# Recovering tin from dissolved solder solution



## Romix (Sep 4, 2014)

Hello all, do you know percentage of tin in solder on boards? (computers, cordless and mobile phones...)
If I boil them in hcl, neutralize or evaporate acid that left unreacted and after displace tin with zinc. 
After filtering and washing the crystals that formed on zinc, dissolve them again, and recover tin by electrolysis. 
Would I get 99.9% pure tin? 

Because tin is very useful element in gold refinery and recovery. It needs to be recovered! and copper and nickel too!!

Message for the local binman, I saving up all the boards with out gold for you. Copper, Tin, Nickel. 
I will live them in a see through bag. 8)


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## Lino1406 (Sep 4, 2014)

Tin turns mostly to tin dioxide after AP treatment


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## bswartzwelder (Sep 4, 2014)

Tin in cell phone circuit boards makes up 0.689% of the boards weight.


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## Romix (Sep 5, 2014)

Lino1406 said:


> Tin turns mostly to tin dioxide after AP treatment


SnO2 + 2H2 ----> Sn + 2H2O


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## Romix (Sep 5, 2014)

bswartzwelder said:


> Tin in cell phone circuit boards makes up 0.689% of the boards weight.



I asking about % in solder not of the whole board weight, it contains impuritys of other metals.


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## butcher (Sep 5, 2014)

Romix,
In this reaction you posted:
SnO2 + 2H2 ----> Sn + 2H2O
This looks to me to be a reduction reaction, where they are reducing tin dioxide with a melt, or fusion process using hydrogen gas in the process, it is hard to tell without knowing more details or having more information or of where you found this formula.

Tin dissolved in HCl gives stannous chloride SnCl2
Sn + 2HCl --> SnCl2 + H2(g)

Tin dissolved in copper II chloride (CuCl2) can give a different salt of tin, besides stannous chloride, much of what is produced can also depend what other metals are also dissolved in solution, whether these other metals or salts will react with the copper chloride, or tin chloride salts, you can have several oxidation reactions and reduction reactions going on, 

CuCl2 can be reduced by the tin chloride solution.
With just copper II chloride in solution with tin or with stannous chloride in the solution, the tin or stannous chloride can reduce the copper from solution, giving a stannic chloride in solution, and precipitating copper I chloride, or even reducing the CuCl to metallic copper, it really depend on how much tin is in solution and how far these reactions are carried, and as I stated other metal in solution will also react in this mix or mess, the more metals or salts in solution the more complicated these reactions can become in solution, which can have many different things going on in solution....
CuCl2 + Sn --> Cu(s) + SnCl2
CuCl2 + SnCl2 --> CuCl + SnCl4 (SnCl4 =stannic chloride)
2CuCl + SnCl2 --> SnCl4 + 2Cu(s)

SnCl2 + 2FeCl3 --> SnCl4 + 2FeCl2

Unless tin is the only metal you dissolve in the chloride solution, (the solution can hold other metals or salts beside the tin in solution, and as you can see they will react with each other in oxidation and reduction reactions). Raising pH to precipitate the tin will also precipitate many of these other metal hydroxides.

I think this whole idea you have here, is much more complicated than you seem to think it is.

edit: I did not have the reaction above balanced properly , Thanks to Göran g_axelsson and his sharp eyes, who noticed it and provided us with the properly the balanced equation, we see we had 2 moles of ferrous chloride and the stannic chloride produced from the reaction with the stannous chloride and the 2 moles of the ferric chloride in the above reaction.


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## the iron dwarf (Sep 21, 2014)

I was thinking of using dilute HCL for desoldering boards in order to get components to recover PMs from and to use AP to remove gold plating.
I could then pass the solution through a sieve to remove loose components and thoroughly wash the boards and components,
filter the solution to remove the insoluble lead chloride then I only need to work out how to remove the tin and I could reuse the HCL for more desoldering.
I do have need of metallic Tin and though this may not be an economic way to get it the fact that at the same time I can desolder boards to get the components and foils and reuse the HCL may make it more worthwhile.


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## kurtak (Sep 21, 2014)

electro winning cell 

Kurt


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## butcher (Sep 21, 2014)

I see several problems with that idea.

HCl will react with many metals above Hydrogen in the reactivity series, and the resulting solution will be a combination of these. 

It will dissolve tin and break down the lead to a lead chloride powder, to loosen components and other junk, but it can also loosen gold foils in this junk.

Tin in solutions hydrolyze, or oxidizes, especially on standing or with dilution making filtering solution a real problem, and making separations of values from the unwanted material a real problem.

Metals below hydrogen make your solution a dissolved salt of these metals, they also take the hydrogen from the acid to form hydrogen gas that leaves the solution, without this hydrogen you no longer have acid but a salt of the acid and the metal, with this solution you will have several metals in this salt solution that were involved in the circuit board materials.

