# Dealing with gray metastanate gunk



## Reno Chris (Apr 18, 2014)

*Here is a little example / tutorial of one way to deal with grey metastanate powder:*
So the original reason I searched out this forum was that I inherited several pounds of gold plated pins (There is a novel way of acquiring PM scrap). The pins belonged to a friend of a friend, then when he passed away my friend got them after helping the guys wife sell off a bunch of his mining equipment, and when my friend passed away a few years later, after helping his wife sell off a bunch of his mining related equipment, I ended up with the pins and a jar of gold foils intimately mixed with a gray powder. I did see notations on the forum about the metastanate that may form, but I figured that a number of forum members deal with this from time to time, so I should be able to handle it also. So I digested the pins in nitric acid which I had on hand. It worked fine for the digestion of the copper, but just like the bottle of foils in gray powder, my nitric digestion generated a gray metastanate powder that was impossible to separate from the gold. Turns out the body of the pins was a phosphor-bronze, and probably had 3 to 6 % tin by weight. 
That is shown in the first picture which is both my foils and the the jar of foils with gray powder combined. 
So after reading the forum and seeing various way of dealing with the problem, I decided to try digestion in strong hydroxide solution. I figured if I needed to let it stand all summer to fully digest, I really didn't care. I've now had this stuff for several years anyway. I let the whole thing settle overnight and poured as much water as possible off. I then added about a teaspoon (maybe 20 grams) of Potassium Hydroxide into about 150 ml of foils and metastanate solution mixture. The light gray powder darkened fairly quickly to a darker gray. I let it sit for a few hours, but I did no incineration, heating or other unusual procedures. Afterward while stirring the mix, I noticed that it was very uniform, and so I added water to see what it would do. As I expected, the metastanate had formed a colloidal suspension allowing the gold the settle and separate. (see photo No. 2) (for forum members who don't know about colloids, Google it and look at the wikipedia entry). I then just poured off the colloid after allowing time for the gold to settle and repeated the process of adding water, settling the gold and pouring off until the liquid above the gold was clean and clear. (See photo 3). It was slick and very easy, so I wanted to share it with you all.


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## joubjonn (Apr 18, 2014)

Nice! I believe incinerating would of worked also. And then an HCl bath to dissolve the tin produced.


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## Reno Chris (Apr 18, 2014)

Oh I am not saying incineration or other methods don't work, just that this is one easy method to do it that worked well for me in this instance.


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## Geo (Apr 18, 2014)

That is pretty neat.


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## joubjonn (Apr 18, 2014)

It's a good workaround. I like it. Nice job !


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## butcher (Apr 18, 2014)

Thanks Chris for sharing.

From what I understand, potassium hydroxide KOH precipitates metastannic acid H2SnO3, which is converted to a salt of potassium.which can be soluble in water or dilute KOH solution.

I have read about this but never tried to see how it worked.


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## Reno Chris (Apr 19, 2014)

> From what I understand, potassium hydroxide KOH precipitates metastannic acid H2SnO3, which is converted to a salt of potassium.which can be soluble in water or dilute KOH solution.



I think the original gray gunk formed through the reaction of the metallic tin and the oxidizing effect of the nitric acid is metastannic acid, and by adding a strong amount of KOH, what I sort of expected was the formation of K2SnO3, a soluble potassium stannate. Heating the solution might have accelerated the reaction, but I was satisfied to see it progress at a slow rate. I am not 100% sure how the colloid forms, but it may be through some reversible reaction of 2 KOH + H2SnO3 <-> K2SnO3 + 2 H2O


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## butcher (Apr 19, 2014)

While studying tin, its salts and Amphoterism of metals I have these notes in one of my note books

Stannic salt, adding a caustic alkali to a solution of stannic salt will form a voluminous gelatinous white precipitant.
example: SnCl4 + 4 OH --> 4Cl + Sn(OH)4
this precipitant if dried in air forms Sn(OH)4, but if dried over sulfuric acid would form H2SnO3 (meta stannic acid).

Sn(OH)4 or H2SnO3 precipitate dissolves readily in excess of alkali hydroxide, forming salts which are not derived from either of the above compounds but from H2[Sn(OH)6]
H2SnO3 + 2KOH --> K2[SN(OH)4]

(the hydroxide also dissolves in ammonia solution, but only in the absence of ammonium salts).

