Organikum
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Separation of tin and lead
This was for sure covered a thousand times, but somehow I couldnt find a good solution.
I got asscheap some kilos of solder which consists of 60% tin and 40% lead. Now I havent so much to solder and would love to separate the tin and the
lead as I would have quite many uses for those metals, provided they are pure (97% would suffice).
I did some research and to my astonishment it turns out that it seems not so easy to get this separated, electrolysis is told to be near to impossible
as the metals are so close together on the voltages and in addition tin is told to build up trees which shorten the cell quickly.
One way would be to blow chlorine through the molten mixture, this will form SnCl2 which reacts with Pb to yield PbCl2 (an equilibrium reaction, lower
temperatures just above the melting point favor PdCl2 formation. Nevertheless this reaction is astounding...).
This might be worth to think about if it was to purify a 97% Sn/3% Pb mixture, but for the real large amount lead?
Another way might be to chlorinate the metal at about 110-115°C up to the formation of SnCl4 what could be distilled out. I dont know if there
would be a formation of a tin/lead double salt what could make such impossible. Somebody knows?
Any other ways?
(I dont have the equipment for separating by distillation. The temp. necessary is out of reach by now)
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The_Davster
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A few weeks ago I was working with that same type of solder. I managed to create spongy lead and tin(II) chloride, both of reasonable(I think)
purity. First this solder was melted and cast into electrodes. I then electrolysed a saturated solution of sodium chloride using these electrodes.
The electrolysis was continued till the electrodes had both decomposed completly(I switched the polarity once one electrode had dissolved). The tin
was in solution as tin(II) chloride, tin hydroxide had also precipitated, and any lead present was instantly plated out due to it being a more
powerfull oxidizing agent, thus a higher reduction potential. It was necessary to scrape the lead that was plated out off the electrode many times.
The mix was a dirty grey. I added some HCl(till litmus indicated the mix was slightly acidic) and the mix cleared up.
From here the mix was filtered, the filter kept the spongy lead. I am unsure of the purity of this lead however. To the filtrate was then added
baking soda to precipitate tin(II) carbonate. The tin(II) carbonate was washed, dried and dissolved in a slight excess of HCl.
The solution was allowed to evaporate and a nice crystalline solid was obtained, tin(II) chloride.
The first time I did this experiment my tin(II) chloride was pure white. The second and third time I did this experiment my tin(II) chloride was piss
yellow while in solution. I am still working on how to remove this as it is from an unknown contamination source.
[Edited on 11-7-2004 by rogue chemist]
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Nick F
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That's crazy, I'm having a go at seperating tin and lead from solder too!
Well, I assume it's a tin/lead solder, I don't actually know for sure...
My plan was to dissolve the solder in nitric acid, ppte PbCl2 with NaCl soln, then electrolysis to get tin which I could then melt into a nice little
ingot. I don't have a use for tin (yet...), I was just bored and wanted an experiment!
Strangely, the salt mixture I have after dissolving the solder in nitric is yellow, and doesn't seem very soluble, but I have not had a chance to
play around with it properly.
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BromicAcid
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Dissolving tin in nitric usually just yields SnO2 (might be different with an alloy) as a solid particulate that settles to the bottom. I've
dissolved silver/tin bars in nitric to get solutions of silver nitrate that are fairly contaminate free, filtering off the SnO2 afterwards. If that
works with these lead alloys then dissolve in nitric, filter off the SnO2, then reduce your SnO2, thermite reaction?
After surfing the web for a little bit I've found that some sites say almost all the tin forms SnO2 which is insoluble, and some of the sites say
that concentrated HNO3 produces meta stannic acid which would be soluble. In addition cold dilute HNO3 acting on Sn produces Sn(NO3)2 and NH4NO3. I
guess the amount of SnO2 produced and the overall solubility of the product depends on the heat at time of reaction and concentration of HNO3 to an
extent not mentioned on the internet.
[Edited on 7/11/2004 by BromicAcid]
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Organikum
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Dissolving the alloy completely in HCl and cooling down the mixture. PbCl2 will precipitate already whilst dissolving and should (almost completely)
fall out of the solution so this contains still some HCl and is cooled down.
SnCl2.2H2O soluble in H2O 1/1 w/w.
(even more in dil. HCl which also inhibits the formation of the oxychloride)
PbCl2 sparely soluble in cold water 1/90 w/w and almost not soluble in dil. HCl.
(HCl is used to precipitate PbCl2 from solution)
But this leaves me with dihydrate SnCl2. But I read that the water can be removed by azeotropic distillation. The reference used phenol/chloroethylene
for this, any suggestions what more common solvents might get used? Taking in regard the reducing powers of SnCl2? Would plain toluene work?
