# Precipitating Au from electrolytic plating fluid.



## GregerG (Jan 19, 2012)

Which would be the easiest way to drop the Au from electrolytic plating fluid, is there a chemical way?
SMB has no effect as the pH is ~8'ish.
Oxalic acid perhaps?
Doesn't matter if it gets polluted as I will be re-affining it again....

Cheers
//Greg


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## GregerG (Jan 19, 2012)

Replying to ones own post is perhaps a sign of impatience,
but it dropped as a stone just adding HCl to the solution.

But I'm still interested in other ideas and thoughts about the subject.


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## Geo (Jan 19, 2012)

lower the PH with addition of hcl then sodium metabisulfite, sodium sulfite, ferric sulfate,SO2 gas or cementing with zinc or copper just to name a few.


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## 4metals (Jan 19, 2012)

You make no mention of whether or not the plating solution was a cyanide solution or not. Adding acid to the solution because you are impatient could be a recipe for a quick trip to the morgue. 

The solution is best dropped with zinc powder which can be dried and roasted before adding HCl to dissolce away the excess zinc. The remaining gold can be refined in aqua regia.


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## GregerG (Jan 19, 2012)

4metals said:


> You make no mention of whether or not the plating solution was a cyanide solution or not. Adding acid to the solution because you are impatient could be a recipe for a quick trip to the morgue.
> 
> The solution is best dropped with zinc powder which can be dried and roasted before adding HCl to dissolce away the excess zinc. The remaining gold can be refined in aqua regia.




It was cyanide free solution, however I also have hydrogencyanide based powder solution which I was going to ask for in another topic, 
I know the cyanide is "quite harmless" untill you add acid to it, so the question is how to get rid of the cyanide?
Seems fairly simple to convert to sodium cyanide, but I haven't been in chemistry class for a long time, so I haven't dared trying to drop this yet.
Any pointers?  I've got the exakt amount of gold/per cyanide (by weight)... Do you have any suggestions?
Is there any way to neutralize the cyanide (in either form)?

//Greg


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## Geraldo (Jan 19, 2012)

GregerG said:


> It was cyanide free solution, however I also have hydrogencyanide based powder solution which I was going to ask for in another topic,
> I know the cyanide is "quite harmless" untill you add acid to it, so the question is how to get rid of the cyanide?
> Seems fairly simple to convert to sodium cyanide, but I haven't been in chemistry class for a long time, so I haven't dared trying to drop this yet.
> Any pointers?  I've got the exakt amount of gold/per cyanide (by weight)... Do you have any suggestions?
> ...



In the mining industry, cyanide in solution is dilute and is typically destroyed with oxidation. Modern operations tend to use hydrogen peroxide, since it is reliable and fast.

Failing that, add some diluted sodium hydroxide to maintain a pH above 10.5 and then slowly add sodium hypochlorite (chlorine bleach). This assumes you have a fume hood, are stirring, and can monitor the pH (at least with pH paper). You can test for the endpoint with potassium iodide, which turns blue (I think) in an excess of the bleach (e.g. after all the cyanide is converted to cyanate). With time and excess bleach, you can eventually turn all the cyanate to CO2, at which point it is finally "safe". This is commonly done in the electroplating industry. However, it doesn't work if the cyanide is part of a stable complex like ferrocyanide.

There are other oxidants and cyanide destroyers, like sodium thiosulfate.

Of course, then you have a problem in that your gold solution now contains high chlorites, thiousulfates etc.

Don't just do this stuff. Look it up, read the chemistry books, use careful lab practice...or die. Your choice, I guess.

Best Regards, Gerald


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## nickvc (Jan 20, 2012)

I know the cyanide is "quite harmless" untill you add acid to it, so the question is how to get rid of the cyanide?

Well there's a comment that needs to be pointed out as incorrect....cyanide gives you no second chances if you don't know exactly what your doing don't touch it. If treated with respect it is fairly harmless but one slip up and it's curtains not only for you but maybe your family and neighbours.
Remember this is an open forum with members whose first language is not English and younger members who maybe won't read all the data on the forum about safety or understand it.
I repeat if you aren't 100% sure you know what your doing leave cyanide well alone.......


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## GregerG (Jan 20, 2012)

nickvc said:


> I know the cyanide is "quite harmless" untill you add acid to it, so the question is how to get rid of the cyanide?
> 
> Well there's a comment that needs to be pointed out as incorrect....cyanide gives you no second chances if you don't know exactly what your doing don't touch it. If treated with respect it is fairly harmless but one slip up and it's curtains not only for you but maybe your family and neighbours.
> Remember this is an open forum with members whose first language is not English and younger members who maybe won't read all the data on the forum about safety or understand it.
> I repeat if you aren't 100% sure you know what your doing leave cyanide well alone.......




I totally agree, that's why I need to make sure first - but I can get ~15oz of pure 24K from this so I really don't feel like just leaving it for the recycling station either 
Always safety first, that's why I got this stuff locked away in a safe, awaiting my proper knowledge before dealing with the stuff


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## nickvc (Jan 20, 2012)

Now that's a sensible reply...with patience and some reading and maybe a little advice from a member with personal experience you will I'm sure safely recover your gold, it's not going anywhere so make sure your fully ready to safely recover your gold before you start. 
Always remember that no amount of gold is worth anyones life, we stress safety on the forum as no one wants to be responsible for hurting or worse you, your family, neighbours or the environment.


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## Harold_V (Jan 20, 2012)

GregerG said:


> I know the cyanide is "quite harmless" untill you add acid to it, so the question is how to get rid of the cyanide?


