Reclaim silver from test strips, scrap prints, etc.?

[Steve Goldstein]

Everyone knows that one of the most important items in a darkroom is a big wastebasket, but it's always bothered me that I'm throwing away (probably trivial amounts of) silver when I discard test strips and scrap prints. Would use of a strong rehalogenating bleach followed by fixing allow me to get this silver into solution for subsequent recovery? Or is there something I'm missing here?

Full disclosure - in real life I'm an electrical engineer, not a chemist.

 

[railwayman3]

I've had the same concerns, though I don't do much darkroom printing at the moment, mainly just film processing. I'm sure that your suggestion of bleach and fix would work, though you would need to consider the arrangements (and economics) of the subsequent recovery. I think that there have been a few threads on here relating to disposal of silver-containing solutions.

 

[Ian Grant]

When I worked in the precious metal industry we recovered silver from X-ray films, this was done by first soaking in a re-halogenating bleach actually ferric chloride based then we had large tanks of fixer to dissolve the Silver Chloride. We were actually re-using spent fixer that we collected from hospitals, NDT labs, etc which we'd already recovered the silver from in large electrolytic plating units.

Ian

 

[KenS]

You might 'do better' reclaiming the silver from your used fixer.... pour it into a brown glass carboy.. to that add some used developer... shake every day then let it stand.... pour out (syphoning down to an inch or so of the 'remaining' is the easiest add as much used fixer again until you syphon off enough for he carboy to accept the next tray/tank/bottle of well used fixer
Eventually you will observe a precipitate settled at the bottom. This is what is known as "Black Silver' ...probably the 'purest' form of silver. collect that by 'filtration' of the carboy's contents. Have it 'melted' to a solid lump and sell it.
It is better to collect over a period of time rather than pouring it all down the drain.

Ken

 

[Steve Goldstein]

I do already reclaim the silver from my used fixer with one of those electrolytic gadgets, which is why I was thinking about getting the additional silver from my scraps prints and test strips. I don't do it for financial reasons, but to reduce the amount of silver I'm putting into the environment.

KenS, I've heard of the steel-wool technique, as well as electrolytic recovery, but your method of using old developer is a new one to me.

 

[Ian Grant]

We used and sold wire wool Silver traps at work, small ones are used as tailing units after electrolytic recovery to ensure the residual Silver level is below 5ppm. Larger units such as those made by Metafix and CPAC are used typically used by mini-labs. You can make your own for small scale use.

Ian

 

[Mr Bill]

Would use of a strong rehalogenating bleach followed by fixing allow me to get this silver into solution for subsequent recovery? Or is there something I'm missing here?

Like the first two responses say, yes, it ought to work.

The downside is that the amount of silver is really small. I don't have any actual silver loading numbers on b&w materials, but as a wild guess I'd say that an 8x10 inch sheet may contain somewhere around 1 or 2 cents (US) of silver. Give or take one or two factors of two. (I'm sure you can get better estimates if you want to work at it a bit.) Now, most of that silver typically ends up in the fixer unless your prints are largely black. Another wild guess is that, in a typical scene, perhaps 20% of the total silver is developed; this ~20% is the total amount of extra silver available when you bleach and fix your images. So, carrying on the wild guesses, you miglht be saving 1/5 to 2/5 cent of silver for each 8x10 inch print. Personally, I would not bother with it.

On a different note, if you really want to recover a bit more silver, I'm pretty certain there's some more to be had from your fixer - possibly more than from the test strips, and probably easier than bleaching test strips. But still probably pretty insignificant in the grand scheme of things.

My experience comes from a large studio chain outfit, where I spent considerable effort working on "effluent control" schemes. Most people don't realize how much silver can be (or is) lost to the wash water due to fixer carryover - the amount of fixer carried, by the wet paper, into the wash water. It's not possible to put a number on this loss, without a whole lot of specs, but if someone is processing in trays, with a one-stage fixer, heavily used, I would not be surprised if more than, say, 1/4 of their total silver was ending up in the wash water.

The trick, really, is to keep the silver concentration in the fixer tank as low as possible, AND keep the fixer carryout as low as possible. So it seems that you want to use the fixer only very slightly, AND use a squeegee on the paper before putting it in the wash. The big problem with this is that the fixer starts to get expensive, AND we have a hard time desilvering it (because it has a large volume at low silver concentration, the total "silver leakage" is greater). So our next step is a multi-stage fixer; this lets us reduce the amount of fixer used while still keeping the carryout silver the same. Squeegees between the two stages will help keep the second tank "cleaner." Etc., etc.

Anyway, I am not suggesting that you should do these things, just that there might be as much to gain here as by bleaching and fixing test strips.

 

[revdoc]

I used to bleach out printed paper in exhausted fixer, which took several weeks. Then I'd remove the bleached paper and add some aluminium foil, which would replace the silver in the solution. The result was usually black silver percipitate.

I'm not sure it was ever worth it in my case; maybe if you use a lot of film and paper it would be.

 

[juan]

I make my own albumen paper and I’m concerned about the amount of silver I wash off after exposure. No one has ever been able to suggest a way to reclaim that. Any suggestions here?

 

[Mr Bill]

I make my own albumen paper and I’m concerned about the amount of silver I wash off after exposure. No one has ever been able to suggest a way to reclaim that. Any suggestions here?

Hi, I don't know anything about the albumen process. What form is the silver in when you wash it off?

 

[NedL]

Albumen or salt prints have a small excess of silver nitrate that comes out in the wash water.
Many people add a pinch of salt to the wash water which tends to precipitate it as fine insoluble silver chloride ( you can see the milky suspension with your eyes ). Depending on how the wash is carried out, there could be more or less silver nitrate in the wash along with suspended silver chloride.

I've been thinking about a similar problem lately too but for a different reason. I save the wash water for disposal, and I've been thinking that as long as there is a molar excess of salt then the silver chloride could be filtered out and the remaining liquid ( containing nitrates and sodium or ammonium ) would not need to be taken to the hazardous waste disposal. I generate many gallons of silver nitrate / gallic acid waste compared to fixer waste.

Edit: now that I think of it, possibly it would not work as well if ammonium chloride was used to salt the paper.