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Bacterial Leaching.

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Kayleigh Innes Open Book Paper - Bacterial Leaching. Water running out of copper mines contains dissolved copper ions that have been leached from copper minerals by bacteria. Some mines make use of bacterial leaching as a means of extracting copper from low-grade ore and tailings from conventional mining. The bacteria thiobacillus ferro-oxidants and thiobacillus thio-oxidants get the energy they need to survive by oxidising Fe2+ ions and S2- ions. The S2- ions are present in insoluble copper minerals, zinc and lead. The action of the bacteria releases the metal ions into solution where they can be extracted. When this process is applied to industry, the low-grade ore, and tailings are piled up on an impermeable base layer, and sprayed with an acidic leaching solution containing thiobacillus ferro-oxidants and thiobacillus thio-oxidants. The bacteria do not need any organic materials to feed off, just Fe2+ ions, S2- ions carbon dioxide, and oxygen. ...read more.


The following reaction occurs: Cu2+(aq)+2LH(organic) = CuL2(organic)+2H+(aq) (L= Ligand.) This removes the copper ions from the water and places them in a solution where they are in higher concentration. The copper ions are removed from the solution through an 'electro-winning' process, in which an electric current is passed through the solution, and the metal collects at the negative electrode. The metal can then be removed in sheets. A similar process can be used for mining gold. Extracting gold from the ground is difficult. Up to 30% of the world's gold occurs as refractory minerals - microscopic particles of gold trapped within other minerals. Treating the refractory sulphides with the bacterium 'sulpholobus acidocalderius'. The bacteria catalyse the oxidation of the sulphide minerals encasing the gold. The extract is then cyanised, and the gold recovery can be up to 100%. ...read more.


This produces a sulphide concentrate, which is then roasted to liberate the gold. The resulting mixture is then treated with aerated sodium cyanide to extract the gold. This final process is called cyanidation. The traditional method of extracting gold used a lot of energy, and produces a lot of pollution in the form of sulphur dioxide and arsenic (III) oxide, which causes environmental damage. Roasting the gold does not always liberate all the metal, so it yields only a fraction of contained gold. Bacterial leaching yields at least 92% of the contained gold, is much cheaper, and produces no gasses. Bacterial leaching is usually used for secondary extraction of copper because the traditional methods produce the copper faster, and produce a higher yield than bacterial leaching, which is more useful for extracting the remaining copper from the tailings and low-grade ore. It is, however, more suitable for the primary extraction of gold, as it produces a much higher yield of gold than traditional methods, and causes little pollution. ...read more.

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