (Dast et al., 1999;Akcil et al., 2007;Córdoba et al., 2008). Al igual que en los procesos de biolixiviación de minerales sulfurados, la extracción de metales desde los residuos electrónicos se ve influenciada por este parámetro. ...
... Por el contrario, la solubilización de los cultivos de A. thiooxidans es baja, producida por la acción química del H2SO4 adicionado en la formulación del cultivo (Figura 3). Akcil et al., 2007y Xia et al., 2008 demostraron en sus experimentos de lixiviación en concentrados de calcopirita y esferalita, que los cultivos mixtos de A. ferrooxidans, A. thiooxidans y L. ferrooxidans logran tasas de recuperación de Cu y Zn más altas que los cultivos puros de cada una de estas bacterias. En el caso de los residuos electrónicos, Wang et al., 2009y Liang et al., 2010, demostraron el mismo efecto para cultivos mixtos de A. ferrooxidans y A. thiooxidans. ...
Article
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Resumen La finalidad de esta investigación fue evaluar y caracterizar la capacidad de solubilizar de metales contenidos en las placas de circuitos integrados ( scraps ) de teléfonos móviles en desuso mediante biolixiviación enriquecida con electrolitos de baterías en desuso (EBD). Se evaluó la capacidad catalítica de cultivos puros y mixtos de bacterias acidófilas A. ferrooxidans ATCC 23270 (A.f) y A. thiooxidans DSM 9463 (A.t). Los resultados obtenidos mostraron que los cultivos mixtos presentan la mejor actividad catalítica para solubilizar Cu y Ni desde scraps de teléfonos móviles a 240 horas de incubación. Estos cultivos logran solubilizar Cu, Ni en cantidades de 9.685 y 211,8 mg/L respectivamente, representando al 65 y 58,8 % del contenido metálico presente en las scrap . Adicional a esto, se determinó la adhesión bacteriana sobre la superficie de las scrap durante el proceso lixiviativo evidenciado que el proceso es realizado por bacterias adheridas y planctónicas. Por lo tanto, se logró establecer la factibilidad de solubilizar el contenido metálico presente en las scrap de teléfonos móviles mediante biolixiviación enriquecida con EBD, siendo una posible alternativa para el tratamiento de los desperdicios electrónicos.
... Selection of the suitable microorganisms for the leaching is one of the important factors. Various studies have shown that a mixed culture containing the iron and sulphur oxidizing bacteria is more effective than pure culture [23, [63][64][65]. Iron and sulfur-oxidizing cultures are important for efficient degradation of chalcopyrite, probably due to demands for ferric iron as an oxidizing agent; and for the removal of elemental sulfur that could be formed on the mineral surface [64] (Table 2). Smelter's dust mix: Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans Stirred tank reactor [81] In addition, the strain which is used should also be taken in to account, because there are variations of the biological characteristics of the bacterium with the same genome [82]. ...
... Various studies have shown that a mixed culture containing the iron and sulphur oxidizing bacteria is more effective than pure culture [23, [63][64][65]. Iron and sulfur-oxidizing cultures are important for efficient degradation of chalcopyrite, probably due to demands for ferric iron as an oxidizing agent; and for the removal of elemental sulfur that could be formed on the mineral surface [64] (Table 2). Smelter's dust mix: Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans Stirred tank reactor [81] In addition, the strain which is used should also be taken in to account, because there are variations of the biological characteristics of the bacterium with the same genome [82]. ...
Article
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Mining and metallurgy are the necessary economy branch in the global technological development on which relies a large part of other industries. Mining and ore processing are changing geological conditions, producing a tremendous amounts of waste worldwide, causing negative consequences for the environment and lead to climate change. Negative effect on the environment can be mitigated by treatment of resource from mining and metallurgy with microorganisms. Microorganisms can be used for the leaching of metals from ore, concentrates and waste materials, but also for the bioremediation of acide mine drainage. On that way, it reduces the release of metals into the environment. In this paper is considered the application of Acidithiobacillus ferrooxidans in biological treatment of resource from mining and metallurgy of copper in order to utilization of it for recovery of metals.
... For instance, mesophilic bio-oxidizing bacteria, Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans, coexist in bacterial communities found near acid mine drainage (Xiang et al. 2010). Many studies have reported the use of a mixed consortium of these bacteria in bioleaching for enhanced metal recovery from primary metal sources such as covellite and chalcopyrite (copper ore) (Akcil et al. 2007;Falco et al. 2003). A consortium of these mixed mesophilic bacteria has also been used for metal recovery from secondary sources such as fly ash and printed circuit boards (electronic waste) (Xiang et al. 2010;Ilyas et al. 2007;Ishigaki et al. 2005). ...
... Hence, it is likely that intercellular communication and symbiosis amongst the isolates may favour bioleaching. Increase in copper recovery (by 1.5 to 3 times) has been observed in mixed cultures of mesophilic acidophilic bacteria from ores such as covellite and chalcopyrite (Akcil et al. 2007;Falco et al. 2003). Metal recovery from secondary sources such as fly ash (at higher pulp densities) and printed circuit boards was enhanced by ∼20-30 % with a consortium of mixed mesophilic bacteria (a sulfur-oxidizing bacterium and an iron-oxidizing bacterium, Sulfobacillus thermosulfidooxidans, and an unidentified acidophilic heterotroph, respectively) (Ilyas et al. 2007;Ishigaki et al. 2005). ...
Article
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With the gradual depletion of high-grade copper ore deposits, secondary wastes are gaining importance as a source for metal recovery. However, the alkalinity and low copper concentration in some of these resources underscore the need for selective leaching agents. In this work, indigenous alkaliphiles from a fly ash landfill site with inherent pH tolerance, metal tolerance and copper leaching capability were isolated and investigated. Four isolates, namely Agromyces aurantiacus TRTYP3, Alkalibacterium pelagium TRTYP5, Alkalibacterium sp. TRTYP6 and Bacillus foraminis TRTYP17, each selectively leached about 50 % copper from 1 % (w/v) of fly ash. Mixed culture of these bacteria resulted in higher leaching of copper. The optimal combination was TRTYP3, TRTYP5, TRTYP6 and TRTYP17 in the ratio 1:1:3:1, which leached 88, 81, 78, 76, 70 and 55 % Cu from 1, 2.5, 5, 10, 15 and 20 % (w/v) of fly ash. While Cu and Pb were bioleached into solution, Fe and Zn were precipitated.
... Among these factors, microorganisms are the most important. A number of studies show that mixed cultures and consortia of microorganisms are more efficient and stable in the oxidation of sulfide minerals than pure cultures (Akcil et al. 2007;Falco et al. 2003;Fu et al. 2008;Baker and Banfield 2003;Johnson 2001). From this point of view, developing and optimizing microbial consortia for use in commercial leaching systems remains an important challenge. ...
... For the creation of such designed consortia, the decisive factors are temperature, pH, concentration of metals, toxic ions, etc. A number of researchers have shown that cultures obtained by this method are most effective in accelerating the oxidation of certain minerals (Johnson et al. 2008;Akcil et al. 2007;Okibe and Johnson 2004;d'Hugues et al. 2009;Bryan et al. 2011;Mejia et al. 2009). ...
Chapter
Biohydrometallurgy is a modern, steadily developing alternative metal production technology based on the use of microorganisms and their metabolic products, such as ferric iron, sulfuric acid, etc. for the extraction of metals from ores. Microbiological processing of ores and concentrates has economic, technical and, most importantly, environmental advantages over traditional technologies. Heap leaching is successfully used for recovery of copper from a secondary mineral—chalcocite (Cu2S). However, the main world reserves of copper are found in the form of chalcopyrite (CuFeS2). Chalcopyrite is the most refractory mineral and undergoes chemical or biological oxidation at a very low rate. One of the most common ways to enhance copper extraction from chalcopyrite is the use of thermophiles. Besides, the intensity of biooxidation of sulfide minerals depends on the pH, redox potential, Fe²⁺/Fe³⁺ ratio, metals ion concentration and the microorganisms used. It was revealed that the mixed cultures and consortia of moderate thermophilic microorganisms were more efficient and stable in the oxidation of chalcopyrite than pure cultures. From this point of view, developing and optimizing microbial associations for use in commercial copper leaching systems remain an important challenge. In this paper bioleaching of chalcopyrite by pure and mixed cultures of moderate thermophilic bacteria S. thermosulfidooxidans and thermotolerant sulfur or iron oxidizing bacteria L. ferriphilum CC, as well as the influence of physicochemical factors on this process have been investigated.
