Problems with matastannic acid

[denim]

I have read many times here on the forum about metastannic acid creating problems during the refining process. Can anyone expain to me what type of problems occur with metastannic acid other than slow filtering when processing gold from say cell phone boards, and/or other boards which contain solder. Does metastannic acid reduce yields? When I process 'solder boards' in nitric I end up with a lot of this gray/silver colored stuff mixed in with the foils. I clean this up with HCL. I then end up with some pretty clean foils that have mixed in with them some brownish, kind of fluffy small particulate material. Is this brown material the dreaded metastannic acid? And if so, could this be prevented by removing the solder with dilute HCL prior to processing with nitric to remove foils? If I am thinking correctly I need to first depopulate the boards, then remove the solder in dilute HCL, then remove foils with nitric, then incinerate foils to deal with metastannic acid, and then dissolve foils in poor mans AR. Does anyone care to share their ideas for processing boards with solder on them? At this time I have some boards in dilute- 3/1 - HCL to remove solder. I will process these and see if I get any of that brown fluffy stuff mixed with the foils. By the way, this brown fluffy stuff does not seem to dissolve in HCL/Cl, which through a search on the forum seems to be the case with metastannic acid. Thanks in advance.

 

[Geo]

metastannic acid is the white gooey sticky stuff that forms when dissolving tin with nitric based solutions. it causes value loss by trapping values in the form of solids and liquids. also being tin, unless the is an incomplete dissolution of the tin (it never is) it will follow the gold through many different processes. tin in solution is a strong reducing agent and will cause all PM's to precipitate out of solution as a colloid (very tiny particles that remain suspended in solution for a very long time). its best to remove tin before starting any process or refining.

 

[maynman1751]

If you pretreat in HCl to remove solder I see no need to incinerate. Also, I would remove foils with AP instead of my valued nitric. There should be no reason to end up with metastannic acid if you pretreat properly. Just my 2 centavo!

 

[Lino1406]

Unfortunately pretreatment with HCl is
good with lead free solder only
Lino1406, author "25 recovery procedures..."

 

[stardust18]

Good day to all. Brown fluffy particles is likely to lead or bismuth chloride, which may be part of the solder. Photos would help identify it. Excuse my English. Alex.

 

[denim]

Thanks to all who replied. Good info indeed.

 

[Ayham Hafez]

metastannic acid is the white gooey sticky stuff that forms when dissolving tin with nitric based solutions. it causes value loss by trapping values in the form of solids and liquids. also being tin, unless the is an incomplete dissolution of the tin (it never is) it will follow the gold through many different processes. tin in solution is a strong reducing agent and will cause all PM's to precipitate out of solution as a colloid (very tiny particles that remain suspended in solution for a very long time). its best to remove tin before starting any process or refining.

Could you check this video



It's done by my friend, he's chemist and experienced refiner.

At minute 8:00 he shows that when we dissolve metastannic acid into HCl we get stannic ions that doesn't precipitate any PM's unlike stannous ions.

I didn't try to incinerate metastannic acid before, usually I just dissolve it into AR after finish nitric acid parting with no issues.

 

[Yggdrasil]

Could you check this video



It's done by my friend, he's chemist and experienced refiner.

At minute 8:00 he shows that when we dissolve metastannic acid into HCl we get stannic ions that doesn't precipitate any PM's unlike stannous ions.

I didn't try to incinerate metastannic acid before, usually I just dissolve it into AR after finish nitric acid parting with no issues.

Metastannic acid do not dissolve.
If it creates problems or not is solely a function of amount.

 

[Ayham Hafez]

Metastannic acid do not dissolve.
If it creates problems or not is solely a function of amount.

From the video and from my experience, metastannic acid dissolve completely in HCl, usually I use concentrated nitric acid to part E-waste alloy that has tin, so no way to get tin nitrates, I get a white cloudy metastannic acid that took long time to precipitate to the bottom of the beaker, after finish I make abd filtration then add HCl with some heat all metastannic acid dissolved.

 

[Yggdrasil]

Tin dissolves in HCl but if the metastannic acid has formed it is too late for HCl.
It will not dissolve in any of our common acids as far as I know.
That is why it is considered as our curse.
You will have to roast it in order to dissolve it in HCl.
If it dissolves, it is not Metastannic acid but something else.

 

[Ayham Hafez]

Tin dissolves in HCl but if the metastannic acid has formed it is too late for HCl.
It will not dissolve in any of our common acids as far as I know.
That is why it is considered as our curse.
You will have to roast it in order to dissolve it in HCl.
If it dissolves, it is not Metastannic acid but something else.

What about the shared video, tin solders dissolved in concentrated nitric acid, is it not metastannic acid?

 

[Yggdrasil]

What about the shared video, tin solders dissolved in concentrated nitric acid, is it not metastannic acid?

I have not seen the video.
I'm on a phone at the time.
Videos in general have a serious issue, and that is that we only see what the producer wants us to see.
So they are as trustworthy as our trust to the producer.
Since he is a friend of yours, you could have a talk with him and ask how he do it?

