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Tin Monster Tin Monster rears its ugly head. by glondor » January 27th, 2013, 2:45 pm Hey all. Looking for some advise. Processing 15 pounds of pins. Nice looking material. The issue.... They have reduced to a massive amount of metastanic acid/ gold foil goodness. I cleaned out as much of the foils as I could using a screening method. >>>>> I am left with this.>>>>> about:blank 1 of 11 13-02-01 11:45 AM

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Page 1: Tin Monster

Tin Monster

Tin Monster rears its ugly head.

by glondor » January 27th, 2013, 2:45 pm

Hey all. Looking for some advise. Processing 15 pounds of pins. Nice looking material. The issue.... They have reduced to amassive amount of metastanic acid/ gold foil goodness. I cleaned out as much of the foils as I could using a screening method.>>>>>

I am left with this.>>>>>

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I will have the mass dried in a few hours, and will put the heat to it then. (incinerate)

My question.... Does any one have a better/faster way? There is at least 4 pounds in the dish....

Cheers and thanks for your help Mike.Sodium Metabisulfite

by Geo » January 27th, 2013, 2:59 pm

when that happens to me, i incinerate and boil the solids in hcl. the copper will oxidize and be removed and the tin willdissolve too. it will leave some off white colored powder that is non-soluble in hcl and gold foils."knowledge is power"

by glondor » January 27th, 2013, 3:06 pm

Hey Geo. Thanks. Yes that is the plan. I wonder, do you know how much hcl for 5 pounds of this goo?Sodium Metabisulfite

by Geo » January 27th, 2013, 3:11 pm

unsure. incinerating will reduce the weight to a few ounces though. right now most of the weight is liquid. i would thinkbetween 500 to 1000 ml's."knowledge is power"

by glondor » January 27th, 2013, 10:57 pm

After drying, incineration and crushing...

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Next HCL boil.Sodium Metabisulfite

by Lino1406 » January 28th, 2013, 12:07 pm

I think there is mismatch here between tin whichcan dissolve in HCl and tin dioxide which cannot

by glondor » January 28th, 2013, 1:45 pm

Can you tell us more Lino. After a long hard boil in HCL there is still a lot of crumble left. And as usual, the hcl wash is positivefor gold. Putting the crumble in A/R now. (after a wash)Sodium Metabisulfite

by vegaswinner » January 28th, 2013, 1:59 pm

Have you tried sulphuric? According to Hoke (P70/71) the tin paste will dissolve in dilute or concentrated sulphuric.

by butcher » January 28th, 2013, 2:40 pm

Incineration is a very good method to use.

If I had a large amount of these salts, I may choose another option.One different method I may have tried to deal with this large batch of salts, would be to take the blue copper and tin salts withgold foils, add them into a distilling rig, add a dilute sulfuric acid (about 50% H2SO4), distilling off nitric acid, capture thecondensed nitric acid which formed, this would leave a copper and tin sulfates with gold foils, in which the tin sulfate andcopper sulfate could be dissolved away from the gold foils with boiling hot water.

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The tin sulfate SnSO4 has a solubility of 33 grams in 100ml water @ 25 degrees C.

The copper sulfate is easier to dissolve in boiling water if done before hard crystals form, copper sulfate solubility in water,310g/L @ 0 deg C, and 2033g/L @ 100 deg C.

Tin in this mix may reduce some of the copper salts to copper oxide or copper (if very large amounts of tin were involved), thissmall amount of copper or copper salts (if they did happen to be formed) could be dissolved away from gold foils, beforeprocessing the gold.

by glondor » January 28th, 2013, 3:52 pm

Amazing. Thanks guys. So there is a conversion we can all do that will make a water soluble tin. So butcher, you say, (afterincineration) just add sulfuric and distill and it will make nitric and make the tin wash away in boiling water. That is fantastic.

Does anything have to be added with the sulfuric to make it distill nitric acid? I have never tried to make Nitric and am not atall familiar with the chemistry.

