# Biomining



## alshangiti (7 أكتوبر 2011)

Biomining is a new approach to the extraction of desired minerals from ores being explored by the mining industry in the past few years. Microorganisms are used to leach out the minerals, rather than the traditional methods of extreme heat or toxic chemicals, which have a deleterious effect on the environment.
Overview
The development of industrial mineral processing has been established now in several countries including South Africa, Brazil and Australia. Iron-and sulfur-oxidizing microorganisms are used to release occluded copper, gold and uranium from mineral sulfides. Most industral plants for biooxidation of gold-bearing concentrates have been operated at 40°C with mixed cultures of mesophilic bacteria of the genera _Thiobacillus_ or _Leptospirillum ferrooxidans_. In subsequent studies the dissimulatory iron-reducing archaea _Pyrococcus furiosus_ and _Pyrobaculum islandicum_ were shown to reduce gold chloride to insoluble gold.
Using _Bacteria_ such as _Acidithiobacillus ferrooxidans_ to leach copper from mine tailings has improved recovery rates and reduced operating costs. Moreover, it permits extraction from low grade ores - an important consideration in the face of the depletion of high grade ores.
The potential applications of biotechnology to mining and processing are countless. Some examples of past projects in biotechnology include a biologically assisted in situ mining program, biodegradation methods, passive bioremediation of acid rock drainage, and bioleaching of ores and concentrates. This research often results in technology implementation for greater efficiency and productivity or novel solutions to complex problems. Additional capabilities include the bioleaching of metals from sulfide materials, phosphate ore bioprocessing, and the bioconcentration of metals from solutions. One project recently under investigation is the use of biological methods for the reduction of sulfur in coal-cleaning applications. From in situ mining to mineral processing and treatment technology, biotechnology provides innovative and cost-effective industry solutions.
The potential of thermophilic sulfide-oxidizing archaea in copper extraction has attracted interest due to the efficient extraction of metals from sulfide ores that are recalcitrant to dissolution. Microbial leaching is especially useful for copper ores because copper sulfate, formed during the oxidation of copper sulfide ores is very water-soluble. Approximately 25% of all copper mined worldwide is now obtained from leaching processes. The acidophilic archaea _Sulfolobus metallicus_ and _Metallosphaera sedula_ tolerate up to 4% of copper and have been exploited for mineral biomining. Between 40 and 60% copper extraction was achieved in primary reactors and more than 90% extraction in secondary reactors with overall residence times of about 6 days.
The oxidation of the ferrous ion (Fe2+) to the ferric ion (Fe3+) is an energy producing reaction for some microorganisms. As only a small amount of energy is obtained, large amounts of (Fe2+) have to be oxidized. Furthermore, (Fe3+) forms the insoluble Fe(OH)3 precipitate in H2O. Many Fe2+ oxidizing microorganisms also oxidize sulfur and are thus obligate acidophiles that further acidify the environment by the production of H2SO4. This is due in part to the fact that at neutral pH Fe2+ is rapidly oxidized chemically in contact with the air. In these conditions there is not enough Fe2+ to allow significant growth. At low pH, however, Fe2+ is much more stable. This explains why most of the Fe2+ oxidizing microorganisms are only found in acidic environments and are obligate acidophiles.
