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Biohydro-metallurgy is a new field, which combines metallurgy and biotechnology.

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Introduction

Chemistry Open Book Paper Biohydro-metallurgy is a new field, which combines metallurgy and biotechnology. It is used in the extraction of metals from their ores using bacteria. The method used, referred to as bacterial leaching/ bacterial oxidation, can be used to extract copper and gold from their ores. In the extraction of copper, the bacteria Thiobacillus ferro-oxidans and Thiobacillus thio-oxidans are used. These bacteria live by obtaining energy from the oxidation of Fe2+ ions and S2- ions, as seen below: Fe2+ ? Fe3+ + e- S2- + 4H2O ? SO42- + 8H+ + 8e- (equations from Chemical Storylines) This is useful when extracting copper, as S2- ions are present in insoluble minerals of copper. When the bacteria oxidise the S2- ions, copper ions are released into the solution. They can then be extracted from the solution. When applied to copper production, a simple method is followed. The rocks to be leached (usually low grade ore and tailings) are piled up over an area with impermeable ground- in order that the solution formed may easily be drained. ...read more.

Middle

The copper ions are then extracted from the solution by an 'electro-winning' process. An electric current is passed through the solution and the copper is collected on the negative electrodes. The process can be seen in the diagram shown below (from Article 1): The bacterial leaching process has proved better than the original method of smelting the ores in many ways. Smelting 1 tonne of copper ore produces 2 tonnes of sulphur dioxide. Bacterial leaching does not form any polluting waste. This is not only beneficial to the environment, but it also means that firms will not have to pay due to restrictions on sulphur dioxide emissions. It is also a much cheaper process. Biohydro-metallurgy costs less than �70 per tonne, whereas smelting copper ore costs �130-�200 per tonne. Also, biohydro-metallurgy enables even low-grade ore and tailings to be used, and therefore cuts down on this polluting factor. It also provides a method of underground mining, without environmental damage. Unfortunately this process is extremely slow and therefore is not profitable. ...read more.

Conclusion

oxide, both of which are polluting and have unwanted economic implications. However this method produces no gases and the waste water produced can be treated to remove the impurities as precipitates and can be neutralised by crushed limestone. There is the possibility that acid rain or river water may react with the waste water and dissolve the arsenic(V). However, 'the highest concentration of arsenic in such waters does not reach the US Environmental Protection Agency limit of 2 ppm'- (Article3, Box1) and can therefore be seen as safe. The factor most in favour of the new method is the fact that the cost of running the plant is roughly only $30 per tonne of concentrate. This includes power, chemicals, maintenance and labour. Here is where a problem may arise. Only one person is needed per shift. This means that many people will lose jobs. Another advantage of the bacterial method is that other base metals are recovered during gold extraction. This alone 'is feasible and economically competitive with conventional process'- (Article3) ...read more.

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