# Depopulating PCB with selective solder recovering



## soltysek0383 (May 20, 2014)

Hi 

Its my first post on this forum .

I have a question if someone tried to recover selectively solder from the PCB without chemical damages to the remaining metals.

Hypothetically, such a process can be carried out very simply boiling at 235 * C in a liquid such as glycerine or sulfolane .

Hypothetically, glycerin is best suited for this purpose because It do not react directly with the metal and it's boiling point is 290 * C .

After cooking remain pure PCBs and Electronic Components and in the vessel bottom clean solder. At a price of tin in my country about 14 $/kg and the content of tin in sludge about 97%. Taking the relative simplicity and low cost process seems more profitable than copper recovery at Price 4,5$/kg . Additionally, you can count about 1.5 % - 3 % silver content .

Jar of glycerin should suffice for centuries . Under one condition that before cooking remove all plastic and organic dirt .
After removing PCBs from the vessel must also be repeatedly rinse with distilled water . Water can be boiled off from the glycerine.

I do not want to reinvent the wheel if someone try this


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## Geo (May 20, 2014)

This sounds very interesting to me. Glycerin for me is not a problem and if this does as you claim, it will remove one of the most troublesome metals when dealing with electronic scrap. Thank you for sharing.

One question, is the glycerin effecting the tin directly or one of the other components of the solder?


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## soltysek0383 (May 20, 2014)

I did not test this yet , i wait until i finish my lab , i just woke up today night with idea  teoreticly glycerin is not reacting with any of metals but provide temperature transfer , when solder start to melt glycerin replace it pushing it out , if not you can help her with a litle shake or magnetic whirpool :lol: But still some research need i was just Wonder if some one try this . Ther is 3 or 4 fluids that have boiling temperature over solder melting point and are preety safe to use . Will be nice to work easier in less hazard env. Glycerins have positive Work on skin but do not try this when its 235*C hot


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## Sucho (May 20, 2014)

flash point of a glycerol is 160°, 176° respectively.

theoretically, silicon oil which is widely used for oil baths in chemistry is suitable


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## soltysek0383 (May 20, 2014)

From info I have 
195-199*C ignition 
370*C self ignition

But from research I made today sulfolan is best suited for this operation but price of 100% clean one is 72€ for 500ml way to expensive from other hand 99,75% recoverable .


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## Anonymous (May 20, 2014)

Isn't silicon oil non flammable?


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## Sucho (May 20, 2014)

i found these numbers for glycerine/glycerol in various sources. self ignition is cca 204 °C.

flash point of silicon oil varies according to viscosity, normally it is higher than 300 °C. its price ( lab. grade ) is cca 10 E / liter, so much cheaper that sulfonan( i really dont know which chemical compound you mean with this name )


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## Anonymous (May 20, 2014)

Thanks, any suggestions as to where to buy this please? If it works I have a particular use for it.


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## Sucho (May 20, 2014)

theres a rule in lab. 

never heat up your high temperature bath up to the flashpoint of the liquid you use.not even 20°C below the flashpoint.you never know where the static discharge comes from. and ALWAYS use STIRRER!!


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## soltysek0383 (May 20, 2014)

About sulfolane http://en.wikipedia.org/wiki/Sulfolane it's very safe and as I see it's don't have flash point.\
It seems that it's not so perfect safe especially when it's not perfect wash out before using nitric acid ( nitroglycerin ) in home made garage :> }


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## Sucho (May 20, 2014)

thats the proper name of the compound !
its flashpoint is 165°C.

its also miscible with water. and according to the molecule, its not very safe... i think silicon oil would be quite better choice.


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## soltysek0383 (May 20, 2014)

Sucho I where you found this all flash point coz I can't found them .
And btw flash point is not auto/self ignition gasoline have flashpoint -43 and diesel 52 so always there is a risk .


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## joubjonn (May 20, 2014)

Would you be able to recover the solder from this solution? Would it conglomerate or disperse?


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## Geo (May 20, 2014)

Dupont Krytox. From Dupont website : Compatibility with Metals

Because DuPont™ Krytox® XHT oils are chemically inert, they have little or no adverse effect on metals in temperatures below 288 °C (550 °F). http://www2.dupont.com/Lubricants/en_US/applications/Extreme_Temperatures.html

http://en.wikipedia.org/wiki/Krytox

Use in a fume hood or with good fume control.


