Metastannic acid discovery?

[Wonka]

Unless he push the pH past 7, he would just convert the HCl to NaCl and water.
HCl + NaOH gives NaCl and H₂O

Then he dries it and add acetic acid which dissolves the Meta Stannic Acid H₂O₃Sn
by creating Tin Acetate, which is soluble in HCl.

If you roast it after the neutralization you will create a mess by melting the NaCl.

On the other hand if you roast it without adding NaOH you will convert the
Meta Stannic Acid H₂O₃Sn to SnO2 which also is soluble with HCl.

Anyway the easiest is to not make Meta Stannic Acid in the first place.

I have a question. Since tin has such a low melting point can’t I just throw this in the induction heater, melt it, then put it into hcl?

Nevermind, I just looked up tin oxide and it’s very high. What a pain. The processors I’m working with must have a tin base under the BGAs. I think I might approach these in a different way in the future.

 

[Wonka]

Well if it is indeed Silver Chloride and MetaStannic acid.
Silver Chloride will not react at all with Acetic acid.
Mind you, I have not tried nor tested with Acetic acid.
But if it works, what will be left, are Silver Chloride and other insolubles.

Wouldn’t the sodium hydroxide cause the silver chloride to breakdown into silver oxide?

 

[Thomas M Joseph]

Metastannic acid will not react with acetic acid.

 

[Yggdrasil]

Metastannic acid will not react with acetic acid.

Are you sure, Geo's recipe indicated he had used it successfully.
Anyway, my go to if I need it, is to roast it and then HCl

 

[Yggdrasil]

Wouldn’t the sodium hydroxide cause the silver chloride to breakdown into silver oxide?

No, you are neutralizing the solution not making it alkaline. pH 7

 

[Wonka]

Are you sure, Geo's recipe indicated he had used it successfully.
Anyway, my go to if I need it, is to roast it and then HCl

What do you use to roast it in? I imagine it sticks to everything if it gets red hot.

 

[Yggdrasil]

What do you use to roast it in? I imagine it sticks to everything if it gets red hot.

We are not roasting the Tin, just the Meta Stannic acid.
Melting dish has been good, but a Stainless Steel pan would do the job I'd guess.
An old frying and such.

 

[Thomas M Joseph]

Are you sure, Geo's recipe indicated he had used it successfully.
Anyway, my go to if I need it, is to roast it and then HCl

Geo's process will work, but the chemistry is this: metastannic acid and sodium hydroxide produce sodium stannate with no excess of sodium hydroxide (pH 7). If the solution becomes alkaline an undesireable precipitate of sodium p stannate will occur. The sodium stannate produced will be a hydrated form called sodium hexahydrate tin IV. This must be dehydrated to form anhydrous sodium stannate(Geo's drying step), which can then be reacted with acetic acid to form stannous acetate (soluble in slightly acidic solution with HCl). Sorry to answer my own question but it took a while to find because of the different reactions that can occur with complexes of tin. Thanks for your help in understanding the process as inevitably, we have all produced metastannic acid at some point.

 

[Joseph Pramudito]

Geo's process will work, but the chemistry is this: metastannic acid and sodium hydroxide produce sodium stannate with no excess of sodium hydroxide (pH 7). If the solution becomes alkaline an undesireable precipitate of sodium p stannate will occur. The sodium stannate produced will be a hydrated form called sodium hexahydrate tin IV. This must be dehydrated to form anhydrous sodium stannate(Geo's drying step), which can then be reacted with acetic acid to form stannous acetate (soluble in slightly acidic solution with HCl). Sorry to answer my own question but it took a while to find because of the different reactions that can occur with complexes of tin. Thanks for your help in understanding the process as inevitably, we have all produced metastannic acid at some point.

Those Belgrade Univ researchers that refered by "Elemental" on page 1 of this thread have another paper specifically addressing leaching of tin iv oxide a.k.a metastannic acid that the detail might of interest to you.

https://cherry.chem.bg.ac.rs/handle/123456789/4276
They found that Magnesium will leach out 99% of metastannic acid. But you have to bring it to 90°C so tin II will be the only final product instead of a mixture with tin iv. The Gibbs of tin iv is closer to zero than tin II at 90°, inverted from room temperature. Note that in this Mg processes H2 is released, so NaOH might go a similar path with the hydroxide became water.

 

[Yggdrasil]

Those Belgrade Univ researchers that refered by "Elemental" on page 1 of this thread have another paper specifically addressing leaching of tin iv oxide a.k.a metastannic acid that the detail might of interest to you.

https://cherry.chem.bg.ac.rs/handle/123456789/4276
They found that Magnesium will leach out 99% of metastannic acid. But you have to bring it to 90°C so tin II will be the only final product instead of a mixture with tin iv. The Gibbs of tin iv is closer to zero than tin II at 90°, inverted from room temperature. Note that in this Mg processes H2 is released, so NaOH might go a similar path with the hydroxide became water.

Magnesium is not that cheap either, so it might be more expensive than just plain roast it directly.

 

[Geo]

Dear Yggdrasil, you misunderstand my question. I was assuming that the reaction of metastannic acid and sodium hydroxide produced sodium stannate. Then the addition of acetic acid produced stannous acetate. Correct me if this is wrong. Balanced equations would help me...especcially for the stannous acetate. Thanks for your input.

The sodium is too weak to displace the tin. The tin will react first as it is less reactive than sodium metal. If tin displaced sodium in solution, that would make someone super rich.

