|I always included the platters with the other aluminum. I believe they're usually an aluminum alloy and then coated with magnetic material. No doubt there's going to be some nasty metals involved but I doubt it's much of a problem once it's all melted down with the aluminum.|
Some electronic recyclers expect you to pay them to get rid of electronics but most metal recyclers will let you drop off any metals, and of course they pay for aluminum, copper and other desirables.
But really, if they're working, see if they're worth something. Many years ago I scrapped hundreds of old MFM hard drives and 5.25 floppy drives that are now getting good prices on ebay.
Now that's what I call a sticky situation