I will have to try it I guess....
The precipating of the PbCl2 was done by me just before and this works well. The addition of the HCl clears the solution immediately, all small
crystals swimming around vanish at once - fall to the bottom.
Azeotropic distillation sounds much better than "heating under a steady stream of dry HCl" 
I will prepare some more SnCl2 and try this next.
All suggestions on usable water-carriers for the distillation are highly welcome.
Addon: Damn, I just found out that SnCl2 is insoluble in toluene. But soluble in alcohols as it seems.
The reference says: "..azeotropic removal of the water by suitable mixtures of solvents..." Hm. And whats defines "suitable"?
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fritz
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Some month ago I had the same problems. My favourite way was dissolving the alloy in hot HCl and cooling the (filtrated) solution to precipiate the
PbCl2 (which may be purified by recrystallisation from water). To remove traces of of Pb from the SnCl2-solution it is precipiated as PbSO4 (which may
be converted to PbO by heating it with strong NaOH). Because my intrest was primarely in getting lead I have not much experience with the tin-part.
But I guess the suggested electrolysis would be a good way. Also for obtaining lead-metal electrolysis may be a possibility. If somebody is not able
to carry out an electrolysis he/she may convert the lead to lead-acetate which is decomposed to lead-metal by heating (this procedure -I left out some
steps- I found as a possibility to obtain very pure lead-metal). If your desire is not the metal but lead-compounds I would suggest to precipiate all
lead as PbSO4. This may be washed several times with hot water to remove all impuritie of Sn. Then it is converted as mentioned above to PbO which
also is washed with hot water to remove impurities. You now should have relatively pure PbO from which you can easily obtain easily other lead-salts.
To Organikum:
I have no experience with SnCl2 in special but genarally you may dry substances azeotropic with Toluene (or xylene) which are insoluble in toluene.
Also it is possible to remove traces of water from mixtures (e.g. ester-productions from acids/alcohols) azeotropic with toluene. And I really could
recommend this method!!
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jimwig
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My metallurgical mileu is lead/antimony and lead/copper/precious metal (gold).
Most favored and likely approaches are from C W Ammen in the "Recovery and Refining of Precious Metals" - despite title there are a lot of
non precious contaminants that are dealth with here.
It seems from memory that dissolving the mixtures in solution and then treating either for purification or elimination. He does this for a variety of
metals and the book is readily avialable in libraries. Second edition is now out.
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JohnWW
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Re: Separation of Sn and Pb in Solder
I think that some types of solder contain appreciable amounts of either Sb, Bi, As, Zn, Cd, or Ag, to harden them and obtain slightly higher melting
points, e.g. where greater mechanical strength is required or there is a possibility of the finished article being subjected to high temperatures in
use. These are likely to be undesirable in Sn or Pb obtained from it for chemical use.
BTW Is there anywhere from which C.W. Ammen's book "Recovery and Refining Of Precious Metals" can be downloaded?
John W.
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Organikum
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Yes of course there are thousands and thousands of different kinds of special solders.
Whats your point btw.?
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Twospoons
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Its not just *special* solders that have other metals added. Copper is a very common addition(~0.5% IIRC) as this helps reduce soldering iron tip
errosion. This might explain the yellow colour someone mentioned further up the thread.
2% silver is also common.
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The_Davster
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I really doubt that the yellow that I obtained was a copper compound. First, it was not precipitated by addition of carbonate and secondly it did not
form crystalls when evaporated.
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kazaa81
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I've made one electrode composed of
50/50 Pb/Sn and put them in a conc.
solution of NaCl. The other electrode
was in graphite.
This tin-composed electrode was linked
to the positive pole (because Cl- will
go to it and dissolve tin) and then
started to pass current in the electrolyte
(I used 5 Volts). A milky-like compound was
detaching from Sn/Pb-anode and settling on
the bottom. Spongy lead has deposited to
the catode. Some times this sponge deposit
was removed.
Because I won't to run the cell
until the Sn-anode will dissolve (it is
much thick), I've run current in the
electrolyte only 24 hours.
I've added 30% HCl to the electrolite
until the solution become clear (some
bubbles has evolved, probably Cl2 from NaClO,
even if the solution wasn't yellow at all),
waited some minutes, then added sodium
bicarbonate (NaHCO3).
Very much bubbles (CO2?) has formed,
I added NaHCO3 until them stopped.
A white cream-like to see precipitate has
formed, tin carbonate (SnCO3?).