 

[KKris]

Hello Everyone.
I think I also have problem with metastannic acid. But a little different one. We have a smelting process where we smelt shredded printed circuit boards in a furnace. The output is a billet with 75%-78% copper and rest 10-15% Iron and 10-12% tin, precious metals and a few other metals. This we dissolve in sufuric+Nitric acid mixture to leach out copper and then take the remaining sludge through nitric and aqua regia process. The challenge we face is when after dissolution of the billet, this metastannic acid doesnt settle down. Also it is trapping gold particles so our recovery of gold takes longer time and is also not efficient. Is there any solution to this. For eg, before leaching out copper if we can do something to leach out tin. Or add some cheap coagulant to make this tin settle?

 

[Yggdrasil]

Hello Everyone.
I think I also have problem with metastannic acid. But a little different one. We have a smelting process where we smelt shredded printed circuit boards in a furnace. The output is a billet with 75%-78% copper and rest 10-15% Iron and 10-12% tin, precious metals and a few other metals. This we dissolve in sufuric+Nitric acid mixture to leach out copper and then take the remaining sludge through nitric and aqua regia process. The challenge we face is when after dissolution of the billet, this metastannic acid doesnt settle down. Also it is trapping gold particles so our recovery of gold takes longer time and is also not efficient. Is there any solution to this. For eg, before leaching out copper if we can do something to leach out tin. Or add some cheap coagulant to make this tin settle?

The only solution I see is to leach the Tin before smelting.

 

[FrugalRefiner]

I have no experience in smelting, but from what I've read, it seems that at least the tin, if not also most of the iron, should go into the slag during smelting.

Are you doing any oxygen sparging during the smelt?

I hope one of our experienced smelters will weigh in on this.

Dave

 

[KKris]

The only solution I see is to leach the Tin before smelting.

How do we do that for shredded boards? And what reagent do we use?

I have no experience in smelting, but from what I've read, it seems that at least the tin, if not also most of the iron, should go into the slag during smelting.

Are you doing any oxygen sparging during the smelt?

I hope one of our experienced smelters will weigh in on this.

Dave

Yes Dave, we use oxygen lancing. But still aren’t able to drive away iron and tin fully into slag. There needs to be a fire refining step but that eats away refractory lining of furnace faster.

 

[Yggdrasil]

How do we do that for shredded boards? And what reagent do we use?

Yes Dave, we use oxygen lancing. But still aren’t able to drive away iron and tin fully into slag. There needs to be a fire refining step but that eats away refractory lining of furnace faster.

What state are boards in before shredding?
Are they "clean" or do they still have components on them?

 

[Joseph Pramudito]

Hello Everyone.
I think I also have problem with metastannic acid. But a little different one. We have a smelting process where we smelt shredded printed circuit boards in a furnace. The output is a billet with 75%-78% copper and rest 10-15% Iron and 10-12% tin, precious metals and a few other metals. This we dissolve in sufuric+Nitric acid mixture to leach out copper and then take the remaining sludge through nitric and aqua regia process. The challenge we face is when after dissolution of the billet, this metastannic acid doesnt settle down. Also it is trapping gold particles so our recovery of gold takes longer time and is also not efficient. Is there any solution to this. For eg, before leaching out copper if we can do something to leach out tin. Or add some cheap coagulant to make this tin settle?

If you have the option to dilute the acid you use to leach out copper, you may avoid creating meta stannic acid. I don't know the exact number for "sulphuric + nitric", but for nitric just keep it under 4M concentration (about 1+3 of 65~70% HNO3 + water).

source: https://eprints.ncl.ac.uk/65770

 

[Yggdrasil]

If you have the option to dilute the acid you use to leach out copper, you may avoid creating meta stannic acid. I don't know the exact number for "sulphuric + nitric", but for nitric just keep it under 4M concentration (about 1+3 of 65~70% HNO3 + water).

source: https://eprints.ncl.ac.uk/65770

I believe that as long as you have a majority of Nitric, it will create MetaStannic acid.
If one were to use predominantly Sulfuric acid it would dissolve both the Copper Lead and Tin(Maybe).
How effective at which concentrations I can't say.

 

[Joseph Pramudito]

If you have the option to dilute the acid you use to leach out copper, you may avoid creating meta stannic acid. I don't know the exact number for "sulphuric + nitric", but for nitric just keep it under 4M concentration (about 1+3 of 65~70% HNO3 + water).

source: https://eprints.ncl.ac.uk/65770

Don't go too dilute. Under 2.73M of nitric only (about 1+5) it will cease leaching out copper.
With your billet contains 75% copper, all remaining tin and iron that happen to be located under copper can not react as well.

Should you by any cause unable to dilute the acid, and prefer to use coagulant to extract the meta stannic acid, make sure to desulphur before you continue with another wet process on the extract. It tend to form Sn-S cover that protect the meta stannic.

 

[andu]

I got some of that gray goo, i tried to dissolve some barely magnetic connectors, fairly light in weight and with gold plating, the solution barely reacted with oxy water grade peroxide, so, just in case i decided to, eventho still transparent to keep dissolving that batch of magnets in a different container, I done very well because i got A LOT of that gray goo there after, it still sitting there in a separate container this might come in handy.

Anyhow, my point is that it could be something else than tin.
It will dissolve in fresh acid/hp but will re-cement on something after a while.