Ag stripping from solar cells

[aviasolar]

hi.. looking for a easier way to strip silver of polycrystaline solar cells silver on the front with aluminum layer on the back ..trying to keep away from nitric as much as possible ..any ideas or suggestions appreciated...
silver deposition of 60-80 micron

 

[Justincase]

I have two large industrial unit's about two meter square each.Both smashed during transport..
Sandwiched glass ,P type silicon,N type silicon,conductive strips.And so forth.
The material has a high Specific heat capacity so is hard to pyrolyse even after crushing.
One of Lou's rotary calciner's might have been good but with a limited shop they are a bit of a pain.
My small test run only showed about 25g on the entire unit so have put them to one side.
I look forward to seeing how others have tackled them.

 

[nickvc]

Both HCl and lye will dissolve aluminium so if the silver is backed by it you should be able to remove the aluminium while leaving the silver, it may take some time but it's worth a try.

 

[g_axelsson]

If you can't use nitric acid then working with silver is problematic at least.
Nothing I would try myself.

Göran

 

[Justincase]

The problem I found was the laminate.
The original post may have been about smaller unit's.but the one's I have are very well weather proofed.
The layers of glass are held together very well and smash down to small cubes much like safety glass.
Each cube is a layer of electrical grid laminated in between glass,to let acid penetrate effectively you must first denature the bonding.
I have had mine up to a very good heat and only effected the top most crust.
Gave it several hours and mixed by hand as best I could.
pyrolyzation so easy on a small scale but quite hard to scale up effectively.
I did think of a solvent approach but that would lightly cost more than the recovery would yield.

 

[rickbb]

Sounds like a similar problem with Plasma TV glass. The glass is not laminated together but is glued down to the aluminum backing plate. Makes the labor cost of separating the glass from the mount/backing cost more than the silver you get out of them.

I understand that large scale operations that handle them put the broken glass in a ball mill to make a glass powder then leach the silver with a thiosulfate based leach.

 

[aviasolar]

thanks for the ideas ..when i posted this i has 5000 cells .... problem now is i have about 1,000,000 of these cells.. most are tabbed but all are silver bearing mono and poly crystalline silicon.. they are all broken to the point they are not worth laser cutting for smaller cells due to to the tabbing ...
I tried chipping them into smaller pieces and used naoh to remove the aluminum then tried going after silver but it will take for ever to pull at this rate .. when i tried nitric acid with the aluminum still on them the nitric reacted with the aluminum as you start to increase the volume of material in the bath .. I tried 20% 25% 30% 35% solutions of nitric and found that the only way to remove the silver and keep the aluminum from reacting was to keep the solution around 70deg f and 30% but it takes hours to dissolve the silver ....

I guess the question is if i smash these things up and remove the tabbing wire i can do this fast and end up with pieces from 100 mesh up to 2 inches in size then whats the fastest way to strip the silver with out having to play with acid?? i ran some thru a hammer mill (100 mesh )and come up with a nice pretty powder that doesnt burn with a sparkler so i guess the aluminum volume in the mix is not dangerous enough to worry about .... what fast other methods reasonably priced could i use to get the silver ...


any ideas would be appreciated...

 

[g_axelsson]

Can you show us some pictures of what you have? How thick is the aluminum? How is it attached to the silicon? Is the silver covered by a protective layer?

It would give us some more ideas of what you have and possibly some ideas.

Does incineration separate the aluminium from the solar cells?

If you could prepare the material and separate the aluminium from the silicon material then it might be possible to find a partner to help out with the acid part.

Göran

 

[aviasolar]

the cells basically look they way they do in the pic of the white drum after chipping ...
the tabbing wire comes out perfect and is easy to catch the silver off with electrolysis...

the pic of the powder is from taking some cells and hammer milling them to 100mesh and less ..
i used flotation to seperate out a bulk of the aluminum powder from the mix as the density of aluminum at this mesh is below water (probably actually comming thru smaller

the aluminum is pasted and baked on the back side .. 60-70 um / overall thickness of cell 250um silicon around 180um

 

[Lino1406]

If the amount was meaningful, a silicone etcher would be a justified way, but it is not

 

[Geo]

If it is aluminum and the only other metal is silver, wouldn't dilute nitric acid remove the silver without effecting the aluminum?

Really, there's no other good way to process it.