Tin Recovery From E-Waste part 1: Viewer Request Special  

Your final procedure when processing Printed Circuit Board (PCBs) is actually my initial procedure. Removal of solder (tin recovery) liberates all electronic components from PCBs, making it so easy to sort out the loose components for further processing; therefore, it's always done before attempting to recover gold, silver, copper, or any other values. Most backyard refiners refuse to accept that time is their best friend. They want "results" here and now. Contrary, it's much more profitable to use less acids, use methods that enables you to recover spent acids and chemicals, use procedures that demands the least physical attention, and instead let the time work for you. Your fear of getting iron in the solution is founded in the fact that your HCl is far too concentrated for solder removal. Very weak HCl will dissolve most of the tin, some of the lead, an insignificant amount of iron, and won't touch silver. It just takes a little longer. Tin behaves odd in many ways. One of them is if tin solder has been in contact with copper (or gold), a phenomenon called metal diffusion have occurred. It's best illustrated if you use a cheap soldering iron with a copper tip. Over time the tip inevitably becomes shorter and shorter as the tin solder absorbs a tiny part of the copper tip every time you use it. Therefore, dissolved solder from fully gold plated pins do contain gold! Metal diffusion is one of the reasons why a two-step process is needed for complete removal of solder from PCBs. A small part of the solder is encapsulated in the diffusion layer of tin/copper. HCl cannot dissolve copper unless an oxidizer is present, but HNO3 can. Caution: Don't try to remove solder solely with nitric acid as the first step, unless you love to fight with that slimy goo called metastannic tin. Be aware there are two types of solder. The old type (commonly 63% tin + 37% lead), and the new lead free type (at least 90% tin + around 5% copper + 1 to 4% silver + around 1% other metals, usually bismuth). The two types behave different during dissolving and must be processed accordingly. Very weak HCl, between 4 to 6,5% is ideal for solder removal. Reaction time is up to 6 hours for old PCBs with thick tin/lead soldering, around half the time for PCBs with lead free soldering, and around one third of the time for newer PCBs (surface mounted components) with very thin soldering. Heating speeds up chemical processes. It has been common practise to heat the HCl solution to 80 C (some even say 90 C but it's around the boiling point of 6.5% HCl, and too near the boiling point of 4% HCl). An annoying side effect occurs when lead is exposed to HCl: Lead develops a passivation layer! That's why HCl can't remove more than around half the lead from the old type solder, but removes 90 to 95% of the tin (5 to 10% is trapped under the lead passivation layer). Regarding the lead free solder, HCl removes around 98% of the tin (2% is trapped in the metal diffusion layer), but none of the copper and silver from the solder. The thickness of the passivation layer is not linear proportional to the temperature, at higher temperatures just a slight increase in the temperature causes the layer to double in thickness. The latest scientific research has shown that the heating temperature must not exceed 75 C to keep the passivation layer at a manageable level. At 60 C the layer will be rather thin, although this temperature prolongs the dissolving process. Nevertheless, 60 C is the optimal temperature. If this method is used for a combination of depopulation and at the same time solder recovery, it's important not to submerge the PCBs in the acid. Weak HCl dissolves some other metals too, though rather slowly. However, aluminium parts will not only be lost, but also immediately consume the HCl, and worse the acid solution will be contaminated with aluminium causing nothing but problems. To avoid that I use several flatbottomed 90 liter plastic tubs. The PCBs are placed in a single layer and weak HCl is poured slowly into the tub to a level of maximum 5 mm. This way none of the components comes in contact with the acid, only the legs/pins. Due to the low quantity of acid in the tub, already at the next batch a few ml of full strength HCl must be added when the reaction slows down. Be careful not to add too much HCl in order to keep the acid concentration below a maximum of 6.5%. You added H2SO4 before filtering to create lead sulfate. If you had filtered the solution prior to addition of H2SO4, you could have removed the lead chloride; which is easy to recover metallic lead from by electrowinning. Such process has the added bonus of recovering all of your spent HCl for reuse to dissolve more solder = free HCl acid! Tin is a heavy acid consumer. Prior to the second step in solder removal a thorough cleaning of the PCBs must be done to eliminate all traces of HCl. Either by dipping them shortly in boiling water, or better by pouring boiling water on them. Avoid any extended contact with boiling water as some electronic components, like aluminium cased electrolytic capacitors, poses a risk of exploding if heated. HCL is very effective for dissolving tin but struggles with lead. HNO3 will finish the process, now that almost all tin is gone. Weak HNO3, between 6 to 9% maximum, will dissolve all the remaining tin, lead and/or silver/copper present in the solder; both from the lead passivation layer and from the metal diffusion layer. Heat to near 75 C (60 C is optimal). Reaction time is pretty fast. Thin solder residue is removed in 10 minutes, remaining thicker solder layers take more than ½ an hour. Never leave the PCBs in this solution for more than 1 hour as nitric attacks most other metals too, thus damaging components if you use this method for depopulation. If solely bare boards are treated, you can leave them for as long as needed for full recovery of all exposed copper on the boards. Notice: If the concentration of HNO3 is kept at a maximum of 6.5% no metastannic tin is formed! Lately I've found that a large fine-mesh plastic net/sheet is excellent for lifting up the PCBs and all liberated components from the acid solution in one go. It's placed in the tub before any PCBs are spread out on the bottom. The bare boards are later processed for Bromine extraction and pyrolyzed, yielding Raw Pyrolysis Oil. Warning: In the '70s and '80s lots of PCBs were made of various fiber material impregnated with resins containing formaldehyde. When such boards are heated they'll give off dangerous fumes which will contaminate the pyrolysis oil, requiring purification because it's illegal to use as is. After purification I run this Raw Pyrolysis Oil through another unit, cracking it to petrol/gasoline, diesel, and fuel oil. Last step is separating out the copper layers. What remains is solely glass fibers, which is only profitable to sell in shipments of 10 tons or more. Luckily, a glass recycler picks up any kind of glass for free so at least I have no expenses for disposal. I process all high/medium/low grade PCBs at home for recovery of virtually every bit of value from both the boards, as well as all the individual electronic components. I never waste time manually depopulating any kind of Printed Circuit Boards!

