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cazzie's avatar

You mean for gold? It’s an ancient thing, I don’t think they do it anymore, but some metals are found in the ground in an amalgam with mercury and they need to be separated.

Gold mining is very bad for the environment, thought. They mined for gold in New Zealand it was very controversial because of the poisons it introduced.

Zaku's avatar

I don’t see mercury listed in the Wiki on smelting except as something to vaporize out of ore.

Ltryptophan's avatar

@zaku it dissolves gold and silver

kritiper's avatar

When gold bearing ore is crushed, it is then sent across a plate of copper that has been covered with mercury. The mercury coats the copper. At the bottom edge where the water and other rock debris leaves the mercury covered copper plate, the plate is curved back under itself. Everything in the water that is not gold leaves the plate but the gold adheres to the mercury. Then the gold collects on the bottom curved edge of the plate where it is collected. The gold/mercury mixture is then placed inside a goatskin and squeezed very tightly and the excess mercury escapes through the pores of the goatskin, leaving an amalgam of gold and mercury. When heated to a very high temperature, the mercury vaporizes and the gold is left. (Lead, which is also found with gold, will also vaporize when subjected to high heat.) Further processing removes more of any other metals, such as silver, to produce gold ingots of .9999 fine.

cazzie's avatar

@kritiper the mercury way of purifying the gold ore is outdated. They use Cyanide now. (which is still horrific) They do need to sometimes purify the gold if it is amalgamated with mercury, but they use Nitric or Sulfuric Acid for that.

(I’m still stunned what I remember from my inorganic chemistry because I hated it!)

kritiper's avatar

@cazzie What kind of cyanide?
And the cyanide is used at the mine site to subtract the gold from the ore, not (necessarily) to purify it at the smelter. (Inadequate space for the cyanide leaching process.)
Mercury could still naturally appear in small amounts in the ore, or from gold ores that were recovered from old tailings/mill sites where mercury was used.

kritiper's avatar

Both gold and mercury can be found naturally in and with calcite and pyrite.

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