AP on my way

[VolkD]

I would be really interested to see how it works cold with no bubbler and just occasional stirring by hand, by comparison to your current setup.

This is my first attempt, I will definitely try it without the bubbles. I have an idea for a double container, the inner plastic one will hold the printed circuit boards, and there will be a place for magnetic stirring under it. It will be for an experiment, but for anything more it is too complicated.
Both the bubbles and the sodium persulfate contribute to oxidation. The bubbles of course mix the solution which is essential, since I just shook the powder (persulfate) into the container and it needs to be distributed as evenly as possible. But the sodium persulfate definitely contributed to a larger portion of the oxidation.

 

[VolkD]

It seems more like the original approach of "AP", but we could never add that much peroxide without dissolving the gold as well.

The combination of hydrochloric acid and sodium persulfate does not dissolve gold. Tested and proven. Not even 300g/l sodium persulfate + hydrochloric acid 30% dissolve gold.

Hint: ask chatgpt

 

[haveagojoe]

The combination of hydrochloric acid and sodium persulfate does not dissolve gold.

Yes, for me that's what makes your approach so interesting. Potentially it could be completely passive, without heating or even a bubbler, but with a big enough amount of persulfate to carry the etch through to completion in a reasonable timeframe.

 

[VolkD]

4 hours later...

The PCBs are now free of gold plating (at least I think so). I took the PCBs out and put them in a glass container. What's left is going to be filtered.

 

[VolkD]

This looks promising, but you need to know that these foils are really, really thin.
What excites me is that filtering is not a nightmare, but it goes very nicely and quickly.

 

[Yggdrasil]

4 hours later...

The PCBs are now free of gold plating (at least I think so). I took the PCBs out and put them in a glass container. What's left is going to be filtered.
View attachment 67314

Can the Persulfate be rejuvenated?
Or are it consumed?

 

[VolkD]

This is what's left of 100g of sodium persulfate. I didn't weigh it, I estimated that I used a little more than half, 60g. I added it based on the color of the solution. I could probably use less and get the same good result. I'm comforted that it's left in the solution and I'll use it tomorrow when I do the next experiment.

 

[VolkD]

Can the Persulfate be rejuvenated?
Or are it consumed?

Persulfate is consumed during oxidation. If there is too much of it and there is no substance to oxidize, it remains in solution.

 

[VolkD]

These are the printed circuit boards that I pulled out of the liquid. You can see that there are still gold flakes in many places. I hope it will be possible to collect them.

 

[VolkD]

I used a water jet to separate the gold foil from the printed circuit boards.Note, I have a latex glove on my left hand, my right hand is not in danger, as it is only holding the syringe.
I put the cleaned printed circuit boards in another container. When I run out of them, I have a container with water and flakes. I simply pour everything into a beaker and wait for the gold to fall to the bottom.

 

[VolkD]

I was sure that the printed circuit boards had been in the solution long enough, or that the bubbles had moved the boards well enough. I was wrong. The photo shows five boards with the gold coating still on them It's nothing serious, I'll add it to the next batch. But it's good to know that something was right on the border.

 

[haveagojoe]

Wow yea 4 hours is turbo speed for Copper Chloride etching. Amazing!

 

[VolkD]

For now I have a few more printed circuits that are gold-plated but not soldered. Later comes a more difficult task - I have a lot of printed circuits that are gold-plated but unfortunately are soldered. I removed the electronic elements from these circuits with hot air (my other hobby is electronics). But I tried very hard to remove as much solder as possible. Not everything can be removed.So far I have not developed an idea how to remove solder chemically.

 

[VolkD]

Wow yea 4 hours is turbo speed for Copper Chloride etching. Amazing!

Well, I don't know if it's exactly 4, but all the photos have the full exif and it's possible to determine the exact date of creation (the location is also visible).

 

[haveagojoe]

to remove solder chemically

As I suggested above, a cold HCl soak will do it nicely. Just don't leave it too long or it will start to eat copper and form CuCl₂, and then start releasing foils before you're ready.

 

[VolkD]

...it posed problems was when PGM's were involved.

What is PGM?

 

[VolkD]

As I suggested above, a cold HCl soak will do it nicely. Just don't leave it too long or it will start to eat copper and form CuCl₂, and then start releasing foils before you're ready.

So you're suggesting I have one container in which I'll remove the solder and then another working one for quickly removing the copper?
That would ensure fewer problems with filtering.

 

[FrugalRefiner]

The combination of hydrochloric acid and sodium persulfate does not dissolve gold. Tested and proven. Not even 300g/l sodium persulfate + hydrochloric acid 30% dissolve gold.

Hint: ask chatgpt

I find that dubious.

First, I would never rely on chargpt for my refining information. It will probably also tell you that HCl alone will not dissolve gold. While that is technically true, the oxygen in the air will dissolve into HCl and act as an oxidizer, which WILL slowly dissolve gold. That's not a statement based on a chat bot. It's real life experience.

Since you're doing all this as an experiment, may I suggest you take some of the bits of gold foils you recover and put them in some fresh HCl and add some fresh persulfate. Let us know how that turns out after soaking it for a couple of days.

Dave

 

[Yggdrasil]

What is PGM?

Platinum Group Metals

 

[haveagojoe]

So you're suggesting I have one container in which I'll remove the solder and then another working one for quickly removing the copper?

Yea. If the solder-removing bath starts to go green, change it to fresh acid as it's starting to form CuCl₂. You just want HCl for the solder; if you keep copper out of it, it can be reused many times.

Edit to add: The cold soak will not be able to keep up the pace with your turbo etching though! I have never tried it hot, I imagine it would work fine but getting the timing right would be more difficult