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Mining for Gold and Copper using Biohydrometallurgy.

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Introduction

Mining for Gold and Copper using Biohydrometallurgy Biohydrometallurgy is an application in mining which uses biology to aid metallurgy (as the name suggests). In its natural state a metal such as copper is found combined with other elements in the mineral chalcopyrite1. A bacterium is then used to form the compound copper sulphate (CuSO4), which in turn can be treated chemically to obtain pure copper. This microbiological mining process is used only with low-grade ores and currently accounts for 10%2 of copper production worldwide. Copper can be extracted from its ores by using bacteria. This is done by, firstly the low-grade copper ore and also the tailings (left from an earlier traditional mine) are stacked up where the ground has been made impermeable. The ground is then sprayed with the acidic leaching solution (Thiobaccillus ferro oxidans and Thiobaccillus thio-oxidans 3). This solution is used because the bacteria used, thrive in acidic conditions and they also don't need any organic material on which to feed. The bacteria require Fe3+ ions, or S2- ions, oxygen and carbon dioxide. The bacterium may also need bacterial nutrients containing nitrogen and phosphorus. ...read more.

Middle

The copper can also be concentrated and separated by displacing the copper with Fe from scrap iron: Cu2+(aq) + Fe(s) -> Cu(s) + Fe2+(aq) The electrons lost by the iron are taken up by the copper. Copper is the oxidising agent (it accepts electrons), and iron is the reducing agent (it loses electrons). The left over leaching solution flows into an open pond, where T. ferro oxidans catalyses oxidation of the remaining Fe2+ ions to Fe3+ 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. Gold could also be extracted in a similar way, using bacteria. Fifteen to thirty percent4 of the world's gold reserves are trapped in refractory minerals such as chalcopyrite. Firstly the refractory sulphide concentrate (from the minerals) 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 o C. Cyanidation of the final and resulting extract led to a breakthrough, in which the gold recovered increased from 10% to 100%5. ...read more.

Conclusion

Bacterial leaching is used as a secondary process in the extraction of copper because the process is to 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. Summary This type of bacterial chemistry in order to obtain metal from its ore is a new technology but the industry is still yet to recognise it. Its main advantage is it cheap and mostly environmentally friendly compared to traditional methods. This type of process will lead us into the future. ...read more.

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