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Thread: Silver Recovery

  1. #21

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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?

  2. #22
    richard ide's Avatar
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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.
    Richard

    Why are there no speaker jacks on a stereo camera?

  3. #23
    Steve Smith's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    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.
    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.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  4. #24

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    Quote Originally Posted by Joe VanCleave View Post
    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
    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...

  5. #25
    Jim Jones's Avatar
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    A google search for photographic silver recovery lead to much information, but mostly not for small scale users. Kodak's publication J-215, Recovering Silver from Photographbic Processing Solutions, http://www.kodak.com/eknec/documents...03/J215ENG.pdf is one overview of the subject.

  6. #26

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    Quote Originally Posted by Jordan View Post
    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.
    This is an easy way to remove some silver out of the solution, but the efficacy of such treatment is known to vary hugely depending on the exact composition of the steel, shepe of the cartridge, and the forced flow mechanism. The regulation for residual silver content in many areas is very low, and the steel wool method often does not meet the standard. In small scale amateur darkrooms, steel wool method is better than doing nothing, but don't assume this is the satisfactory solution in all situations.

    Best silver removal method in terms of efficacy and cost is electrolytic system using stainless steel and moving carbon electrodes. The SS electrode will corrode very unevenly if the carbon electrode is not moving circularly around the SS disk.

    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.
    Although I don't like to heat acidic food in non-anodized aluminium cookware, the whole "aluminium-pan can cause Alzheimer's disease" thing was a malicious rumor made by stainless steel industry in the past. In reality, alum is used in pickling (tho I don't use it), and some baking powders contain aluminium compounds as well. (Note that baking powder is a mixture containing baking soda, but not by itself.)

  7. #27

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    Quote Originally Posted by Joe VanCleave View Post
    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?
    As I wrote in my previous post, this is not sufficient. The electrode should move around so that all parts get used evenly.

    Also, are there any gasses produced in the reaction that I would need to be concerned about, such as hydrogen?
    The electrodes are made from stainless steel and carbon. The most advanced electrolytic system maintains the cathode potential at or upward (more positive) of -0.55V with reference to saturated calomel electrode. It's also best to adjust the pH to about 7 to 8 range before starting silver recovery (the pH of Clearfix is ideal for silver recovery system without any adjustment, and most color fixers are not far from it either).

    A recent report on electrolytic silver recovery system was published by Mina and Chang of Kodak Rochester Lab in 1982. Mina, R. and Chang, J. C. 1982. Electrolytic silver recovery from spent fixing solutions---an electroanalytical study. Photo. Sci. Engr., 26, 223-7.

  8. #28

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    Quote Originally Posted by Jordan View Post
    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.)
    Agreed. Precipitation of silver halide in spent fixer is impractical unless thiosulfate is fully decomposed. But such an approach will have to deal with elemental sulfur, and will lead to another kind of sludge.

    To the best of my knowledge, all methods of silver recovery involve reducing the silver somehow (either electrolytically or chemically).
    A very simple, easy and fast way to remove silver out of spent fixer is to form any of a few insoluble silver compounds, such as silver sulfide. If you add sodium sulfide or liver of sulfur in exhausted fixer, you can easily see that silver sulfide is forming. There are other chemical agents that can precipitate insoluble silver compounds or metallic silver in the spent fixer bath. HOWEVER, the difficulty is that any of these methods will make particles smaller than 1 micron, and no inexpensive filtration method works to separate sludegs from a large quantity of treated solutions. (Most laboratory paper filters will let the particles go through, and the fine mesh filters will clog very fast.)

    Ryuji
    Last edited by Ryuji; 04-16-2007 at 06:22 PM. Click to view previous post history.

  9. #29

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    silver recovery unit devise

    much to my surprise and delight, i found in "Porter's" a silver recovery unit. Does this really work? If i use this device, can I pour the silver free fixer down the drain?

  10. #30

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    it depends on your local regulations. At one lab I worked at that was indeed the case, at another, one town over even our recovered waste had to be taken out by truck.

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