If that is all there is to it........ Many of us will be slapping our fore heads. I read dozens and dozens of posts on this last nightand it seemed everyone is left hanging unsolved. Thanks so much Butcher, you may have the answer to the biggest pain inescrap recycling.Sodium Metabisulfite

by Geo » January 28th, 2013, 7:34 pm

of course, i didnt ask if you digested the base metal with nitric acid or AP. i was assuming AP for some insane reason. i dounderstand what it means when i assume.

sorry about that"knowledge is power"

by butcher » January 28th, 2013, 11:41 pm

glondor,

Incineration would drive off the NOx gas from the tin meta-stannic salts SnO3, and copper nitrate saltsIncinerating the Cu(NO3)2 would form copper and tin oxides with your gold flakes, as the NOx gas was drive off by the heat,notice we drove off the previous acid of these salts, the gas from incineration could be captured and bubbled into water toform some nitric acid, but with incineration this is a bit difficult to do.

Also notice after incineration we no longer have nitrates, so we could not take the copper and tin oxides and make nitric now,at least not easily or we would not want too at this point after incineration.

So continue with the process your using now to dissolve the tin and copper oxides from your gold with HCl boil and washes.

What I was saying was instead of incineration; I may have used the copper nitrate salts (with meta-stannic salts, and gold foils)to make nitric, and tin sulfate and copper sulfate.

Copper nitrate distilled with sulfuric acid, gives nitric acid and copper sulfate.

Cu(NO3)2 + H2SO4 --> 2HNO3 + CuSO4

Tin nitrate would react in a similar manner.

Both tin sulfate and copper sulfate are water-soluble; the gold is not soluble as a sulfate.

The reaction would need to be distilled until the nitric acid has been distilled off, the solution would change from a green colorto a blue color when all of the nitric was distilled off, the blue thick liquid solution would be copper sulfate, tin sulfate, and yourgold foils, when reaction was completed distilling the nitric you would need to add boiling water to the blue solution beforeletting it cool, (we do not want it to cool and form crystals that would take more water or be harder to re-dissolve) once thiscopper sulfate solution was diluted with boiling water, to keep copper and tin soluble we can let it sit, and our gold wouldsettle to the bottom of the vessel, and then we could decant the tin and copper sulfate solution from our gold.

Reading this process I use to make nitric acid while removing gold plating from copper pins, may help in understanding thismore:

http://www.google.com/search?hl=en&as_q ... s_occt=any

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I also assumed this was copper nirates with tin from a nitrate solution because I believe you mentioned Meta stannic acid(which would be a salt of tin and nitric acid).

by g_axelsson » January 29th, 2013, 2:18 am

butcher wrote:What I was saying was instead of incineration; I may have used the copper nitrate salts (withmeta-stannic salts, and gold foils) to make nitric, and tin sulfate and copper sulfate.

Copper nitrate distilled with sulfuric acid, gives nitric acid and copper sulfate.

Cu(NO3)2 + H2SO4 --> 2HNO3 + CuSO4

Tin nitrate would react in a similar manner.

.... snip ....

I also assumed this was copper nirates with tin from a nitrate solution because I believe you mentioned Meta stannicacid (which would be a salt of tin and nitric acid).

I started to write that "There isn't any tin nitrate, tin reacts with HNO3 to form metastannic acid, H2SnO3, a white substanceinsoluble in alkalies or acids." but then researching the subject further I found that according to Analytical Chemistry TinTin in strong nitric acid isn't dissolved, it is oxidized into our metastannic acid.3Sn + 4HNO3 + H2O = 3 H2SnO3 + 4NOBut in weak nitric acid it dissolves tin into tin nitrate. How weak, I don't know, haven't tried it but now when I read about it Iwould like to try. 8)

Reading further I see that tin nitrate and sulfate is unstable and breaks down into acid and stannic hydroxide.

So when trying to distill nitric acid from nitrates with metastannic acid it is only the copper and zinc nitrates that forms nitricacid. It would be better to decant / filter off the nitrates from the solids and create your nitric acid from that. Then treat thesolids separately.