... Among these factors, microorganisms are the most important. A number of studies show that mixed cultures and consortia of microorganisms are more efficient and stable in the oxidation of sulfide minerals than pure cultures (Akcil et al. 2007;Falco et al. 2003;Fu et al. 2008;Baker and Banfield 2003;Johnson 2001). From this point of view, developing and optimizing microbial consortia for use in commercial leaching systems remains an important challenge. ...
... For the creation of such designed consortia, the decisive factors are temperature, pH, concentration of metals, toxic ions, etc. A number of researchers have shown that cultures obtained by this method are most effective in accelerating the oxidation of certain minerals (Johnson et al. 2008;Akcil et al. 2007;Okibe and Johnson 2004;d'Hugues et al. 2009;Bryan et al. 2011;Mejia et al. 2009). ...
Chapter
Metal-rich natural and artificial habitats are extreme environments for the development and evolution of unique microbial communities, which have adapted to the toxic levels of the metals. Diverse bacterial groups have developed abilities to deal with the toxic metals by bioaccumulation of the metal ions inside the cell actively or passively, extracellular precipitation, efflux of heavy metals outside to the microbial cell surface, biotransformation of toxic metals to less toxic forms, and metal adsorption on the cell wall. Metalophilic microbes are found in all bacterial and archaeal groups studied, but mostly appear among aerobic and facultative anaerobic chemoheterotrophic and chemolithoautotrophic microorganisms of the Bacillus, Pseudomonas, Staphylococcus, Actinobacteria, Cuprividus, Acidobacterium, Acidithiobacillus, Thiobacillus, Ferroplasma, and Sulfolobus genera. The phenomenon of microbial heavy metal resistance has fundamental importance and is particularly relevant in microbial ecology, especially in connection with the roles of microbes in biogeochemical cycling of heavy metals and in the bioremediation of metal-contaminated environments. The heavy metal resistance mechanisms and different applications of metal resistant/metalophilic bacteria and archaea have been expounded deeply in this chapter.
... Our research deals with the effect of particle size, pH, and pulp density due to the importance of these factors and its goal is to intensify the overall gain of metals. There is much work on bioleaching using different types of microorganisms, mixtures of bacterial cultures, fungi, and archaea [1,[24][25][26][27][28], but the effect of pH is not sufficiently studied. Different size fractions and pulp densities are among the major aspects of the process and the results should clarify the choice of conditions for further studies of bioleaching and their subsequent use in practice. ...
... Leaching with A. ferooxidans is economically advantageous due to lower temperatures and no significant corrosive processes as in the case of thermophiles [10]. Akcil et al. [28] have shown a direct relationship between the efficiency of metal extraction and the amount of bacterial content in the medium. During the tests, the optimal conditions were maintained for the sufficient multiplication of microorganisms in order to ensure the most efficient dissolution of metals. ...
Article
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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.
... The efficiency of bioleaching processes depends on the characteristics of the ore (Ghorbani et al. 2011;Dhawan et al. 2013), the type of used microorganisms (Akcil et al. 2007;Fu et al. 2008;Tao et al. 2021), and the provided physical and chemical conditions for growth and development of microorganisms (Petersen and Dixon 2002;Pradhan et al. 2008;Vilcáez et al. 2008;Watling et al. 2013;Maluckov 2020). ...
Article
Full-text available
In nature, microorganisms developed at various places and adapted to the various weather and geological conditions. Microorganisms participate in geological transformations leading to the dissolution of some minerals and conversion to others. While some microorganisms with their metabolic activity increase the mobility of metals, others cause precipitation of metals and the formation of new minerals. These biogeochemical interactions found practical application in the recovery of metals. In the article, the proposals for improvement of existing engineering commercial processes for recovery of metals are given which can enable the formation of nanogold and nanogold compounds. Key points • Amino acids in pretreatment can increase the dissolution of the layer around the gold.• Amino acids in the complexing stage can increase gold leaching.• After the complexing stage, the bionanosynthesis of gold and its compounds is possible.Graphical abstract
... The enhancement in bioleaching efficiency has been obtained using mixed consortia of microorganisms (Akcil et al., 2007;Kaksonen et al., 2016;Panda et al., 2015;Vestola et al., 2010). Sometimes iron oxidation forms precipitate known as jarosite deposited on the material surface (Zhao et al., 2017;Nazari et al., 2014). ...
... The enhancement in bioleaching efficiency has been obtained using mixed consortia of microorganisms (Akcil et al., 2007;Kaksonen et al., 2016;Panda et al., 2015;Vestola et al., 2010). Sometimes iron oxidation forms precipitate known as jarosite deposited on the material surface (Zhao et al., 2017;Nazari et al., 2014). ...
... Akcil et al. (2007) suggested that, with increasing pulp density, the bacteria-to-solids ratio would likely become too low to generate sufficient Fe(III) and, consequently, maintain an ORP lower than the critical value under which chalcopyrite dissolution is more favorable. 43) Hence, to test this hypothesis, the chalcopyrite bioleaching experiments were conducted under different pulp densities of 1%, 2%, and 4% (w/v). Figures 4(a)(d) show Cu leaching efficiency, ORP, total Fe concentration, and the Fe(III):Fe(II) ratio as a function of time at different pulp densities, while other parameters were held constant (i.e., initial pH = 1.5, temperature = 45°C, initial Fe(II) concentration = 5 g/L). ...
Article
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This study examines the effects of several operating parameters on copper leaching from chalcopyrite ores using an adapted mesophilic bacterial culture. Three temperatures (35, 40, and 45°C), three pulp density (1, 2, and 4% (w/v)), and three initial ferrous ion (Fe(II)) concentrations (5, 10, and 20 g/L) were employed as variable parameters, and their effects on the bioleaching efficiency of chalcopyrite were investigated. After 14 days, the maximum copper bioleaching efficiency was estimated to be ∼64% at a temperature of 45°C, a pH of 1.5, an initial ferrous concentration of 5 g/L, and a pulp density of 4%. More specifically, the chalcopyrite dissolution tests conducted at different temperatures showed a minimal effect of temperature and low leaching efficiency (<20%) regardless of temperature. The trend of chalcopyrite dissolution at different pulp densities showed that Cu extraction tended to increase with increases in pulp density. Moreover, the Cu leaching efficiency associated with mesophilic microorganisms largely decreased when the initial Fe(II) concentration was greater than 10 g/L. The Cu leaching behavior in different test conditions was evalauted with concentrations of total iron (Fe), Fe(II), and ferric ions (Fe(III)), as well as the oxidation-reduction potential (ORP) of the solution used in the test. The Cu leaching rate increased under lower ORP conditions, lower Fe(III):Fe(II) ratios, and balanced Fe(II)–Fe(III) cycles.
... An increase of bioleaching efficiency can also be achieved through the application of mixed microbial cultures ( Akcil et al., 2007;Kaksonen et al., 2016;Panda et al., 2015a;Vestola et al., 2010). For example, coupled incubations with sulfur and iron oxidizing acidophiles can enhance the metal extraction from waste deposits ( Kaksonen et al., 2016). ...
Article
Smelting activity by its very nature produces large amounts of metal-bearing waste, often called metallurgical slag(s). In the past, industry used to dispose of these waste products at dumping sites without the appropriate environmental oversight. Once there, ongoing biogeochemical processes affect the stability of the slags and cause the release of metallic contaminants. Rather than viewing metallurgical slags as waste, however, such deposits should be viewed as secondary metal resources. Metal bioleaching is a “green” treatment route for metallurgical slags, currently being studied under laboratory conditions. Metal-laden leachates obtained at the bioleaching stage have to be subjected to further recovery operations in order to obtain metal(s) of interest to achieve the highest levels of purity possible. This perspective paper considers the feasibility of the reuse of base-metal slags as secondary metal resources. Special focus is given to current laboratory bioleaching approaches and associated processing obstacles. Further directions of research for development of more efficient methods for waste slag treatment are also highlighted. The optimized procedure for slag treatment is defined as the result of this review and should include following steps: i) slag characterization (chemical and phase composition and buffering capacity) following the choice of initial pH, ii) the choice of particle size, iii) the choice of the liquid-to-solid ratio, iv) the choice of microorganisms, v) the choice of optimal nutrient supply (growth medium composition). An optimal combination of all these parameters will lead to efficient extraction and generation of metal-free solid residue.
