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How is gold made?
Question Date: 2002-10-01
Answer 1:

Gold is made in the interior of massive stars.

When these stars end their lives, they often blow up and produce SUPERNOVA. During these giant explosions many elements that have high atomic number get made. This is where the gold (Au) comes from. Au is the way to write the symbol for gold.

It is amazing to realize that the iron (Fe) and the gold (Au) and in fact all the elements heavier than helium (He) were once within a star ! Billions of years ago when OUR star (sun) formed, the cloud of gas and dust that condensed had tiny amounts of gold (Au) and other heavy elements from previous generations of extinct stars. AMAZING BUT TRUE.

Answer 2:

Gold, in its pure form is not made - it occurs naturally in an elemental form. On a side note, the history of alchemy was largely based on the desire of people (probably kings!) to combine other (cheap and abundant) elements and compounds to make gold. Most of the "gold" products such as jewelry , etc., have a rating in karats, as you probably already know. One karat is 1/24 part (by weight) pure gold, so pure gold is 24 karats.

Many products use various gold alloys for various reasons, but most do because the alloys are cheaper (usually silver, copper, zinc, nickel, etc. are mixed in), but sometimes gold is alloyed to make it a stronger and less malleable material.

Answer 3:

Theoretically, all you need is some other stuff made of elements with atomic number smaller than gold and a source of neutrons. If you feed in the neutrons appropriately you can build up the nucleus up in mass until you get gold nuclei.

Along the way, some of the the neutrons will decay into a proton and electron and neutrino. The nucleus ejects the electron and neutrino and the atomic number steps up by one since there is now an extra proton in the nucleus. In practice, I think people have actually done this but it is not really practical; it costs a lot more to make the gold than it is worth. So where did the gold we have on Earth come from? I believe that the source of gold is stars that have gone supernova.

When the star blows up there is a lot material, free neutrons, and energy available to create the elements that have more protons than iron. These elements then spread into the intergalactic medium during the explosion and contaminate surrounding gas clouds. As these gas clouds collapse to form stars and planets (perhaps in part due to pressure waves caused by supernova explosions) the heavy elements get collected as well. Then once a planet like Earth is formed, somehow geologic forces take over and process the gold into enriched forms until we find it. Another possibility is that other elements that are formed from supernova and are radioactive and have a higher atomic number than gold decay into gold.

Answer 4:

I am assuming that you know that gold is not made but found as ore in rocks. So what you really want to know is probably how gold is mined and purified.

Let me try to answer this. First let us find out where gold is found. My geology book tells me: gold was carried toward the Earth's surface from great depths by geologic activity, often with other metals as a solid solution within molten rock. After this solid solution cooled, its gold content was spread through such a great volume of rock that large fragments were unusual. Because of its poor chemical reactivity, gold is found uncombined but it occurs in association with ores of copper , nickel, silver,etc, in quartz veins, in the gravel of stream beds, and with pyrites (iron sulfide).

Seawater contains astonishing quantities of gold, but it is too expensive to recover. How do we obtain gold? Two principal mining methods, placer and vein mining, can obtain gold. It is often a by-product of the mining of other metals. In placer mining, freely occurring gold is found in deposits of sand and gravel from which it can be easily separated by simple physical methods. The sand and gravel are suspended in moving water; the much heavier metal sinks to the bottom and is separated by hand.
Vein, or lode mining, is the most important of all gold recovery methods. The gold in the veins can be in many different forms like nuggets or sheets, or in gold compounds.

In recovering gold from vein ore, the ore is first crushed in rod or ball mills. In this process the ore is crushed to a powdery substance from which the gold can be extracted by gravity separation. The gold dust then goes into the cyanidation mill, where it is dissolved out into a solution (the technique was pioneered by MacArthur and Forrest). The gold is recovered from this solution either by the more traditional method of adding zinc dust, which has the effect of taking gold's place, allowing it to be precipitated out, or, increasingly, by the modern technique of carbon-in-pulp.

The next stage is smelting. The gold is heated in a furnace with silica, borax and soda ash which soaks up most of the impurities, forming a slag which rises to the top of the furnace while the heavier gold settles to the bottom. This gold is poured into the bars that are shipped from the mine to be refined.

The last step of the purification is by electrolysis if higher purity is needed or platinum group metal contaminants are present. The Wohlwill electrolytic process gives 99.9% purity.

MacArthur-Forrest Process.
In the MacArthur Forrest process the ore is crushed to a fine powder and circulated through tanks containing a weak solution of cyanide, which has an affinity for gold. The solution dissolves the gold and the remaining rock pulp is filtered off.
Zinc dust added to the cyanide solution to replace the gold causes the fine specks of gold to be precipitated out and the precipitate is then refined.

A recovery process in which slurry of gold ore, free carbon particles and cyanide are mixed together. The solution is passed counter current through a series of tanks containing activated carbon particles. Gold has a natural affinity for carbon and the carbon adsorbs the gold as it passes through the circuit. Loaded carbon is removed from the slurry by screening. The loaded carbon is stripped in a caustic cyanide solution under heat and pressure, prior to the recovery of the gold by electrolysis or by zinc precipitation. The carbon is treated for re-use.

Wohlwill process
The electrolytic method of gold refining was first developed by Dr. Emil Wohlwill of Norddeutsche Affinerie in Hamburg in 1874. Dr. Wohlwill's process is based on the solubility of gold, but the insolubility of silver, in an electrolyte solution of gold chloride (AuCl3) in hydrochloric acid. The impure gold is cast into anodes of about 100 ounces each, which are suspended in porcelain cells, while the cathodes are thin strips of pure gold. By passing an electric current from anode to cathode through the electrolyte solution, the anodes are gradually dissolved and the gold therein is deposited on the cathodes; any silver, which is insoluble in the electrolyte, and any platinum group metals are precipitated to the bottom of the cells. The sequence takes about two days, following which the gold-coated cathodes are removed, melted and cast into bars. The initial process can produce gold up to 999.5 fine, with further treatment bringing it up to 999.9.

I got most of my information from a Google.com search. Here is a web site with a lot of information: click here

Here to return to the search form.

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