Any gold dissolved in HCl?

[Tahmoures]

Hello everyone
newbie is posting.
I was dissolving tin in 32% HCl and this happend that is shown in the picture uploaded.
In chemistry gold wouldn't be dissolved in HCl but i couldn't find out why does these fingers color changed?
These are ddr/ddr2 ram fingers.
There is another picture from a tablet main board that was gold plated and same happend to this board too.

Could you please help me to findout?

Thanks for your attention
Tahmoures

 

[Yggdrasil]

Hello everyone
newbie is posting.
I was dissolving tin in 32% HCl and this happend that is shown in the picture uploaded.
In chemistry gold wouldn't be dissolved in HCl but i couldn't find out why does these fingers color changed?
These are ddr/ddr2 ram fingers.
There is another picture from a tablet main board that was gold plated and same happend to this board too.

Could you please help me to findout?

Thanks for your attention
Tahmoures

There are no pictures.
And you are right, Gold are not touched by HCl, but base metals dissolved in the HCl might cement out on the Gold even if it should not.
A lot if real life things happen when things get complicated even sometimes defies general theories.
In these cases I think they react to the Nickel plating under the Gold.

 

[Yggdrasil]

Hello everyone
newbie is posting.
I was dissolving tin in 32% HCl and this happend that is shown in the picture uploaded.
In chemistry gold wouldn't be dissolved in HCl but i couldn't find out why does these fingers color changed?
These are ddr/ddr2 ram fingers.
There is another picture from a tablet main board that was gold plated and same happend to this board too.

Could you please help me to findout?

Thanks for your attention
TahmouresView attachment 56125View attachment 56126

Aah now the pictures arrived. There should not be much gold in there.
But I suppose my explanation still holds.

 

[FrugalRefiner]

All HCl requires is an oxidizer to dissolve gold. The oxygen in the air is sufficient. The air dissolves into the HCl, and the gold can dissolve.

Dave

 

[Yggdrasil]

All HCl requires is an oxidizer to dissolve gold. The oxygen in the air is sufficient. The air dissolves into the HCl, and the gold can dissolve.

Dave

I have seen this happen before, when there is sufficient Tin dissolved. and you put in fresh in my case pins.

 

[Tahmoures]

All HCl requires is an oxidizer to dissolve gold. The oxygen in the air is sufficient. The air dissolves into the HCl, and the gold can dissolve.

Dave

Dear Dave
Thanks for your reply and your point.
I was bubbling air for better reaction between HCl and tin and reaction was running for an hour and a half.
But I'm a little confused, if HCl and air can dissolve gold how AP process can dissolve base metals without dissolving any of gold?

And in this case how can I get the gold ut of my solution?

Thanks again

 

[Tahmoures]

Aah now the pictures arrived. There should not be much gold in there.
But I suppose my explanation still holds.

Hi!
Thanks for your answer
I was thinking about it too. Im using nitric acid for the next step for dissolving copper and ill do it tomorrow. I'll do it tomorrow with a small batch as an observation for getting an answer
I was thinking about what dave said and I'm so happy that I have you guys with a lot of experience that you share with me.

So there is a question in my head after that and it is how we use AP as base metar removal method when CuCl2 or peroxide that is used is an oxidizer as same as oxygen in the air?

 

[FrugalRefiner]

In the AP process, a small amount of gold can dissolve, but because the gold and base metals are electrically connected, the chemical reaction goes for the base metals as the easier target. Any gold that dissolves eventually cements out on the base metals and is eventually recovered along with the foils.

Dave

 

[Saddiq NG]

I have for a very long time been suspecting that HCl can dissolve some gold even without nitric acid.
In this case however I do not think the gold is dissolved since the PCB substrate below the gold plating is not revealed.
It is the tin that the HCl dissolved that is being deposited on the gold.
Whenever you see this, just add a few drops of dilute (1:3) nitric acid on the affected area, and the gold plating will re-appear.

 

[Yggdrasil]

I have for a very long time been suspecting that HCl can dissolve some gold even without nitric acid.
In this case however I do not think the gold is dissolved since the PCB substrate below the gold plating is not revealed.
It is the tin that the HCl dissolved that is being deposited on the gold.
Whenever you see this, just add a few drops of dilute (1:3) nitric acid on the affected area, and the gold plating will re-appear.

It is not necessary, the HCl will remove it eventually during the AP process.
The Nitric together with the HCl will dissolve some of the Gold and create a paste of Stannic acid to bind the cemented Gold particles.
It won't affect much of the Gold but it creates unnecessary complications.

 

[kurtak]

In this case however I do not think the gold is dissolved since the PCB substrate below the gold plating is not revealed.

It is the tin that the HCl dissolved that is being deposited on the gold.

This is correct - if you rub the gray area with your finger or a wet paper towel it will expose the gold under that gray deposit on the "surface" of the gold plating

It is nothing to be concerned with as it will be removed in the next step of recovery of the foils that are plated on the copper whether you use CuCl2 (AP) or nitric acid in the next step to get rid of copper to recover gold foils

In other words - the gold is still there - it is just under that gray deposit on top of the gold - & it will take care of it self as you proceed with the rest of the processing of getting to the final product of you melted gold button

Kurt

 

[Ayham Hafez]

I got same results before, and I expected that gold still exist, after using AR I got the gold but I felt that I got less than expected.

If I wash the PCBs with NaOH after HCL leaching, does it will remove the tin cemented on the gold foils? And does washing PCBs with NaOH before using AR will affect the gold recovery?

 

[Yggdrasil]

I got same results before, and I expected that gold still exist, after using AR I got the gold but I felt that I got less than expected.

If I wash the PCBs with NaOH after HCL leaching, does it will remove the tin cemented on the gold foils? And does washing PCBs with NaOH before using AR will affect the gold recovery?

Read this thread thoroughly.
And no I do not think using NaOH will change much other than add cost to your project.
Besides that read my reply to your question in the other similar thread.