... One important approach is the selection microorganisms. Compared with pure cultures, mix cultures can enhance copper extraction efficiency (Akcil et al. 2007). The majority of researchers have focused on the application of mesophilic microorganism (pure culture and mixed culture), including Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Acidithiobacillus thiobacillus (Moghaddam 2010;Xu et al. 2013;Jiang et al. 2015). ...
Article
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This study used an artificial microbial community with four known moderately thermophilic acidophiles (three bacteria including Acidithiobacillus caldus S1, Sulfobacillus thermosulfidooxidans ST and Leptospirillum ferriphilum YSK, and one archaea, Ferroplasma thermophilum L1) to explore the variation of microbial community structure, composition, dynamics and function (e.g., copper extraction efficiency) in chalcopyrite bioleaching (C) systems with additions of pyrite (CP) or sphalerite (CS). The community compositions and dynamics in the solution and on the ore surface were investigated by real-time quantitative PCR (qPCR). The results showed that the addition of pyrite or sphalerite changed the microbial community composition and dynamics dramatically during the chalcopyrite bioleaching process. For example, A. caldus (above 60%) was the dominant species at the initial stage in three groups, and at the middle stage, still dominated C group (above 70%), but it was replaced by L. ferriphilum (above 60%) in CP and CS groups; at the final stage, L. ferriphilum dominated C group, while F. thermophilum dominated CP group on the ore surface. Furthermore, the additions of pyrite or sphalerite both made the increase of redox potential (ORP) and the concentrations of Fe3+ and H+, which would affect the microbial community compositions and copper extraction efficiency. Additionally, pyrite could enhance copper extraction efficiency (e.g., improving around 13.2% on day 6) during chalcopyrite bioleaching; on the contrary, sphalerite restrained it.
... thiooxidans, bacterial growth was seen to reduce after day 18, while this decrease was observed after 30 days for mixed culture. Low pH values might have adversely affected the performances of bacterial cultures, particularly in the final phase of the bioleaching process [35]. The highest bacterial growth was determined to be 2.87 Â 10 9 cells/mL at 1% (w/v) solids and 7% (w/v) sulphur in the experiment using mixed culture. ...
Article
The extraction of precious metals, such as nickel (Ni) and cobalt (Co), from a low-grade nickel laterite ore - supplied from the Çaldag deposits in Manisa, Turkey - has been investigated by employing pure and mixed cultures of mesophilic acidophiles (Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans). The study examines the effects of parameters such as the pulp density, the amount of externally added elemental sulphur and ferrous iron, and pure and mixed bacterial cultures on the bioleaching of the lateritic ore. The increase in the pulp density adversely influenced the leaching activity of the pure and mixed cultures. Mixed culture (At. ferrooxidans and At. thiooxidans) displayed a better performance than pure cultures on the extraction of nickel and cobalt from the ore. The maximum dissolution of Ni and Co after 40 days was found to be 97% and 95%, respectively, by a bioleaching process that contained 7% (w/v) elemental sulphur, 2.24 g/L of ferrous iron, 1% (w/v) solids and the mixed culture.
... On the other hand, those studies (Table 1) are mainly focused on the cultures consisted one specific microorganism while in the industry, mixed microorganisms are mostly used for the bioleaching process [33]. Where using a mixed culture with different microorganisms can lead to the cooperative effects and bioleaching may show a higher efficiency than pure cultures [34][35][36][37][38][39][40]. This study investigated influences of two typical flotation frothers pine oil (PO) and methyl isobutyl carbinol (MIBC) on a population (microorganisms count) of a traditional mixed mesophilic microorganisms culture (Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, and Acidithiobacillus thiooxidans). ...
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.
... Numerous researches have shown that the mixed culture had better performance than a pure culture in chalcopyrite bioleaching (Akcil et al., 2007;Zhang et al., 2009aZhang et al., , 2008. Various interactions, such as competition, synergism, mutation and predation exist among different cultures utilized in bioleaching (Zhang et al., 2015). ...
... Whereas, sulphur oxidizing bacteria avoid the formation of a passivation layer on the mineral surface through the accumulation of elemental sulphur. 3,11) The column was aerated and irrigated at constant rates during the entire process. Ferrous to ferric oxidation rates, solution pH, sulfate production, and arsenic removal were analyzed to obtain insights into the phenomena involved in column bioleaching of mine tailings. ...
Article
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Heap bioleaching for detoxification of mine tailings is a promising technology; however, long-term studies that aim to understand the potential of this process are scarce. Therefore, this study assesses the feasibility of column bioleaching as an alternative technology for treatment of mine tailings with high concentrations of arsenic during a long-term experiment (436 days). To accomplish this objective, we designed a 350-mm plastic column that was packed with 750 g of mine tailings and inoculated with an acidophilic bacterial culture composed of A. thiooxidans and A. ferrooxidans. Redox potential, pH, ferric ion generation, and arsenic concentration of the off-solution were continuously monitored to determine the efficiency of the technology. After 436 days, we obtained up to 70% arsenic removal. However, several drops in removal rates were observed during the process; this was attributed to the harmful effect of arsenic on the bacteria consortium. We expect that this article will serve as a technical note for further studies on heap bioleaching of mine tailings.
... The enhancement in bioleaching efficiency has been obtained using mixed consortia of microorganisms (Akcil et al., 2007;Kaksonen et al., 2016;Panda et al., 2015;Vestola et al., 2010). Sometimes iron oxidation forms precipitate known as jarosite deposited on the material surface (Zhao et al., 2017;Nazari et al., 2014). ...
Article
Bioleaching (microbial leaching), being an economical and environmental friendly process, is investigated extensively for metal extraction from secondary solid wastes, viz., electronic wastes, spent catalyst, sludge, slag and fly ash. Bioleaching using acidophiles is routed through generation of ferric (Fe III) and sulphuric acid. Other microbes such as the fungi carryout bioleaching by acidolysis,complexolysis (generation of organic acids), redoxolysis and bioaccumulation method. The cyanogenic microbes in particular possess the ability to extract metal(s) by producing hydrogen cyanide. The bioleaching process is achieved by one-step, two-step and spent medium-step in batch mode or by continuous mode reported to be promising on quantitative extraction of various metals (Ni, Co, Mo, V, Fe, Zn, Cu, Cr, Cd, W, Pb and Mn). Enhanced metal extraction can be accomplished by implementing pretreatment methods like, adding a catalyst, prior adaptation of microbes, bioleaching followed by bioleaching or chemical leaching, ultrasound, and also by optimising the process parameters. Additionally, the use of small size waste particles, low pH, low solid concentration and higher operating temperature could also enhance metal leaching to considerable extent. The review compiles extensive studies on treatment of secondary solid wastes employing chemolithotrophs (acidophiles) and organotrophs (fungi and cyanogens) for metal extraction. The mechanism of bioleaching, candidate microbes, metal extraction efficiency, operational strategies and process improvement are extensively reviewed, discussed and reported.
... To achieve efficient bioleaching, it is reasonable to use a consortium of acidophilic bacteria rather than a pure culture (Akcil et al. 2007;Fu et al. 2008;Nguyen et al. 2015). Consequently, Acidithiobacillus ferrooxidans FT-22, Acidithiobacillus ferrooxidans FT-23, Acidithiobacillus ferrooxidans BF and Acidithiobacillus ferrivorans SU-8, which has been previously isolated from sulfide ore sites, were used in the present work. ...
Article
This investigation compares bacterial leaching to chemical leaching to solubilize copper from a copper containing ore of the new site Northern Qarashoshaq in Zhylandy (Kazakhstan) which is currently under commercial development. From ICP-OES analysis, the bulk ore sample contains 1.5% of Cu and a trace level at 0.0024% of Ag. Phase analysis shows the main copper containing minerals are covellite, chalcocite, malachite, chrysocolla and chalcopyrite. According to X-ray diffraction analysis, silver is mainly presented as jalpaite (Ag3CuS2) minerals. Copper leaching was carried out by acidophilic bioleaching for comparison with extraction by chemical methods involving the addition of sulfuric acid and Fe3+ or only sulfuric acid in flasks, as well as column leaching tests to simulate heap leaching. Ag was extracted by cyanidation methods again in flasks as well as column leaching tests. Results showed that copper extraction is up to 95% when using bioleaching in the flask, 83% in the case of Fe3+ with sulfuric acid and 76% for sulfuric acid. Furthermore, subsequent extraction of Ag reaches 97% for bioleaching and 92% for chemical leaching. Column bioleaching tests showed an 82.3% yield of copper after 70 days of the experiment and a 70% of silver, whereas for chemical leaching the yield of copper is 66.8% and silver is 51%. In conclusion, this investigation demonstrated higher extraction for both copper and silver from the primary ore in the bioleaching sample compared to the chemical leaching sample. More silver was extracted in the bioleaching case as there was less copper remaining to compete for the cyanide anions.
