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In this article we will discuss about some examples of leaching.
1. Copper Leaching:
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Copper leaching is practical, feasible and in use throughout the world for many years. In this process, the leaching solution contains sulphate and iron carries the microbial nutrients in and dissolved copper out. The copper containing solution is precipitated. About 5-6% of the world copper production is obtained via microbial leaching of chalcocite, chalcopyrite or covellite.
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Chalcopyrite is oxidised as given below:
2CuFeS2 + 8 ½ O2 + H2SO4 → 2 CuSO4 + Fe2 (S04)3 + H2O
Covellite is oxidised as below:
CuS + 2O2 → CuSO4
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2. Uranium Leaching:
This is an indirect process in which the microbes do not interact with uranium ore directly but act on iron oxidant. Ferric sulphate and sulphuric acid can be obtained by Thiobacillus ferrooxidans from the pyrite within the uranium ore.
The reaction is given below:
2FeS2 + H2O + 7.5O2 → Fe2 (SO4)3 + H2SO4
In this process, the dissolved uranium is extracted from the leach liquor with organic solvents such as tributyl phosphate and the uranium is subsequently precipitated. Another recovery process is the use of iron exchanges.
The uranium process is quite significant because of moving such a vast amounts of uranium. In the leaching process insoluble tetravalent uranium is oxidixed with hot H2SO4/Fe3+ solution to soluble hexavalent uranium sulphate.
The reaction is as below:
UO2 + Fe2 (SO4)3 → UO2SO4 + 2FeSO4
