Chemical Process
The Thiobacillus ferrooxidans after being adapted to the substract, they accelerate the reactions of dissolution of the sulphurs. The main advantage of the biological oxidation over other processes of oxidation, is that this process occurs at atmospheric pressure and near to the environment temperature.
In general, the reactions which occur during the biological oxidationof the pyrite and arsenopyrite are indicated as follows:
Pyrrite
- Bacterial lixiviation:
- 2 FeS2 + 7 O2 + 2 H2O – 2 FeSO4 + 2 H2SO4
- 4 FeSO4 + O2 + 2 H2SO4 – 2 Fe2 (SO4)3 + 2 H2O
- Chemical Reaction:
- FeS2 + Fe2 (SO4)3 – 3 FeSO4 + 25°
- Bacterial Lixiviation:
- 25° + 2 H2O + 3 O22 – 2 H2SO4
Arsenopyrrite
- Bacterial Lixiviation:
- 4 FeAsS + 13 O2 + 6 H2O – 4 H3AsO4 + 4 FeSO4
- Chemical Reaction:
- 2 FeAsS + Fe2 (SO4)3 - - 2 H3AsO4 + 4 FeSO4 + 2 H2SO4 + 6 O2 + 4 H2O.
The silver liberated during the bacterian lixiviation, after a stage of neutralization, will be recuperated through cyanidation.
Reactions of Precipitation
Chemical Reaction:
The use of the biological oxidation as technic of pretreatment of minerals and concentrates has some limitation for its application:
- Minerals which are high consumers of acid.
- Dissolution of silver and gold during the biological process, even though this is not a common problem.
- Poor characteristics of sedimentation or filtering in the case that it requires continuous changes of solution.
- High content of sulphur which conduces to high levels of oxidation of sulphur.
- Large volumes of mud which could be difficult to treat.
- Difficulty in the diffusion of air in the pulps which contain very fine particles.
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