... Among these microorganisms, different types of interactions such as competition, predation, mutualism, and synergy, have been described (Johnson, 1998). However, many studies have indicated that mixed cultures containing a variety of microorganisms tend to be more robust and more efficient in oxidizing sulfide minerals due to their extensive interactions (Akcil et al., 2007;Zhang et al., 2008;Deng et al., 2017). Further, the ecological function of the microbial community was often associated with its structure and diversity. ...
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The introduction of Acidithiobacillus thiooxidans A01 strengthens the positive interactions between physiologically distinct microorganisms and enhances the bioleaching ability of the consortium. However, the effect of introducing an exogenous strain, A. thiooxidans A01 on the structure and function of the adsorbed and planktonic microbial consortia during bioleaching of low-grade copper sulfide remains unclear. In this study, A. thiooxidans A01 was introduced into an indigenous leaching microbial community on the 0th (group B), 24th (group C), and 36th day (group D). Results revealed that the copper leaching efficiency was highest in group D, in which the Cu2+ concentration in the solution reached 251.5 mg/L on day 48, which was 18.5% higher than that of the control (group A, no addition of A. thiooxidans A01). Restriction fragment length polymorphism (RFLP) analysis of the microbial community in group D revealed the presence of Leptospirillum ferriphilum, Acidithiobacillus ferrooxidans, Acidithiobacillus caldus, Sulfobacillus sp., Acidiphilium spp., and Acidithiobacillus albertensis before introduction of A. thiooxidans A01 on the 36th or 48th day; however, A. albertensis was absent on day 48 in group A. Further, the proportion of dominant A. caldus, L. ferriphilum, and A. ferrooxidans became altered. The results of real-time PCR in group D showed that A. thiooxidans A01 was primarily adsorbed on the surface of the ore, with the adsorption reaching the maxima on day 42; while the free A. thiooxidans A01 in solution grew slowly, reaching its maximum concentration on day 45. Compared with that in the control group, the abundance of both free and attached A. caldus and Sulfobacillus sp. decreased following the introduction of A. thiooxidans A01, while that of L ferriphilum, A. ferrooxidans, and Acidiphilium sp. increased. Functional gene arrays data indicated that the abundance of genes involved in sulfide and iron oxidation in L. ferriphilum and A. ferrooxidans, as well as that of the metal (loid) resistance genes of A. ferrooxidans, L. ferriphilum, and Acidiphilium sp. increased, while the abundance of genes involved in sulfur metabolism in A. caldus and Sulfolobus spp. decreased. Taken together, these results provide useful information for application of bioleaching of copper sulfide in industry.
... En experimentos realizados sugiere que la exposición de éste tipo de microorganismos a altos concentrados de sulfuros puede resultar en la disminución o inhibición de la actividad metabólica (Gómez et al., 1999), esto por la reducción de la cantidad de oxígeno disuelto, el daño que ocasiona las partículas por la fricción a la pared celular, también debido a efectos nocivos de los iones metálicos como el As 3+ , As 5+ y Fe 3+ , entre otros (Akcil et al., 2007;Mousavi et al., 2007;Marhual et al., 2008). Sin embargo, la bacteria A. ferrooxidans puede ser adaptado para incrementar su tolerancia a estos ambientes y disminuir los efectos inhibitorios; mejorando notablemente los procesos de beneficio mineral ( El método que se emplea comúnmente para la adaptación de la cepa de Thiobacillus es la de cultivos sucesivos, consiguiendo de esta manera la adaptación (Natarajan et al., 1994), pero el problema con esta metodología en algunos casos es que el proceso puede durar varios años (Brahmaprakash et al., 1988y Das et al., 1998. ...
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En los procesos de disolución y adsorción de metales, se requieren la contribución de especies bacterianas previamente adaptadas a los ambientes específicos, con la finalidad de lograr buenos resultados (Barrie J., 2006). En la adaptación de las cepas de Thiobacillus existen diversos mecanismos y reactivos, como es el uso de medios nutrientes ideales conteniendo sustancias en función a la efectividad para lograrlo. Por tal motivo se ha modificado el medio 9k, con el objetivo de hallar un medio adecuado logrando incrementar la población bacteriana de cepa Thiobacillus Ferrooxidans aislada de la Unidad Minera Recuperada, modificando el contenido de sulfato de hierro en el sustrato y el control estricto del pH. Siendo estos valores 22.4 gr/Lt de sulfato de hierro y un pH de 1.8 A las condiciones de trabajo, en las primeras 48 horas se genera un consumo de protones de hidrogeno, lo cual reduce la acidez a 2.3 – 2.4, siendo menor el efecto a bajas concentraciones de sustrato. La producción de ácido sulfúrico por el mecanismo indirecto de oxidación bacteriana (Álvarez M. T., 2005), es apreciado del 3º día en adelante estabilizando el pH entre 1.9 a 2.0 siendo los más ácidos los que tienen mayor contenido de sustrato (44.4 g/Lt). Además, ocurre la precipitación de hidrosulfuros de hierro depende positivamente del pH y del Sulfato de Hierro, significa que siempre se tendrá producción de precipitados, en función a la cantidad de sustrato adicionado, la que se reducirá controlando la acidez del medio y evitar la inhibición de la bacteria durante el proceso de de biooxidación de minerales.
... Typical copper bio heap leaching characteristics are ore particle size distribution (PSD) 19-25 mm, lixiviant irrigation rates between 5 and 20 L/m 2 /h, aeration rates from 0.1 to 0.5 Nm 3 /m 2 /h, heights of 6 to 10 m, leaching period of 4 to 36 months, and final pregnant leach solution (PLS) with 2 to 10 g/L copper concentration (Petersen 2016), but the copper bio heap leaching faces challenges such as high temperatures (Dixon 2000), microbial succession (Brierley 2001), formation of secondary reaction products (Daoud and Karamanev 2006), difficulties in heat management over aeration-irrigation (Dixon 2000, Crundwell andNorton 2009), and pyrite content (Akcil et al. 2007). Definitely, numerous research works have been carried out to find scientific solutions for these problems. ...
Article
The formation of hydrolyzed ferric iron (Fe (III)) as jarosite could limit the bioleaching of copper and significantly lower the dissolution rate of low-grade chalcopyrite ore. Thus, to improve the rate through overcoming the hindered dissolution of chalcopyrite, this study investigated the influence of chloride addition into leaching lixiviant. As a microbial source, mixed mesophiles, moderately thermophilic, and thermophilic microorganisms were adapted to about 120 mM NaCl solution. After optimization of the ore bioleaching in 64 controlled mini-columns, the scaled tests in 2-m tall columns were conducted to study the overall leaching procedure and precipitation of the jarosite. Under normal aeration conditions (0.05 Nm³/m²/h) with hybrid irrigation (120 mM NaCl in H2SO4 solution at pH = 1.5), copper recovery reached 80% after 120 days while it was approximately 50% with limited one (0.003 Nm³/m²/h). The limited aeration column had a moderate oxidation–reduction potential (ORP) with values < 450 mV. This significant improvement in dissolution is explained by the reduced precipitation of passivating layer (mainly jarosite). These conclusions were also confirmed by the estimation of pyrite and natrojarosite with a modified ASTM D-2492 (MASTM D-2492). Moreover, to identify the microbial communities in the columns, DNA extraction and 16Sr RNA gene PCR amplification and sequencing were done.
... Bioleaching is a simple, environmentally friendly, and cost-effective method of processing sulfide mineral feeds [5][6][7]. This is due to the fact that sulfide deposits are a natural habitat for acidophilic microorganisms that oxidize iron and sulfur [8]. This method is promising in terms of processing various mineral feeds-low-grade ores, tailings dumps, fine concentration tailings, and other industrial waste-containing non-ferrous and precious metals. ...
