Friend of vladi57 said:
Special thanks to goldsilverpro! Completely agree with the calculations, but he will be surprised to know that beginner doctors or engineers in our country work for $2 per hour...But chemicals are cheap - liter of nitric acid is $1.50, same is for sodium hydroxide. The rolls are in my garage, and take space. I can burn them in the stove for heating purposes, not bothering with the silver,but why not trying to extract it? I am targeting burning, as the other methods are labor intensive and expensive. Resulted ash will soak in nitric acid and after this will run it through electrolysis - I have cell with graphite anodes and rotating stainless steel cathode I used it hundreds of tones of photographic solutions. If this method makes sense, what must be the concentration of the nitric acid? If this is bad idea, I can run the ash trough sodium hydroxide and then use corn syrup - is there any substitute for it?.
Friend of vladi57,
Damn, what country are you talking about?
I don't think you realize how much bulk you will have until you remove it from the rolls, which you would probably have to do to efficiently burn it. And, here again, Burning 400 layers all to white ash (necessary) would be quite difficult and would take a long time if you left it on the rolls. 30,000 ft2 (a square 173' on a side) is enough to cover the floors of 2 small 3 bedroom houses.
Your cell is designed for hypo solutions. A nitric solution is different. For one thing, the crystalline silver will mostly all fall off of the cathode. If you use too much nitric, any silver deposited will re-dissolve until most of the nitric (more than about 4-5% free nitric) is consumed. At first glance, I don't care much for your process. I think there are better ways to do it.
Since the film is exposed, there will be a small amount of seed silver areas, but most all of the silver should still be as silver halides, AgBr mainly.
If this stuff were mine, I would sell it and move on to something less labor intensive and something that would turn a profit. If I couldn't sell it, I would find out if a landfill would take it? If someone was holding a gun to my head, that's about the only way I would process it.
I surely wouldn't burn it, mainly due to the potential 30% loss. There's no profit in this even if you were able to get all the silver, so I sure wouldn't want a big loss. It would be really dumb to burn it in the stove for warmth (maybe if the burner is outside and away from your residence). You have no idea how much toxic smoke the emulsion will generate. Do it wrong and you could kill somebody or, at least, hurt them, maybe badly. Everything about this project is labor intensive, whether you burn it or not. Pyrolysis (essentially, vaporizing) is better but, if the equipment design is faulty, it could easily explode if the off gasses reach a certain temperature and are confined. I'm thinking that the critical temperature for this is usually in the 400C-500C range, but don't quote me on this. If you got the material itself above about 700C, the AgBr would start vaporizing.
If a gun were held to my head and if I had your equipment, I would definitely first consider hypo. It doesn't remove the emulsion, like most stronger chemicals (e.g., sodium hydroxide) do and the worst thing you could do would be to remove the emulsion. That would make it a whole different ballgame, one that would much more equipment. Hypo is fairly innocuous. Anything stronger would likey weaken the paper and could even pulp it - you don't want that. I don't how how much of the AgBr would be converted to Ag by exposure but I would guess it would be nearly immeasurable. If it's more than I think, you could use a Blix solution instead of plain hypo to convert the silver to silver chloride and dissolve it. I would try to design a system that would run the film through the solution(s) directly from the reels, powering it by a take up reel and have some rollers built (or placed) into the tank(s). I've done this a couple of times on other applications. However, paper gets weaker when it is wet and could break. The tension on the paper would have to be fine-tuned. If you take the paper off the rolls, I assure you that you will be overwhelmed by the vast amount of bulk you have and now must deal with.
I would first go through the Hypo solution and then follow in 2 or 3 rinse tanks. The speed of the takeup reel or puller would have to be slow enough to give it time to dissolve all the AgBr. Then, of course, run the solution through your rotating cathode system. You could just collect the paper coming out the end in cutoff drums or gaylords, although a take up reel would end up less cumbersome and more tidy. Paper soaks up solution and, instead of a take up reel, I would think that 2 rollers set close enough to grab the paper and pull it through, with the paper in between, would squeeze out most of the liquid into a container.
With some ingenuity, you could probably set all this up fairly cheap.
An alternative to electrolytic recovery of silver from hypo would be the direct precipitation of silver sulfide using a sodium sulfide solution. I like this process very much, mainly because you get it all, simply, with not a lot of equipment, and it's fairly fast. The best info on it was written by Juan Manuel Arcos Frank, our very good silver friend and humorist from Mexico. I wish you would post more, Manuel.
http://goldrefiningforum.com/phpBB3/search.php?keywords=silver+sulfide&terms=all&author=Juan+Manuel+Arcos+Frank&sv=0&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search
The only experience I've had with photo papers was to analyze them for silver. However, in the early 2000's, I spent 3 days a week for 4 years as a consultant and analyst for a company that was processing a million pounds a month of scrap film. They also ran much silver chip, truck loads of canisters, and a few solutions that were run in rotating cathode units. During that time, I ran about 6000 assays (30 per week) on about every type of photo film under the sun. I did analyze a few of the papers but these were infrequent and about the only one I recall that was close to being valuable was a certain paper that was actually a negative - white letters on a solid black background. Called something like PXB, or some other 3 letter acronym. Popular in the'80s. Even with all that black, I'm thinking it only ran 0.025 tr.oz. Ag ($0.39) per pound, about 1/4 of rare earth medical film.
Good luck!
