Gold plated pins in aqua regia

[Marcel]

Recently a thread was started by a member using sodium persulfate on plated pins. It seems much faster than the AP method and will not dissolve as much base metal as aqua regia (easier to treat the waste). Since you have 75 pounds it may be useful to check out this thread

I am currently doing some experiments with the objective to find good, cheap and safe alternatives for the usage of nitric acid.
Right now comparing Copper Sulfate and Sodium Persulfate. Both just as an etchant and electrolysis, with special regard to pins and other electronic mechanical as well as semiconductors material mix, which we usually have.

I am not through with it yet, but they might be a viable alternative. But all have their Pros and Cons. Anybody interested in the findings, sub my YT channel at: https://www.youtube.com/@adrenalinemedia/videos (if you have not done already) . I will publish the findings, numbers and "secret" recipes from next week on. (It may be several parts because I really filmed a lot and will reveal how effective that has been)

All in all, in this case here an electrolysis in Sodium persulfat may have worked out, It works like a strong AP, etching the Copper and Nickel underneath the Gold. May run for around 2-3 hours (should be checked for progress every 15 minutes or so.) Once the Gold has been seperated from the main body, the pins need to be removed. No Anode basket required, only copper and Gold in the slimes that falls to bottom. Can be seperated later with HCl.


Copper Sulfate Electrolysis. 3D printed special anode basket. (Image from my upcoming YT video)



Etching with Sodium Persulfate. 3D printed special anode basket. (Image from my upcoming YT video)

I know it nerves, to ask for subscription, likes, comments and so on, forgive me that, but I want to revive my old YT channel where I posted recovery videos more than 10 years ago, but due to the new algorithms it needs new subscribers and likes to be displayed in the search and suggestions. So therefore, support me and support yourself, so you will not miss my new findings. And yes I am also very busy with the 3D printing and AI tech. But my experience with those technologies will both be used in my new recovery videos as well, so they serve as great tools for me.

 

[Marcel]

I have about 75 pounds of these pins, and I didn't pay a whole lot for them. I'm just trying to find which process works best for me with small batches.

Based on the calculations before (I assumed a diameter of 5 mm and a lenght of 10 mm, if you wnat better numbers give me the average diameter and lenght of each pin), this is the derived yield calculation, for what you can expect (0.05 ym plating):

Estimated Gold Yield for 75 Pounds of Thick Pins​

• Weight: 75 pounds = 34,019 grams
• Gold content (for thick pins, 0.05 µm plating): 0.108 g per kg
• Total gold yield estimate:

(34,019 g/1000)×0.108≈3.67 g of gold(34,019 \text{ g} / 1000) \times 0.108 \approx 3.67 \text{ g of gold}
So from 75 pounds of thick pins, you can expect around 3.67 grams of gold under ideal conditions.

 

[Marcel]

That works for copper-based pins but not so much with kovar and other types. Dilute Nitric acid would do it, but I reckon a Sulfuric cell would be the way to go with these if there are a lot of them.

Edit- Copper Chloride etching can work to release foils from pins if they have a Copper or Nickel layer under the gold plate, I've found that Hydrogen Peroxide can give it a bit of a boost to release the foils quickly before the acid starts to attack the substrate and gets messed up with the other metals. I wouldn't normally add peroxide but when there is a lot of base metal substrate it can help. Sometimes though the plate just refuses to budge, I guess where it's plated directly onto Stainless etc.

Just a tiny bit too much peroxide, and you end up with colloidal Gold (which gives a very nice purple color in solution), while all values are cemented out. You never really know when “too much” is too much. I dissolves finely dispersed Gold in the blink of an eye, turning the entire process into an unresolvable messy mystery. (Typical forum topic: “HELP!!! All my Gold is gone—how can I get it back?”, text "I found this great forum here with all you wonderful, experienced and helpful people. I read Hoke and like in a video I watched, added just a tiny bit of Peroxide to my solution......" )

Because of the geometry of the pins and the fact that the underlying copper/brass is in a huge excess, it is very likely that fine Gold particles will be dissolved by the peroxide and then cement out on the remaining body of the pins as a super-thin black coating.

