Checking my understanding, cpu pin nitric method

[aussie_noob]

Doing nitric base metal removal from gold plated contact pins of 10kg of old 1980s/1990s cpus. Part way through dissolving, thought I'd show some photos.
Critique my understanding and method, give tips:



1. Used heat gun to remove contact pins. Got about 400g of pins, solder attached. Pins were popping off everwhere! Lost a few %.


2. Added to warm nitric solution, about 400ml nitric 66% and 2 litres water. Topped up reaction with more nitric



You can see the ferromagnetic nickel underlayer causing cpu pins to magnetically attract. Greenish partially dissolved stuff is nickel. Blue murky is dissolved / partially dissolved copper base metal.

3. Waited 12 hours


Greenish murky stuff is partially dissolved metals of nickel and copper?


Closeup, non magnetic hollowed gold pins floating on surface. Nitric appears to be working but a lot of material is still undissolved. Many tiny bubbles in solution.

Hoping the solution clears up and its just a transparent solution with gold pins and gold flakes? Dunno what to expect. No idea how much gold will be in pin/flake form vs tiny particals / colloids etc. Anyone have estimates on this?

Thanks heaps guys, this is pretty fun stuff!

 

[Yggdrasil]

Doing nitric base metal removal from gold plated contact pins of 10kg of old 1980s/1990s cpus. Part way through dissolving, thought I'd show some photos.
Critique my understanding and method, give tips:

View attachment 64025

1. Used heat gun to remove contact pins. Got about 400g of pins, solder attached. Pins were popping off everwhere! Lost a few %.View attachment 64026


2. Added to warm nitric solution, about 400ml nitric 66% and 2 litres water. Topped up reaction with more nitric
View attachment 64027
View attachment 64028

You can see the ferromagnetic nickel underlayer causing cpu pins to magnetically attract. Greenish partially dissolved stuff is nickel. Blue murky is dissolved / partially dissolved copper base metal.

3. Waited 12 hours

View attachment 64029
Greenish murky stuff is partially dissolved metals of nickel and copper?

View attachment 64030
Closeup, non magnetic hollowed gold pins floating on surface. Nitric appears to be working but a lot of material is still undissolved. Many tiny bubbles in solution.

Hoping the solution clears up and its just a transparent solution with gold pins and gold flakes? Dunno what to expect. No idea how much gold will be in pin/flake form vs tiny particals / colloids etc. Anyone have estimates on this?

Thanks heaps guys, this is pretty fun stuff!

There are Tin in there as you can see form the Metastannic cloud, a good time in HCl prior the the Nitric would have taken care of that.
Roasting in between, to make sure the HCl is removed can be an idea.

 

[aussie_noob]

There are Tin in there as you can see form the Metastannic cloud, a good time in HCl prior the the Nitric would have taken care of that.
Roasting in between, to make sure the HCl is removed can be an idea.

Ahh dammit! Guess i'll try filtering with glass fibre filter paper, collect the gold and tin solids and then redisolve the tin. Hopefully the filter paper won't clog too much.
Maybe could alternatively just let it settle, decant, rinse out nitric with water and decanting, then hcl to dissolve the tin product before another decant / filter?

Edit: Wait it's the lead, not the tin in the solder that becomes an insoluble precipitant!

 

[Yggdrasil]

Ahh dammit! Guess i'll try filtering with glass fibre filter paper, collect the gold and tin solids and then redisolve the tin. Hopefully the filter paper won't clog too much.
Maybe could alternatively just let it settle, decant, rinse out nitric with water and decanting, then hcl to dissolve the tin product before another decant / filter?

If you manage to let it settle, you can either dissolve the Metastannic with concentrated HCl or roast it and dissolve in ordinary HCl.
Then go to filter out your Gold.
Dissolve in HCl/Bleach or better HCl/Peroxide.
Better than AR since there are no Nitric to worry about.

 

[aussie_noob]

If you manage to let it settle, you can either dissolve the Metastannic with concentrated HCl or roast it and dissolve in ordinary HCl.
Then go to filter out your Gold.
Dissolve in HCl/Bleach or better HCl/Peroxide.
Better than AR since there are no Nitric to worry about.

I've had a suspicion that hcl + peroxide can slowly dissolve gold, I'd expect the chemistry to work similar to aqua regia with the peroxide replacing the role of the oxidative nitric. Any truth to this? We are exposing high surface area to volume gold here, I suspect gold losses. But probably still cheaper than using expensive nitric here in aus.

 

[Yggdrasil]

I've had a suspicion that hcl + peroxide can slowly dissolve gold, I'd expect the chemistry to work similar to aqua regia with the peroxide replacing the role of the oxidative nitric. Any truth to this? We are exposing high surface area to volume gold here, I suspect gold losses. But probably still cheaper than using expensive nitric here in aus.

Yes, but the 3 and 6% is not enough.
I'm not sure where the limit is, I have used some old 30%, and due to age I don't think it is much over 20%, but it works like a charm.
Anyway the Bleach has a significant draw back and that is that it neutralize the HCl.
Better use pool chlorine tablets then.

 

[anarxi]

Diluted nitric acid does not dissolve nickel and nickel-based alloys well.

 

[anarxi]

https://goldrefiningforum.com/threads/15lbs-of-gold-plated-pins.34142/page-2

instructions for you

 

[kurtak]

You can see the ferromagnetic nickel underlayer causing cpu pins to magnetically attract. Greenish partially dissolved stuff is nickel. Blue murky is dissolved / partially dissolved copper base metal.

The pins from CPUs are NOT copper (or brass) they are made of Kovar which is an iron alloy

https://en.wikipedia.org/wiki/Kovar

You should have done a HCl leach on the pins to remove the tin before trying to dissolve the pins

You are now going to have a mess to deal with because of the meta stannic acid (tin paste)

Kurt

 

[aussie_noob]

The pins from CPUs are NOT copper (or brass) they are made of Kovar which is an iron alloy

https://en.wikipedia.org/wiki/Kovar

You should have done a HCl leach on the pins to remove the tin before trying to dissolve the pins

You are now going to have a mess to deal with because of the meta stannic acid (tin paste)

Kurt

Ahhh kovar! Reduced thermal expansion of kovar for contact pin longevity, makes sense now. I have a mix if cpu pins with solder, so iron, copper, tin, lead, nickel, cobalt, gold.

Redisolving the heavy decanted stuff in more concentrated nitric. Thought this would be simple, ganna take work.