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topic 53511

Separation of Gold metal from Potassium Gold Cyanide salt





A discussion started in 2009 & continuing through 2017

November 3, 2009

Q. I have worked in plating processes for about two years and I am interested in knowing how to separate the Gold from Potassium Gold Cyanide salt.

Gorgolino Moraila
Engineer - Mexico City, DF, Mexico

November 4, 2009

A. Hi, Gorgolino. I'm not confident that I fully understand your question, but you can electroplate some of the gold out of the solution in your standard plating tank. When the gold level drops to where the process is inefficient, you can use a specialty electrolytic cell or ion exchange. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 4, 2009

A. Gold Potassium Cyanide is significantly more valuable than the gold it contains due to the rather specialised process required to manufacture it. If you have GPC, sell it to a plating company and use the cash to buy gold if you need to.

geoff smith
Geoff Smith
Hampshire,
       England



November 9, 2009 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi

I am Zul from Penang, Malaysia
I am interested to learn the process of extracting the gold contained from PGC or gold salt.
Please advise.

Amril Idrus
goldsmith - Penang, Malaysia


November 12, 2009

A. About the only people I can think of that would legitimately want to recover gold from PGC are refiners. However, I am going to assume that you have honest intentions in wanting to do this.

In its purist form, which is usually used in acid gold baths, the PGC will contain about 68.3% gold. If it is used for cyanide baths, it might also contain some potassium cyanide, which would lower the gold percentage. If it is used for acid baths, it could also contain a little nickel or cobalt and will have a green or pink color. The presence of these won't interfere with the recovery of the gold.

(1) Dissolve the PGC in water. At room temperature, you can dissolve about 143 grams of PGC in a liter of water. This would contain about 3 troy oz of gold, if it is the 68.3% variety. Since the solubility of PGC varies considerably, based on temperature, I would only dissolve about 2/3 of that in the water or, about 2 oz of gold per liter.

(2) Too prevent the very dangerous evolution of hydrogen cyanide gas in the following steps, first adjust the pH to 12 with potassium hydroxide. Try not to exceed this pH, since too much hydroxide will increase the amount of zinc needed in the step below.

(3) If the PGC is of the 68.3% variety, it would help the gold precipitation to also dissolve about 15 grams of potassium cyanide per liter in the solution. Without the extra cyanide, you may or may not have a problem dropping the gold. The gold may finally drop, but it will be slower. It is best to add the extra cyanide.

(4) With constant stirring, add 325 mesh zinc powder until all the gold has dropped out. This should take from 1 to 2 oz of zinc per oz of gold. The gold will drop out and appear as a brown powder. To insure all the gold has dropped out, you'll need a slight excess of zinc, which is of a gray color. Add the zinc in increments, allow it to work for a couple of minutes, and observe the color. When the observed powder is of a uniform gray color, all the gold should be out.

The zinc powder tends to clump when stored and must be broken up before adding. The easiest way to break it up is to weigh out what you think you'll need and place it in one of those small flour sifters that has a squeeze handle on it. Add the zinc to the solution directly from the sifter.

(5) Allow the powder to settle overnight. To prevent any gold from re-dissolving, hang a couple of zinc bars in the solution.

(6) Either siphon or dip off most of the solution without disturbing the settled solids.

(7) Filter the solids and rinse several times with hot water in order to remove any cyanide solution.

(8) Remove all the solids from the paper and put them into a plastic bucket. Keep the paper(s) for future incineration.

(9) Cover the solids with water and stir a bit to break up the solids and create a slurry.

(10) UNDER A FUME HOOD!, add a small amount of concentrated nitric acid. You should see an immediate reaction. When the reaction subsides, give it a stir and add a little more nitric. Repeat until an addition of nitric produces no reaction. You MUST use a fume hood for this, just in case you didn't rinse out all of the cyanide. The combination of acid and cyanide will produce deadly hydrogen cyanide gas

(11) Transfer the solids to a beaker, cover with water, and heat to a little below boiling. Add some nitric and heat for about 15 minutes.

(12) Filter the solids and rinse several times with hot water. Remove the solids from the paper and slowly dry.

(13) At this point, you should have 99+% gold powder. To purify it further, you can use the standard aqua regia method.

NOTES:
(1) Wear rubber gloves and a full face shield for all operations.
(2) In the above, I suggested using Potassium hydroxide and Potassium cyanide because the solution is Potassium to start with. I think it would work as well using Sodium hydroxide and Sodium cyanide instead.