 

[haveagojoe]

Just a tiny bit too much peroxide, and you end up with colloidal Gold (a very nice purple color), while all values are cemented out. You never really know when “too much” is too much—once it dissolves, the Gold can become finely dispersed in the blink of an eye, turning the entire process into an unresolvable mystery. (Typical forum topic: “HELP!!! All my Gold is gone—how can I get it back?”, text "I found this great forum here with all you wonderful, experienced and helpful people. I read Hoke and like in video I saw, I added just a tiny bit of Peroxide......" )

I've never ended up with colloidal gold. Peroxide with HCl can dissolve gold, but it will cement out again pretty quickly if there are base metals present. In my experience its minimal when there are other things for it to attack, it's usually only a problem on PCB-type material when all the foils have been released and there's no metal left. But even then, it's easily recovered with copper, there's no such thing as an unresolvable mystery.

 

[anarxi]

I don't have very much information about the pins just that they were used in the transportation industry. The smaller pins are slightly magnetic but the larger ones are not.

it's a nickel sublayer coated with gold.
I think the big pins are magnetized too, you just can't tell because of their weight and size.

 

[anarxi]

75 pounds is a lot.
perhaps it would be more practical to resell them to professional recyclers.
melt down a hundred pins of different thicknesses (proportional to their number from the entire batch)
and "shoot" this bar with an x-ray gun.
to know the total amount of gold in the batch.

 

[anarxi]

and there are several ways to extract gold from them.
1) complete dissolution and precipitation of gold.
2) cyanide leaching
3) electrolysis in concentrated sulfuric acid
4) smelting into ingots with the addition of copper, then a copper cell and work with sludge.

 

[haveagojoe]

Based on the calculations before (I assumed a diameter of 5 mm and a lenght of 10 mm, if you wnat better numbers give me the average diameter and lenght of each pin), this is the derived yield calculation, for what you can expect (0.05 ym plating):

Estimated Gold Yield for 75 Pounds of Thick Pins​

• Weight: 75 pounds = 34,019 grams
• Gold content (for thick pins, 0.05 µm plating): 0.108 g per kg
• Total gold yield estimate:

(34,019 g/1000)×0.108≈3.67 g of gold(34,019 \text{ g} / 1000) \times 0.108 \approx 3.67 \text{ g of gold}
So from 75 pounds of thick pins, you can expect around 3.67 grams of gold under ideal conditions.

This is way off. Even low grade pin-type material can give 1g/kg. AI is useless for this kind of thing, don't copy-paste answers without experience to back it up.

 

[Yggdrasil]

This is way off. Even low grade pin-type material can give 1g/kg. AI is useless for this kind of thing, don't copy-paste answers without experience to back it up.

Joe you are barking up the wrong three.
Marcel have what you you are asking for.
He even showed calculated numbers for both thin and thick pins.

 

[haveagojoe]

Joe you are barking up the wrong three.
Marcel have what you you are asking for.
He even showed calculated numbers for both thin and thick pins.

It's not me asking for it, in fact I don't think anyone asked for it. I think it's unwise and unfair to bandy about figures like that for completely unknown material. Anarxi has the right approach for an accurate figure- melt a sample and get an XRF.

 

[Yggdrasil]

It's not me asking for it, in fact I don't think anyone asked for it. I think it's unwise and unfair to bandy about figures like that for completely unknown material. Anarxi has the right approach for an accurate figure- melt a sample and get an XRF.

Nobody is going to have exact numbers for this or other material for that matter, it will always be estimates or better yet, guesstimates for each batch.
And of course if one, like here, when one have 30-40Kgs, one can afford to get it tested so you have exact numbers depending your sampling are correct.
But for most of us it will be a guessing game.
Then it will be better to take it to the safe side and do a conservative guessing than an optimistic one and loose money.

