HCL Leach

I combined a small amount of green fiber CPU's with HCL about a week ago. I am not able to heat them at the moment, and didn't really plan on getting to them for a while. Since the weather has been a little chilly, I know that it's probably reacting at a snails pace. I figured a good long leach wouldn't do any harm, even if it was reacting very slowly. I haven't done anything other than add a couple cups of HCL and topped it off with tap water. A couple days ago I noticed a pinkish color developing. It has never shown a greenish color, as I would expect to see with copper. I decided to let it sit a while longer, and observe any changes. Well, today I took another look. It has darkened a little. Still a pinkish color. I've read some of the posts, and done some additional reading. Cobalt seems to pop up, but I'm curious if anyone else has had an issue like this? If so, has this complicated matters anyone? If my guess is correct, I guess it dissolves easily in HCL. Even when it's chilly. First time I've seen this. If I'm way off the mark, let me know. Thanks!

You are very correct.

Add HCl and it will turn blue.

Sam,

Thanks for responding and confirming my suspicion. All the lids were removed, so I'm guessing that the cobalt is in the solder/heat sink paste as well? Any ideas? Will this hinder the uptake of copper?

The pins are made of Kovar, a nickel-cobalt ferrous alloy.

The solder may be Sn/Pb or Sn/Ag.

I had the very same thing happen. I was soaking ram boards (without fingers) to remove the chips. I thought possibly colloidal gold. Does Sn/Ag produce a purple color?

maynman1751 said:

Does Sn/Ag produce a purple color?

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Should be Au=gold, Ag=silver

Eric

he had it right Eric. colloid silver can be purple.

mjgraham just posted about this very thing. The thread is "purple HCl". You see those little parts that are soldered on top of those cpus? They are soldered on with tin. So when the small amounts of gold go into solution... You guessed it. The tin that is in solution turns the gold purple(colloidal). This amongst other things is why I think AP is the wrong way to go for anything other than cleanly cut, tin free, fingers.

I posted in the other thread mentioned but I have a similar question for here as well. Both of these posts refer to placing components into HCl. No mention of AP is made other than in replies. If the components were placed in straight or dilute HCl, wouldn't the Copper and other higher metals be unaffected? HCl alone doesn't react with Copper, the Copper Chloride created in the AP process is what etches the copper, converting it into more Copper Chloride. I don't process Gold so I have no hands on experience with the AP process, that is just my understanding of the reaction. Am I wrong? Will HCl react with Copper or silver on its own? I was thinking that dilute HCl would be a good way to de-solder components from boards.

In my limited experience I know that HCl can absorb some oxygen directly from the air, in affect making a very weak AP. Ordinarily HCl alone will only attack the solder, so yes, it is excellent for removing solder or soldered-on components. In the process of soaking ram sticks in HCl to remove the chips I have had the acid dissolve some of the tiny gold 'tubes' that cover some sticks. And yes, I cleaned the sticks to make sure that the gold was gone and not just plated over!

in my experience, if you place clean copper in straight hcl and leave it there long enough, copper chloride will form. this is self replicating and will continue until the copper is consumed or the hcl is consumed.

Your exactly right Geo. One thing we left out though? The oxygen drives it and of course this can just come from the air. Given an indefinite amount of time the copper would be consumed. Hcl will not dissolve copper. The oxide layer is formed from the ox at first that has been absorbed and then the copper chloride with the help of the oxygen molecule gives it that driving force.
It's like which came first? The chicken, or the egg? :mrgreen:

Geo said:

he had it right Eric. colloid silver can be purple.

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I have to disagree what he posted was he put ram in HCl. he did not produce colloid Ag If anything it was AgCl that could have been produced and it can change to purple in light.

when he posted "I thought possibly colloidal gold. Does Sn/Ag produce a purple color?" I took it that it was a typo.

maynman1751 said:

I had the very same thing happen. I was soaking ram boards (without fingers) to remove the chips. I thought possibly colloidal gold. Does Sn/Ag produce a purple color?

Click to expand...

Eric

etack said:

Geo said:

he had it right Eric. colloid silver can be purple.

Click to expand...

I have to disagree what he posted was he put ram in HCl. he did not produce colloid Ag If anything it was AgCl that could have been produced and it can change to purple in light.

when he posted "I thought possibly colloidal gold. Does Sn/Ag produce a purple color?" I took it that it was a typo.

maynman1751 said:

I had the very same thing happen. I was soaking ram boards (without fingers) to remove the chips. I thought possibly colloidal gold. Does Sn/Ag produce a purple color?

Click to expand...

Eric

Click to expand...

Eric, I can see your confusion about my post. I meant that I thought it was colloidal gold, but also was asking if tin/silver could produce a purple color. I knew silver would not dissolve in HCl alone, so I was asking if, in the presence of tin, could silver present as purple. This is all very confusing to me!
I had stated earlier that small amounts of gold had indeed dissolved from the ram. Therefore I came to the assumption of colloidal gold. Does that make sense now?

thanks for clearing that up.

Sn has nothing to do with the dissolution of a metal in a chemical reaction. It will precipitate out metals thats why it is use in stannous chloride it precipitates out colloids of the metals.

In a physical reaction Sn will dissolve metals with heat. You can see this when you wash your desoldered pins in HCl if they are fully plated you will see a black powder it the gold that was mixed when the solder was applied.

Cheers

Eric