bioleaching word

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ABSTRACT

Bioleaching is an emerging technology with signicant potentials to add value to the mining

industries so as to deliver attractive environmental and social benets to all the associates.

Thiobacillus ferrooxidans and T. thiooxidans are the main chemolithotrophic bacteria which

convert insoluble metal sulphides into soluble metal sulphates. Heterotrophic bacteri and fungi

also involve in non-sulfide ores and minerals treatment for metal recovery. The production of

organic acids and chelating and complexing compounds which excreted into the environment

enhances the metal extraction. Nowadays, bioleaching is used for recovery of copper, uranium

and gold. There are three main techniques applied in bioleaching which are heap, dump and in

situ leaching. The other activities benefits from bioleaching are detoxification of industrial waste

products, sewage sludge and soil contaminated with heavy metals.

1. INTRODUCTION

Bioleaching is the use of bacterial microorganisms to extract precious metals, such as

gold, from ore in which it is embedded. As an alternative to smelting or roasting, miners use

bioleaching when there are lower concentrations of metal in ore and they need an efficient,

environmentally responsible method to extract it. The bacteria feed on nutrients in minerals,

thereby separating the metal from the ore. Other metals that are commonly extracted via

bioleaching include silver, zinc, copper, lead and uranium.

This process works because of how special microorganisms act on mineral deposits.

These microorganisms are catalysts to speed up natural processes in the ore. The types of

bacteria most often used in this process include Leptospirillum ferrooxidans , Thiobacillus

ferrooxidans and certain species of Acidianus, Sulfolobus and Sulfobacillus.


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2. MICROORGANISMS

2.1. Thiobacillus

Genus Thiobacillus is the most active bioleaching bacteria. The bacteria grow under

aerobic conditions which they are Gram-negative and non-spore forming rods. Most thiobacilli

use the carbon dioxide from the atmosphere for the synthesis of new cell material known

chemolithoautotrophic species. The energy derives from the oxidation of reduced or partially

reduced sulfur compounds, including sulfides, elemental sulfur and thiosulfate, the final

oxidation product being sulphate. In an acid environment, at pH values between 1.5 and 3,

bacterial leaching is carried out in which metals ions remain in solution. Therefore the

acidophilic species Thiobacillus ferrooxidans and T. thiooxidans are of particular importance.

Other thiobacilli which grow only at higher pH values which metal ions do not maintain in

solution are also able to oxidize sulfur and sulphides. T. thiooxidans , isolated in 1922 by

Waksman and Joffe, is well known for its rapid oxidation of elemental sulfur. Sulfuric acid also

generated by the utilization of other partial reduced sulphur compounds then decreasing the pH

in the medium to 1.5 to 1.0 and even lower. 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, T. Ferrooxidans play the most important role in bacterial leaching. This

bacterium was first isolated in 1947 by Colmer and Hinkle from acid coal mine drainage. The

cells are identical to T. Thiooxidans morphologically but they differ from the latter by the much

slower course of the oxidation of elemental sulfur. The differences of T. ferrooxidans differs

from all other thiobacilli is that besides deriving energy from the oxidation of reduced sulfur

compounds ferrous iron can be used as an electron donor. T. ferrooxidans is still able to grow on


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reduced inorganic sulphur compounds in the absence of oxygen by using ferric iron as an

alternative electron acceptor. There are two new species of acidophilic thiobacilli which are T.

Prosperus , represents a new group of halotolerant metal-mobilizing bacteria and T. cuprinus is a

facultatively chemolithoautotrophic bacterium which oxidizes metal sulfides but does not oxidize

ferrous iron. This microorganism is described as preferentially mobilizing copper from

chalcopyrite. Because of their physiological peculiarities both strains may have some potential

in bioleaching.

