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Effect of sulphur and iron-oxidizing bacteria on metal recovery in leaching of Kure piritic copper ore

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Abstract

Recently, chemical recovery of metallic values from low-grade sulphur-bearing ores or concentrates has been replaced by biological treatment; an important recovery process from the environmental and economical respects.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.

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... AMD is a recognized problem and is covered in curricula of mining faculties in Turkey. There are very few studies related to AMD except biological ore enrichment, hydrometallurgy, and mine abatement studies (Aytekin and Akdagi 1996;Akcil and Ciftci 2003;Kesimal et al. 2003;Akcil and Koldas 2006;Ozcelik 2007). The district of Can in the Canakkale province in northwest Turkey is rich in lignite. ...
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... AMD is a recognized problem and is covered in curricula of mining faculties in Turkey. There are very few studies related to AMD except biological ore enrichment, hydrometallurgy, and mine abatement studies (Aytekin and Akdagi 1996;Akcil and Ciftci 2003;Kesimal et al. 2003;Akcil and Koldas 2006;Ozcelik 2007). The district of Can in the Canakkale province in northwest Turkey is rich in lignite. ...
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The mechanism and kinetics of bioleaching of chalcopyrite concentrate by the thermophilic archaea Acidianus brierleyi was studied in batch and continuous-flow stirred tank reactors (CSTR). In the batch reactor, the thermophile A. brierleyi solubilized chalcopyrite much faster at 65°C than did the mesophile, Thiobacillus ferrooxidans at 30°C. The chalcopyrite leaching with A. brierleyi was found to take place with a direct attack by adsorbed cells on the mineral surface, the chemical leaching with ferric iron being insignificant. Rate data collected in the batch reactor were analyzed to estimate kinetic and stoichiometric parameters for the growth of A. brierleyi on chalcopyrite. The batch model and the estimated parameter values were used to find optimum levels of initial cell concentration and initial mineral/liquid loading ratio. Simulations based on continuous reactor model and the parameter values were used to predict the leaching fraction as a function of the number of reactors connected in series.
Article
Chalcopyrite oxidation was evaluated with two acidophilic thiobacilli that are important in bioleaching processes. Acidithiobacillus thiooxidans in pure culture did not oxidize CuFeS2 but oxidized externally added S0 in the presence of CuFeS2. Acidithiobacillus ferrooxidans released Cu2+ and soluble Fe from chalcopyrite, and the time course lead to a gradual passivation of chalcopyrite whereby Cu2+ dissolution leveled off. Fe3+ acted as a chemical oxidant in CuFeS2 leaching and was reduced to Fe2+. Parallel bacterial re-oxidation of Fe2+ contributed to a high Fe3+/Fe2+ ratio and an increase in redox potential. Chemical oxidation of chalcopyrite was slow compared with A. ferrooxidans-initiated solubilization. X-ray analysis revealed new solid phases: (i) jarosite, found in solids from A. ferrooxidans cultures and in chemical controls that initially received Fe2+ or Fe3+, and (ii) S0, found mostly in iron-amended A. ferrooxidans culture and the corresponding chemical controls.
Article
Aim of the present study was to compare copper and zinc extraction from GMDC polymetallie concentrate in shake flasks, stirred tanks and large reactors. The concentrate used in the study contained chaleopyrite, sphalerite, galena and pyrite as main constituents. Thiobacillus ferrooxidans consortium used in this study was adapted to a high pulp density upto 20% of the concentrate. Scale up experiments were performed at 0.1 dm3, 3 dm3 and 100 dm3 levels at 30°, 40° and more than 40° C temperatures. During the experiments, 16 to 26 g of sulphuric acid was consumed per kilogram of the concentrate. At the end of experiment, the attained pH was 2.05±0.1. Solubilized Fe2+ and oxidation reduction potential ranged between 0.13 to 1.89 g.1-1 and 337 to 456 mV respectively on fifteenth day of experiment. Long lag phase was observed in all the scale up levels where the temperature was more than 38° C.In 100 dm3 pilot reactors, temperature raised to 46° C during the process. The developed consortium in first cycle of experiment resulted in 66.4, 62.0, 56.3 and 38.6% copper and 94.3, 71.8, 75.7 and 48.0% zinc extraction in shake flasks incubated at 30° and 40° C temperatures, 3 dm3 STR (40° C) and 100 dm3 (40° to 46° C) reactors respectively in 15 days of bioleaching~ time. Once temperature tolerant consortium was selected, both copper and zinc extraction reached to 54±2% irrespective of the level of scale up within 7 days of contact time. The consortium and 100 dm3 pilot reactor developed in this study is a promising step towards large scale economical process for metal extraction from the polymetallic concentrate.
