Suggestions for deplating spool of gold plated wire (1% w/w)

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spentfire

spentfire

Member
Supporting Member
Joined
Apr 27, 2011
Messages
17
Greetings all!

I was asked by a contact to recover the gold from a ~3 kg net weight spool of fine gold plated wire. I believe the wire is gold over copper over iron (its slightly magnetic). I've run some of it in a sulfuric cell and some in an iodide leech, so I know there is over 1% by weight gold on the wire. Unfortunately, I have had a difficult time with both separation methods. The iodide leech seems to form a lot of copper (I) iodide, which is a pain to separate from the gold, and both methods have problems with the small spools of wire I've made shielding itself and not stripping fully.

One of the problems at the bottom of all of this is that the base metal is extremely tensile, so I can't easily respool it into other shapes. At first I thought I'd just turn the material into coils on my old chain mail mandrel, but it won't coil tightly, and springs back to 4 times its diameter once it is released of tension. I've thought of heat treating the whole mess to reduce its hardness, but I haven't figured out a good way to remove the wire from the thermoplastic spool it came on.

There likely won't be a panacea for this problem and I'll have to run it bit by agonizing bit through on of these two processes, but I thought I would ask the forum members for some suggestions. I've been looking at this problem for too long, and I might be missing something obvious (it happens all too often)!

Any assistance is greatly appreciated! :)
 
Since it is only slightly magnetic, that is probably due to a nickel barrier layer between the copper alloy base and the gold. From its stiff characteristics, the base metal sounds like beryllium copper or phosphor bronze, both of which are high copper alloys used to make springs. To see if it is a copper alloy, try to dissolve a small piece in a small amount of moderately hot 50/50 nitric acid in a small beaker. If everything except the gold (as a foil) dissolves completely and produces a blue or green solution, it is copper.

In any situation like this, you basically have 3 choices: (1) dissolve only the gold, (2) dissolve everything except the gold, or (3) dissolve everything.

For (1), you could use the sulfuric cell, iodine/iodide, or cyanide. You tried the sulfuric and the iodine without much luck. The cyanide would probably be my choice but it's dangerous, there are legal problems, you have to go through a learning curve, and I don't think you have enough material to warrant setting it up.

For (2), you would dissolve the base metal with either AP or 50/50 nitric and then dissolve the remaining gold in aqua regia or HCl/bleach. If copper base, I prefer the 50/50 nitric. However, for 3kg, it would take about 6.6 gallons of 50/50 nitric (or, 3.3 gal. of 70% nitric).

For (3), you would dissolve everything in aqua regia. In general, this is a poor method. Due to the large amount of base metals dissolved with the gold, this can produce problems precipitating the gold.
 
Maybe you could sell it as is to someone with a use for it for the estimated gold value?
And save money on time and chemicals. I know that takes the fun out of it.

Jim
 
Would the bombing technique that jewelers use strip the gold sufficiently. It would be my first thought.
But I agree that just finding a buyer might be the best route.
 
Thinking further about this.

When using any method to strip only the gold, there will be areas that won't strip because of what you called "shielding" - where the wires are touching each other. I think you would have the same problem with cyanide.

Therefore, I think you'll have to dissolve the base metal first, as in (2) in my previous post. Use nitric on a small sample, as I mentioned before, and let us know the results.
 
GSP:

Will do. I'm going to try and carve out some time today to run a small sample in just nitric. Hopefully, the diameter isn't so small that the acid can't get to the base material.

Will report back...
 
spentfire said:
GSP:

Will do. I'm going to try and carve out some time today to run a small sample in just nitric. Hopefully, the diameter isn't so small that the acid can't get to the base material.

Will report back...
Click to expand...

Do you know what the diameter is? If the gold is thick enough (usually 50 - 100 microinches, depending on the type bath used to plate the gold), the porosity could be reduced to a point where the acid might not penetrate. On your sample, try it first at room temperature. If it doesn't penetrate within about 30 minutes, apply heat. If it still doesn't penetrate, you'll have to consider a plan B. Keep us posted.
 
I've started an experiment as GSP suggested, I'll know in a 1/2 hour if I've had any success at room temperature.

As to the thickness, I have a very rough gestimate:

The thickness of the wire appears to be around 0.48 mm. I know that the material is approximately 1.5% (w/w) gold (d=19.30 g/cm3), and assuming the base metal is pure copper (d=8.96 g/cm3), the gold should be ~0.71% by area. That yields a gold thickness of about 2 microns, or 79 microinches. My guess is that this is indeed too thick. :(
 
Update:

It took a fair amount of heat, but I was able to attack the base metal with hot nitric acid leaving gold foil. From watching it, I believe it was attacked in several places, not just the ends of the wire. The solution is blue-green, so GSP's guess of a copper alloy sounds right on. So I guess that leaves me with either trudging through trying to strip it piece by piece with one of the above methods, or investing in a bunch of nitric? Bummer :)
 
I have another question about this material. Could I melt the wire into a 95%+ copper slug anode and affect a separation of the gold via a copper sulfate or copper nitrate cell? Wouldn't the gold report in the anode slimes?
 
spentfire said:
I have another question about this material. Could I melt the wire into a 95%+ copper slug anode and affect a separation of the gold via a copper sulfate or copper nitrate cell? Wouldn't the gold report in the anode slimes?
Click to expand...

Maybe it would work. Maybe not. The gold would definitely report in the anode slimes. However, you really don't know the composition of the base metal yet and how the particular impurities will affect the copper cathode deposit. Success in electrolytic separation is very dependent upon the integrity of this cathode deposit. If it doesn't adhere to the cathode well and plates as a sponge, you could have a mess that would be difficult to deal with. At first, the deposit would be sound but, after awhile, the impurities build up in the solution and the deposit degrades rapidly.

If you do try this, to give you the best chance of success, I would definitely use a sulfate solution rather than nitrate. Also, the sulfate solution should be made with a similar composition that is used in the copper refineries. A formula for this is given in this thread.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=6652&p=59443&hilit=copper+sulfate+sulfuric+acid+current+density#p59443

You will also need a controllable power supply.

I can understand your not wanting to use nitric. However, to me, it is the most straight forward method and, if you do it right, it would give you the best chance of getting all the gold in the least amount of time.
 
Any success yet?
Please, let us know so we can learn from your success.

:)

/Göran
 
Göran:

Sorry for the lateness of this reply. Yes, I did have success on this project! I ended up following GSP's suggestion and ran the material with nitric acid, collecting the NOx gases from the top of the reaction vessel with an inverted funnel connected to a two-stage bubble trap which was held under partial vacuum to generate draw. I went through a fair amount of nitric acid, but I have reclaimed a lot of copper nitrate which I can use to regenerate dilute nitric acid using another cell.

In the end, it wasn't as elegant a solution as I had wanted, but you can't argue with the results - great yields, low cost, and FAST! As with all things, unnecessary elegance costs time and money :)

Spentfire
 
Being that its gold on a copper base could you cut it up and throw it AP with a bubbler? Or use the crockpot method on it?
I understand there is alot of base metal to break down but it seems either of those would be a cheaper way to go.
Just my thoughts :roll: :roll:
 

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