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Metal recovery from sulfide minerals is based on the activity of chemolithotrophic bacteria, mainly Thiobacillus ferrooxidans and T. 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.
Thermophilic bacteria. Heterotrophic microorganisms. Bioleaching mechanisms. Direct bacterial leaching. Indirect bacterial leaching. Factors in? O2 and CO2. Mineral substrate. Heavy metals. Surfactants and organic extractants. Leaching techniques. Bosecker bgr. Published by Elsevier Science B. Laboratory investigations. Percolator leaching. Submerged leaching. Column leaching. Industrial leaching processes.
Dump leaching. Heap leaching. Underground leaching. Tank leaching. Industrial applications. Future aspects. Industrial waste products.
Heterotrophic leaching. Bauxite dressing. Introduction Microbial leaching methods are being increasingly applied for metal recovery from low-grade ores and concentrates that cannot be processed economically by conventional methods.
As is the case with many biotechnological processes such methods may have been used since prehistoric times and probably the Greeks and Romans extracted copper from mine water more than years ago. However, it has been known only for about 50 years that bacteria are mainly responsible for the enrichment of metals in water from ore deposits and mines .
The solubilization process is called bioleaching and occurs in nature wherever suitable conditions are found for the growth of the ubiquitous bioleaching microorganisms. Microorganisms 2. Thiobacillus The bacteria most active in bioleaching belong to the genus Thiobacillus. These are Gram-negative, non-spore forming rods which grow under aerobic conditions. Most thiobacilli are chemolithoautotrophic species which use the carbon dioxide from the atmosphere as their carbon source for the synthesis of new cell material.
The energy derives from the oxidation of reduced or partially reduced sulfur compounds, including sul? Bacterial leaching is carried out in an acid environment at pH values between 1. Therefore the acidophilic species Thiobacillus ferrooxidans and T. Other thiobacilli are also able to oxidize sulfur and sul? Other partially reduced sulfur compounds are also utilized and sulfuric acid is generated, decreasing the pH in the medium to 1.
The intensive sulfuric acid production leads to a rapid decomposition of rocks so that acid-soluble metal compounds can pass into solution as sulfates. However, the most important role in bacterial K. This bacterium T.
C . Ferrous iron is used as the energy source, but growth is observed only in the presence of yeast extract . Extremely thermo- was? Morphologically the cells are identical to philic bacteria growing at temperatures above 60? C from the latter by the much slower course of the oxidation of elemental sulfur.
In the absence of oxygen T. An knowledge of excellent overview of the species was provided by current Leduc anaerobic conditions elemental sulfur is used as an electron acceptor and is reduced to H2 S. Members of the genus Sulfolobus are aerobic, facultatively chem- this olithotrophic bacteria oxidizing ferrous iron, elemental sulfur and sul?
The same compounds and Ferroni . Two new species of acidophilic thiobacilli been described by Huber and Stetter [7,8] : perus represents a new group of halotolerant metalmobilizing bacteria , T. Growth, however, will only occur in the presence of yeast extract. Heterotrophic microorganisms Heterotrophic bacteria and fungi which require organic supplements for growth and energy supply may contribute to metal leaching.
As in the case of manganese leaching, metal solubilization may be due to enzymatic reduction of highly oxidized metal compounds  or is e? Because of their physiological peculiarities both strains may have some potential in bioleaching. Leptospirillum Leptospirillum ferrooxidans is another acidophilic obligately chemolithotrophic ferrous iron oxidizing bacterium, which was? This microorganism tolerates lower pH values and higher concentra- ganic acids e.
The heterotrophic microorganisms do not have any bene? Therefore, by itself, L. This can only be done together with T. Thermophilic bacteria Thiobacillus-like bacteria, so-called Th-bacteria, are moderately thermophilic bacteria and grow on pyrite, pentlandite and chalcopyrite at temperatures 3.
Bioleaching mechanisms At based the present or time bioleaching on and processes the activity are of T. The most important reaction steps are summarized in a simpli? In principle metals can be released from sul?
Direct bacterial leaching 3. Indirect bacterial leaching In direct bacterial leaching, there is physical contact between the bacterial cell and the mineral sul? In this process, pyrite is oxidized to iron III sulfate  according to the following reactions: bacteria 4FeS2? The direct bacterial oxidation of pyrite is best summarized by the reaction: 4FeS2?
In indirect bioleaching the bacteria generate a lixiviant which chemically oxidizes the sul? In acid solution this lixiviant is ferric iron, and metal solubilization can be described according to the following reaction: MeS? To keep enough iron in solution the chemical oxidation of metal sul? The ferrous iron arising in this reaction can be reoxidized to ferric iron by T.
In indirect leaching the bacteria do not need to be in contact with the mineral surface. They only have a catalytic function because they accelerate the reoxidation of ferrous iron which takes place very slowly in the absence of bacteria. The sulfur arising simultaneously Eq.
Therefore direct bacterial leaching can be described according to the following reaction: bacteria? MeSO4 where MeS is the metal sul? There is some evidence that the bacteria have to be in intimate contact with the mineral surface. The mechanism of attachment and the initiation of metal solubilization are not completely understood.
Obviously the bacteria do not attach to the whole mineral surface but prefer speci? The role of T. A well known example of an indirect bioleaching process is the extraction of uranium from ores, when insoluble tetravalent uranium is oxidized to the water-soluble hexavalent stage of uranium: UIV O2?
The lixiviant may be generated by T. Besides the indirect leaching of uranium there is some evidence that T. Particular importance must be attributed to the cycle of ferrous and ferric iron. In nature and in technical application both mechanisms, the direct and the indirect leaching, will undoubtedly occur in concert. The authors have indications that pyrite is degraded to sulfate via thiosulfate in a cyclic mechanism. The degradation is mediated or at least initiated by the ferric iron being complexed in the exopolymeric compounds of T.
In addition, these iron III ions enable the bacteria to attach to the pyrite surface by an electrochemical mechanism. The function of leaching bacteria is thought to be in maintaining a high redox potential by keeping the ferric iron in the oxidized state to optimize the indirect attack on the metal sul?
In the laboratory this can be achieved by aeration, stirring, or shaking.
The direct bacterial oxidation of pyrite is best summarized by the reaction: 3 Investigations by Torma [23 , 36 ] have shown that the following non-iron metal sulfides can be oxidized by T. Therefore direct bacterial leaching can be described according to the following reaction: 4 where MeS is the metal sulfide. There is some evidence that the bacteria have to be in intimate contact with the mineral surface. The mechanism of attachment and the initiation of metal solubilization are not completely understood. Obviously the bacteria do not attach to the whole mineral surface but prefer specific sites of crystal imperfection, and metal solubilization is due to electrochemical interactions [24—26 ]. In acid solution this lixiviant is ferric iron, and metal solubilization can be described according to the following reaction: 5 To keep enough iron in solution the chemical oxidation of metal sulfides must occur in an acid environment below pH 5.
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The traditional method of extraction is to heat the copper sulfide. Copper II sulfide gives copper and sulfur dioxide during thermal decomposition. Thermal decomposition means that the compound breaks down into other substances when it is heated. Service Online Bioleaching metal solubilization by microorganisms 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. We have professional technicians to provide the machine selection of the relevant models. Welcome to visit and test the machine.
silver ore bioleaching
Among the fungi Asper- easier. Therefore, processes tested on individual types of ores cannot be transferred to other ones. The Actino- bacteria, Bacteroidetes, Cyanobacteria, and Deinococcus-Thermus phyla were also encountered. There was a problem providing the content you requested Thiobacillus and even lower.