Data
The composition of bacterial populations in copper bioleaching systems was investigated by analysis of DNA obtained either directly from ores or leaching solutions or after laboratory cultures. This analysis consisted of the characterization of the spacer regions between the 16 and 23S genes in the bacterial rRNA genetic loci after PCR amplification. The sizes of the spacer regions, amplified from DNAs obtained from samples, were compared with the sizes of those obtained from cultures of the main bacterial species isolated from bioleaching systems. This allowed a preliminary assessment of the bacterial species present in the samples. Identification of the bacteria was achieved by partial sequencing of the 16S rRNA genes adjacent to the spacer regions. The spacer regions observed in DNA from columns leached at different iron concentrations indicated the presence of a mixture of different bacteria. The spacer region corresponding to Thiobacillus ferrooxidans was the main product observed at high ferrous iron concentration. At low ferrous iron concentration, spacer regions of different lengths, corresponding to Thiobacillus thiooxidans and ''Leptospirillum ferrooxidans'' were observed. However, T. ferrooxidans appeared to predominate after culture of these samples in medium containing ferrous iron as energy source. Although some of these strains contained singular spacer regions, they belonged within previously described groups of T. ferrooxidans according to the nucleotide sequence of the neighbor 16S rRNA. These results illustrate the bacterial diversity in bioleaching systems and the selective pressure generated by different growth conditions. Copper bioleaching is increasingly being used because of its economical and environmental advantages. It consists of the acid leaching of copper from the copper sulfides after oxida-tion, enhanced by acidophilic autotrophic bacteria (11, 23). Agglomeration of mineral ores has been incorporated into an industrial copper bioleaching process increasingly applied in Chile since 1984. This process essentially consists of irrigation of nonflooded heaps of agglomerated crushed ore with diluted sulfuric acid solutions at ambient temperature, permitting a high bacterial growth (2) that allows studies of complex bac-terial populations expected in bioleaching systems (29). Cul-ture studies reveal the presence of a small number of bacterial species including the commonly found Thiobacillus ferrooxi-dans, other autotrophs, such as Thiobacillus thiooxidans and ''Leptospirillum ferrooxidans,'' and frequently also heterotrophs belonging to the genus Acidiphilium (7, 10, 14, 27) (the genus Leptospirillum did not appear on the Approved List of Bacte-rial Names and has not been validated). In situ predominance of non-T. ferrooxidans bacteria in leaching industrial opera-tions (1) and in desulfuration of coal (19) has been suggested from studies using fluorescent antibody techniques. Also the presence of an unidentified 5S RNA, different from that of T. ferrooxidans, has been previously reported in an industrial leaching pond (17). These observations and the evolutionary widespread capacity for sulfur and/or iron oxidation observed among the cultured bacteria (16) suggest the participation of potentially diverse bacterial species in bioleaching. Direct molecular analysis of DNA has greatly enhanced the ability to assess the diversity of microorganisms growing in an ecosystem (31), and analyses of rRNA genes have confirmed the view that conventional identification methods requiring culturing miss many of the bacteria originally present in the system (6, 18, 28, 32). The complexity of the DNA obtained from samples derived from bioleached agglomerated copper sulfide ore was analyzed by PCR of the spacer regions between the 16 and 23S rRNA genes (12) to improve the characteriza-tion of the bacterial population participating in the bioleaching of copper. Comparison of the size of the amplification prod-ucts by gel electrophoresis with those from the main species isolated from bioleaching systems showed relationships to par-ticular bacterial species. Here we describe the analysis of the spacer regions and 16S rDNAs observed in the bacterial pop-ulation present after leaching chalcosite/covellite ores and the selection observed upon culturing of the bacteria in the leach-ing solution in medium containing ferrous iron as energy source.
