# - Oxalic Gold Reduction



## samuel-a

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:



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

Edit: change video


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## Noxx

Nice!


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## Barren Realms 007

Now that is beautiful... 8)


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## machiavelli976

Great !
Is there a hot plate beneath the sand ?


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## Sucho

lead iodide :lol: :lol:


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## samuel-a

Sucho said:


> lead iodide :lol: :lol:



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




machiavelli976 said:


> Great !
> Is there a hot plate beneath the sand ?



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)


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## goldenchild

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?


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## samuel-a

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



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?





samuel-a said:


> Here is the reaction of oxalic acid with Chloroauric acid:
> HAuCl4 + H2C2O4 = Au + CO2 + HCl


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.


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## goldenchild

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)


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## samuel-a

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)



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)


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## samuel-a

I might as well add the picture of the dry gold powder and of it when melted.


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## HAuCl4

Beautiful photos. Did you measure the fineness Sam?. 8)


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## Noxx

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.


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## samuel-a

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


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## stihl88

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

Nice Shot too, looks to be of fine purity.


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## HAuCl4

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.



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


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## HAuCl4

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
> 
> 
> 
> 
> 
> 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.


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## dtectr

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=67&t=10432&hilit=+hypnotic#p100818


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## samuel-a

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.



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.


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## dtectr

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.
> 
> 
> 
> 
> 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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## NoIdea

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.
> 
> 
> 
> 
> 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...



Without going into the maths, this would depend on how much of each you add and their end solubilities within your mix. Equillibrium is the solutions goal. I would say a mixture of both, how much each, pass. Someone with a better understanding of solubility products should be able to crunch some numbers for you. Just need the concentration of each of your reactants.

Deano

Hope this helps


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## NoIdea

Assuming everything you add reacts would help.


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## Lou

That gold is probably over 4N, easily.


Oxalic acid produces the highest quality gold of any precipitant. 

Sulfur dioxide (thus sulfite, SMB, dithionite*, etc) drag down both copper and palladium. Copper (I) chloride is an especially common contaminant if the pH rises overmuch. Pd tends to hitch a ride.
It is considerably quicker than oxalic acid, but the quality of gold obtained is not as good. In any case, both are quantitative. Oxalic acid isn't expensive, it's something like $1.25/lb. SO2 is about $0.65/lb. 

For what it's worth, it's quicker to dropwise add the gold solution to the hot, well-stirred almost saturated ammonium oxalate solution (make it strong so it buffers at 6.5, as indicator one may use bromocresol green and let it drip until blue-green goes to yellow at which point, add more ammonia). You must rinse more on the other end though.


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## NoIdea

That's good to know lou, it's funny how things play in your mind, i was thinking about those eqa's this afternoon, and if the NH4Cl was around it would drop palladium, would it not? Retorical question.

Deano


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## samuel-a

thanks for the input.

Thing is, Oxalic is very soluble in water, that we know, i was able to dissolve 80g in 100ml hot water.
Upon addition of NaOH, lots of sodium oxalate dropped. I seperated the oxalate powder from that solution, and got gold to precipitate with the addition of either one of them (aq & solid).

I think i do not fully understand the dynamics yet... will it be more practical to produce sodium/ammonium oxalate and adding it dry (like with SMB) to gold bearing solution with no pH adjustments...?


On other occasion (in the link at the starting post), i added the gold solution to a very dilute and hot oxalic solution where no sodium oxalate had precipitated from. The guys talked about how it looks like a Moral mushroom... thing is, that was only a few drop of gold solution that ware added, it was about an inch big lump and when melted down it weight 0.1g.




NoIdea said:


> That's good to know lou, it's funny how things play in your mind, i was thinking about those eqa's this afternoon, and if the NH4Cl was around it would drop palladium, would it not? Retorical question.



Hi Deano
NH4Cl will not drop Pt at this low presence and dilution (assuming it's a second refining), let alone Pd that needs to be further oxidized with Cl to precipitate.


