# ammonium oxalate



## Anonymous (Mar 22, 2010)

I am trying to reduce gold (AuCl3, HAuCl4) from AR solution with ammonium oxalate, woundering anyone can tell me the chemical reactions, and the amount of the ammonium oxalate is needed?


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## leavemealone (Mar 22, 2010)

Are you reffering to Ferric amonium oxalate?
If not,then you are dealing with one of the deadliest powders around.Why wouldn't you simply use smb,copperas,sulfer dioxide gas,there are countless reducing agents available to pretty much everyone.And while oxalic acid appears to cause precipitaion,I do not know what affects,if any,the ammonia will play in that role.I fear you may be traveling down a very dangerous road for a lost cause,no offense meant.
Johnny


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## Anonymous (Mar 23, 2010)

I was following the instructions to make potassium gold cyanide chemically: to dissolve the gold in AR, reduce with ammonium oxalate, then react with potassium cyanide. I'll appreciate any suggestion of a safer approach.


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## leavemealone (Mar 23, 2010)

Im sorry but that procedure is out of my knowledge base.I would certainly advise using one of the many methods that we use here on the forum.We will be more than happy to help you learn these methods.But as I stated before I am most concerned with you using the ammonium oxalate.
I did some research and while it is highly dangerous,it is not as dangerous as I first thought.Its a lot more dangerous than SMB,but not as dangerous as 70% nitric.
If you'd like some help we can point you in the right direction.
Johnny


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## Harold_V (Mar 23, 2010)

Edyu said:


> I was following the instructions to make potassium gold cyanide chemically: to dissolve the gold in AR, reduce with ammonium osalate, then react with posassium cyanide. I'll appreciate any suggestion of a safer approach.


I made a gold plating solution simply by evaporating the gold chloride until it was quite concentrated, then dissolving it in cyanide. Amazing how the dark red/brown solution suddenly becomes almost colorless. 

I have no clue what purpose the ammonium osalate serves, but be very careful of gold solutions that are combined with ammonia. You may be looking for problems you'd rather not experience. 

It might pay to ask Lou about your process. It may be perfectly harmless. Or not.

By chance, did you mean ammonium oxalate? 

Harold


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## Anonymous (Mar 23, 2010)

Thanks to Johnny and Harold in responding to my post, I think the purpose of using ammonium oxalate is to make the precursor "fulminating gold", before reacting with potassium cyanide, to yield potassium gold cyanide crystals I want, the fulminating gold is the danger/explosive powder that you are referring to. I think gold oxide, Au2O3 and gold hydroxide Au(OH)3, can also react with potassium cyanide to form potassium gold cyanide, but am not sure how to proceed from gold chloride in the AR solution, to gold oxide or gold hydroxide, and eliminate the chlorine or chloride at the same time, all advices are appreciated.


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## Juan Manuel Arcos Frank (Mar 23, 2010)

As far as I know working with potassium/sodium cyanide in an acid media is dangerous because hydrogen cyanide could be released,safe pH is 10 at least so check your gold´s chloride pH solution before adding cyanide.We want you alive.

Best regards.

Manuel


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## Harold_V (Mar 23, 2010)

It's simple. Evaporate and replace the lost HCl with water. Don't be too concerned about the pH, assuming you have a fume hood. Avoid the step with ammonia---it is NOT necessary-and definitely not worth the risk. 

Mind you, I'm not making light of the potential hazard, but if you evaporate properly, the solution will have little free acid, and the volume of gold chloride will be exceedingly small. When it is combined with a cyanide solution, there is little reaction----the gold simply gets absorbed and changes color. If you do that work in a fume hood, any traces of hydrocyanic acid that may be released will be harmlessly discharged. 

Harold


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## rongraf (Feb 22, 2018)

I am a gold plater and made potassium gold cyanide from gold chloride once. The reason for adding the ammonium ion to precipitate the fulminating gold is so that it can be washed clean of the chloride ions. Most gold plating is done with gold (I) cyanide but the gold (III) cyanide will form easily in the presence of chloride, making plating baths under-perform. The reason I think for the oxalate ion I think is to help the gold (III) reduce to gold (I) after one dissolves the fulminating gold with potassium cyanide. The problem is if you wash the fulminating gold I would think the oxalate washes away, eliminating any benefit. So I am thinking that the Ammonium oxalate is being added after the washing. But in this case one is leaving ammonium ions in the plating solution which may not be called for in the bath formulation. 

Method: I would add dilute ammonium hydroxide to the dissolved and diluted gold chloride condensate (syrup crystal) thus precipitating the fulminating gold. Stir well and filter the fulminating gold. Do not leave unattended long enough that the fulminating gold would ever dry as it is explosive when dried. Wash fulminating gold with deionized water at the final filtration. Dissolve the precip in just enough potassium 100g/l cyanide solution to get it all to dissolve. You now have a solution of potassium gold cyanide of both gold (I) and gold (III) species. Add a reducing agent that is compatible with your plating bath, for example, potassium oxalate or sodium hypophosphite. To keep the gold from precipitating or making purple colloid keep PH 10-12 and experiment to find the right amount with a small sample first. (I used about 4g of hypo per liter, which had about 20g of PGC.) Also heating to 50-60C for 8+ hours is necessary to complete the reaction. If you want to store for long period you should condense at 30-40C to a concentrate (maybe 100g/l ) and then put in a freezer at temp -5C or 20F and harvest the crystals of pure PGC.


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## g_axelsson (Feb 22, 2018)

Thanks for the explanation rongraf.

You mention that gold cyanide bath made with Au(III) under-perform compared to Au(I) bath. Is that just in current efficiency or is there other problem with plating bath higher in Au(III)?

Göran


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