# How to separate silver and tin



## wjbtd (Feb 27, 2012)

Our company got some silver scrap(about 85% silver and 15% tin ,).
We dissolved the scrap in nitric acid,the tin became tin oxide.
It's really hard to filter.Tin oxide is a very find and viscos particle .
Can someone give me some instrutions (We only recycle the silver).Thanks a lot.


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## goldsilverpro (Feb 27, 2012)

wjbtd said:


> Our company got some silver scrap(about 85% silver and 15% tin ,).
> We dissolved the scrap in nitric acid,the tin became tin oxide.
> It's really hard to filter.Tin oxide is a very find and viscos particle .
> Can someone give me some instrutions (We only recycle the silver).Thanks a lot.



If it is truly 85/15 Ag/Sn, with no cadmium, I would just run it through a horizontal (Thum) silver cell. The metastannic acid formed from the tin stays on top of the filter cloth.


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## Nurlela (Feb 28, 2012)

goldsilverpro said:


> wjbtd said:
> 
> 
> > Our company got some silver scrap(about 85% silver and 15% tin ,).
> ...


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## Westerngs (Feb 29, 2012)

If you have already dissolved all the scrap and do not have the option of electrolytic refining, the best available option may be to let the solution sit for a few days, let the metastannic acid settle, and pump off the majority of the silver nitrate. Unfortunately, I know of no acids or bases that will dissolve the metastannic acid and I have had trouble filtering it even with ultrafiltration columns.

Good luck.


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## goldsilverpro (Feb 29, 2012)

I'm thinking Harold gave a way to dissolve metastannic acid with HCL.


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## Harold_V (Feb 29, 2012)

goldsilverpro said:


> I'm thinking Harold gave a way to dissolve metastannic acid with HCL.


I dealt with it when processing gold that was contaminated by incinerating, then digesting the solids in HCl. Whether it eliminates the stannous chloride or not I can't say, but it does convert the material to a substance that can be filtered. That allowed the gold chloride to be filtered without problems. I had this experience a few times when I played with escrap. I did not normally process the stuff, however, so my exposure was limited. I followed this same procedure when processing eye glass frames, however, and it paid huge dividends in yielding a solution that was easy to filter after the values had been dissolved. Incineration with a succeeding HCl wash is quite critical to easy filtering of material contaminated with tin. 

I did this routinely, when I processed dental amalgam, After it was retorted, it was subjected to being heated in an open vessel (I used an old staginess fry pan) until the remains were melted. Due to the tin content, that happens at a relatively low temperature, although I am at a loss to specify what that may be. The material was stirred and kept molten for a short period of time, and then was stirred with heat removed, so it was broken up upon freezing. The resulting alloy was then digested in dilute nitric. 

I *did not filter*, nor is it required. The resulting material was quick to settle, so the solution, which was poured off, including the light material that was in suspension, was allowed to settle. It happened quickly. It was then siphoned, with copper introduced to cement the contained silver. All goes without a hitch. The remaining solids, which would have accumulated in the settling vessel, along with traces of solution, can then be filtered, seemingly without problems. 

Anything that followed the silver when it was cemented, I'm quite comfortable, was removed by fluxing, and if not, it was separated in the silver cell. Bottom line here is that tin contaminated silver can be successfully processed, but you must do some work prior to digesting, otherwise you may be stuck with one hell of a mess. 

Harold


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## dtectr (Feb 29, 2012)

According to an older text I found in google books Incineration to red heat converts the metastannic acid (insoluble in all acids and bases) to tin oxide, soluble in concentrated HCl and H2SO4.


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## Alkymida (Sep 26, 2012)

Hi - Especially Harold

I bought 1 kg af dental alloy very, very cheap. :0)
It is powder in a bottle containing 67% Silver, 27% Tin, 5% Copper and 1% Zink.

I would like to process it without melting it first because I have difficulties doing that where I live.

Wouldnt HCl be the acid of choice to start with?

