# Help needed: Grounded solar panels processing



## Mojeho (Apr 2, 2012)

Hello,

I've ran into ton of grounded solar panels(particles size approx 0,5 - 0,01 mm) with approximate(very approximate, only trustowrthy is silver(AgCl tested)) composition: 0,5% Bi, >1% Pb, >1% Sn, 3% Cu, 2%Ag, 92% Si

What is my problem: When processing with nitric, it starts to form foam and increases it's volume about 10 folds(not much problem here though, got lots of space for reaction chambers), but: Is it possible to dissolve silver by other mean than by HNO3? I've tried thiosulphate, but it dissolves too little silver. Never tried ammonia leaching - someone knows how-to?

Also, second interesting thing:
When mixing sand with HNO3 and some water(to make it miscible, otherwise it starts to make clumps of sand), reaction with metals takes place, forminx NOx fumes(so far so good), but after temperature reaches approximately 90 deg. Celsius, something starts reacting with water - *very *exothermic, starts boiling massively, no NOx fumes, no HNO3 fumes, only clear water is going out. If not cooled, it boils for about 3 minutes until complete.
My ideas:
Si+H2O - no idea whether it's possible, but sand partices size is very small, so extremely large reaction surface
Cementation of some metal on other metal, but i've never seen cementation reaction THIS exothermic.

Have anyone heard about some possible reaction of Si +H2O - I'm out of ideas as about what is happening.

I'll try to get exact assay of metal content in sand today and post it.
Also, if someone did something like processing this sand, or similar , please advise.

Best Regards
Marek "Moje"


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## Photobacterium (Apr 2, 2012)

a section on using dilute HCl to dissolve materials that cause foaming.

this is in the context of Chlorine leaching for gold recovery, but might be applicable to what you are doing.

from the book "75 Gold Recovery Methods" -
http://www.scribd.com/doc/43820757/75-Gold-Recovery-Methods#outer_page_49


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## Mojeho (Apr 2, 2012)

Thanks for info, but i'm afraid of using HCl to reduce foaming, as it would introduce Cl- ion into the sand, and it would be very hard to get rid of it(would be making AgCl when dissolving with HNO3). 
Due to low amount of Ag in the sand, i'd rather stay away from chlorides.

Nice link though, thanks a lot


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## 4metals (Apr 5, 2012)

Is it possible the metal was coated to minimize tarnishing? An organic coating on the pieces could cause them to foam heavily. You didn't sat if you melted the material first before nitric but if you do, you will burn off any protective coatings. Then it should be less aggressive.


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## Mojeho (Apr 6, 2012)

4metals:

Tried baking a test batch @ 900deg. celsius, still did foam afterwards. Melting is not possible due to high Si content.


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## TXWolf01 (Apr 7, 2012)

you probably would of made more money selling the panels as is then recoverable pm's. Solar is becomeing a big thing and companies might of purchased them from you locally.


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## EDI Refining (Apr 9, 2012)

Whats the main value driver in scrap solar panels? The Ag or the Si ? Anymore have more information ?


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## TXWolf01 (Apr 9, 2012)

Wondering if they are complete solar panels or just the solar cells themselves?


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## AztekShine (Apr 10, 2012)

He said grounded but he ment ground up solar pannles. They were .5-.01 mm


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## TXWolf01 (Apr 10, 2012)

OK thank you for pointing that out, now I will go back to my corner for futher viewing


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## Mojeho (Apr 18, 2012)

AztekShine said:


> He said grounded but he ment ground up solar pannles. They were .5-.01 mm



Aye, that's right... grounded up... sorry.

Anyway, not a problem anymore, we have received new batch not grounded up, so foaming and massive boiling is not a problem anymore.

Also, main value is in Ag.

When working with solar panels, pay attention to contents of scrap, some (thin film panels) do not contain silver, but cadmium telluride instead - no values there.

Best Regards
Moje


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## g_axelsson (Jul 2, 2013)

Cadmium telluride solar panels should be possible to recycle as the limiting factor for manufacturing this type of solar panel is the production of tellur. The complete tellur production of the world is only a couple of hundred tons. (140 tons if my memory is correct)

I haven't checked if there are any places that accept cadmium telluride for recycling but a lot of documents about the technology mentions recycling as an important part of the life cycle of cadmium telluride cells.

Made a quick search...
https://www.google.se/search?q=cadmium+telluride+recycling

This one was interesting... 
http://www.bnl.gov/pv/files/pdf/abs_189.pdf
*Extraction and Separation of Cd and Te from Cadmium Telluride Photovoltaic Manufacturing Scrap*


> _ A dilute aqueous solution of hydrogen peroxide and sulfuric acid was suffi-
> cient to completely leach out cadmium and tellurium from these samples. The same
> method successfully removed cadmium and tellurium from actual manufacturing
> scrap; copper was partially extracted._



Göran


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## samuel-a (Jul 2, 2013)

Mojeho said:


> very exothermic, starts boiling massively, no NOx fumes, no HNO3 fumes, only clear water is going out. If not cooled, it boils for about 3 minutes until complete.
> My ideas:
> Si+H2O - no idea whether it's possible, but sand partices size is very small, so extremely large reaction surface
> Cementation of some metal on other metal, but i've never seen cementation reaction THIS exothermic.



You have probably witnessed a reaction between some organic compound (perhaps PVA, which is a popular capping agent) with nitric and water.
One should always think twice before mixing organic compounds (especially alcohol and its derivatives) with nitric acid.
Be safe.


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## Lino1406 (Jul 5, 2013)

HNO3 with water reacts as acid.
Silicone with metals form silicides.
Silicides and acids give silane.
Silane with air gives water and sand.
Lino1406, author "30 recovery procedures"


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