- Oxalic Gold Reduction

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samuel-a

samuel-a

Well-known member
Joined
Oct 7, 2009
Messages
2,190
Thought i should follow up on this thread

Here's a short video i made of reduction with oxalic acid, it is very pretty.
Later i'll take better picturs... this is from my phone cam:
20072011506.jpg

[youtube]http://www.youtube.com/watch?v=aeC7LT4mDm8[/youtube]

Edit: change video
 
Sucho said:
lead iodide :lol: :lol:
Click to expand...

This reaction is by far more impressive... man... it was almost hypnotic. :shock:


machiavelli976 said:
Great !
Is there a hot plate beneath the sand ?
Click to expand...

Yes sir, otherwise it won't precipitate.

Here's a better close up:
(and again, the picture does absolutely no justice with the gold powder and it's crystallization. Yes, i said crystallization, Dendrite shapes)
 

Attachments

  • ArOxalic.JPG
    ArOxalic.JPG
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Beautiful! Reminds me of a tiger's eye gemstone. Samuel. What is the procedure when using oxalic acid? Is it as straight forward as adding the needed amount and then heating? I think I remember reading somewhere that the solution will stay orange/yellow so I assume you have to test with stannous occasionally? Also, what is the smell like compared to the dreaded SMB stench?
 
Hi Mario

I attached the procedure as i described it in the link above:
samuel-a said:
step wise for Oxalic acid:
  • Oxalic acid (dehydrate) used at 1:1 weight ratio for the expected gold from solution.
    (I use a slight excess Oxalic)
  • Dissolve in D. water, water level should not exceed one 1/3 height of the beaker.
  • Raise pH with ammonia solution/NaOH to about 6.
  • Heat both gold solution and Oxalic solution to near boil.
  • SLOWLY add gold solution to oxalic solution, by slow i mean a few drop at a time with a glass pipette. The more concentrated your gold solution is the more vigorous the reaction is. (cover the oxalic beaker almost completely with a watch glass while adding the gold to contain splattering)
  • When done adding the gold, give it a good stir with glass rod and keep the reaction beaker 10 more minutes on the hotplate at near boil.
  • Remove beaker from heat and allow it to settle over night.
  • the following day, Solution should be clear and colorless (assuming it is a second refining), test with SnCl. If negative, filter the solution and discard, if slightly positive, decant the solution to another beaker, add some SMB and let is sit for few more hours or over night.
  • Wash gold powder: 3x water, 3x HCL, 3x D. water.
  • Dry gold powder
  • Melt
Click to expand...

The only differnce in this latest batch is that the pH was more loosely controlled.
And the Oxalic solution was added to the gold (i found it to be less violent reaction).

goldenchild said:
Also, what is the smell like compared to the dreaded SMB stench?
Click to expand...
samuel-a said:
Here is the reaction of oxalic acid with Chloroauric acid:
HAuCl4 + H2C2O4 = Au + CO2 + HCl
Click to expand...
Balanced:
2 HAuCl4 + 3 H2C2O4 = 2 Au + 6 CO2 + 8 HCl

In essence, you're looking at CO2 gas and HCl fumes (from heating).
If it is a re-refining job you would expect nothing less then a colorless solution when you are done, if dirty, then expect the respective color of your contaminate chloride.

Oxalic procedure
Pro:
- exelent purity.
- easy to handle end product.
- its cool to look at.

con:
- expensive.
- time consuming and labor intensive.
- voluminous waste solution.
 
I see. So it's a little more involved. I honestly don't see any advantages in using this method over SMB but it's cool to experiment. Again. Nice work 8)
 
goldenchild said:
I see. So it's a little more involved. I honestly don't see any advantages in using this method over SMB but it's cool to experiment. Again. Nice work 8)
Click to expand...

Thanks.
You probably are correct. I reckon you should save this procedure for occasions where PGM's are reported in your gold (such as dental gold or white gold)
 
I might as well add the picture of the dry gold powder and of it when melted.

finepowder.jpg

fineshots.jpg
 
I like it, very pretty.

One question though; why did you use Oxalic Acid ? Is it because you didn't have SMB ? Because IIRC, Oxalic will tend to drag down copper with gold, unless it was removed before.
 
Hi, no i don't have access to xrf at the moment. I can only guesstimate it at 99.95 or above...

I decided to go with oxalic this time mainly from interest and not necessity... Since it was a re-refining job, base metals presence was at minimum, and when melted, no crust or film was present.

spelling
 
Sure looks interesting Sam, it looks like the surface of a bowling ball.