Diagram of activities of T. ferrooxidans in bioleaching


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Diagram of some species of bacteria involve in bioleaching


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2.3. Thermophilic bacteria

Microorganisms can be subdivided into:

Bacteria Temperature optima

Mesophic 20 40 C

Moderate thermophilic 40 60 C

Extremely thermophilic Above 60 C

Thiobacillus -like bacteria, so-called Th-bacteria, are moderately thermophilic bacteria

and grow on pyrite, pentlandite and chalcopyrite at temperatures in the range of 50C. It used

ferrous iron as the energy source, however only in the presence of yeast extract, the growth is

observed. Extremely thermophilic bacteria growing at temperatures above 60C were isolated by

Brierley, Norris, Karavaiko and their co-workers. Acidianus brierleyi , was originally described

as Sulfolobus brieleyi and reclassified as Acidianus brierleyi by Segerer at 1986 year, is

chemolithoautotrophic organism, facultatively anaerobic and extremely

acidophilic Archaeon growing on ferrous iron, elemental sulfur and metal sulfides. Elemental

sulfur is used as an electron acceptor and is reduced to H 2S under anaerobic conditions. Members

of the genus Sulfolobus are aerobic, facultatively chemolithotrophic bacteria oxidizing ferrous

iron, elemental sulfur and sulfide minerals. The same compounds are used as energy source

by Sulfobacillus thermosulfidooxidans , a spore-forming facultatively autotrophic bacterium.

However, the growth will only occur in the presence of yeast extract.


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2.4. Heterotrophic microorganisms

Heterotrophic bacteria and fungi which require organic supplements for growth and

energy supply may contribute to metal leaching. Metal solubilization may be due to enzymatic

reduction of highly oxidized metal compounds or is effected by the production of organic acids.

As in the case of manganese leaching, it is also affected by compounds with at least two

hydrophilic reactive groups (e.g., phenol derivatives) which are excreted into the culture medium

and dissolve heavy metals by direct displacement of metal ions from the ore matrix by hydrogen

ions and by the formation of soluble metal complexes and chelates. From the metal leaching, the

heterotrophic microorganisms do not have any benefit. Genus Bacillus is most effective in metalsolubilization, with regard to the fungi the genera Aspergillus and Penicillium are the most

important ones. Citric and oxalic acids are produced by fungi. The other bioleaching fungi are

Spergillus niger , Yarrowia lipolytica and Saccharomyces cervisiae .


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3. BIOLEACHING PROCESS AND TECHNIQUES

3. 1 Bioleaching Process

The bacteria use a chemical reaction called oxidation to turn metal sulphide crystals into

sulfates and pure metals. These constituent parts of ore are separated into valuable metal and

leftover sulphur and other acidic chemicals. Eventually, enough material builds up in the waste

solution to filter and concentrate it into recoverable metal.

The extraction of iron can involve numerous ferrous and sulfur oxidizing bacteria,

including Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans . For example,

bacteria catalyse the breakdown of the mineral arsenopyrite (FeAsS) by oxidising the sulfur and

metal (in this case arsenic ions) to higher oxidation states whilst reducing dioxygen by H 2 and

Fe3+. This allows the soluble products to dissolve .The contributions of the leaching mechanisms

depend on the types of sulphide mineral and on the operating conditions.

3. 2 Bioleaching Techiques

The bioleaching technology is a simple and effective for processing of sulfide ores and is

used on a technical scale mainly for the recovery of copper and uranium. There are two main

techniques which are laboratory investigation and industrial leaching processes

In laboratory investigation, percolator leaching is used. The process is determined on the

basis of pH measurements, microbiological investigations and chemical analysis of the metals

that have passed into solution. Because the oxygen supply is often inadequate and the surface

ratio is unfavorable, percolator leaching is not very efficient. Therefore, percolator leaching has

been substantially displaced by submerged leaching using fine-grained material which is
http://www.wikipedia.org/wiki/Acidithiobacillushttp://www.wikipedia.org/wiki/Acidithiobacillushttp://www.wikipedia.org/wiki/Catalysthttp://www.wikipedia.org/wiki/Arsenopyritehttp://www.wikipedia.org/wiki/Sulfurhttp://www.wikipedia.org/wiki/Oxygenhttp://www.wikipedia.org/wiki/Oxygenhttp://www.wikipedia.org/wiki/Sulfurhttp://www.wikipedia.org/wiki/Arsenopyritehttp://www.wikipedia.org/wiki/Catalysthttp://www.wikipedia.org/wiki/Acidithiobacillus