On the bottom of page 274 in the document above it is mentioned that

Analytical Chemistry, Tin wrote:If the beta-stannic [metastannic] acid is treated for a long time with concentratedhydrochloric acid, the Sn5O5 group is finally broken down, and the tin goes into solution in the form of ordinaryalpha-stannic chloride

That sounds like the metastannic acid could be dissolved with hydrochloric acid... but if we comes from a nitric solution wewould form aqua regia and dissolve our gold. If we incinerate to get rid of the nitrate we turn the metastannic acid into tinoxide which is another story for another day.

It is obvious that I won't solve the tin problem today...

Göran

by Geo » January 29th, 2013, 2:34 am

i thought that by calcining the tin oxide, it would drive off one of the oxygen atoms. i was told it was more complicated thanthat. until i better understand the chemistry all i can go by is cause and effect. if you heat tin oxide whether it comes fromdecomposed tin chloride or nitric acid to a glowing hot state, the tin will dissolve in hot hcl acid. that amount of tin oxide(metastannic acid) could only have come from bronze pins. i doubt there was that much solder in the mix. i get it when imdissolving alot of computer pins in AP given the amount of oxygen i put in solution. thats the way i deal with it.incinerate andremove what will dissolve with hot hcl and whats left is more easily dealt with."knowledge is power"

by butcher » January 29th, 2013, 4:21 am

g_axelsson,Quote:"So when trying to distill nitric acid from nitrates with metastannic acid it is only the copper and zinc nitrates that forms nitricacid. It would be better to decant / filter off the nitrates from the solids and create your nitric acid from that. Then treat thesolids separately."

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The salts in discussion were concentrated and almost dried so they would contain nitrate salts of copper (zinc) and tin all ofwhich would form HNO3 in the reaction of distilling with sulfuric acid, and be converted to sulfates in the reaction.

The tin in solution as mettastannic acid H2SnO3 really does not dissolve, if captured in a filter as gelatin or dried to salts (withthe copper salts), would be a salt of nitric acid and tin, thus a tin nitrate salt, although I am unsure how acidic the tin saltswould remain with the copper (zinc) salts, the tin is still a salt of nitric acid thus a tin nitrate salt.

The soluble copper nitrate solution when dried or almost dry to crystallized salts also is a salt of nitrates as well as any zinc ifthese salts came from brass instead of just copper scrap.

Adding these nitrate salts (I presume Mainly copper nitrate due to proportion of metals dissolved to from these salts), to adistilling rig, adding dilute sulfuric acid, and distilling.

The sulfuric acid will begin reacting with these nitrate salts, dissolving them into solution, and NOx gas would begin to evolve,beginning to convert them into copper and tin sulfate, but also the hydrogen from the sulfuric acid would also again form nitricacid in this solution.

So at the beginning we would have a solution of copper sulfate and copper nitrate, mixed with tin sulfate and metastannicacid, (and zinc if involved) some NOx gases evolving but most of this gas would just stay in the dilute solution.

At first in the dilute solution of sulfuric acid most of these gases would not leave solution to much extent, but with heat thesewould begin to evolve, at first mostly water vapors with very little acidic fumes or NOx fumes, but as the distilling of thesolution proceeded the nitric vapors would be more concentrated, until the 68% HNO3 was distilling off with the NOx gas, thecopper and tin nitrates would further be convert to copper and tin sulfates in solution as the nitric acid was removed from thesystem by distilling it off, eventually you would be left with no nitric or nitrates in the distilling rig only copper (zinc if thesesalts came from brass) and tin sulfates dissolved in solution left in the boiling vessel with your gold.

(Nitric acid will distill off leaving only a soluble metal sulfate solution, and the insoluble undissolved gold).

The metals do not leave as gas in the fumes, from the distilling rig, and neither will the sulfuric acid (too high of a boilingpoint).

Another action of the reaction is as we are distilling, as the nitric leaves solution and the sulfuric acid in the boiling reactorconcentrates the sulfuric acid, taking over the metals in solution, the tin is no longer metastannic acid but converts to tinsulfate, the copper converts to copper sulfate, and the gold is freed to settle in this solution of water soluble metal sulfates.

