# Reverse electroplating gold of copper base



## Prospectorbob (Jun 14, 2022)

Copper items dipped in 24k gold. I am getting set up to reverse electroplate them in sulphuric acid, will my 12v 4amp battery charger do the job, or should I have a controller for the current. Waiting for parts for the fume hood, so I have time to get other things right. I did think of just going straight to AR but the gold is testing as 24K on these first items. All advice appreciated


----------



## Lino1406 (Jun 14, 2022)

Prospectorbob said:


> Copper items dipped in 24k gold. I am getting set up to reverse electroplate them in sulphuric acid, will my 12v 4amp battery charger do the job, or should I have a controller for the current. Waiting for parts for the fume hood, so I have time to get other things right. I did think of just going straight to AR but the gold is testing as 24K on these first items. All advice appreciated


In order to get purer gold you have to optimize voltage according to bath resistance




Prospectorbob said:


> Copper items dipped in 24k gold. I am getting set up to reverse electroplate them in sulphuric acid, will my 12v 4amp battery charger do the job, or should I have a controller for the current. Waiting for parts for the fume hood, so I have time to get other things right. I did think of just going straight to AR but the gold is testing as 24K on these first items. All advice appreciated


----------



## Prospectorbob (Jun 14, 2022)

Thanks Ki, I will aquire a digital voltage regulator to give me control


----------



## Martijn (Jun 14, 2022)

Sulfuric acid is a very bad conductor. As long as there is gold on the copper to be stripped and there is good contact between the pins there will be a current. 
Depending on the size of your cathode and anode basket, I think 12 V will do just fine. Check the temerature often with a simple laser thermometer. Keep it below 50 degrees C. 
Have an ampmeter in series to see when the current drops to zero. That's when all gold is stripped. Don't bother chasing the tiny spots leftover on the copper, it is much less than you think. 
My stripping video is in this post: 








Sulfuric stripping gold plating video


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...




goldrefiningforum.com




Martijn.


----------



## Shark (Jun 14, 2022)

I think the meaning of Ki that Lino posted means potassium iodide. It is used to strip gold plate as well and does not use sulfuric acid.


----------



## Prospectorbob (Jun 14, 2022)

Martijn said:


> Sulfuric acid is a very bad conductor. As long as there is gold on the copper to be stripped and there is good contact between the pins there will be a current.
> Depending on the size of your cathode and anode basket, I think 12 V will do just fine. Check the temerature often with a simple laser thermometer. Keep it below 50 degrees C.
> Have an ampmeter in series to see when the current drops to zero. That's when all gold is stripped. Don't bother chasing the tiny spots leftover on the copper, it is much less than you think.
> My stripping video is in this post:
> ...


Thanks Martin, I will put up my results when done.


----------



## Prospectorbob (Jun 14, 2022)

Shark said:


> I think the meaning of Ki that Lino posted means potassium iodide. It is used to strip gold plate as well and does not use sulfuric acid.


Thanks Shark, I missed that.I’ll look into potassium iodide


----------



## Prospectorbob (Jun 14, 2022)

Lino1406 said:


> In order to get purer gold you have to optimize voltage according to bath resistance
> 
> 
> 
> Ki


Haha!! Lino, I though you were signing off with Ki, but now I know it’s potassium iodine so I’ll look into it Thanks


----------



## Lino1406 (Jun 14, 2022)

No, ki is a pen error, I try to delete, what becomes harder lately


----------



## Shark (Jun 14, 2022)

Seems we all made a mistake.


----------



## olawlor (Jun 15, 2022)

Normally a 12V battery charger is too many volts and not enough control for decent plating work, where a lab power supply is preferred. But "reverse electroplating" is just electrically carpet bombing all the base metals off the anode, freeing the gold, so a battery charger should work fine. 

Be ready for the charger to overheat, I've had them catch fire on a short. The anode bubbles can also throw up a fine acid mist laden with heavy metal ions, so I'd use a good fume hood setup, or a secondary container.


