Depopulating PCB with selective solder recovering

[Anonymous]

I think the idea is dead in the water. The solder will stick to the metal it sits on, it's called surface tension. To have it in a fluid will just help it against the force of gravity, if it doesn't drop off when melted in air, why should it do it in a liquid where the liquid will make the tin less heavy.

The solder will also dissolve more metals while molten, for example copper, and become more stuck to the surface (or maybe it is oxides).
Anyhow, anyone that have replaced soldered components knows that when you have worked with molten tin for too long it get's harder to melt and the best way to fix it is to remove the old tin and add new.

Göran

Goran I agree that if you were letting them sit inert in the liquid that it would be pretty pointless. However if you were agitating the boards it could work. Now don't think that I'm being a complete fruitloop here but what about stacking cards vertically and combining the heat with ultrasound or a vibration generator? Alternatively you could have a dipping mechanism. Either way it could work.

 

[soltysek0383]

I found trace info that NaOH 50/50 water + h2o2 30% will disolve tin in solder but I can finde if it's true . I'm looking for way to selectively get ride of solder before proces in HCl or minimal loss in others metal +\~15% and tin is still in much better price then copper from difrent assay I have info that tipical mainboard have from 40- 75g of tin so around 100g per kilo of main boards ( look pretty high by the way ) .

 

[g_axelsson]

I think the idea is dead in the water. The solder will stick to the metal it sits on, it's called surface tension. To have it in a fluid will just help it against the force of gravity, if it doesn't drop off when melted in air, why should it do it in a liquid where the liquid will make the tin less heavy.

The solder will also dissolve more metals while molten, for example copper, and become more stuck to the surface (or maybe it is oxides).
Anyhow, anyone that have replaced soldered components knows that when you have worked with molten tin for too long it get's harder to melt and the best way to fix it is to remove the old tin and add new.

Göran

Goran I agree that if you were letting them sit inert in the liquid that it would be pretty pointless. However if you were agitating the boards it could work. Now don't think that I'm being a complete fruitloop here but what about stacking cards vertically and combining the heat with ultrasound or a vibration generator? Alternatively you could have a dipping mechanism. Either way it could work.

Shaking will dislodge some tin, more if you don't have it in a liquid. Horizontally or vertically won't make much difference. Some components might drop off and some not.
Personally I wouldn't get within five meters of the bath, not only is shaking 235 degrees C liquid scary, add to that the danger of a heavy component dropping down into the liquid and splashing liquid all around, you also have the danger of exploding components. Any electrolytic capacitor is a ticking time bomb. It's bad enough when a small one blows, just imagine one of the bigger going off when covered with hot liquid!

This is just a stupid and dangerous idea in my opinion.

One of the methods for soldering PCB:s is to condense a high boiling point liquid onto the board so some of the boards have already been wet with melted solder without the solder dripping off. (During limited time to not damage components)

Göran

 

[soltysek0383]

I made a little test today NaOH + 4% H2O2 mixed half half after 6 h solder get darker gray but that's it i did not notice of disolving , I will try difrent way tomorrow my by warm it up , unfortunely I have only 4% H2O2 for now .

 

[Anonymous]

Personally I wouldn't get within five meters of the bath, not only is shaking 235 degrees C liquid scary, add to that the danger of a heavy component dropping down into the liquid and splashing liquid all around, you also have the danger of exploding components. Any electrolytic capacitor is a ticking time bomb. It's bad enough when a small one blows, just imagine one of the bigger going off when covered with hot liquid!

Göran

Ahh that's a very good point Goran!

 

[kjavanb123]

Solty,

Did you finish this project? I am going to give this a try. I like to strip tin solders prior to put the depopulated boards into my grinding machine to recover copper.

Glycerin boiling point is 290c, but lead/tin alloy is 230c, so I will test this in a baking pan, fill it up with glycrine, boil it, while the PC board is in it, if it worked I can do it on my 600lbs of already depopulated boards


Thanks
Kevin

 

[kjavanb123]

All,

I tried boiling glycerine and put small pieces of PC boards, and it successfully melted most of the solders, but had to stop because I forgot to remove a tiny aluminum capacitor which blew up.
So conclusion is to use a pressure cooker put remove all the components, specially plastic covering and all capacitors. Boiling produced some smokes since this was only a test of 25ml, it did not produce much, but pressure cooking pan should take care of it.

