Depopulating PCB with selective solder recovering

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soltysek0383

Member
Joined
Apr 19, 2014
Messages
20
Location
Danmark EU
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 :)
 
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?
 
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 :)
 
flash point of a glycerol is 160°, 176° respectively.

theoretically, silicon oil which is widely used for oil baths in chemistry is suitable
 
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 .
 
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 )
 
Thanks, any suggestions as to where to buy this please? If it works I have a particular use for it.
 
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!!
 
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.
 
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 .
 
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.
 
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 :)
 
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
 
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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