From another note:
concentrated nitric acid and tin converts to a white insoluble powder metastannic acid, which is a hydrated oxide of tin, H2SnO4 or H2SnO3
Sn + 4HNO3 --> H2SnO3 + H2O + 4NO2
Metastannic acid is different from stannic acid because it is insoluble in acids. and with alkalies it forms salts like K2Sn5O11 or Na2Sn5O11

Tin seems to be a very complicated metal to study.


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## nickvc (Apr 19, 2014)

Chris excellent information and one to be saved as it does seem to remove the gunk, metastannic acid,without the need for incineration and further hydrochloric treatments.
For one I like it 8)


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## Platdigger (Apr 19, 2014)

Very nice! 8)


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## solar_plasma (Apr 19, 2014)

nickvc said:


> Chris excellent information and one to be saved as it does seem to remove the gunk, metastannic acid,without the need for incineration and further hydrochloric treatments.
> For one I like it 8)



I like it, too. And it is definately a new tool in my toolbox, but I think, it should only be used without further ventliatios in cases, you have material, that doesn't need to be incinerated, - like foils.


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## stardust18 (Apr 21, 2014)

Hello everyone .
Want to share my way of dealing with beta tin acid.
Take about a teaspoon of oxalic acid per 100 ml . water and pour this solution gray mess. Put on the heat and kept at a temperature of 85-95 degrees Celsius
about three hours , stirring occasionally. Beta tin acid dissolves to form soluble oxalate complex. If necessary, the solution was emptied and continue on with a new portion of oxalic acid. The results are pretty decent , unfortunately still can not upload pictures, but I'll try . This is my 2 cents in the matter .


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## necromancer (Apr 21, 2014)

i will make a tutorial of how to upload photos on this forum, need to go out for a smoke first.

please continue with this great topic.

this is from a post here, not sure who the OP was

title is: avoiding Metastannic acid

Metastannic acid H2SnO3 is what forms in nitric acid, by the strong oxidizing properties and the highly acidic solution of nitric acid.

Tin with HCl forms stannous chloride SnCl2.

Tin in aqua regia forms stannic chloride SnCl4.

Tin with cold very-very dilute nitric acid forms stannous nitrate and ammonia.

Tin in nitric acid forms meta-stannic acid H2SnO3.

Tin in hydroxides can form Sn(OH)2 or Sn(OH)4.


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## stardust18 (Apr 22, 2014)

necromancer said:


> i will make a tutorial of how to upload photos on this forum, need to go out for a smoke first.
> 
> please continue with this great topic.
> 
> ...


Hey. I'm sorry for my english, I'm not quite myself clear.
The problem is not that I can not upload photos.
At the moment I do not have a gray powder Metastannic acid to film the process step by step.
Earlier experiments I did not take off, so the photo is not there.
If the opportunity arises, I will gladly do and lay out the photo.


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## necromancer (Apr 22, 2014)

not a problem stardust18,

the tutorial has been made, if you do not need it i am sure it will be used by someone


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## MarcoP (Sep 21, 2014)

Very very all-in-one-informative thread, I love this forum.


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## gold4mike (Jan 20, 2015)

butcher said:


> From another note:
> concentrated nitric acid and tin converts to a white insoluble powder metastannic acid, which is a hydrated oxide of tin, H2SnO4 or H2SnO3
> Sn + 4HNO3 --> H2SnO3 + H2O + 4NO2
> Metastannic acid is different from stannic acid because it is insoluble in acids. and with alkalies it forms salts like K2Sn5O11 or Na2Sn5O11



Am I correct in assuming that Sodium Hydroxide would cause the formation of a salt also soluble in water? I don't have Potassium Hydroxide on hand but do have Sodium Hydroxide.


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## butcher (Jan 20, 2015)

The sodium hydroxide will work just fine.


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## yvonbug (Jun 25, 2015)

I just replied to another post and told about my experience with the blue goo. I talked about how I got it to desolve in strong sulfuric acid that left my gold free. And it still works for me. But here I read that metastannic acid doesn't do anything in other acids. Why does it work for me?


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## kurtak (Jun 26, 2015)

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=15324&p=236142#p236142

Kurt


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