This is an interesting topic.
Well, for this kind of moral dilemma, I give you an example, but this is rather an ironic one: I live in a country, pretty resourceless but highly industrial, called Japan. One of the latest news is that there are apparently a countless number of thieves in the country who drive around their pickup trucks at night and steal metals in public to sell them for money. They cut the copper wires from the powerlines, pull out the bike posts from the sidewalks, and take the manhole lids from the streets, etc. Unbelievable. Now what they are doing is truly "recycling", but that's a different story.
But seriously, it might be too hard to have an argument with the silver part of the story. I think what could convince your audience is to go into other areas of recycling or to have a much bigger picture to start related to photography or whatever. I mean, for example, the consumer market dumping tons of still-usable film cameras and lenses seems already harmful enough to the environment and we know it, but we don't quite act so. These cameras have a lot of metals, and how are they being recycled if they are? Are they recycled 100 percent of the time? Or do they just get scrapped, burned, and/or burried somewhere? And where are the dumpsters we use? I don't mean some third-world countries and below, but where do they end up eventually? And you can always argue about the cars, too.
Anyway If I were you to do a research, I would start from there and trace back to where we buy and use to practice photography. Sorry this is more than talking about the use of silver, but it just seems so inevitable.