Kind of left out how the AgCl got reduced.
For those who haven't done this, his warnings about nitric fumes aren't even strong enough. I presume he's starting with normal lab grade stuff - around 70% purity which is about the most concentrated you can have it and it be stable at all. I make 100% pure (and fuming) here and it's wicked stuff and very unstable.
The danger is the nitric fumes aren't like chlorine or ammonia where you'll reflexively stop breathing and get away before any real damage is done to you. They smell kind of not-so-bad, but one cc of that crap in your lungs and you'll be coughing up nitrated lung tissue for weeks - I know this from experience and now I do this under fume hood or even under some vacuum, with the fumes blowing through a bucket of alkaline solution to get them before they get me.
Note, nitric acid is "on the list" for terrorism and drug manufacture. You can make it, but it's not easy or quick or safe. I can show how if anyone is interested. You can still buy the stuff around the 'net, but buying a lot is going to get you some attention, and it's not cheap, which is why miners don't use this technique much, it's just not cost effective on low grade ore.
Note that indium and gallium are quickly becoming precious metals themselves, and are present in modern tech in larger amounts than the more conventional PMs.
Indium is used for the semi-transparent conductive traces in nearly all displays to "talk to" the pixels, as indium-tin oxide. Gallium is a major component of most leds, and some high frequency transistors.
http://www.rotometals.com/Indium-Ingot-s/7.htm
I use a fair amount of indium here in the lab, it's pretty neat stuff. It wets glass used in a solder alloy, makes great gaskets for vacuum systems (and is reusable).
It's used in various low melting alloys, which is why those are expensive.
Gallium is going nowhere but up in price. The long liquid range is interesting, you can make thermometers with it that go from room temp to orange hot. Like water, it breaks containers when it freezes just below room temp. It dissolves aluminum and renders it extremely reactive with water, giving off hydrogen - there's a guy who has a patent on this as "hydrogen storage".
Back to silver, keyboards aren't the only place you see it - some lower volume PCB's used it for the tracks too. In that case it's mixed with a binder, so a solvent might be the preferred way to get it back - that *should* work with keyboard mylars too, and avoid some of the expense and chemical transformations required. Shouldn't be too hard to find a solvent that eats the glue and leaves the mylar behind.
Heck, I have a couple egg crates full of keyboards I've worn out. Gotta try this - just as soon as I remember which storage building they are in.