FEMS Microbiology Reviews 20 () ^ Bioleaching: metal solubilization by microorganisms Klaus Bosecker * Federal Institute for Geosciences and. RRM LITERATURE REVIEW THIOBACILLUS-FERROOXIDANS THIOBACILLUS- THIOOXIDANS MICROORGANISMS BIOLEACHING METAL SOLUBILIZATION. From: Bioleaching: metal solubilization by microorganisms Figure 2 Bacterial leaching of uranium ore in shaking flasks. Extraction of uranium during leaching.

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Skip to main content. Log In Sign Up. 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 mixroorganisms 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.

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Surfactants and organic extractants. Published by Elsevier Science B. Most thiobacilli solubilizatlon chemolithoautotro- phic species which use the carbon dioxide from the Microbial leaching methods are being increasingly atmosphere as their carbon source for the synthesis applied for metal recovery from low-grade ores and of new cell material. The energy derives from the concentrates that cannot be processed economically oxidation of reduced or partially reduced sulfur com- by conventional methods.

Solubilizztion and Romans extracted copper from mine Bacterial leaching is carried out in an acid envi- water more than years ago. However, it has ronment at pH values between 1.

Therefore the are mainly responsible for the enrichment of metals acidophilic species Thiobacillus ferrooxidans and in water from ore deposits and mines [1]. Other partially reduced sulfur com- 2. Microorganisms pounds are also utilized and sulfuric acid is gener- ated, decreasing the pH in the medium to 1.

Thiobacillus and even lower.

The intensive sulfuric acid produc- tion leads to a rapid decomposition of rocks so that The bacteria most active in bioleaching belong to acid-soluble metal compounds can pass into solution the genus Thiobacillus.

These are Gram-negative, as sulfates. Morphologically the presence of yeast extract [13]. Extremely thermo- cells are identical to T. Acidianus brierleyi, for- from all other thiobacilli by the fact that besides merly associated with the genus Sulfolobus [17], is a deriving energy from bioleaaching oxidation of reduced sulfur chemolithoautotrophic, facultatively aerobic, ex- compounds ferrous iron can be used as an electron tremely acidophilic Archaeon growing on ferrous donor.

In solubjlization absence of oxygen T. Under still able to grow on reduced inorganic sulfur com- anaerobic conditions elemental sulfur is used as an pounds using ferric iron as an alternative electron electron acceptor and is reduced to H2 S. Members of acceptor [5]. An excellent overview of the current the genus Sulfolobus are aerobic, facultatively chem- knowledge of this species was provided by Leduc olithotrophic bacteria oxidizing ferrous iron, elemen- and Ferroni [6].

The same compounds Two new species of acidophilic thiobacilli have are used as energy source by Sulfobacillus thermosul- been described by Huber and Stetter [7,8]: Growth, however, will only occur mobilizing bacteria [7], T. Heterotrophic microorganisms This microorganism is described as bioleachjng mobilizing copper from chalcopyrite [8]. Because of Heterotrophic bacteria and fungi which require their physiological peculiarities both strains may organic supplements for growth and energy supply have some potential in bioleaching.


As in the case of manganese leaching, metal solubilization may be due 2. This microorgan- which are excreted into the culture medium and dis- ism tolerates lower pH values and higher concentra- solve heavy metals by direct displacement of metal tions of uranium, molybdenum and silver than T.

The heterotrophic microorganisms do [10,11]. Therefore, by itself, L. This can only be done to- Among the bacteria, members of the genus Bacillus gether with T. Bioleaching mechanisms Thiobacillus-like bacteria, so-called Th-bacteria, At the present time bioleaching processes are are moderately thermophilic bacteria and grow on based more or less exclusively on the activity of pyrite, pentlandite and chalcopyrite at temperatures T.

Indirect bacterial leaching chemical oxidation reactions into water-soluble met- al sulfates. The ferrous iron arising in surface, and the oxidation to sulfate takes place solubiliztion this reaction can be reoxidized to ferric iron by several enzymatically catalyzed steps. In indirect fate [22] according to the following reactions: The sulfur arising simultaneously Eq.

Therefore direct bacterial leaching can be de- A well known example of an indirect bioleaching scribed according to the microorganis,s reaction: The The lixiviant may be generated by T. Obvi- solubi,ization with uranium ore. In the laboratory this can be achieved by aer- on the interaction of biological and chemical oxida- ation, stirring, or shaking.