Once the reaction is complete the vessel opened and this solution is diluted with boiling water, the reason for the boiling wateris because this should be done while the concentrated copper sulfate solution is still hot, this keeps from breaking the glasswith thermal shock, and dilutes the thick copper sulfate syrup while still hot so the crystals will not form before solution iscooled and thus easier to be diluted.

The gold in this copper and tin sulfate solution can now be left to cool, the gold will settle to the bottom of the vessel, and thenwe can decant the sulfate solution from our gold.

(This method will also work for other salts or very concentrated solutions, as an alternative. or a pre-step to break the colloids,dissolve (or convert) the tin and copper or other metals, the hot concentrated sulfuric acid can also break the colloids of thegold if any chlorides were involved or if we had a solution of HCL or copper chloride salts and colloidal gold mixed with goldflakes, the HCl can be distilled off, the concentrated sulfuric breaking the gold colloids, tin in solution converted to soluble tinsulfate, and copper chloride converted to copper sulfate, and the gold freed to settle in the solution of soluble copper, tin orother metal sulfates).

The gold separated by this method can then be incinerated (without the large volume of other metal salts) before treatingfurther.

This distilling method would be best with large batches of metal salts, or large batches of concentrated solutions, wherefiltering or separating gold from the large volume of salts or solutions would be troublesome, or it would be troublesome toincinerate this large volume of salts, because of the large volume of gases that would form from the volume of salts, and thevolumes of toxic gases formed by the incineration of these metal salts.

butcher

by g_axelsson » January 29th, 2013, 5:13 am

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Hi Butcher, I agree with most of what you are saying but this is what I'm reacting on.

butcher wrote:The tin in solution as metastannic acid H2SnO3 really does not dissolve, if captured in a filter asgelatin or dried to salts (with the copper salts), would be a salt of nitric acid and tin, thus a tin nitrate salt, although Iam unsure how acidic the tin salts would remain with the copper (zinc) salts, the tin is still a salt of nitric acid thus atin nitrate salt.

This is where I think you make a mistake. Just because the metastannic acid is created by nitric and tin doesn't mean it is asalt of nitric acid.

A salt of nitric acid contains the nitrate ion NO3- but the metastannic acid is H2SnO3 and contains no NO3

- ion. You can'tcreate the ion by adding sulfuric acid, the only nitrates in the mix is the ions coming from the copper (and zinc) nitrate.Just as auric chloride isn't a salt of nitric acid even though you can create it by aqua regia and gold the nitric acid reaction withtin is an oxidation of the tin.

Just think of what would happen when the copper (and zinc) nitrate is filtered off, could you still distill nitric acid off themetastannic acid and sulphuric acid?

I'm already late for work so I have to dig deeper into this discussion later tonight. Tin chemistry isn't easy, it has a lot ofdifferent faces and is even compared to the silicates as it has a lot in common with how SiO2 work in mineralogy.

Hey, this is fun, discussing and arguing with you. I hope you feel that too. 8)

Göran

by butcher » January 29th, 2013, 5:41 pm

Göran,

“Hey, this is fun, discussing and arguing with you. I hope you feel that way too.”

Hey it is better than fun, I do not feel like we are arguing, I feel you seen something I did not, I also feel we are just debating apoint so that we both learn, or at least here I am learning.

I was more focused on the copper salt, I did not even think that much about the Tin salt that much of being an oxide or nitrateof tin, I was not as concerned whether it would form nitric acid as I was of converting it to a sulfate and to remove it from thegold.

It is not arguing it is learning and sharing Ideas and what we are learning.

I see now, what you are saying, (this man slaps palm of hand up against his thick hard scull).

I was thinking the tin salt (or gelatin powder of metastannic acid) being formed from a metal of tin in nitric acid formed a tinnitrate salt, not an acidic oxide or tri-oxide of tin or an oxidized salt of tin as it has, I did not think enough about the reaction oftin in nitric acid, to see the tin is only oxidized by the strong oxidizing action of the nitric acid, probably breaking down to anoxidized tin metal just floating around in acid, being a passivated oxide of tin that would NOT form a nitrate but would just jelly.

I guess I really did not look closely enough at the formula H2SnO3 to see it did not contain the nitrate anion.

