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shadeT
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gold separation
Can you explain a bit how could gold be separated from other materials like CaCO3 or some other ... ?
I was searching a bit on the net , and found that it can be separated by adding the rock ( or other material with gold in it ) in some acid . The acid
should react with everthing except gold .
Which acid did they mean ?
Other method add everything in water and steer , becose the gold is very heavy metal , it should stay on the bottom all the time when all other
supstances would cruise around in water ...
And the third tek , which i don't realy understand is - to disolve gold in something that doesn't disolve other materials ... What could
disolve gold ?
Sorry if this is a dumb topic , but i'm realy interested ...
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JustMe
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A very old technique (which is still used in 3rd world countries on a small scale) is to dissolve the gold in Mercury. It dissolves in Mercury like
salt in water.
The Mercury is distilled off and condensed to be used again. But then, Mercury itself is quite the toxic substance.
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axehandle
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| Quote: |
Which acid did they mean ?
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Most likely nitric acid.
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And the third tek , which i don't realy understand is - to disolve gold in something that doesn't disolve other materials ... What could
disolve gold ?
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Aqua regia, a mix of nitric acid and hydrochloric acid. It dissolves not only gold, but even platinum.
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Magpie
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separting gold from carbonate
I think if you just want to dissolve a carbonate and leave the gold as a sediment almost any acid would do - even acetic acid as found in vinegar.
I, too, am interested in isolating gold but from quartzite ore. A miner gave me several pounds that he said had gold at 30 oz/ton, which is a high
assay as money can be made at 1 oz/ton. I want to do a classic "fire assay" to see if I can prove him right. But (moan) I have no lab.
There is a very good book available on practical metallurgy by C. W. Ammen. It tells you how to isolate all kinds of valuable metals from recycled
junk as well as as ores.
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shadeT
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well , my cousin digged on his garten when he was building his house and he found some rocks with little particles that looked like gold ...
He gave it on analysis and they found out it is gold ... He has now two bags ( i think about 70 kg ) this ore ...
I have one of the rocks right now in my hand and im going to try something now ... Im going to put the rock in hydrochoric acid , im very interested
what will happen ...
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JustMe
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Carbonates will dissolve, but I don't think that Hydrochloric Acid will affect silicates, and definetly not the gold. I believe that the free
chlorine in Aqua Regia is what attacks gold.
Two other things it dissolves in is liquid Bromine and Potassium Cyanide solution in the presence of oxygen. But these are not refinement techniques,
only crude extraction techniques.
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shadeT
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Yeah , hydrochloric acid just reacted with a part of the stone ( carbonate ) and the SiO2 part was unreacted , so this won't work ...
Well , i plan to get some ammonium chloride to make some aqua regia t try it out ...
There is a nice synth for it here - http://www.phantomplay.com/aqua_regia.htm
.......................................
Anyway , does anyone else have some ideas how to separate it from carbonate and SiO2 rocks ?
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lordnick
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Try using hydrofluric acid. It is good at dissolving silicates, thats why you don't use high concentrations of it with glass.
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froot
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Not sure if this is an option but here they use a weak cyanide solution to dissolve the from the ore.
Try this: Crush your ore to powder if possible. If you can, get some sodium cyanide, or any soluble cyanide, make a weak solution in water, place your
ore in the solution. Using a fishtank pump, oxygenate the solution. The cyanide requires oxygen to dissolve the gold.
It's difficult to determine at what stage all the gold has been leached. Remove the ore from the solution. The gold can be extracted in a couple
of ways.
1) simple electrolysis
2) Placing pieces of charcoal in the solution to absorb the gold. Burn the charcoal leaving the gold.
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The_Davster
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Wouldent the electrolysis method yield HCN also? I dont have a redox table with cyanide in it so I cannot check.
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unionised
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Presumably, crushing it and panning it is too dull and unscientific.
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Centimeter
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I am doing gold seperation and refining from electronic scrap for my extended essay. I have the Ammen book if anybody wants some info. Aquaregia is
made by mixing 1 part concentrated HNO3 with 4.5 parts muriatic acid. The ratio is different if you use concentrated HCL. This process produces a lot
of chlorine gas and NO2 gas. The gold can the be precipitated using either SO2, NaNO2 (not NaNO3!), copperas, etc. You must make sure that all traces
of nitric acid are removed before precipitating or else the gold will just redissolve. It is suggested that you use urea, however I find that this is
not very effective. Perhaps I will use a solution of urea next time. You are going to want to use quantitative filter papers so that you can burn
them off in a melting crucible and not get any ash. You are also going to want to buy some stannous chloride to help you test the purity of the gold.
