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Extraction by Bacteria Leaching

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Extraction by Bacteria Leaching Copper and Gold can be extracted from their ores by using bacteria leaching. A long time ago, engineers investigating the possibility of reopening the Roman workings noticed a blue-green liquid running from the mountains of excavated rock. When the fluid ran across old iron implements, it left a brown film. When scraped off, the film was pure copper. In 1947, US microbiologists discovered that the transformation was in fact the work of microorganisms. Bio leaching process is studied to leach copper and zinc from low-grade ores; and zinc silicate waste, respectively by Thiobacillus. Bacteria such as Thiobacillus ferro-oxidans and Thiobacillus thio-oxidans obtain the energy they need to live by oxidising Fe2+ ions and S2- ions respectively. The S2- ions are present in insoluble minerals of copper, zinc and lead. The oxidation of the S2- ions by bacteria releases these valuable metal ions into solution. Humans can achieve the same result only by smelting ores at high temperatures, a far more polluting and energy-intensive approach. ...read more.


Secondly, the copper ions are removed using another solvent. The left over leaching solution flows into an open pond, where Thiobacillus Ferro oxidans catalyses oxidation of the remaining Fe ions to Fe ions. This process of oxidation recharges the leaching solution, which is pumped back to the top of the pile for the cycle to begin again. The copper is separated from its ore because the leaching solution containing bacteria react with the ores and a form of ionisation takes place and electrons are knocked of the ore and the copper is liberated. (Article 1 Mining with Microbes by John Merson) Gold could also be extracted in a similar way. Firstly, the refractory sulphide concentrate was treated with the thermophillic bacterium sulpholobus acidocalderius. These bacteria then catalysed the oxidation of the encapsulating sulphide minerals by dioxygen under fixed aqueous conditions at 70 degrees. Cyanidation of the final and resulting extract led to a breakthrough, in which the gold recovered increased from 10% to 100%. The advantage of using bacterial leaching rather than traditional extraction methods is that it cost much less than the traditional method. ...read more.


The industry is also concerned with the reliability of this biological process because of the length of time it occurs in. (Article 3 A Golden Opportunity by Jack Barrett and Martin Hughes) Bacterial leaching is used as a secondary process in the extraction of copper because the process is too slow and uneconomic because less money is made. Also when using the traditional method when extracting copper, more copper can be obtained from the ore. The bacterial process of extracting gold is used as a primary process (secondary process is the traditional method) because the research and technology has been developed fast. More economic because more gold is produced so more money to be made. There is also a low cost of running the plants. Also the whole process is more feasible and economically competitive with the conventional process. For a new process for bacterial leaching to become commercial the government and political powers must approve and also regulate a new process and may need to provide funding. A Political power may need to hold an enquiry into the effects of this new technology to check if it is mandatory and safe. Thus granting permission for the new technology to go ahead. ...read more.

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