Kinda an OSD forum topic...

When you PROPERLY dispose of a hazardous product containing lead, mercury, etc, at a site that takes this sort of waste, how do THEY get rid of it? i.e. Do they put it in sealed containers and bury it in a mountain? I know it's a trivial question, but I'd like to know, and I haven't really found any answers by googling it.

Mercury is usually recycled. There multiple companies that will take your fluoresent bulbs and reclaim, purify, and resell the mercury.

Lead, I do not know.

Greenpeace says we are exporting most of our heavy metal scrap to 3d world countries that do not have effective safety and environmental regulation because it can't be recycled here at a reasonable cost.
I think a lot of it simply gets dumped in the landfill. Certainly the stuff regular consumers generate like small quantities of flourecent tubes, consumer electronics and NiCad batteries end up there. Modern landfills are lined so the trash is usually fairly well sequestered.