Electrochemistry Is reverse plating OK to recover the gold from 24K GP metal

[aem123]

Is reverse plating OK to recover gold from 24K gold plated metals

 

[Dr. Poe]

This is just from memory, I don't remember the finer details.
Binding the gold plated items together with copper or silver wire, then hanging them in a cell on the positive pole (anode).
The cell bath is dilute sulfuric with dichromate added. I don't remember the voltage.
The gold flakes off and settles to the bottom of the cell or porous bag. I hope that I've helped you. I'm Dr. Poe (geochemist)

 

[aem123]

Does it matter if it is 10K or 24K plating

 

[Harold_V]

Plating of gold can be removed by a sulfuric cell, but the cell operates on concentrated sulfuric, not dilute. Do a search on the forum for such a cell. Ignore the advice to use glycerin in the sulfuric--it performs no function.

Harold

 

[Dr. Poe]

Harold_V; You are right of course, the sulfuric should be above 66% to penetrate the plate. I stand corrected.
I believe the extra oxidation from dichromates or some other oxidizer does help to promote flaking. Glycerin coupled with caustic reduces platinum salts to metal (platinum black), but I've never understood why one would think it would help in a acidic stripping cell. Dr. Poe

 

[nickvc]

The higher the concentration the better, 95%+, as it stops the acid attacking the copper so quickly.
Its odd that concentrated acids can be frequently less reactive than dilute ones, but very true.

 

[Palladium]

Harold_V; You are right of course, the sulfuric should be above 66% to penetrate the plate. I stand corrected.
I believe the extra oxidation from dichromates or some other oxidizer does help to promote flaking. Glycerin coupled with caustic reduces platinum salts to metal (platinum black), but I've never understood why one would think it would help in a acidic stripping cell. Dr. Poe

I don't have time to type it but here's the reason. :arrow:

It has nothing to do with penetrating the plate. It works because high current in the proximity of the anode converts concentrated sulfuric acid to persulfuric acid. That dissolves the gold. As the gold migrates away from the anode (the part(s) being stripped), the electrolyte reverts back to sulfuric acid, which can not hold gold in solution, so it precipitates as colloidal gold---the black substance that darkens the electrolyte.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=86&t=11453&p=112263&hilit=sulfuric+acid+gold+cell#p112263

 

[goldsilverpro]

I think we're talking apples and oranges here.

Using dilute sulfuric (say, 10-15%) will dissolve the copper base without dissolving the gold and the gold can then be collected as flakes. The problem would be at the cathode. If the copper base is pure, a sound deposit can be achieved. If not pure, the deposit will likely be fluffy and non-adherent and this can cause all sorts of problems.

Using a much more concentrated sulfuric will remove the gold, which precipitates as a powder, without attacking the copper or most other base metals. In the original patent on this, #2185858, Mason suggests using 1.65 SG (about 74%, by weight) sulfuric. In my experience, this is too weak and, especially when it heats up from the electrolytic reaction, it will attack the copper. However, to get any speed at all, some water is needed. Using technical grade sulfuric, which is usually about 95-96%, I add 5% water, by volume. When diluting, ALWAYS ADD THE ACID TO THE WATER!!! and NOT the water to the acid.