Aqua regia process post sulfuric stripping

[gregory-d]

Peroxide is an oxidizer. HCl and an oxidizer dissolves gold. HCl and a strong peroxide can be used in place of AR, or HCl and nitric acid. For AP a 3% peroxide is the usual, but if you go to 12% or even 30% it will put very fine gold powders into solution.

AP is HCl with a tiny bit of, usually, 3% peroxide. Just enough to start the copper oxidizing without putting the gold into solution. Or at least as little gold as possible. This can also be done using an air supply, such as an aquarium air pump. This takes a little longer, but reduces the risk of the gold going into solution.

This is another way for many people to still work with gold in countries where nitric just isn't available. It also is another method in the tool kit for those interested in the science and wanting to know as many ways as possible to get to the gold.

Ok thank you I have some High concentration old 35% Hydrogen Peroxide so I'll give it a go It will be easier to handle the off gas as I haven't yet built a scrubber.
I am guessing that there may still be some solids after doing it so I will save the residue and put it through the AR process later.

 

[Yggdrasil]

Ok now I am getting confused again HCl and Peroxide is AP?
What I understand is that it doesn't dissolve the gold it just dissolves everything else leaving the gold as a solid.
Is that right?
But what about silver chloride I read here that it precipitates out in acid. So that will also be in the sludge as well won't it.

Silver will not dissolve much if Chlorides are present.

 

[gregory-d]

Silver will not dissolve much if Chlorides are present.

Ok thanks

 

[gregory-d]

Well I went with AR as I thought I had more information on it but my first attempt was a total failure.
I thought I had a reasoable amount of gold from the sulphuric stripping cell but ended up with absolutely nothing to show for my efforts apart from one small but powerful wiff of the Nitric gas.
Wow that stuff is dangerous stuff it wasn't even strong.
I tried to keep the reaction slow by keeping the temperature down, maybe that was why I ended up with nothing but what looks like SMB in bottom in the end.
Yes I over shot the hell out of the nitric and tried to use copper.
I ended up with blue green liquid (ie. copper in solution) maybe the gold bound to that.
I'll cement it all out and future Gregory might know what to do about it.
The fume hood did most of the extraction but it would not have handled a strong reaction.
I will build a better one and a scrubber as well before I do that again.
I will persist. I am learning and making many mistakes but still moving on.

Just a question not sure if this should be a new thread but it sort of fits here as well.
If I drop the tin with HCl and heat after the sulphuric stripping and before the nitric,
is it really worth bothering about removing the solder when I depopulate the PCBs (I have a lot of telecom gold plated PCBs)?

 

[Yggdrasil]

Well I went with AR as I thought I had more information on it but my first attempt was a total failure.
I thought I had a reasoable amount of gold from the sulphuric stripping cell but ended up with absolutely nothing to show for my efforts apart from one small but powerful wiff of the Nitric gas.
Wow that stuff is dangerous stuff it wasn't even strong.
I tried to keep the reaction slow by keeping the temperature down, maybe that was why I ended up with nothing but what looks like SMB in bottom in the end.
Yes I over shot the hell out of the nitric and tried to use copper.
I ended up with blue green liquid (ie. copper in solution) maybe the gold bound to that.
I'll cement it all out and future Gregory might know what to do about it.
The fume hood did most of the extraction but it would not have handled a strong reaction.
I will build a better one and a scrubber as well before I do that again.
I will persist. I am learning and making many mistakes but still moving on.

Just a question not sure if this should be a new thread but it sort of fits here as well.
If I drop the tin with HCl and heat after the sulphuric stripping and before the nitric,
is it really worth bothering about removing the solder when I depopulate the PCBs (I have a lot of telecom gold plated PCBs)?

PCBs has no business in a Sulfuric stripping cell.
But HCl on solder has always a place.

 

[Martijn]

Ok thank you I have some High concentration old 35% Hydrogen Peroxide so I'll give it a go It will be easier to handle the off gas as I haven't yet built a scrubber.
I am guessing that there may still be some solids after doing it so I will save the residue and put it through the AR process later.