Nice Shot too, looks to be of fine purity.
 
samuel-a said:
Hi, no i don't have acsess to xrf at the moment. Ican only guesstimate it at 99.95 or above...

I decided to go with oxalic this time mainly from interest and not necessety... Since it was a re-refining job, base metals presence was at minimum, and when melted, no crust or film was present.
Click to expand...

One can manufacture oxalic quite cheaply, at home, with nitric acid, sugar, and a catalyst (vanadium pentoxide). Look it up in google or wikipedia.
 
samuel-a said:
Hi Mario

I attached the procedure as i described it in the link above:
samuel-a said:
step wise for Oxalic acid:
  • Oxalic acid (dehydrate) used at 1:1 weight ratio for the expected gold from solution.
    (I use a slight excess Oxalic)
  • Dissolve in D. water, water level should not exceed one 1/3 height of the beaker.
  • Raise pH with ammonia solution/NaOH to about 6.
  • Heat both gold solution and Oxalic solution to near boil.
  • SLOWLY add gold solution to oxalic solution, by slow i mean a few drop at a time with a glass pipette. The more concentrated your gold solution is the more vigorous the reaction is. (cover the oxalic beaker almost completely with a watch glass while adding the gold to contain splattering)
  • When done adding the gold, give it a good stir with glass rod and keep the reaction beaker 10 more minutes on the hotplate at near boil.
  • Remove beaker from heat and allow it to settle over night.
  • the following day, Solution should be clear and colorless (assuming it is a second refining), test with SnCl. If negative, filter the solution and discard, if slightly positive, decant the solution to another beaker, add some SMB and let is sit for few more hours or over night.
  • Wash gold powder: 3x water, 3x HCL, 3x D. water.
  • Dry gold powder
  • Melt
Click to expand...

The only differnce in this latest batch is that the pH was more loosely controlled.
And the Oxalic solution was added to the gold (i found it to be less violent reaction).

goldenchild said:
Also, what is the smell like compared to the dreaded SMB stench?
Click to expand...
samuel-a said:
Here is the reaction of oxalic acid with Chloroauric acid:
HAuCl4 + H2C2O4 = Au + CO2 + HCl
Click to expand...
Balanced:
2 HAuCl4 + 3 H2C2O4 = 2 Au + 6 CO2 + 8 HCl

In essence, you're looking at CO2 gas and HCl fumes (from heating).
If it is a re-refining job you would expect nothing less then a colorless solution when you are done, if dirty, then expect the respective color of your contaminate chloride.

Oxalic procedure
Pro:
- exelent purity.
- easy to handle end product.
- its cool to look at.

con:
- expensive.
- time consuming and labor intensive.
- voluminous waste solution.
Click to expand...

Not sure what the reaction is exactly, but it isn't that one. The reaction is with ammonium oxalate which is what you get by raising pH to 6 with ammonia. fwiw.
 
Thanks for the oxalate tip, HAuCl4.

HAuCl4 said:
Not sure what the reaction is exactly, but it isn't that one. The reaction is with ammonium oxalate which is what you get by raising pH to 6 with ammonia. fwiw.
Click to expand...

Now i'm not sure either.
I'm just playing around now with these equations... maybe a chemist could advise?

HAuCl4 + Na2C2O4 = Au + CO2 + HCl + NaCl
HAuCl4 + C2H8N2O4 = Au + CO2 + HCl + NH4Cl

Nice dtectr, i haven't seen this video... i guess the keyword here is "hypnotic" :mrgreen:
It really is....
And you got this effect using SMB? Cool.
 
samuel-a said:
Thanks for the oxalate tip, HAuCl4.

HAuCl4 said:
Not sure what the reaction is exactly, but it isn't that one. The reaction is with ammonium oxalate which is what you get by raising pH to 6 with ammonia. fwiw.
Click to expand...

Now i'm not sure either.
I'm just playing around now with these equations... maybe a chemist could advise?

HAuCl4 + Na2C2O4 = Au + CO2 + HCl + NaCl
HAuCl4 + C2H8N2O4 = Au + CO2 + HCl + NH4Cl

Nice dtectr, i haven't seen this video... i guess the keyword here is "hypnotic" :mrgreen:
It really is....
And you got this effect using SMB? Cool.
Click to expand...
I understand completely - I thought for a more descriptive word for several minutes - there just isn't one! You can see it was winter - After precipitation had begun, I would add a couple of handfuls of clean snow to settle - don't remember if I did this time or not.

I still don't understand whats happening here, but its, well ... Cool! 8)
 

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