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The feasibility of processing low-grade copper-nickel ores by heap bioleaching was investigated. It was found that an iron-oxidizing strain of acidophilic microorganisms, Acidithiobacillus ferrivorans, is effective in the leaching of sulfide ores from the deposits in Russia’s Murmansk region. Sulfide mineralization of the studied mineral feeds was described using the methods of X-ray phase analysis and optical microscopy. In the process of leaching, the pH and Eh values and the concentrations of ferric and ferrous iron, nickel, and copper ions were monitored. By the end of the experiment, 16.5% of nickel and 7.5% of copper was recovered from the ore of the Allarechensk technogenic deposit, while 22.5% of nickel and 12.7% copper were recovered from the ore of the Nud II deposit. By silicate analysis of the solid phase, patterns of ore chemistry change were described during the process of bioleaching.
... One of the topics of interest is using mixed cultures in the bioleaching of sulfide minerals. It has been shown that using mixed cultures resulted in a higher metal extraction rate than using pure cultures (Akcil et al., 2007;Liu et al., 2011;Panda et al., 2015). On mesophilic and/or moderate thermophilic conditions, Acidithiobacillus spp., Leptospirillum spp., Sulfobacillus spp., and Ferroplasma spp. ...
Article
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Low-temperature biohydrometallurgy is implicated in metal recovery in alpine mining areas, but bioleaching using microbial consortia at temperatures <10°C was scarcely discussed. To this end, a mixed culture was used for chalcopyrite bioleaching at 6°C. The mixed culture resulted in a higher copper leaching rate than the pure culture of Acidithiobacillus ferrivorans strain YL15. High-throughput sequencing technology showed that Acidithiobacillus spp. and Sulfobacillus spp. were the mixed culture’s major lineages. Cyclic voltammograms, potentiodynamic polarization and electrochemical impedance spectroscopy unveiled that the mixed culture enhanced the dissolution reactions, decreased the corrosion potential and increased the corrosion current, and lowered the charge transfer resistance and passivation layer impedance of the chalcopyrite electrode compared with the pure culture. This study revealed the mechanisms via which the mixed culture promoted the chalcopyrite bioleaching.
... In recent years, bio-metallurgy technology developed rapidly and was applied in the smelting process of arsenic-bearing refractory gold ore and secondary copper sulfide [7]. For chalcopyrite bioleaching technology, the development is slow due to the following reasons: the high lattice energy of chalcopyrite [8], its difficulty to be oxidized in the bioleaching process, and the passivation layer produced by the insoluble substance that inhibits the further diffusion of bacteria and reactant [9][10][11][12][13][14][15]. ...
Article
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Bacteria–mineral contact and noncontact leaching models coexist in the bioleaching process. In the present paper, dialysis bags were used to study the bioleaching process by separating the bacteria from the mineral, and the reasons for chalcopyrite surface passivation were discussed. The results show that the copper leaching efficiency of the bacteria–mineral contact model was higher than that of the bacteria–mineral noncontact model. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) were used to discover that the leaching process led to the formation of a sulfur film to inhibit the diffusion of reactive ions. In addition, the deposited jarosite on chalcopyrite surface was crystallized by the hydrolysis of the excess Fe3+ ions. The depositions passivated the chalcopyrite leaching process. The crystallized jarosite in the bacteria EPS layer belonged to bacteria–mineral contact leaching system, while that in the sulfur films belonged to the bacteria–mineral noncontact system.
... Significant copper resources in Turkey are scattered in the north of the country, and Küre copper ore deposit is one of the most important ones. Some studies have been carried out on leaching of Küre chalcopyrite concentrate using with some lixiviants [74][75][76][77][78]. However, it has not been used in roasted the concentrate leaching in previous studies. ...
Article
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Chalcopyrite (CuFeS2) is commonly used ore in production of copper, but leaching of this ore is very slow and inefficient due to “passivation” during leaching at atmospheric conditions. In this study, in order to overcome drawbacks of the passivation layers, the concentrate supplied from Eti Bakır A.Ş. Küre Plant in Turkey was roasted at 600 °C for 1 h and after leached. Box–Wilson procedure of statistical experimental design was utilized to identify the effects of significant leaching variables for instance leaching time (X1; 10–120 min), solid/liquid ratio (X2; 0.01–0.20), and H2SO4 concentration (X3; 0.01–1.00 M) on Cu extraction (%) from roasted concentrate and was tried to be optimized. The coefficients of response functions have been calculated by regression analysis, and the estimates have been found to be well in line with the experimental outcomes. The optimal leaching parameters, time, solid/liquid rate and H2SO4 concentration were determined as 115 min, 0.116, and 0.71 M, respectively, and the highest Cu extraction (%) value was calculated as 92.45%.
... This experiment has shown that up to 85% of copper recovery from the chalcopyrite concentrate could be achieved using A. copahuensis, confirming that thermoacidophilic microorganisms could be successfully used in a bioleaching process with refractory minerals. The maximum extraction achieved in this experience was clearly greater than that achieved using mesophilic microorganisms, usually less than 40-50% [44]. The fundamental role of the microbial contact mechanism and the importance of surface colonization in the process of chalcopyrite bioleaching were also demonstrated. ...
Article
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Studies of thermophilic microorganisms have shown that they have a considerable biotechnological potential due to their optimum growth and metabolism at high temperatures. Thermophilic archaea have unique characteristics with important biotechnological applications; many of these species could be used in bioleaching processes to recover valuable metals from mineral ores. Particularly, bioleaching at high temperatures using thermoacidophilic microorganisms can greatly improve metal solubilization from refractory mineral species such as chalcopyrite (CuFeS2), one of the most abundant and widespread copper-bearing minerals. Interfacial processes such as early cell adhesion, biofilm development, and the formation of passive layers on the mineral surface play important roles in the initial steps of bioleaching processes. The present work focused on the investigation of different bioleaching conditions using the thermoacidophilic archaeon Acidianus copahuensis DSM 29038 to elucidate which steps are pivotal during the chalcopyrite bioleaching. Fluorescent in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) were used to visualize the microorganism–mineral interaction. Results showed that up to 85% of copper recovery from chalcopyrite could be achieved using A. copahuensis. Improvements in these yields are intimately related to an early contact between cells and the mineral surface. On the other hand, surface coverage by inactivated cells as well as precipitates significantly reduced copper recoveries.
... A laboratory stock of mixed meso-acidophillic chemolithotrophic microbial consortium was used for bioleaching studies (discussed in Section 2.4.2). Since, mixed consortium is considered to be more effective than a pure culture (Ciftci and Akcil, 2010;Akcil et al., 2007), a consortium predominantly comprising At. ferrooxidans, Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans strains were used in the present study. The standard 9 K + media containing (NH 4 ...
Article
Dumping of poor but metal containing industrial waste is associated with several environmental issues. Exposure of these wastes to the natural environment offers serious concerns for the mineral processing industries to utilize them for metal recovery and check environmental pollution. In the present study, a novel sequential bioreduction-bioleaching and bioreduction-chemical leaching route as a hybrid process is compared and discussed for the enhanced recovery of copper from an industrial concentrator plant ball milling unit rejected sample. A mixed consortium of metal reducing bacteria (DMRB) initially adapted to high Fe(III) concentrations was found to cause mineralogical/matrix alteration (possibly silicate weathering) including Fe(III) bioreduction in the sample and dissolute 29.73% copper during the first 35 days under facultative anaerobic conditions. Sequential leaching of the bioreduced waste sample (generated from the first step) using a mixed meso-acidophilic bacterial consortium predominantly Acidithiobacillus ferrooxidans showed additional 28.72% copper dissolution within 2 days using 1 gL- 1 Fe(II). On the other hand, a comparative chemical leaching of the same bioreduced sample using 0.5 M H2SO4 yielded additional 32.17% copper within 4 days of leaching and indicated better performance than the bioleaching tests.
... In the last several decades, many types of conventional technologies, such as hydrometallurgy (Arslan and Arslan, 2002;Banza et al., 2002;Petersen, 2016), pyrometallurgy (Gyurov et al., 2011;Sarfo et al., 2017;Ye et al., 2003;Zhang et al., 2007), and bioleaching (Akcil et al., 2007;Carranza et al., 2009;Potysz et al., 2018), have been proposed to recover metals from slags. Such studies have confirmed that a higher metal recovery rate can be realized, and the resulting data are useful for the optimization of the recovery process. ...