To test if it is really tin carbonate (much
precisely a tin salt), not sodium bicarbonate,
I've picked up a little of it, added Na2S
and watched the brown compound formed
(typical reaction: formation of brown SnS, stannous sulphide).
Now that I've a tin salt, how can I make
SnCl4 (stannic chloride) or SnS2 (stannic sulphide)?
Thanks all for help!
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The_Davster
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You currently have SnCO3. Dissolve this in HCl, and then bubble chlorine through until the calculated mass increase indicates all SnCl2 is now SnCl4.
Evaporate to get crystals, or if you want SnS2, bubble H2S through the solution until SnS2 stops precipitating.
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kazaa81
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Dissolving SnCO3 in HCl to get SnCl2, then bubble chlorine to get SnCl4...this is the SnCl4 crystallized with water...if I want it in the liquid form?
Thanks at all for help!
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bismuthate
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Tin chloride is soluble in ethanol and acetone lead chloride is not.
http://en.wikipedia.org/wiki/Lead(II)_chloride
http://en.wikipedia.org/wiki/Tin(II)_chloride
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AgCollector
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Quote: Originally posted by The_Davster  | A few weeks ago I was working with that same type of solder. I managed to create spongy lead and tin(II) chloride, both of reasonable(I think)
purity. First this solder was melted and cast into electrodes. I then electrolysed a saturated solution of sodium chloride using these electrodes.
The electrolysis was continued till the electrodes had both decomposed completly(I switched the polarity once one electrode had dissolved). The tin
was in solution as tin(II) chloride, tin hydroxide had also precipitated, and any lead present was instantly plated out due to it being a more
powerfull oxidizing agent, thus a higher reduction potential. It was necessary to scrape the lead that was plated out off the electrode many times.
The mix was a dirty grey. I added some HCl(till litmus indicated the mix was slightly acidic) and the mix cleared up.
From here the mix was filtered, the filter kept the spongy lead. I am unsure of the purity of this lead however. To the filtrate was then added
baking soda to precipitate tin(II) carbonate. The tin(II) carbonate was washed, dried and dissolved in a slight excess of HCl.
The solution was allowed to evaporate and a nice crystalline solid was obtained, tin(II) chloride.
The first time I did this experiment my tin(II) chloride was pure white. The second and third time I did this experiment my tin(II) chloride was piss
yellow while in solution. I am still working on how to remove this as it is from an unknown contamination source.
[Edited on 11-7-2004 by rogue chemist] |
Quite an old thread, I know, maybe a new topic would be better? But at any rate, I'm interested in testing this out but don't have much experience
with electrolysis. It seems like one would want a low voltage to avoid oxidizing water at the anode but do you have any suggestions on voltage as
well as cell design? Metal strips clipped inside a glass jar?
Also seems like it involves water reduction at the cathode to form hydroxide which precipitates with the tin; was there much hydrogen gas production?
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DraconicAcid
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| Quote: Originally posted by bismuthate | Tin chloride is soluble in ethanol and acetone lead chloride is not.
http://en.wikipedia.org/wiki/Lead(II)_chloride
http://en.wikipedia.org/wiki/Tin(II)_chloride |
That sounds like the best way to separate them. Vogel uses sulphide to separate them (tin forms SnS3(=) ions), but that's something we all want to
avoid.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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egret
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| Quote: Originally posted by BromicAcid | Dissolving tin in nitric usually just yields SnO2 (might be different with an alloy) as a solid particulate that settles to the bottom. I've
dissolved silver/tin bars in nitric to get solutions of silver nitrate that are fairly contaminate free, filtering off the SnO2 afterwards. If that
works with these lead alloys then dissolve in nitric, filter off the SnO2, then reduce your SnO2, thermite reaction?
After surfing the web for a little bit I've found that some sites say almost all the tin forms SnO2 which is insoluble, and some of the sites say that
concentrated HNO3 produces meta stannic acid which would be soluble. In addition cold dilute HNO3 acting on Sn produces Sn(NO3)2 and NH4NO3. I guess
the amount of SnO2 produced and the overall solubility of the product depends on the heat at time of reaction and concentration of HNO3 to an extent
not mentioned on the internet.
[Edited on 7/11/2004 by BromicAcid] |
The nitric acid method works. Add the concentrated nitric acid slowly to solder filings until the fumes of nitrogen oxides go out. The SnO2
precipitates, Pb(NO3)2 stays in solution.
I reducted SnO2 in furnance by charcoal. A very good washing of SnO2 is necessary othervise you get a firework. I have destroyed my furnance due of
improper washing.
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