On a technical scale, par- tion processes. Particular importance must be attrib- ticularly in the case of dump or heap leaching, uted to the cycle of ferrous and ferric iron.

Carbon dioxide is the only carbon source direct and the indirect leaching, will undoubtedly required, yb there is no need for addition of CO2. However, referring to newest publications by Sand 4.

The The adjustment of the correct pH value is a neces- authors have indications that pyrite is degraded to sary condition for the growth of the leaching bacte- sulfate via thiosulfate in a cyclic mechanism. The ria and is decisive for the solubilization of metals. At compounds of T. The function of leaching bacteria is addition of acid [32]. The mineralogical composition of the leaching 4. Nutrients substrate is of primary importance. In general the mineral nutrients leaching bacteria, can be achieved by external addi- are obtained from the environment and from the tion of acid, but this may not only cause the forma- material to be leached.

The rate of leaching also er with ammonium, phosphate and magnesium salts. A de- crease in the particle size means an increase in the 4.

Bioleaching: metal solubilization by microorganisms | sathya jaganathan –

O2 and CO2 total particle surface area so that higher yields of metal can be obtained without a change in the total An adequate supply of oxygen is a prerequisite for mass of the particles. A particle size of about 42 Wm good growth and high activity of the leaching bac- is regarded as the optimum [36]. Percolator leaching Details of laboratory test methods are described 4. Heavy metals by Bosecker [41] and Rossi [42].

In the simplest meatl, the percolator an increase in metal concentration in the leachate. Very often it is possible to adapt individual culation. Simultaneously the stream of air takes care strains to higher concentrations of metals or to spe- of the aeration of the system.

From: Bioleaching: metal solubilization by microorganisms

Solvent extraction is currently preferred for the concentration and re- covery of metals from pregnant solution. When bac- terial leaching and solvent extraction are coupled the solvents become enriched in the aqueous phase and have to be removed before the barren solution is recirculated to the leaching operation. Therefore, processes tested on individual types of ores cannot be transferred to other microorgnisms. Leaching of low-grade microorganismd ore in air-lift percolators.


Column leaching Column leaching operates on the principle of per- colator leaching and is used as a model for heap or dump leaching processes. Depending on their size, the columns may be made of glass, plastic, lined concrete, or steel Fig.

Their capacities range from several kilograms to a few tons.

Metap various distances most column systems have devices for tak- ing samples or for installing special solubiization for measuring temperature, pH, humidity, oxygen or carbon dioxide. This gives information about what has to be expected in heap or dump leaching and how the leaching conditions can be optimized.

Industrial leaching processes Fig. Ex- traction of uranium during leaching with T. The simplest way of conducting microbial of the leaching process liquid samples are taken at leaching is to pile the material in heaps, allow water intervals and the state of the leaching microorbanisms is de- to micrlorganisms through the heap and collect the seepage termined on the basis of pH measurements, micro- biological investigations and chemical analysis microorfanisms the metals that have passed into solution.

Higher rates of aeration and a more ac- curate monitoring and control of the various param- Fig. There are three main procedures in use: Dump leaching Dump leaching is the oldest process. The size of the dumps varies considerably and the amount of ore may be in the range of several hundred thousand tons of ore.

Be- fore recirculation, the leachate may pass through an oxidation basin, in which the bacteria and ferric iron are regenerated. The procedure is similar to that of dump leaching. In some heap leaching operations, pipes are placed in strategic positions within the doned mines. The water collects in deeper gen. The best known application 5.

Underground leaching of this procedure is at the Stanrock uranium mine at Underground leaching is usually done in aban- Elliot Lake in Ontario, Canada [47].

Ore deposits that cannot be mined by convention- al methods because they are too low-grade or be- cause they are too small can be leached in situ. So- lutions containing the appropriate bacteria are injected into boreholes in the fractured orebody. Flow sheet of a dump and in situ leaching process [41]. Bioleaching of copper ore in Chile.

Open-cast mining of copper ore. Preparation of dumps for leaching.

Irrigation by perforated tubes. Dump leaching area, covered for insulation. Overall view of the leaching operation plant 1: During the last 25 years bioleaching of min- Tank leaching is more expensive to construct and erals has opened up new opportunities for extrac- to operate than dump, heap, or in situ leaching biolaching tive metallurgy and biohydrometallurgy is now esses.

But the rate of metal extraction is much higher practised in the copper and uranium industries, metap currently this technique is successfully used for especially for the treatment of low-grade ores bioleaching of refractory gold ores. There are copper were recovered every day by bioleaching.