Non-Chemical Low strength HCL

[KarlB]

Hi, I'm new to this but have been doing some reading up and just have a few questions.
I have a ton of old processors and gold plated connector pins to process.
Ideally I would use nitric acid to first remove all the base metals. Although after scouting around today all I could find was HCL at 16% when most guides call for around 30%. I also got some hydrogen peroxide at 6%.
So I started with a small test batch. A few smashed CPUs and connector pins in a jar with around 100ml HCL at 16% and around 10ml hydrogen peroxide.
Initially I was skeptical that it would work due to the low concentration of the HCL but after a few minutes the liquid turned green and it was bubbling away. The jar also got quite warm. After a few hours there are gold flecks floating around and the liquid looks quite sparkly, but the CPU pins are not completely dissolved.
Do I just need to leave it for longer or is the acid not strong enough?
Thanks

 

[joubjonn]

How are acid strengths determined? Water content. With AP water content is needed. You can use heat to evaporate your 16% to make higher concentrated acid. Sounds like it's working. Wait until all base metals are dissolved.

 

[KarlB]

I didn't think that you could concentrate HCL that way. I thought that when heating, the hydrogen chloride evaporates off before the water does?
Anyway, I will be leaving it overnight and I'll see how it is tomorrow.

 

[joubjonn]

you can only concentrate up to around 32% past that and it's tricky and dangerous, i believe 100% HCl is a gas at room temp and pressure. so i do believe with 16% you can vapor the water and get to 32% but not more.

 

[Ian_B]

The boiling point of the HCL is lower than the boiling point of the H2O (water) the HCL would evaporate first.

 

[joubjonn]

Yea your right. It is possible to concentrate a weaker HCl solution but not without some lab equipment.

 

[KarlB]

Ok, so I can't easily concentrate the HCL further given that I don't have lab equipment.
Will 16% HCL just take longer but still do the job? Or will it not be enough no matter how long I leave it?
What about when I get to the second step of dissolving the gold with clorox and HCL? Will 16% work for that?

 

[Ian_B]

Yes it will still do the job but just take longer,

It should still work with Clorox, just be sure to adjust the amount you use accordingly ( and it will take longer again)

 

[KarlB]

Thanks for the info.
To dissolve the base metals, I have seen some guides say 24-48 hours with 32% HCL, some even say a week. How long can I expect with 16%?

 

[butcher]

Dilute HCl acid can be concentrated up to its Azeotrope, HCl azeotrope at 20%, below the azeotrope water will vapor off first with evaporation, after this the 20% HCl will also vapor off with further concentration or evaporation. it is possible to concentrate HCl further above its azeotrope , but with what we do with HCl there is no point in it.

http://www.qvf.com/glass-process-systems/mineral-acids/concentrationing-hydrochloric-acid.html

 

[joubjonn]

Thanks butcher! I remember reading that but couldn't remember if it was possible to concentrate up to 32-38% which is about as concentrated as you can get HCl at atmospher and 70F. With 100% being a gas.

 

[KarlB]

Ok, I am now heating the AP in a pyrex flask which is in a pan with some water in it so that the heat is applied gently. I have it on the lowest heat on my hob and I will attempt to evaporate off some of the water to get up to the 20% azeotrope with my pins in whilst heating.
At first it seems to go well, when I add a few drops of hydrogen peroxide the solution goes from clear to a deep green very quickly, and the CPU pins bubble, but after around an hour the green gradually fades and it goes back to a completely clear solution.
If I then add a few drops more peroxide it goes a bright yellow around the area where the drops were added, and then when I stir it in the solution goes green. Although after leaving for a while longer the solution goes back to clear.
What is happening here? Shouldn't the solution gradually get darker? Is the copper dropping back out for some reason? Please help

 

[butcher]

It does not sound like you have a solution of copper II chloride (that you are calling AP), it is the copper II chloride that is the leach.

It sounds like you just have some HCl, and are adding H2O2 as an oxidizer, this will also dissolve metals but is not the copper II chloride leach (acid peroxide or AP).

