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I'm a writer. I have a scenario in which a sizable amount of gold needs to be rendered unusable, preferably completely destroyed. I know an acid like aqua regia is able to dissolve gold, but would there be a way to make it impossible (or at least not worth the cost) to chemically salvage the gold from the acid, or another way to permanently destroy gold?

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    $\begingroup$ Remember the plot of Goldfinger? $\endgroup$ – Waylander May 31 '18 at 19:12
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    $\begingroup$ Short of nuclear reactions, you can't permanently destroy a chemical element. Then again, dissolving it and pouring the solution into the sea might be a viable alternative. $\endgroup$ – Ivan Neretin May 31 '18 at 19:19
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    $\begingroup$ @ivan neretin nobody has mentioned dissolving it in the ocean in an answer yet, you should $\endgroup$ – arp May 31 '18 at 21:15
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    $\begingroup$ Another place to ask these sort of questions is worldbuilding.stackexchange.com $\endgroup$ – Acccumulation May 31 '18 at 22:42
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    $\begingroup$ Not a chemical means, but you could pulverize the gold into dust by mechanical means and then release it from an airplane or balloon at high altitude. Good luck recovering more than a tiny fraction of it. $\endgroup$ – Michael Seifert Jun 1 '18 at 14:51
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Other than a nuclear reactor, the only other chance is to dump it into a volcano. Having a much higher density than magma, it will just fall through until it hits earth's mantle. Then it's really gone. OK, dissolved and diluted in the Atlantic is also quite safe.

P.S. Warning: If the bullion gets stuck in the volcano, which later explodes Krakatau-style, your gold brick might land in someone's front lawn. Making a hole five meters deep, but it may be salvaged easily.

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    $\begingroup$ They way of the magma in the volcanos are probably not linear, so it won't sink until the core of the Earth, but probably even this will be enough. $\endgroup$ – peterh May 31 '18 at 20:30
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    $\begingroup$ Can you please remove the line about the Earth's core because that's complete rubbish. There's a whole 2800 km of solid mantle for it to get through before it reaches the core, even aside from the fact that it would melt in many magmas, especially if it sinks a bit first. $\endgroup$ – bon May 31 '18 at 20:41
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    $\begingroup$ No the mantle really is very solid on short timescales. It has a viscosity of $\mathrm{\sim 10^{20} - 10^{21} ~Pa~s}$. Also, it won't even reach the mantle if you dump it in a volcano. It might get a hundred metres down if you're very lucky before it melts. $\endgroup$ – bon May 31 '18 at 20:59
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    $\begingroup$ "Next to the nuclear reactor, the only other chance is to dump it into a volcano. " Are there any volcanoes next to a nuclear reactor? That seems quite unsafe. $\endgroup$ – Acccumulation May 31 '18 at 22:39
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    $\begingroup$ With full understanding of the intended meaning...pretty sure some of the nuclear reactors in japan are physically quite close to volcanoes :P $\endgroup$ – Ruadhan2300 Jun 1 '18 at 12:40
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As other answers have pointed out, you can't 'destroy' gold chemically.

Putting it in a nuclear reactor for an extended period of time will functionally convert most of it to an isotope of mercury. If you really want to get rid of it, and you have lots of funding, you could launch it on a rocket into the sun (or another star, or better yet a black hole).

If you just want it to be very difficult to recover, you have lots of other options depending on the desired difficulty:

  • Dissolving it in aqua regia is a decent start, as you can then dump the result into almost any large body of water, which would make it extremely difficult to recover.

  • Dropping it into an active but not erupting volcano would be decent too, it will melt reasonably quickly (gold has a somewhat low melting point), and then diffuse throughout the magma.

  • Somewhat lower tech, but if the setting is before submarines became common, drop it in the ocean over a subduction zone. It will sink very quickly, and slowly be pulled into the mantle by the subduction zone, so if you drop it close enough, it will end up being unrecoverable by the time people can go that deep.

  • This won't really get rid of it, but gold dissolves readily in mercury at room temperature to form an amalgam. The resulting amalgum can actually be pretty easily separated by just letting the mercury evaporate, but it is a pretty neat way to get rid of the gold temporarily.