----------



## Geo (Jun 15, 2022)

Not trying to nit pick but technically, there is no such thing as reverse electroplating. It is stripping. An electrolytic stripping cell. A voltage regulator is very easy. You can actually run the current through a trim pot or low current potentiometer. A trim pot will need to be adjusted with a tool, like a screw driver, where a potentiometer will normally have some sort of knob depending on the current load. You can buy both amp meter and volt meter on ebay for a few dollars. A power supply out of any desktop PC has 3v, 5v and 12v output. Put a 10 ohm resistor on any yellow wire and black wire to simulate a load so the switching power supply stays "on". I use them as I need them. Anyone that scraps PC's should have a few just laying around handy.


----------



## Prospectorbob (Jun 16, 2022)

Geo said:


> Not trying to nit pick but technically, there is no such thing as reverse electroplating. It is stripping. An electrolytic stripping cell. A voltage regulator is very easy. You can actually run the current through a trim pot or low current potentiometer. A trim pot will need to be adjusted with a tool, like a screw driver, where a potentiometer will normally have some sort of knob depending on the current load. You can buy both amp meter and volt meter on ebay for a few dollars. A power supply out of any desktop PC has 3v, 5v and 12v output. Put a 10 ohm resistor on any yellow wire and black wire to simulate a load so the switching power supply stays "on". I use them as I need them. Anyone that scraps PC's should have a few just laying around handy.


Hi Geo, thanks for your input. My understanding of ‘stripping‘ in the electrolysis of metals industry is the process of removing the refined metal from a Cathode, usually in a sheet form. I suppose reverse electroplating might not be the right term but I’m not sure ‘stripping‘ fits the description either. I have googled it and some answers are definitely not correct but that’s all ok and I mean no offence in this reply to you. I have purchased a DC- DC adjustable step-down module amd installed it on the output side of the 12v 4amp old style battery charger, then run the positive lead through a digital metre and connected it to a 6v torch globe. Switched it on and adjusted the volts on the step down to 3v, and whammy, all good to go. I won’t know what the amps will be until I connect up in the cell. The battery charge have overload protection so I’m not sure yet whether I need anything else in the lines. I guess I’ll know soon. Cheers


----------



## Geo (Jun 16, 2022)

Stripping is a relative term. It can describe several actions. Physical, chemical, electro-chemical. It usually has another descriptor to narrow down the true meaning. Electronic stripping cell is an electro-chemical term. It involves using an electrolytic stripping where a current is applied to the work piece or anode. The current passes through the electrolyte completing the circuit. Since the electrolyte is sulfuric acid, The electrons leaving the anode generates oxygen at the anode with the current forcing the splitting of water molecules with the oxygen combining with the sulfuric acid creating a very small amount of persulfuric acid on the surface of the anode. Gold is dissolved by this minute amount of persulfuric acid and is carried away from the anode with the electron flow. This species of persulfuric acid is short lived and decomposes about as fast as it is generated. Sulfuric acid can not hold gold in a liquid form and so as the persulfuric acid decomposes, the gold falls out of solution as fine metallic particles. In this way, the gold is stripped from the work piece on the side facing the cathode and deposited as a black metal powder on the bottom of the cell. The electrolyte has to be concentrated sulfuric acid.


----------



## Geo (Jun 16, 2022)

You may have used the wrong term in your search.





US4242192A - Electrolytic stripping cell - Google Patents


An electrolytic stripping cell is provided which is particularly adapted for use in processing shredded, silver brazed, stainless steel honeycomb scrap. The cell comprises a mesh anode basket which rotates within a cathode cylinder to provide partial stirring of the cell electrolyte. The anode...



patents.google.com


----------



## Geo (Jun 16, 2022)

Electrolytic Stripping – a “Greener” Alternative to Immersion Stripping | Specialty Chemical Finishing Products


We provide specialty chemical finishing products for pre-treatment, powder coating and plating.




asterionstc.com


----------



## Prospectorbob (Jun 16, 2022)

Geo said:


> Stripping is a relative term. It can describe several actions. Physical, chemical, electro-chemical. It usually has another descriptor to narrow down the true meaning. Electronic stripping cell is an electro-chemical term. It involves using an electrolytic stripping where a current is applied to the work piece or anode. The current passes through the electrolyte completing the circuit. Since the electrolyte is sulfuric acid, The electrons leaving the anode generates oxygen at the anode with the current forcing the splitting of water molecules with the oxygen combining with the sulfuric acid creating a very small amount of persulfuric acid on the surface of the anode. Gold is dissolved by this minute amount of persulfuric acid and is carried away from the anode with the electron flow. This species of persulfuric acid is short lived and decomposes about as fast as it is generated. Sulfuric acid can not hold gold in a liquid form and so as the persulfuric acid decomposes, the gold falls out of solution as fine metallic particles. In this way, the gold is stripped from the work piece on the side facing the cathode and deposited as a black metal powder on the bottom of the cell. The electrolyte has to be concentrated sulfuric acid.


