Occurrence and extraction of Hg from Cinnabar

Mercury is extracted from the ore cinnabar, HgS. Traditionally the ore was heated in a wood fire and the mercury was collected from the ashes. However, modern methods are much more efficient. The cinnabar is crushed and separated, and then it is heated with a stream of air. The reaction is

HgS + O2 --> (600C) Hg + SO2

If the ore is especially rich, scrap iron or quicklime can be added to promote the extraction process:

HgS + Fe --> Hg + FeS

or

4HgS + CaO --> 4Hg + 3CaS + CaSO4

The crude mercury can also be washed in nitric acid and air to remove oxides and other impurities. More purification can be achieved if the process is performed at lowered pressures.

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