Looking for info on cyanide leaching for plated items.

[Mcnew32(Ag)]

Tried to search for cyanide leaching through the search bar. If anyone can link me to a good thread for cyanide leaching of gold plated material I would appreciate it.

 

[goldsilverpro]

Tried to search for cyanide leaching through the search bar. If anyone can link me to a good thread for cyanide leaching of gold plated material I would appreciate it.

I recently sent this as a PM to a member. Before attempting this, make sure you have read up and understand how to work safely with cyanide. There are some good websites with this info.

You might read these threads first.
https://goldrefiningforum.com/search/4730/?q=plunger+zinc+cyanide&c[users]=goldsilverpro&o=date
About all I can do is tell you how I do it. I always tumble the gold plated parts (pins, fingers, etc) in a portable cement mixer using sodium cyanide plus a small amount of 30-35% hydrogen peroxide. No other chemicals. It's very fast and no excess oxidizer will be present to cause problems in precipitation.

I prefer a steel mixer because it's easier to cover the opening. When tumbling, drops of the solution will occasionally fly out. To prevent this, I use 4 magnets, one on each corner, to hold a sheet of thin flexible plastic over the opening. I use 2 of the very strong neodymium magnets (from hard drives) and 2 weaker horseshoe Alnico magnets. When I want to open the mixer, I stop it so the neodymium magnets are at the top, remove the 2 Alnico magnets, and then fold the plastic up over the top, leaving the 2 neodymium magnets in place securing the plastic. This is much easier to do than to explain.

Using this process, I have stripped 6 drums of material in an 8 hour day, by myself.

(1) Add 1.5 to 2 gallons of hot (about 50-60C) tap water to mixer.
(2) Add parts to be stripped. You can strip quite a lot at one time - say, 5-10 kilos, or even more, depending on how bulky the parts are. The pile of parts added can stick up out of the water - everything will get wet as you tumble it. You'll have to experiment with the amount of parts you can run at one time.
(3) Add about 100-200g of Sodium Cyanide (NaCN) and tumble until dissolved - about 1 minute.
(4) Add about 50ml of the hydrogen peroxide (H2O2). Cover the mixer opening and tumble. The H2O2 will heat the solution even more due to its reaction with the cyanide.
(5) After about 2 minutes, stop the mixer when the strong magnets are on top, remove the lower weak magnets. and fold the plastic over the top. With plastic gloves on, lift a handful of parts, wash with a little water from a squirt bottle, and see if they are stripped. If you see white nickel and/or uniform pink copper color on all the parts, the stripping is complete. If there is still yellow gold present or if you see a black smut (gold that's dissolved and cemented back onto the copper) on the parts, add about 50g of NaCN + about 20ml H2O2, and run for about 3 more minutes. Repeat. If, after doing this a total of 3 times, there is still gold or smut present (very rare - maybe 1 out of 25 batches), start with a fresh solution on the same parts.

Note: Essentially all gold plating on electronic material has a layer of nickel plating under the gold. If the nickel is thick (or, if the base metal is magnetic towards a weak magnet), the stripping will likely be finished in 1 to 2 minutes. If the Ni is very thin, the abrasion caused be the tumbling can remove it and expose the copper. In that case, there is a battle between the gold wanting to dissolve and the dissolved gold wanting to cement back onto the copper. When copper is exposed, the stripping will go slower.

(6) When the parts are stripped, carefully tilt the mixer and collect the solution in a 5 gallon plastic bucket without pouring off any parts. Put 2 gal of clean water in the mixer, tumble for a minute or so to rinse the parts. The same rinse water can be used for 3 or 4 batches.

When finished, transfer all solutions and rinses into a suitable sized plastic container - 5 gal bucket, open top 55 gal drum, etc. Place the container high enough so you can siphon all of it imto another container. While dropping the gold, stirring is quite important. A prop type electric stirrer is nice, but the same results can be achieved with a homemade "plunger" stirrer. To tell how much zinc to use, you must be able to see the color of the gold/zinc powder. This requires a lifting motion while stirring the solution. A 5" dia. plastic disk mounted of the end of a plastic pipe will work great, with an up and down stroke. Go slow on the upstroke or you'll slosh the solution on you.

