AP on my way

[VolkD]

I am amateurly extracting gold from gold-plated telecommunications printed circuits. First I remove all the elements and get only the printed circuit board, which is gold-plated. There is solder over most of the pads.I am doing the AP process, using CuCl. So no peroxide. I work outside and do not heat the solution (15 -20°C). I blow air in with an aquarium pump.I have an idea to add sodium persulfate as an additional oxidant. At the same time I would heat it to about 40 °C.I think this would speed up the process a lot. What do you think about it?

 

[Yggdrasil]

I am amateurly extracting gold from gold-plated telecommunications printed circuits. First I remove all the elements and get only the printed circuit board, which is gold-plated. There is solder over most of the pads.I am doing the AP process, using CuCl. So no peroxide. I work outside and do not heat the solution (15 -20°C). I blow air in with an aquarium pump.I have an idea to add sodium persulfate as an additional oxidant. At the same time I would heat it to about 40 °C.I think this would speed up the process a lot. What do you think about it?

I really do not know how the Persulfate will behave with together with the HCl.
If might be strong enough to dissolve the Gold.
And that is not what we want.
Why do you want to add something to the AP?
Why not just heat it?

 

[4metals]

Welcome to the forum. As I am sure you are aware sodium persulfate is the preferred etchant for printed circuit manufacture. And it conveniently produces a solution where copper can be recovered. But that is in a solution where copper is masked and only exposed copper dissolves and there are no other metals dissolving. With scrap you are entering a different barn yard, full of other metals and solder that can interfere. Plus the Hydrochloric Acid will effect the reaction. I do not know of any commercial refiners using persulfate so it likely will not speed up the releasing of the foils to the point where you will get a lot of benefit because you are still etching copper covered by gold so speeding that up may be enhanced by agitation or temperature and not necessarily with a new oxidant.

But if you have the chemicals you can compare copper chloride with air to water and sodium persulfate and you may discover an alternate pathway.

 

[VolkD]

Sodium persulfate is a fairly strong oxidizer, but still not as strong as peroxide. It does not attack gold together with hydrochloric acid. Of course, I will heat the solution, but an appropriate amount of sodium persulfate will provide additional oxidation, since I think that introducing air (oxygen) with an aquarium pump is not effective enough. Sodium persulfate releases sulfate radicals (SO4•−SO4•−), which oxidize copper and CuCl back to CuCl₂:Cu+Na2S2O8→Cu2++2Na++2SO42−Cu+Na2S2O8→Cu2++2Na++2SO42−2CuCl+Na2S2O8→2CuCl2+2Na++2SO42−2CuCl+Na2S2O8→2CuCl2+2Na++2SO42−This means that sodium persulfate regenerates CuCl₂ faster, even if the aeration is not complete.

 

[VolkD]

But if you have the chemicals you can compare copper chloride with air to water and sodium persulfate and you may discover an alternate pathway.

Tnx...

Sodium persulfate corrodes copper (printed circuit board industry) Interestingly, it is very selective only for copper. For these reactions, approximately 200g of sodium persulfate per 1l of water is needed. In my case, I do not want to etch copper, but rather accelerate oxidation. I think that 10g of sodium persulfate on 1 l (calculated via mmol) would be enough.

I expect a reaction time of up to 6 hours.

 

[4metals]

Unless someone else has experience here, you are in the land of experimental chemistry. I do not have any experience adding the persulfate oxidizer to Hydrochloric Acid.

 

[VolkD]

Unless someone else has experience here, you are in the land of experimental chemistry. I do not have any experience adding the persulfate oxidizer to Hydrochloric Acid.

I'll try it, I'll report back!

 

[4metals]

Thank you, we appreciate it. You may become the resident persulfate expert.

 

[haveagojoe]

Very interesting proposal.
I think it would be a good idea to remove the solder first with a pre-soak in HCl, otherwise you'll get SnO₂ sludge mixed with the foils.

 

[4metals]

I think it would be a good idea to remove the solder first with a pre-soak in HCl,

Getting complicated. Hydrochloric Acid and air bubbles is pretty simple.

 

[haveagojoe]

Getting complicated. Hydrochloric Acid and air bubbles is pretty simple.