Very cool

thank you very nice formula tinclorite to tin metalics very beautiful

Your making more work for me. I was about to scrap a bunch of boards. But now i have to keep them. Thanks

Thank you for uploading. Was curious how to recover tin

Black dust from the first filtration may contain silver and gold. Silver from the solder and gold from the connector on the chips.

Just started processing floor sweeps after a lot of de-populating. I was planning on doing electrolysis to my HCL boils to recover tin. Your timing of this video is perfect for me. I was curious if there was another method for recovering tin that would be more efficient for me. Thanks for your time and effort. Looking forward to part 2.

thanks for the valuable experiment, it helped me a lot to get the tin chloride from the soldering wire

That was a great explanation on how to do this. I cringe at all the tin I have discarded Thank you

Mike that was an AWESOME explanation of the process I truly appreciate it

Okay.. might have wanted to filter before & after sulfuric acid... 🤔🤔

Just save up the boards and give them to the scrapyard for free along with stuff you're already turning in for money. Even if they wouldn't want to pay for them, the copper is still in there and it's better to let them have it to recover than sending it to a landfill.

Electrolysis is the way to go for recovery of tin

A thought on the waste boards, stripping the solder mask with Sodium Hydroxide the putting the exposed copper clad boards into Sulfuric acid to get copper sulfate, then electroplating the copper back out to reuse the acid in a cycle?

The bathtub ring will come off with isopropyl alcohol. I boil my memory chips in Muriatic acid to remove the solder before I incinerate them. I don't want tin in my aqua regia when I extract the gold from them. I always assumed that the ring was from the adhesive that was under all the stickers on the chips, But that stuff keeps forming on the glass. I have found that pouring a little isopropyl alcohol in the glass and wiping it down with a napkin really gets it off easily.

Theres lots of palladium on those ram sticks. Prolly some gold traces. Id use heat to get the tin and ap to get the gold

If you ever see a circuit board with the letters sn ag cu silkscreened on it, you're looking at a board that uses lead-free solder. The Sn is TIN, Ag for Silver and the Cu is for copper. There may be Silver in that Tin you're extracting from those circuit boards.