Thanks again Geo, that makes complete sense and adds to my education.I really appreciate the time you have put into answering. This is a great forum and I am sure I will be able to fine tune my metallurgy journey with this type of help. Again, Thank you. Regards, Bob


----------



## willworld.whr (Jun 17, 2022)

So curious what would happen if sulfuric was replaced with salt water?


Geo said:


> Stripping is a relative term. It can describe several actions. Physical, chemical, electro-chemical. It usually has another descriptor to narrow down the true meaning. Electronic stripping cell is an electro-chemical term. It involves using an electrolytic stripping where a current is applied to the work piece or anode. The current passes through the electrolyte completing the circuit. Since the electrolyte is sulfuric acid, The electrons leaving the anode generates oxygen at the anode with the current forcing the splitting of water molecules with the oxygen combining with the sulfuric acid creating a very small amount of persulfuric acid on the surface of the anode. Gold is dissolved by this minute amount of persulfuric acid and is carried away from the anode with the electron flow. This species of persulfuric acid is short lived and decomposes about as fast as it is generated. Sulfuric acid can not hold gold in a liquid form and so as the persulfuric acid decomposes, the gold falls out of solution as fine metallic particles. In this way, the gold is stripped from the work piece on the side facing the cathode and deposited as a black metal powder on the bottom of the cell. The electrolyte has to be concentrated sulfuric acid.


As


----------



## Geo (Jun 17, 2022)

It would form chlorine gas in solution and start dissolving base metal. After the chlorine is liberated, it will start forming hydroxide next.


----------



## willworld.whr (Jun 17, 2022)

So curious what would happen if sulfuric was replaced with salt water?


Geo said:


> Stripping is a relative term. It can describe several actions. Physical, chemical, electro-chemical. It usually has another descriptor to narrow down the true meaning. Electronic stripping cell is an electro-chemical term. It involves using an electrolytic stripping where a current is applied to the work piece or anode. The current passes through the electrolyte completing the circuit. Since the electrolyte is sulfuric acid, The electrons leaving the anode generates oxygen at the anode with the current forcing the splitting of water molecules with the oxygen combining with the sulfuric acid creating a very small amount of persulfuric acid on the surface of the anode. Gold is dissolved by this minute amount of persulfuric acid and is carried away from the anode with the electron flow. This species of persulfuric acid is short lived and decomposes about as fast as it is generated. Sulfuric acid can not hold gold in a liquid form and so as the persulfuric acid decomposes, the gold falls out of solution as fine metallic particles. In this way, the gold is stripped from the work piece on the side facing the cathode and deposited as a black metal powder on the bottom of the cell. The electrolyte has to be concentrated sulfuric acid.


As


Geo said:


> It would form chlorine gas in solution and start dissolving base metal. After the chlorine is liberated, it will start forming hydroxide next.


So capturing gold through electrolyte solution of salt water is possible but leaves you with base metals to separate mixed with your gold, correct?


Geo said:


> It would form chlorine gas in solution and start dissolving base metal. After the chlorine is liberated, it will start forming hydroxide next.


----------



## Shark (Jun 17, 2022)

Saltwater requires a much higher consumption of electricity. It results in a very fluffy precipitate that quickly fills the cell and when cleaned up results in a very tiny amount of gold compared to the original volume. The use of larger amounts of amps also causes faster dissolution of the base metals. Saltwater has its own set of problems that may not be any easier to deal with over sulfuric. Sulfuric can be “cleaned up” and reused, salt water I’m not sure about. The attempts I have tried also seems that saltwater reaches a point that it stops working. I still have not figured out why or what causes it.


