Removing solder

[bswartzwelder]

With the weather finally breaking, it's about time to start thinking about restarting my R&R (recovery/refining) processes. I have amassed some gold plated pins from computer circuit board connectors.

I plan on giving the Sodium Hydroxide/Peroxide method a try. I know that for every ounce of powdered NaOH, I will need about 1 ounce of water to make a 50% solution. I have 34% H2O2 and will most likely use about an ounce for every pint of solution.

Now, the dilemma. How much solder will 1 pint of solution dissolve? While I don't have any way to accurately measure the solder on the pins because some pins have a lot in proportion to the size of the pin, but most just have a little on the bottom of the pin. I will use 10% of the total weight of the pins as an estimate of the amount of solder present. Therefore, I would assume 1 pound of pins to have about 1.6 ounces of solder.

I have soaked some circuit boards in HCl to remove the solder, but the results left a little to be desired. That's why I would like to try this process on the pins. Thanks to all.

 

[solar_plasma]

Sn + 2NaOH -> Na₂SnO₃ + H₂O

There are two mol NaOH (about 80g for 2mol) per one mol Sn (about 119g). Lead has 207g/mol, so you can calculate as if it only were tin and you have a little lye left over.

On the other hand this relation can only be used as a rule of thumb. For the first the reaction will slow down when most of the lye is used up. For the second there are so many different hydroxides, plumbates and stannates, that we maybe can't be sure the stoichiometry is correct.

Theoretically 1 ounce of tin might dissolve in 1 ounce of your 1:1 solution, but I doubt. I guess you will need 3 times that much. I never tried this.

 

[solar_plasma]

Please tell us how well it worked. If it works well on solder and if it is handy in usage, I would like to examine the applicability to the preparation of mlcc's for a straight nitric leach.

It has been told, that silver is an catalyst for H2O2, so if I would try this, I would make sure to be prepared for a violent reaction...just to be on the safe side (large vessel, only filled up to max. 20% of volume, working over a shell to catch boil overs, full face shield (always when using conc.NaOH, I know what I talk about :mrgreen: ), exhaust hood etc.)

 

[bswartzwelder]

Thank you for your reply. I will be getting started on this within the next week or two as I still have 4 motherboards and several other circuit boards to depopulate. Looks like I'll use your 3 parts solution to 1 part pins as my starting point. I have no idea how fast or slow this will take to work.

One of the wild cards in this mess would be all the different formulations of solder. A 50/50 tin/lead is an older type of solder not used as much today. The electronics solder for years has been 60/40. I have no idea what rohs compliant solder would have, but these circuit boards are much older that rohs. And, we must not forget that there are some solders out there with silver in them.

 

[solar_plasma]

Also, we have to think over how to treat the waste. I don't know, if it just can be made strongly acidic and then treated as usual. Or if a cell would be a good way to go.

 

[solar_plasma]

Dissolve lead and tin only!

I read the H₂O₂ is added in small increments until the solder is dissolved. Obviously it should not be premixed according this link.

 

[MarcoP]

In past I've tried to add 35% H2O2 in small increments (2-3ml each time, total of about 12-15ml in 300ml [stt]HCl[/stt] 50% NaOH) on a small scale using one PCI card only, all I've got was lot of foam and not solder removed ... I'm sure I've done something wrong, not heat was used for safety sake and I've waited days but foam was still there, about 5cm high.

Marco

edit2: added H2O2 concentration

 

[bswartzwelder]

Marco,

I think you misunderstood what I'm trying to do or how I'm planning on doing it.

We are not adding H2O2 to HCl. It is a totally different process using NaOH and H2O2 as a catalyst. In this application, the H2O2 has to be 30% or greater to work.

 

[solar_plasma]

I guess Marco did mean NaOH instead of HCl. The foam seems to describe a NaOH reaction.

I see 2-3 possible reasons already, why this method has not found its way into the main stream style. H2O2 is for many not easy to get and if, not quite inexpensive compared to the value of the task. It is somewhat nasty work with conc. NaOH, it tends to hot reactions evt. with foam. If I would try this, I would start with only some gramm of solder, then there is less mess to fix.

 

[MarcoP]

I've corrected the error, not the first time I call something with a different name ... no good at all. Sorry guys, but it did made sense when I wrote it but I had to quickly switch back to what I was doing instead of double checking the reply.

 

[hatemelborai]

HBF4 + H2O2 is commonly used to dissolve Pb/Sn solder.

 

[hatemelborai]

SnST-550A Tin stripping technology

 

[Geo]

http://www.pcbfab.com/tin-stripping/

Ideas on the stabilizer and suspending agent?

 

[Geo]

SnST-550A Tin stripping technology

This contains no useful information and is a commercial for the stripper.

 

[hatemelborai]

SnST-550A Tin stripping technology

This contains no useful information and is a commercial for the stripper.

to use SnST-550A we have to add nitric acid & water

About 58.6 g of 67% tin/33% lead solder were stripped from various PCBs in 426 g of a solution composed of:
22.780% Nitric acid (HNO3)
8.635% Ferric nitrate (Fe(NO3)3
68.585% Water

 

[solar_plasma]

Interesting:

http://www.google.com/patents/US5512201

http://www.uwin-nano.com/pdf/Eco-recycling of Precious Metal from E-waste.pdf (page 17)

Since the ingredients are readily available (Methanesulfonic acid 1l 92€ amazon, beta-alanin 500g 18,49 amazon) it would be nice if the chemists could cast an eye at the patent. Is it something you know already? Do you know anything about the reaction, the final products and possible recovery? Hidden dangers?

As far as I understand the patent, the solder is oxidized by nitric, the tin is held in solution as SnCl2 and the amine prevents the formation of meta stannic sludge. A corrosion inhibitor prevents from dissolving copper, I guess the same would be true for gold, then.

The composition looks very much like a kind of AR, that is selectively inhibited.

The ingredients seem to cost about twice or thrice as much as the acids would cost alone. Very interesting method, lovely to look at, but in the end I doubt if this is cost effective even to the bigger small refiners.

A more useful point could be to understand the mechanism how this composition prevents the formation of metastannic and if this can be applied to other contexts.

 

[kjavanb123]

I just got a price quota from the tin stripper company, for 5000 grams of SnST tin strippet cost is $200.

This can depopulate close to 1 metric ton of circuit boards, and one can recover the tin oxide from the stripper solution.

Amazing stuff. Anyone tried it yet?

 

[anachronism]

I just got a price quota from the tin stripper company, for 5000 grams of SnST tin strippet cost is $200.

This can depopulate close to 1 metric ton of circuit boards, and one can recover the tin oxide from the stripper solution.

Amazing stuff. Anyone tried it yet?

No because it's just not worth the extra time and effort. By the time all the man hours and extra processes are taken into account it's not profitable in real terms.

 

[kjavanb123]

But doesn't tin oxide or tin recovered from processing a ton of circuit boards have some values? To me this system once accompanied by pyrolysis, smelting can recover 3 base metals ( tin, lead, copper), and 3 precious metals ( gold, silver and palladium).

I just checked out their site, they have stripper for Pd plating, Pt, that have potential usage for catalytic converters, and stripper called ITO stripper for recovery of Indium from flat display screens.

 

[upcyclist]

But doesn't tin oxide or tin recovered from processing a ton of circuit boards have some values?

The spot price of tin right now is about $9/lb or $20/kg. After you've bought the stripper, added in labor, and possibly converted the oxide back to metallic tin, is that worth it to you at your scale of operations?