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Vlad
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[*] posted on 8-10-2006 at 07:22
HIO3


I have pure concentrated (standard ~69% I think) nitric acid and iodine crystals.

I have been wondering many times about mixing the two to make iodic acid as a powerful gold solvent. I'm not sure though how safe it would be. I'm used to dissolving gold with aqua regia and neutralizing (slowly) with ethanol (yes I know, dangerous but I prefer it to boiling down). Then extract the goldchloride out with diethyl ether and/or precipitate with sodium or potassium (bi) carbonate or hydroxide.

Assuming the gold dissolves in iodine crystals dissolved in nitric acid. What would be the best way to get the gold back out? I think I read somewhere that KIO3 can be dangerous even if in solution so I figured titrating the gold-iodide/iodate(?) solution might be dangerous.
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[*] posted on 9-10-2006 at 00:58


KIO3 is not dangerous at all. Of all halates, it is the least toxic and the least reactive one. I did quite some experiments with KIO3, even mixed it with finely divided red P. Such a mix burns nicely (like a coarse mix of KNO3 and C), but nothing really impressive. KBrO3 and KClO3 on the other hand are insanely dangerous with red P (looking bad at it may make such makes explode already).

I wonder how fast the reaction between HNO3 and I2 will be. I have serious doubts about that reaction, probably it will be very slow. I have an old german text book and it tells that HIO3 kan be made from HNO3 and I2, but it requires KClO3 as well to get the reaction going. Cl2 is released in that reaction and HIO3 is formed.




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Jdurg
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[*] posted on 9-10-2006 at 04:43


Yeah, I don't think I2 is a strong enough reducer on its own and I don't believe that HNO3 is strong enough to oxidize I2 on its own. There would definitely need to be some extra component in there in order for the reaction to occur.



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Vlad
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[*] posted on 9-10-2006 at 11:03


I may try it and add some H2O2 to see how that helps.
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[*] posted on 9-10-2006 at 21:51


This thread http://www.sciencemadness.org/talk/viewthread.php?tid=6324 was discussing recovering platinum, but the problems are similar. In that thread was a reference to a method using a bromide, H2SO4, and an oxidiser. I know that gold has be dissolved using acidicd bromide solutions and MnO2 or even air. These methods might be simplier that making HIO3.
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[*] posted on 10-10-2006 at 11:13


I've read the thread before.
The thing is that gold dissolution is not 'as it seems'.

For example. Gold won't dissolve in phosphoric acid.
Take some ore that contains gold. Put it in aqua regia. Extract the chloroauric acid from the aqua regia with diethyl ether. Evaporate and dillute with water.
Upon precipitation with sodium (or maybe I used potassium, not sure, doesn't really matter that much) hydroxide, a red precipitate of gold is obtained. I assume it is gold, and in a relatively small metallic particle size (red color typical of finely divided gold) since a professional chemist specialized in aquaous chemistry told me this method and said only gold should dissolve in the ether and not any other heavy-toxic metals. Besides I tested it by another subjective method (sublingual ingesting/taste) and it's similar in effects to a similar white precipitate made from pure gold so I assume it's not another metal.

Now add phosphoric acid to the red precipitate of gold. It dissolves again.
Precipitate it again. It precipitates as a white precipitate.
(Repeating this step seems to bring it out white again).

It didn't seem to work by simply adding phosphoric acid to chloroauric acid made from pure gold. Comes out as a brown calx if you neutralize the solution the same way as above.

I assume this is because common dissolution of gold in aqua regia does not produce fine small gold particles like pure AuCl3 but large 'clusters' of hundreds of gold atoms (still like metallic chunks) with large amounts of chlorine and water around it keeping these clusters of gold in solution.

By precipitating your gold (dissolved the above way) out of aqua regia using for example iron sulfate or SO2 gas as miners typically use, you're bound to get 'brown calx' which is typically melted to a gold pellet.
Or you can add alkaline salts really slowly to the acid soluton by titrating and get different kinds of colored gold solutions. Or add organic acids like citric acid or ascorbic acid to get 'colloidal gold' solutions.

What I want though is a simple one step process that radically dissolves gold in such a way that the particle size is quite small and the gold doesn't come out as a brown calx after adding phosphoric acid (seems to help in breaking down gold clusters once they are a certain small particle size) to the chloroauric acid and neutralizing. I believe iodine might be good for this purpose but it's slow acting.

If I'd add chlorine to a mixture where iodine is present as halogen, the chlorine would tend to attach itself to the gold and this usually produces undesired results similar to common dissolution in aqua regia.

And bromine I don't like... dangerous stuff to keep around and work with.

So the thing is, I either would have to perform a lengthy process of careful precipitating of chloroauric acid to a finely divided state (such as the one you get by adding sodiumbicarbonate) and wait a long time for the gold to settle out of soluton (and probably lose some gold that stays suspended in solution), or always use ores to extract fine gold clusters, because in a way ending up with gold dissolved in small gold clusters is what I want.


[Edited on 10-10-2006 by Vlad]
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[*] posted on 3-11-2014 at 14:36
YES, HNO3, I2 and H2SO4


http://www.sciencemadness.org/talk/viewthread.php?tid=41465
or https://www.sciencemadness.org/whisper/viewthread.php?tid=41...

i think it worked, what we want, the gold in auri-iodic acid form. i think the electrodes were unnecessary as there was gold deposit on the negative electrode, but i am not sure.

i did the weighing and calculating and found that from the .353g Au put in the reaction with a recovery of .127g Au, there is .126g that seemingly must be in solution.

if auri-iodic acid is HAuI4 the a ratio of gold:iodine 1:4 seems that .3247244099g iodine is used

there was seemingly much more than that in the flask and just estimating from what sublimed, there seems to be enough to dissolve more gold as there is no undissolved iodine, save for the sublimed.

the electrodes are seemingly pointless. if the solution can hold more gold
; then, perhaps the pulling of it from solution on the negative terminal was faster than it dissolved in the boiling mixture.

the electrode was run after the heating was removed due to a broken pump, so i am guessing that there is room for more gold and perhaps more iodine.

the technique, you mentioned using diethyl ether to extract the chlorauric may then work for the iodauric.

the red powder you mention is most likely the sodium or potassium salt of chloraurate.
as for the phosphoric acid part, i don't know yet what that may be. sounds interesting.

[Edited on 4-11-2014 by quantumcorespacealchemyst]
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