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Copper Extraction

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Introduction

Open Book Paper 2002 Copper Extraction Biohydrometallurgy is applied for copper extraction. Low-grade ore and leftovers from conventional mining methods are pilled up on a base of impermeable ground. Then the bacteria Thiobacillus ferro-oxidans and Thiobacillus thio-oxidans are sprayed onto the pile in an acidic leeching solution. The bacteria thrive in this environment and don't need any organic material to live on. All they need is a supply of Fe�+ or S�- and oxygen and carbon dioxide. The overall result is that the insoluble sulphide minerals are converted into a solution of the ions present. As the base is impermeable, the solution containing the copper ions is easily drained off and another solvent removes the copper. T. Ferro-oxidans then renew the leeching solution ready to be used again. The copper is then formed into sheets using an "electro-winning" process. This is basically electrolysis and is a costly process. ...read more.

Middle

Their diet consists of pyrite, arsenopyrite and other metal sulphides such as chalcocite and chalcopyrite. This is good for the extraction of gold as it is found in these mineral sulphides. The bacteria thrive in acidic conditions and thus the oxidation process takes place at around a pH of 0.5 - 1.5 and a temperature of any where between 30 and 55 degrees Celsius. The process however has been known to work at temperature as extreme as -22 and 55 degrees Celsius. (Ref 4) The process Using arsenopyrite (FeAsS) as the sulphide, bacterial oxidation occurs in two stages. The first is the interaction between the bacteria and the mineral sulphide. The bacteria catalyse the formation of soluble compounds of iron (II), arsenic (III) and sulphur (VI). FeAsS Fe(II) + As(III) + S(VI) The second stage has two different reactions where iron and arsenic are oxidised. There are no gasses produced, as all the products are soluble. ...read more.

Conclusion

Old techniques gave very small percentage yields of just 10% where as bacterial oxidation gives yields as high as 100%. There is no need for extreme conditions as the bacteria can work at 30 to 55 degrees Celsius and 0.5 to 1.5 pH. The bacteria are also robust and adaptable and can be used again and again reducing costs of maintaining the process. Although the set-up cost of the oxidising plants may be high, this soon repays for its self and is kinder to the environment. This is why bacterial oxidation is preferred to roasting. Summary For a new mining process to become commercialised it needs to be assessed for cost effectiveness, yield of metal, how polluting it is, the initial cost and how lucrative the process will be. Also the speed of the extraction is a major factor and it may be developed further to increase the speed. All these have to be considered and not all are industrial factors. A lot factors that go unnoticed are financial and even political. ...read more.

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