... Several efforts have been taken towards the process improvement of heap bioleaching by studying the influential parameters like temperature, the inocula, and redox potential (Córdoba et al., 2008;Gautier et al 2008;Third et al., 2002), albeit only a partial enhancement in leaching efficiency could be obtained. A few studies have shown that the use of mixed cultures exhibiting a strong ability to bioleaching of chalcopyrite than pure cultures, mainly due to the co-existence of different physiological and ecological functions with various microbial species in the same bioleaching system that plays key supplementary roles for metals leaching (Akcil et al., 2007;Qiu et al., 2005). Although the possibilities for using thermophiles have considerably improved reaction kinetics by avoiding the excessive passivation of chalcopyrite, which usually inhibits the progress of bioleaching process (Sandström and Petersson, 1997;Gomez et al., 1999a,b); the application was found to be expensive and difficult. ...
Article
The bioleaching of chalcopyrite concentrate, intensified by the adapted mesophilic culture in the continuous stirred tank reactors (CSTR) was investigated. The cumulative bioleaching efficiency of copper was found to be increased from 34.8%–49.3% in CSTR-1, 40.3%–71.2% in CSTR-2, and 44.3%–73.8% in CSTR-3, while the temperature was elevated from 30–37 °C, respectively; whereas, the pulp density (10%, w/v), agitation speed (350 rpm), aeration (400 cc/min), and retention time (7 days across the three reactors) were also optimized to keep constant. Further, the activation energy calculated for copper dissolution under the continuous flow indicated that the surface-diffusion was the overall rate-limiting step for the bioleaching process. Instrumental analysis of solid samples could reveal the degradation pathways of chalcopyrite bioleaching as: CuFeS2 → Cu2S → Cu0.3333Fe0.6667S → H9Fe3O18S8. It follows a complex mechanism that includes the occurrence of polysulfide and cooperative mechanism along with the passivation onto mineral surfaces.
... The mixture of all studied microorganisms showed the highest efficiency of oxidation of both sulfide minerals and elemental sulfur. This agrees with the results of numerous studies that reported the advantage of combined cultures of iron-and sulfur-oxidizing acidophiles over their pure cultures during oxidation of various substrates, including those containing chalcopyrite, pyrite, and covellite [50][51][52][53][54][55]. The most common explanation for the high efficiency of the microbial community is a more successful removal of the products of oxidation reactions (including elemental sulfur) from the surface of sulfide minerals. ...
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A two-step process, which involved ferric leaching with biologically generated solution and subsequent biooxidation with the microbial community, has been previously proposed for the processing of low-grade zinc sulfide concentrates. In this study, we carried out the process of complete biological oxidation of the product of ferric leaching of the zinc concentrate, which contained 9% of sphalerite, 5% of chalcopyrite, and 29.7% of elemental sulfur. After 21 days of biooxidation at 40°C, sphalerite and chalcopyrite oxidation reached 99 and 69%, respectively, while the level of elemental sulfur oxidation was 97%. The biooxidation residue could be considered a waste product that is inert under aerobic conditions. The results of this study showed that zinc sulfide concentrate processing using a two-step treatment is efficient and promising. The microbial community, which developed during biooxidation, was dominated by Acidithiobacillus caldus, Leptospirillum ferriphilum, Ferroplasma acidiphilum, Sulfobacillus thermotolerans, S. thermosulfidooxidans, and Cuniculiplasma sp. At the same time, F. acidiphilum and A. caldus played crucial roles in the oxidation of sulfide minerals and elemental sulfur, respectively. The addition of L. ferriphilum to A. caldus during biooxidation of the ferric leach product proved to inhibit elemental sulfur oxidation.
Article
The article describes results of research on copper recovery from low-grade copper ore by heap bioleaching method. The objects of investigation are ores of the Benkala deposit. Results of chemical analysis by atomic-emission spectrometric method and chemical phase analysis present ores element composition and identify copper and iron forms existing in the ores. Ores were subjected to bioleaching by chemolithotrophic bacteria, which oxidizes sulfur and iron compounds. Acidithiobacillus ferrooxidans FT-24 and BF, Acidithiobacillus thiooxidans BS, Acidithiobacillus ferrivorans SU-8 and Sulfobacillus thermosulfidooxidans ST-12 strains were used in the research. It was modeling the process of bacterial heap leaching of low-grade ore in percolation columns. Comparison of efficiency of sulfuric acid and bacterial leaching in percolation columns shows advantage of bioleaching. The copper yield was 47 % at using conventional sulfuric acid leaching, while utilizing bacterial leaching increased the copper recovery up to 86 % during 90 days of the experiment. The values of oxidation-reduction potential (ORP) at sulfuric acid and bacterial leaching of copper ore presented are in accordance with yield of copper. The values of ORP at standard sulfuric acid leaching are between 330-360 mV, at bacterial leaching more high and are 480-550 mV due to high content of ferric iron. During the extraction of copper, the effect of the organic reagent LIX 984N in concentrations 50 and 250 mg/L on the activity of microorganisms was studied. As a result, the extraction reagent has a little effect on the growth of microorganisms and the extraction of copper. Without adding the extraction reagent, the total copper recovery was about 83 %, while the addition of the extraction reagent with concentration 250 mg/L decreased it to 81 %. So using bioleaching technology allows deep processing of copper ore due to oxidation of copper sulfide minerals.
Article
We adapted a mixed culture of acidophiles to high arsenic concentrations to confirm the possibility of achieving more than 70% biooxidation of refractory gold concentrates containing high arsenic (As) concentration. The biooxidation process was applied to refractory gold concentrates containing approximately 139.67 g/kg of total As in a stirred tank reactor using an adapted mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The percentage of the biooxidation process was analyzed based on the total As removal efficiency. The As removal was monitored by inductively coupled plasma (ICP) analysis, conducted every 24 h. The results obtained with the adapted culture were compared with the percentage of biooxidation obtained with a non-adapted mixed culture of A. ferrooxidans and A. thiooxidans, and with their respective pure cultures. The percentages of biooxidation obtained during 358 h of reaction were 72.20%, 38.20%, 27.70%, and 11.45% for adapted culture, non-adapted culture, and pure cultures of A. thiooxidans and A. ferrooxidans, respectively. The adapted culture showed a peak maximum percentage of biooxidation of 77% at 120 h of reaction, confirming that it is possible to obtain biooxidation percentages over 70% in gold concentrates containing high As concentrations.
Article
In order to assess the feasibility of uranium removal technology from radioactive contaminated soil by combined bioleaching bacterial consortia, mixed bacterial culture and pure culture of four strains (Acidithiobacillus ferrooxidans ATCC 23,270, Leptosirillum ferripHilum YSK, Acidithiobacills thiooxidans A01, Acidithiobacillus ferrivorans YL15) were comparatively investigated on uranium removal from a radioactive contaminated soil. The results showed that the mixed bioleaching bacterial consortium exerted good adaptability to the surroundings, showing high biological activity and uranium removal capacity. In the whole cleaning process of uranium contaminated soil, the mixed bioleaching bacterial consortium showed complementary advantages, and the synergistic effect improved the uranium removal efficiency, and the maximum uranium removal of the combined bacteria was achieved to 85.81%. Additionally, the linear fitting analysis showed that the uranium removal was positively related to redox potential and negatively related to pH. Lastly, the soil residue after cleaning was detected by SEM/EDS. The results showed that the liberation degree of uranium-contaminated soil increased significantly after bacterial oxidation, which was conducive to the contact of bacteria and Fe3+ to soil particles, thus improving the uranium removal rate.
