# Electronics Solder Recovery



## meatheadmerlin (Mar 11, 2015)

I have seen many people talk about recovering silver from solder,
and have really found no consensus on a process for it.

My local scrap yard pays for solder by the pound.
I have been considering recovery of precious metals from solder,
since some solders contain small amounts of Silver,
and Tin will absorb small amounts of Gold and Silver from contacts.

If I limit the types of solder I work with to solder from electronics boards only, 
I should avoid Cadmium(Cd) (which I understand can be found in solders for Silver contacts in switches).
I could run into several different solder alloys, mostly containing some of the following:
Lead(Pb), Tin(Sn), Copper(Cu), Silver(Ag), Bismuth(Bi), Indium(In), Zinc(Zn), Antimony(Sb), 
and other metal traces (according to the Wikipedia)

With as long as it will take me to collect a pound of solder, I figure I can play with it in the meantime.
If I have a kind of "stock pot" for solders and use hydrochloric/peroxide(AP) to dissolve them,
then the silver and gold should not readily dissolve.

I should then be able to use the Reactivity Series to selectively cement out metals,
First Copper to take out and Indium, Silver and Gold.
Then Lead to cement Copper, Bismuth, and Antimony (I'd like to try collecting antimony).
Then Iron to cement Tin and Lead, which would be melted and sold as scrap solder.
Then a pH change would drop the iron and should leave a waste solution I can safely dispose.
This would leave Zinc in solution? (I'm not sure what other traces to expect so can't place them).

Any thoughts on the feasibility of this process? Or concerns I might not be seeing?


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## g_axelsson (Mar 12, 2015)

I see one problem... what good would hydrogen peroxide do?

As I haven't done it this is pure speculation from my side. When stannous chloride goes bad it is by oxidizing from exposure from the air, it turns into a white insoluble solid precipitate. Adding hydrogen peroxide would convert any stannous chloride into a white mess.

The reactivity series is an ideal model. In reality the different metals will mix, some will oxidize and lead would get passivated by a surface of lead chloride when trying to cement onto it. what would happen to the other metals in your mess I don't know but separating metals isn't this easy or they would use it in industrial scale.

Göran


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## meatheadmerlin (Mar 12, 2015)

Thank you for your reply pointing out those issues.
I am still building a good working knowledge of the chemistry involved.

The thought originally was that hydrogen peroxide would help any copper present to dissolve.
I was more worried that the number of times I tried to cement in a row
might require me to add more acid at each step.
I hadn't considered that lead will passivate, or that tin will oxidize into a white powder.

I suppose it might try skipping the peroxide for dissolving the solder,
and not let the solution sit long to prevent tin oxides.

I could also be more selective with the solders I choose to work with, 
choosing solder only from newer and higher end electronics.
This could reduce the presence of lead and hopefully be
less likely to deal with passivation of lead in the original dissolving,
with it being in the presence of significant quantities of other metals.

Then If I skip cementing with lead,
I would first cement with copper to ensure that the PMs are cemented out,
then iron to drop the rest of the metals.
That could then cause problems with the copper
when I tried to melt the mixture of metals
back into a lump of solder to sell as scrap.


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## g_axelsson (Mar 12, 2015)

I would suggest looking into how refining tin and lead is done. If I remember correct it's done electrolytically, though separating lead and tin in a first step could be tricky.

Almost all refining is done by refining the dominant part of the metal and minor inclusions is recovered from the left overs. For example when refining copper, nickel dissolves and is extracted from the electrolyte, copper is transferred from anode to cathode and all the precious metals drops off as sediments and is collected and processed in the next step.

To try to dissolve 96% tin chemically and cement the 1-3% silver economically via wet chemical processes is a fools errand. It will cost you a lot more in chemicals than the value you recover and I'm not that sure you can recover all of the metals in the end. Fine grained metals will easily oxidize and create metal oxides that you can't recover unless you use smelting procedures.

If you want to do it as a learning experiment, then I would suggest that you first try to learn basic chemistry and do all the acquaintance tests in Hoke before trying anything as complicated as refining tin and lead from solder.

Göran


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## meatheadmerlin (Mar 12, 2015)

Thank you for your helpful insights.
I suppose it is back to the drawing board.
I'll have plenty of time to formulate a plan before I have enough solder to do much of anything with.
In the meantime, I will be separating my solder into two categories
based on my guesses of their lead content.

I still have much in the way of tools, materials, and knowledge to gather.
I am currently up to chapter XII in Hoke's on my first read through.
It will take a few more readings and the acquaintance experiments
before I can feel like I've truly absorbed much of it.

I guess I will look into processes involving parting cells
for this fools errand of recovering PMs from solder.


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## g_axelsson (Mar 12, 2015)

Now you get it!

If you have a 1% gold in copper alloy you could either dissolve the copper and refine the gold remnants creating 99% waste. But if you part the copper in a copper cell then you have 99% copper and 1% gold without a lot of wastes to deal with.

If you can reduce the solder into something you can part electrolytically then you have reduced the problem a lot.

Another way to go is to do some google searches as refining solder isn't anything new. I found a patent from 1936 that added zinc to a melt to extract precious metals and other contaminants.
http://www.google.com/patents/US2119197

This seems to be the simplest way to do it... Parkes process, liquid liquid extraction of gold and silver. (liquids here is molten lead-tin and zinc)
http://www.eurometaux.eu/DesktopModules/Bring2mind/DMX/Download.aspx?Command=Core_Download&EntryId=7170&PortalId=0&TabId=57


MR/GC/EIPPCB/NFM_Draft_3 2014 said:


> Desilvering is carried out by the Parkes process, which makes use of the preferential solubility of silver in zinc. Zinc is added to the lead at about 470 °C and the mix is then allowed to cool to 325 °C. A silver-lead-zinc alloy separates and forms a crust on the surface. The crust is removed and zinc is separated from the silver by vacuum distillation. The silver bullion is further refined using oxygen to produce crude silver. Excess zinc is removed from the desilvered lead by vacuum distillation and then by treatment with caustic soda.



This is just a part of the information I found with one quick search.

The information is out there, do an extensive search and collect relevant information and write a report (including links to information) to share with us other.

Göran


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## goldsilverpro (Mar 12, 2015)

In the 80's, the U.S. Bureau of Mines came out with a method that's sort an adaptation of the Parkes process. Instead of zinc, though, it used aluminum, which is probably safer. The Al collected the Au & Ag and floated on top. It's main function was to remove Au & Ag from the 60/40, Sn/Pb solder used in huge amounts for wave soldering. I think a patent was given to the U.S. for it.


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## g_axelsson (Mar 12, 2015)

When you mentioning it I remember that discussion... and here it is.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=86&t=11029&start=0

Almost everything has already been discussed on the forum.

Göran


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