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suspended in the leaching liquid and kept in motion by shaking or stirring. Other technique is

column leaching that operates based on the principle of percolator leaching and is used as a

model for heap or dump leaching processes.

In industrial leaching processes, bioleaching technology is used for the treatment of low-

grade ores which generally contain metal concentrations below 0.5% (w/w). The simplest way of

conducting microbial leaching is to load the material in heaps, allow water to filter through the

heap and collect the seepage water (leachate). Since the bacterial oxidation of sulfides is much

slower than other biotechnical processes the leachate is recirculated. There are three main

procedures in use: dump leaching, heap leaching and underground leaching.

Heap leaching is mainly used for fine-grained ores that cannot be concentrated by

flotation. The leaching is practised in large basins containing up to 12 000 tons of ore. In some

heap leaching operations, pipes are placed in strategic positions within the heaps during its

construction to provide the deeper portions of the heap with sufficient amounts of oxygen. Heap

leach mining works well for high concentrations of less ores, as less Earth needs to be ground

onto leach pads in order to extract the same amount of materials. It also requires less energy

consumption to use these methods, which many consider to be an environmental alternative.

Figure 1 : Heap leaching


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Figure 2: Underground leaching

4. FACTORS INFLUENCING BIOLEACHING

The leaching effectiveness depends largely on the efficiency of the microorganisms and on the

chemical and mineralogical composition of the ore to be leached. The maximum yields of metal

extraction can be achieved only when the leaching conditions correspond to the optimum growth

conditions of the bacteria. There are seven (7) factors affecting bioleaching which are; (1)

nutrients, (2) oxygen and carbon dioxide gases, (3) pH, (4) temperature, (5) mineral substrate, (6)

heavy metals, and (7) surfactants and organic extractants.


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microorganisms. On a technical scale, particularly in the case of dump or heap leaching, carbon

dioxide is the only carbon source required, but there is no need for additional of this gas supply.

4. 3 pH

pH is the third factor contributing in influencing bioleaching process. The adjustment of the

correct pH value is a necessary condition for the growth of the leaching bacteria and is

significant for the solubilization of metals. The example of leaching bacteria is T. ferrooxidans .

T. ferrooxidans is an acidophile, living in environments with an optimal pH range of 1.5 to 2.5.

Thus, pH values in the range of 2.0 2.5 are optimum for the bacterial oxidation of ferrous iron

and sulfide. At pH values below 2.0, a considerable inhibition of T. ferrooxidans will occur

but T. ferrooxidans may be adapted to even lower pH values by increasing addition of acid.At

acidic pH, elemental sulfur is inert to abiotic oxidation, although other reduced inorganic sulphur

species such asthiosulfate and tetrathionate are oxidised abiotically. In the absence of sulphur

oxidisingmicroorganisms, more than 90% of sulde sulphur is trans formed to elemental sulfur.

The role of sulfur oxidising microorganisms in the oxida tion of mineral suldes at low pH is

therefore very important.

4.4 Temperature

Another important factor that can induce the bioleaching process is temperature. The

optimum temperature for ferrous iron and sulfide oxidation by T. ferrooxidans is between 28 and

30C. Normally, below the optimum temperature the microbes become inactive, but at

temperatures above it, they are rapidly destroyed. In this situation, at lower temperatures a

decrease in metal extraction will occur, but even at 4C bacterial solubilization of copper, cobalt,


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nickel and zinc was observed. At higher temperatures between 50 C to 80 C thermophilic

bacteria can be used for leaching purposes.