 

[Josecuervohr]

Based on the calculations before (I assumed a diameter of 5 mm and a lenght of 10 mm, if you wnat better numbers give me the average diameter and lenght of each pin), this is the derived yield calculation, for what you can expect (0.05 ym plating):

Estimated Gold Yield for 75 Pounds of Thick Pins​

• Weight: 75 pounds = 34,019 grams
• Gold content (for thick pins, 0.05 µm plating): 0.108 g per kg
• Total gold yield estimate:

(34,019 g/1000)×0.108≈3.67 g of gold(34,019 \text{ g} / 1000) \times 0.108 \approx 3.67 \text{ g of gold}
So from 75 pounds of thick pins, you can expect around 3.67 grams of gold under ideal conditions.

I would be stoked if I could get 3 grams. Considering that the only "money" I would have invested is in chemicals needed. I got the pins through a trade for something I had been given so no money lost there.

 

[anarxi]

Nobody is going to have exact numbers for this or other material for that matter, it will always be estimates or better yet, guesstimates for each batch.
And of course if one, like here, when one have 30-40Kgs, one can afford to get it tested so you have exact numbers depending your sampling are correct.
But for most of us it will be a guessing game.
Then it will be better to take it to the safe side and do a conservative guessing than an optimistic one and loose money.

in fact, an experienced operator with an x-ray gun (well calibrated) will give a fairly accurate answer by "shooting" just one pin.
but the key word here is experience.

 

[Yggdrasil]

in fact, an experienced operator with an x-ray gun (well calibrated) will give a fairly accurate answer by "shooting" just one pin.
but the key word here is experience.

Most of us do not have access to a XRF.
So calculating and estimations are the closest we come to predicting content.

 

[haveagojoe]

Most of us do not have access to a XRF.
So calculating and estimations are the closest we come to predicting content.

Yea that's fair, and I sometimes do such calculations too. But from experience I would be disappointed with such a low yield from 34 kilos of material. I think OP can be a little more optimistic. The thickness of the plating could easily be 5x thicker on pins. Then there's the karat to consider, the calculation assumes 24kt which it won't be, which would send the calculation in the other direction. Then they are not all the same size and shape, and not all fully plated... I agree that such calculations can sometimes be helpful but in such a case the ballpark is so broad it's really just a guess, better to at least base an estimate on someone else's empirical yield data.

 

[4metals]

Just yesterday, I posted an old thread in the library about sampling. Reading it you will realize that in the business of refining, accurate sampling can mean the difference between success and bankruptcy. These pins are a perfect example as they are mixed pins, small pins, big pins, different plating thicknesses, and lots of other potential variations to consider. We are not doing the OP any favors by suggesting either high or low yields as we have no way of knowing the intricate details of the entire lot. For starters, I suggest reading the thread HERE

One thing I will caution the OP about is refining small lots of pins. Let's for point of discussion assume the pound of pins processed contains 1 gram of gold. Recovering that 1 gram out of a small beaker of aqua regia is a skill that is learned with practice. The forum is filled with new members having added too much nitric or too much urea and as a result not recovering small quantities of metal from solution. If it were my material I would not be trying to re-refine the little amount of gold dropped already because it is not as easy as it seems for someone new to this. I would select a method to strip the pins (even if it is the method he just used) and collecting all of the smaller fractions of dirty gold before re-refining. Then careful, tiny additions of nitric with heat and dropping the gold (all of it at once) will be easier.

So many people have read the age old ratio for aqua regia of 1:3 or 1:4 and just add the nitric and dissolve the gold. That is where nitric raises its ugly head. Adding all of the cemented gold to Hydrochloric Acid, warming it up, and adding Nitric Acid drop-wise until all of the gold dissolves will require no urea or sulfamic because the reaction will consume almost all of the nitric and the metabisulfite additions will drop Gold metal and any slight excess of nitric remaining (notice I said slight) will be consumed as gold re-dissolves until there is no nitric and the gold will drop completely.

