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Bacterial Leaching in the mining industry

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Bacterial Leaching in the mining industry Introduction What is bacterial leaching Bacterial leaching is the process by which micro-organisms are used to extract valuable elements from compounds. The bacteria achieve this extraction by oxidising the compounds; (this is how the bacteria obtain their energy to live) separating the compound into its separate elements. How is it applied to the mining industry In mining, bacteria such as the Thiobacillus thio-oxidans obtain the energy they need to live by oxidising S2- ions. 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 (from where the metallic elements can be extracted). An example of where widespread leaching can be found San Manuel in Arizona, a mine consisting of five holes drilled into an ore deposit, an acidic leaching solution containing bacteria is pumped down the central hole where the bacteria do their work. The resulting solution is pumped from the other holes and processed. The leaching solution is recycled. Leaching Gold Explanation Between 15% and 30% of the world's gold reserves occur as refractory minerals - microscopic particles of gold encapsulated in a mineral matrix. ...read more.


2FeAsS+ 7O2 + 4H+ + 2H2O --> 2Fe3+ +2H3AsO4 + 2HSO4- Bacterial oxidation occurs in two stages: Stage 1 Stage 2 Leaching copper Explanation Performed to heaps of waste ground ore irrigated in closed circuit with an acidic leaching solution; it contains Kerosene, T ferro-oxidans and T thio-oxidans (These bacteria thrive in an acidic environment, and require only a supply of Fe2+ ions, or S2- ions, O2 and CO2). The overall result is that the bacteria convert the insoluble sulphide minerals into a solution containing Cu2+, Fe2+ Fe3+ & and SO42- ions. The solution is then pumped to the recovery section. Because the piles sit on an impermeable base layer, it is easy to drain off the solution carrying the copper ions. Copper ions, Cu2+, can be selectively removed from bacterial leaching solutions by the process of ligand exchange solvent extraction. Other metal ions, such as Fe2+ and Fe3+ are left behind in the aqueous solution. The remaining leaching solution flows into an open pond, where T ferro-oxidans catalyses oxidation of the remaining Fe2+ ions to Fe3+ ions. This recharges the leaching solution, which is pumped back to the top of the pile for the cycle to begin again. ...read more.


Moreover, the rates of O2 and CO2 transfer occurring are limited and the leaching rates are low, so extended periods of operation are required in order to achieve the desired conversions. Why bacterial leaching is a secondary mining process for copper, but a primary extraction method for gold. In bacterial leaching for copper, the extraction process is too slow to provide enough capital per annum to be profitable. This means it is impractical for companies to use. The higher tax rates on traditional methods still do not reduce profits made by a company sufficiently to make it a less cost-effective extraction process. However, in gold mining, the increase in gold extraction by leaching is so significant, that the slower processing still outweighs income made from other methods. How is a mining process developed to industrial use? 1. Mining process is thought up by individual or workgroup 2. Tests are carried out in a lab to check how well process works in a reaction vessel 3. a medium-sized laboratory plant is built for further testing 4. A large-sized Pilot plant is built for further testing in various mines 5. ...read more.

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