What did you do with the lead sulfate. Same compound found in lead acid batteries... Did you rinse off the depleted RAM sticks before tossing them in the trash. One to neutralize the acid and two to get all the tin solution included in your recovery process?

it's seems no one removed tin from soldered board then recovery gold from soldered gold plate pad.😢

OK so I tried this with all the lose solder I had from de-populating stuff. After I added sulfuric acid filtered the HCL it was clear but then it sat for a week and the top few inches turned yellow. so a put a few tin balls in and they started to react. the next day some metal (I think the metal that made your solution purple) fell out, I filtered it and slowly added lye crystals straight into it. The tin fell out of a clear solution. the waste solution I heated a little and added some hcl and lead crystals(i think) fell out . I did it several times and once it changed to a white powder I know was lead. so check your waste maybe?...Fixed..... in the end I added HCL when it should have been sulfuric acid. warm the solution and add sulfuric acid and the lead will come out of solution. it also come out if you just leave the solution about a week.

Also wondering about tin recovery, from AP solution heavy with copper and tin I would imagine ... Thank you 😊😊 always good stuff 👍

Have you tried freezing them : tin became dust with cold

Hcl will stay active until you neutralize it.

i just need to know how to convert lead sulfate back into Metallic lead please now

this is good stuff mate

Hi Mike could you have use baking soda (cheaper) SnCl2 + 2NaHCO3 → SnO + 2NaCl + H2O + 2CO2

Mike I recently did the AP method on my boards and I was wondering how do I collect the lead and tin out of the solution if you get a chance to do a video on that I would really love it

Mike I've seen you use PH test strips before (with the colour comparison chart). Why use litmus paper this time?

I skipped to the end so maybe you already mentioned this, but if you just soaked the entire ram sticks in hcl then you'd probably recover more tin, and also that would remove the chips from the pcbs. Two birds with one stone.

Lie is a good word... For this ? Video ? OOOOOPS - I meant lye.

Hi Mike, Fascinating! I think I'll wait until you do part 2 to see the other options. Since I have 5 - 60 gallon drums full of boards - I'll have to think about this! One question - would aluminum capacitors cause any problems being left on the boards? ooppss - one more....would the exothermal heat get hot enough to distort or damage a 25 gallon plastic drum? See what you've done!! Now my brain hurts! Thanks for all your R&D to educate us! Thumbs up! Stay safe. Jim

This tin will be very dirty with copper etc

Wouldn't there be copper in this - dissolved by the hydrochloric acid ?

Save and send them to Jason so he can get the copper out

Are you going to melt or smelt the tin into a solid metal??

Mike, question for you. I used vinegar-salt-h202 to free gold foils from random boards. There is a bark grey sludge forming. Presuming it is coming from the solder. Will H2SO4 release it from the gold foils, or do I go a different direction.

Is there any gold under the solder mask? Was wondering if I should save those ram boards.

I am thinking of doing this but wondering if adding sulphuric acid from a car battery will still precipitate the lead sulphide or would the sulphic acid already be loaded with lead as it came from a lead acid battery?

How is it acidic if your ph was above 7 in the first place

That heavy sediment you had before you added the sulfuric acid was likely gold. I hope you didn't throw away that filter paper.

The cost of acids and electricity and time is not worth the price of the end result. The chemistry is cool though

Stannous chloride is not a reactive test to detect gold in solution?

I buy tin in the form of lead free fishing weights from Wally World. This is a good chemistry experiment, but in no way profitable.

ahhhh, I could have ran those through my granulator... 😞

A copper II chloride leech will take the copper plating off the boards before you pitch them. You can easily recover that with a little bit of aluminum tossed into the copper II chloride. And as you know the copper II chloride is essentially self regenerating. You just got to refresh it every once in a while with some HCL and its cheap enough that you're going to be losing money by throwing your copper away like that. I mean this is about recycling isn't it? this whole thing?

Let's spend 30 dollars and a bunch of time to recoup maybe 5 dollars

The first part with hcl is useless.

Not worth the time and cost but the chemistry is cool if you just want to explore the chemistry

Melt the copper out

Another way of extracting the tin is via electrolysis... Save you the cost of the lye