Now the OP just needs to figure out which method to remove the gold, either AP or sodium persulfate or even aqua regia, is best suited for him to accumulate cemented gold to process in aqua regia adding his nitric carefully and frugally. (To use a term near and dear to our friend @FrugalRefiner)

 

[Marcel]

This is way off. Even low grade pin-type material can give 1g/kg. AI is useless for this kind of thing, don't copy-paste answers without experience to back it up.

I guess I do have some experience in both fields. I am a studied engineer (electrotechnology), I worked 20 years in that field in a company that produced electronic components and assembled PCBs. I got into recycling of electronic components in the early 2000s. And I wrote about this context in a book from 2013 called "Gold from Scrap", where I calculate a similiar case (Manually, no AI involved). Get the book and find it on page 91! I think the link is even in my forum signature below.
Today I mainly work as a consultant on AI for companies and you may find another 3 books dealing with the correct usage of AI. Latest one was an ebook called "Deepseek Ai - all you need to know" from February 2025.
And if you check my posting, you may notice that right now I am processing gold plated pins using different methods. I did post the photos as well.
Which does not mean that I am always right and I know everything. But if you have better arguments bring them foward please! If not, you have just learned that: The smaller gold plated pins are, the higher the yield per Kg!
Bigger is not better in this case.

The main point is that this is a problem of scale. The ratio of surface/weight or surface /volume of an object increases if the diameter gets smaller. Just think a little bit about it.
To use AI correctly you need to know what you are doing. I just did not invest the time to calculate with a pen and a piece of paper. But I could have done it as well.

It is a math problem, a problem of geometry. And therefore stating that "bigger pins yield more Gold" is simply wrong! The opposite is true....

Now here is page 91 calculated by me manually. Just for those who got the impression I googled that info somewhere or the AI wrote it all for me.
AI is just an assistant, a secretary that keeps annoying routine work away from me. So I have more time to be creative.

 

[anarxi]

I guess I do have some experience in both fields. I am a studied engineer (electrotechnology), I worked 20 years in that field in a company that produced electronic components and assembled PCBs. I got into recycling of electronic components in the early 2000s. And I wrote about this context in a book from 2013 called "Gold from Scrap", where I calculate a similiar case (Manually, no AI involved). Get the book and find it on page 91! I think the link is even in my forum signature below.
Today I mainly work as a consultant on AI for companies and you may find another 3 books dealing with the correct usage of AI. Latest one was an ebook called "Deepseek Ai - all you need to know" from February 2025.
And if you check my posting, you may notice that right now I am processing gold plated pins using different methods. I did post the photos as well.
Which does not mean that I am always right and I know everything. But if you have better arguments bring them foward please! If not, you have just learned that: The smaller gold plated pins are, the higher the yield per Kg!
Bigger is not better in this case.

The main point is that this is a problem of scale. The ratio of surface/weight or surface /volume of an object increases if the diameter gets smaller. Just think a little bit about it.
To use AI correctly you need to know what you are doing. I just did not invest the time to calculate with a pen and a piece of paper. But I could have done it as well.

It is a math problem, a problem of geometry. And therefore stating that "bigger pins yield more Gold" is simply wrong! The opposite is true....

Now here is page 91 calculated by me manually. Just for those who got the impression I googled that info somewhere or the AI wrote it all for me.
AI is just an assistant, a secretary that keeps annoying routine work away from me. So I have more time to be creative.

your numbers for microns and microinches are strange.
20 microinches is approximately equal to 0.5 microns.
(I looked at the table in Google)
twenty microinches is like a standard for industrial equipment in the West and in America.
Soviet pins with a yield of tens of grams/kilograms were coated with a thickness of about 3 microns.
but there was also 999 gold there

 

[haveagojoe]

stating that "bigger pins yield more Gold" is simply wrong! The opposite is true....

Where did I state this?

 

[4metals]

Gentlemen please, how is this pissing contest helping the OP get the gold off his pins? Regardless of the quantity of Gold?