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> Gold Electrolysis Process
Areal Person
Posted: April 15, 2008 05:16 am
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PC Board gold fingers

Iíve got allot of PC boards that have the gold fingers
Gold plated pins, etc.

Can I set up an standard electrolysis process to transfer the gold
atoms / ions whatever to an ingot ?

Or is there a problem / hazard with this ?

And where is the most gold located in electronics ?

Thanks,

-Areal
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draget
Posted: April 15, 2008 11:14 am
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No, water (E0 = -0.82V) will be oxidised at the anode instead of gold (E0 = -1.5V)
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Sch3mat1c
Posted: April 15, 2008 11:40 am
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No, I have:
1/2 O2(g) + 2H+ + 2e- <--> H2O, Eo = 1.2291V
(Although this still doesn't explain why persulfate can be in solution (S2O8(2-) + 2e- <--> 2 SO4(2-), Eo = 2.01V).)

Gold is often complexed in solution, hence I also have AuCl4(-) + 2e- <--> AuCl2(-) + 2Cl-, Eo = 0.926V for Au(III) to Au(I), and 1.154V for the reduction from Au(I) to metal. I don't have the voltage for the cyanide complex, but it's probably lower. Besides, if it were true that gold cannot go into solution, how is it that it does?

In any case, the amount of gold in electronics is so vanishingly small that it's hardly economical to recover it, even on a massive scale. Send your boards to a recycling center and feel good about yourself. There, they may process the boards for useful parts (e.g., salvage chips) and burn the boards in large furnaces (~100 ton capacity), where the carbon content fuels itself, the glass content (with added fluxes) forms a slag layer and the copper, tin, lead, iron and precious metals settle to the bottom. Offgasses include dioxins, HCl and other nasties from the chlorinated plastics, best handled by industrial scrubbers.

The metal product is refined, probably by a selective electroplating process. This probably uses a copper electrolyte, passing iron, tin and lead into solution (or precipitating some of them, for instance, tin as the hydrous acid and lead as sulfate), plating copper out of solution, and leaving precious metals (silver, gold, PGMs) as a sludge to be further refined.

Tim


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tekwiz
Posted: April 15, 2008 07:14 pm
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I have been wondering on this myself. Years back, you used to be able to buy these electroplating guns that would apply gold plating with a cloth pad wet with a special solution & hooked to a DC supply. Wouldn't it be possible to reverse this action to selectively remove gold from a copper substrate? The loaded pads could then be burnt off & the gold recovered from the ashes. cool.gif


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Areal Person
Posted: April 16, 2008 02:41 am
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Wow, I had no idea... blush.gif

Thanks for helping me to understand that !

Darn, And I was hoping to get enough $doe$ to buy some good
electronic test equipment. sad.gif

I guess it's back to picking up aluminum cans.

However, I did find this cool metal film gift wrapping paper
at the dollar store, its in a thin plastic film with a chrome colored metal coating
on one side (and has other metal colors on the other side) It's conductive ! It's called "Sparkle Metalized Tissue" and a LARGE sheel (Poster board size) sales for $1.00us. It's made by Bleyer Industries in Vally Stream NY.

I took an old wheat penny (1918) and did the elecrolysis process using the tissue.

It now looks like a newer chrome penny tongue.gif

I'm gonna try making some flexable film circuits, sensors and maybe even some caps with the tissue !.

It's really cool stuff.

Thanks,
-Areal blink.gif
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Village Idiot
Posted: April 16, 2008 02:42 am
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Coincidentally, I have in front of me the process flow diagram for a current gold mine project.

Gold will dissolve in a weak Sodium Cyanide solution (about 1% cyanide or less) at a high pH (10 or more), but the efficiency depends on particle size. Electrolysis is unnecessary at this stage.

Once it is in solution, in the form of Gold Cyanide, it is then electroplated out onto a metal cathode.

The overall commercial process is far more complex than just the two stages mentioned above. There are a number of steps done to concentrate the solution before electrolysis.

As Sch3mat1c mentioned, it's not worth the trouble and the danger of the toxic chemicals to recover a few cents worth of gold plating.

If one had a huge pile of gold plated boards, the simplest recovery method likely would be to grind them up, and leach the gold off using the above process.
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tekwiz
Posted: April 16, 2008 07:01 pm
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Yeah, but what levels of other metals, if any, would dissolve in the cyanide solution? I'll bet it will dissolve more than gold. cool.gif


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Village Idiot
Posted: April 17, 2008 02:22 am
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Since gold is less reactive than most other metals, the copper and any other metal on the PC boards could be leached out using other reagents, prior to the cyanide leaching. That's one of the reasons for grinding up the boards. It would allow complete removal of the unwanted copper which would otherwise be protected by the gold plating for part of the process, but probably would still end up in solution in significant amounts.
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tekwiz
Posted: April 17, 2008 06:51 pm
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So, I guess there is no way to selectively unplate the gold from right on top of the copper? With gold pushing a kilobuck an ounce, incentive is strong. Of course, one could always scrape the gold off, then remove all other metals from the scrapings with more conventional reagents, like PCB etchant. Hmmm.... cool.gif


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For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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Sch3mat1c
Posted: April 18, 2008 04:30 am
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Meh, go after rhodium. wink.gif


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Jimthecopierwrench
Posted: April 18, 2008 05:01 am
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How much in the average cat ya think?


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Sch3mat1c
Posted: April 18, 2008 11:22 am
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About an RCH's worth. Cats are mostly water, with some flesh and bone. Not much rhodium at all. tongue.gif

Tim


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Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
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tekwiz
Posted: April 18, 2008 06:35 pm
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QUOTE (Jimthecopierwrench @ April 17, 2008 08:01 pm)
How much in the average cat ya think?

Must be a decent amount, considering they have become popular theft items. cool.gif


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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gunslignerfrank
Posted: April 19, 2008 12:58 am
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I thought they were swiping them for the platnium in them.



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tekwiz
Posted: April 19, 2008 01:56 am
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Platinum, palladium, rhodium, they are all in the same class of precious metal catalysts & they are all used in catcons. cool.gif


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Trouble rather the tiger in his lair, than the sage among his books.
For to you, kings & armies are things mighty & enduring.
To him, mere toys of the moment, to be overturned at the flick of a finger.

Fortuna favet fortibus.
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