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## soltysek0383 (May 21, 2014)

Joubjonn that's a point of it . To recover solder for future processing for pure tin and silver sometime they use bismuth also and remove most of the most annoying metal for next steps of processing . 
Theoretically molten tin in oil will be like mixing oil with water but will fall on bottom of jug , how fast depend of weight of oil/m3 and stickiness of both of materials . But be aware that it need to be filtered ( still hot ) or you end up with mix of tin mlcc resistors and anything else . Molten tin have high stickies to metals but in fluid environment this ability should be pasivated .The good idea is to split RoSH from not RoSH and process them separate then almost exactly you know what you have in solder lead or silver . For me is important to remove easy solder off then I can with NaOH remove solder mask and recover copper from PCB . The value of copper tin silver in one PCB will be equal if not higher then gold it self . 


Geo nice found about fumes producer say that's problem ocure over 260 . Normal RoSH solder 215-235 before RoHS 175-200 so theoretically we work under fume border how in practice test will show


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## g_axelsson (May 22, 2014)

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


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## soltysek0383 (May 23, 2014)

I dig out some studies about leaching PCB in different solutions and it's effect also a table of % metals in main-boards PCB 

Comparing the results for Sn and Cu extraction after 120 minutes obtained with the various leach systems, 3.0N HCl + 1.0N HNO3 exhibited the highest percentage values for simultaneous Sn and Cu extraction (98.1%Sn and 93.2% Cu). The results for tin extraction are similar to those obtained by Barakat (1998). The poorest results were produced by the 2.18N H2SO4 system (2.7% Sn and <0.01% Cu). The secondary leaching of the 2.18N H2SO4 + 3.0N HCl system reached a level of 90% Sn extraction and only 12.3% Cu extraction from the primary leaching residue. The 3.0N HCl system gave 89.1% Sn and 33.2% Cu extraction. Based on the experimental results, secondary leaching proved to be efficient in reaching a higher percentage of tin extraction as compared to those leach systems performed in only one stage.


From whot I understand using H2SO4 + HCL can be used as pretty selective way of depopulating large area with only little (12%) effect on copper .

I also post table of metal in PCB compare to total weight with ceramic and bio/epoxied


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## soltysek0383 (May 23, 2014)

And some more tables :

Link to article if some one more interest in it : http://www.scielo.br/scielo.php?pid=S0104-66322009000400003&script=sci_arttext#tab1


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## Anonymous (May 23, 2014)

Geo

Thanks mate I appreciate that.


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## Geo (May 23, 2014)

No problem. 8)


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## Anonymous (May 24, 2014)

g_axelsson said:


> 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.
> ...



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.


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## soltysek0383 (May 24, 2014)

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 ) .


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## g_axelsson (May 25, 2014)

spaceships said:


> g_axelsson said:
> 
> 
> > 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.
> ...


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


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## soltysek0383 (May 25, 2014)

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 .


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## Anonymous (May 26, 2014)

g_axelsson said:


> 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!


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## kjavanb123 (Jun 13, 2014)

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


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## kjavanb123 (Jun 14, 2014)

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


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## kjavanb123 (Jun 17, 2014)

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


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## kjavanb123 (Jun 17, 2014)

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


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## samuel-a (Jun 22, 2014)

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.


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## kjavanb123 (Jun 22, 2014)

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


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## kjavanb123 (Jun 28, 2014)

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


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## kjavanb123 (Jun 29, 2014)

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


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## solar_plasma (Jun 29, 2014)

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.


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## solar_plasma (Jun 29, 2014)

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


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## kjavanb123 (Jun 29, 2014)

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


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## eastky (Jun 29, 2014)

kjavanb123 said:


> 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.
> ...


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## solar_plasma (Jun 29, 2014)

> 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.


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## kjavanb123 (Jun 30, 2014)

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


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## butcher (Jun 30, 2014)

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.


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## kjavanb123 (Jun 30, 2014)

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


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## kjavanb123 (Jul 1, 2014)

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


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## kjavanb123 (Jul 2, 2014)

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


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## solar_plasma (Jul 2, 2014)

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.


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## kjavanb123 (Jul 4, 2014)

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


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## solar_plasma (Jul 4, 2014)

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:


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## Harold_V (Jul 4, 2014)

kjavanb123 said:


> 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


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## kjavanb123 (Jul 5, 2014)

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


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## solar_plasma (Jul 5, 2014)

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.


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## kjavanb123 (Jul 7, 2014)

samuel-a said:


> 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.
> ...



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


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## Geo (Jul 7, 2014)

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


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## kjavanb123 (Jul 7, 2014)

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


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## kjavanb123 (Jul 8, 2014)

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


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## kjavanb123 (Nov 25, 2017)

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


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