Sciencemadness Discussion Board

gold separation

shadeT - 11-5-2004 at 01:40

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 ...

JustMe - 11-5-2004 at 10:22

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.

axehandle - 11-5-2004 at 15:18

Quote:

Which acid did they mean ?

Most likely nitric acid.
Quote:

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 ?

Aqua regia, a mix of nitric acid and hydrochloric acid. It dissolves not only gold, but even platinum.

separting gold from carbonate

Magpie - 11-5-2004 at 18:17

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.

shadeT - 12-5-2004 at 08:59

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 ...

JustMe - 12-5-2004 at 18:02

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.

shadeT - 12-5-2004 at 23:39

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 ?

lordnick - 18-5-2004 at 23:05

Try using hydrofluric acid. It is good at dissolving silicates, thats why you don't use high concentrations of it with glass.

froot - 19-5-2004 at 07:07

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.

The_Davster - 19-5-2004 at 14:35

Wouldent the electrolysis method yield HCN also? I dont have a redox table with cyanide in it so I cannot check.

unionised - 19-5-2004 at 15:39

Presumably, crushing it and panning it is too dull and unscientific.:)

Centimeter - 19-5-2004 at 17:14

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?

The_Davster - 19-5-2004 at 19:09

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.

Centimeter - 19-5-2004 at 20:34

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.

vulture - 20-5-2004 at 06:09

Are you sure it's gold? How did you determine that?

Fools goold, pyrite, is very unreactive too.

shadeT - 20-5-2004 at 09:43

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]

shadeT - 22-5-2004 at 09:44

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 ?

unionised - 22-5-2004 at 15:01

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.

"blick" or "wink"

Magpie - 2-6-2004 at 20:28

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.

froot - 22-6-2004 at 09:22

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?

Polverone - 22-6-2004 at 09:36

H2O2 can oxidize cyanide to cyanate, which in turn can hydrolyze to form ammonia.

jimwig - 22-6-2004 at 18:15

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.

Esplosivo - 22-6-2004 at 20:58

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]

Reverend Necroticus Rex - 22-6-2004 at 22:50

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 :D

Esplosivo - 23-6-2004 at 01:34

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. ;):)

Reverend Necroticus Rex - 23-6-2004 at 01:38

I think a complete thread on fulminates would be a good ldea, various fulminates have indeed been discussed, but I think we need a dedicated thread, what do you think?

I'm sorry I haven't read this thread before!

Tacho - 23-6-2004 at 04:03

This guy has many pages with all you want to know (and many detailed things you didnt want to know) about amateur gold extraction. This is his page about cyanide:

http://webpages.charter.net/kwilliams00/bcftp/docs/cyanide.htm

Its difficult to browse the pages because it doesnt seem to have an index. Try this:

http://webpages.charter.net/kwilliams00/bcftp/docs/

Good luck!

Polverone - 23-6-2004 at 08:21

Quote:
Originally posted by Reverend Necroticus Rex
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 :D

No, fulminates and cyanates are isomeric, but not the same.

Sciocrat - 15-7-2007 at 08:42

Which method is less dangerous - extracting the gold with mercury (having in mind the potential risk of mercury fumes when distilling), or extracting using some cyanide salt (having in mind the toxicity of cyanide compounds)?

I have access to few hundreds kilograms of gold ore, so i guess extracting with mercury would be a huge waste of time, so i think ill rather just try to find some NaCN (although, it is much harder to find NaCN than mercury here)

Does anyone know a relatively safe NaCN synthesis?

[Edited on 15-7-2007 by Sciocrat]

Nerro - 15-7-2007 at 09:04

Would a solution of NaNO<sub>3</sub> and hydrochloric acid also work? Solid nitrates are a helluva lot easier to come across then cyanides are (not to mention a helluva lot safer to work with).

In that case you could crush the rock to a powder and add the powder to the solution of NaNO<sub>3</sub> in HCl(dil/conc). I presume you can comfortably wait for a week?

Eclectic - 15-7-2007 at 09:52

A mixture of bromide and bromate salts will dissolve gold.

Sciocrat - 15-7-2007 at 12:23

Quote:
Originally posted by Nerro
Would a solution of NaNO<sub>3</sub> and hydrochloric acid also work? Solid nitrates are a helluva lot easier to come across then cyanides are (not to mention a helluva lot safer to work with).

In that case you could crush the rock to a powder and add the powder to the solution of NaNO<sub>3</sub> in HCl(dil/conc). I presume you can comfortably wait for a week?


What about HCl reacting with other compounds that form the ore, creating salts that could also dissolve in the solution and thereby affect the extraction?
Quote:
Originally posted by Eclectic
A mixture of bromide and bromate salts will dissolve gold.


Can you provide more information about this type of extraction?

Nerro - 15-7-2007 at 13:14

The acid will most probably react with the carbonates in the ore, the silicates will not really be affected by it. I believe gold ore is mostly quartz and carbonates so there will not be a lot of unexpected reactions like H<sub>2</sub>S formation etc.