[HN Gopher] Natural Piezoelectric Effect May Build Gold Deposits
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Natural Piezoelectric Effect May Build Gold Deposits
Author : FairDune
Score : 77 points
Date : 2024-09-03 19:27 UTC (4 days ago)
(HTM) web link (arstechnica.com)
(TXT) w3m dump (arstechnica.com)
| amelius wrote:
| So, in absence of quartz we could put large voltage sources on
| rocks and get gold out?
| kragen wrote:
| basically, yes, but the voltage required is very low (what
| needs to be large is the current), and you need to get the gold
| to dissolve.
| https://www.sciencedirect.com/science/article/abs/pii/S08926...
| is one of an enormous number of papers on the process, and ipmi
| has a careers video on youtube:
| https://www.youtube.com/watch?v=hAkWMdrLXmo. shandong xinhai
| mining equipment corporation has a bunch of youtube videos
| marketing their equipment for this purpose to gold mine owners
| itronitron wrote:
| Ocean water contains dissolved gold, although I wonder if the
| other elements in sea water would attach to the quartz or
| rock electrode first.
| kragen wrote:
| i haven't tried, but as i understand it, gold is one of the
| easiest metals to reduce; even trivalent gold is at +1.52
| volts above the she: https://en.wikipedia.org/wiki/Standard
| _electrode_potential_(..., and monovalent gold is the
| noblest of all metals at +1.83 volts. that table doesn't
| have another reduction to metallic state until platinum at
| +1.188 volts, then palladium at +0.915 volts, silver at
| +0.7996 volts, mercury at +0.7973 volts, trivalent thallium
| at +0.741 volts, etc. the commonplace metals are far away
| from this: univalent copper is at +0.52 volts, the more
| usual divalent copper at +0.337 volts, trivalent iron at
| -0.04 volts, divalent lead at -0.126 volts, tin at -0.13
| volts, nickel at -0.257 volts, cadmium at -0.4 volts,
| divalent iron at -0.44 volts, zinc at -0.7618 volts, etc.
|
| in water you can't really electrodeposit metals that are
| much more negative than zinc because at -0.8277 volts+ you
| start reducing hydrogen from the water instead of reducing
| the dissolved metal. so things like silicon (-0.909 volts
| from quartz), vanadium (-1.13 volts) and titanium (-1.37
| volts from trivalent titanium ions) are out of reach. by
| contrast, the difficulty with gold is that you can't _keep_
| it from depositing--so you can 't get it into solution in
| the first place
|
| voltages like 0.8 volts may not sound like much, but that's
| because we're used to currents that are, compared to the
| number of free electrons in the metal, unbelievably small.
| 0.8 volts is enough to rip apart a piece of metal atom by
| atom. consider a mole of zinc anodically dissolving; every
| atom loses two electrons. avogadro's number of electrons is
| about 96485 coulombs, about 26.8 amp hours. so, if your
| other electrode is the she, anodically dissolving a mole of
| zinc (65.39 grams) yields 2 * 96485 coulombs * 0.7618 volts
| = 147 kilojoules, which works out to about 2.2 megajoules
| per kilogram. that's a substantial amount of energy
|
| because of gold's extreme nobility people usually complex
| it with cyanide or thiourea in order to do things like
| electroplating. its standard electrode potential to go to
| metallic state from the dicyanide complex is only -0.6
| volts. but i don't know what form it's in in the oceans
|
| ______
|
| + these potentials are all under standard conditions: unit
| activity for every reagent, 25deg temperature, one
| atmosphere, etc. things like acidity and temperature can
| shift them a bit;
| https://en.wikipedia.org/wiki/Pourbaix_diagram is all about
| how they change with acidity, for example. but i don't
| think there exist conditions extreme enough to electrowin
| metallic vanadium or titanium
| 9dev wrote:
| That is as close to alchemy as we're probably ever gonna get
| then!
| steve1977 wrote:
| Not really I think, as this is not transforming something else
| into gold, it just kind of lumps existing gold together (if I
| understood the article correctly).
| djtango wrote:
| We have a name for that kind of alchemy - nuclear
| fission/fusion.
|
| Because gold is so inert (a noble metal) its counterintuitive
| to see it in other forms eg in solution. In that sense
| manipulating gold in other forms than its elemental form
| probably feels like alchemy in common parlance.