Here are some pictures.

This is the sample piece of board for testing,


Boiling inside glycerine,


Residue mostly the plastic cover of aluminum capacitor which exploded later, and the solders


Washing the junks and clean solders,


Result,


More result and photos tommorow, glycrine price is $2.5 per kg.

Regards
Kevin

 

[kjavanb123]

All
After my initial testing glycerin to extract tin solders I tried to scale it up using 1200ml glycerine and couple of small boards which I removed all the aluminuim electrolyt capacitors prior to this, and once it started to boil I shook the beaker a little, here is the result.

Boards after being inside the boiling glycrin,


Results after it was washed,



Thanks
Kevin

 

[kjavanb123]

All,

This link seemed interesting, in order to remove tin solders on circuit boards, leach large batch of circuit boards in a bucket, with dilute hcl, then use this method to electrolyically recover tin. Once all the tin is removed from boards most of the mounted SMDs and MLCCs drop to the bottom of beaker, and can be collected for Palladium and silver refining.

I will try this tommorow.

Thanks
Kevin

 

[samuel-a]

Kevin,

Iv'e seens this done on a large scale, however, used motor oil is being used where the BP of the oil is >280C. It is not brough to boil as most soft solders melt under 260C.
It is done inside of large 55 gal preforated steel drums being thumbled inside a large SS bath being heated from the bottom (from the outside) with simple resistance elements. The setup is very similar to a cyanide leaching operation.

The smaller components and solder can be collected and shipped off to smelter who can returnpayment against Sn+In+PM's.
larger components and boards can be further processed in house or shipped as well to a refiner.

 

[kjavanb123]

Samuel,

Thanks for your input, I put 303kg (606lbs) of my already depopulated boards into this large bucket, and poured 120liter of muratic acid, first batch dissolved most of the tin solders, and all the surface mount caps or resistors were so easy to shake and drop into another bucket, I continued this and today is the last batch of 303kg is in the same hcl bath.
Note the next batches took longer for acid to dissolve the tin, I also tried to recover tin alloy solder electronically, using graphite anode and cathod and 9V, 12A DC, amper dropped after few hurs to around 4A.

Hcl leach bucket with depopulated boards in it,


Mixture of MLCCs and SMD caps and resistors plus some solder masks and wires small ICs,


After panning the plastics, screening it through a mesh 20,


My tin electorlytic parting set up,


Tin plated on graphite after few minutes running the cell,


My plan is to recover all the tin which was dissolved by hcl, and collect all the SMDs and use induction furnace to smelt them.

Your comments are welcome as always.

Regards
Kevin

 

[kjavanb123]

Tin recovery from tin chloride solution update,

I modified the rectifier setting from 9V,12A to 3.6V,12A and got this nodule like deposit on cathode


Closer look at cathode,


Thanks all for your information.

Regards,
Kevin

 

[kjavanb123]

All,

This is what happened to cathodes recovering tin from chloridesolution after 20 hrs running 4V, 12A. I swtiched the ampre to 24A, and its voltage increased to 5.6V.



Close up


Regards,
Kevin

 

[solar_plasma]

As always, very interesting, Kevin! Isn't there produced chlorine gas, too? How do you handle this? Do you want to send this tin to a lab for analysis or are you able to test the contents on your own?

Maybe this cell would be more effective,if you used some more of anodes and cathodes with parallel connections, a narrower electrode distance, a stirrer at the bottom or a pump for better circulation and a slightly higher temperature by thermo isolating the tank. I've read about the usage of tiny amounts of surfactants, that help avoiding fumes in copper sulfate cells, but this might not work well in this setup. Whenever I read about cells, I watched out for easy available additives for finer deposits, but the only ones I've found were saccharin sweetener and vanilin for nickel cells. Sooner or later I will try them on other cells. I do not expect, that this will work, - but if it works, this would be a nice trick.

A higher electrode areal per volume of solution, would warm the solution up and vaporize some water and fresh electrolyte could just be added, since removing tin and chlorine will dilute the electrolyte and lessen the conductivity and the deposition rate, I think.