Now that I see your point (a very good point I had missed).With that in mind let me add more to this discussion of tin in nitricacid.________________________________________________________________________Concentrated nitric acid will break down tin to an oxide of tin powder insoluble in the acid as metastannic acid, evolvingnitrogen dioxide gas: the tin does not really dissolves but stays as an oxide powder in solution forming a gelatinous substancehard to filter.

Sn + 4HNO3 --> H2SnO3 + NO2(g) + H2O

But in dilute cold nitric acid we actually form the nitrate salt of tin Sn(NO3)2 (tin nitrate salt) when we slowly dissolve the tin.(this may mix with some meta stannic acid of this I am unsure):

In this reaction of cold dilute nitric acid reacting on tin the NOx gas does not escape, and thus forms ammonium nitrate andstannous nitrates, in this reaction tin is given 2 positive charges, and a part of the nitrogen from the nitric acid is reducedforming a positive valence of five (toward oxygen) to a negative valance of three (toward hydrogen), therefore losing eightcharges, so one molecule of nitric acid oxidizes four atoms of tin, eight more molecules of nitric acid form stannous nitrate,and one form ammonium nitrate.

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Reaction of tin in cold dilute HNO3 slowly forms tin nitrate salt Sn(NO3)2 and ammonium nitrate salt NH4NO3 in solution:

4Sn + 10HNO3 --> 4Sn(NO3)2 + NH4NO3 + H2O

I am unsure if this is a mute point as we concentrate the dilute solution, and may just form metastannic anyway. Withconcentration or drying of the tin salts, as you stated the tin and its salts is a very complicated science.

Göran, I do enjoy these discussions and like to (argue) discuss the science with you I seem to learn a lot in our discussions.

Thanks for showing me the error ofmy ways of my thinking (thinking has always got me into trouble)

by Sucho » January 30th, 2013, 1:33 pm

Guys,

i never trying to filter this tin gel ( H2SnO3 , or SnO2. xH20, it depends on literature, in older you will find metastannic acid orstannic acid, in new literature i found its hydrated tin dioxide, which can have same summar formula as metastannic acid, butdifferent structural constitution and charge arrangement - different orbitals in bond)

the thing i do when this happens ( it happens almost everytime - Cu/Sn/Zn and other alloys with Sn are used widely), i only letit settle for a day or two. it is never more than 1,5 litre of glue in my 10k beakers i use for settling after 1 kilo batch of pins

then i siphon copper nitrate solution till i reach tin gel surface

after this i only pour some HCl to it. Most of copper nitrate and other less abundant nitrates are away in siphoned solution, restcontains mostly hydrated tin dioxide and some residual nitrates.

when you add HCl to this mixture, aqua regia is produced and gold foils are dissolved in a while leaving greenish gellysuspension ( suspended tin dioxide in "Aqua Regia"- CuCl2, HAuCl4 and other chlorides)

when you heat this suspension for some time ( 1-3 hours ) to cca 80 degrees celzius, it will change to crystalclear dark greensolution

now it is possible to filter it without problems

little problem comes in final step

Sn is in oxidation state +4 in chloride form. if it is in ox. state +2 - gold reduced to colloidal particles -this wasnt prooved

solution contains in decrease Sn +4 , Cu+2 and some Au+3 in chloride forms

precipitation is quite risky, but i used only SMB as reducing agent

it has to be used almost no excess of SMB at very low pH ( because SMB can also reduce Sn +4 to Sn+2 and looses are in agame) so you have to know how much gold is inside

butyl diglyme/ dibutyl carbitol L/L extraction is also possible, but this solvent has high uptake also for Sn +4

i would try different precipitants ( oxalates , nitrites, hydrazine, FeSo4 etc) and find out which precipitant gives most rigid,quantitative reduction of Au+3 to Au0 without reducing of Sn+4 to Sn+2 with a subsequent formation of colloidal Au particles

by g_axelsson » January 30th, 2013, 5:02 pm

butcher wrote:Göran,

“Hey, this is fun, discussing and arguing with you. I hope you feel that way too.”