Edit to add text.

 

[Shark]

Since he is a friend of yours, you could have a talk with him and ask how he do it?

Best all around reply to that. And it could shed some light on it for more of us here as well.

 

[Ayham Hafez]

I have not seen the video.
I'm on a phone at the time.
Videos in general have a serious issue, and that is that we only see what the producer wants us to see.
So they are as trustworthy as our trust to the producer.
Since he is a friend of yours, you could have a talk with him and ask how he do it?

Edit to add text.

I already talked to him, and this is what he said:

To solubilize metastannic acid many refiners suggest incineration then dissolution but this is what I've found , metastannic acid is soluble in high concentrated HCl and solubility increased by adding Aluminum. Further metastannic acid on its own will not cause losing PMs just it contaminates them. Also in one section Hoke referred Tin white paste is soluble in 50% sulfuric acid solution but it wasn't feasible

Stannic has no effect on gold unless another reducing metal is present in the solution (like Aluminum zinc iron, in metallic form)
Once i tried to precipitate gold from a contaminated (tin) solution with zinc powder . And all of my solution turned into a deep purple... To fix that i just added bleach and precipitate it again with Ferrous sulfate

Done.

 

[Yggdrasil]

I already talked to him, and this is what he said:

To solubilize metastannic acid many refiners suggest incineration then dissolution but this is what I've found , metastannic acid is soluble in high concentrated HCl and solubility increased by adding Aluminum. Further metastannic acid on its own will not cause losing PMs just it contaminates them. Also in one section Hoke referred Tin white paste is soluble in 50% sulfuric acid solution but it wasn't feasible

Stannic has no effect on gold unless another reducing metal is present in the solution (like Aluminum zinc iron, in metallic form)
Once i tried to precipitate gold from a contaminated (tin) solution with zinc powder . And all of my solution turned into a deep purple... To fix that i just added bleach and precipitate it again with Ferrous sulfate

Done.

Nobody has said it has any effect on Gold, it just hides the foils and powders in the Tin paste so you can't get to it.
And precipitating/cementing it into existing Tin paste just plainly is not a good idea.

 

[Ayham Hafez]

Nobody has said it has any effect on Gold, it just hides the foils and powders in the Tin paste so you can't get to it.
And precipitating/cementing it into existing Tin paste just plainly is not a good idea.

I have a nitrate solution for e-waste alloy parting that has metastannic acid cause its cupellation not done well,will finish dissolving base metals within few hours, this is not the first time I have such solution and test, but today will incinerate the filtered material after adding HCl and making AR to see if there any PM's lost, also its very easy to make the test shown in the video, some tin solders dissolve in nitric then use HCl to dissolve it

 

[Ayham Hafez]

Two experiment has been done, first was a nitrate solution has metastannic acid as the picture, it was very hard to filter, after finish filtering I added concentrated HCl with some heat, all metastannic powder dissolved and after added some nitric drops, it make no precipitation or any stannous test colors in the solution.


Second, simply added nitric to tin solders and after been dissolved, I added HCl, the metastannic acid dissolved in HCl, when tried to make stannous test with same solution on a gold bearing solution it gives no stannous results, so simply adding HCl to metastannic acid dissolves it easily and it doesn't make stannous chloride.

 

[Yggdrasil]

Two experiment has been done, first was a nitrate solution has metastannic acid as the picture, it was very hard to filter, after finish filtering I added concentrated HCl with some heat, all metastannic powder dissolved and after added some nitric drops, it make no precipitation or any stannous test colors in the solution.


Second, simply added nitric to tin solders and after been dissolved, I added HCl, the metastannic acid dissolved in HCl, when tried to make stannous test with same solution on a gold bearing solution it gives no stannous results, so simply adding HCl to metastannic acid dissolves it easily and it doesn't make stannous chloride.

Interesting.
What is that last picture showing?

 

[Ayham Hafez]

Interesting.
What is that last picture showing?

After dissolving metastannic acid, I got white precipitation because I didn't make filtration very well, this is lead chloride and some silver chloride.

 

[Martijn]

Could you check this video



It's done by my friend, he's chemist and experienced refiner.

At minute 8:00 he shows that when we dissolve metastannic acid into HCl we get stannic ions that doesn't precipitate any PM's unlike stannous ions.

I didn't try to incinerate metastannic acid before, usually I just dissolve it into AR after finish nitric acid parting with no issues.

It looks like you just debunked a phenomena we took as a fact of life.

Could the boiling action of the metastannic acid in HCl be the oxidizing factor, like incinerating, so that HCl can attack it? Like oxygen and HCl can dissolve copper, but HCl alone can not.

Good find, so you suggest to use this procedure to be able to filter pm dust and foils from the soluble stannic acid and recover the tin before converting with aluminum to stannous chloride.

For those cases where the tin paste can not easily be avoided, it will be a great option.