Article
A systematic study of the bioleaching of chalcopyrite (CuFeS 2 ) was conducted using axenic cultures of 11 species of acidophilic Bacteria and Archaea to obtain a direct comparison of the microbial chalcopyrite leaching capabilities of the different cultures and to determine the factors that affect Cu release. The characteristics of chalcopyrite leaching by the moderate thermophile Sulfobacillus thermosulfidooxidans , the mesophile Acidithiobacillus ferrooxidans , and the thermophile Acidianus brierleyi were used to elucidate the leaching process. Moderately thermophilic cultures of Sulfobacillus acidophilus, Acidimicrobium ferrooxidans , and Acidithiobacillus caldus were used to study the effects of different metabolic capabilities and relate those to leaching efficiency. The greatest rate of Cu solubilization from chalcopyrite was achieved at high temperatures (up to 70°C) at redox potentials below +550 mV (Ag/AgCl). The enhanced Cu solubilization observed at high temperatures resulted from accelerated chemical reaction rates, rather than from the rates at which individual acidophiles generated the mineral leaching reactants such as Fe 3+ .
Article
Thermophiles have been shown to be the only micro-organisms to leach chalcopyrite successfully. Heap leaching may be a feasible alternative to conventional bio-reactors, providing a high temperature environment can be maintained within the heap without external heating.In the present study thermophilic heap leaching of a chalcopyrite concentrate coated onto inert support rocks (the GEOCOAT™ process) was studied in sets of small heated columns. The temperature was gradually increased to 70 °C, while successively introducing various mesophile and thermophile cultures. Individual columns were dismantled after progressively longer leach periods and the residual concentrates analysed. Copper extractions in excess of 90% were achieved within 100 days.On the basis of head and residue analyses the rate of reaction heat generated was calculated. A comprehensive heap heat conservation model was used to determine whether the experimental temperatures can be achieved and maintained in a full scale heap. Results indicate that operating hot heaps successfully is possible within a certain range of process parameters.
Article
The purpose of this paper is to review the leaching of base metal sulfides and of uranium oxides by acidic ferric ion media. A description is also given of the preparation, regeneration, and properties of such leaching media. From the discussion of the kinetics of reaction of various minerals with ferric ion, it emerges that, for many minerals, the reaction rates are sufficiently rapid to be of commercial interest for recovering the sought-after metal. A brief discussion of actual and proposed commercial processes using ferric ion leaching is also given.
Article
Currently, low-grade and complex ores and mining wastes can be processed economically by using bacteria in heap and agitation leaching processes. Bacterial leaching tests are performed on the run-of-mine ore which is a mixture of two different massive and dissemine copper ores, fed to Küre Copper Plant. In this leaching process, using "Acidithiobacillus ferrooxidans" culture, bacteria count, pH, copper and iron recoveries are monitored during the 576 hours of test period. By increasing the solid ratio (1 %→5 %) the oxidation ability of bacteria decreases, thus the leaching rate. Therefore copper and iron recoveries decreased from 68 %, 35 % and 45 %, 20 %, respectively. As a result of laboratory tests, it is found that as the pulp density increased, the efficiency of copper recovery decreased using this bacterial culture.
Article
A detailed reaction mechanism is proposed for the formation of crystalline elemental sulfur from aqueous sulfide by oxidation with transition-metal ions such as V(V), Fe(III), Cu(II), etc. The first step is the formation of HS• radicals by one-electron oxidation of HS(-) anions. These radicals exist at pH values near 7 mainly as S•(-). Their spontaneous decay results in the formation of the disulfide ion S2(2-). The further oxidation of disulfide either by S•(-) radicals or by the transition-metal ions yields higher polysulfide ions from which the homocyclic sulfur molecules S6, S7, and S8 are formed. In water these hydrophobic molecules form clusters which grow to droplets of liquid sulfur (aqueous sulfur sol). Depending on the composition of the aqueous phase, crystallization of the liquid sulfur as either α- or β-S8 is rapid or delayed. Surfactants delay this solidification, while certain cations promote it. All these reactions are proposed to take place in desulfurization plants working by the Stretford, Sulfolin, Lo-Cat, SulFerox, or Bio-SR processes. In addition, the sulfur produced from sulfide by oxidizing sulfur bacteria is formed by the same mechanism, which now explains many observations made previously (including the formation of the byproducts thiosulfate, polythionates, and sulfate).
