Gold mining methods and more about gold

Gold mining methods and more about gold

Two well-known gold mining methods use the toxic sodium cyanide and also toxic mercury by first dissolving the gold according to:

4 Au + 8 NaCN + O2 + 2 H2O → 4 NaAu(CN)2 + 4 NaOH.
The toxic sodium cyanide has caused a major environmental disaster at the Summitville mine in Rio Grande County, Colorado in the United States.

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Especially in the past, mercury was used because gold dissolves in it (gold-mercury amalgam).

Usually gold occurs as fine grains, scattered in a rock. To be visible to the naked eye, the ratio of gold in gold ore must be more than 30 mg/kg (30 ppm). For most gold mines this means that the gold in the ore is not visible.

Origin

Gold has been present on Earth since the creation of the planet itself, but it has not been formed on Earth because its production requires fusion reactions. There are nuclear fusion reactions in the core of stars, but these nuclear fusion reactions do not provide enough energy for the production of gold.

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Stars that are heavy enough (from about 8 times the mass of the Sun) end their life in a supernova explosion. During this explosion, heavy metals, including gold, are formed through nuclear reactions. After the explosion, dust particles containing tiny bits of gold are thrown into space. When the dust particles enter the gravitational field of a star like the Sun during the formation of the planets, the dust particles become part of the aggregating matter around the star that eventually forms the planets.

Isotopes
Most stable isotopes

Iso RA (%) Half-life VV VE (MeV) VP

195Au syn 168,10 d EV 1,220 195Pt

197Au 100 stable with 118 neutrons

One stable isotope of gold is known and about 18 unstable, of which 195Au with a half-life of more than 168 days is the most stable.

Toxicology and safety
Pure gold is harmless to the human body and most gold compounds are not particularly toxic. However, liver and kidney damage, dermatitis and colitis can occur at relatively high doses of gold compounds (in the order of several tenths of a gram per week) as required for the treatment of rheumatoid arthritis, sometimes with fatal consequences. Colloidal gold can be absorbed by so-called macrophages, cells that play an important role in keeping inflammatory processes going (such as RA), after which they are killed (and the inflammation is inhibited). For this purpose, this gold is often injected into patients (because high doses are required for effect).

Furthermore, gold (as a so-called trace element) can play an important positive role in all kinds of enzymatic processes; and this can probably occur at low levels in the body. The human body (at a weight of 70 kg) contains approximately 0.2 mg of gold by nature.

Applications
Since the 20th century, gold has been practically indispensable in industry. Some applications are:

High-quality electrical switches and connectors.
In aerospace as a coating for satellites because gold reflects ultraviolet radiation well.
Because of its high density, as weight in a self-winding watch, in the higher price range.
Gold is used in many electronic components.
The radioactive isotope 195Au is used in cancer research.
Crowns in dentistry.

Although it is often replaced by other metals, in some monetary systems gold is (still) used for coins.
To cover paper money (silver is also used).
The beautiful shine and good corrosion resistance make gold a popular metal for jewellery.
Because of its lustre and scarcity, gold is a symbol of wealth. Household objects were therefore sometimes made of gold or gilded. The same was true for works of art.
Embroidery (brocade) with gold thread, actually tangent metal.
In the past, art and utensils such as clocks and candlesticks were gilded by blowing vapours of gold dissolved in mercury (amalgam) on the object, whereby the mercury evaporated and the gold was deposited in a thin layer. This is no longer permitted due to the severe toxicity of these fumes.

Approximately half of the gold is used in jewellery and only 10% is used for industrial purposes. As a pure metal, gold is virtually unusable for industrial applications because it is very soft. Instead, it is widely used in alloys because the element has excellent electrical properties and is highly corrosion resistant.

Gold as an investment
Many investors use gold as an investment and about one-third of the gold is set aside for this purpose each year. Finally, central banks buy about one-tenth of the gold on offer each year and put it in the vaults.