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    $\begingroup$ Thank you for the reply! I think the option of aqua regia dissolution, then dumping it into a large body of water would be a somewhat "realistic" (atleast in the realistic writing sense) solution. $\endgroup$ – Mathias L. Magnussen Jun 1 '18 at 7:29
  • $\begingroup$ I'm not sure about the black hole idea. Because of time dilation, an object sent towards a black hole will never cross the event horizon from our perspective, leaving open the possibility to catch up to it and retrieve it before it crosses over. Another issue is that the nearest black holes are at least a few thousand light years away. Presumably the OP wants the gold destroyed in a faster time scale than this. +1 for some good suggestions though. $\endgroup$ – JBentley Jun 1 '18 at 12:10
  • $\begingroup$ @JBentley Sorry for that the Community user rejected your edit suggestion, because it conflicted with my ongoing one. But I dug after in the logs and I did everything as you suggested. Tyvm! $\endgroup$ – peterh Jun 1 '18 at 12:35
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    $\begingroup$ @JBently Time dilation affects everything moving inwards though, so it's still functionally unrecoverable because the vessel recovering it will also be delayed. $\endgroup$ – Austin Hemmelgarn Jun 1 '18 at 18:54
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    $\begingroup$ "you could launch it on a rocket into the sun" Because that means killing 30km/s of Earth's orbital velocity, it's easier to instead use it to your advantage and launch it away from the Sun with only about 16 km/s. While it's possible to catch it, it's all but impossible to bring it back. $\endgroup$ – Schwern Jun 3 '18 at 17:01
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Not destroying gold, but still giving a good appearance, is this time-honored story of how two golden Nobel prizes were "hidden" from the Nazis by dissolving the gold into aqua regia. The aqua regia, of couse, had only a limited shelf life; but the soluble gold species it produced could be retained indefinitely. After the war the gold was reduced, recovered, and recast into the Nobel prizes.

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  • $\begingroup$ From the point of the view of the OP, would simply dissolving it in this fashion, and then dumping the dissolved gold into a suitable water supply suffice? Or even pouring it onto the ground to soak into the soil? Will the gold chloride remain in solution in these circumstances? $\endgroup$ – Jack Aidley Jun 1 '18 at 12:35
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    $\begingroup$ Pouring into water is better. Pouring into the ground could leave the gold concentrated enough to recover. In the actual case it was just left in the spent aqua regia solution(s), and the Nazis never caught on. $\endgroup$ – Oscar Lanzi Jun 1 '18 at 16:11
  • $\begingroup$ @OscarLanzi If you pour it into one spot on the ground, certainly. If you slowly dribbled it across a large area (say, at a drop or two a second out of a car while speeding down the highway), then it would be much harder to recover. $\endgroup$ – R.M. Jun 1 '18 at 18:15
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If you don't use any nuclear technology, you can't destroy gold.

Everything that you can do to the gold, can be undone.1

What you can do: you can make its reconstruction economically infeasible.

However, gold is

  1. Valuable
  2. Very stable (chemically) and non-reactive.

Because of these, gold can be easily extracted from practically any gold compound.

What could work: Maybe mixing it into high-reactive nuclear waste, for example into freshly depleted nuclear fuel rods, and then turning off their cooling. (Depleted fuel cells should be cooled for a while after they are removed from the reactor, to avoid them melting because their own radiation.) The result will be that they melt, and the resulting corium will mix with the gold therein.

1 As @IvanNeretin mentioned in a comment: dissolving the gold in an acid, and then pouring this into the ocean (or throwing in the toilet) would work.

