Gold plating compound

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toober

Member
Joined
May 10, 2010
Messages
9
I have a bit of Potassium Gold Cyanide plating compound (the white powder), still in the original jar from the supplier. I understand that the compound is worth quite a bit more than just the 68-odd percent gold value - but where can I sell this stuff for what it is, rather than just turn it back into gold?

--
Will (a noob)
 
The premium for PGC was only a few dollars an ounce, like $7, the last time I priced it. That was a while ago but if someone is offering you the 68% (actually 68.4% if I remember correctly) take it.

You will run into problems shipping potassium cyanide without the proper permitting. So shipping is out. Are you talking about a sealed bottle or a bottle that has been opened? If it is opened, the doubt about its contents is real. The bottles usually have a seal that indicates it has been tampered with.

We can post a method for removing the gold from a PGC salt but it involves more cyanide and then you have and the waste you will have is an issue.

So the first question, how much is a bit?
 
If the value difference is so little, then I might as well sell it for the gold content.

The jar (one pound) is unsealed, so yes, I realize that anything is possible inside. I tend to think it is the real deal, as I obtained it from an old semiconductor physicist who used it in his experiments. Next time I am near it, maybe I will weigh it and get an accurate number.

While I could go through the motions of getting the gold out myself (I have access to a real chem lab and a friend that is a chemist, and I realize the nasty nature of the process), I would rather just sell it as is at some point.

--
Will
 
Knowing how most buyers would handle this if it were mine, I would be much more confident selling fine gold and getting 98 - 99% of its value than being told some line about it being open and they can't be sure and they have no way of knowing without refining it (an XRF won't work). If it is the real deal and a pound (14.583 troy ounces) it is just shy of 10 ounces or over $11,000.

If you have access to a lab and a chemist it's a no brainer. It is almost guaranteed you will get beat selling this stuff. I'd rather find out for myself that it is not what I thought than spend time second guessing the guy I sent it to.

In a real lab, with exhaust and ability to handle the waste, it's an easy process.
 
4metals said:
We can post a method for removing the gold from a PGC salt but it involves more cyanide and then you have and the waste you will have is an issue.

I assume the process is the one involving fine zinc powder, as explained in http://www.finishing.com/535/11.shtml? How does this compare to the method you know?

Since I am in no hurry, what would be the implication if the extra little bit of potassium cyanide was not added (step 3)? I really do not care if the solution has to sit under the hood all day in order for all the gold to come out.

--
Will
 
Truth be told, any PGC salts I ever did that are opened NEVER EVER ran close to assay, hell some weren't even consistent out of the same bottle. Don't know why. I think some of it was pre-mixed with KCN and or K2CO3 or something but it always ran way less than theory would have you believe. I'm not even sure if it's hygroscopic or not.

Anyway,

If you have access to a lab and a real chemist this should be doable, if not a little dangerous.
A couple options, all done in a fume hood.
Least dangerous, most waste (gallons):
zinc cementation
More dangerous, but less waste:
electrolytic recovery by plating
Most dangerous, but virtually no hazardous waste:
chemical destruction via wet ashing and combustion of HCN (don't just vent it, that's not cool at all)

generally speaking, if he has to ask how to do it, don't let him do it.
 
If Chris Owen posted that method it is as good as it gets! What I would have given you is essentially the same.

In case you didn't know, Chris is Goldsilverpro on this forum. He has been working with the chemistry of refining and electroplating for his entire professional career. You can't get better advice.
 
OK, thanks for the good word about the zinc process.

I am a bit concerned about keeping waste to a minimum, as I have no idea how much of a hassle it will be disposing the stuff at the university lab. I figure less waste means less paperwork. I will consider the electrolytic method - do you have a good, clear method for that?

Yes, I have a chemist friend that said she would help, but I am going to be the one doing the work!

--
Will
 
To recover the salts electrolytically you will need a DC power supply (rectifier) an insoluble anode (stainless or titanium) and a cathode to plate your gold on to. Ideally a gold foil would be used as a cathode but likely you will not have that available. So a copper or brass cathode which will dissolve in aqua regia so you can refine the electroplated gold by dissolving the cathode after all of the gold is plated out to attain pure (>99%) gold.

The problem is then you will still have waste from the cyanide electrolyte and you will have acid waste from the acid process. The benefit is you can set up a 1 gallon cell and keep adding gold salts as the gold plates out. This will reduce the cyanide waste to about 1 gallon plus rinses. The 10 ounces of gold will require about 1.5 liters of acid to dissolve so your acid waste will be about half of 1 gallon.