If i am not far off, much of the lead will crystallize as lead chloride, while the electrolyte gets more and more contaminated/concentrated, and can be removed mechanically from cooled down electrolyte. Only a thought, could be wrong. Another option to remove lead could be a titration-like addition of diluted sulfuric or otherwise sulfate ions in order to drop lead sulfate.

 

[solar_plasma]

Though an excess of sulfate could cause problems, since tin sulfate is not stable in water over longer time.

 

[kjavanb123]

Solar_plasma,

Thanks for your response. I will send it to lab for an ICP test, as far as chlorine fumes, it is just around the tank that hold the solution and cant be smelled a feet from it, and for now I use face mask to handle the cathodes, but in future I plan to have a fume hood hooked to a vaccume fan, to guide the fumes into a limetone tank to convert the chlorine to calcium carbonate.

I thought about circulating it using a pump, which I will add that tommorow and put it through a test. All these deposits are at room temprature, so nothing is added to electrolyt and deposited tin is easily scrapped off.

Lead chloride which is very white is precipitated at the buttom of my holding tank, and I need to remove and test it whether it is lead or silver, which have the result and picture tommorow morning.

Thanks for your support,
Kevin

 

[eastky]

I thought about circulating it using a pump, which I will add that tommorow and put it through a test. All these deposits are at room temprature, so nothing is added to electrolyt and deposited tin is easily scrapped off.

Kevin are you talking about recirculating the acid in your tank? I have researched cells for recovering metals. From my understanding you don't want to disturb the sediments in your tank. They will contaminate the metal you are trying to
plate out.

Just so you know if you are trying to plate just the tin out. When the level of tin in the acid drops to a certain amount
other metals will start plating out.

If I have misunderstood from reading someone please correct me.

 

[solar_plasma]

From my understanding you don't want to disturb the sediments in your tank.

My first thought, too, when I read Kevin's post. But I have seen patents/texts where electrolyte was pumped into a settling tank, before further processed or led back into the tank. Problem would be to get the lead chloride settled fast enough and have good flow at same time.

In a small scale setup it might be less effort to stop the electrolysis before maintaining the electrolyte: filter/syphon/decant off solid chlorides (Ag/Pb - only first time before electrolysis) - concentrate by evaporation - cool down - filter/syphon/decant off solid lead chloride - precipitate left over lead cations - return to cell.

If I understood correct, you dissolved the tin/lead/silver in HCl. Then you have to let the AgCl and PbCl2 settle. The clear liquid contains no silver, since there is no free chlorine and most of the HCl is used up. Mostly tin and a little lead chloride (low solubility, but it is soluble). This can be dropped as almost completely insoluble lead sulfate.

If you get lead chloride precipitates in your cell while you are using inert electrodes in that tin chloride electrolyte, something is wrong.

 

[kjavanb123]

All,

Thanks for your responses. Since boards were alreqdy manually depopulated, there was nothing except the MLCCs and resistors, so I presume only tin or small amount of lead or silver got dissolved in hcl leach, solution should contain tin solders.

I added rinsed water to the hcl solution and it immidately turned to milky color, and it was precipitated as you see in the picture below,


After 3 rinses with boiling water still white powder remained, so this could be silver chloride? Tests will perform tommorow to confirm


I could get 340g of tin plating on my two cathodes running the cell for 24hrs at 5V 24A and without solution circulating.here is the result after 24hrs


And here is what I did to circulate solution for more efficient tin recovery


Keep you posted as soon as I have more result.

Regards
Kevin

 

[butcher]

Kevin,
Thanks for showing us what you have been up to, it is very interesting, and I will watch with interest.

I must say, I like how you stick with something and do not give up easily, not letting a few failures stop your pursuit of the answer to a problem, and it is also interesting to see how much you have learned, I know you have worked very hard to learn, your persistence and not giving up until you find the answers you seek, are quality's to be admired.

This thread makes me realize how much many of our members have learned, those who stick to it, and work hard at it, it is amazing and nice to see how far many of our members have grown or increased their knowledge, since joining this forum, I guess that is just one of the things I love about this forum watching our friends grow.

I am waiting in anticipation for the results of the cathode deposit, and to see more results from your experiments.