# Sulfuric stripping gold plating video



## Martijn (Jan 6, 2022)

Hello, I've made a video of how I stripped my first kilo's of gold plated connector pins. 
It shows the stripping process, diluting the acid, dissolving in AR, SMB precipitation with an excess of nitric and the end result. 
I had to leave a lot of parts out... I was amazed how much I was touching things back then without gloves while putting this video together 

I hope you enjoy it and find it informative. 
Let me know what you think. 



Martijn.


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## MicheleM (Jan 6, 2022)

Nice, a very good I-V compromise ( not too slow and high purity) is 4-5 V , < 3 A


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## Reachingout68 (Mar 22, 2022)

Hi I was the one who commented on youtube, I am not currently interested in using the gold, simply recovering the copper. Should I just follow the steps in your video if that's the case? Or are there any steps you recommend changing? for example Voltage may be too high in my case since my part is very small.


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## Martijn (Mar 23, 2022)

Hi. Welcome to the forum. 

What is the source of the material? 
Each type of scrap needs a different approach. Some can be combined. 

For copper recovery a copper sulfate cell would be a better option. It leaves you with nearly pure copper on a stainless cathode and slimes in the anode bag. The pm's in the slimes are a bonus.

Martijn.


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## Yggdrasil (Mar 23, 2022)

Martijn said:


> Hi. Welcome to the forum.
> 
> What is the source of the material?
> Each type of scrap needs a different approach. Some can be combined.
> ...


Martijn.
I expect he wants to clean the connector from the plating so he can reuse it for some purpose.
That is the only way I see his request making sense. 
If it is to reclaim copper for scrap value, do as Martijn says. Melt it into an electrode and put it in a copper cell.

Bonus, gold in the slimes


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## Reachingout68 (Mar 23, 2022)

Yggdrasil said:


> Martijn.
> I expect he wants to clean the connector from the plating so he can reuse it for some purpose.
> That is the only way I see his request making sense.
> If it is to reclaim copper for scrap value, do as Martijn says. Melt it into an electrode and put it in a copper cell.
> ...


This is correct, my part is made up of sputtered/PVD titanium and sputtered/PVD Gold on a glass cylinder, I then electroplated copper on the gold and left my sample in HF to remove the glass. To my surprise the Gold was still intact on my sample (I cut it in half with a saw and could see it). I thought using gold etch (potassium iodide) could work to remove the gold but it interacts with the copper as well.
So yeah I would like to remove the gold without affecting the copper, the purpose is to see how well the surface that was electroplated onto the gold formed and its overall smoothness/grain size.
This video has a copper basket and it looks like it is not affected as you remove the gold from the pins.

Thank you for the quick replies, I appreciate the help and information on this forum!


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## Martijn (Mar 23, 2022)

Then the sulfuric cell is a good option. 
I believe it was initially used to remove plating from items before replating them. 

I am not sure if any gold could be left in deep holes, where current can't reach. But it goes fine in between the copper mesh, so i expect it will work fine. No idea what the dimensions are of your part. It may not matter. The current looks for the path of least resistance= gold. 
You could try one piece at a time on an alligator clip or in a copper basket. 

Copper is insoluble in concentrated sulfuric acid. So perfect to inspect the surface of the copper. 
Interesting application.
Let us know if you were succesfull please.


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## Martijn (Mar 23, 2022)

Voltage: if you can set a current limit to one amp, it will keep the voltage to the needed level. I would avoid currents over 2 or 3 amps. Just a gut feeling, not scientific.


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## Reachingout68 (Mar 23, 2022)

Martijn said:


> Then the sulfuric cell is a good option.
> I believe it was initially used to remove plating from items before replating them.
> 
> I am not sure if any gold could be left in deep holes, where current can't reach. But it goes fine in between the copper mesh, so i expect it will work fine. No idea what the dimensions are of your part. It may not matter. The current looks for the path of least resistance= gold.
> ...


Here is what the piece looks like, dimensions are about 20mm long and 3mm wide/tall , I will probably hold it with copper wire and have the alligator clips attach to that. I will try and get this done in the next few days so hopefully I will update by next week at the latest.


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## Swissgoldrefiner (Mar 23, 2022)

Nice video!