Chris Owen
- Nevada, Missouri


November 14, 2009

A few additional notes on the process I outlined above.

The purpose of the nitric acid, in steps (10) and (11) is to leach out all of the excess zinc. Also, if any Ni or Co is present, it will also be leached out with the nitric. Step (11) is done to insure all the zinc, etc. is leached out.

This process can also be used for any acid or cyanide gold baths, already in solution form, that contain PGC. Also, it can be used for cyanide/H2O2 or most cyanide/m-NBSS gold stripping solutions. In these cases, just start at step (2). For cyanide baths or gold strippers, eliminate step (3).

The process will NOT work for baths containing sodium gold sulfite. These sulfite baths are rarer than PGC baths, but there's a lot of them out there.

Chris Owen
- Nevada, Missouri, USA


November 12, 2009

thumbs up signHi, Chris. Thanks for the terrific exposition. I'll only reinforce your warning that these instructions are for trained chemists who fully understand cyanide chemistry and toxicity. The internet is a giant one-room schoolhouse where people will overhear instructions for operations that they are not trained, equipped, or situated to safely do.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


April 28, 2011 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sirs,
I am a gold trader and have been offered a quantity of GPC from a customer. I would like to know if there is a safe way of recovering the gold from the material or whether I should avoid it due to its poisonous nature.

Gareth Thomas
Gold buyer - Northampton, United Kingdom

August 1, 2012

A. Hi, Gareth. As you see, we appended your inquiry to a thread which should answer it for you: 1) The GPC may be worth more that the gold it contains, per Geoff Smith's posting. 2) The gold can be recovered, per Chris Owen's posting, but only by trained chemists with deep knowledge of cyanide chemistry.

Best of luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


August 1, 2012

Q. What is the percentage of cyanide in 1 gram GPC (gold potassium cyanide)?

akash kuamr
- delhi, India


August 1, 2012

A. Hi cousin Akash.

Chris Owen has advised us that GPC is 68.3% gold. You will find that you can verify this number in the "Metal Contents of Common Plating Salts" appendix in the Metal Finishing Guidebook, rather than having to rely on an internet posting.

If you'd like to learn how to fish rather than where to buy a fish, the formula for GPC is KAu(CN)2, and the respective atomic weights are --
K: 39.096, Au: 197.2, C: 12.01, N: 14.008.  So, %Au = 197.2 / 288.332

Luck and Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


March 15, 2013

Q. Hi.

I found an old bottle of gold plating replenisher in the garage of a house I bought some years ago. It's a small bottle, about 3 inches tall, amber. The label says it's "Bright Gold Replenisher". It also says it contains 1 oz troy 24K gold. The bottle also has a warning label that it contains potassium cyanide. The contents have separated over the years into two phases of equal volume: a light colored solid and a slightly viscous liquid. For years I thought the gold in in the solid layer at the bottom, but recently a plater told me that the gold most likely is in the liquid layer, in solution with the cyanide. Who would have thought?

Some local platers say the gold could be recovered by plating it out, but none seem interested in getting the bottle. There are apparently also other methods that involve diluting with water, adjusting the pH, and precipitating out the gold cyanide. I have read about this but the process seems a bit complex (although I have a biochemistry degree), a bit risky, and might require supplies and equipment I don't have (well, nitric acid, mainly. I do have a setup in my workshop that could be altered to create a relatively good fume hood).

I might also be able to plate it out, but it would take a fair amount of time, a tank, solutions, etc. I do have a source of lead, a good power supply, stainless to accept the plated gold but release it readily. It could be quite time consuming, at the rate at which 1 oz of gold would be plated out on a relatively small amount of stainless.

Although it would be fun to wind up with a blob of pure gold on my own, my preference would be to take the bottle to a plater and have them pay me more than the value of the 1 oz of 24k gold it contains.

Any advice?

Rich Adams
- San Leandro, California, USA


March 26, 2013

A. Hi Rich. The big question is whether this bottle was ever opened. If not, it presumably has a troy ounce of gold in it, so should be worth over $1000 and worth a plating shop's time to consider (assuming they are not doing ISO or other spec work which demands traceability). If your calls to plating shops haven't worked, you might list it on Ebay or Craigslist.

If it has ever been opened,there's no telling what's in it . . . maybe a solution so exhausted that the previous owner didn't want to pay the disposal fees. You might try one of those "We buy gold" stores that are on every town street corner these days. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


March 27, 2013

thumbs up signTed,

Thanks for the reply.