/Peter


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## Westerngs (Sep 26, 2012)

Alkymida,

Yes, HCl would be the way to start. It would dissolve the tin and zinc. Because of the high surface area of the powder, some of the silver may form silver chloride.


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## etack (Sep 26, 2012)

dilute your HCl and *DO NOT *heat. you shouldn't get any AgCl

Eric


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## Alkymida (Sep 26, 2012)

Thx Westerngs :0)

If I start out with a weak acid it might not be a big problem, and the copper will take the chloride from the silver, I think.

Eric: Just my thoughts. :0)

/Peter


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## etack (Sep 26, 2012)

All that you are really trying to do with the HCl is remove the tin and zinc. After that you will meed to incinerate and the add nitric acid this will dissolve the rest and then you cement it back out with Cu.

Eric


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## Alkymida (Sep 26, 2012)

Hi again Eric

That was my plan. However there is this problem: It´s become illegal to buy/pocess nitric acid beyond 50% in Denmark.

The law to fight terror have given lots of pronblems: No konc. sulphuric acid, no 72% nitric acid, hydroperoxide still weaker - and now someone would have a law against chloric acid because of some assaults recently...

Life as an alchemist ain't so easy no more! :0(

EDIT: I will start with a small portion and put up pictures of the proces.

/Peter


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## etack (Sep 26, 2012)

Nitric acid at 50% will work just fine just don't dilute it add it slow or it will boil over. Finely divided metals react fast with acids. "FYI"

Eric


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## Alkymida (Sep 26, 2012)

Hi Eric

Yes, I know about the reactivity of nitric acid and pulverized metals.
So I´ve decided to do some calculations in a spreadsheet first, put the nitric acid in a large beaker and add the metal in small portions.
The exothermal proces will be easier controlled by the large cold mass versus small reacting mass, I think.
If I put the acid directly on all the metal it will be very hot and create large volumes of NO.
Waste of expensive acid and pretty dangerous.

Have done it before with Sterling silver in a smaller scale and reduced with aluminumfoil.
I got some very pure and very pretty silver crystals.
And I´m in no hurry. :0)

Peter


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## Geo (Sep 27, 2012)

just throwing this out there. if you do some research on metastannic acid, you will find that in all the information about it, its a made up compound. we use the term all the time and you can find literature about it, but its not really a substance. the correct name for it is hydrated tin oxide. View attachment MSDS-002 Metastannic Acid (Acid Tin Oxide).pdf


from the university of Denver "As an acidic element, tin forms H2SnO3, metastannic acid, and H2SnS3, thiostannic acid. A salt of thiostannic acid is important in qualitative analysis, where the reaction SnS2 + Na2S → Na2SnS3 is used to dissolve the sulphide so that tin can be separated from the other cations in its group. Tin forms unstable nitrates, Sn(NO3)2·20H2O, with an extraordinary amount of water of crystallization, Sn(NO3)4, that decomposes at 50°C, and SnO·Sn(NO3)2, which has the temerity to explode when heated."

i will have to hunt some more to find the links for the websites all over again, but, from what ive read about it, metastannic acid became a common term not too long ago.

so, metastannic acid is already an oxide, its just in a hydrated form.


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## 9kuuby9 (May 14, 2013)

Ideally you should Start whit HCl to dissolve problematic base metals such as Sn (tin).

adding H2SO4 to SnO2 (whit extra H2O) or SnO Wil turn in a sulfate salt and that salt is soluble in water, but you'll have to keep the solution under de boiling point of SnSO2 (Tin sulfate) keep it around 25°C; otherwise it will start decomposing back to SnO2 and SO2.

In your case you will have to neutrolize the nitrate solution by deluting it whit water and a litlle heat to drive off excess HNO3. Then adding H2SO4 will drop Pb (lead) from your solution; afterwards the solution will start to clear up from the cloudy SnO2. keep adding until the solution clears up.

And now you can cement or drop your Ag from your solution.


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