# TIN problem



## Blue01 (Apr 4, 2021)

Hello guys 
Any suggestions welcome. 
Recently we have a lot of pins that we refine and we have problems with tin mud. These contacts contain a lot of tin. We dissolve contacts in Nitric acid and extract bigger AU pieces for aqua regia but a lot of  gold is still trapped in SN mud. We have big losses in AU  on this lot.  I have tried to wash mud in hot weather for 5-6 times and leave overnight to wash nitric and salt but some salt  still remains and even after that washing for a couple of times  when we use HCL to eliminate Tin some AU still converts into solution and we are back on the start. After that we dilute  that solution and use ALU foil to drop AU from the solution but AL also drop Tin with rest metals   and we are at the beginning of the problem. We tried a couple times and every time is the same problem.

Thanks.


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## Blue01 (Apr 4, 2021)




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## butcher (Apr 4, 2021)

Incineration, and wash in HCl.


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## Lino1406 (Apr 4, 2021)

While tin dioxide is a problem, tin formed by aluminum or zinc is soluble. Hence I would recommend adding Zn to HCl to dissolve it.
SnO2 + 4H+ + Zn = Sn++ + Zn++ + 2H2O


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## Blue01 (Apr 5, 2021)

Thank you for the info. Since i do not have Zn at the moment, tmr i will try this first method. I will incineration slug, wash in hot water and try with HCL. 
Thanks for help. 
I will let you know result.


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## butcher (Apr 6, 2021)

After incinerating do not wash in water, use concentrated HCl, (water hydrolyzes the tin salts) ( I would take Lino's advice and find you some zinc too, (I believe it would make things go much smoother)...

Thanks, Lino I learn something new every day.
I don't believe I would try aluminum as it forms a gelatinous chloride, although I would consider tin or zinc.

Using zinc as Lino suggested makes a heck of a lot of common sense, in converting both the tin dioxide and the zinc into stannous chloride and zinc chloride leaving the gold.

I do not know why I haven't seen this before, we use tin and HCl instead of zinc to convert stannic chloride to stannous chloride all the time with preserving testing solutions for longer shelf life.

The tin dioxide will slowly dissolve (although hard to dissolve) in concentrated HCl, but it forms a gelatinous hydrolyzed stannic chloride solution very hard to filter.

SnO2 + HCl --> SnCl4 + H2O
and if we add HCl and tin to get stannous chloride .
SnCl4 + Sn + (HCl) -->2SnCl2 +(HCl)

Using zinc metal and HCl we would be converting the tin dioxide to stannous chloride and zinc chloride, making the tin dioxide easier to dissolve into solution as it converts to first to tin and then to stannous chloride along with the zinc chloride solution. (making this a slap my head kind of thing), or easier to dissolve and deal with in the long run. zinc being much more reactive than tin in the reactivity series of metals, I can see where zinc would be a better option (over the idea of using tin to do this with).

SnO2 + 2Zn + 4HCl → Sn + 2ZnCl2 + 2H2O
Then (with using heat to slowly evaporate excess water)
Sn + 2ZnCl2 + 2HCl + --> SnCl2 + 2ZnCl2 + H2 

The equation above is not quite balanced (which probably would be H3O acidic solution and possibly some hydrogen gases evolve along with the water vapors from the solution)



Not sure about where you live, but here in the United States of America you may find zinc in most hardware stores that sell roofing supplies, the zinc flashing metal helps to prevent mold on roofs, otherwise you might try your local scrap metal dealers. You can also try an electrician to get some zinc conduit fittings or electrical boxes...

Tin you may find in solder, and some pewters


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## Blue01 (Apr 6, 2021)

I found today ZnO, Zinc Oxide powder. Can i use that instead of pure Zinc?


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## butcher (Apr 6, 2021)

You need metal, our goal is to use the metal to convert your tin oxide to tin metal, in doing so the zinc is oxidized while reducing tin, Now the tin metal more easily dissolves into solution as stannous chloride along with the zinc chloride.

Zinc oxide does not have an electron to share it's tied up in a bond with oxygen. So it will not help to convert the tin oxide to tin, in order to make it easier to dissolve and to keep in solution at a higher valence...

While zinc metal has a full shell of electrons and willing to share one with a less reactive metal like tin.


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## Platdigger (Apr 6, 2021)

I would try a small sample in warm dilute sulfuric.


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## g_axelsson (Apr 6, 2021)

Sodium hydroxide could probably help too. I've tried it some time and it dissolved some of the finer tin mud and left a coarser remainder that was easier to filter after aqua regia.

Göran


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## Geo (Apr 21, 2021)

Add sodium hydroxide until all of the tin has been reacted forming tin oxide and short lived tin hydroxide. Add acetic acid (vinegar from the market will work) forming tin acetate (tin(II) acetate or stannous acetate). Make sure the material is dry before starting and do not add water. Once all of the tin oxide has reacted to the acetic acid, add HCl in small increments to dissolve the stannous acetate. The tin is now in solution and can be filtered from the gold foils.


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## Rock Boulders. (Jan 7, 2022)

I'm glad to find this post this is my Biggest Problem. I have 80au20sn computer parts, this is for real it is very hard to get off the tin,for gold. But I didnt try it yet to put in The AuSn in delute Royal water, I boiled it first in nitric until it turns dust and put in the Royal water HCl20% Hno65% but in my 20grams sample I loss of so much gold I'd only recover 5grams of 99.9 gold. I think I made A mistake using HCl 20% a.k.a muriatic acid in the toilet?


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## orvi (Jan 7, 2022)

this may be of some help  process is pretty well explained in the article, also given the temperatures and ammounts of reducers (zinc or magnesium).


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