Article
The bioleaching of chalcopyrite in an acidic sulphate nutrient medium was investigated using Sulfobacillus thermosulfidooxidans, a moderately thermophilic iron- and sulphur oxidising bacterium. Copper release to solution was initially rapid but this slowed significantly after about SO hours. The decrease in chalcopyrite dissolution rate coincided with significant precipitation of jarosite on the mineral surface. Cultures of the moderately thermophilic acidophilic bacteria Acidimicrobium ferrooxidans, Sulfobacillus acidophilus and Sulfobacillus thermosulfidooxidans were grown in anaerobic media containing chalcopyrite passivated by jarosite. The moderate thermophiles used the ferric ion in the jarositic surface precipitate as a terminal electron acceptor in place of oxygen in the anoxic environment. Despite extensive bioreduction of the iron-hydroxy precipitates, it was found that the jarosite was not completely removed and that subsequent biooxidation of the treated concentrate achieved no significant increases in copper release compared with concentrate that had not been subjected to prior biooxidation or bioreduction.
Article
The ability of an extreme thermophile to oxidise a concentrate comprising of chalcopyrite (66%) and pyrite (11%) is described. A batch test at 70°C showed that a copper extraction of >98% was possible. A series of continuous tests were carried out in a three-stage pilot plant, employing standard-design mechanically agitated and aerated tanks. The effect of residence time, feed grind and the mass transfer supply of oxygen and carbon dioxide on bioleach performance were evaluated. The results showed that overall Cu extractions of 95% could be obtained. However, compared to mesophilic and moderately thermophilic bioleaching bacteria, the extreme thermophiles appeared to be more sensitive to the solids concentration employed, which may also be related to the particle size of the feed solids. Levels of oxygen consumption approaching the maximum rates currently being employed in commercial-scale bioleach tanks treating refractory gold pyritic concentrates could be achieved. To maintain these high oxidation rates, it was important to ensure that the supply rate of oxygen and carbon dioxide to the reactors was sufficient. The high copper extractions obtained in these tests showed that a process treating chalcopyrite concentrates using extreme thermophiles has the potential for further development and assessment for commercial applications.
Article
This study investigates the bioleaching of the complex Pb/Zn ore/concentrate using mesophilic (at 30 jC), moderate (at 50 jC), and extreme thermophilic (at 70 jC) strains of acidophilic bacteria. The effects of bacterial strain, pH, iron precipitation, and external addition of Fe 2 + on the extraction of zinc were evaluated. The results have shown that the ore is readily amenable to the selective extraction of zinc and lead using the acidophilic strains of bacteria [i.e., majority of lead (>98%) reports to the residue]. Moderate thermophiles displayed superior kinetics of dissolution of zinc compared with the other two groups of bacteria. The pH was found to exert a profound effect on the leaching process controlling the bacterial activity and precipitation of ferric iron mainly as K-jarosite. The K + released presumably from the alteration of the silicate phases such as K-feldspar present in the ore appeared to promote the formation K-jarosite in moderately thermophilic leaching systems. The external addition of iron was shown to be required for the bacteria to efficiently drive the extraction of zinc from the bulk concentrate. These findings place the emphasis on the prime importance of ferric iron for the dissolution of zinc and of mineralogical properties (i.e., iron and silicate content) of an ore/concentrate to be treated via bioleaching processes. D 2004 Elsevier B.V. All rights reserved.
Article
The effect of solids (up to 30% w/w) on the viability of a mesophilic culture of acidophilic bacteria was investigated in stirred tank reactors (STRs) using the Rushton turbine (RT) and the pitched blade turbine impellers in a speed range of 2.01–3.35 m/s. The results showed that hydrodynamic shear alone as a characteristic function of impeller type and speed has a very limited effect on the bacterial cells during mixing in STRs, but mechanical damage to bacterial cells occurs, to a most significant extent, via the attrition by solid particles promoted by the intensity of agitation. Extent of the adverse effect on the bacterial cells was found to depend on impeller design/speed and solids density. The loss in the viability of bacterial population with a tendency to increase with agitation rate and solids density was more extensive with the RT than the PBT impellers under the same experimental conditions e.g. 72% loss in the viability c.f. 40% over 4 h of mixing at 20% w/w solids and 3.35 m/s impeller speed. The kinetic analysis of the experimental data suggest that the rate and extent of oxidation of a substrate in a given process would be controlled by the inoculum size and by the difference between the ''normal'' growth rate and the deactivation rate of bacterial cells incurred at a particular mixing condition (impeller type/speed and solids density) i.e. by the ''actual'' growth rate.
