Bacterial anaerobic corrosion

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

File:Bacterial Anaerobic Corrosion (dumb version).jpg
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 from 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


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