4.5 Mineral substrate

Other valuable influencing factor in bioleaching process is mineral substrate itself. The

mineralogical composition of the leaching substrate is of primary importance. At high carbonate

content of the ore or gangue material the pH in the leaching liquid will increase and inhibition or

complete suppression of bacterial activity occurs. Low pH values, necessary for the growth of

the leaching bacteria can be achieved by external addition of acid, but this may not only cause

the formation and precipitation of gypsum but will also affect the cost of the process.Gypsum is

a common white soft or colourless mineral consisting of the hydrated calcium sulphate, usually

used to make cements and plasters for building.

The rate of leaching also depends on the total surface of the substrate. A decrease in the

particle size means an increase in the total particle surface area so that higher yields of metal can

be obtained without a change in the total mass of the particles. In short, the relationship between

particle size of the substrate and metal yield is non-perpendicular. A particle size of about 42 m

is regarded as the optimum. An enlargement of the total mineral surface area can be obtained

also by an increase in pulp density. An increase in the pulp density may result in an increase in

metal extraction, its relation is perpendicular but the risk is, the dissolution of certain compounds

which have an inhibitory or even toxic effect on the growth of leaching bacteria will increase as

well by increasing the pulp density.


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4.6 Heavy metals

Concentration of heavy metals also one of the influent factor to the of bioleaching

process.The leaching of metal sulfides is accompanied by an increase in metal concentration in

the leachate. In general the leaching organisms, especially the thiobacillus sp. , have a high

tolerance to heavy metals and various strains may even tolerate 50 g/l Nikel, 55 g/l Copper or

112 g/l Zinc. Different strains of the some species may show completely different sensitivities to

heavy metals. Very often it is possible to adapt individual strains to higher concentrations of

metals or to specific substrates by gradually increasing the concentration of metals or mineral

substrates.

4.7 Surfactants and organic extractants

The last factor affecting the leaching effectiveness process is surfactants and organic

extractants.Surfactants and organic compounds used in solvent extraction generally have an

inhibitory effect on the leaching bacteria, mainly because of a decrease in the surface tension and

reduction of the mass transfer of oxygen. Solvent extraction is currently preferred for the

concentration and recovery of metals from pregnant solution. When bacterial 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.


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5.0 INDUSTRIAL APPLICATION

5.1 Background

The results of natural microbial leaching have been known since ancient times. Pliny the

Elder (23 73 AD), who had a passion for observing the wonders of nature, wrote in his article

about a glass- like substance ( vitreolus quasi vitrum ) that was found on rocks on natural

history. One of the earliest records of utilizing the effects of bioleaching is from the island of

Cyprus. Galen, a Greek physician from Pergamum, in 162 A.D., is reported to have collected

cuperiferous solutions from mine water from the mines of Skouriotissa and concentrated them by

evaporation to form crystals of copper sulfate. Recent findings have revealed evidence that prove

this anecdote.

In China, during the East Han Dynasty (206 BC 220 AD), observations have been made

on the natural leaching of copper and the formation of gall springs. The Gall -Copper Process

was recorded as being used during the Song Dynasty (960 1271AD). Copper was precipitated

from solution by dipping iron into the blue vitriol solution which is a process identified as early

as 150 BC in China. Therefore, presumably, the recognition of a natural copper leaching process

can be identified as early as that date. But, it was in 1947 that these phenomena were attributed

to bacteria. Once identified, however, rapid steps were taken to commercialize the process.