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  • $\begingroup$ I was just about to recommend "keep it in a nuclear reactor until its nicely activated". $\endgroup$ – Karl May 31 '18 at 20:26
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    $\begingroup$ @Karl Wow, how much simpler :-) Note, gold has only a single stable isotope, gold-197. Gold-197 with a neutron can make either platinum-197 (due to neutron-proton reaction), which decays back to gold-197 with beta decay. Or it can make Gold-198, which decays quickly to mercury-198, which is stable. $\endgroup$ – peterh May 31 '18 at 20:37
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    $\begingroup$ OK, Pt-197 has a half-life time of 20h, so that will only make the gold unuseable for a few months. As our present hates nuclear fuel reprocessing for some reason, your idea is safer. ;-) $\endgroup$ – Karl May 31 '18 at 21:06
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    $\begingroup$ Gold can be practically extracted from most compounds when the concentration is sufficient. The key to destroying gold's practical value is to "dilute" it either chemically or physically. A nice variation (which, according to The Disappearing Spoon, has accidentally occurred in reality) is to hide gold in materials that will be used to construct something else valuable before it is discovered. $\endgroup$ – supercat Jun 1 '18 at 19:36
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    $\begingroup$ @R..: I recommend the book, but this particular story, in brief, was about a community that discovered that many of the stones that had been used as building material would, if heated, release gold. So gold which could have been easily and cheaply extracted if people knew about it before using the stones to build things ended up being built into structures. $\endgroup$ – supercat Jun 3 '18 at 8:38
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Gold is extremely difficult to get rid of, either chemically or physically.

Gold is produced when a massive star goes supernova. Every single atom of gold in the entire universe is the result of the death of a star. So, a lot of energy went into the actual creation of the gold to begin with. More energy will be needed to destroy it's very atomic structure.

Ways to get rid ot it:

  • Grind it to dust and disperse it;
  • Dissolve it in aqua regia (as mentioned in various other answers);
  • Melt it in a kiln and mix it with something else (metals or ceramics);
  • Others suggested to dump it in a volcano or something like that to make it disappear into the planet's interior
  • Reacting it to a halogen to make AuCl3, AuBr3 or AuI. Any aurohalide can of course be reduced back to it's constituent parts.
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  • $\begingroup$ Are you sure there are no gold atoms that have been artificially created? What about gold in nuclear reactors? Do you consider gold that has been converted to an unstable isotope of platinum and then decayed back to gold created by the death of a star? $\endgroup$ – CJ Dennis Jun 3 '18 at 21:51
  • $\begingroup$ The exception proves the rule ;-) $\endgroup$ – Mausy5043 Jun 5 '18 at 14:48
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Gold has one principal isotope (gold-197) and all other isotopes are unstable and decay mostly by beta emission into isotopes of mercury. Given that its cross section is 98.7, it will act as a neutron poison in reactors transmuting with a 2.7 day half life into mercury-198, which is stable. Given the cross section and short half life, gold was considered a salting agent in radiological weapons. It has been reported that the plutonium pits of US nuclear weapons are all gold-plated to prevent corrosion with the air. The only way to get lighter isotopes would be through spallation.

As you know you cannot destroy an element. Aqua regia could dissolve it but not destroy it. As a matter of fact, George de Hevesy dissolved Max von Laue and James Franck's gold Nobel Prizes medals in aqua regia during the Nazi occupation of Holland. The stupid Nazis were oblivious to the solution sitting in a flask on a shelf at the Niels Bohr Institute. After the war, de Hevesy precipitated the gold and the Nobel society minted them new medals from the comingled gold of their original medals.

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In William Gibson's novel Spook Country, a large quantity of cash is exposed to a radioactive source making it radioactive and permanently unusable. The same thing could be done to "ruin" gold, by contaminating it with a radioactive substance.

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    $\begingroup$ Gold has only a single stable isotope, ${}^{197}Au$. For neutron radiation, it can become either ${}^{197}Pt$, which decays quickly back to ${}^{197}Au$, or ${}^{198}Au$, which decays quickly to ${}^{198}Hg$, which is stable. $\endgroup$ – peterh Jun 3 '18 at 0:40
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Use something that can shot waves of protons with great dynamic to make protons and neutrons separate in gold atoms so it not gonna be gold again! (but if you can decomposite it so you can reform it in some way)

( Just like you use your hand's force to cut a cheese off)

Like an explosion of a neutron star.

Or in an imaginary scenario when you use a rocket to carry all the gold amount and let it detonate itself with a nuclear bomb so there will only be gold dust in the vacuum.

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

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I remember reading many years ago that you could transmute mercury into gold by a suitable nuclear reaction, but it was actually cheaper to transmute gold into a very pure mercury isotope using a different nuclear reaction.

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

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    $\begingroup$ It was already mentioned, with much more detail... $\endgroup$ – Mithoron Jun 1 '18 at 21:31

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