# Reducing gold with oxalic acid



## samuel-a (Nov 2, 2012)

Just finished uploading this video:
[youtube]http://www.youtube.com/watch?v=0yOBdkxk1IE[/youtube]

Took me few weeks to produce this one. Hope you would like the narration (not me speaking). The video speaks for it self... no need to add too much.
As always... qustiones, comments and critique are more then welcomed.


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## Irons2 (Nov 2, 2012)

Very nice. There's more than one way to get the job done, it seems.


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## ericrm (Nov 2, 2012)

my only question, is what do you do with the waste that has oxalic acid in it?? do you neutralise it just like regular chloride/nitric waste or is it something different?

very nice video ,as nice as kadriver one thumbs up to both of you 8)


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## Irons2 (Nov 2, 2012)

ericrm said:


> my only question, is what do you do with the waste that has oxalic acid in it?? do you neutralise it just like regular chloride/nitric waste or is it something different?
> 
> very nice video ,as nice as kadriver one thumbs up to both of you 8)



Oxalic Acid is harmless, unless you ingest a lot of it. It's found in Spinach, Rhubarb and numerous other Plants.


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## ericrm (Nov 2, 2012)

samuel at 3:33 is your beaker at tall form 2000ml?


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## bswartzwelder (Nov 3, 2012)

If the gold you dissolved with AR had any other metals present, would they also precipitate out with the oxalic acid and sodium hydroxide?


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## samuel-a (Nov 3, 2012)

Irons2 said:


> Very nice. There's more than one way to get the job done, it seems.



Thanks Irons2.
Yes, doing this the first few times as per Hoke, i've thought that there must be a more convenient way and tried to alter the process several times. I found this way to be to must efficiant (time and labor wise) with same results.




ericrm said:


> my only question, is what do you do with the waste that has oxalic acid in it?? do you neutralise it just like regular chloride/nitric waste or is it something different?





ericrm said:


> samuel at 3:33 is your beaker at tall form 2000ml?



The majority of the oxalic/oxalate actualy decompose during the process, however if you use excess of it, some will be left in the solution.
After making sure pH is back at 0, I'm adding it to my regular acid waste buckets. (btw, if it is clean enough which usually it is, i keep it and use it as dilute HCl to wash very dirty gold from other process).
Though not Toxic, i wouldn't recommand handling oxalic acid solution without gloves. Chronic exposure to Oxalic acid (ingestion and/or skin absorption) is a known couse for kidney stones.
The flask in 3:33 is not a tall form, just seems that way... i think it is the angle of camera that make it look like that.



bswartzwelder said:


> If the gold you dissolved with AR had any other metals present, would they also precipitate out with the oxalic acid and sodium hydroxide?


Ideally no, but we know there's never 100% refining.
Oxalic excels in seperating Copper and Palladium from gold, less so for Silver (chloride). But for the last, we used dilution and smb in the first refining.
Of course, if pH goes over 1-2 some insoluble oxides/hydroxides of some base metals (if there are any) may form. 
That's why the addition of base is done very carefully and the later HCl washes are very important and should not be skipped.


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## butcher (Nov 3, 2012)

samuel-a,
Nice video.

You do make some very nice tutorials; did you have a formula to begin with, of approximate ratios, how much oxalic acid and sodium hydroxide solution to the volume of or ratio of gold in solution?


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## Lou (Nov 3, 2012)

Resublimed oxalic acid is a polishing step after sulfite or other methods.


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## kadriver (Nov 4, 2012)

bswartzwelder said:


> If the gold you dissolved with AR had any other metals present, would they also precipitate out with the oxalic acid and sodium hydroxide?



Please correct me if I am wrong, but isn't the NaOH added solely to adjust the pH (raise the pH) of the oxalic acid to optimize the oxalic acid for the gold precipitation?

Hoke pg. 172 bottom of the page says,

"sulfur dioxide tends to carry down traces of platinum group metals with the gold; oxalic acid does not. But oxalic acid does tend to carry down tin and copper; sulfur dioxide foes not."

If you dissolve the gold in aqua regia and then precip with sodium metabisulfite (nearly the same as SO2) and then dissolve the resulting gold powder in HCl/Clorox (takes a while) and precip with oxalic, you eliminate lots of impurities.

Said another way, by using two different reagents to dissolve the gold and two different precipitants, many of the impurities that usually come down with the gold get incrementally excluded.

Also, HAucl4 recommends a final boil of the gold powder from the above two steps in nitric acid to get the best quality gold. It makes good sense to me but I have never done it - any comments on this recommendation?

kadriver


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## Lou (Nov 4, 2012)

See the technique for high purity gold in Techniques section.


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## cnbarr (Nov 4, 2012)

kadriver said:


> Also, HAucl4 recommends a final boil of the gold powder from the above two steps in nitric acid to get the best quality gold. It makes good sense to me but I have never done it - any comments on this recommendation? kadriver



Hoke also recommends a final wash in nitric after precipitating with oxalic, I was bit leery to try this myself, but I tried it with the last four oxalic drops I've done with pleasing results. I thought for sure I would be redissolving gold, but every stannous test has been negative.

