Sciencemadness Discussion Board - Tin, Lead, and Silver from Solder

Tin, Lead, and Silver from Solder

DFliyerz - 15-9-2015 at 09:36

For once, I've actually completed a procedure before posting it here, so here we go:

Starting with 15 grams of solder recovered from desoldering various boards, I dissolved the solder in nitric acid and was left with a precipitate of hydrated tin oxide which could then be dried and reduced to tin metal (I didn't do this and threw the oxide away for some reason!) Next, the solution is neutralized with sodium hydroxide before filtering it again and using a copper wire to precipitate the silver. After filtering off the silver I ended up leaving the silver on the filter paper and using a micro butane torch to both burn the paper and melt the silver, which was surprisingly effective and I ended up with a few miniscule balls of silver metal. Finally, sodium chloride solution was added to the remaining solution, precipitating lead chloride which was filtered off. To do next is to recover and reduce the tin oxide with carbon, and to treat the lead chloride with sodium hypochlorite to precipitate lead dioxide which can then be heated to form lead oxide and then reduced. But, there you have it; three somewhat hard to come by metallic elements from waste solder.

[Edited on 9-15-2015 by DFliyerz]

unionised - 15-9-2015 at 11:08

I'm fairly sure that you can reduce the lead chloride directly with carbon in the presence of an alkaline flux like sodium carbonate.

DFliyerz - 15-9-2015 at 11:24

Quote: Originally posted by unionised

I'm fairly sure that you can reduce the lead chloride directly with carbon in the presence of an alkaline flux like sodium carbonate.

If you have any idea on the stoichiometry, I'd love to give this a try!

battoussai114 - 15-9-2015 at 12:52

Seems pretty cool! If I weren't lead-phobic I'd certainly give it try....
To illustrate how-much-phobic I've got a PCB waiting for a reflow work for months now and I don't want to use my oven for it.

aga - 15-9-2015 at 14:41

What Silver ?

Solder was 60/40 Tin/Lead apart from Special Applications (like soldering to Al).

All changed in 2006.

What 'solder' are you using ?

battoussai114 - 15-9-2015 at 15:07

Quote: Originally posted by aga

What Silver ?

Solder was 60/40 Tin/Lead apart from Special Applications (like soldering to Al).

All changed in 2006.

What 'solder' are you using ?

This is for solder sold to the public. Composition may/will varie a lot for industrial applications. For instance high temperature solder contains silver, while solder for BGA and reflow is sometimes made of tin/silver/copper.

Bert - 15-9-2015 at 15:20

There are a HUGE range of materials sold as "solder". Eutectic Pb:Sn is 60:40 (actual eutectic is 63:37, but close enough...)

Pity you discarded the Tin, if you had weighed it at least we could know the proportions of your alloy.

From the ever unreliable Wikipedia:

Quote:

Sn-Ag-Cu (Tin-Silver-Copper) solders are used by two thirds of Japanese manufacturers for reflow and wave soldering, and by about 75% of companies for hand soldering. The widespread use of this popular lead-free solder alloy family is based on the reduced melting point of the Sn-Ag-Cu ternary eutectic behavior (217 ˚C), which is below the Sn-3.5Ag (wt.%) eutectic of 221 °C and the Sn-0.7Cu eutectic of 227 °C

kadriver - 15-9-2015 at 16:47

Quote: Originally posted by DFliyerz

For once, I've actually completed a procedure before posting it here, so here we go:

Starting with 15 grams of solder recovered from desoldering various boards, I dissolved the solder in nitric acid and was left with a precipitate of hydrated tin oxide

[Edited on 9-15-2015 by DFliyerz]

In my refining experience, I was taught that tin dissolved in nitric acid produced a thick paste called metastannic acid that made filtering impossible. To turn it into tin oxide the metastannic acid must be incinerated - heated to redness - the resulting tin compound is not very soluble in acids and it can then be filtered out without gumming up the filter paper.

I think the lead and silver both go into solution. How were you able to separate the tin paste from the two other dissolved metals? Just curious and always looking to learn something new to help me in the future.

kadriver

DFliyerz - 15-9-2015 at 18:59

Quote: Originally posted by Bert

There are a HUGE range of materials sold as "solder". Eutectic Pb:Sn is 60:40 (actual eutectic is 63:37, but close enough...)

Pity you discarded the Tin, if you had weighed it at least we could know the proportions of your alloy.

From the ever unreliable Wikipedia:

Quote:

It was from probably tens of different boards from all different years, so it'd be pretty variable.

DFliyerz - 15-9-2015 at 19:02

Quote: Originally posted by kadriver

Quote: Originally posted by DFliyerz

I just filtered it without any problems, but this time I'm going to modify my procedure and treat the solder with hydrochloric acid first to get tin(II) chloride instead of tin(IV) oxide, which I can then electroplate into nice crystals and avoid carbon reduction entirely.

soniccd123 - 15-9-2015 at 20:55

It is perfectly possible with hot 30% hydrochloric acid, but beware that some of the Lead will dissolve (from my own experience), My resulting solution gave me the classical gold precipitate with Potassium Iodide.

To prepare the solder for the reaction, i melted it (round 20g) and poured it hot in a ceramic tile, so it splashed and formed a very thin spill of solid metal. I cut the spill with scissors in small pieces and used these pieces in the reaction.

I did made only rough measurements before and after the reaction (my precise scale had just stopped working), but from the rough results, it seems to have dissolved Tin and left behind most of the Lead.

unionised - 16-9-2015 at 12:29

Quote: Originally posted by DFliyerz

Quote: Originally posted by unionised

I'm fairly sure that you can reduce the lead chloride directly with carbon in the presence of an alkaline flux like sodium carbonate.

If you have any idea on the stoichiometry, I'd love to give this a try!

I'd not bother worrying- use lots of the two cheap things.

Bert - 16-9-2015 at 20:06

Hasn't anyone else read Georgius Agricola' de re Metallica?

Lots of stuff on Lead, Copper, Silver (and Gold) separation...

Get pragmatic, appropriate physical means of separation to complement the chemical ones.

http://www.gutenberg.org/files/38015/38015-h/38015-h.htm

[Edited on 17-9-2015 by Bert]

DFliyerz - 19-9-2015 at 21:12

Two more pictures for you guys, this time of a completed tin recovery process:
1. Electroplating tin metal from stannous chloride solution.
2. Nice and shiny tin metal after melting down the crystalline tin.

71572633-2289-4e34-8f27-42e4672d4eab~01.jpg - 82kB

BlackDragon2712 - 21-9-2015 at 12:29

If you are interested just in the tin (like myself) would it be better to put the crushed alloy in a concentrated, stoichiometric solution of copper sulphate? It would form tin (II) sulphate which is fairly soluble in water, lead would remain as the metal since the solubility of the sulphate in water is very low. The lead then can be brought into ionic form with nitric acid or another acid, the tin (II) sulphate can be reacted with calcium or barium chloride, precipitating calcium (II) sulphate and leaving tin (II) chloride in solution.

Of course this is just an idea but it seems like a very nice, clean and simple method rather than dealing with strong acids and toxic lead ions in solution, what do you think?

aga - 21-9-2015 at 12:38

Funny.

I wanted some tin yesterday to make Stannous Chloride for Gold detection (cheers kadriver) so attempted tin extraction from some 'lead-free' plumbers' solder.

It simply got thrown in a beaker with some 20% HCl and shiny metal flakes appeared after heating.

In a test tube a small sample was tested with nitric acid and it went Green ?!?!

Not Silver then.

Assuming the same about Solder as Bert just said i just bought some powdered Tin instead.

[Edited on 21-9-2015 by aga]