Article
In order to explore the fluoride tolerance and the community dynamics of mixed bioleaching microorganisms, a co-culture including five typical bioleaching strains (Acidithiobacillus ferrooxidans ATCC 23270, Leptospirillum ferriphilum YSK, Sulfobacillus thermosulfidooxidans ST, Acidithiobacills thiooxidans A01, Acidithiobacills caldus S1) was constructed. The results show that the growth of the co-culture is inhibited by fluoride stress, and the co-culture keeps the stable cell density at high fluoride stress. The sulfur activity of the co-culture is not affected by fluoride stress. Microbial community dynamics of the co-culture was analyzed by real-time fluorescent quantitative PCR technology. The results show that L. ferriphilum YSK and A. caldus S1 are always the dominant species at fluoride stress or non-stress, while the minor is A. ferrooxidans ATCC 23270, S. thermosulfidooxidans ST and A. thiooxidans A01. Besides, S. thermosulfidooxidans ST is inhibited most obviously in the co-culture at fluoride stress, secondly A. caldus S1, A. thiooxidans A01 and A. ferrooxidans ATCC 23270, while the L. ferriphilum YSK still maintains a very stable growth.
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-------Abstract------------------ Compared to conventional extractive techniques, bacterial assisted leaching, also called “biomining” is an eco-friendly technology that provides improved metal/solid separations. These separations are enhanced by the synergistic activities of astonishingly diverse groups of microorganisms, which lead to an extraction process with low energy consumption, low capital investment and low impact on the environment. Recently, biomining has received great attention in a variety of niche areas, especially in the mineral industries and solid industrial waste materials (e.g. galvanic sludge, sewage sludge, fly ash, electronic waste, spent petrochemical catalysts, medical waste, spent batteries, waste slag) where the metals values are low, or where the presence of certain elements would lead to smelter damage, or where environmental considerations favor biological treatments options. It allows the recovery of metal from low-grade sulfide ores and concentrates that cannot be processed economically by conventional techniques, as well as the production of concentrated metal salt solutions, which could be recycled. Bacterial assisted leaching processes are based on the ability of certain microorganisms to solubilize/or expose the metals contained in the ores and concentrates by direct oxidation, or through indirect chemical oxidation instigated by the corrosive metabolic by-products generated by an electrochemical option, or a combination of both of these. The valuable metals in solution can be recovered using conventional hydrometallurgical techniques. If the material of interest constitutes part of or is in the pre-treated residue then it can be further processed for metal recovery. The majority of microorganisms involved in bacterial assisted leaching processes are chemolithotrophs. Carbon dioxide (CO2) and oxygen (O2) are essential nutrients that are used by microorganisms for their growth, maintenance, metabolite production, and survival. This literature review aims to provide a fundamental understanding of the various mechanisms involved in microbial leaching of sulfide minerals and provide a brief look at the various factors affecting this process. Special attention is focused on the mass transfer rates in the gas phase and how they exert a pivotal role in microbially assisted leaching of sulfide minerals. Also reviewed are the major parameters that can affect gas phase mass transfer, with particular emphasis on how it is related to the efficiency of bacterial assisted leaching. ----------Keywords-------- Biomining; Bioleaching; Biooxidation; Sulfide minerals; Microorganisms; Gas transfer ---------------------------------- ----> This review has been written and prepared jointly by Dr. Akrama Mahmoud and Professor Andrew Hoadley (Monash University, Australia). We would like to thank all authors of the papers given in the reference list for obtaining a great deal of useful information on biomining processes, and thus in helping to prepare this paper. The principal author (Dr. Akrama Mahmoud) would like to thank Jean Michel Sorbet and Olivier Gelade for their kind technical assistance and help. Finally, Dr. Akrama Mahmoud dedicate this paper to his parents for their love and sacrifices.† For more information, Please go to: A review of sulfide minerals microbially assisted leaching in stirred tank reactors. International Biodeterioration & Biodegradation Volume 119, April 2017, Pages 118-146. http://www.sciencedirect.com/science/article/pii/S0964830516304097. https://doi.org/10.1016/j.ibiod.2016.09.015
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Microbial solubilization of rock phosphate is getting more and more attention recently. However, the microorganisms used in previous studies were mostly single or known species, and seldom studies focused on the mixed microorganisms or microbial consortia from natural environments. In this study, a microbial consortium taken from activated sludge was used to solubilize two different mid-low grade rock phosphates. Results showed that the microbial consortium could effectively solubilize the rock phosphates in National Botanical Research Institute's phosphate growth medium and released soluble phosphorus in the broth. The biomass increased gradually, whereas the pH decreased sharply during the solubilizing process. The maximum phosphorus solubilization was recorded at particle size of 150 µm. Higher or lower than this optimal particle size, the phosphorus solubilization decreased. The phosphorus solubilization gradually decreased with a larger pulp density from 1% to 5%, and the optimal pulp density was 1%. The solubilization level of microbial consortium varied with different rock phosphates. Results revealed that the soluble phosphorus released from high-silicon ore was higher than which from high-magnesium ore. A strong positive correlation between biomass and phosphorus solubilization in the broth was observed from regression analysis results, and the phosphorus solubilization also had a significant negative correlation with pH in the broth.
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Whilst bioleaching is primarily used to recover minerals from low-grade ores, the increasing demand for Rare Earth elements combined with supply chain concerns is opening up new avenues of extraction from mine tailings, waste products and recyclable materials. Exploration of new, novel and economically viable techniques are required to manage the coming shortage and volatility of global markets with more environmentally sound alternatives to traditional mining operations holding the key.
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In the present work, key parameters in copper bioleaching from chalcopyrite have been investigated at long term operation. In detail, the type of mixed microbial consortium (origin and adaptation); the composition of two mineral media (the growth medium and the modified 9K medium); its buffer capacity by the buffers HCl/KCl and Na2HPO4/KH2PO4; and the influence of different ore grades in relation with the potential alkalinity associated have been investigated. For the first time, a mixed microbial consortium, obtained from a gas‐phase biotrickling filter treating high loads of H2S, was employed revealing significant copper extraction by biological leaching. Results reveal that a single adaptation step of this biomass improved both kinetics and process efficiency, nearly doubling the amount of copper obtained compared with the non‐adapted consortium. Nevertheless, the growth medium also influences the efficiency of the bioleaching process, enhancing copper extraction at higher sulphate concentration. The ore containing the metal is also a determining factor, obtaining same copper extraction for biotic and abiotic in one case, and enhancing up to 50 times from the abiotic in the other. Thus, this becomes a relevant limitation for the applicability of bioleaching for some ores, mainly due to the composition of the matrix. This article is protected by copyright. All rights reserved.
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Bioleaching is a promising technology for removal of metals from sludge and improvement of its dewaterability. Most of the previous studies of bioleaching were focused on removal of metals; bioleaching in cold environments has not been studied extensively. In this study, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans were acclimated at 15 °C and co-inoculated to explore the optimal conditions for improvement of sludge dewaterability and removal of metals by the sequencing batch reactors. The data show after 6 days of bioleaching at 15 °C, 89.6% of Zn, 72.8% of Cu and 39.4% of Pb were removed and the specific resistance to filtration (SRF) was reduced to ∼12%. In addition, the best conditions for bioleaching are an initial pH of 6, a 15% (v/v) inoculum concentration, and A. thiooxidans and A. ferrooxidans mixed in a ratio of 4:1. We found that bioleaching of heavy metals is closely related to final pH, while the sludge SRF is dominated by other factors. Bioleaching can be completed in 6 days, and the sludge dewaterability and removal of metals at 15 °C meet the requirements of most sewage treatment plants.
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In this study the adaptation of Acidithiobacillus ferrooxidans-like to high concentrations of chalcopyrite, sphalerite and galena were evaluated with two mineral-particle sizes: 200 and 325 Tyler mesh. The strain was adapted using two simultaneous processes. The first one consisted in a gradual decreasing of the main energy source, ferrous sulphate. The second one consisted in a gradual increasing of the mineral content. Finally, a test was made without ferrous sulphate. The serial subculturing was found to be an efficient strategy to adapt Acidithiobacillus ferrooxidans-like to higher concentrations of chalcopyrite, sphalerite and galena. This indicates that a suitable protocol was employed. The results showed that Acidithiobacillus ferrooxidans-like is more resistant to high concentration of sphalerite, chalcopyrite and galena in descendant order. The particle size played an important role in the adaption of microorganism to the mineral.
