Depopulating PCB with selective solder recovering

[kjavanb123]

Dear Sir,

I am truly honored and speechless reading your kind and encourging words about my progress here. Whatever I have accomblished in my refining ablity is due to my curiosity and addiction to this but mostly because of these treasure forum with all ita great mentors who are willing to share their hard earned experiences with others for free. I am still awaiting for the moment I can make a profit which hopefuly be very soon and dedicate a portion of that as a very small donation to all your posts and vast information here on many subjects.
I am truly speechless and thankful for your kindness in sharing with us such valueble information.

Best regards
Kevin

 

[kjavanb123]

All,

I tried the silver cementing method using zinc powder with dilute sulfuric acid on white powders left from addition of tab water to my hcl solution' and I got the following impure silve metal,


I still have more batches of white silver chloride that already converted, this is from dissolving solders of 303kg of motherboards in hcl leach.


I will try to melt them to silver anode and run a silver cell Thum style to get the pure silver.

Thanks forum.
Kevin

 

[kjavanb123]

All,

I melted some of the gray powder produced from my silver cementing but due to its high contamination did not produce a silver bead, so I dissolved everything in dilute nitric filtered it and added hcl and very white silver chloride appeared, which used the method called silver cementing adding zinc to dilute sufuric acid and lots of mixing. Here are

Silver chloride being filterd, only one batch of two batches shown here,


Silver metal after converting silver chloride using zinc and 15:1 water sulfuric acid, then washed with hcl,


Next plan would be melting these silver cement with little borax and refine them using a silver cell.

Thanks
Kevin

 

[solar_plasma]

Next time you have dissolved it in nitric you would be better off cementing on a piece of copper. Silver chloride is somewhat hard to wash and zinc will also cement copper and other impurities. So, in the worst case your silver is still not as pure as it could have been by less work.

Thanks for sharing, I follow your experiments with great interest.

 

[kjavanb123]

Solar,

Thanks for your info on using copper wire to cement silver from nitric solution, but I tried it with a copper wire and nothing happened, so I am curios if this is a silver chloride I got or can bismuth or lead also precipitate as chlorides when adding hcl to nitric solution.
Anyhow I could get total of 570g of silver metal out of leaching 303kg boards consists of 248kg telecomm boards and rest graphic and Chinese and non Chinese MB (motherboards).

I will try to melt them cast into anode then refine them using electrolysis.

But there exists some gray powder undissolved in nitric and hcl and turns the color of nitric acid as following picture I first tested for Pd but since I did not have DMG was not able to do so, but what is indication for this color change of nitirc acid?

Here is 570g silver metal


And this is nitric solution after addition to gray residue which did not dissolve in hcl or nitric but changed nitric color tothw following,


Best regards
Kevin

 

[solar_plasma]

Regarding the silver chloride: Expose it to your Arabian desert sun and it should get violet within a few minutes, then a violet-black, whatever, if it darkens, it is silver chloride.

When AgNO₃ doesn't cement on copper as expected, there might be not enough nitric left or the solution might be very diluted, which causes a slow cementing or it is no silver nitrate. I would give it a try next time.

It would be plausible, if you had some traces of palladium, since you might have dissolved some of the contact layers from the mlcc's. SnCl₂ would have reduced it quickly and it would have ended in the precipitates together with lead chloride and silver chloride.

Harold said once, it takes not much palladium to get that tea color. Test it with SnCl₂. You have a lot of it :lol:

 

[Harold_V]

Thanks for your info on using copper wire to cement silver from nitric solution, but I tried it with a copper wire and nothing happened,

That is most likely due to the fact that you don't have silver present. The material you've recovered doesn't even remotely resemble silver.

Harold

 

[kjavanb123]

Harold,

Thanks for your post. Please kindly note the color of recovered materials have changed to the following gray color, I dissolved part of it in nitric acid and it partially got dissolved and the residud turned whitr color, filtered thr nitric solution and this time as soon as a piece of copper wire was inside, white color materials started to precipitate.