Hey it is better than fun, I do not feel like we are arguing, I feel you seen something I did not, I also feel we are justdebating a point so that we both learn, or at least here I am learning.

You are so correct, I'm sorry I expressed my self in that way, sometimes the finer nuances of English is lost on me or I'mthinking on a nearby Swedish word that means almost the same thing. I think the expression argumentation is closer todiscussion and was what I tried to say.

I was more focused on the copper salt, I did not even think that much about the Tin salt that much of being an oxideor nitrate of tin, I was not as concerned whether it would form nitric acid as I was of converting it to a sulfate and toremove it from the gold.

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It is not arguing it is learning and sharing Ideas and what we are learning.

Exactly and that is what makes this forum so great. 8)

... I cut out a lot of relevant things that I agree with fully ...

butcher wrote:But in dilute cold nitric acid we actually form the nitrate salt of tin Sn(NO3)2 (tin nitrate salt) when weslowly dissolve the tin.(this may mix with some meta stannic acid of this I am unsure):

I've read that even in cold solutions the tin nitrate is unstable and easily breaks down to metastannic acid.

... even more detailed description of what happens with tin in nitric acid ...

butcher wrote:Göran, I do enjoy these discussions and like to (argue) discuss the science with you I seem to learn alot in our discussions.

Thanks for showing me the error of my ways of my thinking (thinking has always got me into trouble)

I enjoy it too. In over 5000 posts I found one that you made an error in, it wasn't easy to find, I've read a lot of your postingsand many times I learn something new. I've learned a lot out of our discussion too, I had to do some deep research on tinchemistry just to be able to put forward my arguments for my point of view... did I get it right this time?

I think we are on the same page now... but we still have left the question of what to do with a metastannic mess, if there is anygeneral solution.I think that the best way to treat it (from a purely theoretical point of view) is incineration that turns it into cassiterite (SnO2),grind it to a fine powder and then treat it with hydrochloric acid.

I had prepared this response but Sucho posted an interesting description before I was done writing. I'll just add my answerhere too.

Sucho, could this explain why your aqua regia is able to dissolve the tin?According to

Analytical Chemistry, page 274 wrote: "If the metastannic acid is treated for a long time with concentratedhydrochloric acid, the Sn5O5 group is finally broken down, and the tin goes into solution in the form of ordinaryalpha-stannic chloride:Sn5O5(OH)10+20 HCl=15 H2O + 5SnCl4

I guess that this is what happens when you treat it with heat for a longer time.Would it be possible to cement the gold onto copper from this mixture?That could be one way to avoid the risk of creating new metastannic acid.

Göran

by srlaulis » January 30th, 2013, 9:33 pm

testerman wrote:

srlaulis wrote:This thread makes my head hurt. So much to learn

Yeah, but it's a pleasurable pain. It's called knowledge. There is so much to learn on this forum, and I try my best toread all the threads I can, especially for the task that I'm working on.

Kevin

Yeah I read every post throughout each day. Comprehending this one is a little more challenging. I too love it though.

by Geo » January 30th, 2013, 9:49 pm

i was told you cant reduce tin oxide by calcining (incineration) like you can with other oxides. even though the thread i started

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really kind of petered out, it was generally accepted that the only way to deal with it was to incinerate and BOIL in hcl. i wastold by Harold to grind or mill and screen and grind again and boil in hcl until there was no color change in the solution. i maynot understand the chemistry but it has always worked for me."knowledge is power"

by Sucho » January 31st, 2013, 11:11 am

Goran ! your post hit me like lightning and opened my mind !

Tin chemistry is quite tricky due to its amphoterous character, complexicity, ox. states etc

If the metastannic acid is treated for a long time with concentrated hydrochloric acid, the Sn5O5 group is finallybroken down, and the tin goes into solution in the form of ordinary alpha-stannic chloride:Sn5O5(OH)10+20 HCl=15 H2O + 5SnCl4

this equation changed my point of view...

according to reaction between Sn and nitric acid

Kunkel likewise recorded the fact that to dissolve tin the nitric acid employed must be cold, or calx of tin would beprecipitated. The explanation of these observations is that whilst tin dissolves slowly, in very dilute nitric acid toproduce stannous nitrate, the stannous nitrate first formed, when hot and more concentrated acid is employed, isvery unstable and quickly decomposes, yielding the form of hydrated stannic oxide known as β-stannic acid.Probably α-stannic acid is first produced from stannic nitrate, which then passes into the β-form.