I usually start off by giving the powders a quick rinse with cold water to wash away any residual salts or excess oxalic, then three hot water washes, a boil in dilute nitric, then one final hot water wash. It might or might not be the best method but I've been happy with the resulting gold. 

I know it goes against the logic of the standard washing procedure, but I think it's the final polishing on almost flawless gold!

Chris
edited: to add photo


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## samuel-a (Nov 4, 2012)

Very very pretty cnbarr !!


I'll answer some qustion i have been asked privately here as i feel it might interest others as well.



> I am having a difficult time determining how much oxalic to use. As a result I think I am using too much of it.
> 
> In your experience, how much oxalic do you use per troy ounce of gold expected?



In a nut shell: (by weight) 1:1.2 Expected gold : Oxalic acid (dihydrate)
This represent about 20% excess of Oxalic acid then what actually needed to ensure complete reduction.
If you want the complete explanation and calculation, just say so.



> Next time I use oxalic I plan to add the boiling gold solution to the boiling oxalic.



Be extra careful when doing that. The reaction is very violent that way, even one drop of the gold solution could create a boil over (depends on concentration).
Also, the gold formed that way is very voluminous and spongy.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=61&t=10029&hilit=oxalic#p96828
The picture in the link is just one drop of concentrated gold solution added to oxalic solution. The final weight of this sample was only about .15g. The vial is about 2" tall and 1" wide.


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## cnbarr (Nov 4, 2012)

Thank you Sam, I really like your video, as always great job!

I use about the same ratio as you of oxalic to gold, I use ammonia though to bring up the ph. I have found that it takes about 3-4ml of 10% ammonium per gram of oxalic to raise the Ph to 5. Then I add the room temp gold solution to the boiling oxalic solution, but I've noticed that once the gold solution is added in the ph immediately drops back 0, so it is necessary to add more ammonium to bring the ph back up to get full precipitation. 

I have had a solution that was crystal clear with no color and appeared to be fully precipitated, but was still heavily laden with gold as per testing. Once I added more ammonium it flashed and dropped the rest of the gold, so for anyone new trying oxalic ph is very critical in it's success.



samuel-a said:


> Be extra careful when doing that. The reaction is very violent that way, even one drop of the gold solution could create a boil over (depends on concentration)..



Sam's right on this one, I learned the hard way! If both solutions are boiling plan on spraying gold everywhere!!! :evil:


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## bswartzwelder (Nov 4, 2012)

As always, a great video.

If I have cell phone boards and I depopulate them with my heat gun, could I then just boil them in HCl to get rid of the solder and then process in AR? If so, then process in Oxalcia and HaOH? This just seems like it might be a little easier than some of the other methods (if it will work).


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## kadriver (Nov 4, 2012)

cnbarr - that bar looks like a drop of candy - very nice!

Thanks to both you and sam for the warning about adding the gold solution to the oxalic, I will take caution.

Also sam, thanks for those numbers.

kadriver


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## ericrm (Nov 6, 2012)

samuel why do you add the hydroxide after the boiling,cant you mix everything before boiling/why?


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## samuel-a (Dec 24, 2012)

ericrm said:


> samuel why do you add the hydroxide after the boiling,cant you mix everything before boiling/why?



Can't say that i have ever tried this... maybe this could work too, but i'm not sure.

Anyway, i have completed the full tutorial and it is availble here:
Gold Reduction with Oxalic Acid – Complete Process

Let me know if you find any mistake or have any questions.


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## gold4mike (Dec 27, 2012)

Thank you Samuel.

I plan to refine all of my accumulated gold sometime in the spring since some of my buttons are more pure than others. 

This method should get me to the purity I desire for my long term savings plan.


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## lazersteve (Feb 4, 2013)

Sam,

Your video is nice, good job.

In my opinion Oxalic acid is just another way of precipitating your gold, but more of a headache. Having used Oxalic acid, I have found that I can achieve the same purities with proper sorting, cooling, dilution, filtering, SMB, and flux. I've recently come to realize that the extra time and expense of these 'alternate' precipitants is only going to serve to slow down my lab's daily throughput, with no real benefit to my bottom line or gold purity in the long run. When production time lines, waste management, and lab overhead are all factored into the equation, there is no need for me to go through the hassles of using anything except dry SMB. If my gold buyer were paying more for the extra ten thousandths in purity (if even that), I may have a different view. Even then I would first hone my current methods further before changing gears entirely. For me a little DMG and vacuum filtration solves any Palladium issues.

If your goal is academic, then you have succeeded. If you are going for the fastest route to pay the bills with high purity gold, oxalic acid is not required or desirable. I have a true appreciation for the splendor and science of all aspects of gold refining, but as I have grown into a full time refiner, I have a greater appreciation of the fundamentals of refining and the beauty of their harmony when properly applied. 



Unknown said:


> You always return to your roots.



The fundamentals are not always the most glamorous, but they will never let you down.

Great job on the video again Sam.

Steve


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## lazersteve (Feb 4, 2013)

ericrm said:


> samuel why do you add the hydroxide after the boiling,cant you mix everything before boiling/why?



I've always mixed my base with the oxalic acid prior to mixing. The results I achieved was beautiful gold foils.

Steve


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## ericrm (Feb 4, 2013)

ok thank you Steve


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## samuel-a (Feb 6, 2013)

Thanks Steve.


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