So more tests needed to identify this materials,


Dropped a few gram in nitric acid partially got dissolved into milky color, dropped a piece of copper wire and it precipitated the white color material,


Also melted few grams of plated tin and this is the result of the melt,


Regards
Kevin

 

[solar_plasma]

If you wish to melt the silver cement (if it is silver), you should work very cleanly. Never precipitate from a milky solution. Whenever I only had minor impurities of especially chloride, I was (with my weak melting skills) not able to melt the silver to a button.

 

[kjavanb123]

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.

Samuel,

Today I tried boiling in used motor oil, the whole board went very soft, and it is mess to clean it up, all MLCCs were easily removed, but were dirty, so I used some petrol to clean up the used oil from boards.
How long was it running? Do they have scrubber for that nasty fumes?

Here is the picture,


And SMDs after hcl leach and black parts are from board in boiling oil,



Thanks
Kevin

 

[Geo]

Used motor oil is considered toxic. It contains heavy metals such as chromium. http://www.nature.nps.gov/hazardssafety/toxic/oilused.pdf
...whereas used motor oilcontains more metals and heavy polycyclic aromatic
hydrocarbons (PAHs) that would contribute to chronic
(long-term) hazards including carcinogenicity (see
Chem.Detail section below). Metals of concern include
lead; and often to a lesser degree, zinc, chromium,
barium, and arsenic

 

[kjavanb123]

Geo,

Thanks for the safety information on used motor oil. I also noticed very unbearable smell along with gray smoke. The whole test ran for 10 mintues, then shut it down and result were not so clean as you can see from the photo. I stick to use hcl leach, because you can control and scrub the fumes, it will dissolve lead and tin alloys so further processing boards would elimiate the existance of those troublesome metals. Plus tin solder dissolved can be recovered electronically.

Solar_plasma,
In regards to this powder that first thought would be silver, I dissolved it in nitric acid today and diluted it with water, then filtered it. I would say about 60% of it dissolved in nitric to this milky color which did not react when I had copper inside of it,



This is part of alleged silver metal that did not dissolve in nitric.


To recap what I did to get to here, I rinsed the hcl leaches of depopulated boards, since it was white and undissolveble in hot boiling water I assumed it is silver, so I used zinc powder to dilute sulfuric acid mix with this white powder, turned into the last picture, I dissolved that and this is what I got. Could thid be bismuth?

Thanks
Kevin

 

[kjavanb123]

All,

This the result for leaching tin off 70lbs of mixed boards (motherboards, and telecomm boards), I used the same hcl which was used for leaching tin off the 606lbs of boards. They have to be in it for 24hrs. These are part of it, another batch is ready here.

Using dam separator to clean them up,


After cleaning them up,


Closer picture,


Next wouod be purchasing a SiC crucible, mixing the right flux and smelt them, analyzing based on the ICP result add more silver to make it silver anode.


Regards,
Kevin

 

[kjavanb123]

I did a test today which is related to this post. I had some low grade boards which is difficult to depopulate.

I tried glycerine boiled to 300 degrees while having few boards in it, after I manually removed the aluminum capacitors.

Once thing I noticed, as I used my burner to heat up the stainless steel container holding the glycerine, there were fumes coming out of the liquid.

As I cranked up the heat, and glycerine was boiling, it flashed and there was flame on the surface of the liquid. No smoke or fumes at this point.

I turned off the heat, and let it cool for a while, decanted the liquid, save it for later usage.

It cleaned the boards and solder mask was also removed.

Starting material,


Depopulated components,


Boards after depopulation,


Boiling glycerine flash point,


Since this was done outside, away from any population, I did not control the fumes. In my next experiement I will try to condense the fumes.

I also noticed once the glycerine was boiling it stopped making fumes, but since heat source was very hot it started to flame.

I am planning to build a depopulation system based on heat transfering liquid like glycerine.

I also noticed the level of glycerine had lowered by 5 mm. I will test if water can be added to make up the lost glycerine next time.

Thanks and regards
Kj