Article
The effect of solid loading (mineral pulp density) on thermophilic bioleaching of pyrite by Sulfolobus metallicus (BC) was investigated in a batch reactor. Different mineral pulp densities in the range 3–18% (w/v) were tested. With mineral pulp densities ranging from 3 to 9% the bioleaching proceeded in a single stage with a relatively constant rate. The bioleaching rates calculated for pulp densities of 3, 6 and 9% were 0.10, 0.11 and 0.09 kg iron m−3 h−1 respectively. By contrast the bioleaching of pyrite at pulp densities of 12 and 15% proceeded in two distinct stages. During the exponential phase of microbial growth a sharp and linear increase in concentration of released iron was achieved. This increasing trend levelled off in the presence of non-growing cells and the second stage of bioleaching continued with a slower rate. For the pulp density of 12% the bioleaching rates of the first and the second stages were 0.09 and 0.02 kg iron m−3 h−1 respectively, whereas the calculated rates in the presence of 15% mineral were 0.07 and 0.017 kg iron m−3 h−1 for the first and the second stages. Application of 18% mineral adversely influenced the activity of the cells and the extent of bioleaching in this case was insignificant.© 2000 Society of Chemical Industry
Article
Bioleaching is a simple and effective technology for metal extraction from low-grade ores and mineral concentrates. Metal recovery from sulfide minerals is based on the activity of chemolithotrophic bacteria, mainly Thiobacillus ferrooxidans and T. thiooxidans, which convert insoluble metal sulfides into soluble metal sulfates. Non-sulfide ores and minerals can be treated by heterotrophic bacteria and by fungi. In these cases metal extraction is due to the production of organic acids and chelating and complexing compounds excreted into the environment. At present bioleaching is used essentially for the recovery of copper, uranium and gold, and the main techniques employed are heap, dump and in situ leaching. Tank leaching is practised for the treatment of refractory gold ores. Bioleaching has also some potential for metal recovery and detoxification of industrial waste products, sewage sludge and soil contaminated with heavy metals.
Article
Galvanic interaction between particulate chalcopyrite (CuFeS2) and copper results in the rapid conversion of chalcopyrite to chalcocite. The effects of temperature, surface area, concentration of sulfuric acid and agitation were systematically evaluated. The kinetics were found to be controlled by a steady-state current flow controlled by the effective anodic and cathodic surface areas involved in the galvanic couple. The experimental activation energy was 11.5 and stoichiometric data and reaction products have been characterized. The overall kinetic system has been evaluated based upon an electrochemical model.
Article
The literature on the ferric ion leaching of chalcopyrite has been surveyed to identify those leaching parameters which are well established and to outline areas requiring additional study. New experimental work was undertaken to resolve points still in dispute. It seems well established that chalcopyrite dissolution in either ferric chloride or ferric sulfate media is independent of stirring speeds above those necessary to suspend the particles and of acid concentrations above those required to keep iron in solution. The rates are faster in the chloride system and the activation energy in that medium is about 42 kJ/mol; the activation energy is about 75 kJ/mol in ferric sulfate solutions. It has been confirmed that the rate is directly proportional to the surface area of the chalcopyrite in both chloride and sulfate media. Sulfate concentrations, especially FeSO4 concentrations, decrease the leaching rate substantially; furthermore, CuSO4 does not promote leaching in the sulfate system. Chloride additions to sulfate solutions accelerate slightly the dissolution rates at elevated temperatures. It has been confirmed that leaching in the ferric sulfate system is nearly independent of the concentration of Fe3+, ka[Fe3+]0.12. In ferric chloride solutions, the ferric concentration dependence is greater and appears to be independent of temperature over the interval 45 to 100 °C.
