Bacterial anaerobic corrosion

Bacterial anaerobic corrosion is a bacterially-induced oxidation of metals.

Diagram of bacterially-induced corrosion.

In a humid environment and anoxic conditions the corrosion of metals occurs as a result of a redox reaction that generates molecular hydrogen from hydrogen ions, requiring bacteria, unlike anaerobic corrosion that occurs spontaneously.

A base metal, such as iron (Fe) goes into aqueous solution as positively charged cation, Fe2+. As the metal is oxidized under anaerobic condition by the protons of water, H+ ions are reduced to form molecular H2. This can be written in the following ways under acidic and neutral conditions respectively:

Fe + 2 H+    Fe2+ + H2
Fe + 2 H2O    Fe(OH)2 + H2

Usually, a thin film of molecular hydrogen forms on the metal. Sulfate-reducing bacteria, oxidize the molecular hydrogen to produce hydrogen sulfide ions (HS) and water:

4 H2 + SO42−    HS + 3 H2O + OH

The iron ions partly precipitate to form iron (II) sulfide. A reaction with water also occurs, producing iron hydroxide.

Fe2+ + HS    FeS + H+
3 Fe2+ + 6 H2O    3 Fe(OH)2 + 6 H+

The net equation comes to:

4 Fe + SO42− + H+ + 3 H2O    FeS + 3 Fe(OH)2 + OH

This form of corrosion by sulfate-reducing bacteria can, in this way, be far more harmful than anaerobic corrosion.

See also

References

  • Georg Fuchs (Hrsg.): Allgemeine Mikrobiologie, 8. Auflage. Thieme, Stuttgart 2006. ISBN 9783134446081.
  • Holger Brill (Hrsg.): Mikrobielle Materialzerstörung und Materialschutz - Schädigungsmechanismen und Schutzmaßnahmen. Gustav Fischer Verlag Jena, Stuttgart 1995, ISBN 3-334-60940-5.
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