Commercial application of bacterial leaching began in the late 1950s at the Kennecott

Utah Copper Companys Bingham Canyon Mine near Salt Lake City, Utah where it was

observed that blue copper-containing solutions were running out of waste piles that contained

copper sulfide minerals. It is something that should not have happened in the absence of


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powerful oxidizing agents and acid. Investigation revealed that naturally occurring bacteria were

oxidizing iron sulfides in the piles, and the resulting ferric sulfate and sulfuric acid was acting as

an oxidizer and leachant for copper sulfides. These bacteria were given the name

ferrooxidans for their ability to oxidize iron sulfides. A second set of bacteria was also identified

and given the name thiooxidans for their ability to oxidize sulfur to yield sulfuric acid. The

bacteria, which were native to the soil, in effect created a completely natural metallurgical

processing plant.

5.2 Introduction

Bioleaching using microorganisms is widely practiced in commercial operation to

process ores of copper, uranium, cobalt, zinc as well as in gold processing and coal

desulfurization. At present, bioleaching is being used commercially only for the recovery of

copper, uranium and gold. In copper leaching, the microorganisms catalyze the oxidation of iron

sulfides to create ferric sulfate and sulfuric acid. Ferric sulfate is a powerful oxidizing agent. So,

the copper sulfide minerals are oxidized by the ferric sulfate which is formed by the oxidation of

iron sulfides. Then, the copper contained is leached by the sulfuric acid formed.

In the case of uranium, the microorganisms are used for the oxidation process to form

ferric sulfate and sulfuric acid. However, the ferric sulfate oxidizes the tetravalent uranium oxide

which is insoluble in acid to its soluble form, hexavalent uranium oxide. Then, the hexavalent

uranium oxide is leached by the sulfuric acid. In gold processing, the microorganisms are used tooxidize, to make a soluble iron sulfide matrix in which the gold particles are imbedded. Thus, the

gold is available for cyanide leaching.


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5.3 Copper

Following early development work and application in the United States, Chile has

become a major developer of bioleaching on an industrial scale. Chile is the world's major

copper producing country. The first Chilean plant to be put into operation was S.M. Pudahuel. In

this country, bioleaching is still being operated even at 4200 m above sea level in Quebrada

Blanca. The production of copper in Chile is 75 000 tons annually. In 2001, bioleaching

constituted approximately 10% of copper production in Chile meanwhile the heap and dump

leaching, in general, constituted approximately 30% of Chiles production.

In the 1970s, the largest plant for microbial leaching was that for dump leaching of the

Kennecott Copper Corporation at Bingham, UT, USA. The contents of the dumps stored there

were estimated at more than 3.610 9 tons and about 200 tons of copper were recovered every

day by bioleaching. It is expected that within the next years, several industrial applications of

bacterial leaching will be operated. It will lead to the yield of 250 000 tons of cathodic copper

per year which will be equal to about 16% of the present total copper production in Chile.

Copper ores include copper (II) oxide and copper (II) sulfide. Some copper ores are

called low-grade ores because it contains less than 1% copper. However, it is still valuable. To

extract copper from its low-grade ores, bioleaching is applied. The separation of the metal from

the ores is done by some bacteria which can live using the energy by the bond between sulfur

and copper. The bacteria that involve in copper bioleaching are iron-oxidizing bacteria, sulfur-

oxidizing bacteria and heterotrophic bacteria. Mesophiles and thermophiles are also used in

copper bioleaching process. The bioleaching process in copper extraction is more efficient


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because it consumes less energy than the traditional methods. But, it is a slow process and it is

time-consuming.

5.4 Uranium

Uranium could also be recovered by certain microorganisms that can catalyze the

oxidation of uranium. Commercial application of bioleaching of uranium from low-grade ores

has been practiced since the 1960s. Industrial-scale bioleaching of uranium is performed by

spraying stope walls with acid mine drainage and the in-situ irrigation of fractured underground

ore deposits. Best known are the in situ leaching operations in the underground uranium mines in

the Elliot Lake district of Canada including the Stanrock, Milliken and Denison mines. At that

time, the annual production of uranium from the Stanrock Mine was about 50 000 kg

U3O8 whereas 60 000 kg U 3O8 was produced in the Milliken Mine after improvement of the

leaching conditions.

