Gold plated steel ICs and transistors

[Bertho]

I keep reading the posts and all say "remove iron before proceeding". Unfortunately this scrap is a mixture of gold plated steel IC leads and housings with internal gold wire bonds. I will remove the pins with the nylon. I have had bad experience with nylon before.
It is a hobby and I am trying to process different types accumulated over decades.
What process steps do you suggest?
I have build a de-plating cell that I used for regular pins but this is presumably not suitable for it.
I got a fume hood, furnace, and equipment and have previously gone through different regular material and processes.
I have ball-milled gold ore concentrate that is next on my list to try.
Bertho

 

[butcher]

a search using the phrase
top hats
https://goldrefiningforum.com/phpBB3/search.php?keywords=top+hats

 

[snoman701]

Incinerate then digest steel in a mixture of nitric and a little sulfuric acid. Fast reaction likely to boil over and produces a lot of NOx.

Or, incinerate then just let it sit in hot hcl for a couple days. It helps if you add a bubbler...and it helps immensely to bring it to a light boil on the first day for a bit.

Depends on how much time you have.




Sent from my iPhone using Tapatalk

 

[Bertho]

Thank you Butcher and Snoman.
It took a very long time to follow up on Butcher's Top Hat links.

 

[butcher]

Hopefully, in that very long time you have found some answers to a few questions you did not think of asking, and then maybe a few more questions to work with those answers.

 

[anachronism]

Hopefully, in that very long time you have found some answers to a few questions you did not think of asking, and then maybe a few more questions to work with those answers.

So true. I've lost track of the times I have searched for something in particular only to then spend hours learning other things that have cropped up browsing posts.

 

[Bertho]

butcher wrote: ↑15 Oct 2019, 23:15
Hopefully, in that very long time you have found some answers to a few questions you did not think of asking, and then maybe a few more questions to work with those answers.

Anachronism wrote:
So true. I've lost track of the times I have searched for something in particular only to then spend hours learning other things that have cropped up browsing posts.
---------------------------------------
( I got to figure out how to quote)

Well, after two days on the hotplate @ 80C it is very, very slowly dissolving my tests batch of the 88g test batch.
Then I goofed up: I forgot to replace the watch glass cover and it all dried up. Cooled it off and added 250ml EDIT: HCL, not HNO3 and back on the hotplate. A day later there is still a good amount of undissolved stuff in the beaker.

I got Snoman's advice too late about incinerate which I will do for the next batch.
How much is "a little" sulfuric acid to add to the HCL?
What is chemically happening with the extra sulfuric?
I am off reading again and very likely get sidetracked on other interesting processes. Pyrolysis sounds interesting.

 

[butcher]

Back up a bit and explain better of your plans, and the chosen process.

I may be confused, but it sounds to me from the question you are asking about two different processes.

 

[Johnny5]

( I got to figure out how to quote)

Click the quotation mark symbol in the upper right hand corner of any post.
Once you have that persons quote, you can delete parts of the quote, so that only certain parts remain.
If you want to add another persons quote to your post, once you open up a reply window, scroll down until you find the post you want to quote from, and look for the same quotation mark in the upper right hand corner, when you click on it, the quote will be added to your current reply.

You can play around with this, and at anytime you can hit "preview" to see what the reply looks like. Just don't hit the "submit" button on the bottom, until you are satisfied.

 

[niks neims]

butcher wrote: ↑15 Oct 2019, 23:15
Hopefully, in that very long time you have found some answers to a few questions you did not think of asking, and then maybe a few more questions to work with those answers.

Anachronism wrote:
So true. I've lost track of the times I have searched for something in particular only to then spend hours learning other things that have cropped up browsing posts.
---------------------------------------
( I got to figure out how to quote)

Well, after two days on the hotplate @ 80C it is very, very slowly dissolving my tests batch of the 88g test batch.
Then I goofed up: I forgot to replace the watch glass cover and it all dried up. Cooled it off and added 250ml HNO3 and back on the hotplate. A day later there is still a good amount of undissolved stuff in the beaker.

I got Snoman's advice too late about incinerate which I will do for the next batch.
How much is "a little" sulfuric acid to add to the HCL?
What is chemically happening with the extra sulfuric?
I am off reading again and very likely get sidetracked on other interesting processes. Pyrolysis sounds interesting.

I messed up when I first tried to process material like this (mine were USSR transistors), I tried to dissolve them in HNO3, the "hats" were kovar (magnetic) I think, and did not budge, so I decanted copper nitrate and nuked everything with AR, made sure it dissolved everything metallic and cemented the gold out on copper, worked out fine I guess... It was quite a while ago, and while I'm sure that my yield suffered, I remember thinking it was OK...

 

[Bertho]

First, thanks guys for your help. I also now know how to quote

Back up a bit and explain better of your plans, and the chosen process.

I may be confused, but it sounds to me from the question you are asking about two different processes.

