Bioleaching reaction

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Giving the overall reaction:
Giving the overall reaction:
2UO<sub>2</sub> + O<sub>2</sub> + 4H<sup>+</sup> → UO<sub>2</sub><sup>2+</sup> + 2H<sub>2</sub>0
2UO<sub>2</sub> + O<sub>2</sub> + 4H<sup>+</sup> → 2UO<sub>2</sub><sup>2+</sup> + 2H<sub>2</sub>0

Revision as of 14:54, 11 September 2007

Bioleaching microbes cause mineralytic effects by:

  • The formation of organic or inorganic acids (protons)
  • Oxidation and reduction reactions
  • Excretion of complexing agents

Microorganisms are catalyzing the production of leaching reagent (often the oxidant Fe3+).

The type of sulfide mineral will affect by what mechanism the oxidation will proceed.

This difference in mechanisms explains why sulfur oxidizers are able to leach some minerals but not others.


Pyrite is the most common of the sulfide minerals. In bioleaching of pyrite there is an initial chemical leaching where Fe3+ oxidises the mineral:

FeS2 + 2Fe3+ → 3Fe2+ + 2S

The ferrous iron (Fe2+) and elemental sulphur formed is then oxidised with the aid of bacteria according to the following reactions:

4Fe2+ + O2 + 4H+ → 4Fe3+ + 2H20

3S + 3O2 + 3H20 → 3H2SO4

The overall summary reaction of pyrite oxidation is as follows:

4FeS2 + 15O2 + 2H20 → 2Fe2(SO4)3 + 2H2SO4

Pyrite + Oxygen + Water → Ferric sulfate + Sulfuric acid

UO2 + 2Fe3+ → UO22+ + 2Fe2+

Fe3+ is used as oxidant in the leaching of uranium from uraninite (UO2)

Again ferrous iron is oxidised to complete the cycle:

4Fe2+ + O2 + 4H+ → 4Fe3+ + 2H20

Giving the overall reaction:

2UO2 + O2 + 4H+ → 2UO22+ + 2H20

Cu2S + 4Fe3+ → 2Cu2++4Fe2++S

Fe3+ is used as oxidant in the leaching of copper from chalcocite (Cu2S)

Contact, non-contact and cooperative leaching

Bioleaching microbes interact with the metal containing material by direct contact or by affecting the water-solution holding the metal containing material.

  • Non-contact leaching: Free iron-oxidizers produce the leaching chemicals Fe3+ and H+.
  • Contact Leaching:
  • Cooperative leaching
Leaching mechanisms
Leaching mechanisms

See also

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