Article
A chalcopyrite concentrate containing 17 pct pyrite was oxidized in 1 mol/dm3 sulfuric acid solution at 90 °C (363.2 K). The suspension potential (Ptvs SCE, in the presence of Fe3+/Fe2+) was maintained constant in the range 0.30 to 0.65 V by controlled additions of KMnO4 solution. The oxidation appeared to be under surface reaction control. The rate constant was nearly independent of total Fe concentration (0.01 to 0.5 mol/dm3), but increased rapidly with a rise in suspension potential until it reached a maximum at 0.40 to 0.43 V, after which there was marked decrease at around 0.45 V. Chalcopyrite in the concentrate was oxidized to form elemental sulfur over the whole of the suspension potential range, whereas the oxidation of pyrite took place only above 0.45 V and yielded sulfate ion. At 0.40 V the apparent activation energy was 47 kJ/mol. An analogy between the potential dependence of the rate and the Tafel correlation for an electrode process is discussed.
Article
The dissolution of metal sulfides is controlled by their solubility product and thus, the [H+] concentration of the solution, and further enhanced by several chemical mechanisms which lead to a disruption of sulfide chemical bonds. They include extraction of electrons and bond breaking by [Fe3+], extraction of sulfur by polysulfide and iron complexes forming reactants [Y+] and electrochemical dissolution by polarization of the sulfide [high Fe3+ concentration]. All these mechanisms have been exploited by sulfide and iron-oxidizing bacteria. Basically, the bacterial action is a catalytic one during which [H+], [Fe3+] and [Y+] are breaking chemical bonds and are recycled by the bacterial metabolism. While the cyclic bacterial oxidative action via [H+] and [Fe3+] can be called indirect, bacteria had difficulties harvesting chemical energy from an abundant sulfide such as FeS2, the electron exchange properties of which are governed by coordination chemical mechanisms (extraction of electrons does not lead to a disruption of chemical bonds but to an increase of the oxidation state of interfacial iron). Here, bacteria have evolved alternative strategies which require an extracellular polymeric layer for appropriately conditioned contact with the sulfide. Thiobacillus ferrooxidans cycles [Y+] across such a layer to disrupt FeS2 and Leptospirillum ferrooxidans accumulates [Fe3+] in it to depolarize FeS2 to a potential where electrochemical oxidation to sulfate occurs. Corrosion pits and high resolution electron microscopy leave no doubt that these mechanisms are strictly localized and depend on specific conditions which bacteria create. Nevertheless, they cannot be called ‘direct’ because the definition would require an enzymatic interaction between the bacterial membrane and the cell. Therefore, the term ‘contact’ leaching is proposed for this situation. In practice, multiple patterns of bacterial leaching coexist, including indirect leaching, contact leaching and a recently discovered cooperative (symbiotic) leaching where ‘contact’ leaching bacteria are feeding so wastefully that soluble and particulate sulfide species are supplied to bacteria in the surrounding electrolyte.
Article
Sulfate-based leaching processes for chalcopyrite (CuFeS2) are attractive because of their inherent simplicity. Unfortunately, high copper extractions are not attainable in a reasonable residence time unless the leaching temperature exceeds 200°C (oxygen pressure leaching) or chalcopyrite is ‘activated’ by a pretreatment method prior to leaching. In the present work, the oxygen pressure leaching behaviour of chalcopyrite in the temperature range 110–220°C was studied to shed new light on the reasons for the slow leaching. Mineral surfaces were examined by Auger electron spectroscopy and X-ray photoelectron spectroscopy to identify the presence of any passivating layers that may form during leaching. The results suggest that chalcopyrite is passivated by a thin ( <1 μm) copper-rich surface layer which forms as a result of solid state changes that occur in the mineral during leaching. This layer is thought to be a copper polysulfide, CuSn where n > 2. The leaching kinetics at low temperature (110°C) can be explained in terms of a mixed diffusion/ chemical reaction model where the reaction rate is ultimately controlled by the rate at which the copper polysulfide leaches.
