## Finding percentage of tin in leaded tin solder

Romix - 4-5-2023 at 06:27

Hello Dear forum members, I'm back and need your help.
I've bought 25kg of bars with density 8928 kg/m3 of a lady that doesn't have knowledge of metals, she thought it's aluminum.
Paid 95£ with delivery to my door.
Bars are very old and unoxidized, that's another reason I'm thinking it's leaded tin solder 60/40.
Knowing that tin sells for 27£ a kg, theoretically only tin in them bars worth at least 405£.
I need a method of finding out the percentage of tin in the solder alloy.
If I dissolve it in diluted nitric acid will all the tin drop out as stannic acid or some may remain in solution?

Romix - 4-5-2023 at 06:28

Here's photo of them bars.

Lionel Spanner - 4-5-2023 at 06:43

The easiest way to work this out is with algebra, assuming it is purely an alloy and doesn't contain intermetallic compounds.

Let x be the fraction of the alloy that is tin (between 0 and 1). The density of tin is 7.3 g/cc, and the density of lead is 11.3 g/cc (to 1 decimal place).
Then, again to 1 decimal place:
7.3x + 11.3(1 - x) = 8.9
7.3x + 11.3 - 11.3 x = 8.9
11.3 - 4x = 8.9
11.3 - 8.9 = 4x
2.4 = 4x
x = 0.6

On this basis, it's likely to be around 60% tin and 40% lead.

Sulaiman - 4-5-2023 at 06:49

Since you know the total mass and it's density you can calculate the total mass of tin.

A few thoughts ;

1 all soluble lead salts are toxic to humans and aquatic life.

2 check with a local scrap dealer if they would buy your recovered tin and at what price.

3 check with a local scrap dealer,
you may be able to make a profit without expending nitric acid or creating toxic products.

4 if you are not short of cash, consider the solder bars as an investment metal.

Romix - 4-5-2023 at 06:59

Don't worry I'll be testing few grams of the material, and will try my best to neutralize everything.
violet sin - 4-5-2023 at 08:06

Have you abused one to see the metallic properties? Does it bend when flexed, does it "cry" when bent. Is it brittle?

I found a few bars of metal at yard sales from time to time. Last time I bought a few without knowing the comp b/c the price was low, but they turned out to be babbitt bearing metal, so not super interesting. The guy was reticent to sell because he thought it might have nickel, and his son said it could kill someone. Hahah. Lead/tin solder would deff be soft and low melting like a solder.

Tin will electroplate whiskers through a HCl sol, dropping bits of lead mud from the solder. Relatively little Pb in sol. to need disposal, keep the mud or dissolve it in sulfamic acid. Plate it out too. If you've a solar panel for free work, could see how long to digest a bar. IDK, my spart time is low, projects long winded and low on the hands on time. It's rarely the method for someone looking for a quick, clean and hassle free path. It's the opposite of that.

Rainwater - 4-5-2023 at 08:59

Tin is difficult to work with in solution.
Both have high solubility in consentrated HCl
Lead chloride has low solubility in cold water

I would take a sample, weight it.
Use consentrated 32% HCl and H2O2 3% do disolive the sample
This will produce the chloride forms
After the solids are dissolved, boil the solution until half the volume is gone.
Then add di water and keep boiling the solution until the HCl is gone.
Repeat as needed
Then allow it to cool.

Edit: sorry. I wrote that backwards.
Fixed now.

[Edited on 4-5-2023 by Rainwater]

Romix - 4-5-2023 at 09:15

What I'm thinking about doing now, is to dissolve few grams in diluted nitric.
Lead will dissolve, Tin drop out as Stannic acid.
Wash it and dissolve in boiling diluted HCl, then displace with 99.99 distilled Zinc and weigh.
The main question of this post is, will all Tin drop out as Stannic acid in diluted HNO3?
At least this method will show presence of Tin in the solder, not sure about accurate percentage of the element.

[Edited on 4-5-2023 by Romix]

Rainwater - 4-5-2023 at 09:48

Using hcl avoids the stannic acid, which is unstable and cant be accurately weighed.
By using the chloride route, any lead and silver will percipitate out.
Allowing you to calculate their % of your sample.
The remaining will be tin + impurities
Didnt see the bit about seperating the two

I have telt with tin and nitric acid before processing electronic scrap, it usually form a goop that is difficult to work with.

[Edited on 4-5-2023 by Rainwater]

Romix - 4-5-2023 at 10:02

Got it now, thanks.
unionised - 4-5-2023 at 10:24

Sell the solder, as such, to a scrap dealer.

If you want to know what sort of solder it is, plot a cooling curve.
I suspect, given the algebra above and the popularity of eutectic 60/40 solder it will essentially all melt at 183C

If you insist on doing chemistry.
Dissolve in HCl/ H2O2.
Ppt PbSO4 with dil H2SO4, and weigh it.

Osmiridium - 4-5-2023 at 11:00

Don't try to dissolve it in nitric acid. If there's Sn in it it won't dissolve fully but form a dispersion that is impossible to filter. Best way would be dissolving it in HCl.