Precipitating the gold:
(1) Weigh out about 2g of 325 mesh "zinc dust" for each gram of expected gold. This is only an approximation - it may take more or less. Note that the zinc will also drop any silver or copper that has dissolved. Before adding, you must break up any zinc clumps that have formed. I do this by putting the zinc through a fine kitchen sieve.
(2) While stirring, add about half of the the weighed, de-clumped zinc. Stir for a minute or two. As you lift up the powder, look at the color. At first, the powder will be brown (mostly gold and/or copper). As you add more zinc, the color will become a uniform light gray color. This happens when all the gold and copper have precipitated and there is an excess of undissolved gray colored zinc. This is what you want to see. At that point, stop adding zinc and stir for 5-10 more minutes.
(3) Obtain a couple of 5 pound (or, so) zinc bars, drill a hole near the top, and hang them in the solution using some insulated house wire. Let the solution settle overnight. The purpose of the zinc bars is to prevent any gold re-dissolving.
(4) Siphon off the solution into a like sized container without disturbing any of the settled solids.
(5) Filter the solids and rinse them 4 or 5 times with hot water.
(6) Transfer the solids and the filter paper to an adequate leaching vessel (I use a 5 gal bucket). UNDER A FUME HOOD, cover the solids and paper with water. Add very small increments of nitric acid, stirring slowly in between additions. When an addition of nitric produces NO reaction, stop adding nitric.
(7) Filter, rinse well, dissolve in aqua regia, precipitate pure gold with SMB, filter, rinse well, dry, and melt.
Note: When dissolving the Au powder in aqua regia.
(1) Transfer filtered gold and paper to a large beaker.
(2) Cover with HCl. Heat to about 60C under a fume hood.
(3) Add a few ml of nitric. There should be an immediate reaction. When the reaction subsides, give it a short stir and add another small amount of nitric. Repeat until a small addition produces NO reaction. Stop adding nitric.

 

[Mcnew32(Ag)]

Thank you! And be assured I will read and take every safety precaution necessary.

 

[Mcnew32(Ag)]

Also which would you recommend, cyanide leaching or reverse electroplate for magnetic pins, connectors and other material?. I figured the non magnetic components I'd dissolve in nitric.

 

[anachronism]

If you're following GSP's process and using cyanide safely then I couldn't see why you would ever bother dissolving pins ever again.

 

[Mcnew32(Ag)]

I guess you are right, the process would be the same for steel pins and copper/brass pins. U think I will have to start getting this together as I am building quite a pile of played items and fingers. Has anyone tried to process ram through this means?

 

[anachronism]

If you mean the fingers from the RAM then yes it works perfectly.

 

[goldsilverpro]

The process will work for any gold plated material, as long as the gold plating is not encased or sealed inside plastic, etc. In other words, when the plating is visible. The process will not work on gold alloys, such as gold brazes.

 

[Mcnew32(Ag)]

Ok thank you. I was just asking if it would work on whole sticks of ram. Once the gold is stripped then I can deal with the IC chips in the blank board. This would be much better than AP I think less filtering and less chemicals to deal with after doing bulk lots of ram.

 

[goldsilverpro]

Something important that I neglected to mention in my process. A problem is always cyanide residues on the material after stripping and rinsing. This can make handling of the final material hazardous. I use a bucket of water with some some lye (not much) and bleach in it and tumble the parts in it after rinsing. Then, I rinse the parts with water.

 

[Mcnew32(Ag)]

Thank you for the important tip! I was thinking about using the goldex method and just buy their reagent. Any experience with that?

 

[anachronism]

There's a whole thread about it.

 

[goldsilverpro]

Some cyanide safety precautions: If I think of any others, I'll add them to this list.

In general:

1 - Don't eat it or drink it or you'll most probably die.

2 - Don't eat, drink, chew, or smoke while working with cyanide.

3 - When I work with it, I prefer short sleeved t-shirts. I would rather get it on my skin, where it's easily rinsed off and neutralized, than on my clothing, where it's not easily rinsed off.

4 - I always wear a full-face plastic face shield when working with it. This prevents flying drips from getting in your mouth, nose, or eyes. Also, cyanide solutions are highly alkaline and can cause blindness. A face shield also prevents you from inadvertently touching your face with your hands.

5 - I "cuff" my gloves to prevent liquid on my gloves from running down on my forearms. I prefer the cloth lined two-toned green or blue gloves.I've used them for 40 years. They're sold most anywhere (about $4-$5) but about the best ones (about $8) are the two-tone green ones sold in farm supply stores for use when working with anhydrous ammonia. I HATE latex or nitrile disposable gloves. I sweat in them and don't trust them with any strong acids. Also, you can't cuff them. The green or blue ones I spoke of loosen up after being worn a few times and can last forever, if you don't handle sharp parts and puncture them. About the only acid you have to watch out for with these gloves is concentrated sulfuric. Of course, the only gloves that will stand up to conc. H2SO4 cost about $50, or more.