β-stannic acid is also called β-metastannic acid or hydrated stannic oxideα-stannic acid has different constitutions of hydroxyle groups and oxygen in space, also secondary structure, it is soluble instrong acids / alkalis

for an explanation what happens when you let your tin gel on air

Gelatinous, precipitated β-stannic acid has the empirical composition SnO2.4H2O, when air-dried SnO2.2H2O, andwhen dried in a vacuum, SnO2.H2O; These formulae do not, however, convey a just idea of the nature of the β-acid,which is gained from a study of its salts and other derivatives.

in my opinion, the most probable structural nature of this compound is a net structure or a ring with oxygens between Sn 4+and hydroxyles above and under the plane of this twisted ring

Sodium β-stannate, prepared by the action of cold sodium hydroxide solution on β-stannic acid, is a sparingly solublecrystalline powder, having the composition Na2Sn5O11.4H2O. Similarly the potassium salt is K2Sn5O11.4H2O. Thusthe molecule of β-stannic acid appears to contain five tin atoms; and the air-dried acid becomes H2Sn5O11.9H2Oinstead of SnO2.2H2O, whilst the acid dried in a vacuum is H2Sn5O11.4H2O instead of simply SnO2.H2O. Alternativeformulae are Sn5O5(OH)10.5H2O and Sn5O5(OH)10 respectively, which suggest that β-stannic acid may possiblycontain a ten-membered ring of alternated tin and oxygen atoms. At least an analogy is suggested betweenβ-stannic acid and the polymerised silicic acids.

as i find out, it is impossible to dissolve dryed "tin gel" in HCl ( read higher - β-stannic acid looses some water molecules- thischanges its structure - properties )

it is important to let your "tin gel" wet, without changing pH ( to avoid structure changes)- that means let it sit and siphonsolution above

Goran, it is not "my aqua regia", it is only reaction of strong acid - HCl with residual nitrates (mostly Cu nitrate ) with aproduction of nitric acid and subsequent production of nitrosyl chloride and gaseous chlorine in situ

to conclusion, my opinion is, that due to highly hydrated status and large structure which contains at least 5 tin atoms it is

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more unstable- that means more reactive friendly for reaction with HCl. after drying restructuralisation occurs with a loss ofwater molecules, this structure is more stable - unable to dissolve

it is possible to cement gold on copper from this mixture, but i dont like this method due to production of very fine particles (few times i got colloidal particles with a transmitance in purple spectra- it can be find what was particle size )

by g_axelsson » February 1st, 2013, 4:01 am

I think I soon join the group with heads that hurt.

I'm not a chemist and I have very little practical experience of chemistry. I'm a physicist, so I have to read a lot to keep up inthis discussion.

Half a year ago I thought that the name metastannic acid was a stupid name, it was only tin oxide, but today I don't feel that

way any more. It is so much more than only tin oxide, it contains H+ in it's formula so to call it an acid is justifiable, although itis a very weak acid. Tin chemistry is really complex. 8)

It seems to be a very good advice to keep the metastannic acid wet if you are going to treat it without incineration. I alsosuspect that time could play a role here. Any material that is kept for a longer time at a high enough temperature is goingthrough recrystallization and smaller crystals disappears as bigger ones grows. In a saturated water solution this is somethingthat happens as long as the water is liquid and not frozen. This is a physical process driven by surface energy of the crystals.There will always be harder to dissolve or chemically react with larger crystals than smaller ones.How much it will differ between an old solution or a fresh one of metastannic acid is something to be found out through someexperiments.

I haven't had time to read any more about tin chemistry so I don't have so much to add to this discussion right now. If I find outsomething new I'll add it later.

I also want to run some experiments, but that has to wait until warmer weather.

Göran

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