Not missing anything; just wondered if there were any old silver recovery hands out there who had some tricks. My experience is limited to running commercial grade extraction units; not doing it piecemeal in my basement...
Hi, I'm an old large-lab guy with quite a lot of silver recovery experience.
FWIW we had considered, at one time, using existing equipment, during the off-season, to "recover" silver from "scrap film" and "trim ends" left over from paper slitting. (We went through about a dozen "master rolls" of color paper every day, which for some time we slitting it ourselves. A master was 50" wide by the better part of a mile long.) The trim ends are the edges of the master roll (beyond the 50" width) which is not fully coated; perhaps 1 to 1.5 inch on each side.
We eventually decided it was not economical for us to do it ourselves, partly because of effluent or Hazardous Waste disposal issues. The US has a law known as RCRA that establishes what a "Hazardous Waste" is. Essentially, as I recall, if there is a liquid, or related things, with a silver concentration greater than 5 mg/liter of silver, then it is an official Hazardous Waste. Now, in the original film, the silver can't leach out, so it can be discarded as "normal waste." But if a person uses photographic fixer then it has to be washed enough to get below that silver level. There are other fine points, but we decided better to sell the waste material as scrap.
Now, assuming that you don't have to worry about these things, my first question would be, "Does your scrap film contain iodide?" If so, this severely limits the reuse of the fixer. Etc., etc. (I am presuming you would electroplate the silver, meaning you MIGHT substantially reuse the fixer.)
Regarding sending your electrolytic silver flake to a refiner, there are a number of issues. The traditional pricing method would be, roughly: they have a "refining fee," some cost per unit of weight. There is an "assay fee" which back in the day was about $40 to $50 US. Then, an "accountability rate," which is where the refiner makes their profit. IF you were a large customer this might be 95% or higher; they would pay you for this proportion of the silver value. The difference, they keep it as their profit. For a much smaller customer the "accountability might only be 50% or so, meaning that they keep the other 50% as profit.
Now, a main problem for the small-scale user is, what will the refiner assay? A couple refiners I was familiar with had furnaces that could take roughly 65 lb charges. So, if you had that much silver flake you could fill a furnaces and no problem to assay the result. But... say you only have a couple lb of silver flake? There is no graceful way to deal with it. Unless you can get in cahoots with a group of other people who collectively have enough silver for a run. In such a case everyone would likely agree to split the return according to the weight they put in. So there is one refining run with a certain final weight of silver and an assay of the purity to be paid out at whatever "accountability" level was set; the collective group would then split it up. Ps... even if you could pull this off, a refiner might still balk at dealing with you. From their standpoint they have no idea what else you might have put in with the flake, etc.
So... I would guess it's a bad deal to, out of the blue, try to use a refiner.
FWIW the electrolytic silver flake has a pretty high purity on its own. We once sent out samples of silver flake from bleach-fix to a specialist doing "fire assays." Blix flake tends to look pretty "dirty," not a clean off-white like fixer silver flake is. We were surprised at how high the purity was. As I recall the specialist found, in three samples, after drying, something like 99.6% to 99.8% purity. I'd expect flake from fixer to be even higher. So... it might be worth considering to try refining it yourself, just for fun.
Ps; I didn't say much about the actual "fixing" stage. It kinda depends on whether the film contains iodide, which sorts "poisons" a thiosulfate fixer. But in general, for highest silver recovery, you would wanna use a multi-stage fixer setup.