For simplicity, I would use the zinc method and dissolve the salts at about 2 ounces per gallon to generate 5 gallons of cyanide solution which, after dropping the gold, can be slowly in the hood evaporated to a crust in a metal tray on a hot plate which is then roasted in a kiln to >1000 F to destroy the cyanide.

Lets see what others suggest, maybe Chris will see this.
 
My advice is take a 10 gram sample and trying zincing it, add 7 grams of zinc dust, if it is GPC you should get 6.8 grams of gold plus the un dissolved zinc when dried. If you don't get a nice dark brown sludge with a little grey from the zinc it's junk that you still have to dispose of safely!
No point in having loads of KCN in solution if it has no value.
 
My advice is take a 10 gram sample and trying zincing it, add 7 grams of zinc dust, if it is GPC you should get 6.8 grams of gold plus the un dissolved zinc when dried. If you don't get a nice dark brown sludge with a little grey from the zinc it's junk that you still have to dispose of safely!

Absolutely true. Always test a small sample when you are unsure of the material to begin with.
 
Will,

I'd think you're best off just shipping it to someone who can process it for you and pay you on the gold than generate the waste and have someone in academia ticked off about paying for it.
 
Lou said:
Will,

I'd think you're best off just shipping it to someone who can process it for you and pay you on the gold than generate the waste and have someone in academia ticked off about paying for it.

Yes, I think that would be the ideal solution. I have only done my gold business (circuit boards and e-scrap) in relatively small amounts through middlemen with varied results. so I am in a place where most noobs are - who can be trusted to do this for me?

I am reaching to point where I am generating enough good scrap that I could eventually start talking to a refiner directly (an acquaintance recommends Sabin up near Rochester), but circuit boards are a different animal from funny white powders. I am not sure I would want to make my first run with a refiner anything but a normal scrap run.

--
Will
 
I think 10 g could be safely wet ashed with sulfuric in a good hood (be warned, it produces HCN) and then over 250C, pure gold. For 10 g, I'd use a 150 mL beaker with a watch glass (to catch potentially gold bearing mist entrained in the prussic acid) and start by pipetting in 50% w/v sulfuric--the bulk of the fizzing happens early on, so rinse down the walls of the beaker and watch glass with the 50% sulfuric. Then strongly heat until the water is gone. After fuming, the sulfuric acid and potassium sulfate solution can be diluted, the gold allowed to settle, decanted, and boiled with hot distilled water (decant and repeat this several times until the liquid is no longer acidic to litmus). The gold is then transferred with DI water to a dry, clean pre-tared crucible and the water decanted and the gold dried at low heat until the water is gone, then slowly heated to 300 C (don't want the gold to pop) on the hot plate. The crucible is weighed again and the difference is the pure gold content estimate.
 
Lou's procedure is the same method that plating shops, which didn't have any instrumentation in their labs, analyzed their gold plating baths.

I was never a big fan of adding Sulfuric to Cyanide. For small analytical samples it's one thing, but for a pound of the stuff it is a different story.

Just go slow and be careful.
 
Lou said:
Truth be told, any PGC salts I ever did that are opened NEVER EVER ran close to assay, hell some weren't even consistent out of the same bottle. Don't know why. I think some of it was pre-mixed with KCN and or K2CO3 or something but it always ran way less than theory would have you believe. I'm not even sure if it's hygroscopic or not.
When I worked for Sel-Rex, they sold 3 types of PGC, sealed, in either 1 or 5 oz (gold content) bottles. All 3 were labeled differently. They were all used primarily to replenish the gold in existing gold plating baths.

(1) Pure PGC - 68.3% gold. No additives. Small, bright white, very heavy crystals. This worked in any bath originally made up with PGC, whether acid or alkaline. For the pure 999.9 gold baths (pH=6-6.5, usually), only pure PGC could be used.

(2) Pure PGC + a small amount of either nickel or cobalt sulfate. Used to replenish the gold and the Ni or Co in hard acid gold baths (pH=4-4.5). The Ni/PGC salts were light green and the Co/PGC salts were light pink. Overall, the purity was only a little less than 68.3% because very little Ni or Co was added.

(3) Pure PGC + KCN. Only for replenishing alkaline baths which were in a KCN matrix. Overall gold purity of 40%, if I remember right. In a cyanide gold bath, the cyanide tends to break down to form K2CO3. The extra KCN mixed with the gold acts to replenish the KCN. I would imagine that the KAu(CN)2 and the KCN weren't well-mixed.

I'm thinking that the few times the gold content was questioned and an assay was required, I had to recover and refine all the gold contained in one or two bottles. I seem to remember that it was always right on.

Other manufacturers probably package their salts differently.
 
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