Article
Electrochemical techniques were conducted to clarify the role of solution potential and temperature under a variety of experimental conditions similar to those found during the mesophilic and thermophilic biooxidation of chalcopyrite (CuFeS2). Despite a large number of publications dealing with the bacterial leaching of CuFeS2, three central aspects remain unclear: How to dissolve preferentially copper from CuFeS2, the effect of temperature on the extent of CuFeS2 passivation, and the behavior of ferric ions on a polarized CuFeS2 surface. Anodic characteristics showed that CuFeS2 passivation was more severe in the potential range 0.45–0.65 V saturated calomel electrode at 25 °C. However, there was no evidence of CuFeS2 passivation at higher temperatures (45 and 65 °C). Cu was preferentially dissolved from CuFeS2 at lower potentials and high temperatures at a ratio copper to iron of about 3:2. Cathodic characteristics showed that the ferric ions inhibited the leaching process when the CuFeS2 surface was polarized at high potentials and low temperatures.
Article
Although current bio-oxidation processes with mesophilic bacteria result from the occurrence of mixed populations, the mutual effect of the various species has not been studied very extensively to date. Mixed cultures made up of pure #Thiobacillus ferrooxidans$, #Thiobacillus thiooxidans$ and #Leptospirillum ferrooxidans$ strains of the DSM collection were batch tested for their ability to oxidize a cobaltiferous pyrite ore. The most efficient population for pyrite oxidation was composed of the three bacterial species. The influence of the relative abundance of the different strains in the inoculum was studied. The cobalt solubilization rate obtained with #T. ferrooxidans$ increased when #L. ferrooxidans$ was present but was not affected by the initial concentration of #L. ferrooxidans$. The bioleaching with #T. ferrooxidans$ was only improved by adding #T. thiooxidans$ when the initial concentration of #T. thiooxidans$ was higher than the initial concentration of #T. ferrooxidans$. During continuous bioleaching of the cobaltiferous pyrite at 20% solids with a natural mesophilic mixed population, rod-shaped and #Leptospirillum$-like bacteria were enumerated in the liquid phase. The 100 l bioleaching unit is made up of 3 or 4 reactors arranged in cascade. The concentration of #Leptospirillum$-like organisms rose exponentially versus dissolved ferric iron, whereas the concentration of rod-shaped bacteria did not change from the value obtained in the first reactor, providing the solution contained less than 60 g/l ferric iron. At higher Fe3+ concentrations, the rod-shaped bacteria performed the earlier steps of pyrite oxidation, whereas #Leptospirillum$-like organisms participated in the later phase of bioleaching. The effluent from the last reactor was treated with CaCO3 in order to precipitate iron... (D'après résumé d'auteur)
Article
A series of bacterial and chemical leaching experiments were conducted to clarify contradictory reports in the literature regarding the role of bacteria in the bioleaching of chalcopyrite. Tests containing a high bacterial concentration showed inhibited leaching, even lower than non-inoculated controls. However, when bacterial cells were washed before inoculation, it was apparent that it was not the bacterial cells but rather the chemical species introduced with them that influenced the leaching rate. In addition, the results of comparative tests with 0.1 M ferrous sulphate or ferric sulphate showed that copper was leached from the ore 2.7 times faster in leach solutions containing ferrous ion, suggesting that ferric ions inhibit chalcopyrite dissolution. The results indicated that the chalcopyrite dissolution rate is strongly dependent on the reduction potential (Eh) in solution, and that this parameter is far more influential than the number or activity of bacterial cells. These results imply that the role of bacteria may only be stimulatory when the prevailing electrochemical conditions are also favourable.
Article
The history of sulfidic ore leaching and the relatively recent discovery of microbial involvement in the process and its commercial exploitation are summarized. A possible future developmental direction is indicated.