It is hard to tell from where I sit what you have, but I suspect you have Kovar pins, and are getting a solution of iron chloride, the dissolved copper you see in solution now and then, may be being pushed out of solution by the iron and other more reactive metals.

 

[g_axelsson]

Firstly, pins and processors are usually separated and treated differently. As Butcher told you, the processors usually have pins made of kovar, an iron alloy. While the connector pins usually are made from brass or bronze and not of pure copper.

I suspect that your HCl + H₂O₂ is dissolving some copper when you start, but when the hydrogen peroxide is used up you stop dissolving copper. When that happens the copper is cemented onto kovar or brass/bronze dissolving iron and zinc instead. That turns the liquid colorless.

I've added almost black copper chloride solution to fresh pins and in just minutes the solution was colorless.

Göran

 

[KarlB]

Ok, I tested my pins with a magnet and confirmed the presence of iron. I have put those to the side and will focus on processing just RAM fingers in AP for now.
As I said, I'm new to this, so lesson learned.
How do I process pins containing iron? Does that require nitric?
Nitric is harder to get around here but if it is the only thing that will work then I'll have to look harder.
Thanks for the advice. I'll let you know how I get on with the RAM fingers.

 

[joubjonn]

Their are some really excellent threads in the forum on the AP process that will explain how it works. It will work with Iron also. It's just a little different. Most of us save our AP fluids and only run one type (copper only base metal or copper/iron/Kovar base metal) together. You can keep your AP fluids to quickly start another AP reaction. Read up on it in the forum. Someone even did a really nice PDF, should be easy to find.

 

[KarlB]

Thanks, I have had a read around about the AP process for iron and copper.
I used a bit more peroxide in my AP mix for my kovar pins and this time, the first wash came out dark brown, it seemed to be saturated so I did another wash with fresh HCL and peroxide, this also came out dark brown. The third wash is now emerald green so I guess I have stripped out all the iron and there is only copper to go.
Two washes have been done on my memory fingers and they come out dark emerald green each time, most of the gold has fallen off but there are a few stubborn ones that I have to scrape with a penknife a bit.
It seems that because I'm using only 16% HCL the solution once saturated is a medium emerald green rather than a very dark green which most of the guides say is what happens with copper saturated AP.
I will continue washing my gold flakes in AP until the solution no longer turns green.
I read about a way to rejuvinate used AP by topping up with a bit of HCL and peroxide. Although why not just use the HCL that I would top up with in a fresh wash? Is the same volume of HCL more effective when added to a saturated AP solution than if used in a fresh wash?

 

[butcher]

I suspect you are not saturating the solution with copper or Iron, and probably using more peroxide than needed or not letting it react long enough, a saturated solution of copper or iron chloride will look dark brown.

 

[FrugalRefiner]

Karl, have you tested all those HCl and peroxide "washes" for gold? You may be dissolving some of it each time you start a new batch of AP. HCl and peroxide will dissolve gold. Once your solution is saturated, the gold will cement back out of solution, but I agree with butcher that you're probably not reaching that point.

The reason we only add some HCl to an existing batch of "AP", is that once it gets going, it's not a hydrochloric acid and peroxide leach any more. It becomes a copper II chloride, or CuCl₂ leach. It's not the HCl that does the work, it's the CuCl₂ that attacks more copper. By starting fresh batches, you're missing out on one of the best things about CuCl₂, the fact that it's reusable.

Keep studying. It's easy to read a bunch of posts and think you've got a good understanding of a process and you can have some success, but as you continue to study you'll begin to understand the finer points.

Dave

 

[KarlB]

Thanks for the advice.
I've found the forum very interesting so far and I'll be sure to carry on reading
Will a saturated solution still look dark brown if I'm using only 16% HCL? It has been difficult for me to find anything more concentrated around here.
I tried to make some stannous chloride to test for gold by putting around 15cm of lead free tin solder (99.3% tin and 0.7% copper) into the 16% HCL. Even after several days it doesn't appear to have done anything. The solder is still there and the liquid is still clear. What colour is it supposed to be? Some guides say clear and some say yellow.
I haven't thrown any AP solution away so I will re-use it until saturated.