Depending on exactly how old that H2O2 is, there may not be much H2O2 left in the container. It breaks down over time.
https://www.thoughtco.com/hydrogen-peroxide-shelf-life-3975974

 

[gregory-d]

PCBs has no business in a Sulfuric stripping cell.
But HCl on solder has always a place.

Thanks Yggdrasil I didn't do the PCBs yet.
My question about solder is do it at the start or do it in after the stripping,
PCBs are a side issue in that case really.
Also why do you say that about PCBs if the ground plane is gold and connected electrically that connection will be maintained by the copper and nickel and it will be out of the bath by then.

 

[gregory-d]

Depending on exactly how old that H2O2 is, there may not be much H2O2 left in the container. It breaks down over time.
https://www.thoughtco.com/hydrogen-peroxide-shelf-life-3975974

Thanks Martijn
That was another reason I went with AR this time. After reading more I thought as much about the peroxide. I did order some new stuff for the next time though.

 

[Yggdrasil]

Thanks Yggdrasil I didn't do the PCBs yet.
My question about solder is do it at the start or do it in after the stripping,
PCBs are a side issue in that case really.
Also why do you say that about PCBs if the ground plane is gold and connected electrically that connection will be maintained by the copper and nickel and it will be out of the bath by then.

Only the electrically connected parts will give up their Gold.
So even in the best case it will be partially stripped.

 

[gregory-d]

Only the electrically connected parts will give up their Gold.
So even in the best case it will be partially stripped.

Yeah but the gold is the ground plane so it is connected over the whole board.
If the gold is stripped the connection will persist via the copper under the gold overlay and via the vias.
Also if there is a section that is not connected and not stripped it will be easy to spot
and deal with in the traditional manner.
That is why I was asking about the solder. I may miss the gold under the solder but if I do the HCl
with heat as you suggested just prior to the nitric it will be easier to get the heat into the reaction.

I kicked myself many times having not clearly read the information you gave me about nitric and overshooting it by way too much.
I did read it properly later but it is easy to be smart in hindsight.
Thank you for your input it is invaluable.

 

[Yggdrasil]

Yeah but the gold is the ground plane so it is connected over the whole board.
If the gold is stripped the connection will persist via the copper under the gold overlay and via the vias.
Also if there is a section that is not connected and not stripped it will be easy to spot
and deal with in the traditional manner.
That is why I was asking about the solder. I may miss the gold under the solder but if I do the HCl
with heat as you suggested just prior to the nitric it will be easier to get the heat into the reaction.

I kicked myself many times having not clearly read the information you gave me about nitric and overshooting it by way too much.
I did read it properly later but it is easy to be smart in hindsight.
Thank you for your input it is invaluable.

Why do you want to use Nitric on something that is stripped already?
And the exceedingly few boards with this much Gold will be better treated in AP directly.
Maybe Nitric directly if the amount of solder is not excessive.

 

[gregory-d]

Why do you want to use Nitric on something that is stripped already?
And the exceedingly few boards with this much Gold will be better treated in AP directly.
Maybe Nitric directly if the amount of solder is not excessive.

Until yesterday I didn't know anything about the high concentration AP.

Are you saying the AP will strip the solid gold straight off the board?

I was under the impression it would only work with gold powder.

I have not yet found much information about using High conc AP on fine gold but it would be much more preferable.
I will definitely look into it.
If anyone has links on using High conc H2O2 AP I would be most grateful.
Most info I found is about low conc AP removing base metals.
I am really interested to see if this will work as the environmental impact is much lower than AR.
Also after today I am even more hesitant using AR. Yes if I have to I will build the correct equipment but AP would save me even that job.

What I am thinking of here unless it can be used directly on the boards.

1 Depopulating the boards
2 then a deep wide sulphuric cell (the boards are about 300mm x 300mm) loading them in vertically so the gold will settle over a smaller area and be easier to collect.
Remove the boards as soon as the current drops and put the boards aside for more processing later.

3? Maybe wash the residue in hot HCl to dissolve any tin (this may not be required) I will listen to the views of others on this.
4 Then use High conc H2O2 AP to dilute the gold.
5 drop the gold
But will SMB drop the gold or is there a better alternative.