I don't think the bottle has been opened, at least not since about 1980, when the previous owner's husband died, and the widow didn't venture into the garage. I actually found two bottles with similar labels. This one, which is filled to the brim, and another one which is completely empty. I tend to think that it's not been opened, but of course since the parties that might know are all long deceased.

I spoke with a couple of local platers and nobody seems interested. For one, not enough material to be of interest - he said they just dumped about $10,000 worth of gold into their plating tank.

He did explain how I could plate it out onto stainless steel, and the plating would fall right off, so it could be collected. Not sure I want to go through all that process, as I'd have to get the tanks and the chemicals and equipment going, which appear to be no small task, although it could be nice to have my own gold plating capability.

Another option is to have it assessed at a local lab, to determine the gold content. But then I still have the issue of extracting/refining the gold.

eBay is an option although I'm not sure how that would go. I'd have to specify a reserve price ($1000?) and of course could not at this point guarantee the contents really do contain gold.

However the former owner worked at a nearby electrical equipment factory, and when it shut down he apparently salvaged a fair amount of stuff. Perhaps this replenisher is from that operation. The local plater stated that the former factory did indeed perform gold plating in-house.

For now the bottle is back in the safe...

Rich Adams
- San Leandro, California, USA


June 15, 2013

Q. Hello everyone,
How do I use zinc dust to precipitate gold from a hot strip caustic cyanide solution, on a laboratory scale?

Samuel Dilu
- Kundiawa, Chimbu, Papua New Guinea



September 2, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear Sir,
As we are a jewel manufacturing company we have exhausted GPC liquid that used for gold electroplating. How to get the remaining gold from that liquid. Kindly give any procedure Actually we made the solution pH to 9 by adding alkaline salts and inserted an aluminium sheet to react for 1 or 2 days and got some gold deposited on aluminium sheet further what to do?

Lavanya Ammaiyappan
- Coimbatore, India



Add sulphide to GPC to precipitate gold?

May 21, 2014

Q. Hello sir, if we add ammonium sulphide or sodium sulphide into GPC solution, gold is precipitated or not?

vivek kapoor
metal refining - ludhiana punjab India
  ^- Privately contact this inquirer -^


Recovery And Refining Of Precious Metals


Gold Refining
George Gajda

May 2014

A. Hi Vivek. Theoretically, yes, gold sulphide is precipitated. But there are probably practical reasons why the Merrill-Crowe process, electrowinning, and carbon in pulp are the principal methods instead. I don't know much about the subject, but it seems to me that precipitating a gold sulphide this way is going backwards from the desired direction of refining the gold :-)
Have you consulted any books for practical process design of gold recovery?

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


August 8, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I want to know what is the process of recovery of gold from GPC dissolved water?

kamalesh sarkar
Hobbyist - kolkata, west bengal, India


August 2014

Hi Kamalesh. We appended your question to a page where it's already answered. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Separating gold, silver, and copper in a cyanide solution

September 23, 2014

Q. This is for lab level. Have gold, silver and copper in cyanide solution. Kindly advise how I can separate each because if add zinc dust, that settles all three combined. Secondly, can we use zinc cans which are used in dry battery cells?

arshad fazal
drugpharma - pakarachi.pakistan


September 2014

A. Hi Arshad. This is a job for a refinery, not a pharmaceutical lab. But if you are saying that you are a student with a student lab assignment, you could try putting two stainless steel electrodes into the solution, and apply a very low voltage (like 0.1 volts) and the deposit should be primarily gold.

As a matter for science class, what you would then do is dissolve the metal you have plated and plate it out again. The second time you would be starting with a solution that was richer in gold than the first time, so the second low voltage deposit would be purer than the first. You could continue that process until you had pure gold. Presumably you are versed in the serious dangers of working with cyanide. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


October 1, 2014

Q. Hi Mooney!

Thanks for your kind response. I'm keeping pH 12 and adding H2O2 from time to time at atmospheric temperature during dissolving ore mesh with NaCN for a day. Is it Okay toward preventing formation of HCN? If you realize any mistake, I would be humble and thankful to you. Secondly, I don't want to and can't use electrochemical method for separation. What if those three elements are treated with H2SO4, so Copper will dissolve and Silver will dissolve and Gold will remain settled. Or any other such reagent method in your expert opinion?

