Silver Recovery

[thebanana]

Several of us use a very nicely laid out darkroom at our local Art Gallery. There are two large sinks, and all chemicals eventually get dumped down them. Each sink is equipped with a recovery unit of some sort. The units are plastic holding tanks, about 20 gal. each. I'm told there are rocks or stones of some sort in each tank. To my knowledge they haven't been cleaned out in 4 or 5 years. Can anyone offer advice on how to go about doing this? Where would one dispose of the sludge that I imagine is sitting in each tank? I assume there is some silver involved, does it make sense to try to recover it? What else should we be aware of? Thanks.
John

[thedarkroomstudios]

Not sure exactly what you may have with rocks and stones unless it's some sort of simple sediment trapping arrangement. Typical silver recovery buckets have a steel wool type of packing which... (do a thread search on that, very long explanations)... but the bottom line is that if it is that type it can be recovered, there lots of buyers out there for it. If it is just sediment trapping, pick a day the local dump accepts "hazmat" stuff - grab a copy of something showing why you have so much of it and your non-profit status (hey, better to have it with you than try to explain 40 gallons of potentially hazardous sludge in the back of the station wagon) and take ti them for disposal.

[Whiteymorange]

The rocks in your tanks are most likely to be limestone, put there to neutralize acidity. We had a darkroom built by the design team that turned an old athletic facility into an art center and they put those tanks in th enagative room and in the darkroom. Every few years ( supposed to be months, I think) we add some more limestone and ceremoniously seal up the tanks again. There hasn't been a sludge problem. I can't say it's useless, though our water is slightly basic, not acidic here in the 'burbs of Boston, but as far as I know it does squat for silver in the system. We're looking for a good solution ourselves. The "cart it to a hazardous waste facility" solution doesn't cut it for us and the town seems to have no problem with us dumping some fix in the sink. I'd just feel better if we reclaimed some silver before the flush.

[Reticenti]

My thinking in getting the silver recovered, is to put salt in the solution. Wouldn't this give you silver chloride? (The only common non-soluble silver compound) Then the problem would be getting the chloride out, but there has to be an easy, cheap way to to do that some how.
Anyways, would the salt method work to de-pollute the solution for dumping down the drain?

thanks

[Jordan]

If you're talking about recovering silver from fixer, the excess thiosulfate in solution prevents the formation of insoluble silver chloride. (Just like fixing film.) To the best of my knowledge, all methods of silver recovery involve reducing the silver somehow (either electrolytically or chemically).

[maxbloom]

hmm...you could try to neutralize the thiosulfate, and then do some sort of oxide substitution. But you'd end up with silver oxide precipitating out.

[Dan Henderson]

a photography instructor told me to put my exhausted fixer in a pail with some steel wool and leave it alone for awhile. Supposedly the steel wool attracts the silver, leaving a clear, silver-free solution on top which can be poured off. I really have no way of knowing whether it works or not, but I am making the effort to not introduce heavy metals into the water supply.

[Reinhold]

To precipitate silver out of fixer, just toss in some of aluminum foil. The aluminum will swap places with the silver which falls to the bottom of the container as a gray metallic sludge. After all the aluminum has disappeared (about 3 or 4 days), I siphon off the spent fixer and pour in another batch. I keep a one gallon wide mouth bottle just for this purpose; by now it probably has a couple of pounds of silver in the bottom.

No more heavy metal into the waste stream...

Reinhold

www.classicbwphoto.com

[Photo Engineer]

If you don't care about expense, adding Potassium Iodide to exhausted fix will cause a yellow precipitate of Silver Iodide to form. This can be filtered out and somehow reclaimed.

Current reclamation methods yield silver metal though.

PE

[fschifano]

To precipitate silver out of fixer, just toss in some of aluminum foil. The aluminum will swap places with the silver which falls to the bottom of the container as a gray metallic sludge. After all the aluminum has disappeared (about 3 or 4 days), I siphon off the spent fixer and pour in another batch. I keep a one gallon wide mouth bottle just for this purpose; by now it probably has a couple of pounds of silver in the bottom.

No more heavy metal into the waste stream...

Reinhold

So if the aluminum swaps places with the silver what you are siphoning off contains dissolved aluminum. That doesn't sound like a good idea. Aluminum can be toxic as well. Haven't there been some studies linking aluminum and alzheimer's disease?