Silver Recovery

Discussion in 'B&W: Film, Paper, Chemistry' started by thebanana, Sep 19, 2005.

  1. thebanana

    thebanana Subscriber

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    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
     
  2. thedarkroomstudios

    thedarkroomstudios Member

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    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.
     
  3. Whiteymorange

    Whiteymorange Member

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    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.
     
  4. Reticenti

    Reticenti Member

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    Possible easy Silver recovery?

    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
     
  5. Jordan

    Jordan Member

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    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).
     
  6. maxbloom

    maxbloom Member

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    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.
     
  7. Dan Henderson

    Dan Henderson Member

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    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.
     
  8. Reinhold

    Reinhold Subscriber

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    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
     
  9. Photo Engineer

    Photo Engineer Subscriber

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    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
     
  10. fschifano

    fschifano Member

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    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?
     
  11. Drew B.

    Drew B. Subscriber

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    There are too many opinions out there about what to do...We need someone who knows what they are talking about (chemist/scientist/environmentalist) to give us exacting directions on how to do this... Who has the written documented proof of why and how?

    forever dazed & confused....
     
  12. Reinhold

    Reinhold Subscriber

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    For those of you that are nervous about aluminum, here's an interesting discussion:

    http://www.thedietchannel.com/Alzheimers-Disease.htm

    I find the phrase "fear mongers" appropriate. The digi-crowd likes to use it against we who prefer traditional photographic processes because "they" have no impact on the waste stream. (Yeah, right; millions of discarded inkjet cartridges, cell phone cameras clogging landfills, etc, etc,...).

    Reinhold

    www.classicbwphoto.com
     
  13. Jordan

    Jordan Member

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    Photo Engineer and I are both chemists.

    When you add a less noble metal to a solution of a silver salt, an oxidation-reduction reaction takes place. The less noble metal is oxidized into solution and the silver salt is reduced to silver metal, which appears as a black sludge.

    I've done this many times by adding steel wool to fixer. After a day or so, the steel wool has partially dissolved and there is silver present as a black suspension or sometimes a "mirror" on the wall of the container. The overall reaction is 2Ag(I) + Fe -> 2Ag(0) + Fe(II). There may also be some Fe(III) present. The principle with aluminum is similar, in that case the reaction goes as 3Ag(I) + Al -> 3Ag(0) + Al(III). Depending on the pH of the solution, your Al(III) will precipitate spontaneously and mix into the Ag sludge.

    It is not a great idea to ingest huge amounts of aluminum salts, but small amounts are okay. Aluminum hydroxide is one of the ingredients of Mylanta, and it dissolves in the stomach to produce soluble Al(III). Aluminum hydroxide flocculation is a major method of wastewater treatment.
     
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  15. Photo Engineer

    Photo Engineer Subscriber

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    There are two feasible ways to remove silver from hypo solution.

    As I stated above, addiing solid or a concentrated solution of KI (Potassium Iodide) to hypo that is exhausted will precipitate yellow Silver Iodide which can be filtered out and reclaimed.

    The second method involves either electrolysis or metal exchange with a metallic surface such as Iron. Often steel wool is suggested. Kits for this are available from several manufacturers.

    There are many posts about this subject here on APUG and also on Photo Net among others.

    Since the latter method I've mentioned is used commercially, it is the best method. It can be easily carried out at home.

    A final mention might be made of a method used formerly at Kodak and by the military, which is no longer in use. The scrap film and used hypo were incinerated leaving behind silver residue in the ash. This is not in use currently and has not been AFAIK for about 50 years.

    I mention this because the heat and oxidation has suggested to me that if you can decompose the hypo by strong acid or oxidant, then the Silver ions would probably precipitate from the exhausted solution. I have never tried this, but it probably would work.

    Reclaiming Silver as Silver ions rather than Silver metal is not very economical.

    PE
     
  16. Steve Smith

    Steve Smith Subscriber

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    The company I work for produces conductive circuits, membrane switches, etc. by screen printing conductive silver ink onto polyester film. Our silver printed waste goes for reclamation which is done by this incineration process.

    Steve.
     
  17. Photo Engineer

    Photo Engineer Subscriber

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    Steve;

    Since the method of incineration can produce toxic byproducts, the incinerator must be very 'clean'. Kodak does incinerate many items, but AFAIK, they no longer incinerate scrap film. That is all I can speak to.

    They do incinerate some chemical waste and vent the smoke through a very very efficient carbon scrubber to removed all toxic waste.

    PE
     
  18. Joe VanCleave

    Joe VanCleave Member

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    Electrolytic Reduction

    Suppose that I wanted to electroplate out the silver onto a cathode; could I put the used fixer solution in a plastic tub, attach metallic electrodes to either side of the container, and connect an appropriate DC current source?

    What would be the 'best' electrode materials, considering both cost and efficiency; and what is the voltage needed?

    Also, are there any gasses produced in the reaction that I would need to be concerned about, such as hydrogen?

    ~Joe
     
  19. Photo Engineer

    Photo Engineer Subscriber

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    Don't use any electricity, just throw in a piece of steel wool (Iron, not stainless). Silver will plate out. Read other posts on this to brush up.

    PE
     
  20. jim appleyard

    jim appleyard Member

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    I believe this is how the 1-hour labs I worked at do it. I don't know the details, however.

    Steel wool works.
     
  21. Reticenti

    Reticenti Member

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    Is the black Ag suspension a colloid, so it will eventually settle? or is it a permanent mixture?
    After these methods, do I collect the silver and sell it then?
     
  22. laverdure

    laverdure Member

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    "After a day or so, the steel wool has partially dissolved and there is silver present as a black suspension or sometimes a "mirror" on the wall of the container."

    ...antique mirrors were made of silver plated somehow onto glass- I don't know anything else about that, except what I've said, and that antique mirrors are really nice- any chance we could be making mirrors with our spent fix?
     
  23. richard ide

    richard ide Member

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    When I was in business, my silver recovery unit had a drum about 6" diameter which rotated at slow speed as one electrode. There were 2 carbon bars as the other electrode. I believe voltage was about 6VDC. When the silver coating on the drum was about 1/8" thick, I would break it off. Kodak made test papers to determine the silver content of the solution. It took about 3 days to remove enough silver so that it was safe to discharge into the sewer system. Acceptable level was around 50ppm.
     
  24. Steve Smith

    Steve Smith Subscriber

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    Yes, it does sound like a horrible process and as our products generally have only about 5% cover with silver ink about 8 microns thick, I find it hard to believe that it is worth doing. The reclamation company must consider it worthwhile though or they wouldn't bother collecting it.

    Steve.
     
  25. Kino

    Kino Member

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    If the current is too high, you can cook the fixer and release Hydrogen Sulfide which will ruin the fixer and is bad for your health.

    We use the big rotating drum silver recovery units from Rotex in nearby Springfield, Ohio.

    Here is the model we use: http://www.rotexsilver.com/series_2500_4000.htm

    I am certainly no chemist, but it is easy to tell when the current is too high; the smell of rotten eggs is a quick alert to lower the amperage.

    Somewhere around this heap of books and cameras, I have a set of plans from Kodak in the 30's or 40's to build your own silver recovery unit with a few bits of wire, a stoneware tub and (basically) a battery charger. Been wanting to do that for a while, so I will start digging.

    Ironic that I am awash in a sea of information, but I can't locate anything to save my life... :mad:
     
  26. Jim Jones

    Jim Jones Subscriber

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