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## Reachingout68 (Mar 28, 2022)

Martijn said:


> Then the sulfuric cell is a good option.
> I believe it was initially used to remove plating from items before replating them.
> 
> I am not sure if any gold could be left in deep holes, where current can't reach. But it goes fine in between the copper mesh, so i expect it will work fine. No idea what the dimensions are of your part. It may not matter. The current looks for the path of least resistance= gold.
> ...



Hello Martijn, I was successful in removing the gold off of the first half, although a black soot like material remained, I will probably try on the second half the same procedure but a lower voltage. On this piece I cranked it up to 30 Volts and it maxed out at 200mA and quickly went down, this process lasted 30 seconds. I dipped my copper in Ammonium persulfate and will dip it in HF to see if it removes the black material. Also I tried the same procedure on a glass slide that had titanium sputtered and gold sputtered and copper electroplated, the copper electroplating was not successful but trying this experiment removed whatever was on the surface and made the copper show through, indicating that copper had indeed been electroplated but that it had a strange reaction with the gold. A before and after is at the bottom of the images.


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## Yggdrasil (Mar 28, 2022)

Are you sure the black soot like stuff are not remnants from organics the sulfuric acid has destroyed?
Was the part completely free from finger fat, machining oils or waxes?


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## Reachingout68 (Mar 28, 2022)

Yggdrasil said:


> Are you sure the black soot like stuff are not remnants from organics the sulfuric acid has destroyed?
> Was the part completely free from finger fat, machining oils or waxes?


To be honest no I am not sure I did not bother cleaning the part beforehand, however with that being said wouldn't the black soot be easy to remove?


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## Yggdrasil (Mar 28, 2022)

Reachingout68 said:


> To be honest no I am not sure I did not bother cleaning the part beforehand, however with that being said wouldn't the black soot be easy to remove?


I wouldn't know, but this kind of things usually finds their way into all kind of pores and crevasses. What did you use to split it?
Powered tool with lubrication?


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## Martijn (Mar 29, 2022)

The gold comes off as a fine black soot. It may get stuck in the microscopic copper surface grains and can be hard to clean off completely. 
Did you try to wash it off?


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## Reachingout68 (Mar 29, 2022)

Martijn said:


> The gold comes off as a fine black soot. It may get stuck in the microscopic copper surface grains and can be hard to clean off completely.
> Did you try to wash it off?


I sonicated it in acetone for 5 minutes right after the electrolysis, not much seemed to wipe off after rinsing in DI water, I then dipped it in ammonium persulfate for 5 minutes and other than making the copper a little shinier did not seem to do much. I left it in HF 50% over night and am sonicating it now in Acetone more vigorously for 30 minutes.


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## Reachingout68 (Mar 29, 2022)

Yggdrasil said:


> I wouldn't know, but this kind of things usually finds their way into all kind of pores and crevasses. What did you use to split it?
> Powered tool with lubrication?


I used a saw with running water that's used to dice glass , I wish I had a better tool for it. When I did that I did clean it afterwards and used gold etch on the half that you see here, after that failed to remove the gold I cleaned it with acetone and 50% HF due to oxidation of copper and put it away for the time being until I did electrolysis, I may have handled it without gloves at some point.


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## Maget (May 4, 2022)

I wonder if is possible to make in such a way so the gold plating will stick directly to a gold wire, leaving behind the base metal.
Maybe to do it directly in Aqua Regia and avoid all the processes, sorry if this sound stupid but I m just beginner and trying to understand if easier methods are available to extract Gold or other precious metals which are bound with cheaper metals.


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## Martijn (May 5, 2022)

Maget said:


> I wonder if is possible to make in such a way so the gold plating will stick directly to a gold wire, leaving behind the base metal.
> Maybe to do it directly in Aqua Regia and avoid all the processes, sorry if this sound stupid but I m just beginner and trying to understand if easier methods are available to extract Gold or other precious metals which are bound with cheaper metals.


I don't think so.


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## Maget (May 5, 2022)

Martijn said:


> I don't think so.


Similar to electroplating process I think maybe possible to reverse this somehow.
Anyway if it does not exist, maybe it will be discovered sooner or later.


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## Martijn (May 5, 2022)

You will need an electrolyte that will selectively dissolve gold at the anode and nothing else. 
Most electroplating is done with a solution already containing the metal salt and an inert anode. 
Electrorefining needs an almost pure anode to work. Wohlwill process its called i believe. 
Great idea, but in the realm of time travel imo.

Martijn.


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