The goal, of course, is to recover the gold from the plating, wire bonds and gold solder.
I have read several suggestions to use HCl and heat to slowly dissolve the base metals, mostly iron in the transistor leads and the covers and kovar for the transistor/IC bases.
After over 3 days at 80C there is a lot of undissolved parts. I also see gold flakes floating around.
Once there is no more action using HCL I then plan to use AR for the rest.

Later I saw Snoman701 suggestion: "Incinerate then digest steel in a mixture of nitric and a little sulfuric acid. Fast reaction likely to boil over and produces a lot of NOx." My question here is how much is "a little"?

It looks like niks neims ran into a similar problem and switched to straight AR. Actually that is what I ended up doing on my first test batch but on this second batch I tried to carefully follow the suggestions but still no good procedure.
Bertho

 

[niks neims]

It looks like niks neims ran into a similar problem and switched to straight AR

It was more of an emotional decision, I felt that those damn kovar top hats are mocking me and my hot nitric, so at that point it was more to show them who's boss AR made short work of them... he he he

When I will run next (much larger) batch of them (have quite a few stockpiled, but not planning to any time soon) I'will try another route, so I would very much like to see how will you end up dealing with your batch; and please take pictures!

If I were to guess the sulfuric is to help with passivation of iron (steel) in concentrated (68%) nitric (sometimes diluting nitric also helps), it is only a guess though, and maybe it doesn't work on kovar

If i were to run a batch of these now, I'd definitely mechanically remove those hats beforehand with some clippers (pliers?)...

 

[butcher]

Ok, so You were talking about several different processes to remove base metals.

Nitric leach;
Iron will passivate in concentrated nitric acid, diluted it will work better.


Hot sulfuric leach:
The H2SO4 with small additions of HNO3 (oxidizer) and heating basically is using sulfuric acid to dissolve base metals.

Cupric chloride leach:
HCl with small additions of oxygen or 3% H2O2 will dissolve copper iron and other base metals.

Ferric Chloride leach:
Ferric chloride and strong heating and high chloride concentration, works much faster (and vigorous) than the cupric leach above.
This is one leach I would consider.

I would consider laying the top hat on its side and smash it flat with a strong hammer blow.

 

[anachronism]

Butcher why do people never mention an alkaline leach as an alternative to copper chloride?

 

[snoman701]

Iron is not passivated in nitric acid past about 55% or so...or less than around 40%.....and it is very temperature dependent. Those numbers are totally made up and drug out of my butthole....the sweet spot for passivating iron is around 50%ish (1 water mass : 2 hno3 67% mass) room temp or colder. That number is based on lots of experience as well as peer reviewed journal articles. Too concentrated or too dilute or too hot and you lose passivation and the reaction goes nuts.

The hot nitric method to dissolve kovar top hats has been discussed before. The sulfuric helps keep the iron in solution, and likely also decreases passivation.


Sent from my iPhone using Tapatalk

 

[butcher]

What alkaline leaches are you referring to?

Like cyanide, thiosulfate, hypochlorous, and (leach...) ???
(Cyanide well then, that is just another topic altogether, with restrictions, availability, and dangers...)

Thiosulfate besides being limited to the types of Ore involved, and its many complications to run effectively.


With mineral ore's the alkaline leaches are more common and can be useful depending on the composition of the ore, but are less common with leaching, or more like etching of) the more elemental metals.

We have had a few discussions on the forum of these leaches.

https://goldrefiningforum.com/phpBB3/viewtopic.php?t=16292&start=20

 

[g_axelsson]

You forgot about the alkaline copper chloride leach. :wink:
Copper chloride dissolved in ammonia. It's popular for etching circuit boards on an industrial scale. Works really fast but is a bit smelly.

Göran

 

[butcher]

I am not that familiar with that etching process. I have heard of it, what I understand is that if the leach is run correctly it would be good for etching copper traces for making circuit boards, I have not tried it but have heard it was smelly.
The fact that this leach is not that popular even as a copper etchant for making traces on circuit boards, can give us some clues of its difficulty and its effectiveness for use in the industry.

It does not seem to me to be much different than the cupric chloride leach except they are using an ammoniacal solution to complex the copper, not all base metals are amphoteric or will complex as easily into the ammonical complex.

 

[Bertho]

I am sorry for adding confusion, there was a typo on my 17-Oct post.
After drying up, I added HCl, not nitric acid.
So in summary, the batch has been cooking for 4 days in hot HCl.
A couple of times I let it cool off and tried to add 10ml of sulfuric acid and a second time 20ml.
There is instant reaction for a couple of seconds and the sulfuric is gone.
Things are getting dissolved but extremely slowly.
What is most surprising to me is that the very skinny gold plated steel transistor and IC leads are in many cases untouched. Is the gold plating so good that it is protecting the steel?
I added a picture of a sample fished out and rinsed.
Bertho

 

[anachronism]

Not quite so Richard.

Try Glycine in an alkali solution of Sodium Hydroxide and see how hungry it is for Copper. Cold not hot. When hot it also goes for Gold.