Aqua regia process post sulfuric stripping

[gregory-d]

Gregory, you should really spend more time studying before forging ahead. I know it's exciting and you want to see a result in your hand, but right now you only have a partial understanding of what you're doing.

First, we never talk about a high concentration AP. AP, as it was originally described, is a leach intended to dissolve the copper underneath the gold on gold fingers. It's actually a copper chloride leach. Although it starts with HCl acid and some peroxide (Acid Peroxide), the peroxide is only there to oxidize a bit of the copper which dissolves into the HCL creating copper chloride (CuCl₂). It is the CuCl₂ that then dissolves more copper from under the gold on the fingers until they release from the circuit board. That's AP.

What you're describing as high concentration AP is never discussed by that name, so you're not likely to find much with a search for that term. The usual way to dissolve gold is with aqua regia (AR), a combination of hydrochloric acid (HCl) and nitric acid (HNO₃). The nitric acid acts as an oxidizer on the gold, causing it to lose an electron. The Cl from the HCl then combines with the oxidized gold. But many members either can't access nitric acid or it is prohibitively expensive. They can use a different oxidizer instead of the nitric. The two most commonly used are high strength hydrogen peroxide or laundry bleach. These both accomplish the same thing as the nitric acid and cause the gold to be oxidized. I hope that gives you some help in finding where it has been discussed.

Once gold has been stripped in a sulfuric stripping cell, there is no need to be trying to clean it with either nitric acid or HCl. Because it is a powder, it will dissolve readily in AR, or HCl plus peroxide, or HCl plus bleach, or HCl and other oxidizers. Once it's dissolved, you can precipitate the gold with a selective precipitant like SMB, ferrous sulfate, etc. That IS refining. If you want to refine it again to get purer gold, don't melt it. Just refine it again while it's still a powder. It will be much easier to dissolve again while it's a powder than if you melt it into a lump.

Most of the really successful members here spend a long time learning before they jump right into trying to refine. By studying extensively they are better prepared when they actually start. Those who are impatient often end up with messes they don't know how to fix, they get frustrated, and they give up and leave the forum.

Dave

Dave

Thanks very much Dave that is really helpful.
You hit the nail on the head in many ways.
I had gotten to the point where I couldn't search on stuff because I didn't know the precise terms.
I did want to understand one step at a time but some things you can't know until you try them.
Yes my first attempt was a dismal failure but I did learn things that you can't learn by reading alone.
I will work on the stripping cell I think I am getting a handle on that part.
I will just stay with that until I have a lot better understanding and just accumulate it in the bottom of the sulphuric siphoning off the clean stuff regularly to reuse and so I don't end up with too much sludge at the bottom which could cause other problems.
Yes I was already almost ready to just give up, so thank you you post is encouraging.

 

[gregory-d]

A piece that really helped explain the AP process to me was this one:

Thanks Martijn that is really really helpful.
I will study it carefully.
Is that in the library I didn't see it but I often don't see stuff until the 10th time looking for something specific.

 

[gregory-d]

Based on many of the current questions your at a point where your becoming a bit confused on very various processes again. This is common for the newer people when reading and asking many questions. This isn't a bad thing so long as it isn't being applied as you go. Take a deep breath, relax and read about what you already know again. This as a habit will teach a better understanding of what you wish to accomplish. For example you use of the term of concentrated AP, technically concentrated AP would mean it has a large amount of copper in the AP. Not a good thing as we want it to dissolve more copper. Adding stronger peroxide or larger volumes doesn't concentrate it, it just adds more oxidizer. Good or bad depends on what you wish to accomplish with it. Isn't chemistry easy?

Keep studying, it almost becomes easier to get a handle on it.

Thanks Shark yes I am having trouble explaining myself properly.
I do have a better understanding now.
I am starting to think these boards are indeed ENIG plated so I will just keep it really simple until I understand more.
I certainly don't expect so much anymore.
I have about 50 of these boards and at least 100 maybe more available if I can get this worked out.
I can use caustic soda to remove the mask on all the boards in one go and start there.
Even though the stripping cell may miss a lot, it is something I have set up and am starting to understand better.
It will generate much less waste and is easy to do so it seems to me the best place to start.
When I get a reasonable amount of sludge from the stripped boards and components then I can refined the residue.
I can collect and dry the residue and store the partially stripped boards for later processing if it is even worth it.
I will try and be more clear in the future.
Youtube is very misleading as many crucial stages are just skipped over for the sake of entertainment.
When you think you have actual information the more you look the more confusing it gets.
At least following this path I will understand one thing at a time.

Thank you everyone.

 

[Shark]

It is a lot to take in. Rushing it just overwhelms a person, even to the point that some just give up. Hang in there, keep studying, you'll get there.

 

[gregory-d]

It is a lot to take in. Rushing it just overwhelms a person, even to the point that some just give up. Hang in there, keep studying, you'll get there.

Thanks Shark
If anything I am persistent.
If it was easy everyone would be doing it.

 

[Martijn]

I can collect and dry the residue

I would keep it stored wet until refined. Dust can get airborne. The only dust i store dry is washed precipitated gold.