A good place to start your research is:
http://www.goldmineworld.net/Aquaregia.html
If you have any questions...ask away. When I was conducting an experiment with aqua regia, the solution boiled over and produced a lot of chlorine gas
and NO2 gas. My teacher flipped out  and she says that I might have to think of
another topic. Any ideas as to how I can prevent this from happening while mantaining efficiency with time. I was thinking that I could place the
vessel in a cool water bath as the violent reaction only occured once the solution became hot. Thoughts?
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The_Davster
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Extended essay, you are in IB arent you?
Anyway, doesent the school have any fumehoods you could use or even take it outside? I can only see your teacher having a problem with it if you do
the reaction the school lab when it is not in a hood. But then again, teachers can be slightly irrational when they dont want to be sued if someone
has an accident. Just keep it cool and in a hood and you should be fine.
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Centimeter
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That's the point...it was in a fume hood. She acted like she had never seen NO2 before; she was on the brink of hyerventilating! She was running
around saying I was going to kill them all. I guess I will just keep it cool, but it is going to take a lot longer. Bah...teachers these days. Tisk
tisk, the simple pleasures of IB.
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vulture
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Are you sure it's gold? How did you determine that?
Fools goold, pyrite, is very unreactive too.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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shadeT
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yes , im sure its gold . I gave some examples to a geological ore laboratory ...
They said , after analysis , that the ore contains some amount of gold ...
[Edited on 20-5-2004 by shadeT]
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shadeT
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Hey , i noticed that my HCl turned in a nice golden color ...
I smashed the rocks in a powder and then i added hydrochloric acid and now it changed color ...
Could this mean that it disolved the gold ? Should i evaporate the solution or what ?
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unionised
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HCl doesn't attack gold unless there is an oxidant present. It will disolve any iron containing minerals (including the sulphide), and give a
yellow colour.
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Magpie
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"blick" or "wink"
C. W. Ammen in his book "Recovery and Refining of Precious Metals", p. 287, describes a flash of light that takes place just as the
gold/silver drop solidifies during the cupelation step of a "fire assay." He says this is due to the latent heat released as the subcooled
liquid solidifies.
Have any of you ever witnessed such a phenomenon? This must occur with other materials also but without visible light emission.
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froot
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I'm trying the cyanide process to extract gold from some possible ore I collected last weekend.
A couple of sources I used are as follows;
http://elvis.engr.wisc.edu:16080/uer/uer97/author4/
http://www.waihi.co.nz/Gold/gold00.htm
apart from some others.
It says that in order for gold to be leeched from the ore, oxygen is required.
I crushed the 'ore' and added a solution of NaCN. To ensure presence of oxygen I added a little H2O2 which I theorised that would decompose
to O2 and H2O because of other impurities in the ore. Now I smell NH3 in the solution.
Could this be what has happened?
H2O2 + NaCN -> NaCO3 + NH3OH -unbalanced I know.
In which case the experiment is a flop. Maybe I'll try adding excess NaCN to ensure gold in solution. Any thoughts?
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Polverone
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H2O2 can oxidize cyanide to cyanate, which in turn can hydrolyze to form ammonia.
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jimwig
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Just for the record gold doesn't "dissolve" in Hg. It forms an amalgam. IT can be retrieved from the amalgam by distilling off the
mercury using a heavy duty retort.
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Esplosivo
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| Quote: | Originally posted by Polverone
H2O2 can oxidize cyanide to cyanate, which in turn can hydrolyze to form ammonia. |
Oooo, that is interesting. Isn't cyanates a synonym of fulminates?!
[Edited on 23-6-2004 by Esplosivo]
Theory guides, experiment decides.
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Reverend Necroticus Rex
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Yes, cyanic acid is a synonym for fulminic acid, that looks like an interesting way to mercury fulminate for the HNO3 impoverished, make or aqquire
the HgCN and add H2O2 
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Esplosivo
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Not only mercury fulminate but even other metal fulminates and maybe some organic fulminates. Well it is off topic but it is really interesting how
easily a cyanide can be converted into a cyanate. 
Theory guides, experiment decides.
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