 

[gregory-d]

actually after today's major failure I am thinking just to
strip the boards in the cell
dilute the sulphuric and filter then Hot HCl the residue filter
Then just melt the results.
At least then I will have a solid not 24k Gold but pretty high if I get the cell right
I can refine all of it later.

 

[FrugalRefiner]

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

 

[Yggdrasil]

Until yesterday I didn't know anything about the high concentration AP.

Are you saying the AP will strip the solid gold straight off the board?

I was under the impression it would only work with gold powder.

I have not yet found much information about using High conc AP on fine gold but it would be much more preferable.
I will definitely look into it.
If anyone has links on using High conc H2O2 AP I would be most grateful.
Most info I found is about low conc AP removing base metals.
I am really interested to see if this will work as the environmental impact is much lower than AR.
Also after today I am even more hesitant using AR. Yes if I have to I will build the correct equipment but AP would save me even that job.

What I am thinking of here unless it can be used directly on the boards.

1 Depopulating the boards
2 then a deep wide sulphuric cell (the boards are about 300mm x 300mm) loading them in vertically so the gold will settle over a smaller area and be easier to collect.
Remove the boards as soon as the current drops and put the boards aside for more processing later.

3? Maybe wash the residue in hot HCl to dissolve any tin (this may not be required) I will listen to the views of others on this.
4 Then use High conc H2O2 AP to dilute the gold.
5 drop the gold
But will SMB drop the gold or is there a better alternative.

Drop this and study first.

 

[Shark]

Boards in a stripping cell run into many problems. The gold does not come off evenly or follow the leading edges. This causes breaks in the gold and underlying base metals and won't allow the metals to be fully removed. Most masks also run to the edge of the boards and will hold a large amount of material under the mask and cause drastic losses as well. By the time these problems are corrected, using AP processing would end up being quicker and cleaner.

 

[Yggdrasil]

Until yesterday I didn't know anything about the high concentration AP.
There are no high concentration AP only HCl/Peroxide which will easily dissolve Gold foils and powder, not well suited at solid Gold.

Are you saying the AP will strip the solid gold straight off the board?
No the Cupric Chloride leach will dissolve the Copper behind the Gold and release the Gold as powder or foils.

I was under the impression it would only work with gold powder.

I have not yet found much information about using High conc AP on fine gold but it would be much more preferable.
I will definitely look into it.
If anyone has links on using High conc H2O2 AP I would be most grateful.
Most info I found is about low conc AP removing base metals.
I am really interested to see if this will work as the environmental impact is much lower than AR.
Also after today I am even more hesitant using AR. Yes if I have to I will build the correct equipment but AP would save me even that job.

What I am thinking of here unless it can be used directly on the boards.

1 Depopulating the boards
2 then a deep wide sulphuric cell (the boards are about 300mm x 300mm) loading them in vertically so the gold will settle over a smaller area and be easier to collect.
Remove the boards as soon as the current drops and put the boards aside for more processing later.
Shark talked about some of the drawbacks of this. The uneven stripping comes form uneven potential over the Gold bearing areas, thickness of the Gold bearing area, distance to the cathode and more factors. Howe many of these boards do you have? I have not seen one suited for a stripping cell, so far.

3? Maybe wash the residue in hot HCl to dissolve any tin (this may not be required) I will listen to the views of others on this.
If you use AP aka Cupric chloride it is not needed, it will dissolve the Tin too.
4 Then use High conc H2O2 AP to dilute the gold. As said no such thing, but what do you mean about dilute the Gold? Dissolve it?
5 drop the gold
But will SMB drop the gold or is there a better alternative. SMB will drop the Gold.

I will elaborate a bit in Bold inside the quote.

 

[Shark]

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.

 

[Martijn]

Also if there is a section that is not connected and not stripped it will be easy to spot

Taking a copper rod connected to the positive lead dan strip such pices manually by pressing it down by hand.
But as said on most PCB's it will not work very good. Components are gone or traces are not connecting.
Another thing is big flat PCB surfaces are rarely plated thick but are ENIG plated. As it it meant to serve as an anti corrosion layer, not a contact point that needs a more robust and thicker gold layer.

 

[Martijn]

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.

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