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Bacterial oxidation was used to pre-treat a refractory gold sulfide concentrate obtained from the flotation of a gold ore from Madagascar. A mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans was used to oxidize the sulfides. The major form of sulfide was pyrite, which represented approximately 24.8% of the mineralogical composition of the concentrate. During the bacterial pre-oxidation, three grain sizes (D80: 75 µm, 38 µm, and 12 µm) were considered with two pulp densities (10% and 20% solids). After 14 d of bacterial oxidation, the bioleached residues were treated using the conventional cyanidation method. After 48 h of cyanidation for the residue bioleached with 10% solids and D80 of 75 μm, 38 µm, and 12 µm, the gold dissolution yields were 49%, 64%, and 83%, respectively. Similarly, for the residue with 20% solids, the gold dissolution yields by cyanidation were 48%, 65%, and 91%, respectively. For cyanidation alone, the gold dissolution yields were 51%, 52%, and 68%, respectively. Based on these results, bacterial pre-oxidation with the finer D80 of 12 µm and 20% solids provided a 20% gain in refractory gold dissolution compared to cyanidation alone.
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Chalcopyrite is one of the most important copper minerals; however, the extracted efficiency of chalcopyrite is still not satisfactory in hydrometallurgy owing to its high lattice energy which leads to its low dissolution kinetics. To overcome the difficulties, many advanced technologies have been developed, including the selection of high effectively bacteria, the inhibition of the passivation film adhered onto the minerals surface, and the maintenance of solution redox potential under an optimum range. Up to date, considerable researches on the first two terms have been summarized, while the overview of the last term has been rarely reported. Based on corresponding works in recent years, key trends and roles of solution redox potential in copper hydrometallurgy, including its definition, effect and maintenance, have been introduced in this review.
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The origin of a rational (scientific) approach to extraction of metal values from ores with the aid of microorganisms (bioleaching) is traced. The removal by microbiological means of ore constituents that interfere with metal extraction (biobeneficiation), an outgrowth from bioleaching, is also traced. © 2004 SDU. All rights reserved.
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Acidic biofilms present on cave walls in the sulfidic region of the Frasassi Gorge, Italy, were investigated to determine their microbial composition and their potential role in cave formation and ecosystem functioning. All biofilm samples examined had pH values Thiobacillus and Sulfobacillus. An acid-producing strain of Thiobacillus sp. also was obtained in pure culture. Stable isotope ratio analysis of carbon and nitrogen showed that the wall biofilms are isotopically light, suggesting that in situ chemoautotrophic activity plays an important role in this subsurface ecosystem.
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An efficient and simple method for the vacuum impregnation of stone is described, based on the formation of an airtight jacket around the object allowing a vacuum to be applied to the surface and acting as a wick for the consolidating material. /// Une méthode simple et efficace pour l'imprégnation sous vide de la pierre est décrite, basée sur la formation d'une enveloppe étanche à l'air autour de l'objet permettant d'appliquer le vide à la surface et agissant comme une mèche pour le matériel de consolidation. /// Ein wirksames und einfaches Verfahren zur Vakuumimpregnierung von Stein wird beschrieben, das auf der Bildung eines luftdichten Mantels um den Gegenstand basiert, welcher die Aufbringung eines Vakuums auf die Oberfläche erlaubt und als Docht für das Konsolidierungs-material wirkt.
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Stromatolites are sedimentary structures produced by the sediment-trapping, binding and/or precipitation activity of microbial communities, in particular by photosynthetic cyanobacteria. They occur today in a wide range of aquatic habitats, both marine and non-marine, from shallow subtidal to supratidal and in lakes, streams and thermal springs. Although uncommon today, stromatolites were widespread in the past, and are the most conspicuous fossils in Precambrian rocks. It has been suggested that microbes played a major role in the development of the banded-iron formations that are widespread in Precambrian rocks, and that they played a crucial role in the formation of atmospheric oxygen. -from Authors
Article
A broth containing the sulfate reducing bacterium Desulfovibrio desulfuricans was used to treat samples of reagent calcium sulfate, gypsum-rock specimens, fragments from a marble monument with a black weathering crust rich in gypsum, and a marble monument with similar crust. Calcite was found to have formed on all treated surfaces suggesting that this microbe has the potential to clean crusted marble monuments whilst also regenerating calcite, the parent mineral of the marble. /// Un bouillon de culture contenant une bactérie réductrice des sulfates, le Desulfovibrio desulfuricans, a été utilisé pour traiter des échantillons de sulfate de calcium, des spécimens de pierre en gypse, des morceaux provenant d'un monument de marbre recouverts d'une croûte noire de vieillissement riche en gypse, et un monument de marbre avec une croûte semblable. Il s'est formé de la calcite sur toutes les surfaces traitées, suggérant que cette bactérie peut nettoyer les monuments de marbre recouverts d'une croûte, tout en régénérant le calcite qui est le principal constituant du marbre. /// Calciumsulfate, gipshaltige Gesteine sowie gipsreiche schwarze Verwitterungskrusten von zwei Denkmälern aus Marmor wurden mit einer Desulfovibrio desulfuricans Kultur in Nährbouillon behandelt. Die Bakterien reduzieren Sulfate. Die Untersuchungen ergaben, daß sich auf allen behandelten Oberflächen Calcit (Calciumcarbonat) gebildet hatte. Dies scheint die Möglichkeit zu eröffnen, mit Hilfe dieser Bakterien Objekte aus Marmor zu reinigen. Der gebildete Calcit ist wiederum der Hauptbestandteil von Marmor.
Article
Lipases, hydrolytic enzymes that act on glycerol-ester bonds, are often used in conservation for their ability to degrade aged oil films, as a non-toxic and often less aggressive alternative to highly polar organic solvents and/or alkaline mixtures. One such enzyme has been used to remove layers of an aged acrylic resin (Paraloid B72) in two instances, a fifteenth-century tempera painting on panel and a nineteenth-century oil painting on canvas. A plausible mechanism for the action of the enzyme is discussed.
Article
Cultures of known species of fungi placed on crystals of Iceland spar calcite resulted in extensive dissolution of the calcite. This organically mediated dissolution produced large patches of spiky calcite within a period of 253 days. The dissolution of the calcite occurred via surface-reaction-controlled kinetic processes that were mediated by the fungi. This occurred despite the lack of vast quantities of fluids undersaturated with respect to calcite. Locally, at least 10 mu m of calcite was removed from the original crystal surface.
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
Abstract Pyritic stromatolite, a rich pyrite ore, is scattered as reef masses in sedex deposits of the Proterozoic Yanshan rift trough. The pyritic stromatolite consists of a core and alternating concentric rims of light colloidal pyrite and dark organic materials. The concentric rims are cemented together by trichomes highly similar to the trichomic microorganisms inhabiting substantively around the black chimneys on the current sea beds while the core is composed chiefly of groups of thermophilous sulphur bacteria. Biomarkers for the molecules of pyritic stromatolite include pristane, phytane, regular isoprenoids paraffin, methyl-heptadecyl, and so on. This study reveals the existence of methane-yielding bacteria in the pyritic stromatolite and reflects the evolution of thermophilous thallophyta. Long pulsation of mineralizing thermal solutions venting up along contemporaneous faults in rift troughs contributed greatly not just to the reproduction of thermophilous organisms living around the vents, but to their adsorption of Fe2+ from the solutions in a reducing environment. Pyritic stromatolite constantly took shape through metabolism and reduction of these organisms. Owing to the uneven development of the organic communities close to the vents or the hydrothermal plumes, pyritic stromatolite occurred eventually as scattered reef masses. This mineralizing mechanism may be summarized as the following procedure: flowing of hydrothermal fluids associated with submarine exhalatio→adsorption and metabolism of thermophilous micro-organisms→reduction of organic materials→formation of deposits of pyritic stromatolite.
Article
Natural precipitates of metastable polymorphs of CaCO 3 , such as vaterite, are rarely found in nature however, they have been widely synthesized in laboratory under particular conditions (ie, supersaturated solutions, relative high temperatures, etc.). By SEM and XRD we recognize vaterite spherulites from culturable microbial colonies isolated from hypogean environments. Spherical bodies (~10 w in diameter), probably composed of vaterite, occur in submilimetric microbial mats and biofilms on volcanic substrates (Saint Callixtus Catacombs, Rome, Italy) and karstic caves (Altamira, Candamo, and Tito Bustillo caves, Spain, and Grotta dei Cervi, Italy) where cyanobacteria and actinomycetes are the major microbial components. These particles form beneath dense biofilms, where particular physicochemical conditions are developed by the microbial activity. Natural biofilms seems to generate microenvironments favoring the formation and preservation of metastable CaCO 3 polymorphs. This also shows a major role of microbes in processes of low-temperature alteration of different hypogean rock-substrates.