How do you get gold out of rock?

Answer 1

How to Get Gold Out of Rocks

Here are opinions and answers from FAQ Farmers:

• Crush the rock to a sand-like consistency, then heat the sand past the melting point of gold. If it's real gold it will settle to the bottom. If it's fools' gold it will turn to iron and hydrogen sulfide gas and make a big stinky smell.

• You can reduce the amount of material that needs to be heated by using a water separation system, much like the old gold panners used. Since the gold is heavier, the crushed sand will move while the heavier gold will work toward the bottom. The advantage to that is that the pyrite (fools gold) will often wash away with the sand, leaving a much smaller amount of sulphur to deal with.

The first method would be for testing if there is gold present, the second is the basis of extraction used in a crushing mill. NOTE: gold is not wetted by water, so no parts of a crushing mill are lubricated by petroleum compounds because the fine gold would float away in the oil. Usually molasses is used as a lubricant around gold machinery.

An additional method involves the above mentioned property of gold not being wetted by water. A slurry of finely crushed gold ore is fed into a tank where fine bubbles are used to rapidly stir the slurry. These bubbles will suspend fine gold which is skimmed from the froth.

Another method is to use Mercury to combine with the gold as an amalgam. This makes a lump of gold that is then heat refined and the mercury condensed for reuse. NOTE: mercury fumes are very dangerous and can lead to brain damage. This is not used much anymore mostly due to the expense of mercury and its hazards.

The most common beneficiation method used in commercial ores that consist of finely dispersed particles of gold, is the cyanide leaching process. This is where a fine slurry of gold ore is mixed with sodium cyanide, this solution has the rare ability to dissolve gold. The gold is then recovered by passing the liquid over zinc shavings and heating the zinc thus melting gold plated on the shavings. Huge piles of low grade ore are treated this way.

Since most gold mined actually comes from silver mines as a part of a solid solution series between gold and silver, nitric acid is used to remove the silver from the gold, with the silver then removed from the silver nitrate solution.

Answer 2

Aqua Regia (a mixture of concentrated nitric and hydrochloric acids) can be used to dissolve gold, which can then be precipitated out using a selective reducing agent.