|
| I know aqua regia is relatively normal but I still find it
| weird to think of gold being dissolved
| lazide wrote:
| Aqua Regia is relatively normal in the sense that being
| threatened with a knife is relatively normal.
|
| If you think it is, you're probably hanging out in a pretty
| bad neighborhood. But yeah, most people won't be surprised
| it exists.
| djtango wrote:
| Well I'd argue getting threatened with a knife is
| relatively normal in London but that's off topic :)
|
| Aqua regia is not particularly exotic as compared with
| all the fancy ways you can harm yourself or react things
| in Chemistry. You can probably prepare it at home using
| stuff that might be buyable over the counter.
|
| Getting your hands on things like azides or Polonium 210
| or having access to a nuclear reactor to do ad hoc
| fission/fusion is a lot less normal on that scale.
|
| Additionally aqua regia has been known for quite a long
| time, from before we even knew about gases
|
| Fwiw I forgot what the magic cleans everything mix was
| but I want to say it was H2SO4 and cif which we'd just
| squirt around in our fume hoods
| BearOso wrote:
| Bad neighborhood like Nazi Germany? And suppose you're
| Niels Bohr? How should you hide those Nobel prize
| medals...
| adrian_b wrote:
| Gold is difficult to oxidize, but once oxidized it has some
| of the biggest ions, which stay easily in solution if no
| reducing agent is present.
|
| The ion Au(I) has about the same size as the ions of
| potassium (which are exceeded in size only by cesium,
| rubidium, thallium and radium).
|
| The ion Au(III) has a more normal size, but it is still
| relatively big, similar to the trivalent ions of the rare
| earths.
|
| The big size of the gold ions is one of the reasons why its
| combinations with small ions, like oxide and sulfide, are
| unstable, so you cannot find such minerals in nature.
|
| On the other hand, the gold ions form stable compounds with
| bigger ions, like telluride. Therefore there are many
| minerals where gold is combined with tellurium (unlike
| silver and copper, which combine with the smaller sulfur).
|
| Nevertheless, on Earth tellurium has an abundance almost as
| low as gold, even if tellurium is abundant in the Solar
| System. The reason is that tellurium is easily vaporized,
| so less of it has condensed when the Earth has formed and a
| good part from what has condensed initially has been lost
| later, when the Earth has been heated by many asteroid
| impacts during its early history.
|
| While tellurium is rare because it went up, being lost as
| vapors, gold is rare because it went down and most of it is
| dissolved in the iron core of the Earth. Because both
| tellurium and gold are very rare at the surface of the
| Earth, the chances of them meeting together in amounts
| great enough to form a mineral are very low.
|
| The result of this scarcity of tellurium on Earth is that
| most of the gold can be found as native gold and only a
| smaller fraction is found in compounds with tellurium. Had
| tellurium not been lost from Earth, the amount of native
| gold would have been very small, similarly with the much
| smaller amounts of native silver and copper that exist
| versus the amounts available in sulfide minerals.
| djtango wrote:
| Thanks for sharing this - excellent content. I've been
| out of the game for a long time now but isn't this just
| the case that Gold is too soft as an ion to mix well with
| stuff like oxides?
|
| Cs(I) should be larger than Au(I) but it seems to form a
| comparatively stable oxide Cs2O. But yes Tellurium is
| also a nice soft element so AuTl have a good affinity for
| one another.
|
| Was unaware of their chemistry, it doesn't even ring a
| bell tbh I wonder if I had ever encountered it before. I
| did enjoy studying the Post Transition Group Metals back
| in the day
| adrian_b wrote:
| Yes, as I have said, size is only one of the reasons of
| incompatibility with oxide ions.
|
| As you say, gold has a much higher electronegativity than
| cesium and rubidium, i.e. not much lower than that of
| silicon, which makes it a "soft" ion, and that reduces
| the stability of any compound with oxide or hydroxide or
| fluoride ions. On the other hand, the incompatibility
| with the "softer" sulfide is mostly caused by the size
| ratio.
| 9dev wrote:
| Obviously my comment was meant in jest, but I still think
| your typical 17th century alchemist would be quite convinced
| you've figured out Chrysopoeia if you showed them this
| process--even if it's just lumping trace amounts of gold
| together.
| lukan wrote:
| No, closer to alchemy is the actual creation of gold from other
| elements with nuclear physics.
|
| Was demonstrated quite a long time ago, but is not really
| practical to get meaningful quantities out of it.