I believe it's good practice to remove tin solder first with HCl anyway when doing Copper Chloride etching the normal way (with an air bubbler), as SnO₂ can be stubborn to deal with, since it's not soluble in HCl or other common acids. The whitish precipitate looks similar to copper (i) chloride but won't redissolve in fresh HCl.

However I am reading that Tin Oxide can be converted to soluble Tin (ii) Chloride by reduction using Zinc metal powder. This could be a way to separate it from the foils in a post-etch cleanup of the foils with fresh HCl.

Edit: To preserve clarity and avoid hijacking this thread, I have moved my comments regarding reduction of Tin Oxide with Zinc to a separate thread with my experiment writeup, here: https://goldrefiningforum.com/threa...per-chloride-etches-experiment-writeup.35821/

 

[Shark]

If you have the same mix of metals in a button that is found in all metals from a dirty board stripped in AP, how would you deal with it?

This isn't a complicated question at all and it isn't meant to be. Simply put, we refine it. This is why we study so much, to understand what we have in the mix and how to separate it from our sought after metal. Of all the boards I ran through AP I never once cleaned them prior to putting them in the copper II chloride solution. I used heat to strip components later and early on I used manual tools to remove them. I found it easier and quicker to deal with in the refining stages and the only times it posed problems was when PGM's were involved. Even then those problems were due to me not realizing that a (or multiple) PGM was involved.

 

[haveagojoe]

My understanding has been that it's easier to eliminate Tin at the first stage rather than risk creating metastannic acid later on. Since OP mentioned that the boards have solder on the pads, a HCl presoak was seems like a cheap and easy way to avoid complications and that's how I do it currently for boards unless I'm running reasonably clean fingers-type material. Perhaps it's not necessary and I will certainly bow to experience, but the presoak acid can be reused many times so I don't really see the harm.

I only just came across the idea of using Zinc, I'm considering it for a current batch of foils I have which have some tin oxide mixed with them as they came from material which included bronze.

 

[Shark]

Another option is a lead bath. A quick dip and the solder melts and stays mainly with the bath. Better known as a desoldering station, they are used by some companies to remove components from boards, often experimental boards, so the board or components, can be reused. Another advantage is the solder on some boards contain silver and it can be reclaimed as it builds up in the bath. I haven't looked in a long time, but they used be available online for a reasonable price. They do require precise heat control in order to not damage the parts or the board.

 

[Shark]

Something like this from Amazon.

Desoldering bath

 

[VolkD]

Very interesting proposal.
I think it would be a good idea to remove the solder first with a pre-soak in HCl, otherwise you'll get SnO2 sludge mixed with the foils.

I have printed circuit boards that are gold-plated but not yet soldered - a leftover from production.

 

[VolkD]

I took 500ml of hydrochloric acid, 100ml of (old) copper chloride, heated it to about 50°C and added air blowing. I added gold-plated printed circuits (without solder). Immediately afterwards I added 30g of sodium persulfate.It is not wise to inhale hot acid, so I moved away - I work outdoors. After exactly 40 minutes I went to check. I was very surprised, because I noticed that gold leaves were floating in the solution.I think it will be fine, although most of the gold is still on the printed circuits.I filtered the liquid as a precaution. What was left in the filter is now definitely mine
Maybe I am overdoing the heating and maybe I added too much sodium persulfate. I will have to investigate.

 

[VolkD]

I'm new here, I have some photos, how do I add them to the text?

 

[haveagojoe]

I took 500ml of hydrochloric acid, 100ml of (old) copper chloride, heated it to about 50°C and added air blowing. I added gold-plated printed circuits (without solder). Immediately afterwards I added 30g of sodium persulfate.It is not wise to inhale hot acid, so I moved away - I work outdoors. After exactly 40 minutes I went to check. I was very surprised, because I noticed that gold leaves were floating in the solution.I think it will be fine, although most of the gold is still on the printed circuits.I filtered the liquid as a precaution. What was left in the filter is now definitely mine
Maybe I am overdoing the heating and maybe I added too much sodium persulfate. I will have to investigate.

Nice work! This could be a great improvement to our process. Perhaps it can be done cold?

I'm new here, I have some photos, how do I add them to the text?

There's an icon above the text box to Insert Image or press Ctrl+P

 

[Yggdrasil]

I'm new here, I have some photos, how do I add them to the text?

You could just paste it or use this "button"