The increase of interest in uranium bioleaching is because it is simple, effective, low

energy consumption and environmentally friendly. It does not require expensive tools. The

presence of microorganisms in leaching operations has been found to be beneficial in catalyzing

the uranium dissolution process. The modest nutritional requirements of microorganisms are

provided by the aeration of mineral suspension containing iron and sulfur in water or by the

irrigation of a heap. The optimum factors of nutrients, pH and temperature are very essential to

maintain the intended growth and activity of the microorganisms. For example, Acidithiobacillus

group of bacteria utilizes the energy from Fe 3+ in acid medium in the presence of oxygen at an

optimum pH of 1.5-2.5 at ambient temperature to leach 70-98% metal content of the substrate.


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5.5 Gold

During the past 10 years, bio-treatment of refractory gold ores has been developed to an

industrial application. There are several tank leaching operations in South Africa, Brazil and

Australia. The refractory gold ores contain finely disseminated gold particles associated with

sulfide minerals including arsenopyrite and pyrite. The decomposition of the mineral sulfide

matrix is required before the gold can be extracted. There are various traditional methods for the

treatment of refractory ores. However, bioleaching was found to be a new, low-energy

alternative. Without pretreatment usually less than 50% of the gold is recovered by cyanidation.

After bioleaching, more than 95% of the gold is extracted depending on the mineral composition

of the ore and on the extent of pretreatment.

The first industrial plant started at Fairview, South Africa, in 1986. The plant capacity is

reported to be 300 tons/month of a pyrite concentrate containing 100 150 g Au/ton. A bio-

oxidation plant in Ghana, constructed during 1994, has a capacity of 720 tons of gold-bearing

concentrate per day. Because the price of gold has risen many mineral companies now take a

second look at deposits that were once considered uneconomical. Many of these deposits are

refractory and tend to resist cyanidation. Bioleaching offers a new low-cost alternative for

oxidizing these refractory ores.


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6.0 FUTURE ASPECTS

At present, bioleaching is being used commercially only for the recovery of copper, gold

and uranium. It is hoped in the future bioleaching can be applied for mining of zinc, nickel,

cobalt and molybdenum. This technology should be of great interest for developing countries. It

has a lot of advantages compared to conventional method such as hydrometallurgy. Bioleaching

requires low cost of investment and operating procedures. It saves transport costs as the

processing plant can be built in the immediate vicinity of the ore deposit. The procedures are not

complicated and are easy to control and there is no requirement of extensive technical

knowledge.

There is an increase in interest in the insoluble metals that left in the residues, e.g. lead

besides the metals recovered in the leachate. Leaching of metals e.g. zinc, cadmium, copper that

interfere with conventional processes for the recovery of the lead can transform inferior lead

sulfide concentrates into high-value concentrates. Similar procedures are being investigated for

the extraction of silver and other precious metals that are finely disseminated in iron, arsenic,

copper and zinc sulfides. The metal sulfides are first removed by microbial leaching and the

precious metals are then recovered from the residue.

6.1 Waste Products

Two famous iron-oxidizing bacteria that are always related with industrial application of

microbial leaching are Thiobacillus ferrooxidans and Lectospirillum ferrooxidans . Most of

mineral industrial waste products are present mainly as oxides rather than as sulfides. Thus they

cannot be treated through that way. Experiments have shown that the metal oxides in such

residues can be leached by acid produced by T. thiooxidans . Depending on the metal compounds


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in the residues, vanadium, chromium, copper and zinc can be almost completely recovered. In

some cases, chemical leaching is easier. Bioleaching using T. thiooxidans is advantageous if

inexpensive sulfur is available. Another advantage consists in the fact that as a consequence of

the sulfuric acid production during growth of T. thiooxidans the pH falls only gradually so that

the metals pass into solution at different rates corresponding to their solubilities and can be

separated from the leaching suspension selectively. Thiobacilli have also some potential for the

detoxification of sewage sludge, soil and sediment contaminated with heavy metals and may

contribute to diminishing some of our environmental problems.