The best studied Fe2+ oxidizing bacterium is _Thiobacillus ferrooxidans_, an acidophililic chemolithotroph. The microbiological oxidation of Fe2+ is an important aspect of the development of acidic pH’s in mines, and constitutes a serious ecological problem. However, this process can also be usefully exploited when controlled. The sulfur containing ore pyrite (FeS2) is at the start of this process. Pyrite is an insoluble cristalline structure that is abundant in coal- and mineral ores. It is produced by the following reaction:
S + FeS → FeS2
Normally pyrite is shielded from contact with oxygen and not accessible for microorganisms. Upon exploitation of the mine, however, pyrite is brought into contact with air (oxygen) and microorganisms and oxidation will start. This oxidation relies on a combination of chemically and microbiologically catalyzed processes. Two electron acceptors can influence this process: O2 and Fe3+ ions. The latter will only be present in significant amounts in acidic conditions (pH < 2.5). First a slow chemical process with O2 as electron acceptor will initiate the oxidation of pyrite:
FeS2 + 7/2 O2 + H2O → Fe2+ + 2 SO42- + 2 H+
This reaction acidifies the environment and the Fe2+ will be formed is rather stable. In such an environment _Thiobacillus ferrooxidans_ will be able to grow rapidly. Upon further acidification _Ferroplasma_ will also develop and further acidify. As a consequence of the microbial activity (energy producing reaction):
Fe2+ → Fe3+
This Fe3+ that remains soluble at low pH reacts spontaneously with the pyrite:
FeS2 + 14 Fe3+ + 8 H2O → 15 Fe2+ + 2 SO42- + 16 H+
The produced Fe2+ can again be used by the microorganisms and thus a cascade reaction will be initiated.
In the industrial microbial leaching process, low grade ore is dumped in a large pile (the leach dump) and a dilute sulfuric acid solution (pH 2) is percolated down through the pile. The liquid coming out at the bottom of he pile, rich in the mineral is collected and transported to a precipitation plant where the metal is reprecipitated and purified. The liquid is then pumped back to the top of the pile and the cycle is repeated.
_Thiobacillus ferrooxidans_ is able to oxidize the Cu+ in chalcocite (Cu2S) to Cu2+, thus removing some of the cupper in the soluble form, Cu2+, and forming the mineral covellite (CuS). This oxidation of Cu+ to Cu2+ is an energy yielding reaction (such as the oxidation of Fe2+ to Fe3+). Covellite can then be oxidized, releasing sulfate and soluble Cu2+ as products.
A second mechanism, and probably the most important in most mining operations, involves chemical oxidation of the copper ore with ferric (Fe3+) ions formed by the microbial oxidation of ferrous ions (derived from the oxidation of pyrite). Three possible reactions for the oxidation of copper ore are:
Cu2S + 1/2 O2 + 2 H+ → CuS + Cu2+ + H2O
CuS + 2 O2 → Cu2+ + SO42-
CuS + 8 Fe3+ + 4 H2O → Cu2+ + 8 Fe2+ + SO42- + 8 H+
The copper metal is the recovered by using Fe0 from steel cans:
Fe0 + Cu2+ → Cu0 + Fe2+
The temperature inside the leach dump often rises spontaneously as a result of microbial activities. Thus, thermophilic iron-oxidizing chemolithotrophs such as thermophilic _Thiobacillus_ species and _Leptospirillum_ and at even higher temperatures the thermoacidophilic archaeon _Sulfolobus (Metallosphaera sedula)_ may become important in the leaching process above 40°C. Similarly to copper, _Thiobacillus ferrooxidans_ can oxidize U4+ to U6+ with O2 as electron acceptor. However, it is likely that the uranium leaching process depends more on the chemical oxidation of uranium by Fe3+, with _T. ferrooxidans_ contributing mainly through the reoxidation of Fe2+ to Fe3+ as described above.
UO2 + Fe(SO4)3 → UO2SO4 + 2 FeSO4
Gold is frequently found in nature associated with minerals containing arsenic and pyrite. In the microbial leaching process _T. ferrooxidans_ and relatives are able to attack and solubilize the arsenopyrite minerals, and in the process, releasing the trapped gold (Au):
2 FeAsS[Au] + 7 O2 + 2 H2O + H2SO4 → Fe(SO4)3 + 2 H3AsO4 + [Au]
The above information can be verified in "NBIAP News Report." U.S. Department of Agriculture (June 1994).​