6 - Optional are rubber boots and a rubber apron, both of which can be easily rinsed off.

7 - I keep a bucket of quite weak HCl (well labeled on 3 sides of the bucket), say 2% by volume, handy but a distance away from the cyanide. After rinsing any cyanide off my hands or arms with water, I stick them in the weak HCl and then rinse them again. This neutralizes the cyanide. You know when cyanide is on your skin because, cyanide, being alkaline, will feel "slick." on your skin, like lye does. A quick dip in the weak HCl removes the cyanide and thus, the slickness. The HCl will find any cuts or abrasions on your hands, of course.

8 - Except for the weak HCl, I don't allow any acids within, say, 25 feet from any cyanide and preferably in a separate room. Cyanide plus acid yields HCN, hydrogen cyanide, the same gas the prisons used to use for capital punishment.

9 - Some people, like myself, are sensitive to cyanide solution on the skin or the fumes that come off when you're working over a warm or hot cyanide solution. This sensitivity results in an unpleasant condition called "cyanide itch". This itch is so strong that it's agonizing. It occurs as tiny blisters and it seems to mainly affect soft skin areas like underneath the forearm and the tops of your fingers. I had it so bad from hot fumes one time that my eyelids were swollen shut. When on your hands or arms, the only way I could relieve the intense itch was to hold my hands under hot tap water. The only way I've found to heal myself was to not be around cyanide for a few days. With my sensitivity, I still work around cyanide. I've just learned to not get it on me and to not work in the fumes when it's heated, at all.

10 - I prefer doing the stripping outside, in a well fenced area. I think it's safer. However, you should only do this if you can keep animals and people away from it and it's quite a ways away from neighbors. To be legal, you should work on a paved area coated with epoxy, surrounded by a berm. Also, to be legal, one needs a bermed area for storage of cyanide solutions and other hazardous liquids. The idea is to have a bermed area that will more than contain all the liquids in all the containers stored inside it, in case they leaked out all their contents at the same time. There are also portable plastic berms of all different sizes. They make them large enough to hold a tractor-trailer.

A guy I knew raised rodeo bulls. He had a big shallow tank, outside, with about an inch of a dried out crust of cyanide in the bottom of it. It was covered with plywood and enclosed with a secure fence. After a year, or so, the plywood rotted and the rain and snow started filling the tank with water. The tank overflowed and carried some of the solution into the grass outside the fence. Two of his prize breeding bulls ate the grass and didn't get 10 feet away before they died. True story.

 

[glorycloud]

WOW - thank you for the safety discourse on how you protected yourself
while working with cyanide. That is most needful and I really trust will
be heeded by those seeking to use your leach process.

 

[Dpetes]

I too want to thank you GSP, for all the info that you have posted here. Especially, cyanide safety precautions # 9.

I have been using the eco-goldex and have this same problem on my arms, even with having a long sleeved shirt on.
Have been wondering what the heck was causing this problem, Now I Know!!! It does drive you nuts. :mrgreen:

Dwayne

 

[nickvc]

The only thing I can think to add to GSPs safety advice is to work with cyanide with awareness and confidence, if your scared of it so not use it and always, always think about each step twice and do once, as I think we all know this stuff gives no second chances if you mess up!

 

[Mcnew32(Ag)]

Here are a few pictures of some of the material I want to run through the goldex solution and am wondering if it would be ok. Please let me know. Also have about half a 5gal bucket full of finger I'm going to run through as well. I will be doing the tests here soon anyway as the regnant is on its way. I am just wondering what you guys thought about running this material.

 

[patnor1011]

Split the tops off CPU's some will have small bit of plating inside. No need to soak non plated one's in anything. I would also pull pins out of housing but that is just me with a lot of time so I would do it to get all that plating when leching.

 

[nickvc]

The cyanide process is very similar in its abilities as the AP process, the items to be stripped need to be fully exposed so the leach can work and it helps to run like items at the same time as it will leach base metals fairly readily which can foul your solution so only running like items help avoid the problem.

 

[Mcnew32(Ag)]

Ok thank you for the advise. I figured it would be better to do some additional mechanical breakdown. It's just very time consuming so I figured if I could just run the whole board it would save on breakdown time. Like I said I will be doing some tests and will post the results here once I get the time to do so. Also I wanted to ask if the Eco goldex solution is renewable? So if I were to throw whole boards in and it becomes saturated with base metals then I can decant solution and renew it for further use.