----------



## Geo (Jun 17, 2022)

If you continue the process to completion, you will wind up with a huge amount of oxides and hydroxides with loose foils mixed in.


----------



## Shark (Jun 17, 2022)

Geo said:


> If you continue the process to completion, you will wind up with a huge amount of oxides and hydroxides with loose foils mixed in.


This would explain the foils I noticed near the end, or as I call it "when the the problems" started adding up quicker. Gold started to strip slower, unevenly, then I started to notice a few foils and called it done. I might try it again one day, but only when I can not get sulfuric to work with.


----------



## willworld.whr (Jun 19, 2022)

Okay yeah your expierence sounds about the same as mine. Oxides and hydroxides , are they what caused the orange reddish Color of the mud left behind Or is this from the impure copper anode I used?


----------



## willworld.whr (Jun 19, 2022)

Picture of mud


----------



## olawlor (Jun 19, 2022)

I get orange mud in my solutions anytime there's some Fe(III) contamination, like from using steel utensils in acid, or springs in jewelry clasps.

Fe(III) is soluble in acidic solution but vividly red; as you raise to around pH 2-5 it precipitates as an annoyingly fluffy orange mud or gel.

(But color is only one clue of many for identifying chemical composition.)


----------



## Geo (Jun 19, 2022)

willworld.whr said:


> Okay yeah your expierence sounds about the same as mine. Oxides and hydroxides , are they what caused the orange reddish Color of the mud left behind Or is this from the impure copper anode I used?


Yes. Acidifying the mass will dissolve it into solution.


----------



## willworld.whr (Jun 20, 2022)

Yes I have another batch of gold plated pieces ready to go. Im going to try this reverse electroplating with sulfuric acid this time. What would be best to use for my anode and cathode this time or what would be best to use??? I was using pure lead for cathode and impure copper for anode before with salt water.


----------



## Yggdrasil (Jun 20, 2022)

Lead and Copper is fine in concentrated Sulfuric.


----------



## Prospectorbob (Jun 21, 2022)

Here is an update on the copper dipped in 24k gold ‘stripping’.
The battery charger and step down module didn’t seem as bright an idea as I first thought, to fiddly to control. Instead, I cut the supply end off a USB cord and attached red and black wires with copper spring clamps. Then plugged into the USB port on my 100 Amp Hr deep cycle battery. Installed a lead plate cathode hanging in Pyrex container and a copper basket anode. Slow going, so I removed the basket and just used the the clamp to hold each piece and dipped it in half way and then turned the piece around and dipped the other half. I don’t know what amps it was running but it would start drawing 5.25 volts and quickly dropped to 2.5 to 3 and the copper was bare. I started with 22.37 grams and the copper remaining is 15.81 grams, so hopefully, I have 6.56 grams of gold in the sulphuric acid. Now wash and melt and see how it goes


----------



## willworld.whr (Jun 22, 2022)

Would like to know what you end up with prospector Bob when it's all done!


----------



## Prospectorbob (Jun 22, 2022)

willworld.whr said:


> Would like to know what you end up with prospector Bob when it's all done!


Just waiting for a bit more settlement in the acid. I should Have a button on the weekend


----------



## Prospectorbob (Jun 22, 2022)

willworld.whr said:


> Yes I have another batch of gold plated pieces ready to go. Im going to try this reverse electroplating with sulfuric acid this time. What would be best to use for my anode and cathode this time or what would be best to use??? I was using pure lead for cathode and impure copper for anode before with salt water.


For the cathode, I used a lead plate out of a sealed gel acid motor cycle battery and attached a very strong spring clamp. It was fairly thin but 3 x 2 inch rectangle. it developed a slight coating of the black/brown dust on the side facing the anode, but when I bumped it, the dust dropped off and joined the rest on the bottom of the container.


----------



## Prospectorbob (Jun 23, 2022)

Well, I have some black powder, but the sulphuric acid is very dark yellow/green without any sediment that I can see. The first rinse water of the powder is a pale blue, so do I have copper in solution. The acid didn’t get hot but while I was playing with the battery, the cell did get a 10 second burst of 12+ volts before I changed to 5v. So what should I do next to clear the acid and maybe find some more gold as well as copper. 
The first photo has a torch light behind it as it is very dark.


----------