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## alshangiti (7 أكتوبر 2011)

*What are Bioleaching and Biooxidation?*

*Bioleaching* Bioleaching is the use of microorganisms to extract metals from an ore. Leaching is the process of removing a soluble substance from a solid structure by making it into a liquid form easy for extraction. In chemical leaching, this is done by treating the soluble substance with a chemical solution. In bioleaching, it is done through contact with bacteria.
Bioleaching is used commercially in the extraction of copper.
*Biooxidation*
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Biooxidation also uses microorganisms, not to extract metals, but to make the metals ready for extraction. Oxidation is the chemical reaction in which an element is changed by the addition of oxygen. Rust is an example of the oxidization of iron. 
Biooxidation is mainly used in gold mining. Gold is often found in ores with gold particles scattered throughout, called refractory ores, and the small particles of gold are covered by insoluble minerals. These minerals make the extraction difficult. Therefore, microorganisms that can "eat away" at the mineral coating are used to pre-treat the gold ores before they can be extracted.
Bioleaching of copper, and biooxidation of refractory gold ores are the only well-established large scale processes that are commercially carried out today.
*The Science – How does Biomining Work?*http://www.biobasics.gc.ca/english/View.asp?x=797#top​Biooxidation and bioleaching processes are usually done in heaps of ground ore. The low-grade ores are ground into powder and piled in an irrigated outdoor facility. The heaps are then treated with an acidic liquid that contains a fraction of the bacterial population required since some are naturally existing within the ore. The liquid with the metals extracted are then pumped into another section where the metal is recovered. 
Biomining in heaps has the advantage of being simple and cheap to perform. However, it has disadvantages such as the lack of complete control over the conditions of biomining, leading to unpredictable or inefficient extraction rates. 
For this reason, biomining is also done in reactors. Reactors are a series of tanks the ore mixture is treated in, and offers control of factors important in biomining, such as temperature and pH levels.
*Uses of Biomining* 

Currently, 25 percent of all copper worldwide is produced through biomining. The process is used on a variety of other metals such as gold and uranium. Biomining is not yet a proven or profitable technology to apply to other metals such as zinc, nickel and cobalt. 
Some advantages of biomining over traditional methods include reduced noxious gas production, and the elimination of toxic liquid waste produced as a result of chemical leaching. Biomining, however, is slower than traditional mining techniques and is not applicable to a wide variety of ores.
*Biotechnology and Biomining *http://www.biobasics.gc.ca/english/View.asp?x=797#top​Biomining uses naturally existing microorganisms to leach and oxidate. As well, studies of microorganism genomes are helping researchers learn more about how microorganism biology works. This may lead to the genetic engineering of organisms for optimal biomining results. 
*Current Research Areas in Biomining *
There are continuing efforts to fully understand the basic biology of microorganisms, such as the _Thiobacillus ferrooxidans_. Researchers are seeking enhanced microbial performance in biomining processes through the identification of better indigenous strains and also through genetic engineering. However, because genetically engineered microorganisms need careful control and monitoring, they will not likely be available for commercial use for several years to come, and then only for controlled processes, like those possible in reactors. 
Canadian researchers are also working on creating biomining conditions that will be optimal in the colder climates like Canada.
*Sustainable Development and Biomining *
Biomining contributes to sustainable development in the same way all microorganism-mediated processes do: it uses existing organisms and mechanisms in nature. Traditional mining is an especially toxic process involving the use of chemicals like cyanide. Although the process of biomining does not yet completely eliminate the use of harmful chemicals, it allows for a lessened use, resulting in lower production costs of cleaning up the mining processes. 
*Bibliography*http://www.biobasics.gc.ca/english/View.asp?x=797#top</SPAN>​Biomining. Access Excellence at the National Health Museum. www.accessexcellence.org/AB/BA/biomining.html
Metals and minerals. The Biotechnology Gateway. www.strategis.gc.ca/bio
Acevedo, Fernando. "The use of reactors in biomining processes." Electronic Journal of Biotechnology, Nature Biotechnology. Vol.3 No. 3, Issue of December 15, 2000. 
Biotechnology in gold extraction. The Hindu. www.hinuonnet.com/thehindu...02/21/stories/20020221000060300.htm
Minerals and Metals Sector. NRCan Biotechnology, FAQ. www.nrcan.gc.ca/cfs/bio/faq3.shtml
Sector Overviews: Mining and Energy. CBS Online. www.strategis.ic.gc.ca/ssg/bh00175e.html 11 June 2002
Canada's Biotechnology Regulations: Who's mining the store? NRCan Biotechnology, Factsheets. www.nrcan.gc.ca/cfs/bio/fact9.shtml
Biotechnology Applications in the Mining Industry: Bioleaching. NRCan Biotechnology, Factsheets. www.nrcan.gc.ca/cfs/bio/fact2.shtml
Environment Consultation Document. CBS Online. www.strategis.gc.ca/cgi-bin/... (product contains )  5 June 2002.
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## المهندس القاضي (7 يناير 2012)

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