Recovering Silver from scrap microfilm
A local archive was disposing of some microfilm they no longer required (I checked, and it was all duplicated and had also been digitised). It was just going to be thrown away, so I asked for some - partly to test the resolution of the microCT scanner at work, and partly to see if I could extract any silver from it.
After some experimentation I worked out that dilute bleach in hot water would rapid strip the silver from the plastic film material. If I had a tray, I could have run the film though the tray though the bleach bath, instead I just cut up sections of film that had lots of silver (they were dark) and socked them for a while in bleach, until they turned clear.
The bleach first seems to breakdown the adhesion between the silver and the plastic film, the silver moves into solution as a dark mass, which then reacts with the bleach to form white silver chloride. The silver chloride settles out of the solution as a fine mass at the bottom of the container.
When it first settles, it looks like there is a lot of silver chloride, but it’s quite a loose mass in the bottle, and there’s probably less than one gram in each bottle.
I tried to collect more silver from the solution by adding a mixture of sodium hydroxide (NaOH) and sugar to reduce any silver ions in solution to metallic silver particles.
Everything was filtered, and the filter papers scraped clean and then burned to give up any remaining silver stuck to them - unfortunately, my filter papers were not ash free, so I collected more ash than silver.
Next step, once I had the silver chloride, was to convert it to silver oxide with a strong solution of sodium hydroxide (NaOH), the colour changes from white to dark grey / black as the silver oxide forms. I used about 30g of NaOH (probably a great excess) in 100ml of water. The solution heats up as the NaOH dissolves and reacts with the silver chloride, care must be taken that it doesn’t boil and throw corrosive solution around - add the hydroxide slowly with good stirring.
Once all the white silver chloride has been converted, I stirred for another 5 minutes then added small spoonfuls of table sugar to the solution, this reduces the silver oxide to silver metal. I didn’t keep a good record of how much sugar I added, but it was less than 100g - any excess will be washed away.
Once again, the solution was filtered, and the solid silver mass collected on the filter papers. The solution was allowed to drain away - it should only contain negligible amounts of silver, if any at the point. The filters and filtrate were dried in an oven at 120 Celsius, before being mixed with about 5g of borax and 2g of sodium carbonate to act as fluxes.
The mixture of silver and flux was heated with a propane torch until I started to coalesce into a bead of metal, unfortunately, the melting dish fractured with thermal shock, but by then I had a lump of metal I could heat separately to further coalesce it.
I couldn’t get enough heat from my torch to complete the melt, the silver down to a nice shiny button, but I got a nice chunk of silver I can either further refine or try to make into something.
This is definitely not a way to get rich, the current price of silver is about £0.57 per gram. I recovered about 3g of silver from 8 rolls of microfilm, at a cost to me of 8 hours of my time and about £10 in chemicals and gas. I really was just exploring the science. If you can get enough film for free and you have experience of the refining you might be able to turn a profit, but it’s a lot of work.
There are other images and videos from the process on my flickr account