chornedsnorkack
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Which chlorine oxidants dissolve gold?
Au is traditionally dissolved in solvents like aqua regia... which is HCl/HNO3 mixture. This and other known solvents for gold are
characterized by presence of HCl and a strong oxidant, or of Cl2.
Now HClO4 does not react with gold up to fairly high concentrations.
But there are other oxidation states between 0 and 7 that Cl has. These are strong oxidants... but not directly converted to Cl2.
HClO3 can oxidize HCl to Cl2. But in the absence of HCl, HClO3 is stable when dilute, and dismutes when
concentrated... to HClO4 and ClO2. ClO2 itself is stable in stable acid solutions. And then there are chlorites.
Does miracle mineral solution cause miraculous disappearance of gold? How does metal gold behave in ClO2-, ClO2 and
ClO3- solutions where Cl- and Cl2 are absent?
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woelen
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I would expect that at low pH gold can dissolve in chlorates (chloric acid). Chlorous acid is not stable, it decomposes to chloride and ClO2. Gold
slowly dissolves in such solutions.
At high pH, I expect gold to be stable towards chlorite and chlorate. At high pH these are not particularly good oxidizers. ClO2 is not stable at high
pH, it reacts to form a 1 : 1 stoichiometric mix of chlorite and chlorate.
Perchlorate is totally inert at neutral pH to high pH, even strong reductors like Fe(2+) and SO2/SO3(2-) are not oxidized. So, gold certainly is not
oxidized. At low pH, perchlorate also is quite inert, as long as it is ionized (that's at concentrations up to around 80% in water!). Only the
anhydrous acid is an extreme oxidizer, I do not know if that is capable of oxidizing gold.
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Rainwater
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I previously wanted to try using potassium or sodium chlorate as an oxidizer for aqua regia.
It is cheaper than nitric acid, easy to synthesis, and much safer to handle, but after researching, it is decided against it due to the risks involved
with chloric acid and perchloric acid.
"You can't do that" - challenge accepted
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khlor
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Cl2 seems simpler and cheaper than even HNO3
"NOOOOOO!!! The mixture is all WROOOOOOONG!"
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Rainwater
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3% H2O2 + HCl works great, and is my new goto for dissolving gold. It does not work very well/fast with other noble metals like platinum due to
accelerated decomposition 9f the oxidizer.
A dropping funnel with 5-10 seconds between drops seams to have the best yield based on peroxide for gold. I setup a 2L rbf with reflux and an
overflow tube, let it run all night. It will randomly foam up 1 out of 20 runs
"You can't do that" - challenge accepted
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barbs09
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Google the "Chlorox" recovery method. It involved adding hypochlorite to HCL, which of course generates Cl2, but it forms an aggressive solution for
dissolving Au. Do outside on in a fume hood!!
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chornedsnorkack
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Quote: Originally posted by woelen  | | At low pH, perchlorate also is quite inert, as long as it is ionized (that's at concentrations up to around 80% in water!). Only the anhydrous acid is
an extreme oxidizer, I do not know if that is capable of oxidizing gold. |
An inconvenient source because it is Google books, but...
The Chemistry of Chlorine, Bromine, Iodine and Astatine: Pergamon ..., Volume 7
By A. J. Downs, C. J. Adams
Page 1442, "Properties":
"Anhydrous perchloric acid is an extremely powerful oxidizing agent;..., and rapidly oxidizes gold and silver."
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pneumatician
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dissolve potassium nitrate in hcl & you get Aqua Regis :-) opppsss!
I've another method very unknown to chemscience?
ha ha ha... contact me if you have 1 milion € free of taxes ho ho ho
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DraconicAcid
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Um, nobody thinks that is something new.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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pneumatician
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nobody thinks that is something obvious???
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DraconicAcid
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Yes, we all know it's obvious.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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