The Method of Extracting Copper and Gold by Bacterial Leaching

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The Method of Extracting Copper and Gold by Bacterial Leaching

The methods of extracting gold and copper have significant differences

and therefore require separate attention. Prior to leaching occurring,

either a tailings pile must be built up upon a base of impermeable

rock or a series of holes drilled into the ore, to provide access for

the bacteriaα.

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At process one the bacteria thiobacillus ferro-oxidans and

thiobacillus thio-oxidans, naturally occurring bacteria that obtain

the energy that they need to survive by oxidising Fe2+ and S2- ionsα,

are added to the copper ore. The bacteria in the acidic leaching

solution then convert the insoluble sulphide minerals into a solution

containing Cu2+, Fe2+, Fe3+ and SO42- ions. The acidic solution

provides the optimum pH for the bacteria to work at. Following the

bacterial action, the solution is drained off of the impermeable rock

or pumped out of the ground through the remaining holes and the

remaining solution prepared for concentration and extraction of the Cu2+

ions.

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Extraction and stripping then occur, here the copper ions are

selectively removed from the leaching solution by the "ligand exchange

solvent extractionγ " method. During this a good ligand (a molecule

containing one or more unshared pairs of electronsδ ) is dissolved in

an organic solvent, such as kerosene, which is immiscible with water.

This solution is mixed with ater containing Cu2+ ions and a

displacement reaction occurs.

Cu2+ (aq) + 2LH(organic) → CuL2(organic) + 2H+(aq) Equation 1γ

The copper ions are transferred from the water where they are of a

high concentr...

... middle of paper ...

... is likely to be placed and a thorough environmental

impact assessment carried out to ensure that the processes do not

cause undue environmental damageι. Finally governmental permission

must be obtained before commercial activity can take placeι.

References

α - Article 1 from examination pack: Mining with microbes, John

Merson.

β - How hydrometallurgy and the SX/EW process made copper the "green"

metal, William

Dresher.

γ - Article 2 from examination pack: Extracting copper from leaching

solutions.

δ - Columbia electronic encyclopaedia.

ε - www.allrefer.com/reference/encyclopaedia

η - Article 3 from examination pack: A golden opportunity, Jack

Barrett and Martin Hughes.

θ - www.gaiaguys.net

ζ - Wikipedia, the free online encyclopaedia.

ι - www.deh.gov.au/industry

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