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## HAuCl4

Hi Sam:

re.
Wash gold powder: 3x water, 3x HCL, 3x D. water.
Dry gold powder
Melt

This is one case where one boil in concentrated nitric acid for 15 minutes would do better improving purity than 3 HCL washes. IMO.


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## samuel-a

HAuCl4 said:


> This is one case where one boil in concentrated nitric acid for 15 minutes would do better improving purity than 3 HCL washes. IMO.



Sure HAuCl4. That's a decent suggestion. 8) 

One would of course, needs to make sure no more chlorides are left before adding the nitric.


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## macfixer01

Very nice. That was neat to watch and reminds me of high school days. There was a local head shop called The Mouse House and besides posters, bongs, and rolling papers, one thing they sold was basically just large pill capsules that contained food coloring and aluminum bronzing powder. You'd dissolve the capsule in a Mason jar filled with water then shake up the jar to cause the aluminum to flow within the colored water. It looked just like in the video.

macfixer01


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## Noxx

Lou said:


> That gold is probably over 4N, easily.
> 
> Oxalic acid produces the highest quality gold of any precipitant.
> 
> Sulfur dioxide (thus sulfite, SMB, dithionite*, etc) drag down both copper and palladium. Copper (I) chloride is an especially common contaminant if the pH rises overmuch. Pd tends to hitch a ride.
> It is considerably quicker than oxalic acid, but the quality of gold obtained is not as good. In any case, both are quantitative.




Thank you for the input.


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## samuel-a

Noxx said:


> Lou said:
> 
> 
> 
> That gold is probably over 4N, easily.
> 
> Oxalic acid produces the highest quality gold of any precipitant.
> 
> Sulfur dioxide (thus sulfite, SMB, dithionite*, etc) drag down both copper and palladium. Copper (I) chloride is an especially common contaminant if the pH rises overmuch. Pd tends to hitch a ride.
> It is considerably quicker than oxalic acid, but the quality of gold obtained is not as good. In any case, both are quantitative.
> 
> 
> 
> 
> 
> Thank you for the input.
Click to expand...


Yes, i just like to point out how right lou is...

The batch was actually devided in two, one half was precipitated with Oxalic and the other, again with SMB.
Both ware later washed 3x water 3x HCl (1x boiling) 3x d.water.
The melt clearly showed the difference, where SMB drop showed some thin film of oxides upon removal of the flame, the gold the ware precipitated with the Oxalic showed absolutely no crusting of oxides film at the surface.

Either way, the gold is good enough for my buyer and his jewelry casting operation, so i don't know how much will i incorporate the use of Oxalic in my re-refining as it doesn't come cheap for me at the moment.


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## Lou

Sam,

You can always leave an excess of ammonium oxalate on the bottom of the reduction container, as more of it is chewed up to CO2, more will go into solution to maintain the concentration. 


Lou


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## Noxx

Hey Lou,

Why are you using Ammonium Oxalate ? Wouldn't Potassium Oxalate or Oxalic Acid be a lot more soluble ?

Or is it because of the cost ?


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## nickvc

Sam
If your gold is going to be alloyed for jewellery so long as the contaminants in your fine gold are either silver or copper it shouldn't matter as both are usually used to make up the alloys anyway.
Check with your customer as to what his alloys are it might save you time and money and not be a problem for your customer so long as he knows the actual assay of your gold.


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## samuel-a

Hi nickvc 

my buyer don't know the exact assay, as well as i.

he recognize fine gold by the wey it melts. I reckon after 30 somthing years on the job, he knows what to look for... anyway, he is OK even with 999.
So, usually i sell him gold that wes inquarted and refined once. 

The last time i was able to xrf, i tested a once refined gold, it came up at above 999 but they wouldn't tell me exactly (for some unknown reason. The test was done for free so i couldn't complain though).


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## alvaschein

dtectr said:


> http://goldrefiningforum.com/phpBB3/viewtopic.php?f=67&t=10432&hilit=+hypnotic#p100818



It remembers me someting like the sci-fi film "Solaris" from Stanislav Lem (surface of the planet).
Very interesting behaviour of the solution (convection current).

Roy


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