Article
Bioleaching of metal sulfides is effected by bacteria, like Thiobacillus ferrooxidans, Leptospirillum ferrooxidans, Sulfolobus/Acidianus, etc., via the (re)generation of iron(III) ions and sulfuric acid.According to the new integral model for bioleaching presented here, metal sulfides are degraded by a chemical attack of iron(III) ions and/or protons on the crystal lattice. The primary iron(III) ions are supplied by the bacterial extracellular polymeric substances, where they are complexed to glucuronic acid residues. The mechanism and chemistry of the degradation is determined by the mineral structure.The disulfides pyrite (FeS2), molybdenite (MoS2), and tungstenite (WS2) are degraded via the main intermediate thiosulfate. Exclusively iron(III) ions are the oxidizing agents for the dissolution. Thiosulfate is, consequently, degraded in a cyclic process to sulfate, with elemental sulfur being a side product. This explains, why only iron(II) ion-oxidizing bacteria are able to oxidize these metal sulfides.The metal sulfides galena (PbS), sphalerite (ZnS), chalcopyrite (CuFeS2), hauerite (MnS2), orpiment (As2S3), and realgar (As4S4) are degradable by iron(III) ion and proton attack. Consequently, the main intermediates are polysulfides and elemental sulfur (thiosulfate is only a by-product of further degradation steps). The dissolution proceeds via a H2S*+-radical and polysulfides to elemental sulfur. Thus, these metal sulfides are degradable by all bacteria able to oxidize sulfur compounds (like T. thiooxidans, etc.). The kinetics of these processes are dependent on the concentration of the iron(III) ions and, in the latter case, on the solubility product of the metal sulfide.
Article
Bioheap leaching of secondary copper ores is applied commercially at operations in Chile, Australia, and Myanmar. Bioheap leaching of sulfidic refractory gold ores has been demonstrated at large scale. There is limited comprehension of what actually occurs microbiologically in full-scale bioheap operations, despite the commercial achievement of copper ore bioheap leaching and the anticipated technical and commercial success of gold ore bioheap leaching. Copper bioheaps are typically inoculated with the bacteria contained in the raffinate or intermediate leach solution, whereas, sulfidic refractory gold ore bioheaps can be inoculated with bacteria developed in a separate reactor. Chemical and physical conditions within bioheaps change radically from the time the bioheap is stacked and inoculated until bioleaching is completed. Redox, acidity, temperature, oxygen and solution chemistry conditions vary widely during the oxidation period. Such conditions likely select for microorganisms or may, in fact, effect a succession of organisms in portions of the bioheap. Bioheap solutions are recycled and constituent build-up over time also affects the microbiology. Organic entrapment in the raffinate from the solvent extraction circuit may influence microbial activity. Heterotrophic microorganisms may also play some role in bioheap leaching. Understanding the microbiology of bioheaps is key to advancing commercial bioheap applications. Such knowledge will increase the ore types as well as the diversity of mineral deposits that can be processed by bioheap technology. It will also enable better control of conditions to improve leach rates, metal recoveries and costs. This paper briefly explains commercial practices, describes chemical, physical and microbiological monitoring of bioheaps, considers conditions that control microbial populations in bioheaps, and examines the types of ore deposits that could be bioleached, if the microbiology was elucidated.
Article
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.
Article
Microorganisms are important in metal recovery from ores, particularly sulfide ores. Copper, zinc, gold, etc. can be recovered from sulfide ores by microbial leaching. Mineral solubilization is achieved both by ‘direct (contact) leaching’ by bacteria and by ‘indirect leaching’ by ferric iron (Fe3+) that is regenerated from ferrous iron (Fe2+) by bacterial oxidation. Thiobacillus ferrooxidans is the most studied organism in microbial leaching, but other iron- or sulfide/sulfur-oxidizing bacteria as well as archaea are potential microbial agents for metal leaching at high temperature or low pH environment. Oxidation of iron or sulfur can be selectively controlled leading to solubilization of desired metals leaving undesired metals (e.g., Fe) behind. Microbial contribution is obvious even in electrochemistry of galvanic interactions between minerals.
Article
The formation of elemental sulphur during the FeCl3 leaching of chalcopyrite has been elucidated. More than 95% S° formation, and less than 5% SO4 generation, is observed regardless of the leaching time (0–90 h), the FeCl3 concentration (0–2 M), the HCl concentration (0–3 M) and the chalcopyrite particle size. Furthermore, the relative amounts of S° and SO4 do not vary systematically with any of the above variables. Surprising is the observation that the presence of air or O2 in the leach reactor has no significant effect on the relative amounts of S° and SO4, and this observation was confirmed in separate leaching tests with pure sulphur. The morphology of the elemental sulphur reaction product also was ascertained. Although discrete globules of S° form on large chalcopyrite particles, smaller chalcopyrite grains (<20 μm) become completely enveloped in a continuous layer of sulphur within the first 15 min of leaching. The morphology of the sulphur does not change with the concentration of either FeCl3 or HCl.