It might be a good idea to not suggest that cyanide is "quite harmless". It is readily absorbed through open wounds, and it takes precious little to get that one way trip to the morgue, as 4metals has alluded. Speak of cyanide, at least on this forum, with due respect, for the deadly substance it is. 

Harold


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## Harold_V (Jan 20, 2012)

GregerG said:


> Any pointers?  I've got the exakt amount of gold/per cyanide (by weight)... Do you have any suggestions?
> Is there any way to neutralize the cyanide (in either form)?


The values would be recovered first, using zinc dust (flour). I'd suggest an ounce of zinc for each ounce of gold expected, and a small excess is a good idea. I'd suggest the solution be placed in a robust plastic container, stirred vigorously, then the zinc flour introduced. Stir well after the zinc has been introduced. You should witness the cementation of gold almost instantly, assuming things are correct. Your solution should contain a small amount of free cyanide, so if you have any at your disposal, I'd suggest you add a couple ounces. 

Once you have separated the values from the solution, you can use calcium hypochlorite to kill the cyanide.

Harold


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## Lou (Jan 20, 2012)

If it's still as white powdered potassium gold cyanide, I would either dissolve it up in 10.5 pH water and plate it out onto a SS304 cathode or else zinc it out. Zinc would kill the purity, so you'd have to give it a good rinse with some hot caustic soda to dissolve the zinc. The left over cyanide solution can be destroyed electrolytically or with bleaching powder.

Seriously though, it's a plating solution. Plate it out with very high current density so that it's a rough deposit and then recover it.


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## goldsilverpro (Jan 21, 2012)

In most every cyanide-free gold plating solution used in industry, the gold is in there as sodium gold sulfite. There is also quite a bit of free sodium sulfite (maybe 30-60 g/l) added to these solutions. In most of these, especially those with a pH of about 8, all the gold can be precipitated by simply acidifying it. I used to use dilute sulfuric. I assume that a lot of SO2 is produced from the acid reacting with the sulfite already present in the solution and that's what drops the gold. However, don't ever do this unless you know *(absolutely-100%-no doubts at all)* that there is no cyanide present. I think there are some newer formulations of gold sulfite solutions that are acidic to start with. With these, the addition of more acid may, or may not, precipitate all of the gold.

Most gold plating solutions, however, contain cyanide in some form. There are basically 2 different categories of these.

Some types, mainly used in the jewelry industry and for electroforming, have (usually) a pH of 10 or higher and also contain a lot of free potassium cyanide (KCN). These are called "cyanide gold baths." The addition of any acid to these will definitely release hydrogen cyanide (HCN) gas, which can kill you quickly.

The most common types of gold baths are the so-called, hard, alloyed, "acid gold baths" used to plate fingers, pins, etc. They usually have a pH of from 4 to 6 and the gold is in there as a complex cyanide ion (a negative one, I might add). The addition of acid to these can possibly generate a small amount of HCN gas. Although you should never add acids to these, if you do, the gold will precipitate as the vivid yellow (yellow yellow, not metallic yellow) AuCN compound. AuCN (gold cyanide) is insoluble in acids. When I used to troubleshoot gold plating systems, I often saw yellow stains here and there on the tank in plating facilities that had allowed the pH to drop too low in an acid gold bath. AuCN is more difficult and is potentially dangerous to work with since it is only soluble in cyanide or ammonia (and, maybe, thiosulfate). It is best to never produce it. Also, if you lived to tell the story, you would see that AuCN would also be produced if you acidified the pH10 type, above, which contains a lot of free KCN.

The moral is to never add acids to gold plating solutions unless you know, beyond any shadow of doubt, that they contain NO cyanide, in any form. Even then, you *must* use a fume hood to prevent breathing SO2 and to be alive just in case you guessed wrong and the bath contained cyanide. I know of no simple spot test for cyanide but there might be one. I do think you can buy cyanide test papers.


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## GregerG (Feb 23, 2012)

Electrolytically plate the gold out of the solution would work - but this is still in powder form and I can't find the datasheet on the proper way to mix it, if it's just water or if I need any special additives...

Sorry for the expression that it's 'quite harmless', what I meant was - if you get this solution on the skin you can rinse it off with soap and water (so the label says), but if the solution is acidic - then it's _really_ poisonous.


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## goldsilverpro (Feb 23, 2012)

What's the brand name and number, if available? What other info on label? How much do you have? Total ounces of gold? This should be on the label.

I can probably walk you through a method.


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## GregerG (Feb 23, 2012)

I'm afraid the bottle isn't labeled except for the warning and contents label, hydrogen cyanide salt 100grams and 200grams Au.
I've had two (unopened) canisters for some years and don't remember the company or product name, it was used for plating pcb's...

I know it's something that shouldn't be handled lightly, and if it were a matter of just a few hundred bucks I would have turned it in for proper destruction instead,
but this much is just too valuable to throw away - however I don't have a deathwish which is why I've kept it untouched for so long.

Now I do have a proper fume extraction cabinet and lab equipment - and chemical handling skills - to give it a try if I can find the safest way to do it.
(it's alot of money but it's to no use if it kills you right  )

I also have a cyanide testing kit, however it's also several years old so I'm not sure if the chemicals are past their due date...


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## nickvc (Feb 24, 2012)

Personally I'm one of those that can smell cyanide, apparently there are many who can't around 30% of the population, it's got a unique aroma similar to almonds which I detest and it's been around me most of my working life.


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## junkwaffle (Oct 3, 2012)

i"m new tothis game i have about 2lbs of sludge from stripping gold from sodium cyanide i need to know what the process is to extract the gold???


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