Kind Regards,

Arshad

Arshad Fazal
Drugpharma - Karachi.Pakistan


October 2014

Hi again. Sorry, I have no experience in refining and cannot suggest what steps can be improved. My initial answer was simply based on my electroplating experience, thinking you might be a student doing a science project.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


October 2, 2014

A. I'd follow Ted's advice about plating out the gold at very low voltage. Then, I'd oxidize the cyanide with hypochlorite or hydrogen peroxide, cautiously acidify with nitric acid (fume hood a must for this) then add sodium chloride. That will precipitate the silver as the chloride, from which it may be recovered by roasting with charcoal. If you wish to recover the copper, add some zinc dust, it'll precipitate.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


October 3, 2014

A. Here's how I would do it:

(1) Precipitate all the gold, silver, and copper with 325 mesh zinc dust. Since it is best to use a slight excess of zinc, there will also be some undissolved zinc mixed with the other metals.
(2) Filter and rinse the solids very well in order to remove the cyanide solution. I prefer hot water rinses.
(3) Transfer the solids along with the filter paper to a large beaker. Place on a hot plate under a fume hood.
(4) Cover the solids with distilled water and heat to about 50 °C. Add 70% nitric in very small increments. With each addition, allow the reaction to subside before making another addition. Repeat. When an addition of nitric produces no further visible reaction, the zinc, silver, and copper have dissolved, leaving the gold as a solid.
(5) Dilute with about an equal amount of distilled water. Filter out the gold powder (plus the pulped filter paper) and rinse it well with distilled water. Dissolve the gold with aqua regia, filter, rinse well, and precipitate the gold with your favorite precipitant (most commonly, ferrous sulfate or sodium metabisulfite).
(6) The dilute nitric now contains zinc, silver, and copper. Cement the silver selectively, as a solid, by suspending copper bars in the solution until all the silver has been removed. The solution can be tested for silver by removing a drop, placing it in a spot plate or a plastic spoon, and adding a drop of table salt solution or hydrochloric acid (HCl) to it. A white cloud indicates that there is still silver in solution. In that case, leave the copper bars in the solution until the solution tests negative for silver.
(7) Filter out the silver powder and rinse well. At this point, zinc and copper remain in the solution. The copper is then cemented out of the solution with scrap iron. If this goes too slow, add a few drops of HCl to the solution. Once all the copper has cemented, the only thing left in the solution is zinc. Also, the green or blue color (from the copper) will be gone and the solution will be close to colorless.

Chris Owen
- Nevada, Missouri, USA


October 4, 2014

thumbs up signDear Chris,

It was simply marvelous you defined. Thanks.

Kind Regards,
Arshad

Arshad Fazal [returning]
- Karachi.Pakistan



March 15, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. My friend is running a gold plating shop; he prepares electrolyte:
Dissolving gold in minimum AR,
Disolve few grams of NaCN or KCN in 1 ltr distilled water,
Mixing both solutions in 1 ltr beaker.

He uses this bath for 2 or 3 days to plate nickel plated jewelry, when the gold deposition becomes blackish he stores the used electrolyte in a bottle.

He sells those used GC Electrolyte filled bottles to an uneducated boy...

That boy is many times exposed to HCN; the way he is extracting gold is deadly:

He is adding 1 kg NaOH to 6 gallons of electrolyte,
Then adds hot solution of KAl(SO4)2 potassium aluminum sulfate,
Coupling white precipitate with lead.

He is using same method to recover gold from high concentration cyanide electrolyte.

One year ago he was with a good health; now he is looking weak, ill, lazy while talking his eyes are flashing.

I tell him stop this method.
Can I suggest him to use carbon anode and stainless steel cathode to recover gold safely? What is pH, voltage, ampere to be controlled for safe work to avoid HCN generation?

Thanks. Is it something good for humanity and living creatures if we could educate him to do the right things?

Waqas Qazi
Student, Hobbyist - Gujranwala, Punjab, Pakistan


March 2015

A. Hi cousin Waqas. The problem, of course, is that "an uneducated boy" should not be working with cyanide -- the more so a boy whose health has already been compromised. But here in the USA, poor uneducated boys use and deal drugs, which is probably equally dangerous -- so what can either of us do except try our best to build a better world where boys won't do such things.

As you see, we appended your question to a thread which discusses it. Best of luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



February 15, 2017

Q. Dear all,
I've got 20 tons of waste solids from copper-gold plating which contains about 10% of copper cyanide, 40 g of gold/ton, and KCN.
Please help me to recover gold from that.
Thanks

Quan Bui
- Ha Noi, Vietnam



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