 Quote: Originally posted by Rainwater Tin is difficult to work with in solution. Lead salts are deadly. tin chloride and lead chloride. Both have high solubility in consentrated HCl Lead chloride has low solubility in cold water I would take a sample, weight it. Use consentrated 32% HCl and H2O2 3% do disolive the sample This will produce the chloride forms After the solids are dissolved, boil the solution until half the volume is gone. Then add di water and keep boiling the solution until the HCl is gone. Repeat as needed Then allow it to cool. Filter and weight the percipitate. Theres your lead Edit: sorry. I wrote that backwards. Fixed now.

This won't work. HCl forms a higher boiling azeotrope with water at about 20% concentration, so you can't drive it out like this. And lead will still be quite soluble as chloroplumbate.

Romix - 4-5-2023 at 11:46

I have a lot of time, thinking washing it differently, pour water in, stir, let it settle and pour water out down to precipitate 10 - 20 times.
And I don't think so that few grams of solder will clog the filter. Bigger quantities, maybe...

Romix - 4-5-2023 at 11:52

Last two washes might boil it, it will coagulate and settle in seconds when taken off of hotplate. I can't guarantee that it will, never done this with Stannic acid, but it works with other metal hydroxides.
Rainwater - 4-5-2023 at 12:03

 Quote: HCl forms a higher boiling azeotrope with water at about 20% concentration, so you can't drive it out like this.

After a lot of goggleing, your right.

I did not know this.
But, from experience it will cause a percipitate, i guess the concentration of HCl drops enough to effect the solubility of the PbCl2

Osmiridium - 4-5-2023 at 12:59

I can imagine it is quite counterintuitive if you think of a volatile gas like HCl forming an azeotrope with a liquid and it has even a higher boiling point.

Yes, of course the concentration change will still have an effect on the overall lead solubility. The chlorides are certainly not the best route anyway to separate lead from tin because although lead chloride is poorly soluble it still dissolves in significant amounts, even in pure water.

 Quote: Originally posted by Romix I have a lot of time, thinking washing it differently, pour water in, stir, let it settle and pour water out down to precipitate 10 - 20 times. And I don't think so that few grams of solder will clog the filter. Bigger quantities, maybe...

I still wouldn't recommend using nitric acid.
You don't want to try things, produce unnecessary waste and mess with soluble lead salts and it doesn't work like intended.
I wouldn't just assume it will coagulate after heating and filter well. This works sometimes, but not always. It will take a lot of washings to remove lead and in close to neutral solution lead also forms basic salts.
The tin precipitates not entirely as stannic acid. It forms basic nitrates. It might still be somewhat soluble in acidic solution. If you want to convert this precipitate to anything useful you would have to dissolve it in hydrochloric or sulfuric acid anyway.

Romix - 4-5-2023 at 13:03

Agree with you, no matter how much you wash Stannic acid, boiling it in HCl dissolves all the gold in it.
But googling the formula of Stannic acid, not showing any nitrate anions.

Osmiridium - 4-5-2023 at 13:06

Of course stannic acid as such doesn't contain nitrate. What I meant is, if you dissolve tin in nitric acid it will form basic nitrates. Like something between tin nitrate (that doesn't exist in aqueus solution) and stannic acid.
Rainwater - 4-5-2023 at 14:03

 Quote: Originally posted by unionised If you insist on doing chemistry. Dissolve in HCl/ H2O2. Ppt PbSO4 with dil H2SO4, and weigh it.

This is the best option i have seen to measure the amount of lead in solution.

As for purification, which I haven't done, electrolysis looks like it will be the easiest amateur route
https://youtu.be/r-YbQN_twpw

Romix - 11-5-2023 at 07:59

No doubt it's 60/40 leaded tin. Not soft enough. And I was wrong leaded tin solder tarnishing with time, this bars doesn't.
Thinking now that it's a Zinc alloy with 90%+ Zn in it. But I'll still give a go dissolving few grams in nitric.
Still a good deal, will use them to precipitate PGMs out of catalytic converters, but first I'll check if zinc and copper displacing Pt and Pd, using 99.95 pure bars. And maybe Rd, minimal order now days is half an OZ which cost almost 4000£. Remember in the first years of COVID pandemic gram of Rhodium cost more then 800£ at some point, and KG of tin more then 40£, prices returned to normal now. Sometimes items with thick plating of Rd showing up on auctions cheap. I'll experiment with them to start with. I know about PGM toxicity, I'm prepared for it, got my self a Belgian army chemical attack suit from Preppersshop's online, paid 20£ with delivery. Produced in 1974, don't think so you can work with pure H2SO4 wearing it, will it decompose suit to carbon?

[Edited on 11-5-2023 by Romix]

Sulaiman - 11-5-2023 at 15:18

 Quote: Originally posted by Romix ... Thinking now that it's a Zinc alloy with 90%+ Zn in it...
zinc density = 7.14 g/cm3
So if your original estimate of 8.928 g/cm3 is correct then it can't be zinc.
The 60/40 Sn/Pb calculation is much more likely.

Romix - 12-5-2023 at 02:17

Seller calculated density wrong, because one side of the bar is thicker then another.
unionised - 12-5-2023 at 23:53

 Quote: Originally posted by Romix Remember in the first years of COVID pandemic gram of Rhodium cost more then 800£ at some point, ... I'm prepared for it, got my self a Belgian army chemical attack suit from Preppersshop's online, paid 20£ with delivery. ... [Edited on 11-5-2023 by Romix]

I remember toilet paper costing that much. :-)

You bought yourself a false sense of security for £20

Romix - 13-5-2023 at 01:05