How to deal with this fun...

I have a pile of CPUs (P3, P4) with the pins removed. About half of them, I hand-removed the capacitors with a hot-air rework station setup. The other half, I did not. I removed all of the plated copper caps from the processors so all that is left is the fiber board and the IC itself.

The half with the capacitors, I have dissolved off the solder with hydrochloric acid (32%), and this has removed the capacitors as well, of course. The result is hydrochloric acid with black precipitate (and a fair amount of it) and capacitors in the dregs... and a nice purple hue. That is where my mind went "Oh crud!".

I filtered off the solids, and have a nice bottle with amethyst-hued purple solution in it. I then went to wash the precipitate with water, and it instantly went from black to a nice milk white, and is settling over the day now.

Here is what I think I have:
- purple solution = HCl + stannous chloride + gold stannate (from the wee bit of gold on the surfaces of the processors for pin 1, etc)
- black precipitate in HCl = silver (maybe lead)
which turned into:
- white precipitate in water (likely actually fairly dilute HCl solution) = silver chloride + maybe lead chloride

So, my questions:
1) what are the chances of dropping any gold from the purple solution? I've read that hot sulfuric might precipitate gold from such a solution, but I'm loathe to work with that stuff unless necessary. I'm aware that I may be losing some to colloidal gold here, but there wasn't that much (I thought) in the first place.
2) am I correct on the black precipitate in HCl?
3) I'm assuming that I can separate lead and silver chlorides with the use of hot water to dissolve the lead chlorides. Is there anything else I'm missing here?
4) if there is cupric chloride in the solution (or precipitate) is there a simple way to separate it?

I'll go back to continuing to read Hoke, BTW. It is a great read, and there is still much to learn (which I'm sure is still obvious!)

You'll have to wait for a response from someone else to get an opinion of what the purple hue's cause is, but HCl alone shouldn't have dissolved any gold, so I don't think you have gold in solution.

If you have (or have what you need to make) Stannous Chloride you can test the solution to be sure.

Umm, that doesn't make sense to me. Stannous chloride + gold gives purple, exactly the color of my solution. Testing with stannous chloride wouldn't do anything at all. Just maybe make it *more* purple

I'm pretty sure that the solution is primarily stannous chloride anyways as I was dissolving solder off CPUs, and even lead-free solder is primarily tin. It had to go somewhere.

Let's see if this will work. Going to try attaching a picture...

something is totally wrong lol
did you use ONLY HCl ,if yes where does it come from???
edit: even better post a picture of your bottle plz

ericrm said:

something is totally wrong lol
did you use ONLY HCl ,if yes where does it come from???
edit: even better post a picture of your bottle plz

Click to expand...

I used muriatic acid from Lowes. Not the "safer" stuff, either. I'm not at home right now, so can't get you a picture for the moment. The MSDS (attached) from the manufacturer clearly indicates 9%-36% HCl (the gallon jug said 32% on it, if I recall correctly), and no other reagents. I didn't dilute it.

To be clear, there were definitely traces of gold sitting in that solution for periods of time, and I'm thinking it may have reacted with the stannous chloride also in the solution (from the tin in the solder dissolving), not dissolved in the HCl on its own.

View attachment mGMA58.pdf

What happens if you put some of that purple solution on a q-tip and place a drop of clean stannous on it?

I'll attempt that tonight. I don't expect any reaction at all, but it's worth a try if you think it would show something useful. Again, if there's gold in there, wouldn't that make it go purple, which it already is? But I'll give it a shot anyways Be a few hours though.

its a colloid, nano particles of gold. you cant precipitate it because its already in its metallic state. add twenty ml's of hcl and add some bleach slowly until the color changes from purple to yellow.

geo
you probably right lol(i wont argue with you :lol: , but how did he disolve the gold in the first place?

hcl can dissolve gold if the temperature is high enough and its boiling. the boiling action aerates the solution with enough oxygen to dissolve some gold.

cross contamination with a nitrate of some kind.

there are a few possibilities how it happened, but from the looks of the picture, thats what happened.

silver nitrate/chloride can also look purple if exposed to the sunlight, but it would also have to be in the form of a colloid.

Maybe it's cobalt. Kovar is 17% cobalt.

cobalt in solution is blue, right? ive seen cobalt and it always reminded me of copper nitrate.

Co²⁺, dissolved in concentrated HCl is blue indeed, the solution turning pink on dilution with water.

freechemist

Geo said:

cobalt in solution is blue, right?

Click to expand...

Depends on pH, may turn pinkish purple if close to 7.

edit: you beat me to it.... :mrgreen:

I think Lou mentioned a long while ago iron could catalyze the oxidation of HCL under the right conditions?

Should this be evaporated to dryness before you attempt to dissolve again?

samuel-a said:

Geo said:

cobalt in solution is blue, right?

Click to expand...

Depends on pH, may turn pinkish purple if close to 7.

edit: you beat me to it.... :mrgreen:

Click to expand...

Heh, well, I'm pretty sure the pH is nowhere near 7. It started as -1.0 (yes -1.0 for 20 Baume HCL which this was!) and I certainly didn't dilute it. Forming chloride salts and of-gassing H2 gas would lower the pH some, but I'm quite sure it never even saw 7.0 at the end of a long dark tunnel. When my digital pH meter shows up in a week or two, I could tell ya for sure

OK, a new batch of clean stannous chloride is in the making (using about 2.5" of flattened solid core solder that the manufacturer identified as 96Sn/3.9Cu/0.1Ag - it only said lead-free, silver bearing on the package). I will try the purple solution with it first thing in the morning, which should give it ample time to dissolve a significant portion of it. Wonder if I should go back and buy some that's Sn/Sb only (if they have any) to avoid the copper?

The washed (once) white/grey precipitate is being filtered over night and I did a second water wash of the remainder, still nice and white/grey. I forgot I was going to add hot water to separate the lead chloride from the silver chloride... Oops. I guess I should plop the filter back in the dish before it gets a chance to dry. Stupid... I'll heat it up to dissolve out the lead chloride tomorrow, I guess.

One thing I noticed... a pile of the capacitors seem to have almost completely dissolved and look like they are in fact a small metal foil only left (rectangular, so I know it was the capacitors, not any pads on the processors). Now I'm curious what exactly that metal is. Seems to be too much to possibly be palladium. If it is, I will be most happy. hehe. Another use for the stannous tomorrow, I guess. I'll try to take a picture of them tomorrow too.

Oh, forgot to post earlier... The new batch of stannous made the expected zero difference to the color of the solution (on a QTip). I will be buying some bleach (ran out) on the way home, and will use that to drip in there as suggested. That would help dissolve the gold, is that the trick? After that, treat it the same as if I'd done HCl/Bleach processing, I would assume?

Anyways, thank you so much all for your input.

if the purple is as it looks to be, metallic gold as a colloid, a small amount of hcl and bleach will put it back into solution. DO add enough hcl to overpower the tin that caused it in the first place.