|
| (That is why I always prefered physics over chemistry - my
| chemistry book in school started with the story of the
| alchimists and concluded that they were bound to fail as gold
| cannot be _created_.
|
| And in my physics book was just the formula to create gold)
| krisoft wrote:
| > not really practical to get meaningful quantities out of
| it.
|
| It is quite practical. You just pour a big pile of hydrogen
| out, let gravity compress it until it starts fusing.
| Initially it will only create helium but near the end of the
| pile's life you will get mountains of the other elements too.
|
| Easy breasy. It just takes time and quite a bit of space and
| hydrogen. Much harder to scale it down of course. But think
| big and aim for a star as they say.
| mr_toad wrote:
| 'Natural' fusion will only get you as far as iron.
| Supernovae may produce heavier elements, but the heaviest
| elements like gold are probably produced in neutron star
| collisions.
|
| https://en.wikipedia.org/wiki/Nucleosynthesis#History_of_nu
| c...
| adrian_b wrote:
| Supernova explosions are good enough to make gold (and
| most other heavier elements until plutonium) by neutron
| capture.
|
| Fusion, as you say, produces quantities that diminish
| very quickly for the elements beyond iron (iron 56 has
| the greatest binding energy of any nucleus and the
| binding energy decreases slowly after it), so that the
| last element that is produced in non-negligible
| quantities by fusion is likely to be germanium.
| kragen wrote:
| > _is not really practical to get meaningful quantities out
| of it._
|
| you can build the entire neutron spallation reactor out of
| materials much cheaper than gold, and you can get unlimited
| quantities; the only impracticality is that the humans are
| still really bad at building machinery
| CamperBob2 wrote:
| Well, there's the excuse I need to build a Farnsworth
| fusor, I guess.
| pfdietz wrote:
| > No, closer to alchemy is the actual creation of gold from
| other elements with nuclear physics.
|
| The place where this happens is in the liquid mercury target
| of the Spallation Neutron Source at Oak Ridge. Here, high
| energy protons shatter (spall) mercury nuclei, producing
| fragments that can include gold. An uncommon isotope of
| mercury can also be converted to gold by neutron capture.
| v3ss0n wrote:
| So , alchemists might had discovered that somehow ?
| kragen wrote:
| they did have aqua regia, and crystallizing previously
| dissolved gold from it was, as i understand it, commonplace
| yieldcrv wrote:
| This isnt a new hypothesis
|
| Several years ago I had read something similar about gold in
| underground water reservoirs forming along the walls based on ...
| essentially earthquakes
| ggm wrote:
| Fred Hoyle wrote a pop sci book in the sixties talking about how
| things worked in early earth formation with prosaic imagery of
| gold squeezing around in quartz.
| OutOfHere wrote:
| What's stopping someone from deploying this in the ocean water to
| capture gold?
|
| Quartz crystal array + electricity -> gold layers?
| gus_massa wrote:
| 1 You have to squish the quartz that cist money unless you put
| the crystalsbetween two tectonic plates.
|
| 2 The concentration of disolved gold is lower in seawater than
| in hot hydrothermal mud.
|
| 3 Perhaps with realistic values, this is very low and even in
| ideal conditions ypu need a few thousands years to get a
| visible chunk of gold.
| throwup238 wrote:
| From the abstract [1]:
|
| _> Gold nuggets occur predominantly in quartz veins, and the
| current paradigm posits that gold precipitates from dilute ( <1
| mg/kg gold), hot, water +- carbon dioxide-rich fluids owing to
| changes in temperature, pressure and/or fluid chemistry._
|
| I don't have access to the full paper but if they tested
| anywhere near those concentrations, it definitely won't apply
| to seawater. The amount of gold in oceans is estimated at 1
| gram of dissolved gold per 100 million liters of seawater. The
| hydrothermal fluids that precipitate out gold in orogenic
| deposits are closer to 100,000 kg per 100 million liters.
|
| This whole experiment is kind of nonsense. Orogenic gold
| deposits form under high pressures when tectonic plates
| collide, creating deep faults and shear zones and causign tons
| of hydrothermal fluid (at 200-450C) to penetrate those new
| cracks and dissolve the gold contained in them before carrying
| it all upwards. The chance that piezoelectricity plays much of
| an effect in those conditions is almost nil.
|
| [1] https://www.nature.com/articles/s41561-024-01514-1
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