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Extraction of Metals

Corrosion (rusting) of Iron and Steel - Sacrificial Protection.

Sacrificial protection is used for ships, under water pipelines
and oil rigs (for example in the North Sea).

Blocks of a more reactive metal (for example magnesium or zinc)
are attached to the ship's hull or the under water pipe.
The magnesium or zinc can also be connected
to a pipeline or oil rig by conducting cables.

Sacrificial protection is similar to a displacement reaction
with the electrons traveling from the more reactive metal to the steel
either directly or through the conducting cable.
This reverses the oxidation process.

3Zn_(s)      3Zn²⁺_(aq) +  6e^-       Zinc is oxidised as it dissolves.

2Fe³⁺_(s)   +    6e^-         2Fe_(s)       Iron ions are reduced to iron atoms.
Rusty steel is returned to iron metal.

The block of zinc or magnesium is sacrificed to keep the steel
from rusting. It must be replaced before it all dissolves. This is
less expensive than rebuilding the ship or replacing the pipe or oil rig.

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