6.2 Heterotrophic Leaching

Thiobacilli cannot be used in the case of oxide, carbonate and silicates ores. Thus, for

these ores, research is continuing done by using of heterotrophic bacteria and fungi. These

bacteria and fungi will dissolve the metals by organic acids or complexing or chelating agents

produced by them. There were studies on silicate nickel ores showed that nickel is dissolved by

organic acids produced by microorganisms. The most effective one was citric acid. With nickel-

tolerant strains of Penicillium , up to 80% of the nickel was extracted, depending on the

mineralization. Various other valuable metals, e.g. gold, titanium, aluminium, chromium, copper,

manganese and uranium, can also be leached by heterotrophic microorganisms, however much

development requires to be done. Besides that, heterotrophic microorganisms can also be used

for upgrading mineral raw materials by removing the impurities. Iron oxides can lower the

quality of quartz sands, kaolins and clays. The impurities can be removed by chemical as well as

by microbiological methods. Microbiological method is based on bacterial and fungal production

of organic acids and other chelating metabolic agents. Most of the bacteria active in iron removal


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are related to the genera Bacillus and Pseudomonas . Among the fungi Aspergillus and

Penicillium were found to be the most effective ones.

6.3 Looking Forward

The current progress of bioleaching in developing countries is encouraging. It is

expected that in the coming years several new commercial-size bioleaching plants will be

installed. It is likely that heap leaching will continue to be the choice for low-grade ores and

tailings, while tank bioleaching technology will probably increase its application for gold, copper

and other base-metal concentrates. The use of thermophilic bacteria and archea will be a major

contribution that can increase the leaching rates and metal recoveries. Developing countries

should increase their efforts in research and development in bioleaching technology, as they have

comparative and competitive advantages in this area. International cooperation should also be

considered in the establishment of new operations that can significantly contribute to the

economic and social development of these countries.


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7. CONCLUSION

Bioleaching is not being considered today only with respect to its ability to recover

valuable metals. There is a demand for less expensive and more environmentally friendly

processes. Further development is necessary with respect to both technical and biological

aspects. The latter includes increasing the rate of leaching and the tolerance of the

microorganisms to heavy metals. Genetic improvement of bioleaching bacteria, whether by

mutation and selection or by genetic engineering, will bring results more quickly than

conventional procedures like screening and adaptation, and in the mean time, considerable

progress has been made on the development of a genetic system for T. ferrooxidans.


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REFERENCES

http://www.docstoc.com/docs/55575505/Copper-ores-bioleaching

http://www.copper.org/publications/newsletters/innovations/2004/05/producing_copper_

natures_way_bioleaching.html

http://www.sciencedirect.com/science/article/pii/S0168644597000363

http://www.igcar.ernet.in/events/anup2010/Abhilash.pdf

http://www.eplantscience.com/index_files/biotechnology/Biotechnology%20and%20envi

ronment/Environmental%20Biotechnology/biotech_eb_microbial_leaching.php

http://cdn.intechopen.com/pdfs/19678/InTech-Microbial_leaching_of_uranium_ore.pdf

http://www.academicjournals.org/ajb/PDF/pdf2010/1Nov/Bayat%20and%20Sari.pdf

Aeration, http://www.mrwa.com/OP-Aeration.pdf page 191

N. Pradhan, K.C. Nathsarma, K. SrinivasaRao, L.B. Sukla, B.K. Mishra. Heap bioleaching of

chalcopyrite: A review,2008Minerals Engineering 21 (2008) 355 365


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ENVIRONMENTAL MICROBIOLOGY

ASSIGNMENT

TITLE: BIOLEACHING

MATRIC NO:

1. 09122742. 09116843. 09199504. 09103925. 0910250

DATE OF SUBMISSION:

28TH NOVEMBER 2012

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bioleaching word