If using copper II chloride you have an oxidizer that will also dissolve copper, with iron in the circuit you will be displacing copper from the solution,as you dissolve iron in solution your solution will begin to become an iron chloride as well as a mixture of many other base metal chloride salts not only will you still have the problem with tin in solution you will also have much more of the gold foils or powders mixed with the other insoluble trash, as these are freed more easily from the base metals they were plated to...

basically you are making a troublesome mess to deal with to try and recover values from.

You will not have a reusable solution of acid, or copper II chloride, you may have a solution of Iron chloride (and other base metals) you maybe able reuse somewhat in some other recovery procedure, but basically your left with a waste solution that is not very useful loaded with base metals.

You will not be able to just easily remove tin or many of the other metals from this Chloride solution, and even if you could easily remove some of the tin or base metals, you would still be left with a chloride (salt), not (chloric) or hydrochloric acid, with out adding hydrogen back to the solution, in which case you would have to add an acid that defeats your purpose, as you would still be contaminating this acid with base metals...

When you add a metal to an acid you oxidize the metal, at the same time you reduce the acid, this is no longer an acid, and no longer a metal, but a salt of that metal, and a salt of that acid.
Here we reduced the acid to a metal chloride, (hydrochloric --> chloride) notice we lost the hydrogen, notice the ending of the spelling (ic) and (ide) showing us the oxidation state, to go from being a metal chloride, back to hydrochloric acid, we would have to remove all metal from the chloride salt, and oxidize the chloride, add back hydrogen, not something easily done, or worth the trouble especially when buying acid is so cheap...

Not to say that you cannot use this idea, for some things, like when removing memory chips from memory circuit boards (with the gold foils already cut off) so that you can process the memory chips by another process, it will work to do that... 

Although time consuming, the best methods of separation are cherry picking separating by hand or mechanical means, and as you will learn from the forum from reading about how others have learned the best way to get the gold separated from the other materials.

Most of your ideas have already been tried and the best way to roll the wheel has become the chosen methods, very seldom will we be able to invent a new wheel, and our best approach is to learn from others what wheel already works best for what we are trying to roll.

As I was writing I noticed Kurt posted the comment (electro winning cell), I have a question on that comment, it is hard to electro win a metal from a solution full of various metals, unless your just trying to push out as much metal out of solution as possible, as a mixture of reduced metals, say like with an inert anode like carbon graphite, and I would not consider that electro-winning , but to form an alkali metal chloride solution, and here you will not get anything but a mixture of reduced metals, and a chloride salt water for all of your trouble...


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## the iron dwarf (Sep 21, 2014)

thank you butcher
I have removed fingers and pins from boards I have got, the pins have solder on them.
have read on here about using a few drops of sulphuric to drop lead from solutions and will do that.

nothing but a little collecting and mechanical stripping of boards will be done till I know a lot more except the current stripping of silver plate in H2O with electrolysis.

will work up to fingers and ceramic chips later and leave more complicated stuff till after that


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## butcher (Sep 21, 2014)

HCl will work on the heavily plated, gold plated copper pins and can be used to clean off the solder, It will Dissolve the tin from the solder, leaving lead in a fine state to form an insoluble lead chloride powder, some of which may stick to the pins, where a boil in water will dissolve the lead chloride.

The HCl will not attack the gold plating or the copper.

Even pins I would separate by type, some pins are heavily plated onto copper with a nickel barrier. 

Some the gold is so thin it will come off as powder.
HCl even without an oxidizer can attack iron, or zinc in the copper based brass, or attack tin in the copper based bronze.

Some pins are not plated onto copper, and the plating of gold is very thin and the base material can be an iron based Kovar, or even a brass, or beryllium type copper.

There can be several ways to recover gold from pins, each person may have preferred methods, or more than one method they like to use.

For the High grade pins, I like to use them to make a batch of nitric acid, the low grade pins I use copper II chloride to dissolve the copper or base metals.

Some like to use nitric acid or the concentrated sulfuric cell.

I have removed fingers and pins from boards I have got, the pins have solder on them.
have read on here about using a few drops of sulphuric to drop lead from solutions and will do that.

If the solution is a chloride solution, most of the lead will form an insoluble white lead chloride powder, with very little lead left in solution (cooling and letting it settle will settle out most of the lead).
The few drops sulfuric acid used is normally used on a solution where we are refining gold (and have already removed most of the lead and base metals before we put our gold into solution), the sulfuric acid is used to remove traces of lead that made it through the other processes of recovery, and is in our refining stage, and may be dissolved in the highly oxidized acid with our gold solution, the few drops of sulfuric acid gives us a way to remove that little bit of lead as an insoluble lead sulfate which will settle out of our gold solution after setting overnight. (usually with the traces of silver chloride formed with the dilution of water).


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